Motor System Flashcards
What are the general functions of the motor system?
reflexes, posture, balance, locomotion, and directed movement
What types of neurons are associated with the motor system?
lower motor neurons, inter neurons, and upper motor neurons
What do lower motor neurons release?
acetylcholine onto skeletal muscles to nicotinic receptors
Where are lower motor neurons located?
on the ventral horn of the spinal cord
What is the function of lower motor neurons?
the innervate skeletal muscles to excite them
Where are inter neurons located?
in the grey matter of the spinal cord
What do inter neurons innervate?
lower motor neurons
True or false: Inter neurons are only inhibitory.
False, they are either excitatory or inhibitory
What do upper motor neurons innervate?
inter neurons
What do the upper motor neurons in the motor cortex control?
directed movement
What do the upper motor neurons in the reticular formation control?
posture
What do the upper motor neurons in the vestibular nuclei control?
balance
Are upper motor neurons excitatory or inhibitory?
excitatory
What is the purpose of the central pattern generators involved in locomotion?
they are a network if neurons in the spinal cord at each limb that move the foot forward, plant the foot on the ground, and move the foot backward
What descending motor tracts are associated with the motor system and the cortex?
the corticonuclear tract and corticospinal tract
Where does the corticonuclear tract begin?
in the primary motor cortex
Where does the corticonuclear tract terminate?
in the motor nuclei of CN III, IV, V, VI, VIII, XI, and XII and the nucleus ambiguous
Where does the corticospinal tract begin and end?
it begins in the primary motor cortex and terminates in the spinal cord where it innervates inter motor neurons
What structures does the corticospinal tract run through?
the internal capsule, crus cerebri, and the pyramids
What percent of the corticospinal tract crosses at the pyrimidal dessucation and what does it become?
75% and the lateral corticospinal tract
What percent of the corticospinal tract descends ipsilaterally at the pyrimidal dessucation and what does it become?
25% and the ventral corticospinal tract
What systems are associated with coordination of voluntary movements?
the primary cortex, somesthetic cortex, visual, and auditory
What do all of the systems associated with coordinated volunary movements communicate through?
the internal capsule
What is the Renshaw cell’s involvement in feedback inhibition?
it is a special local-circuit interneuron that inhibits mostly lower motor neurons that innervate extensor muscles
How does tetanus toxin effect renshaw cells?
they make them unable to provide feedback inhibition
Explain inter segmental modulation by using the stretch reflex?
the stretching of a muscle spindle causes muscle contraction and inhibition of the opposing muscle group
What motor tracts run in the lateral funiculus?
the lateral corticospinal tracts, rubrospinal tract, and medullary reticulospinal tract
What is the function of the motor tracts that run in the lateral funiculus?
excites flexors and inhibit extensors
What motor tracts run in the ventral funiculus?
pontine reticulospinal, ventral corticospinal, and vestibulospinal tracts
What is the function of the motor tracts that run in the ventral funiculus?
they excite the extensors and inhibit flexors
What are extensors also known as?
anti-gravity muscles
What muscles are involved with the maintenance of posture?
the anti-gravity muscles
How do the antigravity muscles maintain posture?
they modulate the stretch reflex
What is the modulation of the stretch reflex determined by?
the reticular formation
What system is associated with balance?
the vestibular system
What spinal tracts are associated with balance?
lateral and medial vestibulospinal
What is the function of the spinal tracts associated with balance?
to excite extensors and inhibit flexors
What clinical signs are associated with lower motor neuron disease?
paresis/paralysis, hyporeflexia/areflexia, and hypotonia/atonia
What toxins affect lower motor neurons?
tick paralysis and botulinum toxin
How does tick paralysis affect lower motor neurons?
it impairs/disables them leading to paresis/paralysis
How does botulinum toxin affect lower motor neurons?
it inhibits transmitter release from lower motor neurons which leads to reduced/lack of communication between LMN and muscle
What is effected in upper motor neuron disease?
the descending tracts are most lukely lesioned
What are the clinical signs associated with upper motor neuron disease?
abnormal gait, paresis/paralysis, hyperreflexia, and hypertonia
What is an example of upper motor neuron disease?
prion disease
What are some examples of prion disease?
bovine spongiform encephalopathy, scrapie, chronic wasting disease
