Working of SenSory receptorS
• a stimulus is some form of energy : light, sound,
pressure, heat, osmotic potential, electric current, and
chemical changes.
• Each type of receptor is sensitive to a specific stimulus
and almost non-responsive to other stimuli. Over
stimulation of any receptor is painful and virtually all
receptor types function as nocireceptors at one time
or another e.g., searing heat, extreme cold, excessive
pressure and chemicals released at sites of inflammation
are all interpreted as painful stimuli.
• an animal responds to a stimulus in a four-step
process:
(i) Sensory transduction : Sensory receptors transduce
(transform) the energy of a stimulus into a localized
nonpropagated electrical response or generator
potential which initiates nerve impulses in the neuron
leaving the receptor.
(ii) Transmission : The sensory neuron relays the nerve
impulse to the brain directly or through the spinal cord.
(iii) Integration : Nerve impulses (action potentials, ften
called receptor or generator potentials) that reach the
brain via sensory neurons are termed sensations. In
the brain, the sensations are analysed and interpreted
as perceptions. Thalamus is the main, and cerebral
cortex is the subsidiary centre of this analysis. The brain
transmits motor impulses to appropriate effectors-
muscles or glands.
(iv) Response : Effectors produce suitable responses.
muscles contract, or glands secrete chemicals, in
response to the information sent to the brain by the
receptors.
claSSification
• receptors are classified under two major divisions of
sensory system. These are :
(i) General sensory system : comprises of receptors in
the skin, joints, skeletal muscles and internal organs.
(ii) Special sensory system : comprises of receptors
present in highly complex organs like eye, ear, nose and
tongue.
classification of receptors according to
their location
exteroceptors
• Exteroceptors are usually located near the surface
of the body, and they detect changes in the external
environment.
• receptors for touch, heat, cold, light and sound are
examples of exteroceptors.
• Bare nerve endings in the skin that detect pain are
also exteroceptors.interoceptors
• They are sensory receptors which receive stimuli from
the inner parts, tissue or cells.
• They are of two subtypes:
(i) proprioceptors
• The proprioceptors are located in the skeletal muscles,
joints, tendons, etc.
• They given information about movement and position
of body. Two types of muscle receptors are muscle
spindle and Golgi tendon organ.
(ii) Visceroceptors
• Visceroceptors are located in the viscera.
• They are affected by stimuli originating within the body
itself and cause sensations, such as pain, hunger, thirst,
fatigue, nausea, sex, etc.
• They also monitor blood pressure, carbon dioxide level,
body temperature, osmotic relationships, ph, etc.
• The visceroceptors are simple and mostly consist of free
nerve endings.classification of receptors according to
their function
• Teloceptors : They are sensitive to changes occurring
at a distance, e.g., ear, eye.
• Nociceptors : They are receptors sensitive to deep
pain and damage to tissue.
• Proprioceptors : Sensitive to changes in tendons,
muscles and joint movements.
• Labyrinthine receptors : Sensitive to the different
positions of body in space.