Synapses

Question 1

What is a synapse

Answer 1

Junction between neurone and another neurone/effector

Question 2

What is the presynaptic neurone

Answer 2

Neurone before the synapse, has swelling at end called synaptic knob which contains vesicles filled with neurotransmitters

Question 3

What is the synaptic cleft

Answer 3

Gap between cells at synapse

Question 4

How do neurotransmitters leave presynaptic neurone

Answer 4

-action potential arrives at synaptic knob of presynaptic neurone which stimulates voltage-gated calcium channels in presynaptic neurone to open
-calcium ions diffuse into synaptic knob(pumped out when action potential finished)
-influx of calcium ions into synaptic knob causes synaptic vesicles to move to presynaptic membrane which fuse with presynaptic membrane and vesicles release NTs into synaptic cleft via exocytosis

Question 5

How do neurotransmitters move across synapse and trigger action potential in next neurone

Answer 5

-diffuse across synaptic cleft and bind to specific receptors on post-synaptic membrane
-causes sodium ion channels to open in postsynaptic neurone, influx of sodium ions in postsynaptic membrane causes depolarisation, action potential generated if threshold reached——> may trigger action potential in postsynaptic neurone/cause muscle contraction/cause a hormone to be secreted from gland cell

Question 6

Why are impulses unidirectional

Answer 6

As receptors only on postsynaptic neurone

Question 7

What happens to neurotransmitters left in cleft

Answer 7

-neurotransmitters removed from cleft so response doesn’t keep happening, broken down by enzyme and products reabsorbed by presynaptic neurone and reused to make more

Question 8

Role of acetylcholine and what is it broken down by

Answer 8

Binds to cholinergic receptors on postsynaptic neurone, those left in cleft broken down by acetyl choline esterase and products reabsorbed and reused to make more ACh. Involved in muscle contraction and control of hr, both excitatory and inhibitory in heart as causes potassium channels to open on post synaptic membrane which hyperpolarises membrane

Question 9

What do excitatory neurotransmitters do

Answer 9

Depolarise post synaptic membrane making it fire its action potential if threshold reached

Question 10

What do inhibitory neurotransmitters do

Answer 10

Hyperpolarise postsynaptic membrane making pd more negative so prevent action potential from firing eg GABA binds to receptors and causes potassium channels to open on postsynaptic membrane