Physiology 5: Motor Units, Golgi Tendon Organs and Joint Receptors Flashcards
where are LMNs located?
soma within the brainstem
ventral horn of the spinal cord
where are UMNs are located?
brain
where do LMNs get input from?
UMNs
proprioceptors
interneurons
alpha motor neurons supply what? what does this allow it to do?
skeletal muscle for FORCE
gamma motor neurons innervate…
muscle spindles
give an example of synergistic muscles
brachialis and biceps brachii
axial muscles control movements of…
the trunk for posture
axons of LMNs exit the spinal cord via..
anterior/ventral roots OR
cranial nerves
where is the greatest number of motor neurons?
cervical enlargement (C3-T1) lumbar enlargement (L1-S3)
name the roots of the cervical enlargement and what they supply
C3-T1
arm
name the roots of the lumbar enlargement and what they supply
L1-S3
leg
a motor unit it is made up of?
an alpha motor neurone and all of the skeletal muscle fibres it innervates
what is a motor neurone pool?
a collection of alpha motor neurones that innervate a single skeletal muscle
LMNs supplying what structures exist most medially in the anterior horn of the spinal cord
axial structures (distal muscle LMNs are more lateral)
LMNs supplying flexors are __ to those supplying extensors
dorsal
muscle strength depends on what 2 things?
neuromuscular activation eg firing and number of LMNs AND
force production by innervated muscle fibres eg fibre size and phenotype
a single AP in an alpha MN causes what to happen to a muscle fibre?
it will twitch
multiple APs in an alpha MN cause what to happen to a muscle fibre?
will contract
slow motor units are recruited before large motor units T or F
T
the speed of a skeletal muscle fibre depends on…
how fast myosin ATPase splits ATP to provide energy for cross bridge cycling
dark red fibres are an example of fast or slow mucle fibres?
slow as they contain alot of myogloin
which type of skeletal muscle fibres are fatigue resistant and contract fast?
type 2a
which type of skeletal muscle fibres are not fatigue resistant and are poorly vascularised? how fast do they contract?
type 2b
fast
which type of skeletal muscle fibres fatigue the quickest?
type 2b
a high tension muscle with a low fatigue threshold will have how many alpha MNs
a lot
what is the myotatic reflex?
the pulling back of a skeletal muscle
what do muscle spindles sense?
changes in length to the muscle
what kind of motor neurone afferents do spindle fibres have?
gamma MN
excitatory synaptic transmission in the spinal cord is mediated by what substance?
glutamate
what is a monosynaptic reflex?
a reflex that only requires afferent/efferent neurons to synapse once
the myotatic reflex is an example of a __synaptic reflex
mono
stimulation of gamma MNs in muscle spindles causes what?
contraction of the spindle fibres
sensory and motor input of intrafusal fibres in spindle fibres?
sensory - sensory afferents (1a to centre, spinal roots to polar ends)
motor - gamma MNs
which type of sensory afferent fibres are the fastest conductors?
type 1a
when would dynamic gamma MNs be needed?
when muscle length changes rapidly and unpredictably
where are golgi tendon organs lcoated
junction of muscle and tendon
what do golgi tendon organs do?
monitor changes in muscle tension
golgi tendon organs are innervated by…
group 1b sensory afferents
what sensory neurons initiate the reverse myotatic reflex?
group 1b sensory afferents
how is the myotatic reflex mediated
an inhibitory interneuron needs to be between the 1b afferent and an alpha MN
where are joint proprioceptors located?
joint connective tissue
what structures are in charge of sensing pain in the joint?
free nerve endings
activation of gamma MNs comes from…
ventral horn of the spinal cord in response to a signal from the brainstem or cerebrum i.e NOT A REFLEX
alpha MN stimulation without gamma MN stimulation would have what effect on the muscle?
would be floppy as no stimulation to the muscle spindle (which keeps the muscle tight)
what nuclear bag fibres are sensitive to rate of change of muscle length?
bag 1 dynamic
bag 2 nuclear fibres are sensitive to…
absolute length of the muscle
