Motor Cortex....power point presentation

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1. Motor Cortex

2. Introduction to Motor Cortex The motor cortex is the region of the cerebral cortex involved in planning, control, and execution of voluntary movements . It is located in the frontal lobe , anterior to the central sulcus. It includes: Primary motor cortex (M1) Premotor cortex Supplementary motor area (SMA) Each area contributes uniquely to the generation and coordination of movement.

3. a) Primary motor cortex b) Premotor cortex c) Supplementary motor cortex

4. Primary Motor Cortex (M1) Location: Lies in the precentral gyrus of the frontal lobe. Brodmann area 4 . Functions: Directly executes voluntary movements , especially fine, skilled movements (e.g., fingers, hands, face). Controls contralateral body muscles (opposite side). Sends output signals via corticospinal and corticobulbar tracts to lower motor neurons.

5. Characteristics: Has a somatotopic organization (motor homunculus). Produces individual and discrete muscle contractions . Responsible for simple movements (e.g., flexing a finger)

6. Premotor Cortex Location: Anterior to the primary motor cortex. Brodmann area 6 (lateral part). Functions: Responsible for planning and coordination of complex movements . Controls postural adjustments needed for voluntary movements. Active during motor learning and movement guided by external stimuli (e.g., seeing a ball and reaching for it). Coordinates proximal muscles and trunk muscles .

7. Connections: Receives sensory input from parietal lobe and visual cortex . Sends outputs to primary motor cortex and directly to the spinal cord .

8. Supplementary Motor Area (SMA) Location: Medial part of Brodmann area 6 (on the medial surface of the hemisphere, superior to the premotor cortex). Functions: Controls bilateral movements (e.g., buttoning a shirt). Involved in motor planning , especially sequential and complex movements . Important for movement initiated from memory (internal cues), rather than external stimuli. Active during mental rehearsal of movement .

9. Additional Roles: Contributes to initiation of movement . Works with basal ganglia for motor pattern coordination .

10. Feature Primary Motor Cortex (M1) Premotor Cortex Supplementary Motor Area (SMA) Brodmann Area 4 6 (lateral) 6 (medial) Location Precentral gyrus Anterior to M1 Medial frontal lobe Function Execute movement Plan movement using external cues Plan movement using internal cues Muscle Control Distal, fine control Proximal and trunk Bilateral and sequential movement Example Finger tapping Reaching to catch a ball Playing piano from memory Comparison Table: Motor Cortex Areas

11. The motor cortex is an intricately organized system where: Primary motor cortex executes specific voluntary movements. Premotor cortex helps in externally guided movements. Supplementary motor area plans internally generated, complex, and bilateral movements.

12. Motor Homunculus

13. Definition: The motor homunculus is a somatotopic map representing how different parts of the body are controlled by specific regions of the primary motor cortex. Key Features: Located in the primary motor cortex (precentral gyrus). The body is represented upside down : Lower limbs = medial cortex Face and tongue = lateral cortex The size of each body part on the homunculus is proportional to the precision of motor control , not its physical size.

14. Examples: Large areas : hands, face, lips (fine motor control). Small areas : trunk, thighs (gross movements). Clinical Relevance: Helps localize brain lesions affecting motor function. Explains focal motor deficits (e.g., stroke in medial cortex affects leg more than face).

15. The motor homunculus provides a visual map that reflects the importance of precision and control in different body parts, making it a key concept in neuroanatomy and clinical neurology.

16. The transmission of signals from the motor cortex to skeletal muscles is primarily carried out by descending motor tracts . These are divided into two major systems: Corticospinal Tract (Pyramidal Tract ) Extrapyramidal Tracts

17. Corticospinal Tract (Pyramidal Tract) Origin : Arises from the primary motor cortex (area 4) , premotor cortex , supplementary motor areas and somatosensory cortex .

18. Pathway: Fibers descend through the internal capsule , cerebral peduncles (midbrain) , pons , and medulla . In the medulla , most fibers form the pyramids and about 75–90% decussate (cross over) to the opposite side in the pyramidal decussation . These crossed fibers form the lateral corticospinal tract , which descends in the spinal cord . The remaining uncrossed fibers form the anterior corticospinal tract (some cross at the spinal segment level).

19. Termination: They synapse on alpha motor neurons or interneurons in the anterior horn of the spinal cord.

20. Function: Responsible for voluntary movements , especially fine, skilled movements of distal limbs (e.g., fingers, hands).

21. Extrapyramidal Tracts 1) Reticulospinal tract 2) Vestibulospinal tract 3) Rubrospinal tract 4) Tectospinal tract 5) Olivospinal tract Origin: These tracts originate from subcortical nuclei in the brainstem (e.g., red nucleus , reticular formation , vestibular nuclei , superior colliculus ). Pathway: These tracts descend in the spinal cord outside the pyramids (hence extrapyramidal ). They may cross (e.g., rubrospinal ) or remain ipsilateral (e.g., vestibulospinal ).

22. Function: Control involuntary and automatic movements , including: Posture Muscle tone Balance Gross motor activities Modulate activity of lower motor neurons via interneurons.

23. Feature Corticospinal (Pyramidal) Extrapyramidal Origin Motor cortex Brainstem nuclei Decussation Yes (mainly in medulla) May or may not decussate Type of control Voluntary, fine motor control Involuntary, postural control Primary target Alpha motor neurons Interneurons, gamma motor neurons Example of movement Writing, playing piano Standing posture, reflexes Comparison Table

24. Summary: The corticospinal tract is essential for precise voluntary movements , especially of distal muscles. Extrapyramidal tracts provide background control of posture, tone, and gross movements needed to support voluntary action .