Motor Tracts Flashcards
Where are UMN contained?
Cerebral cortex or brain stem
What do UMN synapse with?
Synapse with LMN and/or interneurons of
the spinal cord
Examples of UMNs?
Corticospinal tract and corticobulbar
(corticonuclear) tract
What do LMN innervate?
Skeletal muscle
Where are LMN contained?
Cell body in the spinal cord or brain stem
What do LMN synapse with?
Synapse with skeletal muscle fibers
Types of LMN?
- Gamma motor neuron
- Alpha motor neuron
medium sized, myelinated, project to intrafusal fibers in muscle spindle
Gamma motor neuron
large myelinated axons, project to extrafusal skeletal muscle
large cell bodies and
Alpha motor neuron
Examples of LMN
Peripheral nerves and cranial nerves
Somatic Motor Pathway:
- From cerebral cortex to spinal cord and out to muscles
Direct Pathways
Somatic Motor Pathway:
- Includes synapses in brain stem, basal ganglia, thalamus, reticular formation, and cerebellum
Indirect Pathways
Is CST direct or indirect?
Direct
Type of CST?
• Postural muscles
- 10% of fibers
Medial corticospinal tract
Type of CST?
• Limb muscles
• Fractionation
- 90% of fibers
Lateral corticospinal tract
Send collaterals to indirect pathways
CST
Lateral CST Pathway (Direct):
• Cell bodies arise in cortex
• Descends from cortex through the ?
- Continues in the corticospinal tract passing through: ?
- Descends in the ? of the spinal cord
- Synapse with LMNs in the ? of the spinal cord
- posterior limb of the internal capsule
- Cerebral peduncles middle 1/3 (midbrain)
- Anterior pons
- Pyramids (medulla)
- Fibers cross in the pyramids in the lower medulla
- lateral column
- ventral horn
• Primary motor cortex (area 4) in precentral gyrus
initiates ? movement
- Right side motor strip usually controls ? side of body and conversely.
- Area concerned primarily with performance of muscle movements
- voluntary
- left
Homulucus with the most number of motor units
vocal cords, tongue, lips, fingers and thumb
- Lower limb = medial
- Hand = middle 2/3
- Face = lateral
• Controls postural and proximal movements
- Neck, shoulder and trunk
muscles
Medial Corticospinal Tract
• Pathway is the same as Lateral Corticospinal Tract except ?
- 10% of fibers
- Not clinically significant
These fibers don’t cross in the medulla
Arises from ventral part of
cortical area 4
Corticobulbar (Corticonuclear)
Corticobulbar: • Descends into ? and influences muscles innervated by cranial nerves including motor nuclei: ?
• Axons will cross and control muscles on the ? side
- brain stem
- V (trigeminal)
- VII (facial)
- IX (glossopharyngeal)
- X (vagus)
- XI (spinal accessory)
- XII (hypoglossal)
- contralateral
Corticobulbar Tract:
• When descending will travel through the ?
• Continues in the corticobulbar tract
passing through the ?,?, and the ?
• Will stop at its specific motor nucleus
- genu of the internal capsule
- cerebral peduncles, the anterior pons, and the pyramids
• LMN topographically organized
- Found in ?
- Medial LMNs project to ? muscles
- Lateral LMNs project to ? muscles
- LMNs innervating extensor muscles tend to lie ?
- LMNs innervating flexor muscles tend to lie ?
- anterior (ventral) horn
- axial
- limb
- ventral
- dorsal
Tonically activate antigravity and axial LMNs
Indirect pathways
Indirect Pathways:
Medial UMN tracts
- Tectospinal
- Medial reticulospinal
- Lateral vestibulospinal
- Medial vestibulospinal
Indirect Pathways:
Lateral UMN tracts
- Rubrospinal
* Lateral reticulospinal
Medial LMNs receive input from which tracts?
- Tectospinal tract
- Medial vestibulospinal tract
- Medial reticulospinal tract
- Medial corticospinal tract
- Lateral vestibulospinal tract
Lateral LMNs receive input from which tracts?
- Rubrospinal
- Lateral reticulospinal
- Lateral corticospinal tract
• In pons
• Vestibular nuclei to
spinal cord
• Ipsilateral LMNs
innervating postural
muscles and limb
extensors
Lateral vestibulospinal
• In medulla
• Vestibular nuclei to spinal
cord
• To cervical and thoracic
levels (neck and shoulder
muscles)
Medial vestibulospinal
•. In the pons
• Pontine reticular
formation to spinal cord
• Ipsilateral LMNs
innervating postural
muscles and limb
extensors
Medial (Pontine) reticulospina
• Medullary reticular formation
to spinal cord
• Facilitates flexor motor
neurons and inhibits extensor
motor neurons
•Mainly ipsilateral with a little bilateral
Lateral (Medullary)
reticulospinal
• In midbrain
• Red nucleus to
spinal cord
• Crosses to contralateral side
• Innervates upper
limb flexors
Rubrospinal
• In midbrain
• Superior colliculus to
upper spinal cord
• To neck muscles
- Does visual reflexes (due to superior colliculus)
- Goes auditory (due to inferior colliculus)
Tectospinal
Which lesion?
• Flaccid paralysis • Wasting or atrophy • Hyporeflexia or areflexia due to denervation • Hypotonia- decreased muscle tone • Denervation hypersensitivity - Fasciculations
Lower motor neuron lesion
a combination of the loss of the corticospinal tract (direct pathway) and the loss of
regulation from the indirect brainstem motor control
pathways
UMN syndrome
Upper Motor Neuron Signs
- Loss of distal extremity strength and dexterity
- Babinski sign (inverted plantar reflex)
• Hypertonia 1. Spasticity: UNM lesion - Rate dependent resistance - Collapse of the resistance at the end of the range of motion 2. Rigidity: Basal ganglia disease - Not rate or force dependent - Constant throughout the range of motion ~ Lead pipe or plastic-like
- Hyperreflexia: may be seen as clonus
- Clasp-knife phenomenon and spasticity
Lesion Location
- LMNs result in clinical signs on the ? side as the lesion
same
Lesion Location:
UMNs
• Above lower medulla (where corticospinal tract crosses) clinical signs will be ?
• In spinal cord clinical signs will be ?
- contralateral
- ipsilateral
Lesion Location:
Spinal Cord
• Give UMN signs ? level of the lesion
• Give LMN signs at ?
- below
- the level of the lesion
Rule of 5s;
C5 – C6 – C7 – C8 – T1 – L2 - L3 - L4- L5 - S1-
C5 – Shoulder extension C6 – Arm flexion C7 – Arm extension C8 – Wrist extensors T1 – Hand grasp L2 - Hip Flexion L3 - Knee extension L4- Knee flexion L5 - Ankle dorsiflexion S1- Ankle plantar flexion
UMN Lesion:
• Lesion above the level of the red
nucleus
• Thumb tucked under flexed fingers in fisted position, pronation
of forearm, flexion at elbow with the lower extremity in extension
with foot inversion
Decorticate posture
UMN Lesion:
• Lesion below red nucleus, but above reticulospinal and vestibulospinal nuclei
• Upper extremity in pronation and
extension and the lower extremity in extension
Decerebrate posture
Hemisection of spinal cord:
• Pain and temp from ? side of body
- Complete loss of pain sensation occurs 2
to 3 dermatomes below level of lesion (Lissauer’s tract)
• Discriminative touch and conscious proprioception on ? side
• LMN signs at ?
- Flaccid paralysis
• UNM signs on ? side of lesion
- Babinski
- Hyperreflexia and Clonus
- Muscle weakness
- Spasticity
• Pattern of loss is called ?syndrome
- contralateral
- ipsilateral
- level of lesion
- ipsilateral
- Brown-Sequard’s
Formation of cysts within the spinal cord
Syringomyelia
Syringomyelia:
• Pain and temp first affected
- Anterior white commissure
- Resulting pattern is ?
• Motor also lost
- May have LMN signs if
? affected
- May have UMN signs if ? is affected
- shawl or cape
- ventral horns
- lateral corticospinal tract
• Compression or damage to anterior part of spinal cord
- Usually due to SPINAL CORD INFARCTION, INTERVERTEBRAL DISC HERNIATION, AND RADIATION MYELOPATHY
Anterior Cord Syndrome
- Compression and damage to central portion of spinal cord.
* Mechanism of injury is usually CERVICAL HYPEREXTENSION
Central Cord Syndrome
• Lesion of the CORTICOBULBAR tract involving the 7th CN
• Muscles of the upper face are controlled by equal numbers of fibers
from both hemispheres
• Muscles of the lower face are controlled by the CONTRALATERAL
hemisphere
• Lesion rostral to facial motor nucleus results in drooping of muscles
at the corner of the mouth
- On the side OPPOSITE the lesion
Central Seven Palsy
Lesion of Corticobulbar Tract:
IPSILATERAL flaccid paralysis of upper and lower face
Bell’s palsy
Who can wrinkle their forehead, Bells Palsy or Central 7?
Central 7
- Destroys only somatic motor neurons
- UMNs and brainstem and spinal cord LMNs.
• Leads to paresis, myoplastic hyperstiffness, hyperreflexia,
Babinski’s sign, atrophy, fasciculations and fibrillations.
• Cranial nerve involvement leads to difficulty breathing,
swallowing and speaking
Amyotrophic Lateral Sclerosis (ALS)
• Involvement of sensory,
motor and autonomic
• Progressing from distal
to proximal:
- Due to dying-back or
impaired axonal transport - Demyelization may also
contribute
Polyneuropathy
