TBL - Physiology of Synaptic Neurotransmission

Question 1

Which two processes control NT release?

Answer 1

Depolarisation of the active zone

Opening of Ca voltage channels

Question 2

A snake bite causes paralysis & respiratory failure - how might the toxin work?

Answer 2

Is a competitive antagonist to the ACh receptor - meaning NMJ cant work.

Question 3

In non-myelinated neurons, where do you most-likely find the Na voltage gated channels?

Answer 3

Along the span of the axonal membrane = they span the entire length = slow transmission as depolarisation must take place along the entire length.

Question 4

Why are metabotropic receptors considered slow?

Answer 4

Because they have to initiate complex biochemical cascades in the post-synaptic cell in order for effect to occur. Ionotropic is quicker because it only requires an influx of cells to have an effect.

Question 5

How can an increase in frequency of synaptic input cause a neuron to fire?

Answer 5

Each signal generates a graded potential - that summates in order to reach the threshold. If the frequency increase, there is less time for the signals to dissipate, and more chance of the threshold being met.

Question 6

In hormone release, the firing of some neurons is tightly regulated and synchronised - how is this achieved?

Answer 6

Via electrical synapses - allows for instantaneous synchronicity.

Question 7

What two factors of myelination allow saltatory conduction?

Answer 7

There is reduced capacitance (ability to store voltage) of the axonal membrane + increased resistance in the axonal membrane (no leakage where myelinated).

Question 8

Which ion is required to initiate exocytosis?

Answer 8

Calcium

Question 9

What are the three main functions of myelin?

Answer 9

Reduces loss of charge around the axon

Speeds up transmission of the AP along the axon

Increases efficiency of electrical transmission (less ion channels needed - as clustered at nodes of Ranvier)

Question 10

What happens when an AP reaches an area of demyelinated axon?

Answer 10

There is a reduction in the velocity of the AP because
- Capacitance increases = slows the conductance of ions
- Na channels are less dense - more evenly distributed = slows conductance further

Demyelinated axons require more Na channels for conductance

Question 11

What are similarities between MS and GBS (Guillaine)

Answer 11

MS - T cells attack myeline in CNS
GBS - PNS is affected by demyelination

MS - begins with a clinically isolated syndrome - before progressing to relapsing, repeating pattern.

GBS - normally single phase over 2-6 weeks with recovery (complete or incomplete) after

MS - often includes optic neuritis & cerebellar symptoms (balance & coordination) - differs from GBS.

Both - cause sensory changes and weakness in limbs