MOTOR SYSTEM UMN Flashcards
upper motor neuron may arise from the
brainstem or cerebral cortex
lower motor neuron is found in the
Brain stem & spinal cord
Tracts from the cortex
● Corticospinal tract
● Corticobulbar tract
Tracts from the brain stem (anteriomedial pathway)
● Vestibulospinal tract (Lat and Med)
● Reticulospinal tract (pontine & medullary)
● Rubroospinal tract
● Tectospinal tract
control axial muscles, posture and balance
Corticospinal fibers are essential for
corticobulbar fibers innervate
fine and voluntary movements, mainly of the distal extremities (lateral corticospinal fibers) & proximal extremities (anterior corticospinal fibers)
cranial nerves motor nuclei and head and neck region
upper motor neurons thus serve as
the anatomical substrate for voluntary
control of the muscles of facial expression,
eye movements, jaw opening and closing,
and movements of the tongue.
corticospinal tract pathway starts from
Internal pyramidal layer (Layer 5 of cerebral cortex ) of M1(primary mortor cortex ), PMC (premotor cortex), SMA (supplementary motor area), S1(primary somatosensory receiving area)
Primary moter cortex, M1 (Occupies precentral gyrus, may be marked as M1 or B4
(Brodmann 4)
Medial portion
Lateral portion
The medial and superior portions control the muscles of the feet and legs
The lateral portions control the muscles of the thorax, arms and head.
Each primary motor cortex controls the muscles on the opposite side of t
Anteriorly to the PMC is the Brodmann area 6
Supplementary motor area, SMA (medially)
Premotor cortex, PMC (laterally)
Cortex which anticipates and plans movements based on external sensory
cues, such as responses to events that are seen or heard.
premotor cortex
Area that selects and plans complex movements involving both sides of the body based on internal cues, such as thoughts or memory.
supplementary motor area
posterior parietal cortex (or Brodmann
areas 5 and 7) function
It receives and integrates visual, auditory,
and somatosensory (sense of body) inputs
from other brain areas.
From these inputs, it produces information
about the position of the bod
posterior parietal cortex lesion causes
apraxia
lesions of the SMA (or/and PMC) display
Apraxia - the inability to initiate specific, purposeful movements, even though the sensory and motor pathways for the execution of the movement remain intact.
inability to execute a movement upon request.
Ideomotor apraxia
patient to be able to brush his or her hair or tie
inability to conceptualize the movements, and the patient is unable to identify the
sequences of movements that are necessary for carrying out the response in question.
Ideational apraxia
Commonly, the apraxia becomes evident when the patient is asked to perform, simultaneously, different
movements of both arms.
lesions of the PMC,
patient is unable to coordinate the movement of both arms at the same time.
loss of strength in the proximal muscles of the contralateral arm or leg & difficulty in raising or abducting that limb.
posterioir parietal cortex PPC
coordiantes movements or in preparation for a goal-directed response such as reaching out to grab an object.
lesions of the right PPC show two types of disorders:
- Apraxia (smilar to SMA and PMC apraxia)
- Sensory neglect (or anosognosia)
Corticobulbar tract run lateral to the PMC
Descends through the genu of the internal
capsule
Most corticobulbar fibers
directed toward cranial nerve motor nuclei innervate these neurons bilaterally. Exception:
CN 7 & CN 12
Contralateral innervation of ventral cell
groups of the motor nucleus of cranial
nerve (CN) VII (supplies muscles of the
lower quadrants of the face (below the
eyes).
Stroke vs bell’s palsy
Stroke - unilateral UMN with lower face paralysis (forehead sparing)
Bell’s palsy - unilateral LMN lesion of the CN7 nucleus with no forehead sparing
Rubrospinal tract
Receptors is - Red nucleus in rostral half of midbrain tegmentum
facilitate flexor motor neurons and inhibit extensor motor neurons
lesion on the rubrospinal tract
C/L motor disturbances (trmors, choreiform activity, ataxia, )
due to involvement of axons arising from basal ganglia
Tectospinal tract
receptor is in superioir colliculus
Direct head and neck movement in response to visual and auditory stimulus
Lateral vestibulospinal tract
Receptor: Lateral vestibulospinal nucleus (border of the pons and medulla)
I/L extensor alpha motor neurons (extensor muscles of the trunk) and associated gamma motor neurons (I/L limb)
Lesion of vestibulospinal tract
disturbances in maintaining balance and posture
Medial vestibulospinal tract
Receptor : I/L and C/L Medial vestibular nuclei
adjust head position in response to changes in posture (e.g keeping head stable when walking)
lesion of medial vestibulospinal tract
Disturbances in head positioning when body position is afected
Reticulospinal tract
Receptors in medulla- inhibits extensor spinal reflex
Recptors in pons-facilitates extensor spinal reflex
Lesion of reticulospinal tract
in medulla- contribute to spacicity in UMN paralysis
in pons -loss of extensor muscle tone
vascular supply of the primary motor cortex
middle cerebral artery and anterioir cerebral artery
Middle cerebral artery supplies
Lateral convexity of the hemisphere:
broca’s and wernicke’s speech area
face and arm area of the motor & sensory cortices
Frontal eye field
post. limb of internal capsule
The lateral striate arteries (branches of the MCA) supply
internal capsule, caudate nucleus, putamen and globus pallidus
Arteries of stroke are the
Lateral striate arteries (Penetrating branches of MCA)
Homonymous hemianopia (loss of half of the visual field in both eyes) is due to damage
to visual cortex
infarcts of the lenticulostriate arteries of internal capsule (supplying superior internal capsule) cause
PURE MOTOR STROKE - C/L hemiparesis (coricospinal fibers) and lower face droop (corticobulbar fibers)
inferior portion of the internal capsule is supplied by
Anterior choroidal artery
