REGULATION OF POSTURE
REGULATION OF POSTURE
- Posture – Stable equilibrium adopted by an individual.
MECHANISMS OF POSTURE:
- Muscle tone distribution.
- Postural reflexes.
MUSCLE TONE DISTRIBUTION:
- Posture is maintained by reflex adjustments of tone in anti-gravity muscles.
- Anti-gravity muscles – Flexors of upper extremity & extensors of lower extremity.
- Muscle tone is controlled by basic postural reflex mainly, stretch reflex.
POSTURAL REFLEXES:
- Responsible for maintaining a posture, by altering neutral discharges of stretch reflexes.
- Stretch reflex arc integrity is a must for posture maintenance.
IMPORTANT POSTURAL REFLEXES & INTEGRATING CENTERS:
| Sl.no | POSTURAL REFLEX | INTEGRATING CENTER |
| 1. | Tonic labyrinthine reflexes | Medulla oblongata |
| 2. | Tonic neck reflex | Medulla oblongata |
| 3. | Righting reflex | midbrain |
| 4. | Long-loop stretch reflex | cerebral cortex |
| 5. | Hopping & placing reactions | cerebral cortex |
| 6. | Positive supporting reaction | Spinal cord |
| 7. | Crossed extensor reflexes | Spinal cord |
VESTIBULAR REFLEXES:
- Inputs from vestibular reflexes are used for reflex adjustment of posture & eye movements.
- Includes,
- Tonic labyrinthine reflex.
- Labyrinthine righting reflex.
- Visual reflex (vestibulo-ocular reflex).
ASSOCIATED DISORDERS:
Two major types of rigidity involved,
- Decorticate rigidity
- Decerebrate rigidity
| FEATURES | DECORTICATE RIGIDITY | DECEREBRATE RIGIDITY |
| Cause & lesion area | Lesions above superior colliculus. | Lesion below superior colliculus |
| Target lesion area | Removal of entire cerebral cortex leaving basal ganglia intact. | Midcollicular/inter-collicular section of brainstem at upper border of midbrain. |
| Tracts involved |
Rubrospinal tract
Reflex affected – Absent long loop stretch reflex. |
Tracts affected – Corticospinal, corticulobulbar & rubrospinal tract.
Tracts unaffected – Reticulospinal tract, due to intact reticular nuclei below level of section. |
| Rigidity | Upper limb flexed & lower limb extended | Full-extension upper & lower limbs |
| Effects |
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Exam Important
REGULATION OF POSTURE
- In decorticate rigidity, rigidity is less pronounced than decerebrate rigidity.
- Reflex absent in decorticate animal Long loop stretch reflex.
- Decorticate rigidity is not seen as a manifestation of uncal herniation.
- Decorticate child shows in acute brain injury, subthalamic, CT & frontal lobe lesion and shows flexion of arm & extension of lower limb.
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