Skin Physiology Flashcards
Outline skin receptors from superficial to deep
Free nerve endings
Tactile discs
Tactile corpuscles
Lamellar corpuscles
Bulbous corpuscles
Outline free nerve endings
- Mostly unmyelinated small diameter fibres but also some small diameter fibres.
- Usually small swellings at distal ends = sensory terminals
- Respond mainly to thermo, nociceptive, chemical, movement/pressure, itch (histamine), stimuli
- Some wrap around hair follicles (peritrichial endings) which detect bending of hairs
Outline free nerve ending sensory terminals
Sensory terminals have receptors that can respond to various nociception, thermal, and chemical stimuli
Some are cation channels (TRPV1 receptors), others are chemically activated H1 (histamine) receptors.
Activation leads to AP in afferent sensory axons, to CNS somatosensory cortex
Outline tactile (merkel) disks
- Free nerve endings located in deepest layers of epidermis
- Associated with large disc chapped epidermal (merkel) cells
- Abundant in fingertips, very small receptive field = good 2 point discrimination
- Sensitive to an objects physical features (find touch and light pressure, texture, shape, edges)
What allows communication between tactile epithelial cells and nerve endings
Serotonin 5HT
Outline tactile (meissner) corpuscles
- Located in papillary layer of dermis (especially hairless skin, lipids, eyelids, finger pads, external genitalia, soles of feet)
- Encapsulated
- Sense delicate fine or discriminative touch (sensitive to shape and textural changes, movement of objects over the skin). Light pressure, low frequency vibration (2-80 Hertz)
Outline the capsule of tactile (meissner) corpuscles
Spiralling/branching unmyelinated sensory terminals surrounded by modified Schwann cells and then by a thin oval fibrous connective tissue capsule (not wrapped around like myelin, only supportive role)
Deformation of capsule triggers entry of Na+ ions into nerve terminal leading to AP
Outline lamellar (pacinian) corpuscles
- Scattered deep in dermis and hypodermis
- Single dendrite lying within concentric layers of collagen fibres and specialised fibroblasts (layers separated by gelatinous interstitial fluid)
- Dendrite essentially isolated from stimuli other than deep pressure
- Deformation of capsule opens pressure sensitive Na+ channels in sensory axon
- Stimulated by deep pressure when first applied, as well as vibration
Outline how lamellar corpuscles are rapid adapting
Inner layers covering axon terminal relax quickly so AP discontinued
Optimal stimulation frequency is around 250Hz
Outline bulbous corpuscles
- Located in dermis and subcutaneous tissue
- Network nerve endings intertwined with core of collagen fibres surrounding dermis. Capsule surrounds entire section
- Sensitive to sustained deep pressure and stretching or distortion of skin
- Important for signalling continuous states of deformation of tissue (heavy prolonged pressure)
- Also found in join capsules where help signal degree of join rotation (proprioception)
- May monitor slippage of objects across surface skin = modulate grip
Outline smooth muscle in skin blood flow
Smooth muscle in walls of arteries and pre capillary sphincters innervated by the sympathetic nervous system release of noradrenaline/norepinephrine
Outline noradrenaline in terms of skin blood flow
Noradrenaline acts on alpha1 adrenergin receptors on vascular smooth muscle in the skin. GPCRs coupled to intracellular 2nd messenger - increased intracellular Ca+ - constriction - reduced skin blood flow. Reduced SNS activation of alpha1 receptors therefore causes relaxation (dilation) of arteries to skin - increased skin blood flow
What are the 4 primary mechanism of heat transfer
Radiation
Evaporation
Convection
Conduction
What mechanisms of heat transfer (cooling )do not work when temperature > body temp
Radiation, convection, conduction
Outline SNS activation of eccrine sweat glands
Innervated by sympathetic nervous system, releasing acetylcholine onto mAChR (G protein coupled receptor)
