Week 3 MPW Lecture 7

Question 1

What are motor neurons?

Answer 1

Motor neuron have their axons pointing from the spinal cord to the muscle.

Question 2

What are sensory neurons?

Answer 2

Sensory neurons have their axons pointing from the tissue to the spinal cord

Question 3

How are stronger nerve signals obtained?

Answer 3

By more rapid action potentials. This is because the nerve impulse is a transient change in membrane potential, meaning its either all or nothing

Question 4

Explain how a signal can be transmitted from one cell to the next.

Answer 4

Neurotransmitter are stored in vesicles at the end of an axon

a) Arrival of an action potential triggers exocytosis of the vesicles.
b) The transmitter diffuses across the synapse and bind to the acetylcholine receptors.
c) This leads to opening of a channel in the postsynaptic membrane activating the signal

Question 5

How do neural junctions work?

Answer 5

It is s more complicated ‘logic gate’. The transmitted signals produced can either be negative or positive which add up. An action potential in the second neuron will start when the net voltage reaches a threshold.

Question 6

What is the potential across the membrane in the resting state?

Answer 6

-60mV

Question 7

What effect of the action potential has on the cell membrane?

Answer 7

The action potential moving along the cell depolarised the membrane, makes the potential less negative (-40mV). This is enough to open the Na+ channels. Na+ moves in cell. This makes the potential more positive meaning more channels opening. This creates a positive feedback and very rapidly all the Na+ channels open up. This happens until the potential reaches +35mV. The Na+ channel is then plugged.

Question 8

What happens after the cell depolarises?

Answer 8

The delayed K+ channels start to open; this makes the K+ leave the cell because of the positive membrane potential. This pushes the potential to be negative. The flow of` K+ is enough to hyperpolarise the membrane. This happens during the refractory period which ensure that the action potential goes in one direct.

Question 9

Does the size of actional potential get smaller or bigger as it travels down an axon?

Answer 9

Stays the same size, this is because of the concentration imbalance of K+ and Na+ across the membrane.

Question 10

What are the toxins that target different aspects of the actional potential?

Answer 10

Japanese puffer fish (fugu) are poisonous because of tetrodotoxin which blocks the voltage gated Na+ channels
a) Batrachotoxin is a poison from frog skin, which keeps sodium channels open.

Question 11

What are myelin sheaths?

Answer 11

Allow the potential to travel faster. Schwann cells are bound to axons. The myelin sheaths also have gaps roughly about 1micrometer for every 100micrometer. This allows the potential to jump from one node/ gap to the next.

Question 12

What is a dendrite?

Answer 12

a short-branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body.

Question 13

What do the depolarisation, repolarisation, hyperpolarisations and refractory mean?

Answer 13

So;

a) Depolarisation is when the potential becomes more positive
b) Repolarisation is when the potential become negative
c) Hyperpolarisation is when the potential becomes more negative than the resting potential
d) the refractory period is a period of time during which a cell is incapable of repeating an action potential