Hef - Motor Control I&II Flashcards
motor unit
one lower motor unit + all the muscle fibers it innervates
- affects sensitivity
- large motor units –> gross motor (inaccurate)
- small motor units –> fine motor (accurate)
2 types of lower motor neurons
- alpha - extrafusal fibers
- gamma - intrafusal fibers; keep sensitivity alive so muscle spindles keep responding
where are alpha lower motor neuron cell bodies located?
- ventral horn of spinal cord for spinal nerves
- brainstem for cranial nerves
different types of alpha neurons
- large motor neurons –> fast twitch muscle fibers, fast AP
- small motor neurons –> slow twitch muscle fibers, slow AP
muscle spindles
- non-contractile in center, but contractile in periphery
- gamma fibers –> supply tips, polar region
- alpha fibers –> supply bulk of the muscle
dynamic vs. static contraction
- dynamic = sudden elongation/stretch of muscle (only type 1a fibers)
- static = contracting constantly (ex. maintain posture) type 1a and II fibers
difference b/w nuclear chain and nuclear bag fibers
- nuclear bag - contain type 1a fibers (afferent); static and dynamic stretch
- nuclear chain - contain type 1a and type 2; static stretch only
myotatic (muscle spindle) reflex
stretching muscle spindle carries afferent info. on type Ia or II to ventral horn synapsing with alpha or gamma motor neurons to initiate reflex
- type Ia = monosynaptic; fast response
- type II = mono or polysynaptic; slower response
- both types have collaterals to inhibitory neurons of antagonist muscle
upper vs. lower motor neuron lesion
upper motor neuron –> hyperreflexia
lower motor neuron –> hyporeflexia
Golgi tendon reflex (inverse myotatic reflex)
contraction stimulates Golgi tendons –> send info. via type 1b fibers –> inhibitory to same muscle and stimulatory to antagonist muscle
- equalizes contractile forces
- extreme stimulation - lengthening relaxation
flexor withdrawal reflex
- multisynaptic
- harmless stimulation –> limited response and localized flexion response
- harmfull stimulation –> abrupt flexor contraction and withdrawal and cross extension (stimulate flexors inhibit extensors on same side; stimulate extensors inhibit flexors on contralateral)
afterdischarge
keeps withdrawal response longer
-needed for cross extension (want to last longer than flexion)
central pattern generator
in spinal cord - responsible for locomotion independent of cerebral cortex
-sensory feedback needed for fine tuning
reflexes of spinal cord
- positive supportive rxn = extending leg upon stimulus of foot
- rhythmic stepping = alteration b/w flexion/extension
- stumble reflex = ipsilateral flexion, contralateral extension
primary motor cortex
brodmann area 4
- conscious and voluntary movements (association motor is more complex movement)
- low level electrical stimulation (highly sensitive)
M1
where corticospinal tract fibers originate and synapse monosynaptically in ventral horn
supplementary motor area (SMA)
connected to M1 and is involved in complex bilateral movements (ex. hands)
-work with premotor for complicated sequential movement as well as planning
premotor cortex
complex and planning movements with SMA
-mirror neurons –> transfer sensory to motor movement
motor apraxia
damage to premotor, association, or SMA - not fibers
- cannot plan/organize actions
- ex. forgot how to put jacket on
corticospinal tract
originate from M1 = primary motor cortex
- get info. from parietal somatosensory (fine movements)
- most fibers cross –> lateral (fine motor)
- some fibers ipsilateral –> anterior (gross motor)
- lower motor neurons in spinal cord
corticobulbar tract
impulses from primary motor or parietal somatosensory to brainstem to synapse with lower motor neurons of cranial nerves
- bilateral in most CNs
- unilateral for CN7 in lower face –> right side lesion –> left side paralysis
- info. from limbic system along with primary motor
corticospinal tract
monosynaptic with LMNs in spinal cord
- more monosynaptic connections –> more accurate and specificity
- damage –> lose motor functions (especially fine motor)
- pyramidal tract fibers regulate reflex arc –> increase or decrease receptor firing with interneurons
- controls flexors more than extensors
corticorubrospinal tract
info. from cortex –> red nucleus –> spinal cord
- supplementary role (antigravity) and lacks fine motor control
- may help corticospinal tract regain some function
reticulospinal tract
posture, moving toward stimulus, crude movements of extremities, locomotion
- medial tract –> pons –> excitatory info. –> exaggerate response
- lateral tract –> medulla –> inhibitory info. by interneurons to dampen pons
tectospinal tract
turning head or body in response to visual or auditory stimuli
- info. coming from descending fibers of superior colliculus to spinal cord –> auditory or visual reflex
- fibers decussate after superior colliculus to terminate on interneurons and motor neurons
damage to descending corticospinal tract
muscle rigidity and paresis, exaggerated stretch reflex, + babinski, lose voluntary movements, hard to recover fine motor
- UMN lesion
- have descending inhibitory and stimulatory neurons
