Lecture 5 - Descending Motor Systems Flashcards
Upper motor neurons (UMN) originate in the motor region of the _____ ______ or the ________ and synapse on lower motor neurons.
- cerebral cortex
- brainstem
Lower motor neurons (LMN) originate in the ______ ______ gray matter or _____ ____ _____ of the spinal cord and are the last in a chain of neurons.
- anterior horn
- anterior nerve roots
Lower motor neurons (LMN) innervate _______ muscle, and signal muscle ________.
- striated
- contraction
Lower Motor Neurons:
Extrafusal muscle fibers use _____ motor neurons. Intrafusal muscle fibers use ______ motor neurons.
- alpha
- gamma
LMN lesions can result in loss of muscle tone called ______.
atonia
LMN lesions can result in loss of myotatic (knee jerk) reflex called _______.
areflexia
LMN lesions can result in inability of muscles to contract called _____ ______.
flaccid paralysis
LMN lesions can result in spontaneous muscle contractions called ________.
fasciculations
LMN lesions can result in loss of muscle tissue called _____.
atrophy
LMN lesions can result in irregular contractions of individual muscle fibers called _______.
fibrillations
UMN lesions result in _____ _______.
spastic paralysis (paresis)
UMN lesions resulting in increased resting muscle tension called _____.
hypertonia
UMN lesions resulting in twitching/spastic reflexes called ________.
hyperreflexia
UMN lesions may result in a characteristic upward extension of the toes (instead of flexion) upon stimulation of the plantar surface; this is called the _______ sign.
Babinski
Lesions on LMN result in ______ atrophy, while UMN lesions result in _____ atrophy.
- severe
- mild
As a result of UMN lesions, rapid series of alternate muscle contractions in response to the stretching of a muscle is known as a ______.
clonus
One LMN axon in the ventral root divides into many terminal _____ to innervate a muscle. Each of these ends at one _____ _____ _____.
- branches
- neuromuscular junction (NMJ)
LMN controlling axial muscles are _____ to those controlling distal muscles. Neurons controlling flexors are ______ to the extensor group.
- medial
- posterior
1 motor neuron + all myofibers it innervates = ____ ____.
motor unit
TRUE or FALSE:
A larger/less specific muscle has more myofibers per motor unit.
TRUE. More specific/smaller muscles have fewer fibers per motor unit.
Ex: Extraocular = 10 myofibers/unit; Gastrocnemius = 1,000/unit
3 Types of muscle fibers:
- _____ fibers contract weakly for long periods of time.
- _____ fibers contract strongly for short & long periods.
- _____ fibers contract very strongly for very short times.
- There [is/is not] mixing of the different myofibers.
- standing
- running
- jump
- is not
Type ___ muscles are for sustained weight/force bearing, and high in lipids and mitochondria, slow twitch, low glycogen. (duck breast)
Type ___ muscles are for sudden movements, low in lipids/mitochondria, fast twitch, high glycogen. (turkey breast)
- I
- II
- “one (type 1) slow (twitch) fat (lipid-rich) red (appearance) ox (oxidative, mitochondria-rich)”
Higher energy (such as jump type) motor units are [more/less] prone to fatigue, because [more/less] motor units are used than lower energy (such as stand).
- more
- more
TRUE or FALSE:
Basal ganglia, the cerebellum, and the association cortex play a key role in signaling the LMN for complex motor output.
FALSE. Basal ganglia, cerebellum, and association cortex only signal UMN. The UMN then signal the LMN.
TRUE or FALSE:
Damage to UMN’s contribute to the muscular weakness and atrophy because the muscle receive inadequate motor impulses.
FALSE. UMN damage only results in incoordination; LMN damage results in muscle weakness.
The premotor cortex plans movement, tells the motor cortex, then LMN what to do. This top-down signaling is ________ control.
hierarchical
Direct communication of the premotor cortex and LMN without the motor cortex is referred to as _____ control.
parallel
The basal ganglia and cerebellum output to the _____ _____ and motor cortex, but NOT the _____ _____.
- premotor cortex
- spinal cord
Descending motor neurons mostly terminate on _____ horn neurons and ________.
- dorsal *
- interneurons
- double check this… motor neurons should synapse in the anterior horn shouldn’t they?
6 Descending Motor Pathways:
- Cortex to spinal cord = ________ tract
- Cortex to brainstem = _________ tract
- Cortex to basilar pons = _______ tract
- Red nucleus to contralateral anterior horns = ________ tract
- Reticular formation (medulla, pons) to medial anterior horns = ______ tract
- Vestibular nucleus to spinal cord = ________ tract
- corticospinal tract (UMN)
- corticobulbar
- corticopontine
- rubrospinal
- reticulospinal
- vestibulospinal
There are 5 areas in the cerebrum associated with the corticospinal tract. From anterior to posterior, these areas are:
- The _______ area in the frontal lobe
- The ______ ______ area in the precentral gyrus
- The ______ ______ area in the postcentral gyrus
- The ______ ______ _______ (most posterior)
- The ______ ______ area on the medial frontal lobe
- premotor (area 6) (20% fibers)
- primary motor (area 4) (40% fibers)
- somatic sensory (areas 1, 2, 3) (25% fibers)
- superior parietal lobule (areas 5, 7) (5% fibers)
- supplementary motor area (area 6) (10% fibers)
TRUE or FALSE:
There are both motor and sensory homunculi, located in the primary motor cortex and somatic sensory cortex, respectively.
TRUE.
The primary motor area is responsible for ______ voluntary movements, and control of fine ______ movements. It projects to both the _____ and _____ ____. Lesions affect _______ musculature.
- contralateral
- digital
- brainstem
- spinal cord
- contralateral
The premotor area plans movements in response to external ______. It controls ______ and _____ musculature (trunk, shoulder, hip), and may assemble _______ (responsive feeling) facial movements.
- stimuli
- proximal
- axial
- empathetic
Most premotor cortex fibers project to the ______ motor cortex and _______ ______ of the brainstem.
- primary
- reticular formation
Premotor cortex lesions result in moderate weakness of ________ proximal muscles and inability to associate _____ movements to visual and verbal stimuli.
- contralateral
- hand
The part of the brain that learns new sequences, assembles old sequences, and “imagines” movements is the ________ motor area. It projects to the _____ and _____ motor areas for output.
- supplementary
- premotor
- primary
In the parietal lobe of the cerebrum, just posterior to the central sulcus is the _____ _____ area responsible for sensory input. Directly posterior to this is the _____ _____ lobule on the superior aspect of the parietal lobe.
- somatic sensory
- superior parietal
In response to sensory input, the _____ _____ area directs motor patterns in the _____ motor area. Input to this region is received from the _____ and _____ _____.
- somatic sensory
- primary
- brainstem
- spinal cord
The corticospinal tract (CST) originates in the ______ _______ area in the ______ _______ of the cerebral cortex. It also has some fibers originating from ____ cells.
- primary motor
- precentral gyrus
- Betz
CST collaterals project to what 6 areas?
- basal ganglia
- thalamus
- reticular formation
- posterior column nuclei
- posterior horn
- intermediate horns
CST impairment is associated with _____ paralysis and impairment of fine ____ movement.
- flaccid
- finger
The CST leaves the mesencephalon (midbrain) at the _____ _____. It then travels through the anterior ______ _____ of the pons, the _____ ______ of the medulla, and decussates at the __________ junction.
- cerebral peduncle
- basis pontis
- medullary pyramid
- spinomedullary
- the cerebral peduncle is NOT part of the cerebrum
In the ______ CST, 85% of fibers decussate in the medulla and descend in the ______ funiculus (white matter or spinal cord). In the ______ CST, 15% of fibers do not decussate, and descend in the ______ funiculus.
- lateral
- lateral
- anterior
- anterior
TRUE or FALSE:
The CST is somatotopically organized.
TRUE
Clinically, the CST can be damaged by strokes when emboli travel up the internal carotid artery and lodge in the ______ ______ artery.
middle choroidal
The CST is a _____ tract because it travels through the pyramid of the rostral medulla.
pyramidal
Control of shoulder and proximal arm musculature is associated with the _______ tract.
rubrospinal
Control of axial musculature for walking is associated with the ________ tract.
reticulospinal
Control of axial musculature for balance is associated with the _________ tract.
vestibulospinal
Head turning reflexes in response to visual stimuli are associated with the ________ tract.
tectospinal
The vestibulospinal tract receives input from the ______ end organ and _______. The [anterior/lateral] tract travels through the lateral funiculus ipsilaterally for ______ muscle reflexes. The [anterior/lateral] tract travels through the anterior funiculus bilaterally for _____ movements in response to gravity.
- vestibular
- cerebellum (balance)
- lateral
- antigravity
- anterior
- head
The rubrospinal tract receives input from the _____ and _____ motor cortices, and the ______. It decussates at the ventral ______ area, and travels through the [anterior/lateral] funiculus. Innervation is [contralateral/ipsilateral]. It facilitates muscle tone for shoulder and _____ flexors.
- premotor
- primary
- cerebellum
- tegmental
- lateral
- contralateral
- arm
The reticulospinal tract originates in the ______ ______. It receives input from the _____ _____ and _____ _____ cortices. It courses through the medial longitudinal _______ of the brainstem, then the [anterior/lateral] funiculus of the spinal cord [bilaterally/ipsilaterally]. Its function is the support of ______ motor actions like ______.
- reticular formation
- primary motor
- somatic sensory (pain associated w/ reticular formation)
- fasciculus
- anterior
- bilaterally
- rhythmic
- walking
The ________ pathway originates in the face/mouth area of the ______ ______ cortex, and inputs directly on cranial nerves and interneurons in the reicular formation. It ceases to exist after reaching its target nuclei.
- corticobulbar
- somatic sensory
The corticobulbar pathway directly influences cranial nerves ___, ___, ___, ___, and the ______ _____ of the reticular formation.
- CN V
- CN VII
- CN XI
- CN XII
- nucleus ambiguus
The corticobulbar pathway contralaterally innervates ______ facial muscles and bilaterally innervates ______ facial muscles through the ______ ______ nucleus. Therefore, unilateral damage inhibits smiling, but doesn’t affect forehead movement.
- lower
- upper
- facial motor
