12. Motor Tracts

Question 1

Where do upper motor neurons arise from and travel in?

Answer 1

arise and are contained within cerebral cortex or brain stem–> travel in descending tracts

Question 2

What are examples of UMNs?

Answer 2

corticospinal tract and corticobulbar/nuclear tract

Question 3

Where do UMNs synapse?

Answer 3

with the LMNs or interneurons of the spinal cord

Question 4

Where do lower motor neurons (LMN) arise from? what do they synapse?

Answer 4

cell body in spinal cord or brain stem

synapse with skeletal muscle fibers

Question 5

What do LMNs do?

Answer 5

directly innervate skeletal muscle

Question 6

What are examples of LMNs?

Answer 6

peripheral nerves and CNs!!!

Question 7

What are the types of LMNs?

Answer 7

gamma motor neurons- medium sized, myelinated, project to intrafusal fibers in muscle spindle

alpha motor neuron- large cell bodies and large myelinated axons, project to extrafusal skeletal muscle

Question 8

What are the types of somatic motor pathways? what are they?

Answer 8

direct pathways: cerebral cortex–> spinal cord and out to muscles; send collaterals to indirect

Indirect pathway: synapses in brain stem, basal ganglia, thalamus, reticular formation, and cerebellum occur also

Question 9

What is the corticospinal tract and what does it go to?

Answer 9

upper motor neurons arise in cortex and synapse with LMN in spinal cord

medial- postural muscles (10% fibers); voluntary movement

lateral- limb muscles; fractionation (90% fibers)

Question 10

What is the pathway of the direct motor pathway (and lateral corticospinal tract)?

Answer 10

cell bodies arise in cortex–> descends through posterior limb of internal capsule–> continue in corticospinal tract and passes through: cerebral peduncles (middle 1/3), anterior pons, pyramids–> fibers cross in pyramids in lower medulla–> descends in lateral column of spinal cord–> synapse with LMNs in spinal cord

Question 11

What initiates voluntary movement? what neurons are involved?

Answer 11

primary motor cortex (area 4) in precentral gyrus

right side - controls LEFT side motor BODY
left side–> controls RIGHT side motor BODY

UPPER MOTOR NEURONS- corticospinal tract mostly

Question 12

What fibers are involved in the primary motor cortex?

Answer 12

precentral gyrus, supplemental motor area, primary motor cortex (60%)

also have sensory: primary somatosensory cortex and parietal association cortex

Question 13

What is the somatotopic organization of voluntary motor control?

Answer 13

muscles are represented unequally (according to number of motor units)

larger representation (greater cortical area)= what muscles used most (greater motor units)

ex. vocal cords, tongue, lips, fingers, and thumb

Question 14

What is the organization of the posterior limb of the internal capsule?

Answer 14

Legs are posterior, thorax in middle, and arms are most rostral (anterior)

arms are more anterior in the POSTERIOR limb of internal capsule

the posterior limb of the internal capsule is right next to thalamus

Question 15

What is the blood supply to the lateral corticospinal tract?

Answer 15

internal capsule: leticulostriate A. and anterior choroidal A.

midbrain: posterior cerebral A.

Pons: paramedial branches of basilar A.

medulla: sulcal branches of anterior spinal A.

spinal cord: anterior and posterior spinal A.

Question 16

What does the medial corticospinal tract control? what is the pathway?

Answer 16

postural and proximal movements (neck, shoulder, and trunk muscles)

same pathway as lateral except fibers dont cross in the medulla

10% of fibers, not clinically significant

Question 17

What is the corticobulbar/corticonuclear tract?

Answer 17

arises from ventral part of cortical area 4 (coming from lateral 1/3 of precentral gyrus (face!!!)

descend into brain stem to influence CNs!!! (all but eye muscle nerves)- CNV, 7, 9, 10, 11, 12

Question 18

What is the actual pathway for the corticobulbar/nuclear tract?

Answer 18

cell body starts in lateral 1/3 of precentral gyrus/motor cortex

when descending, it will travel through the genu of the internal capsule (not posterior limb -corticospinal)

continues in corticobulbar tract passing through the cerebral peduncles, anterior pons, and the pyramids (medial side of corticospinal)

will stop at its specific motor nucleus

Question 19

What will the axons of the corticonuclear/bulbar tract control?

Answer 19

will cross and control muscles on CONTRALATERAL SIDE

Question 20

What CNs are related to which structures through the corticobulbar tract?

Answer 20

If in the anterior pons–> CN V and Vll

pyramids of medulla–> CN 9, 10, 12

corticobulbar stays ipsilateral and travel with anterior medial corticospinal tract–> to influence CN 11, accessory nucleus

Question 21

What is the corticobulbar tract for trigeminal nucleus?

Answer 21

lateral 1/3 of our premotor gyrus, travel through genu of internal capsule–> middle 1/3 of cerebral peduncle (right next to corticospinal tract)–> continue down into MID pons–> fibers BILATERALLY influence/supply trigeminal motor nucleus (50-50 split) in MID PONS

Question 22

What is the corticobulbar tract for facial nucleus? how is the forehead controlled? how is the lower face controlled?

Answer 22

lateral 1/3 of our premotor gyrus, travel through genu of internal capsule–> middle 1/3 of cerebral peduncle (right next to corticospinal tract)–> continue down into LOWER anterior pons–> fibers branch (supplies forehead eventually)

forehead- bilaterally
lower side of face- contralaterally

Question 23

What is the corticobulbar tract for 9, 10, 12? for 11?

Answer 23

9, 10, and 12: bilateral input; muscles influencing - mainly contralateral projections!!

11- accessory nucleus= ipsilateral

Question 24

What is the organization of the spinal cord?

Answer 24

topographically organized- found on anterior (ventral) horn

medial LMNs- project to axial muscles (proximal)
lateral LMNs- project to limb muscles (distal)

ventral: Extensor LMNs
dorsal: Flexor LMNs

Question 25

What do indirect pathways activate? what tracts are involved?

Answer 25

tonically (firing on always- basal limit) activate antigravity and axial LMNs Medial UMN tracts- tectospinal, medial reticulospinal, lateral vestibulospinal, medial vestibulospinal Lateral UMN tracts- rubrospinal, lateral reticulospinal

Question 26

What is the function of the lateral vestibulospinal tract? where is it?

Answer 26

Facilitation of extension against gravity vestibular nuclei (pons)--> spinal cord IPSILATERAL LMNs innervating postural muscles and limb extensors

Question 27

What is the function of the medial vestibulospinal tract? where is it?

Answer 27

coordination of head movements in relationship to gravity and acceleration inferior and medial vestibular nuclei (medulla) --> spinal cord go to cervical and thoracic levels (neck and shoulder muscles) descends BILATERALLY

Question 28

What is the function of the medial (pontine) reticulospinal tract? where is it?

Answer 28

facilitation of postural reflexes (related to movement and being alert) pontine reticular formation--> spinal cord descend IPSILATERALLY to LMNs innervating postural muscles and limb extensors (like lateral vestibulospinal but not against gravity)

Question 29

What is the function of the lateral (medullary) reticulospinal tract? where is it?

Answer 29

inhibition of spinal segmental reflexes medullary reticular formation--> spinal cord mainly stays IPSILATERAL (with some bilateral) facilitates flexor motor neurons and inhibits extensor motor neurons (make a gradient to move)

Question 30

What is the function of the rubrospinal tract? where is it?

Answer 30

facilitation of upper limb flexors midbrain red nucleus--> spinal cord CONTRALATERAL crossing (corticospinal tract also does this with opposing gravity)

Question 31

What is the function of the tectospinal tract? where is it?

Answer 31

coordination of head with eye movements; visual reflexes which will help turn head where eyes want to go or if theres a visual stimulus superior colliculus in midbrain--> upper spinal cord

Question 32

What is the main function of corticospinal tract?

Answer 32

fine motor control of hand, motor neuron recruitment to increase force, inhibition of postural reflexes

Question 33

What is the main function of corticobulbar tract?

Answer 33

control of muscles of face, chewing, speech and swallowing

Question 34

What occurs with LMN lesions?

Answer 34

Flaccid paralysis= can't move muscle because took away final common pathway (LMN); after period of time, muscle will atrophy and get replaced by CT Hyporeflexia or areflexia due denervation hypotonia= decreased muscle tone denervation hypersensitivity (fasciculations- bc ACh will start to be released and go to presynaptic cleft ot muscle; once nerve dead, ACh gone)

Question 35

What is Upper Motor Neuron Syndrome?

Answer 35

combination of loss of corticospinal tract (direct) and loss of regulation from indirect brainstem motor control pathways

Question 36

What are upper motor neuron signs?

Answer 36

loss of distal extremity strength and dexterity (took fractionation process out)- CST Babinski sign (inverted plantar flex)- CST Hypertonia Hyperreflexia: seen as clonus sometimes (oscillating movement) clasp-knife phenomenon and spasticity

Question 37

What are the two types of hypertonia and what issue are they associated with?

Answer 37

Spasticity= CST or CBT UNM lesion; get RATE/FORCE dependent resistance with more movement; collapse of resistance at end of range of motion Rigidity= basal ganglia disease; NOT rate OR force dependent; constant throughout the ROM (lead pipe or plastic-like); arm resists still tho

Question 38

What clinical exam things should you perform to test motor?

Answer 38

muscle strength, tone, reflexes, pathological reflexes

Question 39

Lesions in the LMNs will present clinically where? Where do signs appear?

Answer 39

on same side of lesion (tells you exactly where!!); IPSILATERAL LMN signs at level of lesion trumps it all!!

Question 40

Lesions in UMNs will present clinically where? Where do signs appear?

Answer 40

above lower medulla (where CST crosses)--> CONTRALATERAL in spinal cord--> IPSILATERAL UMN signs below level of lesion

Question 41

What is the DIRTY rule of 5s?

Answer 41

``` 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 S2- ankle plantar flexion ```

Question 42

What is decorticate posture?

Answer 42

lesion above level of red nucleus (midbrain) thumb tucked under flexed fingers in fisted position, pronation of forearm, flexion at elbow with LE in extension with foot inversion rubrospinal tract intact

Question 43

What is decerebrate posture?

Answer 43

lesion below red nucleus (midbrain), but above reticulospinal and vestibulospinal nuclei UE in pronation and extension and LE in extension rubrospinal tract is OUT

Question 44

What happens with lesion of corticospinal or corticobulbar tract (areas of precentral gyrus) or in internal capsule or anywhere in brainstem?

Answer 44

contralateral side is AFFECTED!!

Question 45

What happens with a complete transection of the spinal cord?

Answer 45

lose all modalities/sensation 1 or 2 levels BELOW lesion (due to overlap of dermatomes) bladder and bowel control lost (neurons cant get there) UMN signs at levels below the lesion: hyperactive reflexes, clonus, babinski, spasticity LMN signs at LEVEL of lesion Spinal shock- loss of tendon reflexes

Question 46

What happens with a hemisection of the spinal cord?

Answer 46

LOSS of pain and temperature from CONTRALATERAL side of body : occurs 2-3 dermatomes BELOW lesion (Lissauers tract) Discriminative touch and conscious proprioception on IPSILATERAL side; bc hit posterior column LMN signs at LEVEL of lesion (flaccid paralysis) UMN signs on IPSILATERAL side of lesion (babinski, hyperreflexia and clonus, muscle weakness, spasticity) get paralysis combined with loss of all sensations information (small region where lost ALL Modalities) pattern called= Brown- Sequards Syndrome

Question 47

What happens with Syringomyelia?

Answer 47

formation of cysts within spinal cord pain and temperature first affected--> affects anterior white commissure FIRST (pattern= shawl/cape) motor also lost: LMN signs if VENTRAL horns affected ; UMN signs if lateral corticospinal tract affected

Question 48

What is the pattern seen in the lateral corticospinal tract?

Answer 48

legs = most lateral; hands = most medial similar to spinothalamic

Question 49

What is anterior cord syndrome? what is damaged?

Answer 49

compression or damage to anterior part of spinal cord (usually due to spinal cord infarction, IV disc herniation, and radiation myelopathy) occlusio of anterior spinal A. or trauma to anterior spinal cord HIT: lateral corticospinal tract (ipsilateral BELOW lesion), lateral spinothalamic tract (contralateral pain and temperature to other side of body), LMNs in ventral horn (ipsilateral symptoms) dorsal horn INTACT BILATERAL ISSUE

Question 50

What is Central Cord Syndrome? What is damaged? What is hit first

Answer 50

compression or damage to central portion of spinal cord usually from CERVICAL HYPEREXTENSION (occluding VERTEBRAL A--> anterior spinal A.) Hit first= AWC (so lose bilateral pain and temperature) if starts to hit anterior horns--> get LMN signs and symptoms; eventually damage lateral corticospinal tract

Question 51

What do both spinal cord syndromes have in common?

Answer 51

Eventually hit lateral corticospinal tract

Question 52

What is damaged in Medial Medullary Syndrome? other name?

Answer 52

Pyramid- contralateral UMN signs and symptoms (Babinski, etc.) Medial Lemniscus- contralateral loss of proprioceptive, vibratory sense, two point discrimination, discriminative touch hypoglossal nucleus- LMN problem (when protrude tongue, genioglossus m. will deviate tongue towards lesion) ALSO CALLED DEJERINE SYNDROME

Question 53

What is damaged in Lateral Medullary Syndrome? other name?

Answer 53

ALS- contralateral loss of pain and temp to body Spinal trigeminal nucleus/tract- ipsilateral loss of pain and temp to face Nucleus Ambiguous- course voice, problems swallowing/dysphagia, palates elevate unevenly, no gag reflex, deviated uvula (lesion 9 and 10) vestibular nuclei- nystagmus, vertigo infereior cerebellar peduncle- ataxia hypothalamic tract- ipsilateral horner WALLENBERG Syndrome

Question 54

What artery is associated with Medial Medullary Syndrome?

Answer 54

Anterior Spinal A.

Question 55

What artery is associated with lateral medullary syndrome?

Answer 55

PICA

Question 56

What is Central Seven Palsy?

Answer 56

Lesion of corticobulbar tract involving 7th CN muscles of upper face controlled by equal numbers of fibers from both hemispheres muscles of lower face controlled by CONTRALATERAL hemisphere lesion ROSTRAL to facial motor nucleus (above lower pons) results in DROOPING of muscles at corner of mouth (on CONTRALATERAL!!!! side of lesion) LMN functioning- so blink reflex works and forehead can wrinkle (forehead has bilateral input

Question 57

What is Bells Palsy?

Answer 57

damage to CN 7--> ipsilateral flaccid paralysis of upper and lower face

Question 58

What is Webers syndrome?

Answer 58

lesion in MIDBRAIN -lesion Corticospinal tract- contralateral signs and symptoms (hyperreflexia) -lesion Corticobulbar tract- contralateral lower face droop see uvula deviate to SIDE of lesion; tongue to contralateral side; trapezius and SM affected (from CN11) CN3 hit: LMN (in midbrain)--> down and out eye, dilated pupil

Question 59

How do you know youre in the midbrain?

Answer 59

red nucleus there--> upper midbrain; also see superior colliculus

Question 60

What is Amyotrophic Lateral Sclerosis (ALS)?

Answer 60

destroys ONLY somatic motor neurons (UMNs and brainstem and spinal cord LMNs) leads to : paresis, myoplastic hyperstiffness, hyerreflexia, Babinskis, atrophy, fasciculations, and fibrillations CN involvement leads to difficulty breathing, swallowing and speaking patients will die!! TERMINAL LEU GERRICKS!!

Question 61

What is Polyneuropathy?

Answer 61

involvement of sensory, motor and autonomic progresses from DISTAL--> proximal (dying back or impaired axonal transport) demyelization may also contribute !