MOTOR CORTEX

PRIMARY MOTOR CORTEX

Largest of all motor areas
Lies in the precentral Gyrus –> Area 4 of Brodmann extending from medial surface to lateral sulcus.
low electrical –> Specific & repeatable movement.
HOMONCULUS (little man) –> Drawn by Penfield & Rasmussen 1950.
- Body is upside down
- legs most medially
- pharynx lateral most.
- SIZE OF REPRESENTATION – More for body parts for fine & skilled movement (Thumb, Fingers, Face, Pharynx, Vocal cords etc), Less for trunk muscles.
Lacks LAYER 4 (Granules). So, called AGRANULAR CORTEX.
Cells are arranged in Columns –> cells from several columns project to same muscles.
about 30% of Corticospinal Tract fibers take origin
provide most refined degree of motor control
Areas enlarge with practice & learning —- CORTICAL PLASTICITY
LESION — Paresis/paralysis of opposite side

SUPPLEMENTARY MOTOR AREA

Medial portion of Area 6 (Anterior & Medial to M1, largely on medial surface of hemisphere)
High electrical stimulation–> Head & Eye movement, vocalization & complex postural movement.
Somatotopic arrangement like M1 —Face, Anterior. Legs, Posterior.
Bilaterally connected through Corpus callosum
Subdivided into 2 areas

FUNCTION :
- Planning & integration of complex (fixations)attitudinal movements.
- more active in bi-manual tasks
- learning of skilled acts.
LESION –> Transient speech deficit (Aphasia) — typically disappears after several weeks. Slowness in generating repetitive movement. Retards the movement of opposite limb.

PRE-MOTOR AREA (PMC)

High stimulation – Proximal musculature
minor contribution to Cortico-spinal Tract.
Major contribution to Extrapyramidal Tracts.
FUNCTIONS:
- Responsible for patterning & posturing
LESION:
- Weakness of opposite shoulder/ hip muscle
- limb movement slower
- Inability in simultaneous coordinated movement of both limbs
2 Subdivisions : DORSAL & VENTRAL

CINGULATE MOTOR AREA (CMA) within Cingulate Sulcus

CMA- r –> Rostral

CMA – d –> Dorsal

CMA – v –> Ventral

3 CMA, each with somatotopic map, contribute to CST. High stimulation similar to motor cortex stimulation.

OTHER IMPORTANT AREAS

FRONTAL EYE FIELD — Controls eye movement
POSTERIOR PARIETAL CORTEX — (5,7)
- Lesion : No motor weakness, but sensory & motor neglect in opposite hemifield —> AMORPHOSYNTHESIS

HISTOLOGICAL STRUCTURE OF MOTOR CORTEX

3 Types of cells are present – 1. PYRAMIDAL CELLS 2.STELLATE/GRANULE CELL 3. FUSIFORM CELLS

6 layers or laminae are present–>

most afferent fibers from the specific nuclei of thalamus make synapses in the laminae I to VI
Afferent projections from non-specific thalamic nuclei & from ascendind reticular system terminate in al laminae of cortex
Laminae II & IV are concerned with sensorial modalities.
Laminae III to V are meant for somatomotor or visceromotor activities.
Laminae I to VI are engaged for integration of association of sensorimotor behaviour.