Topic 3: Nervous System 1 - Neuronal Physiology: Synaptic Transmission at Neuronal Junction + Neuromuscular Junction

Question 1

What does the NS depend on?

Answer 1

• a chain of neurons connected by junctions called synapses

Question 2

What is synaptic transmission?

Answer 2

• presynaptic neuron to postsynaptic neuron transmission

Question 3

What are the steps to synaptic transmission at a neuronal junction? (6)

Answer 3

1) AP Aarrives at axon terminal (synaptic end bulb)
2) Ca++ voltage gates open due to AP, and Ca++ enters (higher [Ca++] outside!!)
3) Rise in Ca++ triggers exocytosis of nt containing vesicles
4) nt diffuses across synaptic cleft, binds to specific receptors on postsynaptic membrane
5) gated ion channels open, allowing movement of ions into or out of postsynaptic membrane
6) creates a GP called a postsynaptic potential (PSP)

Question 4

In synaptic transmission, what are the receptors on the postsynaptic membrane? (2)

Answer 4

• chemically-gated ion channels
• open in response to nt

Question 5

What are the two types of postsynaptic potentials?

Answer 5

• Excitatory and inhibitory

Question 6

Excitatory PSPs are ___ potentials that cause ______ (depolarization/hyperpolarization)

Answer 6

• graded
• depolarization

Question 7

What occurs in EPSPs? (2)

Answer 7

• depolarization due to opening of Na+ (or Ca++) channels, or closing of K+ channels
• nt is often ACh or glutamate

Question 8

Inhibitory PSPs are ____ potentials that cause (depolarization/hyperpolarization)

Answer 8

• graded
• hyperpolarization

Question 9

What occurs in IPSPs? (3)

Answer 9

• hyperpolarization due to opening of K+ or Cl- channels
• inhibits neuron from reaching an AP
• nt is often glycine or GABA

Question 10

Where do postsynaptic potentials occur in a neuron?

Answer 10

• cell body or dendrites

Question 11

What can neurons do to reach threshold, in terms of PSPs? (5)

Answer 11

• many neurons can synapse into one
• if many EPSPs, it can summate
• then large area of membrane depolarized
• spreads to axon hillock
• if sum of EPSPs reaches threshold, get AP

Question 12

What is an exception to how a neuron may not get an AP in terms of PSPs? (2)

Answer 12

• previously, we said that many neurons can synapse onto one to eventually cause an AP
• However, some may be IPSPs where the sum of all EPSPs and IPSPs determine if AP will occur at the hillock

Question 13

What is a neuromuscular junction?

Answer 13

• junction between axon terminal of neuron and an individual muscle fibre

Question 14

The steps for synaptic transmission at a neuromuscular junction is similar to that of a neuronal junctions, with some modifications. What are they? (3 steps, 5 points)

Answer 14

1) neurotransmitter released is ALWAYS ACh
2) Na+ chemical gates on muscle motor end plate (sarcolemma of muscle fiber)
- causes GP (end plate potential) on sarcolemma
3) EPP triggers AP on sarcolemma
- lots of ACh released in (a) of diagram, so we always get an AP from EPP

Question 15

What is an EPP? (2)

Answer 15

• end plate potential
• still a GP but specific for skeletal muscle