Receptor and types of receptor

Receptors are sensory (afferent) nerve endings that terminate in periphery as bare unmyelinated endings or in the form of specialized capsulated structures. Receptors give response to the stimulus. When stimulated, receptors produce a series of impulses, which are transmitted through the afferent nerves.

Receptor and types of receptor


Biological Transducers

Actually receptors function like a transducer. Transducer is a device, which converts one form of energy into another. So, receptors ae often defined as the biological transducers, which convert (transducer) various forms of energy (stimuli) in the environment into action potentials in nerve fiber.

CLASSIFICATION OF RECEPTORS

Generally, receptors are classified into two types:

A. Exteroceptors

B. Interoceptors

EXTEROCEPTORS

Exteroceptors are the receptors, which give response to stimuli arising from outside the body.

Exteroceptors are divided into three groups:

1. Cutaneous Receptors or Mechanoreceptors

Receptors situated in the skin are called the cutaneous receptors. Cutaneous receptors are also called mechanoreceptors because of their response to mechanical stimuli such as touch, pressure and pain. Touch and pressure receptors give response to vibration also.

2. Chemoreceptors

Receptors, which give response to chemical stimuli, are called the chemoreceptors.

3. Telereceptors

Telereceptors are the receptors that give response to stimuli arising away from the body. These receptors are also called the distance receptors.

INTEROCEPTORS

Interoceptors are the receptors, which give response to stimuli arising from within the body.

 Interoceptors are of two types which are as follows:

1. Visceroceptors

Receptors situated in the viscera are called visceroceptors.

2. Proprioceptors

Proprioceptors are the receptors, which give response to change in the position of different parts of the body.

PROPERTIES OF RECEPTORS

1. SPECIFICITY OF RESPONSE – MÜLLER LAW

Specificity of response or Müller law refers to the response given by a particular type of receptor to a

specific sensation. For example, pain receptors give response only to pain sensation. Similarly, temperature receptors give response only to temperature sensation. In addition, each type of sensation depends upon the part of the brain in which its fibers terminate. Specificity of response is also called Müller’s doc

2. ADAPTATION – SENSORY ADAPTATION

Adaptation is the decline in discharge of sensory impulses when a receptor is stimulated continuously

with constant strength. It is also called sensory adaptation or desensitization.

Depending upon adaptation time, receptors are divided into two types:

i. Phasic receptors, which get adapted rapidly. Touch and pressure receptors are the phasic

receptors

ii. Tonic receptors, which adapt slowly. Muscle spindle, pain receptors and cold receptors are

the tonic receptors.

3. RESPONSE TO INCREASE IN STRENGTH OF STIMULUS – WEBERFECHNER

LAW

During the stimulation of a receptor, if the response given by the receptor is to be doubled, the strength of stimulus must be increased 100 times. This phenomenon is called WeberFechner law, which states that intensity of response (sensation) of a receptor is directly proportional to logarithmic increase in the intensity of stimulus.

Derivation of Weber-Fechner Law

WeberFechner

law is derived as follows:

R = k log S

Where,

R = Intensity of response (sensation)

k = Constant

S = Intensity of stimulus

4. SENSORY TRANSDUCTION

Sensory transduction in a receptor is a process by which the energy (stimulus) in the environment is converted into electrical impulses (action potentials) in nerve fiber (transduction = conversion of one form of energy into another). When a receptor is stimulated, it gives response by sending information about the stimulus to CNS. Series of events occur to carry out this function such as the development of receptor potential in the receptor cell and development of action potential in the sensory nerve. Sensory transduction varies depending upon the type of receptor. For example, the chemoreceptor converts chemical energy into action potential in the sensory nerve fiber. Touch receptor converts mechanical energy into action potential in the sensory nerve fiber.

5. RECEPTOR POTENTIAL

Definition

Receptor potential is a nonpropagated transmembrane potential difference that develops when a receptor is stimulated. It is also called generator potential. Receptor potential is short lived and hence, it is called transient receptor potential. Receptor potential is not action potential. It is a graded potential. It is similar to excitatory postsynaptic potential (EPSP) in synapse, endplate potential in neuromuscular junction and electrotonic potential in the nerve fiber.

 

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