Lecture 6 - Synaptic Transmission

Question 1

What does the CNS contain?

Answer 1

brain and spinal cord

Question 2

What does the PNS contain?

Answer 2

nerves that connect the brain or spinal cord w/ the body’s muscles, glands, and sense organs.

Question 3

What is the function of afferent neurons? Where are their parts located in relation to CNS/PNS?

Answer 3

transmit info into CNS; cell body and long peripheral process of axon in PNS, short central process of axon in CNS

Question 4

What is the function of efferent neurons? Where are their parts located in relation to CNS/PNS?

Answer 4

transmit info out of CNS to effector cells; cell bodies, dendrites, and some axon in CNS, most of axon in PNS.

Question 5

What is the function of interneurons? Where are their parts located in relation to CNS/PNS?

Answer 5

function as integrators and signal changers; integrate efferent and afferent neurons to become reflex circuits; entirely in CNS

Question 6

What is the convergence pattern of neuron connections?

Answer 6

many diff presynaptic neurons provide input to single postsynaptic neuron

Question 7

What is the divergence pattern of neuron connections?

Answer 7

each postsynaptic neuron receives input from many diff presynaptic neurons;post-synaptic neurons can have diff rxns

Question 8

What influences the level of excitability of postsynaptic neurons?

Answer 8

number of synapses active at one time; number that are excitatory or inhibitory

Question 9

Tell me about electrical synapses.

Answer 9

have gap junctions that allow uni or bidirectional flow of ions betw the 2 neurons; rare in mammalian nervous system

Question 10

Tell me about chemical synapses.

Answer 10

presynaptic ending that contains NT’s, mito, and cell organelles. Postsynaptic ending contains receptor sites for NT’s. UNIDIRECTIONAL

Question 11

What are the steps for the mechanism of NT release?

Answer 11

1. AP reaches terminal
2. voltage-gated Ca2+ channels open
3. Ca enters axon terminal
4. NT released and diffuses into cleft
5. NT binds to postsynaptic receptors
6. NT removed from cleft

Question 12

What is a critical step in NT release that is target by drugs?

Answer 12

the release of Ca2+ from their voltage-gated channels

Question 13

vesicles floating in the axon terminal will attach to the terminal membrane for release by what mechanism?

Answer 13

Synaptogamin on vesicles will attach to SNARES of the terminal membrane.

Question 14

Ways to inactivate NT?

Answer 14

1. diffusion of NT from cleft
2. degradation of transmitter by enzymes
3. reuptake into re-synaptic cells or reuse
   * can have removal of receptors in post-synaptic membrane

Question 15

What are autoreceptors?

Answer 15

NT bind to the autoreceptor in the synaptic cleft and signal to turn off further release from presynaptic cell

Question 16

What do excitatory postsynaptic potential (EPSP) do?

Answer 16

bring membrane potential closer to threshold for generating an action potential (so making the memb more positive–depolarization)

Question 17

What do inhibitory postsynaptic potential (IPSP) do?

Answer 17

make cell’s memb pot more negative, making it harder to generate an AP.

Question 18

excitatory postsynaptic potential (EPSP)
____ Na+ permeability
____ K+ permeability
____ Ca2+ permeability

Answer 18

• depolarization, so…
  increased Na+ permeability
  decreased K+ permeability
  increased Ca2+ permeability

Question 19

inhibitory postsynaptic potential (IPSP)
____ Cl- permeability
____ K+ permeability

Answer 19

inhibitory postsynaptic potential (IPSP)
increased Cl- permeability
increased K+ permeability

Question 20

A single EPSP can induce an action potential. T/F?

Answer 20

False, EPSPs can summate to influence activity of postsynaptic neuron.

Question 21

Temporal summation occurs due to?

Answer 21

rapid firing of a presynaptic neuron (the same neuron at near the same time frame)

Question 22

Spatial summation occurs due to?

Answer 22

the postsynaptic neuron is stimulated simultaneously by many presynaptic neurons (at different locations); diff neurons that fire at the same time.

Question 23

quantal theory of synaptic transmission?

Answer 23

In a resting neuron, random fusion of a vesicle w/ presynaptic memb causes a release of a quanta of NT, which causes small excitatory potentials known as miniature EPSPs (mEPSPs). These occur at neuromuscular junction often called the miniature end-plate potentials. They also exhibit spatial and temporal summation.

Question 24

Modification of the synaptic transmission can occur through 2 ways, which are?

Answer 24

drugs and diseases

Question 25

How does Clostridium tetani affect synaptic transmission?

Answer 25

it prevents vesicle fusion w/ the membrane, inhibiting NT release for an inhibitory synapse and causes increased muscle contraction.

Question 26

How does Clostridium botulinum affect synaptic transmission?

Answer 26

it interferes w/ the actions of SNARE proteins at excitatory synapses that activate muscles (causes muscle paralysis).