Physiology of Movement Flashcards
Where are upper motor neurons found?
in the brain
Where are lower motor neurons found?
in the brainstem
What are lower motor neurons made up of?
alpha and gamma MNs
What are alpha motor neurons responsible for?
muscle contraction - innervate a bulk of fibres within the muscle
What are gamma motor neurons responsible for?
muscle tone - innervate the muscle spindle
Where do alpha and gamma motor neurons arise from?
laminae VIII and IX
What is a motor neuron pool?
collection of alpha motor neurons that innervate a single muscle
What is a motor unit?
alpha motor neuron and all of the skeletal muscle fibres that it innervates
What is force of muscle contraction graded/controlled by?
frequency of action potential discharge of the alpha MN
recruitment of additional synergic motor units
Which is more medial - LMNs innervating distal or axial muscles?
LMNs innervating axial muscles
What is more dorsal - LMNs innervating flexors or extensors?
LMNs innervating flexors
What does muscle strength depend on?
The activation of muscle fibres - firing rates of LMNs, no of LMNs fired simultaneously
The force production by innervated muscle fibres
What are small motor units innervated by?
small alpha MNs
What are large motor units innervated by?
large alpha MNs
Are fast motor units made up of small or large MNs?
large alpha MNs
What colour are slow oxadative type 1 muscle fibres?
RED
What colour are fast oxadative type 2a muscle fibres?
RED
What colour are fast oxadative type 2b muscle fibres?
WHITE
Describe slow oxidative type 1 muscle fibres?
ATP derived from oxidative phosphorylation
slow contraction and relaxation
small alpha MNs
low threshold
Describe fast oxidative type 2a muscle fibres?
ATP derived from oxidative phosphorylation
fast contraction and relaxation
intermediate alpha MNs
intermediate threshold
Describe fast oxidative type 2b muscle fibres?
ATP derived from glycolysis fast contraction but not fatigue resistant not commonly found in man/mammals large alpha MNs high threshold
How are LMNs excited?
by activation of UMNs
How are LMNs and the muscle fibres they innervate recruited?
in order of their size - small ones more easily recruited
- allows for fine control of muscle
Describe the monosynaptic reflex arc?
stretch of muscle spindle -> Ia afferent fires out action potentials -> excitory synaptic transmission in spinal cord -> activation of alpha MNs -> contraction of homonymous muscle
