Principles of Nerve Conduction and Synaptic Transmission

Question 1

What is the movement of ions across a membrane determined by?

Answer 1

Ionic gradients
Charge of molecule
Membrane potential

Question 2

Describe a neuron at resting state in terms of ions

Answer 2

Inside the cell there is a high concentration of potassium and a low concentration of sodium, chloride and calcium ions
Outside the cell there is a low concentration of potassium and a high concentration of sodium, chloride and calcium ions

Question 3

What is the resting membrane potential and how is it maintained?

Answer 3

-70mV
Maintained by the permeability of the membrane to potassium and an energy dependent pump which moves the ions across the membrane

Question 4

Describe the four main steps of an action potential

Answer 4

• Depolarisation to threshold
• Activation of sodium channels and rapid depolarisation
• Inactivation of sodium channels and activation of potassium channels
• The return to normal permeability and resting state

Question 5

Describe the sodium and potassium channels involved

Answer 5

Both are voltage gated
Sodium channels are fast
Potassium channels are slow

Question 6

Why can the action potential only move in one direction?

Answer 6

When an action potential occurs, sodium channels are opened, in turn causing more sodium channels to open due to the change in membrane potential
Behind the action potential, sodium channels close as they are time dependent, meaning the action potential can only move in one direction

Question 7

Definition of a neurotransmitter

Answer 7

A substance that transmits nerve impulses across a synapse

Question 8

Main characteristics of neurotransmitters

Answer 8

Synthesised endogenously
Available in sufficient quantity in the presynaptic neuron to exert an effect on the postsynaptic neuron
If externally administered, it mimics the endogenously- released substance

Question 9

Describe the process of neurotransmission

Answer 9

Neurotransmitter contained in a vesicle
Membrane depolarisation opens voltage gated calcium channels, triggers vesicles to move to presynaptic membrane
Neurotransmitter moves across the synapse
Binds to a receptor on the post synaptic membrane
Acts on that receptor to increase or decrease activity of the post-synaptic neuron
Acting back on the presynaptic neuron to increase or decrease firing
Specific system for removing the transmitter or stopping its activity

Question 10

What do the postsynaptic effects depend on?

Answer 10

The neurotransmitter

Which receptor it binds to

Question 11

What does a fast excitatory neurotransmission cause?

Answer 11

An excitatory post-synaptic potential

Question 12

What does a fast inhibitory neurotransmission cause?

Answer 12

An inhibitory post-synaptic potential

Question 13

ACh synthesis and reuptake cycle

Answer 13

ACh formed in the synaptic terminal
Packaged into vesicles
Released into the synaptic cleft
Broken down by ACh esterase
Choline taken up, terminating the signal

Question 14

Describe the main monoamine neurotransmitters and their characteristics

Answer 14

Noradrenaline, dopamine and serotonin
Only one receptor is an ion channel, the rest are G protein coupled receptors
Neurons originate in the brain stem projecting up into the cortex and other brain regions as well as down the spinal cord

Question 15

Describe monoaminergic transmission

Answer 15

Monoamines are synthesised in the synaptic terminal
Packaged into synaptic vesicles and released
Action terminated by reuptake- energy dependent mechanism, ATPase creates concentration gradient which drives opening of channel, ions equilibrate as channel opens
Drugs can inhibit reuptake

Question 16

Describe GABA and glutamate’s main characteristics and their synthesis and reuptake cycle

Answer 16

GABA is the major inhibitory neurotransmitter- all the receptors are inhibitory
Glutamate is the major excitatory neurotransmitter- all the receptors are inhibitory
Synthesised as part of the krebs cycle, rapidly taken up from the synapse after they have been released by transporters on glia, turned into glutamine and recycled back into the krebs cycle

Question 17

Features of pre-synaptic receptors

Answer 17

Help to regulate neurotransmission

Often called autoreceptors because they control the release of their own neurotransmitter e.g. A2 adrenoceptor

Question 18

In what ways can the signal end?

Answer 18

Stopping the signal from the presynaptic neuron (no more action potentials, closing Ca channels)
Stopping the release of the transmitter (pre-synaptic autoreceptors)
Stopping the activity of the transmitter by rapid enzymatic destruction, uptake into nerve terminals or neighbouring cells, diffusion away from the synapse followed by one or both of the above

Question 19

How can you change activity at the synapse?

Answer 19

Agonists increase activity
Antagonists decrease activity
Reuptake inhibition- block reuptake/ recycling, increase activity at the synapse
Facilitate release- increase activity
Inhibit synthesis enzymes- decrease activity
Inhibit degradation enzymes- increase activity
Block release- decrease activity