Receptor is a specialized modified sensory nerve ending which undergoes depolarization in response to a specific stimulus and in turn sends information to the CNS.
It’s function is to act as a transducer to convert various forms of energy into electric energy in Neuron.
Each type of sensation (pain, touch, vibration etc) is called modality of sensation and the specificity of nerve fibre for transmitting only one modality of sensation is called labeled line principle and the impression of stimulus anywhere to brain is called law of projection.
Each receptor is differently sensitive to each sensory stimulus and thus insensitive to other
eg: rods and cones are sensitive to light but not to touch, temperature etc.
CLASSIFICATION OF SENSORY RECEPTORS:
A) Skin Tactile Sensibilities (epidermis & dermis)
I) free nerve ending
II) expanded tip endings – Merkel discs
III) spray endings
IV) ruffini endings
V) encapsulated endings – Meissner & Krause Corpuscle
VI) hair end organs
B) Deep Tissue Sensibilities
I) Free Nerve Endings
II) Expanded Tip Endings
III) Spray Endings : Ruffini Endings
IV) Encapsulated Ending: Pacinian Corpuscle
V) Muscle Endings : Muscle Spindle & Golgi Tendon
C) Hearing : Sound Receptors of Choclea
D) Equilibrium : Vestibular receptors
E) Arterial Pressure : Baroreceptors of Carotid Sinus & Aorta
Pain: Free Nerve Ending
Cold & Warm Receptors
Vision : Rods & Cones
A) Taste : Taste bud receptors
B) Smell : Receptors of Olfactory Epithelium
C) Arterial Oxygen : Receptors of Aortic & Carotid Bodies
D) Osmolality : Neuron in & around supraoptic nuclei
E) Blood CO2 : Receptors of medulla and in aortic and carotid bodies
F) Blood Glucose, amino acids, fatty acids : Hypothalamic receptors
TRANSMISSION OF SIGNALS OF DIFFERENT INTENSITIES
Increasing signal strength is transmitted by using greater number of fibres.
Increasing signal strength is transmitted by increasing the frequency of nerve impulse per fibre
*Merkel’s Dics & Meissner’s Corpuscle : perception of touch. Rapidly adapting thus clothes not felt.
*Pacinian Corpuscle : sustained touch & perception of pressure. Rapidly adapting thus we do not feel seat pressure when sitting.
*Ruffini’s Ending : sustained pressure.
*Krause’s Ending : Conjunctiva, papillae of lip and tongue, skin of genitalia.
*Naked Nerve Ending : Nociceptors
PROPERTIES OF RECEPTORS (SLIDE TO VIEW MORE›)
1) Specificity of Response or Law of Adequate Stimulus
The receptors respond maximally only when appropriate specific stimulus is applied and thus adapted to a certain modality of sensation.
eg : warm water stimulates Ruffini’s at low intensity but stimulate Naked Nerve Ending at higj stimulus causing pain.
when a stimulus of constant strength is applied to the reveptor, the frequency of action potential in the receptor decreases over time.
A) Tonic Receptors : slowly and incompletely adapting and thus continue to transmit information for many hours even if stimulus intensity remains constant over days. Eg: Baroreceptor, Chemoreceptor, Temperature Receptors
B) Phasic Receptors : rapidly adapting and respond only when stimulus is changed. Eg: Touch, OlfactorY
3) Law of Projection
No matter where a particular sensory pathway is stimulated along it’s course to the cortex, the conscious sensation produced is referred to location of receptor. Eg: In Phantom limb, pain is felt at the site of receptor.
4) Law of Intensity Discrimination
The brain interprets different intensities of a sensation based on
a) frequency of action potentials generated
b) no.of receptors activated
—Contributed by Dharmin Doshi (MIMER Medical College)