Neuro L6 Flashcards
Importance of Lower motor neuron
Only way movement can be initiated
“Last neuron in chain of neurons”
Alpha motor neurons project to
extrafusal muscle fibers
Gamma motor neurons project to
intrafusal muscle fibers
Lower motor neuron lesion can cause (5)
Atonia: loss of muscle tone (floppy) Areflexia: loss of knee jerk reflex Flaccid paralysis Fasciculations: spont. muscle contractions Atrophy: loss of muscle tissue
Upper motor neuron lesion causes
Spastic paralysis (paresis)
-hypertonia (increased resting tension in arm flexors and leg extensons
-hyperreflexia
Babinski sign
Babinksi sign
Big toe dorsoflexion
fanning of other toes when heal is stoked
LMN vs UMN Strength Muscle tone Stretch relfex Atrophy Other
decrease decrease decrease increase decrease increase severe mild fasciculation and fibrillations vs clonus pathologic reflexes (babinski)
Arrangement of motor neurons
Axial
Flexors
Extensors
(All still in anterior horn)
Axial muscles are more medial
Flexors are posterior
Extensors are anterior
Motor unit
1 motor neurons plus all myofibers it innervates
Large antigravity muscles vs extraocular muscles
Myofibers/motor unit
Extraocular: 10 (10 myofibers/1neuron)
Antigravity: 100s (100s of myofibers/1 neuron)
True or false: One motor unit my contain several different muscle fiber types
False: there is no mixing
Type 1 muscle
One Slow Fat (lipids) Red Ox (mitochondira)
Type 2 muscle
Fast Little lipid High glycogen Little mitochondria White
Damage to basal ganglia, cerebellum or cerebral cortex will cause
DOES NOT cause weakness DOES CAUSE Involuntary movements Incoordination Difficulty initiating movements
Basal ganglia, cerebellum, and cortex role in movement
design, choice and monitoring of movement
BUT NO direct effect on LMN
Outputs go to motor and premotor cortex NOT spinal cord
Hierarchical order of motor control
Premotor cortex plans
Motor cortex
LMN
Parallel arrangement of motor control
Premotor cortex can talk directly to LMN
Most descending motor pathways synapse where
What are the exceptions
interneurons in spinal cord
some directly with primary motor neuron (hand and CST)
Main descending motor pathways
Corticospinal: cortex to spinal cord
Corticobulbar: cortex to brainstem
Corticopontine: cortex to basilar pons
Primary motor area
Area number
Function
Area 4 precentral gyrus
Contralateral voluntary movements
Control fine digital movements
Somatic sensory area
Post central gyrus (brachmanns 312)
Supplementary motor
Area number and location
Function
Area 6 medial surface of cerebrum Plans movements while thinking Learns no sequences Assembles previously learned sequences Imagines movements
Premotor area
area number and location
function
area 6: lateral surface of cerebrum
Plans movements in response to external cues
Corticospinal tract areas
Primary motor Somatic sensory Premotor Supplementary motor Superior parietal lobule
Lesion of Area 4 causes
(primary motor cortex)
paralysis of contralateral muscles
Premotor area has control over
proximal and axial musculature
Empathetic facial movements
Premotor area projects to
primary motor area
reticular formation
spinal cord levels
Lesion in lateral area 6
(premotor)
moderate weakness of contralateral proximal muscles
Inability to associate learned hand movements to verbal or visual cues
supplemental motor area projects to
premotor and primary motor areas
Parietal lobe areas
Project to (2)
Function (2)
Somatic sensory (312)
Superior parietal lobe (5,7)
Project to primary motor: direct patterns in response to sensory impu
Project to sensory brainstem and spinal cord: modulate sensory signals
True or false: All movements depend on CST
False
CST descent
Cerebral cortex, precentral gyrus cerebral peduncle Pons pyramids pyramidal decussation 80% contralateral lateral funiculus 10% ipsilateral lateral funiculus 10% ipsilateral anterior funiculus
Corticospinal fiber location on cerebral peduncle
middle third
Reticulospinal tract
function
May support
control axial musculature- walking
may suppor recovery of motor funtions
Tectospinal tract function
head turning reflexes in response to visual stimuli..unclear function in humans
Vestibulospinal tract
Function
postural adjustments and head movements
antigravity reflexes
(righting reflex in cats)
Vestibulospinal tract
pathway
look at sheet
Rubrospinal tract
Origin
Red nucleus
Rubrospinal tract
function
upper extremity flexor muscles
Like that of vestibulospinal tract
Rubrospinal tract
Pathway
Look at sheet
Reticulospinal tract Origin
Reticular formation
Reticulospinal tract
Pathway
Look at sheet
Corticobulbar pathway
Fiber ending directly on motor neuron
CN XII
Corticobulbar pathway gives no direct input to these CNs
III
IV
VI
Corticobulbar decussation
Descend with CST so no corticobulbar decussation exists
Exception to typical CBP pattern
Facial motor nucleus
Unilateral damage to CBP
inability to smile or show teeth symmetrically
forehead unaffected
