Corticospinal Pathways And Lower Motor Neurons Flashcards
_____ influence the activity of LMN to control voluntary movement of the body.
UMN contain _____ that start in the gray matter of the primary motor cortex and end with synapsing with interneurons or directly with _____ cell bodies.
Upper motor neurons
Corticospinal tracts (pyramidal)
LMN
____ are the final effectors of the motor system. They are known as the final common pathway.
They start in the ___ in the ventral horn of the spinal cord and end at the muscle.
Lower motor neurons
LMN motor nuclei
What are the two types of motor fibers?
Somatic efferent
Special visceral efferent (autonomics)
Somatic efferent motor fibers directly innervate _____. They have cell bodies located in the ____ of the spinal cord and exit in the anterior root and pass into the ____.
They synapse directly with ____ and it’s activity is influenced by ____ and segmental afferent inputs (reflexes).
Skeletal muscles; ventral horn; spinal N
Skeletal muscles; UMN
General visceral efferent have preganglionic fibers that synapse on cell bodies in the ____.
They are short in ____ and long in _____.
Postganglionic fibers innervate ____.
Peripheral visceromotor ganglion
Sympathetics; parasympathetics
Smooth m, cardiac m, and glandular epithelium.
Two types of efferent LMN and what do they innervate?
Alpha: innervate skeletal muscle fibers (extrafusal; voluntary, postural, and reflex motion)
Gamma: innervates muscle spindles (intrafusal)
UMN adjust the sensitivity and activity of _____, therefore adjusting the threshold of the muscle spindle to influence a reflex. They are dependent on ____.
If UMN control is lost, the muscle spindle becomes more sensitive, this causes ____.
Gamma neurons; activity
UMN signs and symptoms
Ventral horn cells have a topographic arrangement of ____ cell bodies.
___ are most medial, ____ is medially, and ____ is laterally.
C4-T1 and L1-S2 levels innervate the extremities, extensor on ____ flexors on ____.
LMN
Axial muscles
Proximal musculature
Distal musculature
Anterior; posterior
Symptoms of a LMN lesion:
- Flaccid paralysis
- Areflexia
- Atonia
- Atrophy
- Fasciculaitons
- Muscle completely limp with inability to contract
- Absence of efferent component of the relax arc
- Loss of gamma motor neuron activity leading to loss of tone
- Loss of stimulation to muscle fibers leading to denervation atrophic changes
- Denervation leading to increased sensitivity of motor end plates causing twitching
LMN signs caused by damage to motor neurons in the ____ or their axons.
Damage to motor neuron and ventral root leading to ____ signs only with ____ intact.
Damage to nerve root leads to mixed ___. There is decreased ____ in a dermatomal pattern; weaknes in ____ innervated by the level involved -> deceased DTR.
Damage to peripheral nerves (neuropathy from nerve entrapment) leads to weakness in ____ and decreased ___ in peripheral nerve distribution.
Ventral horn
Motor signs; sensation
Motor and sensory (radiculopathy; could be from herniated disc)
Sensation; muscles
Specific muscle groups; sensation
Poliomyelitis from a poliovirus infection leads to destruction of ____.
Clinical presentation?
Ventral horn motor cell bodies
Most are asymptomatic
Short viral syndrome: fever, myalgia, HA
Paralytic polio: paresis and paralysis in an asymmetric pattern, decreased of absent tone and reflexes; sensory exam almost always normal (because lesion is in ventral horn)
Corticospinal tract originates in gray matter of the precentral gyrus in the _____.
Fibers descend through the ____.
Most fibers cross at the _____ at the spinomedullary junction. The lateral corticospinal tract contains the ____ fibers and the anterior corticospinal tract contains the ____ fibers.
Primary motor cortex
Internal capsule in the cerebrum -> peduncles in midbrain -> anterior pons -> medullary pyramids -> pyramidal decussation
Pyramidal decussation
Crossed; uncrossed
The lateral corticospinal tract contains _____ fibers.
It is travels through the posterior half of the _____ of the spinal cord.
It terminates at the synapses with the _____ or directly on LMN in the ventral horn.
Fx?
Crossed
Lateral funiculus
Interneurons
Influences and modulates LMN activity to control motion of the body
Anterior corticospinal tract contains ____ fibers. They travel through the anterior funiculus of the spinal cord.
They synapse and terminate on the ____ located ____. Isolated damage the doesn’t result in obvious signs.
Uncrossed fibers
Nuclei of axial skeletal muscles; medially on the ventral horn
UMN lesion clinical presentation:
- Spastic paralysis/paresis
- Hypertonia
- Hyperreflexia
- Clonus
- Velocity dependent increase in resistance to passive movement, typically in a specific direction.
- Increased resting muscle tone due to loss of inhibition from corticospinal tract
- Increase in reflex due to loss of inhibition from corticospinal tract
- Rapid series of alternating muscle contractions in response to sudden stretch
UMN lesion clinical presentation:
- Rigidity
- Disuse atrophy
- Babinsksis
- No velocity dependent increase in resistance to passive motion in all directions
- Decreased muscle, less severe than LMN
- Upward extension motion of the hallux when plantar surface of the foot is stroked (normally response is flexion)
Lesions to the corticospinal tract are caused by?
How do localizing lesions differ?
Cerebrovascular accidents (stroke)
Spinal cord trauma
Localizing lesions: above the decussation -> contralateral signs and symptoms at and below the level of the lesion
Below the decussation -> ipsilateral signs and symptoms at and below the level of the lesion
Localizing lesions to the corticospinal tract convey signs dependent to the area of cortex damaged.
What are the signs from arteries affected in the cortex?
ACA: contralateral LE > UE
MCA: contralateral face and UE > LE
Posterior limb of internal capsule -> lenticular striate A: face=LE=UE
Spinal cord injuries initially present with _____. This causes ____ signs and symptoms for 1 week to 2 months.
The tone and reflexes return leading to ____ depending on the level of the lesion -> severity depends on the extent of damage to the SC
Spinal shock; LMN
Spastic paresis
____ is a group of disorders of the CNS characterized by aberrant control of movement or posture.
When does this occur?
What are the suptypes and where do they affect?
Causes?
Cerebral palsy
Present since early in life; not a result of progressive or degenerative disease
Spastic: cerebral cortex
Dyskinetic: basal ganglia
Ataxic: cerebellum
Mixed: multiple areas
Neonatal stroke, prenatal circulatory disturbances, congenital infections, brain maldevelopment, perinatal asphyxia
_____ is where spasticity is the most predominant impairment sign and symptom.
What are the symptoms?
What are the three subtypes?
Spastic cerebral palsy
UMN S&S: spasticity, hyperreflexia, clonus, babinskis
Spastic hemiplegia: only one side affected
Spastic diplegia: LE affected with little to no UE involvement
Spastic quadriplegia: all limbs affected, children are severely handicapped with increased risk of complications
Amyotrophic lateral sclerosis is an asymmetric mix of ____ signs.
What are the signs for each?
UMN and LMN
UMN: degeneration of the motor neurons in the primary motor cortex as well as axons throughout the corticospinal and corticobulbar (CN) tracts
LMN: degeneration of ventral horn cells; weakness, atrophy, fasciculations
UMN lesions cause what?
Paralyzes movements in hemiplegic, quadriplegic, or paraplegic distribution, not individual muscles
Atrophy of disuse only
Hyperactive DTR
Clonus
Absent abdominal-cremasteric reflexes
Babinski reflex
LMN lesions cause what?
Paralyzes individual muscles or sets of muscles in root or peripheral nerve distribution
Atrophy of denervation
Fasciculation and fibrillations
Hypoactive or absent DRT
Hypotonia
The reticulospinal tract contains two pathways:
The ____ pathway, which activates _____ in an erect position.
The ____ pathway mediates the cortical control of reflexes. It inhibits ____ that may interfere with execution of voluntary motor activity.
What does UMN damage cause?
Pontine reticular; antigravity reflexes
Medullary reticulospinal; postural or flexor reflexes
UMN damage -> loss of reflex inhibition -> reflex hypersensitivity -> UMN signs
____ mediates voluntary motion, especially flexor movement of arms. It originates in the ____ of midbrain.
____ coordinates movement of the head with the eyes. Originates in the ____.
____ maintains posture against gravity, especially the trunk and UE/LE extensor. It originates in the ____.
Rubrospinal tract; red nucleus
Tectospinal tract; superior colliculus
Vestibulospinal tract; vestibular cortex
