Axonal and Synaptic neurotransmission 17.02.23

Question 1

What is an axonal transmission vs a synaptic transmission?

Answer 1

Axonal: transmission of information from location A to location B
Synaptic: Integration/ processing of information and transmission between neurons

Question 2

At rest, what charge does a neuron have?

Answer 2

Has a negative electric charge

Question 3

What substances cross the neuron’s semi-permeable membrane?

Answer 3

• Potassium and Chloride which are electrically charged, cross readily
• Some cross with difficulty (Na+)
• Some not at all (large organic proteins)

Question 4

Are A- (anions, protein) inside or outside the cell?

Answer 4

They are restricted to inside of the cell

Question 5

Are Na+ ions inside or outside the cell?

Answer 5

Mostly outside neuron

Question 6

Are K+ ions inside or outside the cell?

Answer 6

Mostly inside neuron

Question 7

Are Cl- ions inside or outside the cell?

Answer 7

Mostly outside neuron

Question 8

How does the sodium potassium pump distribute ions?

Answer 8

• Active transport Na+ ions out of neuron and K+ in
• 3 Na+ for every 2 K+
• Requires energy supplied by ATP

Question 9

What is the final resting potential of a neuron?

Answer 9

70 mV
- Na+ high conc outside so Na+ movement into the neuron is restricted
- K+ and Cl- can move back and forth across membrane so reach steady state

Question 10

When will an action potential be formed?

Answer 10

• Membrane potential is stable until receptors open ion channels and Na+ channels open
• Action potential created when the membrane potential is depolarised beyond the threshold of excitation
• Na channels then close and cell becomes repolarised

Question 11

What is an EPSP?

Answer 11

Excitatory post synaptic potential
- Postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential.
- Typically, one EPSP is not enough to reach the AP threshold
- Therefore, and AP is generated via the combined effects of multiple synapses

Question 12

What is an IPSP?

Answer 12

Inhibitory Post synaptic potential
- Decreases the probability of an action potential being elicited

Question 13

What begins to depolarise the cell membrane?

Answer 13

• EPSPs begin to depolarise the cell membrane
• The threshold is -60mV, when this is reached Na+ channels open and polarity reverses to +30 inside

Question 14

When do voltage gated Na+ channels close?

Answer 14

• Membrane potential reverses with the inside going positive, this is when the Na+ channels close and K+ channels open
• K+ rushes out
• Restoring membrane potential

Question 15

Why is an action potential self perpetuating?

Answer 15

• voltage changes are caused by the opening or closing of ion channels
• but the channels are opened by voltage changes
• Thus, voltage changes control the ion channels which control the voltage changes
• It is a cycle

Question 16

What speeds up axonal conduction?

Answer 16

Myelination

Question 17

What is saltatory conduction?

Answer 17

• Decremental conduction between nodes (action potential jumps from each node of Ranvier) but it is re-boosted each time
• Very fast along axon
• this happens in most CNS neurons

Question 18

What happens when the action potential reaches the terminal buttons?

Answer 18

• Voltage activated calcium channels open
  -This leads to an influx of calcium, which changes the state of certain membrane proteins in the presynaptic membrane, and results with exocytosis (release) of the neurotransmitter in the synaptic cleft.
• Then a normal synapse occurs and receptors on the post-synaptic membrane accept the neurotransmitter and the action potential continues

Question 19

Why doesn’t the neurotransmitter remain active in the synapse and continually make new action potentials?

Answer 19

• Enzyme degradation (acetylcholinesterase is the enzyme that breaks down the neurotransmitter acetylcholine)
• Reuptake (actively transported back to presynaptic axon)
• Diffuses away from receptor site

Question 20

What does acetyl choline do?

Answer 20

Key neurotransmitter at the neuromuscular junction - it activates muscles

Question 21

What are some fast neurotransmitters?

Answer 21

• acetylcholine
• glutamate
• GABA
  (short lasting effects)

Question 22

What are some slow neuromodulators?

Answer 22

• Dopamine
• Noradrenaline
• Serotonin
  (slower timescale)

Question 23

What drugs affect the transmitter at the neuromuscular junction?

Answer 23

• Cigarettes (nicotine)
• Poison arrows (curare)
• Spider toxins (black widow)

Question 24

What is noradrenaline affected by?

Answer 24

• Antidepressant drugs (blocks re-uptake and blocks break down)
• Stimulants (amphetamine - increases release and blocks re-uptake)

Question 25

How do hallucinogenic drugs work?

Answer 25

Stimulate serotonin and can activate numerous serotonin receptor subtypes

Question 26

What does the resting membrane potential usually sit at?

Answer 26

Sits between -50 and -75 mV and the inside more negative

Question 27

Where are the higher concentrations of K+, Na+ and Cl-?

Answer 27

• K+ ions normally found at higher concentrations inside the cell
• Na+ and Cl- are at higher concentrations outside the cell

Question 28

What causes action potentials to only flow in one direction?

Answer 28

Refractory periods

Question 29

What happens to axonal transmission with multiple sclerosis?

Answer 29

• Degeneration of myelin and development of scar tissue
• This disrupts, and eventually blocks, neurotransmission along myelinated axons

Question 30

What is temporal summation?

Answer 30

input signals arrive from the same presynaptic cells at different times

Question 31

What is spatial summation?

Answer 31

input signals arrive from different locations in the postsynaptic neuron