sensation is very good, because we percive a pain, hot, cold, etc sensation to our CNS parts for integration and giving a proper response.

1. 1-12-2019

2. SOMATOSENSORY SYSTEM:

3. • Somatosensory system is defined as the sensory
system associated with different parts of the body.
• Sensations are of two types:
1. Somatic sensations: (skin, muscles, tendons and
joints - specific receptors).
2. Special sensations: (vision, hearing, taste and smell
- specialized sense organs)
• Generally, somatic sensations are classified into
three types:
1. Epicritic sensations.
2. Protopathic sensations.
3. Deep sensations.

4. Classification of sensations

5. Synthetic Senses:
• Synthetic senses: are the sensations synthesized
at cortical level, by integration of impulses of
basic sensations.
• Two or more basic sensations are combined in
some of the synthetic senses.
• Best examples of synthetic senses are:
1. Vibratory sensation.
2. Stereognosis.
3. Two-point discrimination.

6. Vibratory sensation
Stereognosis
Two-point discrimination

7. SENSORY PATHWAYS:
• Sensory pathways: is a nervous pathways of sensations.
• Sensory pathways carry the impulses from receptors in
different parts of the body to centers in brain.
• Sensory pathways are of two types:
1. Pathways of somatosensory system:
• Convey the information from sensory receptors in skin,
skeletal muscles and joints.
• Pathways of this system are constituted by somatic nerve
fibers called somatic afferent nerve fibers.
2. Pathways of viscerosensory system:
• Convey the information from receptors of the viscera.
• Pathways of this system are constituted by visceral or
autonomic fibers.

8. Somatosensory Pathways:
• Each sensory pathway is constituted by two or
three groups of neurons:
i. First order neurons.
ii. Second order neurons.
iii. Third order neurons.
• For ex: Pathways of some sensations like
kinesthetic sensation have only first and
second order neurons.

10. SENSORY FIBERS OF TRIGEMINAL
NERVE:
• Trigeminal nerve carries somatosensory
information from face, teeth, periodontal
tissues (tissues around teeth), oral cavity,
nasal cavity, cranial dura mater and major
part of scalp to sensory cortex.
• It also conveys proprioceptive impulses from
the extrinsic muscles of the eyeball.

12. LEMNISCUS:
• Lemniscus or fillet is the prominent bundle of sensory
nerves in brain.
• Lemniscus is of four types:
1. Spinal lemniscus formed by spinothalamic tracts in
medulla oblongata
2. Lateral lemniscus formed by the fibers carrying sensation
of hearing from cochlear nuclei to inferior colliculus and
medial geniculate body
3. Medial lemniscus formed by fibers arising from nucleus
cuneatus and nucleus gracilis
4. Trigeminal lemniscus formed by fibers from sensory nuclei
of trigeminal nerve. This lemniscus carries general senses
from head, neck, face, mouth, eyeballs and ears.

14. SOMATOMOTOR SYSTEM:

15. • 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.

16. • 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.

17. • 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.

18. • 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.

19. 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.

20. 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.

21. 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.
• About 30% of the fibers forming corticospinal and
corticobulbar tracts take their origin from primary and
supplementary motor cortex, 30% from premotor area and
remaining 40% from parietal lobe particularly from
somatosensory area.

22. 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.

23. 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.

24. 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

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