This document provides an overview of the somatic motor control system. It discusses the three tiers that control somatic motor activity, with the highest level being the cerebral cortex, middle level for supervision, and lower level for execution. The key components discussed include the motor cortex and descending motor pathways from the cortex, including the pyramidal and extrapyramidal tracts. The document also examines the skeletal muscle as the effector organ and discusses reflexes, regulation of posture and equilibrium, and the role of sensory receptors in providing feedback to adjust motor commands.

1. DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
DEPT. OF PHYSIOLOGY
MOTOR
SYSTEM

2. 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.
Monday, May 16, 2016

3. 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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4. INTRODUCTION.
 Lower Motor Neuron
& Final Common
Pathway – Alpha
motor neuron &
Motor nuclei of
cranial nerves.
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5. 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.
Monday, May 16, 2016

6. 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.
Monday, May 16, 2016

7. 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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8. ROLE OF SENSORY RECEPTORS IN
MOTOR CONTROL ACTIVITY.
 Proprioceptors in skin,
Muscle & joints gives
feedback
&
 Adjust Motor
commands.
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9. 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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10. 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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11. HIGHEST LEVEL OF MOTOR
CONTROL.
 Cerebral cortex.
 Motor cortex.
 Descending motor
pathways from motor
cortex.
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12. CEREBRAL CORTEX
MOTOR 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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13. 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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14. 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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15. TOPOGRAPHICAL REPRESENTATION
OF MOTOR AREAS IN CORTEX
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MOTOR HOMONCULUS

16. DESCENDING MOTOR PATHWAYS
FROM MOTOR CORTEX.
 Pyramidal tracts
 Extra-pyramidal
tracts
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17. CRITERIA TO DESCRIBE
TRACTS
 Synonyms
 Origin
 Course
 Crossing
 Termination.
 Function.
 Applied physiology.
Monday, May 16, 2016

18. 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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19. 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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20. 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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21. 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.
Monday, May 16, 2016

22. 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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23. 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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24. EXTRA-PYRAMIDAL TRACTS
 Remaining tracts other
than pyramidal.
 Rubro-spinal tract.
 Vestibulospinal tract.
 Reticulospinal tract.
 Tecto-spinal tract.
 Olivo-spinal tract.
 Medial longitudinal
fasciculus.
Monday, May 16, 2016

25. 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.
Monday, May 16, 2016

26. VESTIBULOSPINAL TRACT
LATERAL 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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27. 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.
Monday, May 16, 2016

28. 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.
Monday, May 16, 2016

29. 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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30. 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.
Monday, May 16, 2016

31. OLIVOSPINAL TRACT.
 Origin – Inferior
Olivary Nucleus.
 Course & Termination
– Descend ipsilateraly
on ant horn cells
 Function - Movements
arising from
Proprioceptors.
Monday, May 16, 2016

32. 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.
Monday, May 16, 2016

33. 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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34. Monday, May 16, 2016
THANK YOU.