1
Q
What is Brain and Behavior?
A
Brain: Organ that is the center of the nervous system
Behavior: Activities of an organism in response to stimuli
Brain study → Biology
Behavior study → Psychology
2
Q
What is Behavior?
A
Actions or reactions of an organism
Triggered by:
External stimuli (environment)
Internal stimuli (thoughts, emotions)
3
Q
What are David Marr’s 3 levels of analysis?
A
Computational
Algorithmic
Implementational
4
Q
What is the Computational Level?
A
Focus: Goal of behavior
Questions:
What problem is being solved?
Why is it useful?
What information is processed?
5
Q
Example of Computational Level
A
Vision: Convert light → objects
Attention: Focus on relevant stimuli
Brain computes:
Edges
Motion
Salience
6
Q
What is the Algorithmic Level?
A
Focus: How information is processed
Questions:
What is represented?
What rules transform it?
7
Q
Examples of Algorithmic Level
A
Vision:
Edge detection
Motion detection
Attention:
Filtering distractions
Enhancing relevant signals
8
Q
What is the Implementational Level?
A
Focus: Physical brain mechanisms
Questions:
Which neurons/circuits?
Which brain areas?
Which neurotransmitters?
9
Q
Examples of Implementational Level
A
Vision pathway:
Retina → LGN → V1
Attention:
Anterior Cingulate Cortex is involved
10
Q
What was the debate about brain function?
A
(A) Localization: Different brain areas = different functions
(B) Holism: Brain works as one unit
11
Q
What did Jean Pierre Flourens and Karl Lashley find?
A
Rat maze experiments
Deficits depended on size, not location
Conclusion: Brain acts as a whole
12
Q
What did Paul Broca discover?
A
Same speech deficit → same brain area
Broca’s area controls speech production
13
Q
What brain areas are involved in language?
A
Broca’s area → speech production
Wernicke’s area → understanding speech
Located in:
Frontal lobe
Temporal lobe
14
Q
Why is Phineas Gage important?
A
Rod damaged frontal lobe
Personality drastically changed
Showed:
Brain regions control behavior
Prefrontal cortex → decision-making & social behavior
15
Q
What happened to Henry Molaison?
A
Removal of hippocampus
Result:
Severe anterograde amnesia
Could NOT form new memories
16
Q
What did H.M. teach us?
A
Hippocampus = critical for memory formation
Medial temporal lobe → long-term memory
17
Q
What are CNS and PNS?
A
CNS: Brain + spinal cord
PNS: All nerves
18
Q
What are the functions of PNS?
A
Sensory: Environment → brain
Motor: Brain → muscles
19
Q
Difference between autonomic and somatic systems?
A
Autonomic (AC):
Automatic
Controls organs/glands
Somatic (SC):
Voluntary movement
20
Q
What are Sympathetic vs Parasympathetic?
A
Sympathetic (SY):
Arousal
“Fight or flight”
Parasympathetic (PS):
Calming
“Rest and digest”
21
Q
Does the brain act as a single unit?
A
No — brain is specialized
Different regions perform different functions
BUT: Brain areas still communicate with each other
22
Q
How did Jean Pierre Flourens and Karl Lashley contribute?
A
Used lesion experiments
Showed:
Brain damage affects behavior
Different areas contribute to different functions
Helped shape understanding of functional specialization
23
Q
What is the Autonomic Nervous System?
A
Controls automatic body functions
Works without conscious awareness
Includes:
Sympathetic
Parasympathetic
24
Q
What does the Sympathetic system do?
A
“Fight or Flight” response
Activated during:
Danger
Stress
Effects:
↑ Heart rate
Pupil dilation
Sweating
Increased arousal
25
What does the Parasympathetic system do?
“Rest and Digest”
Activated when:
Safe
Relaxed
Effects:
↓ Heart rate
Slower breathing
Pupil constriction
26
What is the Somatic Nervous System?
Controls voluntary movement
Example:
Reflex withdrawal from pain
Pathway:
Receptors → spinal cord → muscles
27
Difference between afferent and efferent pathways?
Afferent (Sensory):
Body → CNS
Carries sensory info
Efferent (Motor):
CNS → muscles/organs
Produces action
28
How does the brain process left vs right?
Left brain → processes right side
Right brain → processes left side
Called contralateral processing
29
Do sensory and motor pathways cross?
Afferent (sensory): cross to opposite side
Motor pathways: Cross then uncross
Result: Opposite brain controls body side
30
What are the main brain cortices?
Visual cortex → vision
Motor cortex → movement
Somatosensory cortex → touch/body info
Auditory cortex → sound
31
Where is the auditory cortex located?
Temporal lobe
Includes:
Broca’s area
Wernicke’s area
32
Difference between short and long loops?
Short loops:
Spinal cord
Reflexes (unconscious)
Long loops:
Cortex
Conscious behavior
33
How do motor and sensory pathways travel?
Sensory: Body → spinal cord → brain
Motor: Brain → spinal cord → muscles
34
What is a stroke?
Loss of blood flow to brain
Causes neuron death
Neurons do NOT regrow easily
35
Common stroke symptoms?
Facial drooping
Arm weakness
Slurred speech
Vision problems
Dizziness
Severe headache
36
How is stroke treated?
Therapy within 48 hours
Types:
Physical therapy
Occupational therapy
Speech therapy
Cognitive therapy
Brain uses neuroplasticity
37
What is epidural anesthesia?
Blocks pain signals
Stops signals from reaching brain
Used in:
Childbirth
Helps study pain perception
38
What is physiology of behavior?
Study of psychology as a biological system
Focus on:
Brain
Cells
Behavior
39
What are glial cells?
Support neurons
Essential for function
“Glue” of nervous system
40
What do neurons do?
Receive information
Process signals
Transmit signals
Use:
Electrical impulses
Chemical signals
41
Parts of a neuron?
Dendrites → receive signals
Soma (cell body) → integrates
Axon → sends signals
Terminal → releases neurotransmitters
42
What are motor neurons?
Control muscles
Long axons
Cell body in spinal cord
Damage → movement problems
43
What is Reticular Theory?
Brain = continuous network
Proposed by Camillo Golgi
44
What is Neuron Doctrine?
Brain made of individual cells
Neurons communicate via synapses
Proposed by Santiago Ramón y Cajal
45
Why is neuron doctrine important?
Established:
Neuron = functional unit
Direction of flow:
Dendrite → soma → axon
46
Why do neurons have different shapes and types?
Structure reflects function
Different neurons:
Process different types of information
Exist in different brain regions
Shape determines:
Input capacity (dendrites)
Output distance (axon length)
Connectivity patterns
47
What are spinal cord motor neurons?
Large multipolar neurons
Location: Cell body in the spinal cord
Function: Send signals to muscles
Key feature:
Long axon → can extend great distances
Role: Voluntary movement
48
What are interneurons?
Located within CNS
Function:
Connect neurons locally
Integrate and modulate signals
Examples:
Amacrine cells (retina)
Basket cells (inhibit nearby neurons)
49
What are reticular formation neurons?
Found in: Brainstem
Structure:
Large dendritic fields
Function:
Integrate widespread sensory signals
Involved in:
Arousal
Consciousness
50
Difference between excitatory and inhibitory neurons?
Excitatory: Increase likelihood of firing
Inhibitory: Decrease likelihood of firing
Balance is critical for: Normal brain function
51
Key neurotransmitters and roles?
Glutamate → Excitatory
GABA → Inhibitory
Acetylcholine → Muscle activation, attention
Serotonin → Mood
Dopamine → Reward, motivation
52
What are glial cells?
“Glue” of nervous system
Support neurons
Do NOT primarily transmit signals
Essential for survival
53
What do astrocytes do?
Connect: Neurons ↔ blood vessels
Functions:
Transport glucose → neurons
Regulate blood flow
Maintain environment
Convert: Glucose → lactate → neuron energy
54
What are microglia?
Immune cells of CNS
Functions:
Destroy pathogens
Remove dead cells (phagocytosis)
Prune synapses
Maintain brain health
55
What do oligodendrocytes do?
Produce myelin sheath
Wrap axons → insulation
Increase signal speed:
Saltatory conduction
Provide metabolic support
56
What is Multiple Sclerosis?
Autoimmune disease
Immune system destroys myelin
Effects:
Slowed/blocked signals
Symptoms:
Fatigue
Vision problems
Weakness
Poor coordination
57
Why is myelin important?
Enables fast communication
Loss → signal failure
Leads to:
Motor issues
Cognitive problems
58
What is an action potential?
A transient depolarizing spike in membrane potential
Rapid, temporary reversal of voltage across membrane
Key features:
Starts at –70 mV (resting)
Spikes to ~+40 mV
Returns back to resting
Enables:
Neuron-to-neuron communication
59
How do neurons communicate?
Electrical signal (axon)
Chemical signal (synapse)
Back to electrical in next neuron
60
Why does the brain use electricity?
Extremely fast
Faster than diffusion
Enables:
Rapid response
Whole-body communication
61
What did Galen believe?
“Animal spirits” flowed in nerves
Thought signals were fluid/gas
Dominated science for 1500 years
62
What did Luigi Galvani discover?
Frog leg twitched with electricity
Showed:
Nerves use electrical signals
Foundation of neuroscience
63
What is an ion?
Charged particle
Types:
Cation (+)
Anion (−)
64
Key ions in neurons?
K⁺ (Potassium)
Na⁺ (Sodium)
Ca²⁺ (Calcium)
Cl⁻ (Chloride)
65
What does the sodium-potassium pump do?
Pumps:
Na⁺ out
K⁺ in
Uses ATP
Creates:
Electrical gradient (battery)
66
What are ion channels?
Protein pores in the membrane
Allow ions to pass
Can be:
Open
Closed
Selective:
Specific ions only
67
What is an electrochemical gradient?
Combination of:
Concentration gradient
Electrical forces
Drives ion movement
68
What is diffusion?
Movement:
High → low concentration
Continues until equilibrium
69
What is a biological membrane?
Thin lipid bilayer surrounding every cell
Creates:
Inside (intracellular) environment
Outside (extracellular) environment
Function:
Separates internal from external environment
Controls movement of substances
70
Why is the membrane called a “charge separator”?
Prevents free movement of ions
Keeps:
Positive and negative charges separated
Creates:
Electrical potential (voltage)
This separation = basis of neural signaling
71
What is hydrophilic vs hydrophobic?
Hydrophilic:
“Water-loving”
Interacts with water
Hydrophobic:
“Water-fearing”
Repels water
Membrane structure:
Outer layers = hydrophilic
Inner layer = hydrophobic
72
Why can’t ions cross the membrane easily?
Ions are charged particles
Membrane interior is hydrophobic
Result:
Ions are blocked
Must use:
Channels
Pumps
73
Difference between intracellular and extracellular?
Intracellular:
Inside the cell
Extracellular:
Outside the cell
Key idea:
Different ion concentrations exist in each
74
What establishes charge separation?
Physical separation of charges
Driven by:
Ion gradients
Membrane barriers
Result:
Potential difference (voltage)
75
Why is the neuron like a battery?
Has:
Positive side (outside)
Negative side (inside)
Stores energy via:
Charge separation
Used for:
Electrical signaling
76
What does the sodium-potassium pump do?
Pumps:
Na⁺ OUT of cell
K⁺ INTO cell
Uses ATP
Maintains:
Ion gradients
Charge separation
77
Why is the Na⁺/K⁺ pump important metabolically?
Uses ~40% of neuron’s energy
Powered by ATP (from glucose/lactate)
Essential for:
Maintaining membrane potential
78
Where are Na⁺ and K⁺ concentrated?
Na⁺ (sodium): High OUTSIDE (like seawater)
K⁺ (potassium): High INSIDE cell
79
Why maintain ion gradients?
Creates: Electrical potential
Allows: Rapid signaling
Drives: Ion movement when channels open
80
What is diffusion?
Movement from:
High → low concentration
Continues until:
Equilibrium reached
Example:
CO₂ leaving soda
81
What is a concentration gradient?
Difference in concentration across space
Drives:
Passive movement of molecules
82
What is an electrical gradient?
Difference in charge across membrane
Opposites attract:
Positive → negative
Negative → positive
83
What is an electrochemical gradient?
Combination of:
Concentration gradient
Electrical gradient
Determines:
Direction of ion movement
84
What determines ion movement?
Two forces:
Diffusion (chemical)
Electrical attraction/repulsion
Together:
Predict ion flow
85
How do uncharged particles move?
Only affected by:
Diffusion
Move:
High → low concentration
86
How do positive ions behave?
Influenced by:
Diffusion
Electrical repulsion/attraction
May:
Move against concentration gradient
If electrical force is stronger
87
How do negative ions behave?
Attracted to:
Positive regions
Movement depends on:
Combined electrochemical forces
88
What is electrical current in neurons?
Flow of ions across membrane
Basis of:
Neural signaling
89
Which way does Na⁺ want to move?
From:
High outside → low inside
Direction:
INTO cell
90
Which way does K⁺ want to move?
From:
High inside → low outside
Direction:
OUT of cell
91
Why are Na⁺ and K⁺ important together?
They move in opposite directions
Creates:
Stable electrical system
Critical for:
Action potentials
92
What are ion channels?
Protein pores in membrane
Allow ions to cross
Passive (no energy required)
93
What are key properties of ion channels?
Selective: Only certain ions pass
Can be:
Open
Closed
Regulate:
Rate of ion flow
94
What controls channel opening/closing?
Changes in:
Voltage
Chemical signals
Causes:
Protein shape change
95
How do ions move through channels?
Move down electrochemical gradient
No ATP required
Driven by:
Existing gradients
96
What happens when channels open vs close?
Open:
Ions flow
Electrical signal possible
Closed:
No ion movement
Signal stops
97
How does the membrane enable neural signaling?
Membrane separates charge
Pumps create gradients
Channels allow ion flow
Ion movement = electrical signal
98
What is the MOST important takeaway?
The neuron is a battery + circuit system
Built from:
Ion gradients
Membrane separation
Channel-controlled flow
This enables:
Fast communication across the body
99
Which ion is most concentrated outside vs inside the neuron?
Outside the neuron:
High Na⁺ (sodium)
Inside the neuron:
High K⁺ (potassium)
This unequal distribution is critical for electrical signaling
100
How is the neuron’s biological battery created?
Created by:
High Na⁺ outside
High K⁺ inside
Maintained by:
Sodium-potassium pump
Result:
Charge separation → electrical potential
101
What is resting membrane potential?
Voltage difference between:
Inside vs outside of neuron
Measured using electrodes
Represents:
Stored electrical energy
102
What is the resting membrane potential of neurons?
Approximately –70 mV
Meaning:
Inside is 70 mV more negative than outside
103
How do scientists measure resting membrane potential?
Insert electrode:
One inside cell
One outside cell
Measure voltage difference
Early experiments:
Early 1900s electrophysiology
104
Why is resting membrane potential negative?
More positive charge outside
More negative charge inside
Due to:
Ion distribution
Membrane permeability
105
Why does maintaining resting potential use so much energy?
Sodium-potassium pump uses ~40% of brain energy
Constantly:
Pumps Na⁺ out
Pumps K⁺ in
Required to:
Maintain readiness for signaling
106
Why is resting membrane potential essential?
Keeps neuron in ready state
Allows:
Rapid action potential generation
Without it:
No neural signaling
107
What does sodium (Na⁺) want to do at rest?
Strongly wants to move:
Outside → inside
Driven by:
Diffusion (high → low)
Electrical attraction (inside negative)
VERY strong inward force
108
What does potassium (K⁺) want to do at rest?
Wants to move:
Inside → outside
Driven by:
Diffusion (high inside → low outside)
109
What is the key balance between Na⁺ and K⁺?
Na⁺ → wants IN
K⁺ → wants OUT
Pump maintains:
Stable resting potential
110
Why is Na⁺ described like a “slingshot”?
Strong inward drive
Prevented from entering by:
Closed channels
Stores potential energy
When released → triggers action potential
111
What is the consequence of Na⁺ entering the neuron?
Inside becomes less negative
Leads to:
Depolarization
If the threshold reached → action potential
112
How fast does an action potential occur?
~1 millisecond (1 ms)
Sets:
Limit for neural processing speed
113
What is the “overshoot” in an action potential?
Membrane potential rises above 0 mV
Can reach ~+40 mV
Caused by:
Massive Na⁺ influx
114
Why was the squid giant axon used?
Very large (~1 mm diameter)
Easy to insert electrodes
Allowed:
First intracellular recordings
115
What did Hodgkin & Huxley discover?
Action potential:
Reverses polarity
Not just 0 mV
Actually becomes positive
116
How is information coded in the nervous system?
Through action potentials (spikes)
Key methods:
Rate coding → frequency of spikes
Temporal coding → timing of spikes
117
What is rate coding?
Stronger stimulus → more spikes/sec
Example:
3 spikes/sec vs 30 spikes/sec
118
How is stretch encoded?
More stretch → higher firing rate
Intensity = spike frequency
119
What is the fundamental unit of brain communication?
Action potential
All behavior depends on:
Patterns of neural firing
120
How does neural signaling work overall?
Ion gradients create battery
Resting potential = stored energy
Na⁺ wants in, K⁺ wants out
Opening channels → ion flow
Action potential generated
Information encoded in spike patterns
121
What key values should you memorize?
–70 mV → Resting potential
–45 mV → Threshold (trigger point)
+40 mV → Sodium equilibrium (peak)
–90 mV → Potassium equilibrium
122
Why are action potentials important?
Fundamental unit of neural communication
Allow:
Sensory processing
Movement
Thought
Self-propagating electrical signal
123
What are the phases of an action potential?
Resting state (–70 mV)
Rising phase (depolarization)
Overshoot (+40 mV)
Falling phase (repolarization)
Undershoot (hyperpolarization)
Return to rest
124
What triggers an action potential?
Membrane reaches threshold (–45 mV)
Caused by:
Excitatory synaptic input
Leads to:
Opening of voltage-gated Na⁺ channels
125
Which ion causes depolarization?
Sodium (Na⁺)
Flows:
Outside → inside
Driven by:
Diffusion + electrical forces
126
Why does depolarization accelerate rapidly?
Na⁺ enters → membrane becomes more positive
More Na⁺ channels open
EVEN MORE Na⁺ enters
This is a positive feedback loop
127
What happens during the upswing?
Massive Na⁺ influx
Membrane rapidly goes:
–45 mV → +40 mV
Inside becomes positive
128
What is overshoot?
Membrane potential exceeds 0 mV
Peaks at ~+40 mV
Inside now more positive than outside
129
Why does Na⁺ influx stop at +40 mV?
Reaches sodium equilibrium potential
No net driving force
Na⁺ channels:
Inactivate (close)
130
Which ion causes repolarization?
Potassium (K⁺)
Flows:
Inside → outside
131
Describe the falling phase.
Na⁺ channels close
K⁺ channels open
K⁺ exits cell
Membrane becomes more negative
132
Why does potassium leave the neuron?
High concentration inside
Positive charge inside repels K⁺
Diffusion + electrical forces push it out
133
What is undershoot?
Membrane becomes more negative than –70 mV
Can approach –90 mV
134
Why does hyperpolarization occur?
K⁺ channels close slowly
Too much K⁺ leaves
Membrane overshoots resting potential
135
How does the neuron return to –70 mV?
K⁺ channels close
Leak channels stabilize voltage
Sodium-potassium pump restores gradients
136
What restores ion gradients after an action potential?
Sodium-potassium pump
Pumps:
Na⁺ out
K⁺ in
Re-establishes:
Charge separation
137
What is an excitatory synapse?
Increases likelihood of firing
Causes:
Depolarization
Allows:
Na⁺ to enter neuron
138
Why is one excitatory synapse not enough?
Small Na⁺ influx
Only slight depolarization (~–60 mV)
Does NOT reach threshold
139
How is threshold reached?
Multiple excitatory synapses activate
Add together (summation)
Push membrane to –45 mV
140
What channels are involved?
Voltage-gated Na⁺ channels
Voltage-gated K⁺ channels
Leak channels
141
What is the order of channel activity?
Na⁺ channels open first
Na⁺ channels inactivate
K⁺ channels open
K⁺ channels close slowly
142
Describe the full action potential sequence.
Rest (–70 mV)
Excitatory input → depolarization
Threshold reached (–45 mV)
Na⁺ influx → rapid depolarization
Peak at +40 mV
Na⁺ channels close
K⁺ exits → repolarization
Undershoot (~–90 mV)
Return to rest
143
What drives ion movement?
Concentration gradient
Electrical gradient
Together = electrochemical gradient
144
Details of EPSP Generation (Excitatory Postsynaptic Potential)
An EPSP happens when the postsynaptic neuron becomes more positive than its resting potential (~ -70 mV).
How it’s generated:
1. An action potential reaches the presynaptic axon terminal.
2. Neurotransmitters (NTs) are released into the synapse.
3. NTs bind to receptors on the postsynaptic dendrite.
4. These receptors open ion channels → typically Na⁺ enters the cell.
5. The influx of positive charge causes depolarization.
If enough EPSPs summate and bring the membrane to about -45 mV (threshold) → an action potential (AP) is generated at the soma-axon junction.
145
Depolarization vs. Hyperpolarization
Depolarization
- Membrane becomes more positive
- Usually due to Na⁺ (positive ion) entering
- Moves neuron closer to threshold → more likely to fire
Hyperpolarization
- Membrane becomes more negative
- Usually due to:
Cl⁻ entering OR
K⁺ leaving
- Moves neuron further from threshold → less likely to fire
146
Function of Myelin in Leak-Free AP Propagation
Myelin (made by oligodendrocytes) acts as insulation around the axon.
Key functions:
- Prevents current leakage across the membrane
- Allows AP to “skip” along the axon (saltatory conduction)
- Greatly increases speed (~10x faster)
- Maintains signal strength so the AP doesn’t die out
Without myelin (e.g., in multiple sclerosis):
Signals degrade
Leads to neurological impairment
147
What is Synaptic Transmission?
- Conversion: Electrical → Chemical → Electrical
- AP arrives → NT released → NT binds → new electrical signal generated
148
“Soups vs. Sparks” Debate
“Sparks” (electrical transmission):
- Direct electrical current flows between neurons
- Fast, continuous
“Soups” (chemical transmission):
- Signal becomes a chemical (NT) in the synapse
- Then converts back to electrical
- Slower but more flexible
Both exist, but chemical transmission is primary
149
Otto Loewi’s Dream Experiment (1921)
Setup:
Two frog hearts in separate fluid chambers
Only Heart 1 had a vagus nerve
Procedure:
Stimulated vagus nerve → Heart 1 slowed down
Fluid from Heart 1 transferred to Heart 2
Heart 2 also slowed down
Conclusion:
A chemical substance (neurotransmitter) caused the effect
Proved synaptic transmission is chemical (“soup”)
150
How Neurotransmitters Are Reabsorbed (Reuptake)
After NTs act, they must be cleared:
Reuptake process:
NTs are taken back into the presynaptic neuron via transporters
Repackaged into synaptic vesicles for reuse
Importance:
Stops continuous stimulation
Allows recycling
Clinical relevance:
Drugs like SSRIs block reuptake → NT stays longer in synapse
Some drugs of abuse reverse transporters
151
Ca²⁺-Dependent Synaptic Vesicle Fusion
This is how NTs are released:
Steps:
AP reaches axon terminal
Voltage-gated Ca²⁺ channels open
Ca²⁺ enters the cell
Ca²⁺ triggers vesicles to fuse with the membrane
NTs are released into synaptic cleft
Important:
Calcium—not voltage directly—triggers fusion
Clinical example:
Botulism toxin blocks this process → prevents NT release → paralysis
152
How NTs Change the Postsynaptic Membrane
After release:
NT diffuses across synapse
Binds to specific receptors (ion channels)
Channels open → ions flow
Two outcomes:
Excitatory (EPSP)
Example: Glutamate
Opens channels → Na⁺ enters
Causes depolarization
Inhibitory (IPSP)
Example: GABA
Opens channels → Cl⁻ enters
Causes hyperpolarization
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