Motor units, muscle spindles and neuromuscular reflexes

Question 1

Is the somatic nervous system voluntary or involuntary?

Answer 1

voluntary

Question 2

What is included within the somatic nervous sytem?

Answer 2

Skeletal muscles and elements of NS that are responsible for sensory output, motor control etc.

Question 3

Axial muscles control muscles of what?

Answer 3

Movements of the trunk proximal muscles are found in the shoulder, elbow pelvis and knee (mediating locomotion)

Question 4

What do distal muscles move?

Answer 4

Hands, feet and digits

Question 5

What are motor neurons of the somatic nervous system?

Answer 5

Upper motor neurons

Lower motor neurons

Question 6

Where do upper neurons arise from and what do they use as a neurotransmitter?

Answer 6

Arise in cerebral cortex

Use glutamate

Question 7

Where do lower motor neurons arise from and what do they use as a neurotransmitter?

Answer 7

Arise from spinal cord

Use acetylcholine

Question 8

What function do upper neurons carry out?

Answer 8

Modulating movement to the lower neurons

Question 9

What are the lower neurons responsible for?

Answer 9

Stimulating the contraction itself

Question 10

How are muscle spindles activated?

Answer 10

A type of lower motor neuron - gamma

Question 11

How do lower motor neurons exit the spinal cord? Roughly how many?

Answer 11

In spinal nerves

-30 spinal nerves which innervate muscles roughly at that spinal segment

Question 12

What do motor neurons provide?

Answer 12

Both motor and sensory supply to skeletyal muscle (and sensory input from skin, visceral receptors)

Question 13

C3,4,5 keeps what alive?

Answer 13

The diaphragm

Question 14

What is a motor unit

Answer 14

alpha motor neuron and all of the skeletal muscle it innervates

Question 15

What is a motor pool

Answer 15

single muscle innervated by a group of alpha motor neurons

Question 16

How is force of contraction from alpha motor neuron influenced? 2 things

Answer 16

• Motor unit recruitment

- Frequency of action potentials generated

Question 17

Where are smaller motor units found and what is the effect of them being small?

Answer 17

eyes, fingers

finer control of movement

Question 18

Larger motor units control postural muscles (pectoralis and erector spine). How are these innervated?

Answer 18

By larger alpha motor neurons

Question 19

Some skeletal muscles fibres are required to be slow and fats. Why is this?

Answer 19

Some functions need to be carried out all the time and for long periods however some things such as looking at something quickly requires a quick response for this to occur

Question 20

Give an example of a slow twitch muscle fibre

Answer 20

Pectoralis major

Question 21

Explain the characteristics of a fast-fatiguing motor units

Give an example

Answer 21

• very high tension
• fast fatiguing
• Large a-MN, high threshold
• Type Iix fibres
• burst power

Weightlifting

Question 22

Explain the characteristics of fatigue resistant motor units

Give an example

Answer 22

• high tension
• slow fatiguing
• intermediate a-MN and threshold
• type IIa fibres
• sustained locomotion

Running

Question 23

Explain the characteristics of slow motor units

Give an example

Answer 23

• low tension
• fatigue resistant
• small a-MN, low threshold
• type I fibres

Yoga

Question 24

Fixed order of recruitment in response to increasing activity of the lower motor neurons stimulating the muscke (the motor pool). What is this order and what is it also known as?

Answer 24

• Starts with slow motor units
• then, fats fatigue-resistant units
• finally, fast fatiguable units

AKA- size principle

Question 25

What causes a twitch action potential?

Answer 25

alpha motor unit

Muscle contraction

Question 26

What sort of AP is shown at 5,10,20 and 40Hz?

Answer 26

5- twitch
10- wave summation
20- unfused tetanus
40- fused tetanus