1
Q
What are the two main parts of the nervous system?
A
Central Nervous System (CNS) — brain and spinal cord; Peripheral Nervous System (PNS) — all nerves outside the brain and spinal cord.
2
Q
What is the main role of the CNS?
A
Acts as the integration and processing center (control system).
3
Q
What is the main role of the PNS?
A
Communication link that brings information to and from the CNS.
4
Q
What are the two divisions of the PNS?
A
Afferent (sensory) division goes towards the CNS
Efferent (motor) division goes from the CNS towards effectors.
5
Q
What are the two branches of the efferent division?
A
Somatic nervous system (voluntary control of skeletal muscles); Autonomic nervous system (involuntary control of smooth/cardiac muscle and glands).
6
Q
What does the ANS consist of?
A
Nerve fibers that innervate smooth muscle, cardiac muscle and glands.
7
Q
What are the two subdivisions of the autonomic nervous system (ANS)?
A
Sympathetic (fight or flight) - stress system
Parasympathetic (rest and digest) - relaxation system
8
Q
What are effectors?
A
Organs or tissues that carry out responses — skeletal muscle (voluntary), smooth/cardiac muscle, and glands (involuntary).
9
Q
What does the Central Nervous System (CNS) consist of?
A
Brain and spinal cord; CNS acts as control system.
10
Q
What does the Peripheral Nervous System consist of?
A
All nerves outside the brain/spinal cord; PNS is the communication network that brings info to and from the CNS.
11
Q
What are the three classes of neurons?
A
Afferent (sensory), interneurons, efferent (motor).
12
Q
What is the function of afferent neurons?
A
Carry sensory input from receptors toward the CNS (Afferent = Arrives).
13
Q
What are the two types of stimuli in Afferent Division?
A
Sensory Stimuli: from outside (touch, sight, sound, etc.)
Visceral Stimuli: from inside the body (blood pressure, pH, stretch in organs, etc.).
14
Q
What is the function of Efferent Division?
A
Carry motor output from the CNS to the body.
15
Q
What two systems is efferent division divided into?
A
Somatic and autonomic systems.
16
Q
What is the Somatic Nervous System?
A
Voluntary control that controls skeletal muscles through motor neurons.
Ex. deciding to move your arm.
17
Q
What is the Autonomic Nervous System?
A
Involuntary control of smooth muscle, cardiac muscle, glands.
18
Q
What are the two divisions of the Autonomic nervous system (ANS)?
A
Sympathetic Nervous System (fight or flight); Parasympathetic Nervous System (rest and digest).
19
Q
What is Sympathetic Nervous System?
A
Fight or flight; increases heart rate, dilates pupils, releases adrenaline.
20
Q
What is Parasympathetic Nervous System?
A
Rest and digest; slows heart rate, stimulates digestion, promotes calm/rest.
21
Q
What are the effector organs?
A
The final targets where nervous signals cause action — Skeletal (voluntary); Smooth muscle, cardiac muscle, glands (involuntary).
22
Q
Explain the pathway example if you touch a hot stove.
A
- You touch a hot stove, sensory info goes via afferent PNS to CNS.
- CNS processes it and sends a motor signal via efferent PNS.
Somatic pathway - skeletal muscles pull your hand away. - At the same time, autonomic signals might kick in (sweating, increased heart rate).
23
Q
What are the three basic functions of the nervous system?
A
Sensory Input (detects what’s happening inside or outside of the body)
Integration (processing that information in the brain/spinal cord)
Motor Output (sends commands to muscles or glands to respond).
24
Q
What is the role of sensory input?
A
Detects changes in the internal or external environment and sends information to the CNS through afferent (sensory) neurons.
25
What is the role of integration?
The CNS processes and interprets sensory information to decide how to respond.
26
What is the role of motor output?
Sends commands through efferent (motor) neurons from the CNS to effectors (muscles or glands) to produce a response.
27
What does 'afferent' mean?
Afferent = Arrives at the CNS; carries sensory information from receptors to the brain or spinal cord.
28
What does 'efferent' mean?
Efferent = Exits the CNS; carries motor commands from the brain/spinal cord to effectors.
29
Give an example of sensory input → integration → motor output.
Touching a cold surface → brain detects cold (afferent) → brain decides to move hand (integration) → hand muscles contract to pull away (efferent).
30
What are the two main divisions of the nervous system?
Central Nervous System (CNS): Brain and spinal cord; control center for processing and decision-making.
Peripheral Nervous System (PNS): All nerves outside CNS; communication link between the body and CNS.
31
What are the functional divisions of the PNS?
Afferent (Sensory) Division — carries information to the CNS.
Efferent (Motor) Division — carries commands from the CNS to effectors.
32
What are the two branches of the efferent division?
Somatic Nervous System (Voluntary): Controls skeletal muscles for conscious movement.
Autonomic Nervous System (Involuntary): Controls smooth muscle, cardiac muscle, and glands automatically.
33
What does the somatic nervous system control?
Skeletal muscles under voluntary control (e.g., moving your arm, smiling).
34
What does the autonomic nervous system control?
Involuntary processes like heart rate, digestion, and gland secretion.
35
What are the two divisions of the autonomic nervous system and their functions?
Sympathetic: 'Fight or flight' — prepares body for action (↑ heart rate, dilated pupils, etc.).
Parasympathetic: 'Rest and digest' — conserves energy and restores calm.
36
What are the three stages of nervous system function in order?
1. Sensory Input → 2. Integration → 3. Motor Output.
37
Which neurons detect stimuli and carry info to the CNS?
Afferent (sensory) neurons.
38
Which neurons send commands to muscles or glands?
Efferent (motor) neurons.
39
What type of neuron performs integration in the CNS?
Interneurons.
40
What is an effector?
A muscle or gland that carries out a response to a neural command.
41
Example of sympathetic vs parasympathetic action?
Sympathetic: Heart rate increases during stress.
Parasympathetic: Heart rate slows after eating or resting.
42
What are the 3 functional classes of neurons?
Afferent neurons, interneurons, efferent neurons.
43
What is the main function of afferent neurons?
Carry sensory information from receptors toward the CNS (Afferent = Arrives).
44
What do afferent neurons detect?
Changes in the external environment (touch, temperature, sound, light)
Changes in the internal environment (blood pressure, pH, stretch, hunger).
45
What types of sensory receptors do afferent neurons have?
Modified nerve endings (e.g., in skin for touch or temperature)
Specialized receptor cells (e.g., eyes for vision, ears for hearing, tongue for taste).
46
What do afferent neurons convert stimuli into?
Action potentials that travel toward the CNS (spinal cord or brain).
47
Do afferent neurons have dendrites?
No — the sensory receptor itself receives the stimulus instead.
48
Where is the cell body of an afferent neuron located?
In the dorsal root ganglion, outside the spinal cord.
49
What are the two main axon parts of an afferent neuron?
Peripheral axon (afferent fiber): carries the signal from the receptor to the cell body
Central axon: carries the signal from the cell body into the spinal cord (CNS).
50
Where are afferent neurons found?
mainly in PNS, but they connect into the CNS through the spinal cord
51
What is a pathway example of afferent neuron function?
Touching a hot stove → sensory receptor in skin detects heat → afferent neuron sends signal via dorsal root ganglion → enters spinal cord → interneuron processes info → efferent neuron activates muscles to pull hand away.
52
Key summary phrase for afferent neurons?
'Afferent Arrives — carries sensory input to the CNS; cell bodies in dorsal root ganglia.'
53
Where are interneurons located?
Entirely within the Central Nervous System (CNS) — in the brain and spinal cord.
54
What percentage of all neurons are interneurons?
About 99% of all neurons in the body.
55
What is the main function of interneurons?
Receives sensory input from afferent neurons, processes and interprets that info, sends commands to motor (efferent) neurons to produce a response
56
What does 'inter-' in interneuron mean?
'Between' — they connect afferent (sensory) neurons to efferent (motor) neurons.
57
What kinds of processes rely heavily on interneurons?
Complex responses such as learning, emotions, coordination, reflexes, and decision-making.
58
Do interneurons extend into the PNS?
No — they are only found within the CNS.
59
What do interneurons allow the nervous system to do?
Enable thinking, reflexes, memory, and conscious decisions by processing input and coordinating output.
60
What happens when you touch a hot object? (Example)
- Afferent neuron detects heat and sends signal to spinal cord
- Interneurons (in the CNS) process the info instantly
- Efferent neuron sends command to muscles
- Effector (muscles) pull hand away.
61
What is considered a reflex?
a fast, automatic response controlled mainly by interneurons in the spinal cord — no brain processing needed first
62
Summary phrase for interneurons?
'Interneurons integrate — they link sensory input to motor output, and most of the nervous system is made of them.'
63
Direction of afferent signal?
From PNS → CNS (Afferent = Arrives).
64
Function of afferent neurons?
Detect stimuli in the internal or external environment and carry that information to the CNS.
65
Examples of afferent stimuli detected?
Touch, temperature, pressure, sound, light, blood pressure, stretch.
66
Structural features of afferent neurons?
Cell body located in the dorsal root ganglion (outside spinal cord)
Peripheral axon: connects sensory receptor to cell body (brings info in)
Central axon: connects cell body to spinal cord (sends info toward CNS)
Mostly within the PNS; No dendrites — the receptor itself receives the stimulus.
67
Example of afferent neuron in action?
Touching a hot stove — sensory receptor detects heat and sends a signal to the spinal cord (CNS).
68
Location of interneurons?
Entirely within the CNS (brain and spinal cord).
69
Function of interneurons?
Integrate and process incoming sensory information and decide the appropriate response.
70
What do interneurons connect?
They form a bridge between afferent (sensory) and efferent (motor) neurons.
71
How abundant are interneurons?
Make up about 99% of all neurons in the body.
72
Example of interneuron function?
In the spinal cord — after sensing heat, interneurons process 'pull hand away' before the brain is even involved (reflex).
73
How does complexity affect interneuron activity?
The more complex the behavior (learning, emotion, coordination), the more interneurons are involved.
74
Direction of signal?
From CNS → PNS (Efferent = Exits).
75
Function of efferent neurons?
Carry motor commands (axons) from the CNS to effectors (muscles or glands) to produce a response.
76
Where are efferent neurons located?
Mostly in the PNS, but their cell bodies originate in the CNS.
77
What do efferent neurons innervate?
Skeletal muscles (voluntary, somatic) or smooth/cardiac muscle and glands (involuntary, autonomic).
78
What is the structure of the autonomic efferent pathway?
Two-neuron chain:
Preganglionic neuron – originates in CNS
Postganglionic neuron – extends to the effector organ (in PNS).
79
Example of efferent neuron function (somatic)?
Spinal cord sends a signal through efferent neurons to arm muscles → hand pulls away from heat.
80
Example of efferent neuron function (autonomic)?
After a scare, efferent autonomic neurons increase heart rate and sweating via the sympathetic system.
81
Where are afferent neuron cell bodies located?
In the dorsal root ganglia, outside the spinal cord.
82
What is the function of interneurons?
Lie entirely within the CNS; integrate sensory input and coordinate motor output; make up 99% of all neurons.
83
What is the function of efferent neurons?
Carry motor commands from the CNS to effectors (Efferent = Exits).
84
What are the two types of efferent pathways in the ANS?
Preganglionic and postganglionic neurons.
85
What’s an example of a complete sensory-to-motor pathway?
Touching a hot stove → afferent neuron sends signal to spinal cord → interneuron processes → efferent neuron activates muscles to pull hand away.
86
What is the CNS responsible for?
- responsible for cognition: the act or process of 'knowing'
- including both awareness and judgement
87
What is meant that the brain works as a whole?
No part of the brain works in isolation from other brain regions.
88
Which is the oldest region of the brain and is continuous with the spinal cord?
Brain Stem.
89
What does the brain stem consist of?
Midbrain, pons, medulla.
90
What does the brainstem control?
Controls many of basic life functions, which are often referred to as 'vegetative functions' (breathing, heart rate, digestion).
91
What does the Cerebellum do?
Maintains proper position of the body (posture + balance)
Coordinates motor activity, key role in learning skilled motor tasks.
92
Which part of the brain is continuous with the spinal cord?
Brain Stem
93
What does the brain stem consist of?
midbrain, pons, medulla
94
What does the brainstem control?
Controls many of basic life functions, which are often referred to as “vegetative functions” (breathing, heart rate, digestion)
95
What does the Cerebellum do?
- maintains proper position of the body (posture + balance)
- coordinates motor activity
- key role in learning skilled motor tasks
96
Where is the Diencephalon?
on top of brainstem, inside cerebrum
97
What does the Diencephalon include?
Thalamus and Hypothalamus
98
What does the Thalamus do?
- relay station for sensory input
- performs some primitive sensory processing
- motor coordination
- role in consciousness
99
What does the Hypothalamus do?
hypo = below (below thalamus)
Regulates homeostasis (temperature, hunger, thirst, endocrine control, sleep/wake cycle)
100
Which is the largest part of the brain?
Cerebrum (80% of brain mass)
Also most highly developed in humans
101
How is the cerebrum divided?
Into right and left cerebral hemispheres, each further divided into lobes.
102
What covers the outer surface of the cerebrum?
The cerebral cortex — a thin, highly convoluted outer layer of gray matter.
103
What lies beneath the cerebral cortex?
The inner core containing the basal ganglia.
104
What is the function of the cerebrum?
It is the most complex integrating area of the brain — responsible for processing sensory information, initiating voluntary movement, language, memory, and higher thought.
105
What is the function of the Cerebrum?
- controls thinking, learning, memory and voluntary movement
- conscious thought, awareness, voluntary actions
106
Why is the cerebrum considered the most advanced part of the brain?
Because it enables conscious thought, learning, reasoning, emotion, and decision-making — functions unique to higher intelligence.
107
What is the main function of the cerebral cortex?
It’s the thinking, planning, feeling, and moving part of the brain — the part that makes you you.
108
What are key functions of the cerebral cortex?
- where you perceive sensory sensations, brain interprets and makes sense of the information
- interprets sensory information (after its sent by the thalamus)
- voluntary movement control
- language and communication
- personality and behaviour
- higher thinking functions; memory, decision-making, creativity, self-awareness
109
Why is the cerebral cortex considered the most advanced part of the brain?
It enables conscious thought, reasoning, and voluntary behavior.
110
What is the main function of the basal nuclei?
Acts as a movement editor — helps refine and smooth voluntary movements.
111
What are key roles of the basal nuclei?
- acts as body’s movement editor
- stops unnecessary muscle activity
- smooths out movements
- refine and filter motor signals so you only perform intended actions
- when malfunction = Parkinson’s disease
Think** muscle tone control, movement coordination, suppression of unwanted motions = basal nuclei
112
How do the basal nuclei interact with the cerebral cortex?
They modify motor commands from the cortex to ensure smooth, purposeful motion.
113
What is the nickname of the thalamus and why?
The “sensory switchboard” — it relays sensory information to the correct area of the cerebral cortex.
114
What are main functions of the thalamus?
- brains control centre (sensory switchboard)
- receives all incoming sensory signals
- routes them to the right area
- helps keep you conscious and coordinated
- relay station for all synaptic input to the cerebral cortex
- crude awareness of sensations
- consciousness or alert regulation
- role in motor control
115
How does the thalamus help sensory processing?
It directs information to the correct part of the cortex for detailed interpretation.
116
What are the main roles of the hypothalamus?
- regulates body temperature, thirst, hunger, and urine output
- maintains homeostasis across many body systems
- acts as a link between the nervous and endocrine systems
- controls basic emotions and behavioral patterns
- plays a role in the sleep-wake cycle
117
How does the hypothalamus maintain homeostasis?
By adjusting autonomic and hormonal activity to keep internal conditions stable.
118
What is the main function of the cerebellum?
Acts as the body’s movement coach — fine-tunes motion and posture.
119
What are key roles of the cerebellum?
Maintains balance
Enhances muscle tone
Coordinates and plans skilled voluntary movements
120
How does the cerebellum support smooth movement?
By comparing intended movement with actual movement and making adjustments in real time.
121
What is the nickname of the brain stem?
The “life support system.”
122
What are key functions of the brain stem?
- controls vital life functions (breathing, heart rate, digestion)
- origin of most cranial nerves; connects brain to body
- regulates sleep/wake cycle
123
Why is the brain stem essential for survival?
It maintains automatic body functions (like heartbeat and breathing) even without conscious control.
124
Which brain region is responsible for thinking, planning, perception, and voluntary movement?
Cerebral Cortex
125
What is an example of efferent neurons in the somatic nervous system?
Somatic example: Touching a hot stove — afferent detects heat → interneuron processes → efferent activates arm muscles
126
Explain what damage to the thalamus would result in?
Thalamus: Sensory relay + perception
Damage: Loss of sensation → later abnormal painful sensations (burning, tingling, pain from light touch)
127
Patient is unconscious but breathing without life support. Which brain area is damaged?
The cerebrum is damaged, but the brainstem is intact.
128
What is the brainstem and cerebrum responsible for?
Brainstem: life support (breathing, heartbeat, vital reflexes)
Cerebrum: consciousness, awareness, voluntary control
129
What state is a patient in who is not conscious?
Coma or vegetative state — alive but not conscious.
130
Patient B is conscious but cannot breathe without a ventilator. Which brain area is damaged?
The brainstem is damaged, but the cerebrum is intact.
131
What functions are lost and preserved in a patient whose brainstem is damaged but cerebrum is intact?
Lost: Autonomic control of breathing and heart rate → brainstem damaged.
Preserved: Awareness, memory, thought → cerebrum intact.
132
Which brain region controls consciousness and awareness?
Cerebrum.
133
Which brain region controls basic life functions like breathing and heart rate?
Brainstem.
134
What is the cerebrum and the brainstem known for?
Cerebrum = Consciousness
Brainstem = Life support
135
A patient suffers a stroke, they lose sensation on one side of the body, then they experience severe burning pain from light touch.
Which brain structure is affected?
Thalamus
- because thalamus is known as the sensory relay station
136
Why does thalamic damage cause loss of sensation initially?
The thalamus is the sensory relay station — all sensory input passes through it before reaching the cortex. Damage disrupts normal signal transmission, causing numbness or sensory loss.
137
Why does pain develop later (burning, tingling, pain from light touch) when the Thalamus is damaged?
Because damaged thalamic neurons misprocess sensory information, sending scrambled or exaggerated pain signals to the cortex.
138
What is it called when you experience pain from light touch?
Thalamic pain syndrome (or central post-stroke pain).
139
What is the main function of the cerebellum?
Coordination, balance, and movement fine-tuning.
140
What brain region is responsible for coordination, balance and movement?
Cerebellum
141
What is the main function of the hypothalamus?
Maintains homeostasis — regulates temperature, thirst, hunger, hormones, and other internal processes.
142
Why is the hypothalamus not the structure affected in sensory loss or pain?
Because it controls internal regulation, not sensory perception or processing.
143
What is the main function of the medulla (brainstem)?
Controls vital life functions such as breathing, heart rate, and reflexes.
144
Which brain region is responsible for survival functions?
Medulla
145
What is the main function of the thalamus?
Acts as the sensory relay center and provides crude awareness of sensations.
146
Which brain region is affected in sensory loss followed by painful sensations?
Thalamus because it disrupts sensory relay and interpretation, leading to numbness first, then abnormal painful sensations (thalamic pain syndrome)
147
Explain cerebrum vs thalamus
“Cerebrum = consciousness; Brainstem = life.”
“Thalamus = sensory relay; damage = scrambled sensations.”
148
What takes up 90% of cells in the CNS?
Glial cells.
149
What are Glial cells also called?
neuroglia cells.
150
What do glial cells do?
support, protect, modulate neurons.
151
What are known as active players in brain function?
glial cells.
152
What do glial cells do?
Physically, metabolically, and functionally support neurons
Essential for learning, memory, and homeostasis
153
What are the four types of glial cells?
1. Astrocytes
2. Oligodendrocytes
3. Microglia
4. Ependymal cells.
154
What acts as the main connective tissue of the CNS?
Astrocytes.
155
What are the functions of astrocytes?
structural support, guide neuron growth, help form blood-brain barrier (BBB), repair injuries (scarring), regulate neurotransmitters and K+ levels, participate in “three-party synapses.”
156
What is the main role of astrocytes in the CNS?
Astrocytes are the main support and regulatory glial cells that maintain the brain’s environment, support neurons structurally and metabolically, and modulate communication between neurons.
157
How do astrocytes provide support and structure in the CNS?
- main connective tissue of the CNS
- holds neurons in place and organizes them
- gives structure to the brain and spinal cord
158
What role do astrocytes play during fetal brain development?
- guide neurons to their correct positions
- act like a GPS that ensures proper brain wiring during growth
159
How do astrocytes contribute to the blood–brain barrier (BBB)?
- astrocytes wrap around blood vessels and signal capillaries to form tight junctions
- this helps control what can enter the brain, acting like bodyguards that protect the CNS
160
What does the BBB formed by astrocytes do?
It protects the brain from toxins and harmful chemicals in the blood, while letting important nutrients like oxygen and glucose to pass through
161
How do astrocytes respond after a brain injury?
They repair and protect damaged areas by forming neural scars to seal off injury sites since neurons cannot regenerate.
162
Why are astrocytes called “first responders” after brain injury?
They clean up debris, patch damage, and form a protective barrier around the injury site.
163
How do astrocytes help regulate neurotransmitter levels?
They absorb and break down excess neurotransmitters like glutamate and GABA to prevent overstimulation and maintain balance.
164
How do astrocytes maintain proper electrical activity in the brain?
They absorb excess K⁺ ions around active neurons, preventing over-excitability and reducing the risk of seizures.
165
What is a “three-party synapse”?
It’s a synapse involving the presynaptic neuron, postsynaptic neuron, and astrocyte, which monitors, modulates, and shapes the signal.
166
How do astrocytes communicate with neurons?
They detect neurotransmitters like ATP and glutamate, respond to neuronal activity, and release their own messengers to influence synaptic transmission.
167
How do astrocytes enhance synapse formation and learning?
They release growth factors that strengthen synaptic connections — essential for memory and learning.
168
Explain the ‘Three-party synapse’
1. Presynaptic neuron: sends the signal
2. Postsynaptic neuron: receives the signal
3. Astrocyte: monitors, modulates, and shapes the signal.
169
How do astrocytes shape brain communication?
Astrocytes and neurons are in constant two-way chatter. Astrocytes respond to neuronal activity, and in turn release chemicals that affect how neurons communicate.
170
How do astrocytes enhance synapse formation?
- release growth factors that help neurons form and strengthen new synaptic connections
Also guide axons and dendrites to the right locations during development
Help neurons build new synaptic connections.
171
How can astrocytes modify synaptic transmission?
Astrocytes can boost or weaken (modulate) the signals between neurons by cleaning up neurotransmitters (glutamate, GABA) or releasing their own chemical messengers (ATP, glutamate, D-serine).
172
What are the two ways astrocytes communicate?
gap junctions and chemical receptors.
173
How do astrocytes communicate?
They communicate with each other and pass information across the brain using both physical connections and chemical signals (gap junctions and chemical receptors).
174
What are gap junctions and how do astrocytes use them?
- tiny tunnels that connect astrocytes, allowing ions and small molecules to pass between them
- forming a network for rapid communication (the “astrocyte group chat”)
175
How do astrocytes communicate through chemical receptors?
Astrocytes detect and respond to chemical messengers released by neurons (ATP, glutamate), allowing them to sense what neurons are doing and adjust their own behavior accordingly.
176
What triggers astrocyte signaling?
A neuronal action potential, when the neuron sends a signal.
177
What does the neuron release during an action potential?
The axon terminal releases ATP and glutamate into the synapse.
178
How do astrocytes detect neuronal activity?
Astrocytes have receptors that sense ATP and glutamate released from neurons.
179
What happens inside the astrocyte when it detects these neurotransmitters?
K⁺ (potassium) ions flow into the astrocyte, activating it.
180
What does the rise in K⁺ inside the astrocyte cause?
It triggers the astrocyte to release ATP.
181
What happens after the astrocyte releases ATP?
The ATP spreads to nearby astrocytes, activating them too.
182
What does ATP do to nearby glial cells?
It activates nearby glial cells, spreading information through the network.
183
What is the overall effect of astrocyte signaling?
The signal travels through the astrocyte network, allowing astrocytes to share information about neuronal activity.
184
Why is astrocyte signaling important?
It helps coordinate how groups of neurons communicate, keeping brain signaling balanced and synchronized.
185
Quick Summary of Astrocyte Signaling Steps
1. Neuron fires an action potential
2. It releases ATP and glutamate into the synapse
3. Astrocytes detect these signals through receptors
4. K+ enters the Astrocytes, activating it
5. The Astrocyte releases ATP, spreading the signal to nearby astrocytes
6. Astrocytes coordinate brain activity and keep the signals balanced
186
How do astrocytes sense neuronal activity chemically?
Through receptors that detect neurotransmitters like ATP and glutamate, triggering K⁺ influx and further ATP release to nearby astrocytes.
187
What happens when astrocytes become active?
They release ATP, which spreads to neighboring astrocytes, coordinating neural activity and maintaining balanced brain signaling.
188
What is meant by a “three-party synapse”?
It’s a synapse involving three participants:
Presynaptic neuron – sends neurotransmitters (e.g., glutamate, ATP)
Postsynaptic neuron – receives and responds
Astrocyte – monitors, modulates, and shapes the signal.
189
Why are astrocytes part of the “three-party synapse”?
Because they actively participate in communication by detecting neurotransmitters, adjusting signal strength, and maintaining synaptic balance.
190
What does the astrocyte do in the three-party synapse?
Monitors neuronal activity
Modulates signal strength (boosts or dampens)
Shapes long-term responses for learning and memory.
191
How do astrocytes communicate with neurons?
Through two-way “chatter” — they detect neurotransmitters released by neurons and in turn release their own chemical messengers (ATP, glutamate, D-serine) to influence neuronal activity.
192
How do astrocytes respond to neuronal activity?
Neurons release ATP and glutamate during action potentials.
Astrocytes detect these signals via receptors.
K⁺ flows into the astrocyte, activating it.
The astrocyte then releases ATP, spreading the signal.
193
How do astrocytes respond to neuronal activity?
Neurons release ATP and glutamate during action potentials. Astrocytes detect these signals via receptors. K⁺ flows into the astrocyte, activating it. The astrocyte then releases ATP, spreading the signal to nearby astrocytes and glia. This creates a network-wide coordination that helps stabilize communication between neurons.
194
What is the main result of astrocyte signaling?
They help coordinate group neuronal activity and keep brain signaling balanced and stable.
195
How do astrocytes enhance synapse formation?
They release growth factors that help neurons form and strengthen new synaptic connections and guide axons and dendrites to correct locations.
196
Why are astrocytes important for learning and memory?
Because their modulation of synaptic activity helps stabilize and strengthen synapses, which is essential for memory formation and learning.
197
How can astrocytes modulate synaptic transmission?
- astrocytes can control how strong or weak neuron signals are by:
1. Cleaning up extra neurotransmitters (GABA, Glutamate) to stop overstimulation
2. Releasing their own messengers (ATP, glutamate, D-serine) to fine-tune the signal
- they adjust neuron communication by cleaning up or adding signals to keep brain activity balanced
198
What chemical messengers can astrocytes release to influence neurons?
ATP, glutamate, and D-serine.
199
How do astrocytes communicate with each other?
Through gap junctions (tiny tunnels allowing ions and small molecules to pass)
By chemical signaling, detecting and responding to neurotransmitters like ATP and glutamate.
200
What are gap junctions, and why are they important?
Gap junctions are tiny tunnels that connect astrocytes, forming a network that quickly shares signals across the brain — like an astrocyte group chat.
201
What allows astrocytes to sense what neurons are doing?
Chemical receptors that detect neurotransmitters released by neurons (ATP, glutamate).
202
What are the steps of astrocyte signaling during neuronal activity?
Neuron fires an action potential, releasing ATP and glutamate. Astrocyte detects these neurotransmitters via receptors. K⁺ influx activates the astrocyte. Activated astrocyte releases ATP. ATP spreads to nearby astrocytes, activating them. Astrocytes share information and coordinate neuronal communication.
203
What is the purpose of this astrocyte signaling chain?
To ensure synchronized brain activity and prevent over-excitation or imbalance in neuronal firing.
204
Summarize the main roles of astrocytes in synapse communication
Astrocytes help control and support communication between neurons
- monitor and adjust neural signalling
- release chemicals that affect neuron activity
- clear away extra neurotransmitters
- connect with each other to share information
- help with learning and memory by strengthening synapses
205
Explain the three party synapse.
Presynaptic neuron: sends signal (releases neurotransmitters ex. glutamate)
Postsynaptic neuron: receives signals (responds to neurotransmitters)
Astrocyte: modulates signal (detects, adjusts, maintains balance).
206
Summarize the key functions of astrocytes.
- Support & Structure: hold neurons in place and give the brain physical support
- Scaffold Development
- Form the BBB (blood-brain-barrier): protect brain by controlling what enters blood
- Repair & Scarring: helps heal damaged brain tissue
- Regulate Neurotransmitters: clears away extra ions like glutamate to prevent overstimulation
- Maintain Ion Balance (K⁺)
207
What is the most abundant glial cells in the CNS?
astrocytes.
208
What do astrocytes do?
They support neurons, help with repair, and maintain the brain's environment. Known as “nanny cells”, they take care of the environment so neurons can work properly.
209
What do oligodendrocytes do?
Produce myelin sheaths around CNS axons for faster signal conduction, wraps around multiple axons per cell.
210
What is the function of Microgolia?
Plays a role in defense of the brain as phagocytic scavengers.
211
What do Ependymal cells do?
- Line internal cavities of brain and spinal cord
- Help make and move cerebrospinal fluid (CSF)
- Can act as neural stem cells that form new neurons and glial cells
212
What are oligodendrocytes responsible for?
Form myelin sheaths around CNS axons to speed up nerve conduction.
213
What is responsible for MS and what is responsible for seizures?
Astrocytes are support and regulation = cause seizures
Oligodendrocytes are insulation and speed = cause MS
214
What disease is associated with oligodendrocyte damage?
Multiple Sclerosis (MS) — demyelination slows or blocks nerve impulses.
215
What is Multiple Sclerosis (MS)?
A chronic autoimmune disease that causes inflammation and destruction of myelin in the brain, spinal cord, and optic nerves.
216
Which glial cells are affected in MS?
Oligodendrocytes, the cells that form myelin sheaths around CNS axons.
217
What does myelin normally do?
It insulates axons and allows fast, efficient nerve signal conduction.
218
What happens to myelin in MS?
The immune system attacks and destroys the myelin sheath, causing demyelination.
219
What is demyelination?
The loss or damage of myelin, which slows or blocks nerve signal transmission.
220
Why are MS symptoms variable between patients?
Because demyelination occurs in different nerves and areas of the CNS for each individual.
221
What are common symptoms of MS?
- muscle weakness
- numbness or tingling
- vision problems
- difficulty with coordination or balance
222
How does MS appear on MRI scans?
- damaged areas form scar tissue (sclerosis)
- visible as multiple lesions on MRI — hence the name Multiple Sclerosis.
223
Why does MS cause slowed or blocked signals?
- myelin loss disrupts the insulation of axons
- prevents proper electrical transmission along neurons
224
Why is MS considered an autoimmune disease?
Because the body’s own immune system attacks the oligodendrocytes and their myelin sheaths.
225
Where are Oligodendrocytes found?
in CNS (brain + spinal cord)
226
Which are the immune cells of the CNS?
Microglia
227
What are microglia derived from?
derived from the bone marrow tissue and during embryonic development
228
What do microglia do?
- immune cells of the brain
- they stay in place until there’s an infection or injury, then activate to remove damaged cells or fight germs
- act as brains cleanup crew and defense system
229
Explain Microglia in resting state
- wispy cells with many long branches radiating outward
- release low levels of growth factors, help neurons and other glial cells survive and thrive
230
Explain Microglia in activated state
- retract their branches, round up, become highly mobile
- move toward the affected area, release destructive chemicals and remove foreign invaders or tissue debris
231
What do microglia do?
Immune cells of the CNS; act as phagocytes, remove debris and pathogens, and release growth factors when resting
232
What are ependymal cells responsible for?
- they line the brains ventricles and spinal cord canal
- make and move cerebrospinal fluid (CSF)
- act as stem cells to create new brain cells
233
What do Ependymal cells do?
- line internal, fluid filled cavities of the CNS
- helps form CSF fluid that surround and cushions brain + spinal cord
234
Which cell bears cilia?
Ependymal cells, they beat rhythmically back and forth
235
What structures protect the CNS?
- Bony enclosure (cranium and vertebral canal)
- Meninges (three layers)
- Cerebrospinal fluid (CSF)
- Blood–brain barrier (BBB)
236
What are the three layers of the meninges (outer to inner)?
1. Dura mater
2. Arachnoid mater
3. Pia mater.
237
Explain Dura Mater
- tough, outermost layer of meninges that protects brain + spinal cord
- also forms venous sinuses that drain blood and CSF
- strong outer covering that protects brain and drains fluid
DURA = Durable (outermost tough layer)
238
What is the dura mater?
Tough, inelastic outer layer; forms dural and venous sinuses for blood drainage and CSF re-entry.
239
Explain the 3 membranes of Meninges
wrapping , protecting, nourishing
Meninges wrap CNS cord from outermost to innermost
Dura Mater: tough outermost layer
Arachnoid Mater: richly vascularized middle layer
Pia Mater: most fragile, innermost layer
240
What is the dura mater?
The outermost, toughest layer of the meninges that protects the brain and spinal cord.
241
What does the term “dura mater” literally mean?
“Tough mother” — referring to its strong, protective nature.
242
What is the main function of the dura mater?
To provide physical protection and a durable covering around the CNS.
243
What is the dura mater made of?
A thick, inelastic membrane composed of dense connective tissue.
244
How many layers does the dura mater have?
Two layers that usually adhere closely together.
245
What are the dural sinuses (or venous sinuses)?
Blood-filled cavities formed where the two layers of the dura separate.
246
What is the function of the dural sinuses?
- act like drainage channels for used blood and CSF
- drain blood from the brain and return it to the heart
247
What else drains into the dural sinuses besides venous blood?
Cerebrospinal fluid (CSF) re-enters the bloodstream at the sinus sites.
248
Why is the dura mater important for CNS protection?
It forms a tough outer barrier that anchors and protects the brain, while also serving as a drainage pathway for blood and CSF.
249
What is the arachnoid mater?
- delicate, vascular middle layer
- contains arachnoid villi that reabsorb CSF into the blood
250
What is the arachnoid mater?
- middle layer of meninges
Delicate, richly vascularized layer that lies beneath dura mater and above pia mater
251
What is Arachnoid Villi?
- small protrusions that project into dural sinuses
252
What is the purpose of Arachnoid Villi?
purpose is to reabsorb CSF from the subarachnoid space back into the venous blood
253
True or False: Arachnoid villi drain CSF into surrounding tissues.
False — they drain CSF into dural sinuses.
254
What is subarachnoid space?
space between arachnoid mater & pia mater
255
What is subarachnoid space filled with?
cerebrospinal fluid (CSF)
256
What does subarachnoid space do?
acts as a cushion and protects the brain while also playing a major role in cerebrospinal fluid (CSF) circulation
257
What is the pia mater?
Thin, vascular inner layer that adheres to the brain and spinal cord; important in CSF formation.
258
What are the main roles of CSF?
- surrounds CNS (cushions the brain and spinal cord)
- acts as a shock absorber
- allows nutrient/waste exchange
259
Explain Meninges from outermost to innermost
1. Dura mater - tough, outer protective layer
2. Arachnoid mater - delicate, web-like middle layer
3. Pia mater - thin, innermost layer that tightly adheres to the brain and spinal cord surface
260
Where is CSF produced?
Choroid plexus (ependymal cells in brain ventricles).
261
Where is cerebrospinal fluid (CSF) produced?
By the choroid plexus within the brain’s ventricles.
262
What is the first step in CSF circulation?
CSF is produced by the choroid plexus and begins circulating through the ventricular system.
263
Through what structures does CSF circulate?
It circulates throughout all brain ventricles (lateral, third, and fourth ventricles).
264
Where does CSF exit the ventricular system?
It exits through the fourth ventricle at the base of the brain.
265
After leaving the fourth ventricle, where does CSF flow?
It flows into the subarachnoid space, located between the arachnoid mater and pia mater.
266
What happens to CSF in the subarachnoid space?
It circulates around the brain and spinal cord, acting as a cushion and shock absorber.
267
How is CSF reabsorbed into the bloodstream?
It is reabsorbed through the arachnoid villi into the venous blood.
268
Where does reabsorbed CSF ultimately drain?
Into the dural venous sinuses, and then back to the heart via venous circulation.
269
Outline the circulation of CSF.
- Produced in ventricles
- Circulates through ventricles
- Exits fourth ventricle
- Flows in subarachnoid space
- Reabsorbed via arachnoid villi into venous blood
270
Quick Summary of CSF Flow Pathway
1. Made by the choroid plexus
2. Flows through the brains ventricles
3. Exist through the fourth ventricle
4. Enters the subarachnoid space (around brain + spinal cord)
5. Re-absorbed by arachnoid villi
6. Returns to venous blood
271
What is the function of the BBB?
Protects the brain by preventing harmful chemicals from entering while allowing essential molecules (O₂, CO₂, glucose).
272
What forms the BBB (blood brain barrier)?
- tight junctions between capillary endothelial cells, which block toxins and harmful chemicals from entering the brain
- its made of tight junctions in brain capillaries that protect the brain from toxins
273
What can cross the BBB easily?
Lipid-soluble molecules (O₂, CO₂, alcohol).
274
What forms the blood-brain barrier (BBB)?
The endothelial cells of brain capillaries, which are tightly joined by tight junctions.
275
What is the function of the BBB?
To protect the brain by preventing harmful chemical fluctuations and blocking toxins or pathogens from entering the CNS.
276
How is the BBB different from other capillaries in the body?
- BBB capillaries are sealed by tight junctions, so there is no exchange between cells
- substances must pass through other capillary cells
277
What types of substances can easily cross the BBB?
Lipid-soluble substances such as oxygen (O₂), carbon dioxide (CO₂), alcohol, and steroids.
278
How does water cross the BBB?
Water can diffuse through small phospholipid gaps in the membrane.
279
How do glucose, amino acids, and ions cross the BBB?
They require selective transport carriers located in the capillary cell membranes.
280
What substances are blocked by the BBB?
Large plasma proteins and most other substances that are not lipid-soluble or have no transport mechanism.
281
Why is the BBB important for brain stability?
It maintains a stable chemical environment for neurons and prevents sudden changes in blood composition from affecting neural activity.
282
What does the BBB Allow vs. Block?
Allows: O₂, CO₂, alcohol, steroids, water, glucose (via carriers)
Blocks: Large proteins, toxins, most drugs, charged molecules
283
What brain regions lack a BBB?
Circumventricular organs (hypothalamus, pituitary, brainstem) — for blood monitoring and hormone release.
284
What is the main function of the blood-brain barrier (BBB)?
To control what substances can move from the bloodstream into brain tissue, keeping the brain’s environment stable and protected.
285
What harmful substances does the BBB protect the brain from?
Toxins, pathogens, and chemical fluctuations in the blood.
286
What essential materials are still allowed through the BBB?
Glucose, oxygen, and other necessary nutrients.
287
What role do astrocytes play in maintaining the BBB?
Astrocytes signal capillary cells to form tight junctions, creating the selective barrier of the BBB.
288
Besides signaling, how else do astrocytes support the BBB?
They assist in the transport of ions (like K⁺) and help maintain the chemical balance of the brain’s environment.
289
Why are astrocytes important for BBB stability?
They act as intermediaries between blood vessels and neurons, monitoring and regulating what enters the brain.
290
Are all regions of the brain protected by the BBB?
No — some specialized areas lack the BBB to allow communication with the bloodstream.
291
What are brain regions without a BBB called?
Circumventricular organs (CVOs).
292
What does the term circumventricular mean?
Circum = around, ventricular = ventricles → regions around the brain’s ventricles where the BBB is absent.
293
Why do circumventricular organs (hypothalamus, pituitary) lack a BBB?
So the brain can directly monitor blood and release hormones into circulation when needed to maintain homeostasis.
294
What are key examples of circumventricular organs?
The hypothalamus, pituitary gland, and parts of the brainstem.
295
What is the function of circumventricular organs?
They act as “windows” between the brain and blood, letting the brain sample blood contents and adjust hormone release for homeostasis.
296
Summary — Astrocytes & BBB
- astrocytes help form the BBB by signalling for tight junctions
- move ions (like K+) to keep balance
- keep brain environment stable
- BBB blocks toxins but lets nutrients in
- some areas (hypothalamus, pituitary) don’t have BBB so they can monitor blood and control hormones
- astrocytes build and maintain the BBB, keeping brain protected and balanced
297
Why does the brain require a constant blood supply?
Because it depends on a continuous delivery of oxygen and glucose to produce energy (ATP).
298
Can the brain produce ATP without oxygen?
❌ No — the brain cannot produce ATP in the absence of oxygen (it lacks anaerobic capacity).
299
Does the brain store glucose?
❌ No — the brain does not store glucose effectively, so it relies on a steady supply from the blood.
300
What happens if oxygen supply to the brain is cut off?
Irreversible brain damage can occur after about 5 minutes without oxygen.
301
What happens if glucose supply to the brain is interrupted?
Neural damage or dysfunction can occur after about 15 minutes without glucose.
302
Why is the brain so vulnerable to interruptions in blood flow?
Because it has a high metabolic rate, but no energy reserves — it depends entirely on constant oxygen and glucose delivery via blood flow.
303
Why is the spinal tap performed below L2?
To avoid injuring the spinal cord.
304
Where does the spinal cord originate?
It extends downward from the brainstem.
305
Where is the spinal cord located and protected?
Inside the vertebral canal, formed by the stacked vertebrae.
306
What is the main function of the spinal cord?
To link the CNS to the rest of the body through sensory (afferent) and motor (efferent) pathways.
307
What emerges from the spinal cord?
Paired spinal nerves that exit through spaces between vertebrae.
308
What type of nerves are spinal nerves?
Mixed nerves — they contain both afferent (sensory) and efferent (motor) fibers.
309
What is the function of spinal nerves?
To carry sensory input to the CNS and send motor output from the CNS to the body.
310
Where does the spinal cord end?
Around the level of L1–L2 vertebrae.
311
What structure is found below the end of the spinal cord?
The cauda equina, a bundle of elongated nerve roots.
312
Why is it called the cauda equina?
Because it resembles a horse’s tail in appearance.
313
What is the function of the cauda equina?
To transmit nerve signals between the spinal cord and lower parts of the body (legs, pelvic organs).
314
What is a spinal tap (lumbar puncture)?
A procedure where a needle is inserted into the vertebral canal to withdraw cerebrospinal fluid (CSF) for testing.
315
Where is the needle inserted during a spinal tap?
Below the level of L2 in the vertebral canal.
316
Why is the area below L2 chosen for a spinal tap?
Because the spinal cord ends around L1–L2, making it a safe site with no risk of injuring the cord.
317
What structures are found below L2 in the vertebral canal?
Only the cauda equina — a bundle of nerve roots.
318
Why is it safe to insert a needle where the cauda equina is located?
The nerve roots float in CSF and move aside when the needle is inserted, preventing injury.
319
What is the purpose of a spinal tap?
To safely withdraw CSF for diagnostic testing (e.g., infection, bleeding, pressure).
320
Where is the spinal cord located?
It is protected inside the vertebral column (vertebral canal).
321
What protects the spinal cord besides bone?
The meninges and cerebrospinal fluid (CSF) provide cushioning and protection.
322
What are the meninges?
The three protective layers around the brain and spinal cord — dura mater, arachnoid mater, and pia mater.
323
What is found in the dorsal root ganglion?
The cell bodies of sensory (afferent) neurons.
324
What does the ventral root contain?
Motor (efferent) fibers that carry commands from the CNS to muscles or glands.
325
What happens when the dorsal and ventral roots join?
They form a spinal nerve, which is a mixed nerve (contains both sensory and motor fibers).
326
What is the function of the intervertebral discs?
They cushion and separate the vertebrae, absorbing shock and allowing flexibility.
327
How many pairs of spinal nerves are there?
31 pairs, each connecting the spinal cord to specific body regions.
328
What two roots join to form a spinal nerve?
The dorsal root and the ventral root.
329
What type of fibers are in the dorsal root?
Afferent (sensory) fibers that carry information toward the CNS.
330
What type of fibers are in the ventral root?
Efferent (motor) fibers that carry signals away from the CNS to muscles or glands.
331
What happens when the dorsal and ventral roots merge?
They form a mixed spinal nerve containing both afferent and efferent fibers.
332
Why are spinal nerves called mixed nerves?
Because they carry both sensory input (afferent) and motor output (efferent) in the same bundle.
333
How is the spinal cord connected to the autonomic nervous system?
Through the sympathetic ganglion chain, which links spinal nerves to autonomic (involuntary) functions.
334
How many pairs of spinal nerves emerge from the spinal cord?
31 pairs of spinal nerves.
335
Where do spinal nerves exit the spinal cord?
Through spaces between adjacent vertebrae.
336
How are spinal nerves named?
By the region of the vertebral column from which they exit.
337
How many pairs of cervical nerves are there, and where are they located?
8 pairs – located in the neck region.
338
How many pairs of thoracic nerves are there, and where are they located?
12 pairs – located in the chest (thoracic) region.
339
How many pairs of lumbar nerves are there, and where are they located?
5 pairs – located in the abdominal (lower back) region.
340
How many pairs of sacral nerves are there, and where are they located?
5 pairs – located in the pelvic region.
341
How many pairs of coccygeal nerves are there, and where are they located?
1 pair – located near the tailbone (coccyx).
342
What are the two primary functions of the spinal cord?
Relay station (links brain and body) and reflex center (automatic responses).
343
List the meninges from outermost to innermost.
Dura mater – tough, outer protective layer
Arachnoid mater – delicate, web-like middle layer
Pia mater – thin, innermost layer that tightly adheres to the brain and spinal cord.
344
What is the function of the meninges?
They protect the CNS and help circulate cerebrospinal fluid (CSF).
345
Where does cerebrospinal fluid (CSF) circulate relative to the meninges?
In the subarachnoid space, located between the arachnoid mater and pia mater.
346
Where is CSF produced?
By the choroid plexus within the brain’s ventricles.
347
What is the pathway of CSF circulation?
Produced by choroid plexus
Circulates through the ventricles
Exits the fourth ventricle at the base of the brain
Flows in the subarachnoid space around the brain and spinal cord
Reabsorbed into venous blood across the arachnoid villi.
348
What is the function of cerebrospinal fluid (CSF)?
To cushion and protect the brain and spinal cord, transport nutrients, and remove waste products.
349
What are arachnoid villi?
Tiny projections of the arachnoid mater that reabsorb CSF into venous circulation.
350
What does cerebrospinal fluid (CSF) surround?
The brain and spinal cord.
351
What is one of the main functions of CSF?
To cushion and protect the brain and spinal cord from injury.
352
How does CSF act as a protective mechanism?
It serves as a shock absorber, preventing the brain from hitting the skull during sudden movements.
353
Besides protection, what is another key function of CSF?
It allows exchange of materials (like nutrients and waste) between neural cells and interstitial fluid around the brain.
354
How is CSF maintained in the CNS?
It is under constant production and flow, circulating through the CNS and then draining into the venous system.
355
What is the overall importance of CSF?
It provides mechanical protection, chemical stability, and nutrient exchange for the central nervous system.
356
Where is grey matter located in the brain?
On the outside of the brain (cerebral cortex).
357
Where is white matter located in the brain?
On the inside, beneath the grey matter.
358
Where is grey matter located in the spinal cord?
On the inside, shaped like a butterfly.
359
Where is white matter located in the spinal cord?
On the outside, surrounding the grey matter.
360
What does grey matter contain?
Neuronal cell bodies, dendrites, interneurons, and glial cells.
361
What is the main function of grey matter?
Acts as the processing hub for integration and decision-making in the CNS.
362
What does white matter contain?
Bundles of axons (nerve fibers) called tracts.
363
What is the main function of white matter?
To transmit information between regions — acts as communication highways.
364
How is white matter organized in the spinal cord?
Into columns (funiculi) containing nerve tracts running up and down the cord.
365
What do ascending tracts in white matter do?
Carry sensory (afferent) information up to the brain.
366
What do descending tracts in white matter do?
Carry motor (efferent) commands down from the brain to the body.
367
How many “horns” is the spinal cord’s grey matter divided into?
Three horns: dorsal, ventral, and lateral.
368
What are the 3 horns of the spinal cord's grey matter?
Dorsal horn: interneurons for afferent output
Ventral horn: somatic motor neurons
Lateral horn: autonomic (sympathetic) neurons.
369
What is found in the dorsal horn?
Cell bodies of interneurons where afferent (sensory) neurons terminate.
370
What is the function of the dorsal horn?
To receive and process sensory input entering the spinal cord.
371
What is found in the ventral horn?
Cell bodies of efferent (motor) neurons that supply skeletal muscles.
372
What is the function of the ventral horn?
To send motor commands from the CNS to skeletal muscles (voluntary control).
373
What is found in the lateral horn?
Cell bodies of autonomic sympathetic nerve fibers.
374
What is the function of the lateral horn?
To control involuntary functions through the autonomic nervous system (e.g., heart rate, digestion).
375
What is the central canal?
A narrow channel filled with cerebrospinal fluid (CSF) that lies in the center of the grey matter.
376
Overall function of spinal cord grey matter?
Acts as the integration and processing center for sensory and motor information.
377
What is the spinal cord white matter made of?
Bundles of axons (nerve fibers) that form nerve tracts.
378
How are the tracts in white matter organized?
Into columns (funiculi), with each tract having a specific function and destination.
379
Where do the tracts of white matter begin or end?
Each tract begins or ends in a particular area of the brain.
380
What do ascending tracts do?
Transmit afferent (sensory) input to the brain.
381
What do descending tracts do?
Relay efferent (motor) commands from the brain to the body.
382
What is the main function of spinal cord white matter?
To serve as communication highways, transmitting information between the brain and spinal cord.
383
What direction do ascending tracts carry information?
Up to the brain — they carry sensory (afferent) information.
384
What direction do descending tracts carry information?
Down from the brain — they carry motor (efferent) commands.
385
What is an example of an ascending (sensory) tract?
Ventral Spinocerebellar Tract.
386
Where does the Ventral Spinocerebellar Tract originate and end?
Originates in the spinal cord and ends in the cerebellum.
387
What is the function of the Ventral Spinocerebellar Tract?
Sends information from muscle stretch receptors to the cerebellum for coordination and balance.
388
What is an example of a descending (motor) tract?
Ventral Corticospinal Tract.
389
Where does the Ventral Corticospinal Tract originate and end?
Originates in the cerebral cortex and ends in the spinal cord (motor neurons).
390
What is the function of the Ventral Corticospinal Tract?
Sends movement commands from the brain to skeletal muscles.
391
How do spinal nerves connect to the spinal cord?
By a dorsal root and a ventral root on each side.
392
What type of fibers does a spinal nerve contain?
Both afferent (sensory) and efferent (motor) fibers — it’s a mixed nerve.
393
What is found in the dorsal root?
Afferent (sensory) fibers bringing information into the spinal cord.
394
What is found in the ventral root?
Efferent (motor) fibers carrying commands out from the spinal cord.
395
What is a nerve in the PNS?
A bundle of peripheral axons enclosed in connective tissue.
396
What is the term for a bundle of axons in the CNS?
A tract.
397
Where is the spinal cord located?
Between the brain and the afferent/efferent fibers of the PNS (Peripheral Nervous System).
398
Why is the spinal cord’s location important?
It allows the spinal cord to act as a link between the brain and the rest of the body.
399
What are the two primary functions of the spinal cord?
Relay Station: links brain and body
Reflex Center: mediates automatic responses.
400
What is the Relay Station function of the spinal cord?
It passes information back and forth between the brain and the body through ascending (sensory) and descending (motor) tracts.
401
What is the Reflex Center function of the spinal cord?
It can directly connect afferent input to efferent output — producing a spinal reflex without involving the brain.
402
Example of the spinal cord acting as a reflex center?
The withdrawal reflex — pulling your hand away from a hot surface before the brain even processes the pain.
403
Which part of the nervous system connects the CNS to the rest of the body?
PNS.
404
What is a reflex?
A response that occurs automatically and without conscious effort, forming part of a biological control system that links a stimulus to a response.
405
What are the two main types of reflexes?
Simple (Basic) Reflexes
Acquired (Conditioned) Reflexes.
406
What is a simple (basic) reflex?
An inborn, automatic response that does not require learning or conscious thought.
## Footnote
Example: Pulling your hand away from a hot surface.
407
What is an acquired (conditioned) reflex?
A learned response that develops through repetition or practice.
## Footnote
Example: Playing piano by reading notes.
408
How do reflexes help maintain homeostasis?
By allowing the body to respond quickly and automatically to internal or external changes without waiting for conscious control.
409
What is a reflex arc?
The neural pathway that carries out a reflex action — it links a stimulus to an automatic response.
410
How many main components are in a reflex arc?
Five components.
411
What are the five basic components of a reflex arc (in order)?
1. Receptor – detects the stimulus
2. Afferent Pathway – carries signal to integrating center
3. Integrating Center – processes information and decides response
4. Efferent Pathway – sends command to effector
5. Effector – carries out the response.
412
What is the role of the receptor in a reflex arc?
Detects a physical or chemical change (stimulus) such as heat, pressure, or pain.
413
What is the role of the afferent pathway?
Carries sensory signals from the receptor to the integrating center (CNS).
414
What does the integrating center do?
Processes the incoming information and determines the appropriate response.
415
Which part of the nervous system usually acts as the integrating center?
Spinal cord or brainstem for basic (simple) reflexes.
Higher brain centers for acquired (learned) reflexes.
416
What is the function of the efferent pathway?
Carries motor instructions from the CNS to the effector organ.
417
What is the role of the effector?
Executes the response — a muscle contracts or a gland secretes.
418
What type of reflex is the stretch reflex?
A monosynaptic reflex (only one synapse between the sensory and motor neuron).
419
What is the classic example of a stretch reflex?
The patellar tendon (knee-jerk) reflex.
420
What happens during the patellar tendon reflex?
The patellar tendon is tapped with a reflex hammer.
This stretches the quadriceps muscle.
Stretch receptors (muscle spindles) detect this and send signals to the spinal cord.
The spinal cord sends a motor signal back to the quadriceps to contract — causing the lower leg to kick forward.
421
Why is the stretch reflex important clinically?
It serves as a preliminary assessment of nervous system function, especially spinal cord and motor neuron integrity (tests spinal function).
422
Why is it called 'monosynaptic'?
Because there is only one synapse between the afferent (sensory) neuron and the efferent (motor) neuron — no interneuron is involved.
423
What muscle response occurs in the stretch reflex?
The stretched muscle contracts to prevent overstretching and maintain posture.
424
What type of reflex is the knee-jerk reflex?
A stretch reflex and a monosynaptic reflex (only one synapse between sensory and motor neurons).
425
What stimulus triggers the knee-jerk reflex?
Tapping the patellar tendon just below the kneecap with a reflex hammer.
426
What happens when the patellar tendon is tapped?
It stretches the quadriceps muscle on the front of the thigh.
427
Which receptors detect the muscle stretch?
Muscle spindles in the quadriceps detect the stretch.
428
What happens after the muscle spindle detects the stretch?
A sensory (afferent) neuron sends the signal to the spinal cord.
The sensory neuron directly synapses with a motor neuron (no interneuron).
429
What does the motor neuron do?
It sends a signal back to the quadriceps, causing the muscle to contract.
430
What is the final action of the knee-jerk reflex?
The quadriceps contracts, and the lower leg kicks forward.
431
Why is this reflex important clinically?
It helps assess spinal cord function and motor pathway integrity, particularly at the L2–L4 spinal levels.
432
What are the steps of the Knee-Jerk Reflex (Patellar Tendon Reflex) in order?
1️⃣ Tap patellar tendon
2️⃣ Quadriceps muscle stretches
3️⃣ Muscle spindles detect stretch
4️⃣ Afferent (sensory) neuron sends signal to spinal cord
5️⃣ Sensory neuron directly synapses with motor neuron (monosynaptic)
6️⃣ Efferent (motor) neuron sends command to quadriceps
7️⃣ Quadriceps contracts → lower leg kicks forward
433
What type of reflex is the withdrawal reflex?
A polysynaptic reflex (involves multiple synapses and interneurons).
434
What is the main function of the withdrawal reflex?
To protect the body from pain or injury, like pulling your hand away from a hot surface.
435
What activates the withdrawal reflex?
Pain receptors (nociceptors) in the skin detect a painful stimulus such as heat.
436
What is the role of the afferent (sensory) neuron in the withdrawal reflex?
It carries the pain signal to the spinal cord from the site of injury.
437
What is the integrating center in the withdrawal reflex?
The spinal cord, which processes the incoming signal and coordinates the motor response.
438
What happens inside the spinal cord during the withdrawal reflex?
Excitatory interneuron: activates flexor muscle (biceps) → contracts.
Inhibitory interneuron: inhibits extensor muscle (triceps) → relaxes.
Ascending interneuron: sends signal up to the brain → pain awareness.
439
What is the role of the efferent (motor) neuron in the withdrawal reflex?
It carries motor commands from the spinal cord to the muscles.
440
What are the effectors in the withdrawal reflex?
Biceps (flexor): contracts to pull the hand away.
Triceps (extensor): relaxes so it doesn’t resist the movement.
441
What is reciprocal innervation in the withdrawal reflex?
It’s when one muscle contracts while its antagonist relaxes (biceps contract, triceps relax).
442
Does the brain control the withdrawal reflex?
No — the reflex occurs before the brain is aware, but the signal later travels up to the brain so you feel pain and remember it.
443
Simplified sequence of the withdrawal reflex:
1️⃣ Painful stimulus (heat) activates receptor
2️⃣ Afferent neuron carries impulse to spinal cord
3️⃣ Interneurons process and send signals
4️⃣ Efferent neurons activate effectors
5️⃣ Muscles contract or relax → hand withdraws
6️⃣ Brain receives info after reflex completes
444
What is Babinski’s Reflex?
Stroking the sole of the foot causes the big toe to extend upward and the other toes to fan outward.
445
What does a positive Babinski’s reflex look like?
Dorsiflexion (extension) of the big toe and fanning (abduction) of the other toes.
446
In which age group is a positive Babinski’s reflex normal?
Infants up to about 2 years old.
447
Why is the Babinski reflex normal in infants?
Because their corticospinal tract is still immature.
448
What replaces the Babinski reflex as the nervous system matures?
Plantar flexion — downward curling of the toes.
449
What does a positive Babinski’s reflex after age 2 indicate?
CNS or corticospinal tract damage/lesion.
450
Is a positive Babinski reflex in adults temporary or permanent?
It can be either, depending on the cause and extent of CNS damage.
451
What is the Crossed Extensor Reflex?
A reflex that ensures the opposite limb supports body weight when the injured limb withdraws from a painful stimulus.
452
When does the Crossed Extensor Reflex occur?
Along with the withdrawal reflex, usually when one leg steps on something painful or sharp.
453
What is the stimulus that triggers the crossed extensor reflex?
A painful stimulus such as stepping on something sharp.
454
What does the afferent pathway do in the Crossed Extensor Reflex?
Carries the pain signal from the injured leg to the spinal cord.
455
What acts as the integrating centre in the crossed extensor reflex?
The spinal cord, which coordinates both the withdrawal reflex and the crossed extensor reflex at the same time.
456
What happens in the withdrawal reflex (injured leg)?
Flexor muscles contract → leg pulls away from pain.
Extensor muscles relax → allows leg to lift.
457
What happens in the crossed extensor reflex (opposite leg)?
Extensor muscles contract → support body weight.
Flexor muscles relax → keeps the leg straight and stable.
458
What are the effectors in the crossed extensor reflex?
Injured leg: flexor contracts to withdraw.
Opposite leg: extensor contracts to bear weight.
459
What is the overall function of the crossed extensor reflex?
To maintain balance and prevent falling when the withdrawal reflex is triggered.
460
Why is the brain stem considered a vital link?
Because it serves as both a communication highway for neural signals and an integration centre for essential life functions like breathing, digestion, heart rate, circulation, posture, alertness, and sleep.
461
What passes through the brain stem?
All incoming and outgoing nerve fibers between the periphery and higher brain centers.
462
What are the five key functions of the brain stem?
1️⃣ Origin of most cranial nerves (majority of the 12 pairs).
2️⃣ Controls cardiovascular, respiratory, and digestive activities.
3️⃣ Regulates postural muscle reflexes.
4️⃣ Contains the Reticular Activating System (RAS) — controls cortical alertness.
5️⃣ Plays a role in the sleep-wake cycle.
463
Which cranial nerves does the brain stem contain?
III-XII (majority of them).
464
What vital body systems does the brain stem control?
The cardiovascular, respiratory, and digestive systems.
465
What is the RAS (Reticular Activating System) and what does it do?
A network within the brain stem that regulates cortical alertness and arousal — keeps you awake and attentive.
466
How does the brain stem contribute to posture and balance?
It regulates postural reflexes to maintain balance and muscle tone.
467
What role does the brain stem play in sleep?
It helps control the sleep-wake cycle through its interaction with the RAS.
468
What is the reticular formation?
- neurons in the brain stem that integrates sensory input such as visual, auditory, and spinal sensory signals
469
What is the Reticular Activating System (RAS)?
The ascending fibres from the reticular formation that activate the cerebral cortex.
470
What are the main functions of the RAS?
Maintains wakefulness and alertness.
Promotes attention and focus.
Plays a key role in the sleep/wake cycle and levels of consciousness.
Filters sensory information to prioritize what reaches the cortex.
471
How does the RAS help the brain process sensory input?
It filters important information, preventing sensory overload and allowing the brain to focus on what matters most.
472
What happens if the RAS is damaged?
The person can become unconscious or fall into a coma due to loss of cortical activation.
473
What is grey matter vs. white matter?
Grey = neuron cell bodies, interneurons (processing).
White = myelinated axons (tracts for transmission).
474
What are the components of a reflex arc?
Receptor → Afferent pathway → Integrating center → Efferent pathway → Effector.
475
What is the stretch reflex?
Monosynaptic reflex (e.g., knee-jerk); tests spinal function.
476
What is the withdrawal reflex?
Polysynaptic reflex — removes body part from painful stimulus.
477
What is the crossed extensor reflex?
Works with withdrawal reflex — opposite leg extends to maintain balance.
478
What is Babinski’s reflex?
Normal in infants (toes fan up); abnormal after age 2 indicates CNS damage.
479
Why is a spinal tap performed below L2?
To avoid injuring the spinal cord (cord ends at L1–L2).
480
What makes up the PNS?
Cranial nerves (12 pairs) and spinal nerves (31 pairs).
481
What connects the CNS to the rest of the body?
The PNS.
482
Which cranial nerve connects the brain to internal organs like the heart and digestive tract?
The Vagus nerve (Cranial Nerve X).
483
What are the key regions of the brainstem?
Midbrain, pons, medulla.
484
What are the main functions of the brainstem?
Controls vital life functions (breathing, heart rate, digestion); origin of most cranial nerves; regulates posture and reflexes; part of sleep–wake cycle.
485
What is the Reticular Formation?
Network of neurons within the brainstem that integrates sensory input.
486
What is the RAS (Reticular Activating System)?
Ascending fibres from the reticular formation that maintain alertness, attention, and wakefulness; filters sensory info.
487
Which brain region refines movement?
Basal Nuclei
488
Which brain region is known for sensory relay?
Thalamus
489
Which brain region is known for homeostasis and hormone regulation?
Hypothalamus
490
Which brain region is for coordination and balance?
cerebellum
491
Which brain region is responsible for basic life functions?
brain stem
492
What is an example of afferent neurons in the autonomic nervous system?
Autonomic example: Blood pressure changes — afferent detects stretch → interneuron processes in brainstem → efferent adjusts heart rate
493
Which part of the brain is responsible for breathing?
brainstem
494
Which part of the brain is responsible for consciousness?
cerebrum
495
What structure is associated with the Olfactory nerve (I)? STUDY
Mucosa of nasal cavity
496
What is the termination of fibers of the Olfactory nerve (I)? STUDY
Termination of fibers of olfactory nerve
497
What structure is labeled with the Olfactory nerve (I)? STUDY
Olfactory bulb
498
What structure is associated with the Optic nerve (II)? STUDY
Retina
499
What muscles does the Oculomotor nerve (III) supply? STUDY
Extrinsic eye muscles; ciliary muscle; muscles of iris
500
What muscle is supplied by the Trochlear nerve (IV)? STUDY
Superior oblique (extrinsic eye muscle)
501
What muscles does the Trigeminal nerve (V) supply? STUDY
Motor—muscles of mastication
502
What sensory area is associated with the Trigeminal nerve (V)? STUDY
Sensory—face and head
503
What muscle is supplied by the Abducens nerve (VI)? STUDY
Lateral rectus eye muscle
504
What glands/muscles are supplied by the Facial nerve (VII)? STUDY
Motor—muscles of face and scalp; salivary and tear glands
505
What sensory area is associated with the Facial nerve (VII)? STUDY
Sensory—taste buds on anterior tongue
506
What does the Vestibular branch of the Vestibulocochlear nerve (VIII) innervate? STUDYB
Cochlea, vestibule, and semicircular canals of inner ear
507
What muscles does the Vestibulocochlear nerve (VIII) supply? STUDY
Motor—muscles of pharynx; parotid gland
508
What sensory functions are associated with the Vestibulocochlear nerve (VIII)? STUDY
Sensory—taste buds on pharynx and posterior tongue; baroreceptors in carotid sinus
509
What muscles/organs are linked with the Glossopharyngeal nerve (IX)? STUDY
Motor—muscles of pharynx; parotid gland
510
What sensory structures does the Glossopharyngeal nerve (IX) connect to? STUDY B
Sensory—taste buds on pharynx and posterior tongue; baroreceptors in carotid sinus
511
What muscles does the Vagus nerve (X) supply? STUDY
Motor—muscles of pharynx and larynx
512
What does the Vagus nerve (X) innervate in the body? STUDY
Bronchi; abdominal organs
513
What sensory areas are associated with the Vagus nerve (X)? STUDY
Sensory—taste buds on tongue and pharynx; thoracic and abdominal organs
514
What muscles are supplied by the Accessory nerve (XI)? STUDY
Muscles of larynx, pharynx, soft palate, and neck
515
What muscles are supplied by the Hypoglossal nerve (XII)? SYUDYB
Tongue muscles
