Sensory and Motor Innervations of Muscles Flashcards
Upper motor neurons originate from which two areas of the brain?
Motor - planning, initiating and directing voluntary movements. Corticospinal
Brainstem - basic movements and posteral control. Cranial nerves
What two parts of the brain assist the upper motor neurons in proper movement and coordination/recognising errors?
Basal ganglia
Cerebellum
What is the local circuit neurons?
most impulses travel down this route
via interferons
involved in reflex action
What are motor neuron pools?
Route involved in innervating spinal muscles
Pattern generation - hard to regain function when this goes wrong
What Brodmann’s areas are involved in the motor cortex?
4 & 6
What are the two tpes of pyramidal cells?
BETZ - part of local circuit
Non BETZ - lower motor neuron circuit
Why do around 5% of fibres in the corticospinal tract descend ipsilaterally and don’t cross till the spinal cord?
essential for postural muscles that have to have both sides working at the same time
How many axons innervate each fibre in a muscle?
One!
Not enough for all muscles therefore fibres diverge
What do alpha neurons do?
Generation of force by muscles
What do gamma neurons do?
Proprioception
What is the segmental distribution of LMN in the spinal cord
Ventral horn
Flexors and Axial muscles = further dorsal
Extensors and distil muscles = further lateral
See slide 12 for image of flexed arm fitting into the ventral horn
Explain where in the body small, medium and large motor units would be used and what for?
Small: extraoccular muscles of the eye - fine movement
Medium: Soleus muscle - postural
Large: Gastrocnemius - power
In what order do motor units get recruited?
Small to large
Gradual increase in force
What are the adaptive features of red muscle fibres?
Resistant to fatigue Low force high in: Myoglobin Blood supply Mitochondria
Where are red and pale muscle fibres located?
Red = small motor units Pale = large motor units
What is a electromyograph used for?
recording motor unit activity
uses a needle
At what frequency of motor neuron firing does initiation of movement start and continue to cause smooth movement?
10-20Hz
What is muscle tone?
The muscles always being under some degree of stretch, caused by muscle spindles and alpha motor neurons
What are muscle spindles?
Intrafusal muscle fibres
Sensory receptors within the belly of a muscle
Detect changes in the length of this muscle - important in proprioception
Lies parallel to muscle fibre
What are the two main classes of spindles and what do they do?
Chain - Ia and II fibres, continue firing as long as muscles are stretched
Bag - Ia fibres only, involved in rapid stretching
What are the differences between alpha and gamma fibres?
Alpha: innervate extrafusal fibres = detecting stretch
Gamma: innervate intrafusal (spindle) fibres = keep spindles taunt to stop the muscle fibres around it collapsing
How do alpha and gamma fibres respond to each other?
If intrafusal fibre is shortened by alpha fibres then extrafusal fibre collapses = loss of sensitivity
Gamma fibres causes extrafusal fibres to contract the same amount to compensate
What is the Golgi Tendon Organ?
Mechanoreceptor
Detects changes in muscle tension (not length) = proprioception
Innervated by Ib fibres
Made of collegen and axons intertwined
What is the Babinski sign and when is it seen?
tickling bottom of foot = toes to point up and fan out
Seen in:
Upper motor neuron syndrome
Newborns - immature corticospinal tract
