Synapses

Question 1

Synapse

Answer 1

Gaps between end of axon of
one neurone and dendrite of
another
impulses are transmitted as
neurotransmitters

Question 2

Role of calcium
ions in synaptic
transmission

Answer 2

Depolarisation of the pre-synaptic
knob opens voltage gated Ca2+
channels and Ca2+ diffuses into
synaptic knob.

stimulates vesicles containing
neurotransmitter to move towards and
fuse with presynaptic membrane and
release neurotransmitter into the
synaptic cleft via exocytosis

Question 3

Why are
synapses
unidirectional

Answer 3

Receptors only present on the post-
synaptic membrane

enzymes in synaptic cleft break
down excess-unbound
neurotransmitter - concentration
gradient established from pre-post
synaptic neurone
neurotransmitter only released
from the pre-synaptic neuron

Question 4

Cholinergic
synapse

Answer 4

The neurotransmitter is
acetylcholine
enzyme breaking down
acetylcholine =
acetylcholinesterase
breaks down acetylcholine to
acetate and choline to be recycled
in the pre-synaptic neurone

Question 5

Summation

Answer 5

Rapid build-up of neurotransmitters
in the synapse to help generate an
action potential by 2 methods:
spatial or temporal
required because some action
potentials do not result in sufficient
concentrations of neurotransmitters
released to generate a new action
potential

Question 6

Spatial
summation

Answer 6

Many different neurones
collectively trigger a new action
potential by combining the
neurotransmitter they release
to exceed the threshold value
e.g., retinal convergence for
rod cells

Question 7

Temporal summation

Answer 7

When one neurone releases
neurotransmitters repeatedly
over a short period of time to
exceed the threshold value
e.g., 1 cone cell signalling 1
image to the brain

Question 8

Inhibitory
synapses

Answer 8

Causes chloride ions (Cl- ) to
move into post-synaptic
neurone and K+ to move out

makes membrane hyperpolarise
(more negative) so less likely an
action potential will be
propagated

Question 9

Neuromuscular
junction

Answer 9

Synapse that occurs between a
motor neurone and a muscle
similar to synaptic junction

Question 10

Compare the NMJ
with a cholinergic
synapse

Answer 10

Both
- Unidirectional - neurotransmitters receptors only on post synaptic membrane
Differences
- NMJ only excitatory vs CS excitatory or inhibitory
- NMJ connects motor neurons to muscles vs CS connects to neurons
- NMJ end point for action potential vs CS new action potential generated in next neurone
- NMJ Ach binds to receptors on muscle fibres vs CS Ach binds to receptors on post synaptic membrane