12. Motor Tracts Flashcards
Where do upper motor neurons arise from and travel in?
arise and are contained within cerebral cortex or brain stem–> travel in descending tracts
What are examples of UMNs?
corticospinal tract and corticobulbar/nuclear tract
Where do UMNs synapse?
with the LMNs or interneurons of the spinal cord
Where do lower motor neurons (LMN) arise from? what do they synapse?
cell body in spinal cord or brain stem
synapse with skeletal muscle fibers
What do LMNs do?
directly innervate skeletal muscle
What are examples of LMNs?
peripheral nerves and CNs!!!
What are the types of LMNs?
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
What are the types of somatic motor pathways? what are they?
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
What is the corticospinal tract and what does it go to?
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)
What is the pathway of the direct motor pathway (and lateral corticospinal tract)?
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
What initiates voluntary movement? what neurons are involved?
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
What fibers are involved in the primary motor cortex?
precentral gyrus, supplemental motor area, primary motor cortex (60%)
also have sensory: primary somatosensory cortex and parietal association cortex
What is the somatotopic organization of voluntary motor control?
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
What is the organization of the posterior limb of the internal capsule?
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
What is the blood supply to the lateral corticospinal tract?
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.
What does the medial corticospinal tract control? what is the pathway?
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
What is the corticobulbar/corticonuclear tract?
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
What is the actual pathway for the corticobulbar/nuclear tract?
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
What will the axons of the corticonuclear/bulbar tract control?
will cross and control muscles on CONTRALATERAL SIDE
What CNs are related to which structures through the corticobulbar tract?
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
What is the corticobulbar tract for trigeminal nucleus?
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
What is the corticobulbar tract for facial nucleus? how is the forehead controlled? how is the lower face controlled?
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
What is the corticobulbar tract for 9, 10, 12? for 11?
9, 10, and 12: bilateral input; muscles influencing - mainly contralateral projections!!
11- accessory nucleus= ipsilateral
What is the organization of the spinal cord?
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
What do indirect pathways activate? what tracts are involved?
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
What is the function of the lateral vestibulospinal tract? where is it?
Facilitation of extension against gravity
vestibular nuclei (pons)–> spinal cord
IPSILATERAL LMNs innervating postural muscles and limb extensors
What is the function of the medial vestibulospinal tract? where is it?
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
What is the function of the medial (pontine) reticulospinal tract? where is it?
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)
What is the function of the lateral (medullary) reticulospinal tract? where is it?
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)
What is the function of the rubrospinal tract? where is it?
facilitation of upper limb flexors
midbrain red nucleus–> spinal cord
CONTRALATERAL crossing
(corticospinal tract also does this with opposing gravity)
What is the function of the tectospinal tract? where is it?
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
What is the main function of corticospinal tract?
fine motor control of hand, motor neuron recruitment to increase force, inhibition of postural reflexes
What is the main function of corticobulbar tract?
control of muscles of face, chewing, speech and swallowing
What occurs with LMN lesions?
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)
What is Upper Motor Neuron Syndrome?
combination of loss of corticospinal tract (direct) and loss of regulation from indirect brainstem motor control pathways
What are upper motor neuron signs?
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
What are the two types of hypertonia and what issue are they associated with?
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
What clinical exam things should you perform to test motor?
muscle strength, tone, reflexes, pathological reflexes
Lesions in the LMNs will present clinically where? Where do signs appear?
on same side of lesion (tells you exactly where!!); IPSILATERAL
LMN signs at level of lesion
trumps it all!!
Lesions in UMNs will present clinically where? Where do signs appear?
above lower medulla (where CST crosses)–> CONTRALATERAL
in spinal cord–> IPSILATERAL
UMN signs below level of lesion
What is the DIRTY rule of 5s?
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
What is decorticate posture?
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
What is decerebrate posture?
lesion below red nucleus (midbrain), but above reticulospinal and vestibulospinal nuclei
UE in pronation and extension and LE in extension
rubrospinal tract is OUT
What happens with lesion of corticospinal or corticobulbar tract (areas of precentral gyrus) or in internal capsule or anywhere in brainstem?
contralateral side is AFFECTED!!
What happens with a complete transection of the spinal cord?
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
What happens with a hemisection of the spinal cord?
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
What happens with Syringomyelia?
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
What is the pattern seen in the lateral corticospinal tract?
legs = most lateral; hands = most medial
similar to spinothalamic
What is anterior cord syndrome? what is damaged?
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
What is Central Cord Syndrome? What is damaged? What is hit first
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
What do both spinal cord syndromes have in common?
Eventually hit lateral corticospinal tract
What is damaged in Medial Medullary Syndrome? other name?
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
What is damaged in Lateral Medullary Syndrome? other name?
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
What artery is associated with Medial Medullary Syndrome?
Anterior Spinal A.
What artery is associated with lateral medullary syndrome?
PICA
What is Central Seven Palsy?
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
What is Bells Palsy?
damage to CN 7–> ipsilateral flaccid paralysis of upper and lower face
What is Webers syndrome?
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
How do you know youre in the midbrain?
red nucleus there–> upper midbrain; also see superior colliculus
What is Amyotrophic Lateral Sclerosis (ALS)?
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!!
What is Polyneuropathy?
involvement of sensory, motor and autonomic
progresses from DISTAL–> proximal (dying back or impaired axonal transport)
demyelization may also contribute !
