NERVOUS SYSTEM: AXONAL PROPOGATION AND SYNAPTIC TRANSMISSION

Question 1

Where does synaptic integration occur? Why does it occur here?

Answer 1

Synaptic integration occurs at the axon hillock, which has the highest density of NaV channels and therefore the lowest threshold for spike initiation. Input is
additive both spatially and temporally.

Question 2

spatial summation

Answer 2

Spatial summation: occurs when stimuli are applied at the same time, but in different areas, with a cumulative effect upon membrane potential

Question 2

temporal summation

Answer 2

Temporal summation: the effects of impulses received at the same place can add up if the impulses are received in close temporal succession

Question 3

define: excitatory postsynaptic potential (EPSP)

Answer 3

Transient depolarization of postsynaptic neuron due to increased conductance of the postsynaptic membrane to Na+/K+ in response to neurotransmitter binding

At RMP, the driving force for Na+ to enter a cell is greater than for K+ to leave, resulting in depolarization.

Question 4

define: inhibitory postsynaptic potential

Answer 4

Transient hyperpolarization of postsynaptic neuron due to (most often) increased Cl- conductance of postsynaptic membrane in response to neurotransmitter binding.

Cl- enters cell at RMP causing hyperpolarization.

Question 5

Nodes of Ranvier function and location

Answer 5

• are densely populated with NaV channels
• Produces ‘saltatory’ conduction, in which an AP ‘jumps’ from node to node

Question 6

The larger the axon, the ____ the conduction velocity.l

Answer 6

faster

Question 7

Conduction is fastest in what type of axons?

Answer 7

large and myelinated axons

Question 8

APs are regenerated at nodes of Ranvier for three reasons:

Answer 8

1) membrane conductance is high
2) membrane resistance is low
3) NaV and KV density is high

Question 9

Between nodes, passive potentials propagate rapidly for two reasons

Answer 9

1) Membrane resistance is high
2) Membrane capacitance is low

Question 10

As myelination increases, how will membrane resistance and capacitance change?

Answer 10

membrane resistance will increase and capacitance will decrease.

Question 11

How can conduction be improved in the axons?

Answer 11

Increase diameter of axon (decrease axial resistance)

Myelinate the axon (increase membrane resistance)

As axon diameter increases, conduction velocity will increase as internal resistance decreases

Question 12

What makes myelin in the CNS?

Answer 12

oligodendrocytes

Question 13

What makes myelin in the PNS?

Answer 13

schwann cells

Question 14

Describe what is happening at the axon when someone has multiple sclerosis

Answer 14

Impaired myelination over some segments due to an immune attack

Leads to decreased conduction velocity → frequency related block → total conduction block → ectopic impulse gneeration → increase in mechanoreceptivity

Question 15

What are the different types of excitatory neurotransmitters?

Answer 15

Glutamate (amino acid): primary excitatory neurotransmitters in brain

Acetylcholine (Ach): in the peripheral nervous system, at the neuro-muscular junction and autonomic ganglia, also CNS in basal ganglia and spinal cord.

Question 16

Describe the two different receptor types for acetylcholine

Answer 16

1. Nicotinic (NAChR) at neuromuscular junction
2. Muscarinic (MAChR) at autonomic ganglia

Question 17

What are the different types of inhibitory neurotransmitters?

Answer 17

Gamma-aminobutyric acid (GABA): inhibitory neurotransmitters in brain

Glycine (amino acid): inhibitory neurotransmitter in spinal cord

Question 18

What is the function of dopamine as a neurotransmitter?

Answer 18

Dopamine: Motivation, motor function, reward and pleasure

Question 19

What is the function of serotonin as a neurotransmitter?

Answer 19

Serotonin: mood, appetite, and sleep

Question 20

Describe the difference between ligand-gated ion channels (ionotropic) and g protein coupled receptors (metabotropic)

Answer 20

Ligand-gated ion channels
- Neurotransmitter binds, channel opens, and ion flows across membrane
- CNS: ionotropic glutamate receptors (NMDA, AMPA)
- NMJ: nicotinic ACh receptors (NAChR)
- CNS: GABAA, GABAC

G protein coupled receptors (metabotropic)
- Neurotransmitter binds to g protein which activates. G protein subunits or intracellular messengers modulate ion channels. Ion channels open, and ions flow across the membrane
- This is a slower response than ligand-gated ion channels.
- CNS/PNS: metabotropic glutamine receptors
- PNS: muscarinic Ach receptors (MAChR)
- CNS: GABAB

Question 21

Conduction of action potentials is unidirectional - once they are triggered they only move in one direction and generally don’t go backwards

What two mechanisms are important for this property of neurons?

Answer 21

1. Nav inactivation
2. Increased PK