The somatomotor system is organized in a 3-tier hierarchical system, with the highest level in the cerebral cortex, middle level in subcortical structures like the basal ganglia and cerebellum, and lowest level in the spinal cord and brainstem. The motor cortex plans voluntary movements and issues commands to the spinal cord via pyramidal tracts. Basal ganglia and cerebellum help coordinate skilled movements and maintain posture and tone. Spinal motor neurons innervate skeletal muscles to enable movement. Proprioceptive feedback integrates signals across these levels of the motor system.

1. SOMATOMOTOR SYSTEM:

2. • Motor activities of the body depend upon
different groups of tissues of the body.
• Motor activities are divided into two types:
1. Activities of skeletal muscles, which are
involved in posture and movement
2. Activities of smooth muscles, cardiac
muscles and other tissues, which are involved
in the functions of various visceral organs.

3. • Various types of movements or motor activities brought
about by these muscles are:
1. Execution of smooth, precise and accurate voluntary
movements.
2. Coordination of movements responsible for skilled
activities.
3. Coordination of movements responsible for the
maintenance of posture and equilibrium.
• Somatomotor system responsible for voluntary actions and
postural movements, plus adjustments of muscle tone.
• Sensory system of the body also plays a vital role in the
control of movements.
• Spinal reflexes are responsible for most of the movements
concerned with voluntary actions and posture.

4. • Stimulation of receptor activates the motor neuron
in spinal cord, leading to the contraction of muscle
innervated by spinal motor neuron.
• Apart from these reflexes, signals for voluntary
motor activities are also sent from different areas of
the brain, particularly the cerebral cortex to spinal
motor neurons.
• Coordination and control of movements initiated
by cerebral cortex depends upon two factors:
1. Feedback signals from proprioceptors in muscle
and other sensory receptors
2. Interaction of other parts of brain such as
brainstem, cerebellum and basal ganglia.

5. • The motor system includes:
a) Spinal cord and its nerves,
b) Cranial nerves,
c) Brainstem,
d) Cerebral cortex,
e) Cerebellum,
f) Basal ganglia.
• Neuronal circuits between these parts of nervous
system, which are responsible for the motor
activities are called the motor pathways.

6. Cortex
lower motoneurons
basal ganglia
CEREBELLUM
brainstem
thalamus
pyramidal
extrapyramidal

7. • SOMATIC MOTOR SYSTEM IS ORGANISED IN 3 TIER SYSTEM
• Highest level of motor control
• Middle level
• Lowest level of motor control

8. • Highest level of motor control = involves activities of various areas of
cereberal cortex
• Concerned with ideas for generating voluntary movements(motor plan)
and issuing motor command for execution
• Middle level of motor control= involves activities of various subcortical
cortical centres=
• Basal ganglion. Brain stem nuclei, Cerebellum,
• Lowest level of motor control = is exerted by cranial nerve nuclei in brain
stem and spinal cord
• Spinal cord contains a final common pathway through which a movement
is executed

9. SPINAL CORD AND CRANIAL
NERVE NUCLEI
• Motor Neurons:
• Spinal nerve:
1. Alpha motor neurons (lower motor neuron) or ‘final common
pathway’ in the spinal cord, which innervate the extrafusal
fibers of skeletal muscles are responsible for the contraction
of muscles in upper limbs, trunk and lower part of the body.
2. Gamma motor neurons, which innervate the intrafusal fibers
of muscle, are responsible for the maintenance of muscle
tone.
• Cranial nerve nuclei:
• Motor neurons of the cranial nerve nuclei situated in
brainstem send their signals to the muscles of neck and upper
part of trunk via cranial nerves.

10. Functions of Motor Neurons:
• Motor neurons responsible for the contraction of
skeletal muscles are arranged topographically in
the ventral (anterior) gray horn of spinal cord.

11. CEREBRAL CORTEX:
• Cortical areas concerned with origin of motor signals are:
1. Primary motor area.
2. Premotor area.
3. Supplementary motor area in frontal lobe.
4. Sensory area in the parietal lobe.
• Cortical areas send their output signals to spinal cord via
corticospinal tracts and to brainstem via corticobulbar
tracts.

12. CEREBELLUM:
• Cerebellum plays an important role in planning,
programming and integrating the skilled voluntary
movements.
• It is also concerned with the maintenance of muscle tone,
posture and equilibrium.
• Cerebellum receives impulses from:
A) Proprioceptors of muscle.
B) Vestibular apparatus.
C) Cerebral cortex.
D) Brainstem.
E) Basal ganglia.
• It interprets these impulses and sends signals to motor
cortex, reticular formation and nuclei of brainstem.

14. The reticular formation
is a complex network
of brainstem nuclei
and neurons that serve
as a major integration
and relay center for
many vital brain
systems to coordinate
functions necessary for
survival.

15. BASAL GANGLIA:
• Basal ganglia play an important role in the:
1. Coordination of skilled movements
2. Regulation of automatic associated
movements
3. Control of muscle tone by sending output
signals to motor cortex, reticular formation
and spinal cord.

16. CLASSIFICATION OF MOTOR
PATHWAYS:
• There are two methods to classify the motor
pathways.
1- In the first method of classification motor pathways
are divided into:
A. Pyramidal tract: (voluntary movements)
B. Extrapyramidal tracts: (regulation of tone, posture
and equilibrium)
2- In the second method, motor pathways are
classified into:
A. Lateral motor system
B. Medial motor systems

17. Functions of lateral motor
system: Functions of medial motor
system: