- Gamma motor neuron - Alpha motor neuron

Motor Tracts Flashcards by Kristina Assaf

Where are UMN contained?

Cerebral cortex or brain stem

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What do UMN synapse with?

Synapse with LMN and/or interneurons of

the spinal cord

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Examples of UMNs?

Corticospinal tract and corticobulbar

(corticonuclear) tract

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What do LMN innervate?

Skeletal muscle

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Where are LMN contained?

Cell body in the spinal cord or brain stem

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What do LMN synapse with?

Synapse with skeletal muscle fibers

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Types of LMN?

Gamma motor neuron

- Alpha motor neuron

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medium sized, myelinated, project to intrafusal fibers in muscle spindle

Gamma motor neuron

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large myelinated axons, project to extrafusal skeletal muscle
large cell bodies and

Alpha motor neuron

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Examples of LMN

Peripheral nerves and cranial nerves

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Somatic Motor Pathway:

From cerebral cortex to spinal cord and out to muscles

Direct Pathways

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Somatic Motor Pathway:

Includes synapses in brain stem, basal ganglia, thalamus, reticular formation, and cerebellum

Indirect Pathways

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Is CST direct or indirect?

Direct

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Type of CST?

• Postural muscles
- 10% of fibers

Medial corticospinal tract

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Type of CST?

• Limb muscles
• Fractionation
- 90% of fibers

Lateral corticospinal tract

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Send collaterals to indirect pathways

CST

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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

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• 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

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Homulucus with the most number of motor units

vocal cords, tongue, lips, fingers and thumb

Lower limb = medial
Hand = middle 2/3
Face = lateral

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• Controls postural and proximal movements
- Neck, shoulder and trunk
muscles

Medial Corticospinal Tract

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• Pathway is the same as Lateral Corticospinal Tract except ?

10% of fibers
Not clinically significant

These fibers don’t cross in the medulla

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Arises from ventral part of

cortical area 4

Corticobulbar (Corticonuclear)

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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