Lecture 17 (Posture)

Question 1

Motor unit

Answer 1

A single motor neuron and all the muscle fibers it innervates

Question 2

Slow-twitch muscle fibers

Answer 2

Oxidative - red (myoglobin)
- Aerobic
- Mitochondria
- Supplied with O2-carrying blood
- Contract weakly & slowly
- able to sustain contraction

Question 3

Fast-twitch (IIX)

Answer 3

Glycolytic
1. White
2. Poorer blood supply
3. Anaerobic catabolism
4. Extensive sarcoplasmic reticula (store and reabsorb Ca2+)
5. ATPase is much faster
6. Contract rapidly but fatigue fast

Question 4

Fast-twitch (IIA)

Answer 4

Oxidative
1. White or pink
2. Intermediate fibers
3. F-t speed combined with oxidative capacity
4. Fatigue resistant - compared to IIX

Question 5

Fast vs. Slow-twitch

Answer 5

Vary in contraction speed
And ATP production (oxidative or glycolytic)
Most muscles contain all three

Question 6

1b - GTO afferent fibers

Answer 6

Adjusts muscle contraction

Question 7

1a - primary spindle endings

Answer 7

Afferent fibers
Monitor rate and degree of stretch of spindle

Question 8

Gp II - Secondary spindle endings

Answer 8

1. Medium size
2. Myelinated
3. Afferents from muscle spindle
4. Monitor degree and stretch of muscle

Question 9

Gp IV - Free nerve endings

Answer 9

1. Unmyelinated
2. Activated by noxious stimuli

Question 10

Roles postural system when stationary

Answer 10

1. Maintain balance
2. Remodel stance in preparation for voluntary movement
3. Alignment of body to maintain erect stance

Question 11

Roles postural system in movement

Answer 11

1. Maintains balance while constant shift in center of gravity

Question 12

Postural UMNs

Answer 12

Originate in brain stem
1. Tectospinal
2. Reticulospinal
3. Medial & lateral vestibulospinal
4. Rubrospinal
(5. Corticospinal)
Medial UMN -> LMN -> posture and girdle muscles
Lateral UMN -> LMN -> distal muscles (fine movement)

Question 13

Tectospinal

Answer 13

1. Arises in superior colliculus
2. Crosses in dorsal tegmental decussation
3. Synapse in cervical spinal cord - head
4. Coordinates head and eye movements
5. Mediates reflex postural movements of the head, primarily in response to visual stimuli

Question 14

Reticulospinal

Answer 14

Medial (MRST)
1. Originates in pontine RF
2. Descend ipsilaterally
3. Facilitates ipsilateral LMN innervating postural muscles and limb extensors
Lateral (LRST)
1. Originates in medullary RF
2. Descend bilaterally
3. Has opposite effect to MRST

Question 15

Vestibulospinal

Answer 15

Support against gravity
Make postural adjustments for balance
Medial (MVST)
1. Bilateral projection (cervical and thoracic)
2. Excitatory and inhibitory
3. Terminate on neck flexor and extensor MN
Lateral (LVST)
1. Ipsilateral
2. Excitatory
3. Facilitates LMN to extensors and indirect relaxation of flexors

Question 16

Vestibular nucleus (VN)

Answer 16

1. receives direct proprioceptive input
2. supports extensor activity in upper & lower body
3. Motor Cortex tonically inhibits VN

Question 17

Vestibular-Ocular Reflex (VOR)

Answer 17

1. Cancels effect of head movements
2. Eyes able to maintain fixation during head movement

Question 18

Rubrospinal

Answer 18

1. Originates in red nucleus
2. Crosses to opposite side
3. Descends and synapses on LMN innervating upper limb flexor muscles (exc)
4. RN (facilitatory to flexors in upper body) and PRF (facilitatory to extensors in upper/lower body)

Question 19

Decorticate rigidity

Answer 19

1. Lesion occurs above brain stem
2. All postural centers still influence LMN
3. Loss of cortical influence

Question 20

Decerebrate rigidity

Answer 20

1. Lesion between mid brain and pons
2. Loss of cortical and RN influence

Question 21

Paresis

Answer 21

Loss of voluntary activation of muscle