Motor System

The cerebral cortex

1.Sensory perception2.Voluntary control of movement3.Language4.Personality traits5.Sophisticated mental events,such as

thinking memory, decision making, creativity, and self-consciousness

Brain component

Major Functions Cerebral cortex

Figure 5.9Page 146Frontallobe

Central sulcus

Parietallobe

Parietooccipitalnotch

Occipitallobe

Preoccipitalnotch

CerebellumBrain stem

Temporallobe

Lateralfissure

FrontLefthemisphere

Primarymotorcortex

Topview

Somato-sensorycortex

Righthemisphere

Frontallobe

Centralsulcus

Parietallobe

Occipital lobe

Back

Figure 5.10Page 147

Centralsulcus Posterior

parietal cortex

Wernicke’s area

Parietal-temporal-occipitalassociation cortex

Primary visual cortex

Cerebellum

Limbic associationcortex

Primary auditory cortex

Broca’s area

PrefrontalAssociationcortex

Supplementary motor area

Primary motor cortex Somatosensory cortex

Posterior parietal cortex

Wernicke’s area

Parietal-temporal-occipitalassociation cortex

Primary visual cortex

Brain stem

Limbic associationcortex

Primary auditory cortex

Broca’s area

Premotor cortex

PrefrontalAssociationcortex

The sensorimotor cortex

Posterior Parietal

5,7

S1

3,1,2M1

4

PMA6

SMA6

Signals converge onto the primary

motor cortexBrainstem &Spinal cord

Sensory input

Primary sensory areas (somatosensory,

visual, auditory cortices)

Higher sensory areas

Association areas

Higher motor areas

Primary motor areas

Motor output

Supplementary motor area (secondary motor cortex (6 & 8): programming of complex movements (both sides)

Primary motor cortex (M1;area4): voluntary movement

Premotor cortex (6): coordination of complex movements, important in orienting the body and arms toward a specific target

Prefrontal AssociationCortex: planning for voluntary activity; decision making; creativity and personality traits

Supplementary motor area, Premotor cortex, Prefrontal Association Cortex command the primary motor cortex

Does not itself initiate voluntary

movement

The idea of a voluntary

movement

Supplementary motor area: stimulation complex patterns of movements e.g., hand open/ close. Lesions do not lead to paralysis but to Motor apraxia.

Primary motor cortex: Lesions lead to paralysis/Paresis (weakness), clumsinessand slowness of movement

Premotor cortex: works in association with posterior parietal cortex. Damage inability to process complex sensory information to accomplish purposeful movement in space.

Prefrontal AssociationCortex: deficits changes in personality and social behaviour

Motor apraxia: loss of learned motor skills

without paralysis

Figure 5.12 (2)Page 149

Lefthemisphere

Cross-sectional view

Temporal lobe

Motor homunculus

The upper part of the face is bilaterally represented but the rest of the body is represented unilaterally

Figure 5.11 (2)Page 149

Lefthemisphere

Cross-sectional view

Temporal lobe

Sensory homunculus

How M1 commands voluntary movement?

• Much of motor cortex is active for every movement

• Activity of each cell represents a single vote for a particular direction of movement

• Direction of movement is determined by a tally and averaging of the votes registered by each cell in the population

• The larger the population representing a type of movement, the finer the possible control.

M1 is organized in terms of movements rather than muscles

Parameters of movement controlled by M1 (area 4)

• Direction– neurons

• Speed:– neurons

• Force:– Firing rate of neurons

Figure 5.13Page 152

Facial area ofmotor cortex

Broca’sarea

Bundle ofinterconnecting fibers

Wernicke’sarea

Visual cortex

Angular gyrus of

parietal-temporal-occipitalassociation cortex

Motor speech area

Sensory speech area

1

2

3

4

Descending Tracts

Corticospinal tract

Lateral pathways Medial pathways

Major descending spinal tracts and their points of origin

Cerebral cortex

Vestibular Nucleus and

superior colliculus

Red nucleus

Reticular nuclei

Spinal cord

Rubrospinal tract

The lateral system

• Includes the lateral corticospinal tract and part of the corticobulbar tract + rubrospinal tracts.

• These pathways influence contra lateral motor neurons that supply the musculature of the limbs, especially the digits, the muscles of the lower face, and the tongue.

• Controls fine discrete movements• Inhibitory to muscle tone and reflexes

The medial system (ventromedial system)

• Includes the – ventral corticospinal, – lateral and medial vestibulospinal, – pontine and medullary reticulospinal,– tectospinal tracts.

• These pathways mainly– affect posture, and – provide the motor background for movements of the

limbs and digits.– Involved in locomotion

• Modulates the skeletal muscle tone (excitatory and inhibitory)

Pathways that originate in the brainstem influence

• posture,

• locomotion, and

• eye movements.

Influences of the brain stem centers on spinal reflexes

(alpha and gamma extensor and flexor motor neurons)

• Lateral vestibular nucleus extensor activity

• Pontine reticular Formation extensor activity• Red nucleus flexor activity• Medullary reticular Formation flexor activity

Relationship of the thalamus, basal ganglia, and cortex in the control of movement

Cerebral cortex

Pontine RF

Vestibular nucleus Medullary RF

Spinal cord+ +

+

-+/-

-

-

-

Antigravity muscles

A high degree of natural excitability

Basal ganglia:Inhibit muscle

tone

Cerebellum:enhance

muscle tone

Role of cortex and other structures in the control of movement

Cerebral cortex

Pontine RF

Vestibular nucleus Medullary RF

Spinal cord+ +

+

-+/-

-

-

-

Decorticate spasticity

Decerebrate rigidity

Flaccid

Antigravity muscles

A high degree of natural excitability