Corticospinal Pathways And Lower Motor Neurons

Question 1

_____ 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.

Answer 1

Upper motor neurons

Corticospinal tracts (pyramidal)

LMN

Question 2

____ 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.

Answer 2

Lower motor neurons

LMN motor nuclei

Question 3

What are the two types of motor fibers?

Answer 3

Somatic efferent

Special visceral efferent (autonomics)

Question 4

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).

Answer 4

Skeletal muscles; ventral horn; spinal N

Skeletal muscles; UMN

Question 5

General visceral efferent have preganglionic fibers that synapse on cell bodies in the ____.

They are short in ____ and long in _____.

Postganglionic fibers innervate ____.

Answer 5

Peripheral visceromotor ganglion

Sympathetics; parasympathetics

Smooth m, cardiac m, and glandular epithelium.

Question 6

Two types of efferent LMN and what do they innervate?

Answer 6

Alpha: innervate skeletal muscle fibers (extrafusal; voluntary, postural, and reflex motion)

Gamma: innervates muscle spindles (intrafusal)

Question 7

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 ____.

Answer 7

Gamma neurons; activity

UMN signs and symptoms

Question 8

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 ____.

Answer 8

LMN

Axial muscles

Proximal musculature

Distal musculature

Anterior; posterior

Question 9

Symptoms of a LMN lesion:

1. Flaccid paralysis
2. Areflexia
3. Atonia
4. Atrophy
5. Fasciculaitons

Answer 9

1. Muscle completely limp with inability to contract
2. Absence of efferent component of the relax arc
3. Loss of gamma motor neuron activity leading to loss of tone
4. Loss of stimulation to muscle fibers leading to denervation atrophic changes
5. Denervation leading to increased sensitivity of motor end plates causing twitching

Question 10

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.

Answer 10

Ventral horn

Motor signs; sensation

Motor and sensory (radiculopathy; could be from herniated disc)

Sensation; muscles

Specific muscle groups; sensation

Question 11

Poliomyelitis from a poliovirus infection leads to destruction of ____.

Clinical presentation?

Answer 11

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)

Question 12

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.

Answer 12

Primary motor cortex

Internal capsule in the cerebrum -> peduncles in midbrain -> anterior pons -> medullary pyramids -> pyramidal decussation

Pyramidal decussation

Crossed; uncrossed

Question 13

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?

Answer 13

Crossed

Lateral funiculus

Interneurons

Influences and modulates LMN activity to control motion of the body

Question 14

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.

Answer 14

Uncrossed fibers

Nuclei of axial skeletal muscles; medially on the ventral horn

Question 15

UMN lesion clinical presentation:

1. Spastic paralysis/paresis
2. Hypertonia
3. Hyperreflexia
4. Clonus

Answer 15

1. Velocity dependent increase in resistance to passive movement, typically in a specific direction.
2. Increased resting muscle tone due to loss of inhibition from corticospinal tract
3. Increase in reflex due to loss of inhibition from corticospinal tract
4. Rapid series of alternating muscle contractions in response to sudden stretch

Question 16

UMN lesion clinical presentation:

5. Rigidity
6. Disuse atrophy
7. Babinsksis

Answer 16

5. No velocity dependent increase in resistance to passive motion in all directions
6. Decreased muscle, less severe than LMN
7. Upward extension motion of the hallux when plantar surface of the foot is stroked (normally response is flexion)

Question 17

Lesions to the corticospinal tract are caused by?

How do localizing lesions differ?

Answer 17

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

Question 18

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?

Answer 18

ACA: contralateral LE > UE

MCA: contralateral face and UE > LE

Posterior limb of internal capsule -> lenticular striate A: face=LE=UE

Question 19

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

Answer 19

Spinal shock; LMN

Spastic paresis

Question 20

____ 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?

Answer 20

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

Question 21

_____ is where spasticity is the most predominant impairment sign and symptom.

What are the symptoms?

What are the three subtypes?

Answer 21

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

Question 22

Amyotrophic lateral sclerosis is an asymmetric mix of ____ signs.

What are the signs for each?

Answer 22

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

Question 23

UMN lesions cause what?

Answer 23

Paralyzes movements in hemiplegic, quadriplegic, or paraplegic distribution, not individual muscles

Atrophy of disuse only

Hyperactive DTR

Clonus

Absent abdominal-cremasteric reflexes

Babinski reflex

Question 24

LMN lesions cause what?

Answer 24

Paralyzes individual muscles or sets of muscles in root or peripheral nerve distribution

Atrophy of denervation

Fasciculation and fibrillations

Hypoactive or absent DRT

Hypotonia

Question 25

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?

Answer 25

Pontine reticular; antigravity reflexes

Medullary reticulospinal; postural or flexor reflexes

UMN damage -> loss of reflex inhibition -> reflex hypersensitivity -> UMN signs

Question 26

____ 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 ____.

Answer 26

Rubrospinal tract; red nucleus

Tectospinal tract; superior colliculus

Vestibulospinal tract; vestibular cortex