Structure and action of axons

Question 1

Define action potential

Answer 1

Firing of a neuron is called an action potential and is powered by the flow change of charged molecules across the neurons cell membrane - graph

Resting potential of the membrane is -70mV
Depolarisation occurs as positive Na+ ions flow into the cell (move rewards 0)
Triggering of action potential occurs when membrane potential reaches -50mV
Refractory period occurs when the membrane is hyperpolarized causing it to decrease below the threshold and be less likely to trigger another action potential

Question 2

Process of action potential

Answer 2

1. Opening of the sodium channel allow Na+ ions to flow into the neuron
2. This influx increases the charge and reduce the charge difference between the interior and exterior (depolarisation)
3. Once enough Na+ for depolarisation over -50mV threshold potassium channels open to allow K+ to leave the neuron (Na+ still entering)
4. After approx 1ms, sodium channels become refractory due to the action potential reaches it peak
5. Charge inside the neuron is more positive and sodium channels are closed
6. Potassium ions are opened and continue to exot the cell making the neuron inside more negative

Question 3

Rate law of action potential

Answer 3

Neuron firing is all or none event - not faster or slower
Frequency of firing is reliant on strength of neural signal
Very intense stimulus leads to faster and faster accumulation - quicker change in the resting membrane potential to reach threshold

Question 4

Propagation of action potentials

Answer 4

Ion can only diffuse in and out of the membrane via gaps between the myelin (nodes of raviner) allowing the action potential to move faster

Question 5

Chemical signalling process in the brain

Answer 5

• Neurotransmitter: often referred to as chemical messengers and are chemicals synthesised by the brain/neuron
• Action potentials stops at the axon terminals for the pre synaptic neuron to specifically target the post synaptic neuron
  1. Action potential in the pre synaptic cell triggers synaptic vesicles to move towards the cell membrane
  2. Two membranes fuse
  3. Neurotransmitter molecules released
  4. Neurotransmitter flows into the synaptic cleft where it is available to bind to receptors on the post synaptic membrane

Question 6

Neurotransmitter release

Answer 6

“Kiss and run”: the merging between the synaptic vesicle and presynaptic membrane to allow the contents to be released into the synaptic cleft

Question 7

Neurotransmitter reuptake

Answer 7

merge and recycle” recycling of of the neurotransmitter molecules after they are released
Endocytosis: reabsorption into the synapse

Question 8

Neural excitation

Answer 8

Excitatory postsynaptic potentials (EPSPs) depolarise the post synaptic cell membrane and increases the likelihood of a action potential occurring in it
Primary excitatory neurotransmitter is glutamate
Increase in positivity

Question 9

Action of neurotransmitters at receptor

Answer 9

Neurotransmitter interact with the post synaptic neuron by attaching to the binding site of a receptor specific to it - doesnt enter
This CAN causes the ion channel to open
Receptors have a specific function and therefore when activated by its neurotransmitter, relays the same response each time

Question 10

Action of drugs at receptor - 2 types

Answer 10

Mimics the chemical structure fo the natural compound
Can be agonists where it activates the receptor like the natural compound
Can be antagonist by blocking the receptor and prevent activation by the natural compound