Posture

Question 1

Describe Slow Twitch Muscle Fibres

Answer 1

• Are Red in colour (due to myoglobin)
• Need oxygen
• High amounts of mitochondria
• Contract weakly and slowly - hence fatigue resistant

Question 2

Describe Fast Twitch Muscle Fibres

Answer 2

Type IIa - Intermediate fibres
- Pink in colour
- More fatigue resistant than type IIx

Type IIx - White in colour
- Poor blood supply
- Uses glycolysis for energy
- Contract rapidly but fatigue fast

Question 3

What is Hennemans size principle?

Answer 3

Muscle recruitment is from small to large.

Question 4

What is muscle tone?

Answer 4

The tonic/continuous partial contraction of a muscle –> maintaining posture.
- loss of sarcomeres result in a decrease in muscle tone

Question 5

What is the final common pathway?

Answer 5

FCP consists of the LMN and all the muscle fibres that it innervates.

Question 6

Features of a LMN lesion

Answer 6

Floppy muscle
- decrease in muscle tone
- Decrease in tendon reflex (areflexia)
- Decrease in voluntary muscular contraction (paresis)

Question 7

Features of a UMN lesion

Answer 7

Spasticity in the muscle
- increase in muscle tone
- Increase in reflex activity (more fibres recruited)
- Decrease in voluntary muscle activity (paresis)

Question 8

Role of the Postural system when stationary

Answer 8

• Maintain balance
• Remodel stance in preparation for movement i.e some muscles have to relax in order for walking to occur

Question 9

Where does the tectospinal tract originate? If crossed, where?

Answer 9

Superior colliculus (visual)
Crosses at the dorsal tegmental decussation

Question 10

Function of the Tectospinal tract

Answer 10

Controls/coordinates movement of the head and eyes.
Synapses in the cervical spinal cord

Question 11

Tectospinal Tract reflex

Answer 11

Mediates the reflex of postural movements of the head in response to a visual stimulus
- e.g. a punch coming for your head, you duck as a response

Question 12

Describe tracts in Reticulospinal tract

Answer 12

Contains two pathways:
1) medial reticulospinal tract (MRST)
- originates in the pontine RT
2) Lateral Reticulospinal tract
- originates in the medullary RT

Question 13

Medial Reticulospinal tract

Answer 13

Originates in the pontine RT
- descends ipsilaterally
- activates anti gravity muscles (aka axial muscles)

Question 14

Lateral reticulospinal tract

Answer 14

Originates in the medullary RT
- Descends bilaterally
- Releases the antigravity muscles - allowing movement for things such as walking

Question 15

Vestibulospinal tracts is made up of..

Answer 15

The medial and lateral VST
- Both originating in the Vestibular Apparatus

Question 16

Medial Vestibulospinal tract

Answer 16

Excites flexors (mainly neck)
Inhibits extensors (mainly neck)

Has Bilateral Projections

Question 17

Lateral Vestibulospinal tract

Answer 17

Excites limb extensors
Has ipsilateral projections

Question 18

What is the vestibular-ocular reflex?

Answer 18

The cancellation of the effect of head movements –> allowing eyes to be able to maintain fixation during head movements

Question 19

What is the Righting Reflex

Answer 19

Receptors in the inner ear (utricle and saccule) detect an abnormality –> hence the reflex brings the neck back to the vertical plane to keep eyes level

Question 20

Describe the Rubrospinal Tract

Answer 20

Originates in the red nucleus
Is a crossed pathway
Excites upper limb flexors

Question 21

Decorticate Rigidity

Answer 21

think removing the cortex
Lesion occurs above the brain stem - hence loss of cortical influence
- Increased activity in all tracts except the Medullary Reticular formation
- Increase in upper body flexors and lower body extensors
- Paresis –> due to no voluntary muscular control

Question 22

Decerebrate rigidity

Answer 22

Lesion between the midbrain and the pons
Loss of cortical and Red nucleus influence
- Increase activity in PRF and VN
- Rigid extension in upper and lower body
- No voluntary muscular contraction