PhD MD MBBS Faculty of Medicine Al Maarefa Colleges of Science & Technology Faculty of Medicine Al Maarefa Colleges of Science & Technology Lecture – 5: Motor system - 1 Nervous System Physiology By Dr. SHAHAB SHAIKH PhD MD MBBS Faculty of Medicine Al Maarefa Colleges of Science & Technology Faculty of Medicine Al Maarefa Colleges of Science & Technology

M O V E M E N T MOTOR THE WORD MOTOR MEANS 2

MOTOR SYSTEM MOTOR CORTEX PYRAMIDAL TRACTS EXTRA PYRAMIDAL TRACTS BASAL GANGLIA CEREBELLUM 3

MOTOR SYSTEM OVERVIEW 4 Corticospinal tracts Corticobulbar tracts Bulbospinal tracts

CORTICAL MOTOR AREAS Includes 1.Primary Motor Cortex (M-I) 2.Supplementary Motor Area (M-II) 3.Premotor Cortex (PMC) Some dedicated areas like –Frontal Eye Field Area –Broca’s Area for speech

CEREBRAL CORTEX AREAS 6

M1: PRIMARY MOTOR CORTEX The primary motor cortex lies in the pre-central gyrus in front of central sulcus, in the frontal lobe Motor cortex controls muscles on the opposite side of the body Motor tracts originating from the motor cortex 7 In the spinal cord they terminate on efferent motor neuron that cause skeletal muscle contraction on the right side Therefore, damage of left motor cortex causes paralysis on the right side of the body and converse cross over in the medulla before passing down

MOTOR CORTEX - HOMUNCULUS In Motor Homunculus Cortical representation of each body part is proportionate in size to the skill of that part being used for fine voluntary movement Therefore Fingers, thumb, muscles of speech, lips and tongue have more representation Both individual muscles and movements are represented in M1 area Cells in cortical motor area are arranged in columns 8

M1: PRIMARY MOTOR CORTEX 9 Most of the cerebral cortex consists of six layers of histologically and functionally distinct cells Each region of M-1 is organized as units of interconnected columns of several thousand neurons arranged perpendicular to the cortical surface and including all six cortical layers Stimulation of a given motor column may activate a single muscle or more commonly activates several muscles to produce a coordinated movement Descending axons forming the cortical output from M-1 arise from the pyramidal cells in cortical layer 5

M1: PRIMARY MOTOR CORTEX 10 Primary motor cortex (M 1 ) along with Premotor and Supplementary motor cortex project directly to the spinal cord via Corticospinal and Corticobulbar tracts. Premotor and Supplementary motor cortex also project to primary motor cortex and are involved in coordinating & planning complex sequences of movement (motor learning). Execution of order for contraction of specific muscle or group of muscle is done by primary motor cortex

PRE MOTOR AREA (Br Area 6) Pre motor area lies 1 to 3 cm anterior to primary motor cortex in frontal lobes. It is more extensive than primary motor cortex (about 6 times) Topographical organization of pre motor cortex is roughly the same as that of primary motor cortex. Projects to brainstem area for postural control and to motor cortex also. Its function is still incompletely understood but maybe concerned with posture and planning of movement. Lesion: –It results in re-emergence of suckling and grasp reflex in adults. –Its lesion do not case paralysis but only slowing of the complex limb movement. –Lesion may result in loss of short-term or working memory. –When damaged with supplementary cortex it may result in APRAXIA. 11

SUPPLEMENTARY MOTOR AREA It is located in the frontal lobe Projects to primary motor cortex Involved in planning and programming of motor sequences With premotor cortex it translates the desire to perform a motor task into a series of motor command that will do the task. 12 Corticospinal and Corticobulbar tracts get fibers from somatosensory area also. Somatosensory area projects to premotor area also Lesions of somatosensory area and premotor area causes defects in motor performance like inability to execute learned sequence of movement SOMATOSENSORY CORTEX

CORTICOSPINAL & CORTICOBULBAR SYSTEM (PYRAMIDAL TRACTS) 13

CORTICOSPINAL & CORTICOBULBAR SYSTEM ( PYRAMIDAL TRACTS ) Motor signals are transmitted directly from the motor cortex to the spinal cord through Corticospinal tracts Corticobulbar tracts means motor neurons from motor cortex to cranial nerve nuclei 14

CORTICOSPINAL TRACTS: It is the most important motor pathway from motor cortex Origin: –30% from Primary Motor Cortex –30% from Premotor and Supplementary Motor Area –40 % from Somatosensory Area Course: –passes through posterior limb of internal capsule and downwards through brainstem. –Majority of fibers (80%) than cross in lower medulla to the opposite side and descend as lateral Corticospinal tracts. –20% uncrossed continue as Anterior Corticospinal Tract. Eventually most of them also cross before termination in Spinal Cord. 15

CORTICOSPINAL TRACTS: Termination: –Terminate principally on the Interneurons, in the intermediate region of cord grey matter, –A few terminate on sensory relay neurons in dorsal horn and –A few terminate directly on Anterior Motor Neuron. –direct innervation of alpha motor neurons by pyramidal tract axons is mainly to distal muscles and is associated with the ability to execute fine, precise movements 16

CORTICOSPINAL TRACT 17

CORTICOSPINAL TRACT FUNCTIONS: LATERAL CORTICOSPINAL TRACT:  Fine movements i.e. skilled voluntary movement VENTRAL CORTICOSPINAL TRACT:  concerned with control of bilateral postural movements by the supplementary motor cortex 18

CORTICOBULBAR TRACTS These axons pass through the internal capsule and terminate either directly on cranial motor nuclei or on interneurons innervating cranial motor nuclei in the brainstem Some fibers decussate and some give bilateral innervation They supply the muscles of Head (e.g. muscles controlling eye movement, muscles of mastication, muscles of facial expression). 19

APPLIED ASPECTS Lesions:- Pure M-I lesions are rare. May have contra lateral weakness in distal muscle (fingers). Ability to control fine movements is gone. 20

MOTOR PATHWAY Motor Pathway is two neuron system Upper motor neuron [UMN] & lower motor neuron [LMN] Upper Motor Neuron –Nerve fibers of Corticospinal & Corticobulbar tracts. –Starts from motor cortex and ends in... Cranial nerve nucleus (Corticobulbar). Anterior horn of spinal cord in opposite side. Lower Motor Neuron –Starts from anterior horn of spinal cord and ends in appropriate muscle of the same side. –E.g. All peripheral motor nerves. 21

References Human physiology by Lauralee Sherwood, 8 th edition Text Book Of Physiology by Guyton & Hall, 11 th edition

23 THANK YOU