Receptors

RECEPTORS Definition- A specialized sensory nerve ending which undergoes depolarization in response to specific stimulus. FUNCTION Transmission of sensory nerve impulses to the CNS. CLASSIFICATION 1. Special sensory receptors located in CNS. specialized for type of sensory stimulating eg vision, olfactory 2. Cutaneous receptors- touch, pain, pressure, temperature 3. Deep receptors - joints, muscles, tendons 4. Viscera- from organs CUTANEOUS RECEPTORS Three types 1) MECHANO RECEPTORS 2) THERMO RECEPTORS 3) PAIN RECEPTORS MECHANO RECPTORS 1. Merkels disc- Receptors concerned with touch perception. They form expanded tips and encapsulated endings respectively on sensory nerve terminals of Aβ and δ fibers. 2. Pacinian corpuscles- They are nerve endings of Aβ fibers and are concerned with pressure. 3. Ruffini end organs- They are endings of myelinated Aδ or unmyelinated C fibers and concerned with warmth perception. 4. Krause end bulbs - Conjunctiva, lips, tongue, eyelids 5. Naked nerve endings—they are endings of myelinated Aδ fibers and concerned with perception of pain /noxious stimuli.

THERMO RECEPTORS SiteChest, nose, nipples, abdomen, anterior surface of arm Divided into z Cold receptors z Warm receptors They are terminals of myelinated A fibers and unmyelinated C fibers.

PAIN RECEPTORS Receptors concerned with pain. They are located at endings of small C unmyelinated and A δ myelinated fibers

PROPERTIES 1. 2. 3. 4. 5.

Adequate stimulus law Adaption law Muller doctrine of special nerve endings Law of projection Law of intensity discrimination

Multiple Choice Questions: 1. Synaptic cleft is a) Space between pre and post synaptic membrane b) Terminal end of presynaptic membrane c) Surface of cell membrane involved in synapse d) All of the above 2. All are properties of synapse except a) One way conduction b) Synaptic delay c) Synaptic fatigue d) Synaptic cleft

3. Ruffini end organs concerned with a) Pressure b) Warmth c) Touch d) Two point discrimination 4. Spinothalamic tract does not contains fibers for a) Touch b) Pressure c) Pain d) Two point discrimination 5. Pain stimulus carried by a) A delta and C fibers b) A delta and B fibers c) A alpha and B fibers d) B and C fibers 6. First order neurons are a) Afferent neurons b) Inter neurons c) Carry information between the neurons d) All of the above 7. Inhibitory transmitter at synapse is a) Ach b) GABA c) Dopamine d) Nicotine 8. True of Chemical synapse is a) Synaptic delay absent b) Synaptic cleft absent c) Insensitive to hypoxia

d) Can transmit signal in either directions 9. EPSP is due to a) Opening of Na+/ Ca+ channels b) Opening of K+ channels c) Closing of Na+ channels d) Closing of Ca+ channels 10. Tactile receptors include a) Ruffini end organs b) Pacinian Corpuscles c) Merkels discs d) Meissners nerve endings