Motor Systems Flashcards
What is the general function of the Basal Ganglia wrt motor control?
suppresses unwanted movements and helps to initiate movements
What is the general function of the Cerebellum wrt motor control?
critical for “motor error” – difference between intended and actual movements – helps correct those
What is a lower motor neuron?
Neurons in the brainstem and spinal cord that directly innervate muscles.
What is another name for a lower motor neuron?
An alpha motor neuron.
What do gamma motor neurons do?
Innervate intrafusal muscle fibers which allows muscle spindles to detect stretch info when the muscle is contracted.
Where are motor neurons located in the spinal cord and how are they organized?
Located in the ventral horn and organized in columns along the rostral-caudal axis.
How are the trunk and limb muscles mapped onto the spinal cord?
Motor neurons (MNs) innervating the trunk are more medial while MNs innervating the limbs are more lateral in the spinal cord.
Where are local circuit neurons located and what are their functions?
located within the spinal cord, are often inhibitory, and make up basic reflex circuits.
What are group 1a afferent axons?
They are axons which detect changes in stretch in a muscle spindle
What are group 2 afferent axons?
Axons which signal the state of stretch in a muscle spindle
What is the typical pattern of muscle activation in a stretch reflex?
It activates one muscle/ muscle group of an antagonistic pair while inhibiting the other.
How do GTOs compare with muscle spindles
Muscle spindles activate the contracting muscle while inhibiting its antagonist. GTOs inhibit the contracting muscle while activating its agonist
What is a “central pattern generator”?
Complex circuitry of the lower motor system that can produce rhythmic movements without the upper motor system.
What does a “central pattern generator” control?
Generally, timing and coordination of rhythmic movements.
What is the common name for amyotrophic lateral sclerosis and describe the pathology.
Also known as ALS or Lou Gehrig’s disease. Degeneration of a motor neurons and of neurons in the motor cortex cause muscles to whither due to lack of use and leads to death.
What is lower motor syndrome and what are the outcomes?
Damage to brainstem and spinal cord potentially resulting in paralysis or weakness of muscles, absence of reflexes, and atrophy of muscles.
How to recover some function after spinal cord injury
Exercise and artificial muscle stimulation ASAP can help to recover some function.
What do the lower motor neurons of the lateral and medial ventral horns control?
Medial ventral horn: Axial and proximal limb muscles
Lateral ventral horn: Distal limb muscles
What do the upper motor neurons of the cerebral cortex and brainstem control and what are their functions?
Cortex UMNs innervate lateral ventral horn neurons and influence skilled limb movements
Brainstem UMNs innervate medial ventral horn neurons and influence posture and balance
Where are the neurons that project down to the lower motor system?
Layer 5 neurons in primary motor cortex (M1)
How do betz cells compare to pyramidal cells in size?
They are much larger
Where do the corticobulbar and corticospinal tracts respectively terminate?
Corticobulbar – terminate in brainstem mostly bilaterally
Corticospinal – terminate in spinal cord
Where does the pyramidal tracts originate?
From the corticobulbar tract that pass through the caudal medulla.
What path/ neurons feed into and form the lateral corticospinal tract?
Axons passing through the medullary pyramid which form the “pyramidal” motor system
What do the axons of the pyramidal path that don’t decussate do?
Form ventral corticospinal tract and terminate bilaterally.
Do most corticospinal tract axons decussate or not?
Most decussate.
What do the axons of the pyramidal path that don’t decussate do?
Form ventral corticospinal tract and terminate bilaterally.
Alpha motor neurons for what regions are directly innervated by lateral corticospinal tract axons?
Alpha motor neurons controlling the forearm and hand.
Where do most lateral corticospinal axons terminate and what are their functions?
Most terminate on local circuit neurons which have less fine control and more activation of rhythmic movements
What are the parts of the corticospinal/corticobulbar pathways from somatosensory regions do?
Modulate proprioceptive signaling.
How is the motor cortex organized?
Could be a map of different movements with the context of general body regions, or of ethologically (species specific) relevant kinds of behaviors.
What does mirror neuron research suggest?
Mirror neuron research suggests that at least some neurons (especially outside M1) are really mapping the intention of performing action
How do M1 neurons code for movement direction?
Individual neurons are tuned for certain directions and the pattern of activation is summed to generate a movement vector.
Compare and contrast premotor and M1 cortex
Premotor: Receives more information from multisensory systems elsewhere in brain and from prefrontal systems involved in intention, motivation, and decision-making
M1: more direct control over movements
What are the lateral portions of the premotor cortex responsible for?
Movement in response to external cues.
What do ventrolateral premotor cortex mirror neurons do?
Fire in preparation for organism’s movement but ALSO when someone else makes the same action
