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
What makes up a muscle spindle?
intrafusal fibres
sensory afferents
fibrous capsule
gamma motor neuron efferents
What regulates the monosynaptic reflex arc?
gamma motor neuron efferents
What do intrafusal fibres consist of?
a non contractile region innervated by Ia sensory neurons
contractile polar ends that recieve input from gamma MNs
What causes the muscle spindle to contract?
gamma MNs
What is the role of spinal interneurones?
gather information to generate an output
What are the two types of spinal interneurones?
inhibitory
excitory
What do inhibitory interneurones mediate?
the inverse myotatic response and reciprocal inhibition between extensor and flexor muscles
What is the flexor reflex?
noxious stimuli causes the limb to flex by contraction of flexor muscles (via excitory interneurones) and relaxation of extensor muscles via excitatory and inhibitory interneurones
What is the myotatic response?
when a muscle is pulled, it pulls back
What mediates the flexor reflex?
excitory interneurones
Whats the crossed extensor reflex?
noxious stimuli causes limb to extend by contraction of extensor muscles by excitory interneurones
- ehances postural support during the withdrawl of your foot
What is the role of the vestibulospinal pathway?
control head and neck
What is the role of the tectospinal tract?
muscles of upper trunk, neck and shoulders
What tracts are part of the lateral pathway?
corticospinal tract
rubrospinal tract
What tracts are part of the ventromedial pathway?
vestibulospinal tract
tectospinal tract
medial and lateral reticulospinal tract