VPB 121: Veterinary Physiology - II (2+1)

CUTANEOUS RECEPTORS

• These receptors mediate sensation of touch, light, pressure, heat, and cold.
• These consist of lamellated connective tissue capsule that surrounds soft core where the axon ends.
• Pain sensations are mediated through the fine free nerve ending.

Expanded tip receptor	Free nerve endings	Krause corpsucle	Meissners corpuscle
Pacinian corpuscle	Ruffinis end organ	Tactile hair	Markel's disc

• Sensing light touch 
  • Mediated by Meissner’s corpuscles, Merkel’s disc and basket arrangement of nerve fibers at the base of the hair follicle.
• Meissner’s corpuscles 
  • Located in the skin papillae beneath the epidermis. It has irregularly coiled nerve endings with capsules of connective tissue. The density of distribution is uneven.
• Merkel’s discs
  • Associated with enlarged epidermal cell with small receptive field. It has group of 3 or more cup shaped discs. The discs have reticulated appearance. Nerve fibre branch out and supplies to each disc.  They are found in the snout of pig and other mammals. They are used for fine tactile discrimination. They are slowly adaptive tonic receptors.
• Basket arrangement of nerve fibers or Root Hair Plexus 
  • Most sensitive. They are located at the base of the hair follicle as wrappings and monitor movement across the body surface. It has short vertical nerve filaments that ends in bulged portions and gets stimulated by slight movement of hair. They adapt rapidly and are phasic receptors. Displacement of hair causes movement of hair follicle. This causes stretching of the sensory nerve ending and stimulates mechanoceptor protein stretch on the dendritic membrane.
• Touch receptors 
  • Mediates through 3 qualities.
    • Tactile localization.
    • Tactile discrimination-Recognition of two different stimuli simultaneously
    • Stereognosis-Recognition of stimuli by touch without visual assistance.
• Pacinian corpuscles 
  • Located in the deep layers of the skin, subcutaneous tissue, periosteum, muscle, tendon, joints, and blood vessels respond to stimuli of unequal firm, deep pressure.  They have lamellated appearance similar to the cross section of an onion.  They help out in recognizing the location of the stimulus with high degree of accuracy (Tactile localization). It mediates pressure sensation and they adapt quickly.