DR NILESH KATE
MBBS,MD ASSOCIATE PROF
DEPT. OF PHYSIOLOGY
MOTOR SYSTEM
OBJECTIVES Introduction. Components of Somatic motor control system. Skeletal Muscle : The Effector organ of somatic
motor system. Reflex activity. Regulation of posture. Vestibular apparatus & equilibrium.
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INTRODUCTION.
Effector organ- Skeletal muscle.
Muscle activity decided by – Rate & Pattern of discharge in Motor neuron.
Motor unit – Single Motor Neuron & muscle fibre that it innervates.
Motor Neuronal Pool – All Motor Neuron for a given muscle.
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INTRODUCTION. Lower Motor Neuron
& Final Common Pathway – Alpha motor neuron & Motor nuclei of cranial nerves.
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SOMATIC MOTOR ACTIVITY. Voluntary Movements –
learns by doing & performance improves with repetition. (Synaptic Plasticity)
Reflex Responses. Rhythmic Motor Activities –
Initiated & terminated voluntarily.
Control Of Posture & Equilibrium –Goal & direction oriented phasic movements.
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MEDIAL VS LATERAL MOTOR SYSTEM.
Medial Motor System. Anterior Cortico-spinal
tract. Corticobulbar tract. Lateral & Medial
Vestibulospinal tract. Reticulospinal tract.
Lateral Motor System. Lateral corticospinal
tract. Rubro spinal tract. Corticobulbar tract.
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CONTROL OF SOMATIC MOTOR ACTIVITY.
3 Tier System to control.
Highest level – Cerebral Cortex for generation of ideas & giving motor commands.
Middle level – for Supervising.
Lower level – for Execution.
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ROLE OF SENSORY RECEPTORS IN MOTOR CONTROL ACTIVITY.
Proprioceptors in skin, Muscle & joints gives feedback
& Adjust Motor
commands.
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OVERVIEW TO STUDY MOTOR CONTROL SYSTEM.
Components of somatic motor control system.
Skeletal muscles: the effector organ.
Reflexes. Regulation of posture
& equilibrium.
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COMPONENTS OF SOMATIC MOTOR CONTROL SYSTEM.
Highest level of motor control. Middle level of motor control. Lowest level of motor control.
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HIGHEST LEVEL OF MOTOR CONTROL.
Cerebral cortex. Motor cortex. Descending motor
pathways from motor cortex.
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CEREBRAL CORTEXMOTOR CORTEX.
Areas of motor cortex. Primary motor cortex
(4) – Frontal lobe within pre-central gyrus.
Premotor cortex 6,8,44,45
Supplementary motor cortex – Medial surface behind Primary Motor Area.
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FUNCTIONAL ROLE OF MOTOR CORTEX.
Primary motor cortex 4 – execution of movements
Premotor cortex- 6 – Proximal & axial movements & skill 8 – Coordination of eye movements. 44,45 – Coordination of muscle of
speech. Head rotation,
Supplementary motor cortex – Responsible for generating idea for Movement. (With Cerebellum & BG)
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PLASTICITY PROPERTY OF MOTOR CORTEX
Motor cortex learns by doing.
Performance improves with Repetition.
Confirmed by PET scan & fMRI. Finger area enlargement
in Musician.
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TOPOGRAPHICAL REPRESENTATION OF MOTOR AREAS IN CORTEX
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MOTOR HOMONCULUS
DESCENDING MOTOR PATHWAYS FROM MOTOR CORTEX.
Pyramidal tracts Extra-pyramidal
tracts
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CRITERIA TO DESCRIBE TRACTS
Synonyms Origin Course Crossing Termination. Function. Applied physiology.
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PYRAMIDAL TRACTS Corticospinal tracts –
axons from cortex to spinal cord.
Origin – Primary Motor
Cortex(4) – 30% Premotor Area – 30% Somato-sensory Area –
40%
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COURSE & TERMINATION. From cortex descend as a
part of Corona Radiata – post limb if Internal Capsule – brain stem forms Pyramid in Medulla.
Then cross & forms 2 tracts Lateral corticospinal T. Anterior T.
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LATERAL CORTICOSPINAL TRACT
80% of fibers crossed to opp side.
Fibres descend terminate on internuncial neurons/ventral horn cells – forms UMN
From ventral horn cells to skeletal muscle – LMN.
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ANTERIOR CORTICOSPINALTRACT.
20% of uncrossed pyramidal fibres.
Descend in Ant white funiculus only up to MID-THORACIC Region.
Then in spinal cord crosses to opposite side & terminate on ventral horn cells.
Thus Cortex on one side connect to ventral horn cells on opposite side.
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SALIENT FEATURES. Fibres are Unmyelinated at
birth. Myelination begins in 2nd
postnatal week & completed by 2 years.
80% - Small & 20% Large diameter.
Large fibres disappears at old age causes Automatic shaking movements.
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FUNCTIONS. Control voluntary fine
skilled Movements. Closely packed in
Internal capsule & brain stem so small lesion causes wide Paralysis.
Send collateral to Basal ganglia, cerebellum. for coordination
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EXTRA-PYRAMIDAL TRACTS Remaining tracts other
than pyramidal. Rubro-spinal tract. Vestibulospinal tract. Reticulospinal tract. Tecto-spinal tract. Olivo-spinal tract. Medial longitudinal
fasciculus.
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RUBROSPINAL TRACT. Origin – Red Nucleus in
Midbrain. Course – From Red nucleus
crosses to opposite side in lower part of tegmentum & descend same as Lateral Corticospinal T.
Termination – Inter Neurons only up to upper 3 cervical segments of cord.
Function – Facilitatory effect on flexors & Inhibitory effect on extensors.
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VESTIBULOSPINAL TRACTLATERAL VESTIBULOSPINAL TRACT.
Origin – Lateral vestibular N(Deiter’s N)
Course – Uncrossed in Ant Funiculus of Spinal cord.
Termination – Ventral Grey horn neurons (VII,VIII) – through inter neurons to α & γ neurons of lamina IX.
Function – Receives from vestibular apparatus utricle, facilitate extensor, inhibit flexors & maintain Balance. (linear)
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MEDIAL VESTIBULOSPINAL TRACT
Origin – Medial Vestibular Nucleus.
Course – Uncrossed in ant funiculus.
Termination – Ant motor neurons or internuncial neurons of cervical segment.
Function- Afferents from Semicircular canal of vestibular apparatus , to Medial Longitudinal fasciculus control movements of Head, Neck, Eyes in response to Visual & Auditory stimuli.
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RETICULOSPINAL TRACT.Medial Reticulospinal Tract
Origin – Medial Pontine Reticular Formation.
Course – Descend Uncrossed in ant funiculus.
Termination – Laminae VII,VIII & through inter neurons to α & γ neurons of lamina IX.
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LATERAL RETICULOSPINAL TRACT.
Origin – Medullary Reticular Formation.
Course – Uncrossed in Lateral funiculus.
Termination – Internuncial Neurons of Laminae VII,VIII & IX.
Function – Control Movements & Muscle tone.
Pontine facilitate & medullary inhibit voluntary & Reflex Movements & Muscle tone.
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TECTOSPINAL TRACT. Origin – Superior Colliculi Course – Cross midline in lower
part of Tegmentum & Descend in Ant white funiculus
Termination – Upper cervical segment in internuncial neurons of Laminae V & VII.
Function – For Turning Head & moving arm in response to Visual, Hearing & other Exterioceptive stimuli.
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OLIVOSPINAL TRACT. Origin – Inferior
Olivary Nucleus. Course & Termination
– Descend ipsilateraly on ant horn cells
Function - Movements arising from Proprioceptors.
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MEDIAL LONGITUDINAL FASCICULUS. Origin – From various nuclei-
vestibular N, reticular formation, superior colliculus, interstitial N of cajal.
Course – Closely related to 3,4,6,7 & 12th cranial nerve along with Medial vestibulospinal tract.
Termination – Ventral horn cells that innervate Neck muscles.
Function – Simultaneous movements of Eye & Neck to Vestibular & Auditory stimuli.
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DESCENDING TRACTS ENDING IN BRAIN STEM
Cortico-Nuclear tracts. Cortico-Ponto-
cerebellar tracts. Cortico-Rubral. Cortico-olivary. Cortico-reticular.
All forms part of Extra-Pyramidal system.
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THANK YOU.