Week 3 (motor system) physiology Flashcards
alpha motor neurons
sends signals of contraction and relaxation to skeletal muscles.
gamma motor neurons
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
a motor unit
an alpha motor neurons and all muscle fibres that it innervates.
a motor neuron pool
For a specific given muscle, all the alpha motor neurons that innervate it.
type S vs F motor units
S is not fatigable (oxidation energy)
F is fatigable (largely anaerobic)
same proportion of S and F
rapid brief activity and sustained contractions (forearm muscle controlling fingers)
higher type S
postural limb muscles
higher type F
oculomotor muscles (eye movements)
differing motor unit size
fine movements: fewer muscle cells in 1 motor unit
higher number of motor neurons that are firing
accumulation of action potential strength as one fires before the previous one decays.
Summation of twitch-tension between motor units - greater total muscle tension.
increase firing rate
Summation of twitch-tension within motor units - greater total muscle tension.
size principle
motor unit recruitment:
small to big motor units (depending on force demand)
muscle spindles - intrafusal fibres
measure length of muscle (prevent over-stretching)
- parallel and between muscle fibres
- testable using myotatic reflex (streching reflex)
golgi tendon organ
measure force of muscle (prevent over-contraction)
located in the tendon
myotatic reflex
- stretching of muscle spindles
- information relayed through type la sensory fibres
- send rapid signals to the spinal cord,
- immediately sends signals through alpha motor neuron to contract
reverse myotatic reflex
- contraction of muscles
- compress sensory terminals
- relayed through lb sensory fibres to spinal cord (inhibitory interneuron)
- inhibition of alpha motor neurons (prevent contraction)
- relax
neuromuscular junction (NMJ)
between an alpha motor neuron (neurotransmitter vesicles) and a muscle fibre (acetylcholine receptor)
upper motor neuron
neurons are located in the motor cortex of the brain and send their axons down to the spinal cord
lower motor neuron
spinal cord to peripheries
(mice models) motor neuron disease
deinnervating, axons withdrawal.
standardisation of measuring NMJ
across labs
compare mice and human NMJ
human: much smaller, thinner axons, nummular (island/coin shaped) end plates - receptors.
- humans: less complexity
- more fragmentation
human NMJ stability vs mice
humans: stable with age
mice: NMJ falls apart (fragmentation) with age.
active zone
better animal model for human NMJ
sheep NMJ has the same size as the human NMJ
better modelling than mice in motor neuron disease
