Synapses

Question 1

What is a synapse?

Answer 1

the gap/junction between neurones

Question 2

How does the action potential travel between neurones?

Answer 2

-action potential cannot cross the synaptic cleft
-instead neurotransmitters diffuse across the synaptic cleft

Question 3

Name a common neurotransmitter

Answer 3

acetylcholine

Question 4

What are the functions of a synapse?

Answer 4

-allow a single action potential along one neurone to be transmitted to several different neurones (simultaneous responses)
-allows for convergence - effect of stimuli at different receptors can interact
-unidirectionality - neurotransmitters only released from the presynaptic membrane
-stops the continuation of response - neurotransmitters are removed

Question 5

What can neurotransmitters be?

Answer 5

-excitatory - depolarise postsynaptic membrane
-inhibitory - hyperpolarise the postsynaptic membrane

Question 6

What is summation?

Answer 6

when the effect of released neurotransmitter is added together

Question 7

Name the two types of summation?

Answer 7

-spatial
-temporal

Question 8

Explain synaptic transmission

Answer 8

-action potential arrives in the pre-synaptic neurone and depolarises the membrane
-Ca2+ ions move into the synaptic knob via the calcium ion channels
-synaptic vesicles move towards the membrane
-at the membrane, synaptic vesicles fuse and release acetylcholine into the gap
-acetylcholine molecules diffuse across the synapse and bind to protein receptors in the post synaptic membrane
-this causes sodium ion channels in the postsyntaptic membrane to open so Na+ ions move in, depolarising the membrane and generating an action potential
-aceytlcholine is broken down by the enzyme acetylcholinerase into ethanoic acid and choline
-these molecules diffuse back into the synaptic knob
-ATP is then used to resynthesise them into acetylcholine

Question 9

What is the difference between temporal and spatial summation?

Answer 9

-multiple nerve impulses from a single pre-synaptic neurone occurring in succession
-spatial summation - multiple pre-synaptic neurone to the same post-synaptic neurone

Question 10

On a graph how could you tell which one is spatial summation?

Answer 10

big peak will have a couple of little peaks before it

Question 11

Name the axis on an action potential graph

Answer 11

y - voltage/potential difference mV
x - time m/s

Question 12

Explain the process in inhibitory synapses

Answer 12

-presynaptic neurone releases a neurotransmitter (like GABA) that binds to Cl- channels on the post-synaptic membrane
-Cl- channels open
-Cl- ions move in by facilitated diffusion
-the binding of the neurotransmitter also causes the K+ channels to open
-so K+ ions move out of the post synaptic neurone
-the combined effect of negative ions moving in and positive ions moving out causes hyperpolarisation
-reducing the chance of of a new action potential occurring as more Na+ is needed to reach threshold