VOLUNTARY MOTOR CONTROL

ORGANIZATION OF MOTOR NERVOUS SYSTEM

CONTROL OF VOLUNTARY MOVEMENT

IdeaAssociation

cortexPremotor +

Motor cortex

Basal Ganglia

Lateral cerebellum

Movement

Intermediate Cerebellum

ExecutionPlanning

1906 - SIR CHARLES SCOTT SHERRINGTON

1906- The Integrative Action of the Nervous system that describes the synapse and motor cortex

Spinal reflex 1932 Nobel Prize

LEYTON SSF & SHERRINGTON CS (1917).OBSERVATIONS ON THE EXCITABLE CORTEX OF THE CHIMPANZEE, ORANG-UTAN AND GORILLA. Q J EXP PHYSIOL 11, 135–222.

Figure 1. Motor maps of the gorilla cortexA, scale drawing of the left hemisphere of one of Leyton & Sherrington’s experiments

on a gorilla (gorilla 1). The numbers and letters encode a wide range of different primary movements evoked by faradic stimulation. Eye movements (372–388) were generally evoked from an area further rostral from the motor cortex. Owing to lack of space, many motor effects were not plotted. B, simplified ‘map’ showing ‘responses grouped diagrammatically’,

BRODMANN’S AREA: 1909

FUNCTIONAL ORGANIZATION OF THE PRIMARY MOTOR CORTEX

MOTOR CORTEX AFFERENT

1. Adjacent cortex1. the somatosensory areas of the

parietal cortex,

2. theadjacent areas of the frontal cortex anterior to the motor cortex, and

3. the visual and auditory cortices.

2. Opposite cerebral hemisphere.

3. Somatosensory fibers directly from the ventrobasal complex of the thalamus.

4. Tracts from the ventrolateral and ventroanterior nuclei of the thalamus, which in turn receive signals from the cerebellum and basal ganglia

5. Fibers from the intralaminar nuclei of the thalamus (RAS).

CONVERGENCE OF MOTOR CONTROL ON THE ANTERIOR MOTOR NEURON

EXTRA-PYRAMIDAL SYSTEM

MORE INTRICATE MOTOR MAPS Intracortical micro-stimulation

of layer V confirms the spatial motor map of Penfield

Stimulation of small regions of the map activated single muscles, suggesting that vertical columns of cells in the motor cortex were responsible for controlling the actions of particular muscles.

Microstimulation with simultaneous EMG recording shows that organized movements represented in motor map

Individual pyramidal cells terminates on group of muscles in anterior horn cells in mosaic fashion

LATERAL AND MEDIAL SYSTEM

The initiation of skilled voluntary movement in primates

Loss of precise movement, retained power movement by lateral corticospinal destruction

Anterior corticospinal system destruction produce axial muscle deficits that cause difficulty with balance, walking, and climbing.

CORTICAL CONTROL OF MOVEMENT

1947 Chang, Ruth could stimulate individual muscle by monkey motor cortex stimulation

1954 Bernhard and Bohm : single shock stimulation produces monosynaptic response in forelimb

Landgren, Phillips and Porter (1962). stimulated the surface of the motor cortex while recording intracellularly from motoneurons and demonstrated the existante of a cluster of neurons which projected monosynaptically to motor neurons

1953, Malis, Pribram and Kruger showed that the motor cortex received afferent inputs from the periphery in the absence of the sensory cortex

CELLULAR ORGANIZATION OF M11. The neocortex (most of the cerebral cortex) consists of six layers

of histologically and functionally distinct cells

2. Each region of M-1 (and the remainder of the neocortex) is organized as units of interconnected columns of several hundred neurons arranged perpendicular to the cortical surface and including all six cortical layers

3. Stimulation of a given column may activate a single muscle ; more usually stimulation of a column activates several muscles to produce a coordinated movement

4. Note: this is sometimes expressed as "The motor cortex thinks in terms of movements, not muscles“

5. Groups of columns control groups of alpha motoneurons to determine the force and direction and velocity of movement

6. Descending axons forming the cortical output from M-1 (and from the cortex in general) arise from the pyramidal cells in cortical layer 5

7. Pyramidal cells in layers 2 and 3 send axons to other regions of the ipsilateral cortex (layer 2) and to corresponding areas of the contralateral cortex via the corpus callosum (layer 3)

8. Note: Axial regions of the body are well represented in corpus callosal axons connecting corresponding contralateral regions of the motor cortex but distal regions are less well represented.

DIRECT CORTICOSPINAL CONTROL OF MOTOR NEURONS IS NECESSARY FOR FINE CONTROL OF THE DIGITS

CORTICOMOTONEURONAL (CM) CELL IS ACTIVE DEPENDS ON THE MOTOR TASK

ACTIVITY IN INDIVIDUAL NEURONS OF THE PRIMARY MOTOR CORTEX IS RELATED TO MUSCLE FORCE AND DIRECTION OF MOVEMENT

DIFFERENT AREAS OF CORTEX ARE ACTIVATED DURING SIMPLE, COMPLEX, AND IMAGINED SEQUENCES OF FINGER MOVEMENTS (XENON PET)

CELL ACTIVITY IN THE MOTOR CORTEX DEPENDS ON WHETHER A SEQUENCE OF MOVEMENTS IS GUIDED BY VISUAL CUES OR BY PRIOR TRAINING

A SET-RELATED NEURON IN THE DORSAL PREMOTOR AREA BECOMES ACTIVE WHILE THE MONKEY PREPARES TO MAKE A MOVEMENT TO THE LEFT

THE VISUOMOTOR TRANSFORMATIONS REQUIRED FOR REACHING AND GRASPING INVOLVE TWO DIFFERENT PATHWAYS

Individual neurons in the ventral premotor area fire during specific hand actions only

MOTOR PLANNING

A. ACTIVITY IN THE NEURON AS THE MONKEY OBSERVES ANOTHER MONKEY MAKE A PRECISION GROUP.B. ACTIVITY IN THE SAME NEURON AS THE MONKEY OBSERVES THE HUMAN EXPERIMENTER MAKE THE PRECISION GRIP.C. ACTIVITY IN THE SAME NEURON AS THE MONKEY ITSELF PERFORMS A PRECISION GRIP. (FROM RIZZOLOTTI ET AL 1996.)

Mirror Neurons

CORTICAL MOTOR AREAS

MOTOR CORTICAL CENTER

THE SOMATOTOPIC ORGANIZATION OF THE MOTOR CORTEX IS PLASTIC

AS A MOVEMENT BECOMES MORE PRACTICED, IT IS REPRESENTED MORE EXTENSIVELY IN PRIMARY MOTOR CORTEX

SUMMARY Primary Motor Cortex:

Codes force and direction of movement Spinal motor neuron are directly under control for

precise movement. Dorsal Premotor Cortex

Movement related neuron encodes sensorimotor transformation for visual and sensory cue

Fire before movement Ventral Premotor Cortex

Encodes learned motor act fire before movement

All cortical neurons are adaptable and plastic

THANKS