(S1W2) Control of Muscle Activation part 1

Question 1

What are the important factors in action potential propagation?

Answer 1

• inactivity of sodium channels
• density of sodium channels
• myelin
• Ranvier nodes

Question 2

Why is the inactivity of sodium channels important?

Answer 2

• so the action potential only travels in one direction along the neuron (refractory period)

Question 3

Why is the density of sodium channels important?

Answer 3

• the more sodium channels you’ve got, the more likely you are to get an action potential
• at the axon hillock (start of the axon), there is a high density of sodium channels which makes it highly likely an action potential can start

Question 4

Why is myelin important?

Answer 4

• it is insulation that protects the signal from interference so it can travel along the neuron faster

Question 5

What are Ranvier nodes and why are they important?

Answer 5

• in the gaps in the myelin, we have Ranvier nodes which are really dense sodium channels that boost the signal

Question 6

Does the action potential actually travel along the neuron?

Answer 6

NO
* The action potential itself doesn’t actually travel along the neuron
* one action potential will trigger another action potential further along

Question 7

What is stochastic resonance?

Answer 7

a phenomenon that involves noise being added to a signal that is not strong enough to reach the threshold without noise, but does reach the threshold with noise

Question 8

Explain how adding noise effects muscle contraction

Answer 8

• with no noise it is harder to achieve a muscle contraction, adding noise makes it easier
• but if you add too much noise you will get muscle contractions all over the place where you don’t want them

Question 9

What is a motor unit?

Answer 9

• the smallest functional unit of the neuromotor system
• includes the motoneuron and all the muscle fibres it innervates

Question 10

Which type of motoneuron is linked to the muscle?

Answer 10

alpha (𝛂)

Question 11

True or False?
One motoneuron can only stimulate one muscle fibre.

Answer 11

False
* one motoneuron can innervate many muscle fibres
* could range from 10 muscle fibres for fine control of something like eye movement, up to about 1,000 muscle fibres for really gross control of something like your leg muscles

Question 12

Can we stimulate single muscle fibres?

Answer 12

No
* Although it is possible to stimulate a single motor unit, you cannot stimulate or inhibit single muscle fibres within that
* So a motor unit is our smallest level of control