Motor System Cerebral Cortex

Motor System The cerebral cortex

Brain component

Major Functions Cerebral cortex 1.Sensory perception 2.Voluntary control of movement 3.Language 4.Personality traits 5.Sophisticated mental events,such as  thinking  memory,  decision making,  creativity, and  self-consciousness

Central sulcus Frontal lobe

Figure 5.9Page 146 Parietal lobe Parietooccipital notch

Occipital lobe Lateral fissure

Preoccipital notch

Temporal lobe

Brain stem

Cerebellum

Front Left hemisphere

Right hemisphere Frontal lobe

Primary motor cortex

Central sulcus

Top view Parietal lobe Somatosensory cortex Occipital lobe Back

Central sulcus Prefrontal Association cortex Broca’s area Primary auditory cortex Limbic association cortex Figure 5.10 Page 147

Posterior parietal cortex

Wernicke’s area Parietal-temporaloccipital association cortex Cerebellum

Primary visual cortex

Supplementary motor area

Primary motor cortex

Somatosensory cortex Posterior parietal cortex

Premotor cortex Prefrontal Association cortex

Wernicke’s area Parietal-temporaloccipital association cortex

Broca’s area Primary auditory cortex Limbic association cortex Brain stem

Primary visual cortex

The sensorimotor cortex SMA 6

S1 M1 4

3,1,2

Posterior Parietal 5,7

PMA 6

Brainstem & Spinal cord

Signals converge onto the primary motor cortex

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

Primary motor cortex (M1;area4): voluntary movement Does not itself initiate voluntary movement

Supplementary motor area (secondary motor cortex (6 & 8): programming of complex movements (both sides) Premotor cortex (6): coordination of complex movements, important in orienting the body and arms toward a specific target Prefrontal Association Cortex: planning for voluntary activity; decision making; creativity and personality traits

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), clumsiness and 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 Association Cortex: deficits  changes in personality and social behaviour

Motor apraxia: loss of learned motor skills without paralysis

Motor homunculus

Figure 5.12 (2) Page 149

Left hemisphere

Cross-sectional view

Temporal lobe

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

Sensory homunculus

Figure 5.11 (2) Page 149

Left hemisphere

Cross-sectional view

Temporal lobe

How M1 commands voluntary movement? M1 is organized in terms of movements rather than muscles • 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.

Parameters of movement controlled by M1 (area 4) • Direction – neurons

• Speed: – neurons

• Force: – Firing rate of neurons

Facial area of motor cortex

Figure 5.13 Page 152

Angular gyrus of

parietal-temporal-occipital association cortex

Sensory speech area 3 4

2

Broca’s area Wernicke’s area

Motor speech area 1 Bundle of interconnecting fibers

Visual cortex

Descending Tracts

Major descending spinal tracts and their points of origin Cerebral cortex Corticospinal tract

Rubrospinal tract

Red nucleus

Lateral pathways

Vestibular Nucleus and superior colliculus

Reticular nuclei

Medial pathways Spinal cord

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 Pontine reticular Formation Red nucleus Medullary reticular Formation

extensor activity extensor activity flexor activity flexor activity

Relationship of the thalamus, basal ganglia, and cortex in the control of movement Basal ganglia: Inhibit muscle tone Cerebellum: enhance muscle tone

A high degree of natural excitability

Cerebral cortex

Pontine RF

Vestibular -

+ Medullary RF

nucleus

+

+

+/-

Spinal cord

Antigravity muscles

-

Role of cortex and other structures in the control of movement

A high degree of natural excitability

Cerebral cortex Decorticate spasticity Decerebrate rigidity

Pontine RF

Vestibular -

+ Medullary RF

nucleus

Flaccid

+

+

+/-

Spinal cord

Antigravity muscles

-