Nerve cells and excitability: Synapses and Neurotransmission

Question 1

Synapse:

Answer 1

Thepointat whichelectricalsignalsmovefrom onenervecellto another.

Question 2

Features of chemical synapsis

Answer 2

presynaptic neuron- synaptic knob- synaptic cleft - postsynaptic neuron

Question 3

Types of synapses in the central nervous system (CNS

Answer 3

Axo-dendritic
Axo-somatic
Axo-axonal

Question 4

Neurotransmitter release by exocytosis

Answer 4

transmitter synthesised and stored in vesicles

action potential invades presynaptic terminal

action potential depolarizes terminal and opens VGCC letting Ca2+ enter

Ca2+ triggers vesicle fusion

transmitter released by exocytosis

transmitter binds to receptors

ion flow causes postsynaptic response

transmitter removed by enzyme breakdown or reuptake

vesicle retrieved from terminal membrane

The substance must be present within the presynaptic neurone
Synthetic pathway
Presence of transmitter alone is not sufficient, precursors, intermediates and synthetic enzymes need to be there

The substance must be released in response to presynaptic depolarization by action potential - release must be Ca2+-dependent.

Specific receptors for the substance must be present on the postsynaptic cell to mediate postsynaptic response.

A mechanism for removal and/or breakdown must be demonstrable

Question 5

Acetylcholine

Answer 5

Cholinergic neurones use acetylcholine (Ach) as the neurotransmitter in both peripheral and central nervous systems.
ACh acts at nicotinic (ion channels) and muscarinic (G protein coupled) receptors.
ACh is synthesised in the presynaptic axon by the enzyme choline acetyltransferase (ChAT)
Degradation of ACh occurs in the synaptic cleft by the enzyme acetylcholinesterase (AChE)

[cholinergic] neurones use acetylcholine as a neurotransmitter. Acetylcholine acts at [nicotinic] ion channel receptors, as well as G-protein coupled [muscarinic] receptors. Acetylcholine is synthesised in the presynaptic axon by the enzyme [choline acetyltransferase] and degraded by [acetylcholinesterase]

Question 6

Glutamate

Answer 6

THE main excitatory transmitter in the CNS
Activates both ionotropic and metabotropic receptor

Excitatory
-Opens ligand-gated ion channel (Na+)

fast

Question 7

GABA

Answer 7

THE main inhibitory transmitter in the CNS
Activates small family of ionotropic and metabotropic receptors

Inhibitory
-Opens ligand-gated ion channel (Cl-)
fast

Question 8

Temporal summation

Answer 8

adding together potentials that occur at the same synapse but at different times

Question 9

Spatial summation

Answer 9

adding together potentials that occur at different sites on the neuron

Question 10

‘SLOW’ neurotransmitters

Answer 10

Activate G-protein-coupled receptors, have a more ‘diffuse’ physiological function

5-Hydroxytryptamine (5-HT) [serotonin]
Acetylcholine (ACh)
Dopamine
Noradrenaline [norepinephrine]