PHYSIOLOGY OF MOTOR CORTEX
INTRODUCTION:
* A Part of the cerebral cortex on activation results in discrete bodily movements.
* Origination point for fundamental impulses causing muscle contraction.
* Primary motor cortex/BRODMANN’S Area 4
* Premotor area.
* Supplementary motor area.
* Controls the contralateral side of body.
* Mainly concerned with voluntary movements.
* Simultaneously stimulates set of synergistic muscles moving “Single” joint.
* No individual muscle action.
* Sequence of motor activity is programmed.
* Entire body is represented upside-down (vertical).
* Roughly figures a highly distorted man with very large thumb, relatively large face, enormous tongue & very small trunk & legs.
* Referred as “Motor Homunculus”.
* In descending order,
* Muscles for vocalization (maximum)
* Muscles for mastication
* Muscles for salivation
* Only areas concerned with highly skilled movement.
* Eg: Face, tongue & lips.
Associated disorders:
* Movements involve “Multiple” joints.
* Important area for motor learning.
* Involves in planning/organizing motor sequence.
* Supplementary motor area/medial premotor area.
* Premotor cortex/lateral premotor area.
* Movements planned in supplementary motor area are executed in primary motor area.
* Complex sequence of movement based on memory/internal cue.
* No involvement of visual/external cue.
* Eg: Hand co-ordination movements.
* Stimulation often results in bilateral contraction rather than unilateral.
* Programming of visually guided sensory movements.
* Hence, movements referred as “Sensorimotor transformation”.
* Eg: “Reaching/grasping movements”
Exam Important
* Premotor area corresponds to Brodmann’s Area 6.
* Cortical representation of the body in the cerebrum is Vertical.
* The most important area involved in planning & organizing complex sequential skilled movements is “Supplementary motor area”.
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