Upper and Lower Motor Neurons I&II Flashcards
medial to lateral homunculus
lower limbs –> upper limbs –> face –> mouth
- inferior parts of the body –> superomedial cortex
- superior parts of the body –> inferolateral cortex
upper and lower motor neuron pathway
upper motor neurons exit via primary motor cortex of cerebral cortex –> corticospinal tract –> synapse with lower motor neurons in spinal cord –> skeletal muscles
-decussate at medullary pyramid
betz cells aka giant cells
neurons that run in corticospinal tract to decussate and synapse with lower motor neurons
anterior vs. lateral corticospinal tract
- anterior - do NOT decussate; control trunk/axial muscles
- lateral - DECUSSATE; control limbs/digits
lower motor neuron innervation
innervate muscle fibers in one muscle –> motor unit
- fine motor control –> few muscle fibers
- gross motor control –> more muscle fibers
lower motor neuron arrangements
anterior –> extensors
post/dorsal –> flexors
medial –> proximal muscles
lateral –> distal muscles
brodman area 4
primary motor area
cerebellum and basal nuclei
affect movement by going through motor areas
-no affect on motor cortex or lower motor neurons with damage, but become uncoordinated
vestibulospinal tracts
postural adjustments to body and head
- lateral - antigravity muscles, ipsilateral pathway
- medial - stabilize head, bilateral pathway
reticulospinal tract
alternative route for voluntary movement, regulate motor neurons and spinal reflex arc, posture, coordination
corticobulbar tract
motor to cranial nerves that innervate muscles
which muscles have unilateral innervation via the corticobulbar tract?
lower facial muscles - innervated by CN7 motor neurons
lower motor neuron damage
strength - decrease tone - decrease stretch reflex - decrease atrophy - severe FML - fibrillations, fasciculations
upper motor neuron damage
strength - decrease tone - increase stretch reflex - increase atrophy - mild conus, pathological conditions (ex. babinski sign, clonus, etc.)
upper motor neuron damage
cause - stroke in primary or premotor cortex
- contralateral flaccid paralysis –> contralateral hypertonicity
- affects upper limb more than lower
- clasp knife affect
- combination of hypertonia and hyperreflexia
motor cortex lesions
damage produces CONTRALATERAL motor deficits due to medulla pyramid decussation
corticospinal tract lesions
unilateral motor cortex damage –> contralateral deficit for limbs, digits, trunk
unilateral damage below pyramidal decussation –> ipsilateral motor deficit for limbs, digits but contralateral deficit for trunk
Bell’s palsy
- lower motor neuron disorder
- hypotonicity, loss of muscle strength, asymmetrical face sagging
- one eye blood shot, the other not
hereditary spastic paraplegia
- affect UMN
- progressive gait disorder - weakness and spasticity of lower limb
- looks like CP
primary lateral sclerosis (ALS)
- affect UMN
- degenerate motor cortex neuronal cell bodies (Betz cells)
amyotrophic lateral sclerosis (Lou Gehrig)
- affect upper and lower motor neurons
- could be limbs or face muscle 1st
progressive muscular atrophy
- affect LMN
- usually effects only one limb
- diagnosed with nerve velocity conduction test
poliomyelitis
- affect UMN and LMN
- acute viral infection –> rapid paralysis, muscle wasting, respiratory muscles
myasthenia gravis
autoimmune disease –> ACh receptors
-neuromuscular junctions disorder
benign fasciculation syndrome
infrequent fasciculations affecting random muscles
