Lecture Final: Chapter 23

Question 1

Simple vs Complex Animals

+ Vertebrate Nervous System (2)

Answer 1

SIMPLE ANIMALS: sense the environment and respond
– Ie flatworm have “eyes” that sense light and allow them to swim away from it to avoid predators
COMPLEX ANIMALS: sense the environment BUT integrate nerve impulses through circuits of thousands of neurons from which higher cognitive functions emerge (ie memory, learning, tool use, symbolic cognition)
– Ie primates

CENTRAL NERVOUS SYSTEM: brain and spinal cord
– Grey matter: location of nerve cells
– White matter: myelinated white nerve tracks
PERIPHERAL NERVOUS SYSTEM:
– Afferent division: sensory receptors sending input to the brain from the body; nerve impulse from the body that relay a sensory detail once it reaches the right part of the brain
– Efferent division: aka output; perception that is generated by the cells in the nervous system that may require a response
> Somatic: nerves that trigger muscular / motor responses
> Autonomic: separate nerves that innervate the same organs
» Parasympathetic: autopilot that maintains homeostatic functions
» Sympathetic: fight or flight

Question 2

Neuron

• Structure (4)
• Types (3)
• Integration

Answer 2

Cell body: contains organelles
Dendrites: branch like; receive signals (sensory input from the sensory receptor) → note: dendrology is the study of trees
Axon: long unit; sends signals (sensory output); velocity of signal dependent on diameter, temperature, and whether myelinated or not
Synapse: fluid filled gapped; allows for release of neurotransmitter from the delivering axon and the receiving neuron

Primarily involved in cell-to-cell communication via nerve impulses

1. Sensory neurons: relay both internal and external sensory data to CNS
2. Interneurons: restricted to CNS; integration, perception, building, and executive functions
3. Motor neurons: relay motor commands from CNS to effectors (muscles and glands)

Integration:

1. Neurons receive AP from thousands of sources that are integrated by the AXON HILLOCK
2. Hillock which will determine via summation whether output is EPSP (excitatory postsynaptic potential) or IPSP (inhibitory)
   - - Some axons bind to the hillock (axosomatic) and are usually inhibitory
   - - Other axons bind to dendrites (axodendritic) and are usually excitatory

Question 3

Membrane Potential (Vm)

• generation (2)
• net flow (2)
• considerations (3)

Answer 3

Vm generated by
– Difference in [ion] across plasma membrane
– Difference in permeability of PM to ions
BUT Chemical gradient and electrical gradient will compete each other and ultimately will cancel each other out (aka determination of equivalent potential for a single ion via Nernst equation)

If net flow of [K+] is from inside to outside, will need negative membrane potential inside to attract K+ ions (reduce desire of K+ positivity to leak out) → ie. - 90 mV
If net flow of [Na+] is from outside to inside, will need a positive membrane potential inside to repel Na+ ions (reduce desire of Na+ positivity from coming in) → ie. + 63 mV

Now have to consider permeability of the membrane too
– If 1/20 Na permeability, will be closer to K potential
> K potential alone: - 90mV
> Na potential alone: + 63 mV
» 1/20 Na permeability with K: - 70 mV
– If Na permeability matches K
> Average of them: -15 mV (~~33/2)
> Usually only happens when an AP comes in, allowing a large influx of Na
» Therefore, change in permeability is caused by a change in membrane potential
– Now throw in a Na/K ATPase
> Causes resting potential in Na/K

Question 4

VOLTAGE Gated Channels
+ Na/K ATPase

vs. LIGAND Gated Channels

Answer 4

VOLTAGE gated channels: alter membrane permeability to specific ions; will undergo a conformational shift in structure in response to change in Vm
– involved in the sending of nerve impulses, aka ACTION POTENTIAL, where the impulse self propagates along an axon at a constant velocity

Na/K ATPase is a voltage gated channel to allow movement of Na through (K is already freely permeable)

1. V gated Na+ channel
   - - Closed: no ion flow
   - - Open: ion flow; closed becomes opened at - 50 mV
   - - Inactive state: something has plugged the sodium channel at + 70 mV; open but no ion flow → back to closed, requires resting potential of - 70 mV
2. V gated K+ channel – easier lmao
   - - Closed
   - - Open: closed becomes opened at + 70 mV → back to closed, requires resting potential of - 70 mV

LIGAND gated channels: also undergo conformational shift in structure BUT will be in response to binding of chemical messenger
– impulse degrades with distance from ion channel and strength of impulse is dependent on [chemical messenger], thus buildup allows for GRADED POTENTIAL to form

Ie. ion channels in postsynaptic membranes and sensory receptors

Question 5

Action Potential Graph

• Pathway (4)
• Periods (3)
• note on hyperpolarization

Answer 5

Graph: time horixontal, mV vertical

Slowly depolarizes from resting potential -70 mV
A) @ - 50 mV, voltage gated Na+ channel will OPEN – Na+ permeability increases, depolarizing it until - 70 mV
B) @ - 70 mV, voltage gated Na+ channel will become INACTIVE – Na+ permeability stops (if wants to begin again, has to close then open once more)
– Cascade of adjacent voltage-gated Na+ channels and K+ channels open in response to above-threshold Vm, raising Vm towards peak (OVERSHOOT)
C) Before hitting @ - 90 mV (due to potassium permeability), will pass - 70 mV → sodium channel goes from INACTIVE to CLOSE (can now open again) ;; potassium channel goes from OPEN to CLOSE (can now open again)
– Extensive loss of K+ to surroundings causes hyperpolarization (UNDERSHOOT)
D) Return to resting potential of - 70 mV

Periods involved:

1. Absolute refractory: absolutely cannot be changed, will happen irregardless – A to C
2. Relative refractory: needs more stimuli than before to cause the neurons to fire – C to D
   - - Membrane will be hyperpolarized bc more negative than resting potential, therefore requires the additional stimuli

Action potential can only flow in ONE DIRECTION due to hyperpolarization – usually, by the time the relative refractory has returned to resting potential, the AP would not be enough to affect its neighbors anymore

Question 6

Nerve Impulses

• Acceleration factors (3)
• Neuron to Neuron Communication Pathway (5)
• Mechanisms of Termination (2)

Answer 6

NERVE IMPULSE IS ACCELERATED BY:

1. Increasing diameter of axon
2. Myelin sheath insulation
3. Increasing temperature

PATHWAY:

1. Depolarization of axon by AP opens voltage gated Ca2+ channels in axon’s terminus
2. Surge of Ca2+ enters inside axon triggering fusion of synaptic vesicles containing neurotransmitters to PM
3. Neurotransmitters released into synaptic cleft and bind to ligand-gated channels in postsynaptic membrane.
4. Higher frequencies of AP in presynaptic neuron increase number of synaptic vesicles fusing to postsynaptic membrane
5. Increased [neurotransmitters] opens greater number of ligand-gated channels, leading to a greater response by postsynaptic neuron → once threshold is reached, signal sent to the brain

TERMINATION:

1. Enzymatic breakdown of neurotransmitter by inactivating enzyme in membrane of postsynaptic neuron
2. Recycling via reuptake of neurotransmitter (ie serotonin)

Question 7

Examples of Neurotransmitters (4)

Answer 7

Acetylcholine released at neuromuscular junctions and by autonomic nerves (parasympathetic pathway)

Biogenic amines (derivatives of tyrosine and tryptophan) that play roles in emotional behavior and from sympathetic neurons
-- ie norepinephrine, dopamine, serotonin

Neuropeptides are mediators of pain and act as natural opiates

Can also be amino acids (ie glutamate) or gases (ie nitric oxide)

Question 8

Types of Synapses

• Electrical (3)
• Chemical (2)

Answer 8

ELECTRICAL

• • Gap junctions btwn nerve cells (connexin proteins)
• • Present in CNS in nerve responsible for kerly movements of eye + hippocampus (memory and emotion)
• • Bidirectional signal transmission and no synaptic delay (faster than chemical)

CHEMICAL

• • Slower because of bottleneck
• • Advantageous because strengthens those that are used a lot and weakening those that are not used so much → learning and memory

Question 9

Neuronal Plasticity

Answer 9

Overall organization of CNS is established during embryonic development
– Connections btwn neurons are strengthened or weakened in response to activity (remodeled dependent upon activity)

Synapses belonging to circuits that link information are maintained, whereas those that convey information lacking context are lost

• • Specifically, when activity of a synapse coincides with that of others, the strength of the postsynaptic response may increase at all synapses involved, reinforcing synaptic connections
• • Conversely, when activity of a synapse fails to coincide with other synapses, weakening synaptic connections

Question 10

Cerebral Cortex

• Comparison btwn Mouse and Humans
• Domains (3)

Answer 10

Billion of interneurons are in outer cortex – single layer of cortical neurons in the mouse brain BUT there are six layers in humans (more complex being)

CEREBRAL DOMAINS CONTAIN THREE TYPES OF FUNCTIONAL AREAS

1. Sensory areas: conscious awareness of sensations
2. Motor Areas: control of voluntary movements
3. Association areas: give meaning to information received; building the perception and response
   - - prefrontal cortex (executive center of the brain; most complicated cortical region) → involved in intellect, cognition, recall, and working memory

Question 11

Somatic Nervous System

Autonomic Nervous System (2)
- Divisions (2)

Answer 11

SOMATIC Nervous System:
– Voluntary movement of skeletal muscles / organs / reflex muscles

AUTONOMIC nervous system (ANS)

• • Maintains stability of the internal environment via a system of motor neurons that innervate smooth and cardiac muscles, and glands
• • Shunts blood to needy areas, adjusts heart rate / blood pressure, body temperatures, and decrease / increase stomach secretions

PARASYMPATHETIC division: promotes maintenance functions and conserves body energy (ie rest and recovery)
– Fibers are craniosacral in origin
– Ganglia near effector organ
SYMPATHETIC division: Mobilizes body during activity, especially in fearful or stressful conditions (ie fight or flight)
– Fibers are thoracolumbar in origin
– Ganglia near spinal cord

Question 12

Comparison of Pathways btwn Somatic and Autonomic

Answer 12

Somatic ——-
One Neuron “Chain”: very FAST conduction
Cell bodies of motor neurons in CNS will have axons that extend to skeletal muscles
» Will release Acetylcholine as neurotransmitter at neuromuscular regions

Autonomic ——-
Two Neuron Chain: conduction is SLOWER than somatic motor system
» PREGANGLIONIC NEURON resides in CNS – release ACh as neurotransmitter for both systems
» POSTGANGLIONIC NEURON resides in ganglia outside CNS, differ by system
release norepinephrine by sympathetic fibers
acetylcholine by parasympathetic fibers