RECEPTORS : The neuron fibers and cell bodies can be excited by small electric shocks, mechanical, chemical, light and temperature stimuli. Receptors detect changes in the external and internal environment of the animal.
The receptor may be a cell. Or neuron ending or a receptor organ.
Classification of receptors :The shape of receptor depends upon the sort of environmental modification or energy thereto the receptor is incredibly responsive.
Receptors are classified into following categories :
- Chemoreceptors : chemo receptors are for smell, taste, and for blood CO2, blood oxygen, blood glucose, amino acids and fatty acids (receptors in the hypothalamus).
- Mechanoreceptors: These receptors detect stimuli of touch (free nerve endings, expended tip ending and stray endings). Pressure and hearing and equilibrium.
- Photoreceptors: They are also called electromagnetic receptors. These respond to stimuli of light, for example rods and cones in eyes.
- Thermoreceptors: thermoreceptors show response to temperature changes, I.e cold and warmth.
- Nociceptors: these are actually undifferentiated and naked nerve endings, which produce the sensation of pain.
MODALITIES OF SENSATIONS :
Each type of the principal type of sensation that we can experience, for example, pain, touch, sight, sound and so forth is called modality of sensation.
Yet despite the fact that we experience these different modalities of sensation, nerve fibers transmit only impulses.
Different nerve fiber transmits different modalities of sensation.
- Each nerve transmits at a selected purpose within the CNS; and also the variety of sensation is decided by the purpose within the system nervous to that the fiber leads.
So touch stimulus is carried by nerve impulse in the ‘touch’ area of the brain. Similarly, fibers from retina terminate in the retina area.
- More over each receptor organ is specialized to receive a particular type of stimulus and this is carried to the particular area of the brain.
There are many receptors which respond to the mechanical conditions of the internal organs. Examples are :
- The receptors of the stomach wall, which may be concerned with arousal of ‘hunger’.
- Stretch receptors within the arteria and arteries of tetrapods have necessary roles within the regulation of pressure.
- Endings with similar properties are found in the bronchial vessels of fishes
SENSORY RECEPTORS OF SKIN :
The receptors in skin are concerned with at least five different senses I.e. touch, pressure, heat, cold, and pain.
Types of sensory endings in skin : There are at least 3 different types of sensory endings in the skin, which are involved in touch stimulus reception.
- Situated at the base of hairs (hair end organs) receive touch stimulus.
- Meissner’s corpuscles (encapsulated endings) which lie in papillae which extend into the ridges of the fingertips. The corpuscle consists of spinal and much twisted endings, each of which ends in a knob. These are touch receptors.
- Pacinian corpuscle- situated quite deep in the body. These are also encapsulated neuron endings and receive deep pressure stimulus. Those located in the limbs probably form a basis for vibration sense.
Transmission of impulses:
The intensity of information received would either be transmitted within the type of recurrent impulses or a lot of fibers carrying the impulse to central nervous system.
Number of receptors :
The relative abundance of various types of receptors differs greatly.
For example : pain receptors are nearly 10 times more abundant than cold receptors.
The cold receptors are nearly 10 times more abundant than heat or temperature receptors.
Distribution of receptors :
The receptors are not distributed evenly over the entire surface of the body e.g. touch receptors are much more numerous in the finger tips than in the skin of the back, as might b expected in view of the normal functions of those two parts of the body.
Pathway of nerve impulse :
The information received by the receptors within the skin that area unit the endings of sensors is passed to the motor neurons via inhume or associative neurons that area unit gift within the brain and via neural structure and impulse is shipped by the motor neurons to the effectors, that area unit muscles and glands.