Posture Flashcards
Describe Slow Twitch Muscle Fibres
- Are Red in colour (due to myoglobin)
- Need oxygen
- High amounts of mitochondria
- Contract weakly and slowly - hence fatigue resistant
Describe Fast Twitch Muscle Fibres
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
What is Hennemans size principle?
Muscle recruitment is from small to large.
What is muscle tone?
The tonic/continuous partial contraction of a muscle –> maintaining posture.
- loss of sarcomeres result in a decrease in muscle tone
What is the final common pathway?
FCP consists of the LMN and all the muscle fibres that it innervates.
Features of a LMN lesion
Floppy muscle
- decrease in muscle tone
- Decrease in tendon reflex (areflexia)
- Decrease in voluntary muscular contraction (paresis)
Features of a UMN lesion
Spasticity in the muscle
- increase in muscle tone
- Increase in reflex activity (more fibres recruited)
- Decrease in voluntary muscle activity (paresis)
Role of the Postural system when stationary
- Maintain balance
- Remodel stance in preparation for movement i.e some muscles have to relax in order for walking to occur
Where does the tectospinal tract originate? If crossed, where?
Superior colliculus (visual)
Crosses at the dorsal tegmental decussation
Function of the Tectospinal tract
Controls/coordinates movement of the head and eyes.
Synapses in the cervical spinal cord
Tectospinal Tract reflex
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
Describe tracts in Reticulospinal tract
Contains two pathways:
1) medial reticulospinal tract (MRST)
- originates in the pontine RT
2) Lateral Reticulospinal tract
- originates in the medullary RT
Medial Reticulospinal tract
Originates in the pontine RT
- descends ipsilaterally
- activates anti gravity muscles (aka axial muscles)
Lateral reticulospinal tract
Originates in the medullary RT
- Descends bilaterally
- Releases the antigravity muscles - allowing movement for things such as walking
Vestibulospinal tracts is made up of..
The medial and lateral VST
- Both originating in the Vestibular Apparatus
Medial Vestibulospinal tract
Excites flexors (mainly neck)
Inhibits extensors (mainly neck)
Has Bilateral Projections
Lateral Vestibulospinal tract
Excites limb extensors
Has ipsilateral projections
What is the vestibular-ocular reflex?
The cancellation of the effect of head movements –> allowing eyes to be able to maintain fixation during head movements
What is the Righting Reflex
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
Describe the Rubrospinal Tract
Originates in the red nucleus
Is a crossed pathway
Excites upper limb flexors
Decorticate Rigidity
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
Decerebrate rigidity
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
