Hef - Motor Control I&II

Question 1

motor unit

Answer 1

one lower motor unit + all the muscle fibers it innervates

• affects sensitivity
• large motor units –> gross motor (inaccurate)
• small motor units –> fine motor (accurate)

Question 2

2 types of lower motor neurons

Answer 2

• alpha - extrafusal fibers

- gamma - intrafusal fibers; keep sensitivity alive so muscle spindles keep responding

Question 3

where are alpha lower motor neuron cell bodies located?

Answer 3

• ventral horn of spinal cord for spinal nerves

- brainstem for cranial nerves

Question 4

different types of alpha neurons

Answer 4

• large motor neurons –> fast twitch muscle fibers, fast AP
• small motor neurons –> slow twitch muscle fibers, slow AP

Question 5

muscle spindles

Answer 5

• non-contractile in center, but contractile in periphery
• gamma fibers –> supply tips, polar region
• alpha fibers –> supply bulk of the muscle

Question 6

dynamic vs. static contraction

Answer 6

• dynamic = sudden elongation/stretch of muscle (only type 1a fibers)
• static = contracting constantly (ex. maintain posture) type 1a and II fibers

Question 7

difference b/w nuclear chain and nuclear bag fibers

Answer 7

1. nuclear bag - contain type 1a fibers (afferent); static and dynamic stretch
2. nuclear chain - contain type 1a and type 2; static stretch only

Question 8

myotatic (muscle spindle) reflex

Answer 8

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

Question 9

upper vs. lower motor neuron lesion

Answer 9

upper motor neuron –> hyperreflexia

lower motor neuron –> hyporeflexia

Question 10

Golgi tendon reflex (inverse myotatic reflex)

Answer 10

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

Question 11

flexor withdrawal reflex

Answer 11

• 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)

Question 12

afterdischarge

Answer 12

keeps withdrawal response longer

-needed for cross extension (want to last longer than flexion)

Question 13

central pattern generator

Answer 13

in spinal cord - responsible for locomotion independent of cerebral cortex
-sensory feedback needed for fine tuning

Question 14

reflexes of spinal cord

Answer 14

• positive supportive rxn = extending leg upon stimulus of foot
• rhythmic stepping = alteration b/w flexion/extension
• stumble reflex = ipsilateral flexion, contralateral extension

Question 15

primary motor cortex

Answer 15

brodmann area 4

• conscious and voluntary movements (association motor is more complex movement)
• low level electrical stimulation (highly sensitive)

Question 16

M1

Answer 16

where corticospinal tract fibers originate and synapse monosynaptically in ventral horn

Question 17

supplementary motor area (SMA)

Answer 17

connected to M1 and is involved in complex bilateral movements (ex. hands)
-work with premotor for complicated sequential movement as well as planning

Question 18

premotor cortex

Answer 18

complex and planning movements with SMA

-mirror neurons –> transfer sensory to motor movement

Question 19

motor apraxia

Answer 19

damage to premotor, association, or SMA - not fibers

• cannot plan/organize actions
• ex. forgot how to put jacket on

Question 20

corticospinal tract

Answer 20

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

Question 21

corticobulbar tract

Answer 21

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

Question 22

corticospinal tract

Answer 22

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

Question 23

corticorubrospinal tract

Answer 23

info. from cortex –> red nucleus –> spinal cord
- supplementary role (antigravity) and lacks fine motor control
- may help corticospinal tract regain some function

Question 24

reticulospinal tract

Answer 24

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

Question 25

tectospinal tract

Answer 25

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

Question 26

damage to descending corticospinal tract

Answer 26

muscle rigidity and paresis, exaggerated stretch reflex, + babinski, lose voluntary movements, hard to recover fine motor

• UMN lesion
• have descending inhibitory and stimulatory neurons