Sensory system carries the sensations from all parts of the body to the brain.
Any sensation is first detected by the receptors in the form of its stimulation.
Receptors transmit the information in the form of impulse to the spinal cord.
The ascending tracts present in the spinal cord carry the information to the brain relaying in the thalamus
From the thalamus the information is projected to the sensory cortex, area number 3, 2, 1
Understanding the meaning of sensation is called perception.
Perception is the function of neural processing of sensory information by the brain.
Sensory unit
A single afferent neuron with all its receptors is known as sensory unit.
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| Sensory unit |
Sensory receptors
They are modified nerve endings capable of converting different forms of energy into nerve impulse.
The sensory receptors are classified as
- Exteroceptors
- Interoceptros
- Telereceptors
- Proprioceptors
1) Exteroceptors
- They are capable of detecting any change in the external environment. Eg: Touch receptors, Pain receptors.
2) Interoceptors
- They are capable of detecting any change in the internal environment. Eg: Baroreceptors, Chemoreceptors.
3) Telereceptors
- They are capable of detecting any change in the environment from a distance. Eg: Receptors for Vision, Hearing.
4) Proprioceptors
- They are capable of detecting any change in the position of different parts of the body in space. Eg: Muscle spindle, Glogi apparatus
The sensory receptors can also be classified according to the type of sensations they subserve as
- Receptors for General sensations
- Receptors for Special sensation
1) Receptors for General sensations
- For touch and pressure
- Rapidly adapting: Meissner’s corpuscles and Pacinian corpuscles
- Slow adapting: Merkel’s disc
- For Pain
- Free nerve endings
- For Temperature: Rufini’s end organ
- For Joint sense
- Muscle length: Muscle spindle
- Muscle tension: Golgi tendon organ
Receptors for Special sensations
- For vision: Rods & Cones
- For Hearing: Hairs cells of organ of corti
- For Taste: Taste receptor cells of taste buds
- For smell: Olfactory neurons
- For Linear and rotational acceleration: Hair cells of vestibular apparatus
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Sensory Homunculus
The representation of the body in the sensory cortex is called sensory homunculus
The body is represented upside down in the sensory cortex
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| Sensory homunculus |
The representation is contralateral that means the right hemisphere of the cerebral cortex receive sensory information from left side of the body and the left hemisphere of the cerebral cortex receive sensory information from the right side of the body
However the face is represented bilaterally
The parts which are involved in fine movements such as hand and finger have larger area of representation.
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