Skin Physiology

types of receptors in skin

free nerve endings (+tactile discs), corpuscles (tactile, lamellar, bulbous)

free nerve endings description

most common, terminals have ion channels and GPCRs

free nerve endings

root hair plexus

different TRPs detect…

different temperature ranges

tactile merkel discs

tactile meissner corpuscles

lamellar pacinian corpuscles

bulbous ruffini corpuscles

tactile discs description

specialised nerve endings associated tactile merkel cells in stratum basale

triggering action potentials in tactile merkel discs

mechanical stimulus opens piezo2 receptors in tactile cell
ions move into cell, causing release of neurotransmitters that depolarise nerve

tactile meissner corpuscles description

branched axon surrounded by specialised schwann cells inside connective tissue capsule

triggering action potentials in tactile meissner corpuscles

deformation of capsule triggers APs in axon

lamellar pacinian corpuscles description

single axon surrounded by layers of collagen, fibroblasts and schwann cells separated by gelatinous fluid

triggering action potentials in lamellar pacinian corpuscles

pressure/vibration transmitted through layers to axon, regaining shape quickly

A-delta fibres vs. C-fibres

A-delta = small diameter, myelinated, sharp fast pain
C = medium diameter, unmyelinated, dull aching pain

bulbous ruffini corpuscles description

branched axon intertwined with collagen fibres continuous with collagen of dermis surrounded by flattened capsule

triggering action potentials in bulbous ruffini corpuscles

force of stretching collagen transmitted to axon triggering AP

what do free nerve endings detect?

temperature, itching, pain, light touch

what do tactile merkel cells detect?

shape, edges, 5-15Hz vibration

what do tactile meissner corpuscles detect?

two point discrimination, light pressure, 10-50hz vibration

what do lamellar pacinian corpuscles detect?

deep pressure, vibration

what do bulbous ruffini corpuscles detect?

stretching in collagen (prorioception), deep pressure

where are tactile merkel discs most commonly found?

fingertips — have small receptive fields

where are tatile meissner corpuscles most commonly found (type of skin + layer of skin)

glabrous/hairless skin, papillary layer of dermis

what layers are lamellar corpuscles found in?

deep dermis and hypodermis

where are bulbous ruffini corpuscles most commonly found (skin type + layer + function)

deep dermis and hypodermis
fingertips (detect slippage) and joint capsules (proprioception)

how does sympathetic nervous system affect precapillary sphincters

release noradrenaline → alpha-1 adrenergic receptors on smooth muscle → vasoconstriction

how does sympathetic nervous system affect eccrine sweat glands?

particular nerves release acetylcholine → cholinergic mAchRs → sweating

what type of receptor are mAchRs?

muscarinic GPCRs

mechanisms of body temperature DECREASE

vasodilation, sweating, increased respiratory rate, behaviour

mechanisms of body temp increase (CONSERVATION)

vasoconstriction, counter-current exchange, goosebumps

mechanisms of body temp increase (GENERATION)

shivering, increased metabolism (adrenal medulla), brown fat cells burning stored energy, increased BMR (thyroxine)