بسم الله الرحمن الرحيم

MOTOR CORTEX & PYRAMIDAL TRACT

LEARNING OBJECTIVES Motor cortex and pyramidal tract: -Describe the different motor areas -How different part of the body are represented in motor cortex -Have concept of motor homunculus -Describe the functions of different motor areas with their role in voluntary movement -Describe the origin and functions of pyramidal tract

Cerebrum Highly developed Makes up about 80% of total brain weight (largest portion of brain) Divided into 2 halves: Right and Left Cerebral Hemispheres Connected to each other by Corpus callosum Inner core houses basal nuclei Outer surface is highly convoluted cerebral cortex caps inner core that houses basal nuclei Highest, most complex integrating area of the brain Plays key role in most sophisticated neural functions Highest, most complex integrating area of brain Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Cerebral Cortex Thin outer shell of gray matter that covers each hemisphere Covers a thick central core of white matter Organized into 6 well-defined layers Layers are organized into functional vertical columns Each half of cortex divided into 4 major lobes: Occipital Temporal Parietal Frontal Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Cerebral cortex Frontal lobe Occipital lobe Temporal lobe Responsible for 3 main functions: Voluntary motor activity Speaking ability Elaboration of thought Occipital lobe Carries out initial processing of visual input Temporal lobe Initial reception of auditory (sound) sensation Parietal lobe Receive and process sensory input Somatosensory processing Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Motor cortex Primary motor cortex ( M1 ; Brodmann area 4) Premotor area (PMA) and Supplementary motor area (SMA) (Brodmann area 6) Note: All the three projects directly to the spinal cord via corticospinal tract. Premotor and supplementary motor cortex also project to primary motor cortex and is involved in coordinating & planning complex sequences of movement (motor learning).

Cerebral Cortex Primary motor cortex Located in frontal lobe and immediately in front of central sulcus in front of somatosensory cortex Confers voluntary control over movement produced by skeletal muscles Primarily controls muscles on the opposite side of the body Damage to motor cortex on the left side of brain produce paralysis on right side Motor homunculus Depicts location and relative amount of motor cortex devoted to output to muscles of each body part

Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Cerebral Cortex Supplementary motor area: -Lies on inner surface of each hemisphere in front of primary motor cortex -Plays preparatory role in programming complex sequences of movement -Complex patterns of movement: Opening or closing hand Lesion: will not produce paralysis but they interfere with performance of more complex movements Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Premotor cortex Located on lateral surface of each hemisphere In front of the primary motor cortex Is important in orienting the body and arms toward a specific target Commands primary motor cortex to produce appropriate muscle contraction for the desired movement, but it should be informed body’s momentary position It is also guided by sensory input from post. parietal cortex

Posterior parietal cortex: -Lies posterior to primary somatosensory cortex When either of these areas is damaged, one can’t process complex sensory information to accomplish purposeful movement ie: manipulating eating utensils

Cerebral Cortex Supplementary motor area Premotor cortex Plays preparatory role in programming complex sequences of movement Complex patterns of movement: Opening or closing hand Premotor cortex Important in orienting the body and arms toward a specific target Posterior parietal cortex Lies posterior to primary somatosensory cortex When either of these areas is damaged, one can’t process complex sensory information to accomplish purposeful movement ie: manipulating eating utensils Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Cerebral Cortex Primary areas of cortical specialization for language Broca’s area Governs speaking ability Wernicke’s area Concerned with language comprehension Responsible for formulating coherent patterns of speech Language disorders Aphasias Most of which result from strokes Speech impediments Caused by defect in mechanical aspect of speech Weakness or incoordination of muscles controlling vocal apparatus Dyslexia Inappropriate interpretation of words Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Cerebral Hemispheres Left cerebral hemisphere Excels in logical, analytic, sequential, and verbal tasks Math, language forms, philosophy Tends to process information in fine-detail way Right cerebral hemisphere Excels in nonlanguage skills Spatial perception and artistic and musical talents Views the world in a big-picture, holistic way Normally, the 2 hemispheres complement each other Left cerebral hemisphere dominance Associated with “thinkers” Right hemispheric skills dominate in “creators” Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Corticospinal tract(Pyramidal tract)

Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

CORTICOSPINAL (PYRAMIDAL) TRACT

Alpha Motor Neuron (A & B)

Origin of corticospinal/corticobulbar tracts The neurons of these tracts are Pyramidal shaped Primary motor cortex (M1;Broadmann area 4) 31% Premotor cortex and supplementary motor cortex (Broadmann area 6) 29% Parietal lobe (Broadmann areas 5 and 7) and primary somatosensory area (Broadmann areas 3,1,2) in the post central gyrus 40%

Corticospinal Tract (CST) Origin – Sensory cortex, primary Motor Cortex, premotor & supplementary cortex (40%) (31%) (29%) Internal Capsule Pons Cerebral Peduncle (midbarain) Medullary Pyramid Pyramidal Decussation (80%) of the fibres cross( lateral CST) & (20%) do not cross (Ventral CST) Ant. Horn of spinal cord through a interconnection α motor neuron of opposite side

FUNCTIONS ( The axial muscles are concerned with postural adjustments & gross movements and distal limb muscles mediate fine & skilled movements). Lateral corticopinal tract controls primarily distal muscle which are finely controlling the skilled movements of thumb & fingers on the opposite side. eg. Painting writing, picking up of a small object etc.

Loss of distal motor function in opposite side. Effect of lesion: Loss of distal motor function in opposite side. Pure corticospinal tract lesion cause hypotonia instead of spasticity The reason is that pure pyramidal tract lesion is very very rare, and spasticity is due to loss of inhibitory control of extrapyramidal tract.

Cerebral Cortex Schematic Linking of Various Regions of the Cortex