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The organs which give a response to external and internal stimuli are known as –
A. Chemoreceptors
B. Receptors
C. Photoreceptors
D. Tactile receptors

Last updated date: 13th Jun 2024
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Hint:A stimulus is an event that invokes a reaction in the body. The stimuli can be chemical or mechanical. Such is the variation of receptors that varied types of stimuli can be perceived.

Complete answer: The stimuli in our body are received by receptors. These receptors, then, transmit the signal via sensory neurons to the CNS. Then, the CNS processes the signal and gives an appropriate reaction by sending a response signal through a motor neuron to the required appropriate effector muscle or effector organ.
1) Internal stimuli include –
Homeostatic imbalances – Homeostatic imbalances are the main driving factors for changes in the body. These are monitored closely by receptors and sensors in different parts of our body. These sensors are –
Mechanoreceptors – respond to pressure. Eg. – Baroreceptors, Merkel’s discs
Chemoreceptors – respond to chemical changes
Thermoreceptors – respond to temperature changes.
Homeostatic imbalances which may serve as internal stimuli are nutrient and ion concentrations in the blood, oxygen levels, and water levels.
Blood pressure – Blood pressure, heart rate, and cardiac output are measured by stretch receptors in the carotid arteries. If the nerves do not detect stretching, the body determines and perceives low blood pressure as a dangerous stimulus, and signals are not sent, thus preventing the inhibition of CNS action, the blood vessels constrict, and heart rate increases, causing an increase in blood pressure of the body.
2) External stimuli include –
Touch and pain – Sensory feelings, especially pain, are stimuli that can produce a large response and cause neurological changes in the body.
Vision – Vision provides an opportunity for the brain to perceive and respond to the changes which occur around the body.
Smell – Smell allows our body to recognize chemical molecules in the air through inhalation.
Taste – Taste records flavors of food and other materials that touch the tongue and pass through the mouth. Gustatory cells are located on the tongue’s surface and the adjacent portions of the pharynx and larynx.
Sound – Changes in the pressure caused by sound reaching the external ear resonate in the tympanum. It articulates with the auditory ossicles,i.e., the bones of the middle ear.
Equilibrium – Semicircular ducts, connected directly to the cochlea, can interpret and convey information about equilibrium to the brain by a similar method as that used for hearing.

So, the answer is option B.

Note: The response to all stimuli are processed by the CNS. The CNS acts as a processing center. All messages are processed either by the spinal cord or by the brain.