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Somatosensory Physiology Notes

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Lecture 11 Somatosensory Physiology- Peripheral terminations of non nociceptive DRG neurons

Somatosensory nervous system o Transmits all sensory (or afferent) neural info, excluding the special senses o Includes nerves sending info from
 Skin; Sensors in muscles and tendons; Sensors in visceral organs and tissues Non-nocicpetive cutaneous afferent fibre types o Glaborous skin
 Pacinian corpuscle

• Non hairy and hairy skin

• 1mm in length

• Fingers, toes, genitals

• 20-60 concentric lamellae of fibrous connective tissue/fibroblasts

• The lamellae are very thin, flat, modified Schwann cells

• Fluid-filled cavity with a single afferent unmyelinated nerve ending

• Detect tap and (particularly) vibration

• Very rapidly adapting low threshold mechanosensitive Abeta fibres
 Meissner's corpuscle

• Responsible for "light touch" and low frequency vibration

• Just below epidermis

• Rapidly adapting low threshold mechanoreceptor, Abeta fibres

• Not in hairy skin

• Unmyelinated endings enclosed in capsule

• Corpuscle=30-140micrometres length; 40-60micrometers diameter Composed of elastin attached to epidermis
 Merkel's cells

• Oval receptor ~10micrometres cells in skin and oral/rectal mucosa and mammary glands

• Synaptic contact with disc like terminal of SA1 low threshold mechanosensitive AB fibres (branch innervating up to 90 cells)

• Stratum basale of epidermis clustered in touch domes

• Light touch (Braille)

• Small receptive field

• Transmitter may be glutamate
 Ruffini end organ

• Slowly adapting mechanoreceptors in deep sites skin (hairy, glabous) & also in joints

• Monitor tissue stretch

• May also sense heat

• Innervated by single Abeta fibres which branch in corpuscle ending
 End-bulbs of Krause

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