Motor tracts Flashcards
upper motor neuron
arise and are contained within the cerebral cortex or brain stem
axons travel in desscending tracts and will synapse with LMN or interneurons of the spinal tract
Corticospinal tract, and the corticobulbar tract
Lower motor neurons
Directly innervate the skeletal muscle
Gamma motor neuron: 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
Ex: Peripheral nerves and cranial nerves
Corticospinal tract pathway
Direct pathway ( from cerebral cortex to spinal cord and out to muscles)
Medial corticospinal tract: postrual muscles (not clinically significant 10 percent of fibers)
Lateral corticospinal tract: limb muscles and fractination
-90percent of fibers
Pathway:
-Cell bodies arise in the cortex
-Descends from the cortex through the posterior limb of the internal capsule
-Continues through the cerebral peduncles, anterior pons, Pyramids
-fibers deccusate in the pyramids in the lower medulla (decusation of the pyramid)
descends the lateral column of the spinal cord and will synapse on the LMN
Voluntary motor control
Primary Motor cortex (brodmanns area 4)
- Precentral gyrus
- initiates voluntary mvmt
- other supplementary motor area and premotor cortex give input to the primary motor cortex as well
similar somatotopographic distribution to somatosensory: Feet medial, arms hand middle, face is lateral
How does the corticospinal tract ascend from the cortex and what is its blood supply in this structure
Posterior limb of the internal capsule
- anterior=Arms
- posterior= legs
blood supply: lenticulostriate arteries
What travels in the sublenticular limb of the internal capsule
Auditory radiation
What travels in the Retrolenticular limb of the internal capsule
Optic radiation
Where does the Corticospinal tract travel in the midbrain and whats its blood supply
Posterior Cerebral A (P1)
and in the middle 1/3 of the Cerebral peduncle
Where does the corticospinal tract travel in the pons and what is its blood supply
Found in the anterior pons with the pontine nucleus and fibers around it
Paramedian branch of the basilar artery
Where does the corticospinal tract travel in the medulla and what is its blood supply
found in the pyramid where it will decussate at the caudal medulla
Anterior spinal artery specifically the sulcal branch
Where does the corticospinal tract travel in the spinal cord and what is its blood supplyy
Posterolateral region in the lateral corticospinal trct
the Arms (medial portion of the tract) get blood supply by the anterior spinal artery
the legs (lateral portion of the tract) get blood supply by the posterior spinal A
Where does the UMN synapse in the spinal cord
on the ventral horn with the LMN
What travels in the medial Corticospinal tract
Controls postrual and proximal movements of the neck, shoulder and trunk muscles
has the same pathway as the corticalspinal tract until the medulla it does not cross and will travel in the medial corticospinal tract
(only 10 percent of the fibers travel this route)
blood supply will be the anterior spinal A
what is the somatotopographic organization all the way down the Corticospinal tract
cortex: legs medial and hand lateral
cerebral peduncle: legs anterior and lateral, hand posterior and medial
pons: legs lateral, hand medial
medulla: legs lateral, hand medial
spinal cord: legs lateral, hand medial
What is the Corticobulbar tract and what does it carry
also called corticonuclear
arises from ventral part of the cortical area 4
descends brain stem and influences muscels innervated by cranial nerves including motor nuclei:
Trigeminal Facial glossopharyngeal vagus spinal accessory hypoglossal
axons will decussate and control muscles on contralateral side
Where does the corticobulbar tract travel in the internal capsule, and in the midbrain , pons, and medulla
the genu
just medial to the corticospinal tract in the cerebral peduncle
in the anterior pons
and in the pyramids
Location of the CN V, VII, IX, X, XII, XI in the brain stem
pons: V, VII
medulla: IX, X, XII
spinal cord: XI
What type of input: ipsilateral, contralateral, bilateral does each CN recieve: V, VII, IX, X, XI, XII
V: bilateral input
VII: bilateral forehead
contralateral lowerface
Muscles of the palate: contralateral
- Uvula will deviate in lesion
- ipsilateral to UMN damage
- Contralateral LMN damage
Muscles of the tongue: Contralateral
- tongue protruds in a lesion
- contralateral to UMN damage
- ipsilateral to LMN
Accessory: Ipsilateral
LMN topographically organization of the ventral horn
Medial LMN project to axial muscles
Lateral LMN project to limb muscles
LMN innervating the flexors are tend to be posterior
LMN innervating the extensors tend to be anterior
Indirect pathways: Medial UMN tracts
Tectospinal tract
Medial reticulospinal tract
Lateral vestibulospinal tract
medial vestibulospinal tract
These go to activate antigravity axial muscles
Indirect pathways: Lateral UMN tracts
Rubrospinal tract
Lateral reticulospinal tract
To activate antigravity LMN of limb muscles
Lateral vestibulospinal tract
Vestibular nuclei to spinal cord
Ipsilateral LMN
Innervating postural muscles of Limb extensors against gravity
Medial Vestibulospinal tract
Vestibular nuclei to spinal cord
to cerviical and thoracic (neck and shoulder muscles)
coordination of head movements
Medial (pontine) Reticulospinal tract
Pontine reticular formation to spinal cord
ipsilateral
Ipsilateral LMN innervating postural extensors and postural reflexors
Lateral (medullary) reticulospinal tract
Medullary reticular formation to spinal cord
ipsilateral
Facilitates flexor motor neurons and inhbits extensor motor neurons
(innhibit of spinal segmental reflexes)
Rubrospinal tract
Red nucleus to spinal cord
contralateral
innervates upper limb flexors
Tectospinal tract
superior colliculus to upper spinal cord
contralateral
to neck muscles to help with coordination of the head with eye movements
Corticospinal tract
Fine motor control of hand and limbs
motor neuron recruitment to increase force
inhibition of postural reflexes
Corticobulbar tract
control muscles of face, chewing, speech, nd swallowing
What happens if their is a LMN lesion
Flaccid paralysis
Wasting or atrophy
Hyporeflexia or areflexia due to denervation
hypotonia - decreased muscle tone
Denervation hypersensitivity - fasciculations
Upper motor neuron signs or lesion
direct: loss of distal extremity strength and dexterity
babinski sign
indirect:
Hypertonia
Spasticity: rate dependant resistance, with collapse of the resistance at the end of the range of motion: clasp knife phenomenon
Rigidity: not rate or force dependant, constant throughout range of motion
Hyperflexia: may see clonus
Pronator drift
either UMN or LMN will tell you the exact level of the lesion?
LMN
If the UMN lesions at or above the lower medulla what side will the clinical signs be on
contralateral
if the UMN lesions at the level of the spinal cord what side will the clinical signs be on
ipsilateral
What is affected when a paitent presents with decorticate posture
lesion above the level of the red nucleus, usually includes the midbrain
thumb tuucked under flexed fingers in a fist position, pronation of forearm, flexion at elbow with lower extremity extension with foot inversion
what is affected when a paitent presents with decerebrate posture
Lesion below red nucleus but above reticulospinal and vestibulospinal nuclei
upper extremity in pronation and extension and the lower extremity in extension
spinal shock mirrors what type of lesion characteristics
LMN lesions
hemisection of the spinal cord
Also called Brown-sequard syndrome
pain and temp from contralateral side of body loss 2 segments below the lesion
Discriminative touch and proprioception on ipsilateral
LMN signs at level of lesion: flacid paralysis
UMN signs on ipsilateral side of lesion
Syringomyelia
Formation of a cyst within the spinal cord
Pain and temp affected first
-Anterior white commissure resulting in cape like deficit area
Motor loss:
- May have LMN signs if Ventral horns are affected
- May have UMN signs if lateral corticospinal tract is affected
Highly correlated with Chiari I
Anterior cord syndrome
Compression or damage to anterior part of spinal cord
-usually due to spinal cord infarction, intervertebral disc herniation and radiation myelopathy
- also can have damage to anterior spinal A
- Lose bilateral Corticospinal tract, ALS and Anterior fasciculus
Central cord syndrome
Compression and damage of central spinal cord
caused by usually cervical hyperextension
symptoms similar to syringomyelia
Medial medullary syndrome
usually an issue with the Anterior spinal Artery
Pyramid is affected= contralateral UMN damage
Medial Lemniscus= contralateral vibration, proprioception, and Discriminative touch is loss
Hypoglossal nucleus = LMN problems so the tongue will potray towards the lesion
Dejerine syndrome
Lateral Medullary syndrome
usually arise with loss of Posterior Inferior Cerebellar Artery
Wallenberg syndrome
ALS = Contralateral Pain and temp to the body
Spinal trigeminal nucleus = ipsilateral Pain and temp to the face
Nucleus ambiguus= ipsilateral hoarseness and swallowing issue, uvula deviate away from lesion
Vestibular nuclei = dizziness and nausea
Restiform body = ataxia and wide base gate
Hypothalamicspinal tract = ipsilateral horners syndrome
Central Seven Palsy
lesion to the corticobulbar tract involving the CN VII
muscles of the upper face are controlled by bilateral so no deficits there
muscles of the lower face are controlled contralateral so there will be drooping of muscles at the corner of the mouth on the contralateral side of the lesion
Bells palsy
LMN damage causing ipsilateral flaccid paralysis of upper and lower face
Weber syndrome
supplied by the Posterior Cerebral Artery P1
in the midbrain
Corticospinal tract = contralateral UMN problems
Corticobulbar tract = Contralateral facial drop
Oculomotor N = dilated pupil and eye looks down and out
Spastic Cerebral palsy
Movement dysfunction :
- abnormal sypraspinal influences
- failure of normal neuronal selection
- consequent aberrant muscle development
Motor disorders:
- Paresis
- Abnormal tonic stretch reflexes, both at rest and during movement
- Reflex irradiation
- lack of postural preperation prior to movement
- abnormal cocontraction of muscles
Amyotrophic Lateral Sclerosis (ALS)
Lou Gherigs disease
Destroys only the somatic motor neurons:
-UMN and brainstem and spinal cord LMN
Leads to Paresis, myoplastic hyperstiffness, hyperreflexia, babinskis sign, atrophy, fasciculations and fibrillations
Cranial nerve involvement leads to difficulty breathing swallowing and speaking
Polyneuropathy
involvement of sensory motor and autonomic
progressing from distal to proximal
due to dying back or impaired axonal transport
demyelinization may also contribute
glove and stocking
