Intro to Motor system Flashcards
What type of movement is walking, chewing etc?
Rhythmic motor pattern (subconscious usually)
What does the nervous system need to know in order to produce movement? (4)
- Initial length of the muscle
- Velocity of muscle length change
- External loads acting to oppose movement
- Visual and vestibular info
What type of fibers innervate GTOs?
Type Ib afferent
What type of fibers innervate muscle spindles?
Type Ia afferent
What is feedback control?
use of sensory information during movement to make corrections to the on-going movement.
What is feedforward control?
- Sensory information contributes to anticipating the effect of planed movement
What is the motor pathway?
Parietal/premotor/supplementary motor cortex to the
Primary motor cortex
Brainstem
Spinal cord
What are the two inputs to the thalamus that affect its output to the primary motor cortex?
Basal nuclei
Cerebellum
What are the two places that the cerebellum sends information to in the motor pathway?
Brainstem
Thalamus
What is the hierarchical organization of the motor control centers?
Cortical areas
Brainstem
Spinal cord
What two parts of the brain modify output from the motor cortex?
Basal ganglia
Cerebellum
What is the difference between UMNs and LMNs?
UMNs go to a ganglia/nucleus
LMNs symapse on effector muscle
What role do gamma motor neurons play in the nervous system?
Innervate intrafusal skeletal muscle fibers, the small muscle fibers within the muscle spindles
What are skeltal-fusimotor neurons?
Nerves that innervate both extrafusal and intrafusal muscle fibers: this is sometimes called beta activation
Where are LMNs found in the spinal cord?
Anterior horn of the gray matter, with their axons leaving the spinal cord via the ventral root
What are alpha motor neurons?
neurons that innervate muscles in the PNS
What is a motor neuron pool?
All the neurons that control one muscle
What is a motor unit?
one alpha motor neuron plus all the skeletal muscle fibers it innervates
What are the four functional components of a motor unit?
- cell body of motor neuron
- axon
- neuromuscular junction
- muscle fibers
Where are small motor units used in the body?
Where fine control is needed (oculomotor muscles in the eyes)
Where are large motor units used in the body?
In strong muscles that do not need fine control
What is the pathogenesis of post-polio syndrome?
surviving motor neurons “adopt orphaned” muscle fibers. This increases stress on these fibers, with repeated remodeling with denervation and reinnervation
What produces graded muscle contraction? (there are two options here)
recruitment of more and more muscle units and/or increase the rate at which the alpha motor neuron of each motor unit is firing.
What is Henneman’s size principle?
order of recruitment of motor neurons = first recruit small neurons, and then larger neurons, since smaller ones will depolarize first
True or false: muscles need constant, low level stimulation. Why?
True, since need muscle protein gene expression
What are the symptoms of a LMN lesion?
Atrophy
Hypotonia
Hyporeflexia
Fibrillations/fasciculations
What causes the weak reflexes seen in a LMN damage?
Loss of alpha motor neurons to the muscle
What are fasciculations?
- visible twitches of muscle that can be seen as ripples under the skin
What are fibrillations?
spontaneous activity within single muscle fibers. They are not visible clinically since they are too small to be seen as movement through the skin
How do you detect fibrillations of muscle?
Electromyography
Fasciculations are a sign of what?
LMN disorder
What is the difference in innervation between fasciculations and fibrillations?
Fasciculations are when entire muscle groups are still connected after a lesion, so contract together.
Fibrillations are when fibers are not innervated together, thus single fibers twitch
What is an injury potential?
Potential generated at site of injury to a motor neuron axon.
What happens to muscles that are denervated that causes them to be super sensitive?
Increased number of Ach receptors
Flaccid paralysis results when what occurs with the nerves?
Total loss of innervation
What is paresis?
paresis refers to partial loss of voluntary contraction or voluntary muscle weakness.
Which type of lesion causes flaccid paralysis? Spastic?
Flaccid = LMN or initially with UMN Spastic = UMN
A complete transection of the spinal cord will result in flaccid or spastic paralysis?
Initially flaccid, then spastic
What is spinal shock?
the temporary loss of spinal cord reflex activity that occurs below a total (or near total) spinal cord injury.
What are the three components/symptoms of spinal shock?
- Flaccid paralysis
- Areflexia
- Loss of autonomic function below level of transection
How long do symptoms of spinal shock last? What then?
a few days to weeks
Progresses to hyperreflexia
Babinski sign it a test for what type of neuron lesion?
UMN
What is the MOA of spinal shock syndrome? (3)
Increased blood supply or loss of edema around spinal cord
Loss of inhibition of gamma motor neurons
What is an UMN?
a neuron in a higher motor area (e.g. motor cortex, premotor cortex, brainstem center) that synapses on a lower motor neuron or on an interneuron which synapses on a lower motor neuron.
Spinal cord lesions (e.g. those caused by a broken neck) damage what type of neurons?
LMNs at the site of injury
UMN if spinal tract involved
What are the two parts of the spinal cord that produce a multitude of symptoms if transected?
The cervical and lumbar enlargements
What is spasticity?
a motor disorder characterized by a velocity- dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, and is one component of the upper motor neuron syndrome.
The oculomotor and trochlear nuclei are UMN or LMNs?
LMNs
True or false: there can be LMNs above UMNs in the spinal cord
True, as long as they are not part of the same tract
True or false:Damage of the spinal cord can damage both LMNs and UMNs
True
True or false: spinal cord lesions always affect all of the descending motor tracts
False–can have only one
Upper motor neuron syndrome is what?
When all tracts of UMNs are lesioned
DTR are overactive in UMN or LMN lesions?
UMN
If a pt presents with both UMN and LMN signs, what should immediately be in your ddx?
ALS
What is the pathogenesis of ALS?
Loss of myelination of UMNs and LMN of unknown etiology
