13.5 Synapses

Question 1

what is a synapse

Answer 1

a gap found between the neurones (or between an a motor neurone and an effector) which electrical impulses cannot pass through

Question 2

as electrical impulses cannot pass through synapses what do neurones release and what does this do

Answer 2

it releases a neurotransmitter from one neurone (the presynaptic neurone) to stimulate an action potential in the next neurone (the postsynaptic neurone)

Question 3

what are the neurones before and after the synapse called

Answer 3

before = presynaptic neurone
after = postsynaptic neurone

Question 4

what’s the space called between the presynaptic neurone and the postsynaptic neurone

Answer 4

the synaptic cleft

Question 5

what’s the swelling end of the presynaptic neurone called

Answer 5

the synaptic knob

Question 6

what are the 6 stages of synaptic transmission

Answer 6

1. An action potential arrives at the end of the presynaptic neurone (the synaptic knob) and triggers the opening of voltage gated Ca+ ion channels
2. Ca+ move into the synaptic knob by facilitated diffusion and trigger the movement of vesicles containing neurotransmitters (eg dopamine or acetylcholine) towards the presynaptic membrane
3. the vesicles fuse with the presynaptic membrane and their contents is released by exocytosis
4. the neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane
5. this triggers the opening of sodium ion channels in the postsynaptic membrane, Na+ ions move into the postsynaptic membrane causing depolarisation and triggering an action potential if the excitation exceeds-55mV
6. the neurotransmitters is removed from the synaptic cleft which prevents continuous stimulation of an action potential in the postsynaptic neurone
   (it’s either reabsorbed by presynaptic neurone or broken down by enzymes in the synaptic cleft)

Question 7

why is it important that receptors that are complementary to neurotransmitters are only found in the postsynaptic membrane not the presynaptic membrane

Answer 7

so the action potential always travels in one direction only and prevents nerve impulses from travelling backwards

Question 8

what is synaptic divergence

Answer 8

when a neurone forms connections to multiple neurones through multiple synapses the action potential can diverge sending information to different parts of the body

Question 9

what’s synaptic convergence

Answer 9

when multiple neurones can all connect to a single neurone causing the action potentials from multiple neurones to converge and become amplified

Question 10

what is summation

Answer 10

it’s when small amounts of neurotransmitter build up to trigger an action potential in the postsynaptic neurone

Question 11

what’s spatial summation

Answer 11

when lots of presynaptic neurones converge on a single postsynaptic neurone although each of the presynaptic neurones are releasing small amounts of neurotransmitter (which alone wouldn’t be enough to exceed the threshold potential) the combined amount is enough to stimulate an impulse in the next neurone

Question 12

what’s temporal summation

Answer 12

it’s when a single neurone fires action potentials in quick succession repeatedly releasing neurotransmitter into the synaptic cleft this caused the amount of neurotransmitter in the synaptic cleft to increase making an action potential in the postsynaptic neuron more likely