motor control and movement disorders ppt 1 Flashcards
what are extrafusal muscle fibres?
the external muscle fibres those attached to tendons
(Muscle spindles are found within the belly of a skeletal muscle. the special muscle fibres inside the spindle are called intrafusal muscle fibers. The regular muscle fibers outside of the spindle are called extrafusal muscle fibers.)
are alpha motor neurons upper or lower motor neurons? which parts of the CNS are they part of
lower motor neurons of the brainstem and the spinal cord
what type of muscle fibres do alpha motor neurons innervate?
extrafusal muscle fibres of the skeletal muscle
what does activation of an alpha motor neuron lead to?
CONTRACTION of ALL the muscle fibres in the respective MOTOR UNIT
what is a motor neuron pool?
all the ALPHA motor neurons innervating a single MUSCLE
what is a motor unit? (structurally and what is its significance)
structurally
a single motor neuron together with all the muscle fibres that it innervates.
significance
It is the smallest functional unit with which we can produce force.
how many muscle fibres does the average motor neuron supply?
600 muscle fibres
do we have more motor neurons or more muscle fibres?
more muscle fibres
(Humans have approximately 420,000 motor neurons and 250 million skeletal muscle fibres)
Where do you think there are more neurons per motor unit ?
more fine movement areas such as fingers
what are the types of motor unit
1) slow (S, type I)
2) fast, fatigue resistant (FR, type IIA)
3) Fast, fatiguable (FF type IIB)
what are the characteristics of type I motor neurons?
C.B. A. C.V. D.T. (CBA FOR A CV Dont Try)
cell body diameter: smallest
axons : thinnest
conduction velocity : slowest
dentritic trees : small
what are the characteristics of type IIA and IIB motor neurons compared to type I?
C.B. A C.V. D.T. (CBA FOR A CV Dont Try)
cell body diameter: larger
dentritic trees : larger
axons : thicker
conduction velocity : faster
which type of motor unit is THE fasteST and strongeST?
fast fatiguable (FF TYPE IIB)
Which motor unit type is most fatigue resistant?
slow (type I)
where is each type of motor neuron located?
they are all distributed throughout the muscle
which motor unit type evokes the STRONGEST force?
type II B fast fatiguable
what are the 2 mechanisms of regulation of muscle force?
recruitment and rate coding
what is the recruitment mechanism for regulation of muscle force and what does it allow for?
-motor units are recruited based on “size principle” from smaller units (slow) first
- allows for fine control for ex in writing
what is the rate coding mechanism for regulation of muscle force?
- motor units start by firing at lower frequencies
- as firing rate increases the force produced by the unit increases due to summation
what is summation?
when UNITS fire at frequency TOO FAST to allow the muscle to RELAX between arriving action potentials so the FORCES generated by subsequent **action potentials **are SUMMED.
what is trophe’ and what are its functions
type of gorwth factor
prevent neuronal death
promote growth of neurons after injury
are the qualities of a motor unit dependent or independent to the nerve that innervates them?
dependent
what is cross innervation and what does it cause?
its when the neurons normally innervating a fast and a slow twitch motor unit interchange and it causes the slow unit to become faster than it was and the fats slower than it was (but not slower/ faster than the original slow/ fast units)
what is the most common case of neuron type transition and in what conditions? (since theres plasticity in motor units)
type IIB to IIA (To fatigue resistance from fatiguable) following training
