Week 3 (motor system) physiology

Question 1

alpha motor neurons

Answer 1

sends signals of contraction and relaxation to skeletal muscles.

Question 2

gamma motor neurons

Answer 2

gamma motor neurons and intrafusal fibers provide feedback to the nervous system about muscle length and tension, which can contribute to motor control and proprioception

Question 3

a motor unit

Answer 3

an alpha motor neurons and all muscle fibres that it innervates.

Question 4

a motor neuron pool

Answer 4

For a specific given muscle, all the alpha motor neurons that innervate it.

Question 5

type S vs F motor units

Answer 5

S is not fatigable (oxidation energy)
F is fatigable (largely anaerobic)

Question 6

same proportion of S and F

Answer 6

rapid brief activity and sustained contractions (forearm muscle controlling fingers)

Question 7

higher type S

Answer 7

postural limb muscles

Question 8

higher type F

Answer 8

oculomotor muscles (eye movements)

Question 9

differing motor unit size

Answer 9

fine movements: fewer muscle cells in 1 motor unit

Question 10

higher number of motor neurons that are firing

Answer 10

accumulation of action potential strength as one fires before the previous one decays.

Summation of twitch-tension between motor units - greater total muscle tension.

Question 11

increase firing rate

Answer 11

Summation of twitch-tension within motor units - greater total muscle tension.

Question 12

size principle

Answer 12

motor unit recruitment:
small to big motor units (depending on force demand)

Question 13

muscle spindles - intrafusal fibres

Answer 13

measure length of muscle (prevent over-stretching)
- parallel and between muscle fibres
- testable using myotatic reflex (streching reflex)

Question 14

golgi tendon organ

Answer 14

measure force of muscle (prevent over-contraction)
located in the tendon

Question 15

myotatic reflex

Answer 15

1. stretching of muscle spindles
2. information relayed through type la sensory fibres
3. send rapid signals to the spinal cord,
4. immediately sends signals through alpha motor neuron to contract

Question 16

reverse myotatic reflex

Answer 16

1. contraction of muscles
2. compress sensory terminals
3. relayed through lb sensory fibres to spinal cord (inhibitory interneuron)
4. inhibition of alpha motor neurons (prevent contraction)
5. relax

Question 17

neuromuscular junction (NMJ)

Answer 17

between an alpha motor neuron (neurotransmitter vesicles) and a muscle fibre (acetylcholine receptor)

Question 18

upper motor neuron

Answer 18

neurons are located in the motor cortex of the brain and send their axons down to the spinal cord

Question 19

lower motor neuron

Answer 19

spinal cord to peripheries

Question 20

(mice models) motor neuron disease

Answer 20

deinnervating, axons withdrawal.

Question 21

standardisation of measuring NMJ

Answer 21

across labs

Question 22

compare mice and human NMJ

Answer 22

human: much smaller, thinner axons, nummular (island/coin shaped) end plates - receptors.
- humans: less complexity
- more fragmentation

Question 23

human NMJ stability vs mice

Answer 23

humans: stable with age
mice: NMJ falls apart (fragmentation) with age.

Question 24

active zone

Question 25

better animal model for human NMJ

Answer 25

sheep NMJ has the same size as the human NMJ
better modelling than mice in motor neuron disease