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
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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.

  • FUNCTION :Preparation & execution of movement.

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
  • BROCA’S AREA — Motor speech area, Area 44.
    • Lesion : Motor aphasia
  • SUPPRESSOR AREAS (4s, 2s, 8s, 19s, 24s) — Inhibition of strech reflex


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.

ORGANISATION OF MOTOR SYSTEM

NEURAL CONTROL OF MOVEMENT

Movement is crucial to all organisms. its performed in higher animals by contraction of & relaxation of the muscles.

Motor system exists in Brain to translate out thought, sensation, emotion & feeling into MOVEMENT.

SENSORY SYSTEM –> transforms physical energy into neural signals

MOTOR SYSTEM –> NEURAL signal is converted to contractile force of muscle and hence converted into MOVEMENT.

SENSORY REPRESENTATION FORM FRAMEWORK IN WHICH –

  1. motor system plans, coordinates & executes.
  2. motor system programmes a purposeful movement
  3. it a highly complicated & integrated system.
  4. ability of human beings to carry out skilled movement while still performing cognitive tasks requires flexibility, integration & skills that no other organism /animal has.

TYPES OF MOVEMENT

ORGANISATION OF MOTOR SYSTEM

  1. IDEA – Posterior Parietal cortex, Association areas
  2. PLANNING – Premotor , Supplementary motor Cortex, Thalamus, Basal Ganglia
  3. PROGRAMMING – Cortex, Basal Ganglia
  4. MOTOR COMMAND – Cortex – {Spinal cord, brain stem } –> via descending tracts
  5. EXECUTION – Spinal cord –> via –> Final common path
  6. ACTION –> contraction of muscle, joint movement
  7. COMPARISON, COORDINATION –> Cerebellum, Thalamus, Sensory pathway

All voluntary activity involves activity of CEREBRAL CORTEX.

ROLE OF DIFFERENT PARTS OF BRAIN IN MOTOR CONTROL :

  1. CORTICAL MOTOR AREA
    • Highest level of motor control
    • 3 criteria :
      • stimulation using low current strength elicits movements
      • destruction of area results in loss of motor function
      • area has output connection directly(or with minimal or intermediate connections) to brainstem or spinal cord.
    • 2 groups : Primary motor Cortex & Secondary motor cortex.
  2. POST PARIETAL CORTEX
  3. FRONTAL EYE FIELD
  4. BROCA’S AREA
  5. SUPPRESSOR AREAS (4s, 2s, 8s, 19s & 24s)

Welcome to MBBS Memory Maps in Physiology

Concepts are the keystones in the architecture of our thinking.

-Paul Hughes

Let’s create road-maps for concepts.

WISDOM IS NOT A PRODUCT OF SCHOOLING BUT OF THE LIFELONG ATTEMPT TO ACQUIRE IT. –Albert Einstein

Hey there!

Let’s just say that studying can be fun too. Preparing concept map has been my thing always. So, now I am here to share my view and maps on physiology/medical topics with the world out there.

A Physiology Professor by profession I have seen students struggling with the basic concepts of the subject and almost everyone scrambling for notes (self-made, borrowed from seniors or copied from a fellow classmate). But I have found that more than so called ‘notes’, you need a clear concept – hence the concept maps.

WHAT IS A CONCEPT MAP?

It is basically a conceptual diagram that suggests or compiles a knowledge or information in form of a arrow diagram or a flow chart. In other words it explains and organizes a complex information in an easy to comprehend diagram or chart. A very useful and organized way to understand, acquire & memorize concepts.

ADVANTAGES OF CONCEPT MAPS –

  1. Simplifies understanding of an complex phenomenon/ subject.
  2. helps in quicker learning. You can finish a bigger chapter in lesser time.
  3. easy to remember and reproduce in exams.
  4. creates memory maps(with less confusions of course!!)

So, see you all later in my subsequent posts where I will share my ‘concept-maps’ mostly related to Physiology, medicine & maybe everything else in due course of time. keep me posted on your view on the same.