3.6.2.1 Synaptic Transmission

Question 1

What are 6 features of a nerve cell?

Answer 1

• Axon
• Cell body
• Dendrites
• Myelin sheath
• Nucleus
• Synapses

Question 2

What is the role of the axon?

Answer 2

• Transfers electrical impulses from the cell body to the synapse

Question 3

What is the role of dendrites?

Answer 3

• Receives electrical impulses from the neighbouring neurones.

Question 4

What is the role of the Myelin Sheath?

Answer 4

• Forms an electrically insulating cover around the axon, made of layers of schwann cells.

Question 5

What is the role of the synapse?

Answer 5

Transmits electrical impulses to neighbouring neurones via neurotransmitters.

Question 6

How is the resting potential established?

Answer 6

• 3 sodium ions are actively transported out of the membrane, whilst 2 potassium ions are actively transported into the axon.
• Sodium ion channels shut.

Question 7

What happens during depolarisation?

Answer 7

• A stimulus occurs.
• The neurone membrane becomes more permeable to sodium ions.
• Sodium ion channels open allowing sodium ions to diffuse into the neurone.
• Potassium ion channels close
• The inside is now more positive than the outside of the membrane.

Question 8

What happens during repolarisation?

Answer 8

• Sodium ion channels close.
• Potassium ion channels open allowing potassium ions to diffuse back out.
• Inside of the neurone becomes more negative again.

Question 9

What happens during hyperpolarisation?

Answer 9

• Potassium ion channels remain open causing the potential difference to become even lower than the -70mV resting potential.

Question 10

What is the Refractory Period?

Answer 10

• A resting period which causes a time delay as sodium ion channels can no longer open.

Question 11

What 3 features does the Refractory period cause to happen?

Answer 11

1. Action potentials are unidirectional.
2. There is a time delay between action potentials.
3. Action potentials don’t overlap.

Question 12

What are gaps in the myelin sheath called?

Answer 12

• Nodes of Ranvier

Question 13

What happens to action potentials at the myelin sheath?

Answer 13

• Action potentials jump between nodes of ranvier.

Question 14

What is meant by the ‘all or nothing’ principle?

Answer 14

• Action potentials only occur if the threshold value is reached.
• All action potentials are the same size.

Question 15

How are stimuli measured?

Answer 15

• Frequency of action potentials
• Value of the threshold.

Question 16

What 3 factors affect the speed of impulses?

Answer 16

1. Myelination
2. Axon diameter
3. Temperature

Question 17

Why does the axon diameter affect the speed of transmission?

Answer 17

• Greater diameter causes less resistance to the flow of ions.

Question 18

How do cholinergic synapses work?

Answer 18

1. Action potential reaches the synaptic knob of the pre synaptic membrane.
2. Stimulates calcium ion channels to open allowing calcium ions to diffuse into the synapse.
3. Pre synaptic neurone fuses with the vesicles which causes acetylcholine to be released.
4. Acetylcholine diffsues across the synaptic cleft.
   - Acetylcholine binds to receptors on the post synaptic membrane.
   - Triggers depolarisation of the post synaptic membrane, causing an action potential to be triggered.

Question 19

Why are synaptic transmissions unidirectional?

Answer 19

• Neurotransmitter is only made and released from the presynaptic neurone’s side.
• Receptors are only found on the post synaptic membrane.

Question 20

Why is summation important?

Answer 20

• Without summation, action potentials would be triggered at a low frequency.

Question 21

What is spatial summation?

Answer 21

• Spatial summation happens when lots of pre synaptic mebranes join to one post synaptic membrane to trigger a large level of depolarisation.

Question 22

What is temporal summation?

Answer 22

• Pre synaptic membrane releases neurotransmitters at timed intervals.

Question 23

What are inhibitory synapses?

Answer 23

• Synapses that reduce the chances of an action potential being triggered.

Question 24

How do inhibitory synapses work?

Answer 24

• Neurotransmitter binds t chlorine ion channels which are negative.
• This causes the inside of the membrane to be hyperpolarised.
• Requires higher amounts of sodium ions to trigger an action potential.

Question 25

What are 3 differences between cholinergic synapses and neuromuscular junctions?

Answer 25

• Cholinergic is neurone to neurone but neuromuscual is neurone to muscle.
• Cholinergic contains inhibitory and excitatory synapses but neuromuscular only contains excitatory.
• ## Action potential ends at the NM, but action potential is continued at cholinergic.

Question 26

What are 4 similarities between NMJ and Cholinergic synapses?

Answer 26

• Both have receptors which trigger an influx of sodium ions.
• Both use a sodium/potassium pump to repolarise the axon.
• Neurotransmitter is transported by diffusion in both.
• Both use enzymes to break down the neurotransmitter.