6.2.2: Synaptic transmission

Question 1

Synaptic transmission

Answer 1

1) Action potential arrives at synaptic knob. Depolarisation of presynaptic membrane.

2) Calcium channels open and calcium ions enter

3) Synaptic vesicles fuse with presynaptic membrane and release acetylcholine

4) Acetylcholine diffuses down concentration gradient across the cleft

5) Acetylcholine attaches to complementary receptors on the postsynaptic membrane

6) Sodium channels open and sodium ions diffuse in leading to depolarisation

Question 2

What is summation?

Answer 2

The rapid build up of neurotransmitters in the synapse to generate an action potential by spatial or temporal summation. This is needed because some action potentials don’t have sufficient concentrations of neurotransmitters being released for an action potential.

Question 3

What is spatial summation?

Answer 3

Different neurones converge at one synapse. Action potential arrives from several neurone at the synapse so enough neurotransmitters can reach threshold and cause an action potential

Question 4

What is temporal summation?

Answer 4

Only one neurone and impulses arrive repeatedly over a short period of time to add up to rough to exceed threshold.

Question 5

What is inhibitory synapse?

Answer 5

Chloride ions move into the post synaptic neurone and potassium ions move out. Resting potential becomes hyper polarised (more negative) and post synaptic neurone is less likely to reach threshold

Question 6

What is an excitatory synapse?

Answer 6

Resting potential becomes less negative so less sodium ions needed for threshold

Question 7

What is the neuromuscular junction?

Answer 7

Synapse between the motor neurone and a muscle

Question 8

Similarities between neuromuscular junction and cholinergic synapse (2)

Answer 8

1) Unidirectional as NT receptors only on post synaptic neurone

2) Both use acetylcholine which bind to acetylcholine receptors

Question 9

Differenced between neuromuscular junction and cholinergic synapse (4)

Answer 9

1) Only excitatory vs excitatory and inhibitory
2) Connects motor neurone to muscles vs connects two neurones (relay, sensory or motor)
3) End point for action potential vs new action potential generated into the next neurone
4) Acetylcholine binds to receptors on muscle fibre membranes vs acetylcholine binds to receptors on post synaptic membrane of neurone

Question 10

How is synapses unidirectional? (2)

Answer 10

• Vesicles containing neurotransmitters only in pre synaptic neurone
• Receptors for NT only on post synaptic neurone membrane