Lecture 3- Skin Physiology Flashcards
Skin Physiology
What are the skin receptors?
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Free Nerve Endings Tactile Discs Tactile (Meissner) Corpuscles Lamellar (Pacinian) Corpuscles Bulbous (Ruffini) Corpuscles
What are Free Nerve endings?
Most common receptor in the skin.
Sensory axon branches and the terminals extends into epidermis.
Sensory terminals have receptors eg TRPV1 (cation channel).
What do receptors (TRPV1) do when the nerve terminal is stimulated (free nerve endings receptors)?
Receptors act as an ion channel and can open and allow cations (sodium and calcium) to come into the sensory terminal, depolarise it and action potentials can be conducted up to the somatosensory cortex, and become aware of the sensation.
what do free nerve endings consist of (2 categories)?
C fibres - small diametre and unmyelinated (conducts slowly 2ms-1)
Aδ (A delta) - slightly larger and myelinated (conduct impulses quicker 5-30ms-1)
Free nerve endings - RESPONDS TO
Temperature (hot / cold)
Painful stimulus
some movement and pressure
Histamine receptors - Itch (mosquito)
Peritrichial endings
Tactile (Merkel) discs (location, Abundant in)
Stratum basale epidermis
Fingertips and very small receptive fields. good for 2 point discrimination.
Peritrichial ending
nerve ending Wrapped around Hair follicles acts as
light touch receptors which detect bending of hairs eg when mosquito lands on skin.
Tactile (Merkel) discs responds to
objects physical features
texture, shape, edges
fine touch and light pressure
Tactile (merkel) discs are associated with large disc shaped…
Epidermal (merkel) cells, where communication between the tactile epithelial cell and nerve ending possibly serotonergic (5HT)
Tactile (Meissner) Corpuscles location (incl examples)
Papillary layer of dermis
Hairless skin, finger pads, eyelids, lips, external genitalia, sole of feet, nipples
Tactile (Meissner) Corpuscles structure (myelinated?, capsule, ions, what does deformation of capsule trigger?)
- Spiralling / branching unmyelinated sensory terminals surrounded by schwann cells and by a thin oval fibrous connective tissue capsule.
- Deformation of capsule triggers entry of Na+ ions in nerve terminal, releases APs
Tactile (Meissner) Corpuscles responds to
- Delicate fine, discriminative touch.
eg Shape & textural changes, reading braille text.
Movement of objects over surface of skin. - Light pressure
- Low frequency vibration (2 - 80 Hertz)
Lamellar (Pacinian) Corpuscles location
Scattered deep in dermis and Hypodermis (can be found in waide variety of other organs)
Lamellar (Pacinian) Corpuscles structure
Single dendrite lying within concentric layers of collagen fibres and fibroblasts
- Layers separated by Interstitial fluid (Gelatinous)
- Dendrite isolated from stimuli other deep pressure
Lamellar (Pacinian) Corpuscles - Deformation of capsule opens…
pressure sensitive Na+ channels in axon
- Inner layers covering axon terminal ‘relax’ quickly so APs discontinued.
Lamellar (Pacinian) Corpuscles responds to
- Deep pressure (1st applied)
- Vibration
(Optimal stimulation frequency is 250Hz which is similar to frequency range of fingertips by textures comprising features < 1 μM
Bulbous corpuscles (Ruffini’s endings) Location
Dermis and Hypodermis tissue.
Found in joint capsules to signal degree of joint rotation.
High density around fingernails to monitor grip.
Similar to Golgi Tendon Organs.
Bulbous corpuscles (Ruffini’s endings) structure
Network of dendrites intertwined with a core of collagen fibres that are continuous with those of the surrounding dermis.
Capsule surrounds entire structure.
Bulbous corpuscles responds to
Sustained deep pressure and stretching / distortion of the skin.
- signal continuous states of deformation of tissues.
Monitor grip.
- monitor slippage of objects across surface of skin.
Eccrine sweat glands
- Supplied by Sympathetic Nervous system. Sympathetic cholinergic ie release ACh onto mAChRs
- Stimulated by Adrenaline on β receptors eg nervous sweating on palms and soles (Axilla)
When body temperature increases..
If blood temp goes above set point heat loss centre is activated.
Vasodilation
- decrease SNS activation of α1 on skin blood vessels.
Sweating
- increase cholinergic activation of mAChRs on sweat glands
Behavioural changes
- increase respratory rate
what are not effective heat loss mechanisms when environmental temp > body temp
Radiation, conduction, convection
Central thermoreceptors
The Preoptic area of hypothalamus that contains heat and cold sensitive neurons
Central Thermoreceptors detects
Temperature below set point which activates the heat gain centre
Heat generating mechanisms
Shivering
Non Shivering thermogenesis
Increase Thyroxine
Shivering
due to oscillatory contractions of agonist and antagonist muscles mediated by muscle spindles (stretch receptors).
Heat generating mechanisms.
Increase tone of skeletal muscle.
Non shivering thermogenesis
Increase sympathetic nerve activity & increase Adrenaline / noradrenaline from adrenal medulla.
Increase cellular metabolism eg increase glycogenolysis in liver & muscle.
Uncoupling of oxidative phosphorylation ie heat produced instead of ATP (occurs in brown fat in infants).
Heat generating mechanism.
Increase Thyroxine
Response to TRH & TSH.
Increase basal metabolic rate.
In adults take several weeks exposure to cold before thyroid reaches new level of thyroxine secretion.
Arrector Pili muscles
Attach hair follicle to upper dermis.
Smooth muscle stimulated by SNS (α1 receptors).
Contraction pulls hairs uprights and dimples skin (goosebumps).
Compresses sebaceous glands (lubricates skin).
physiological feed forward.
Arrector pili muscles
Hairy mammal
Traps layer of warm air around skin, makes you look bigger scarier and more formidable.
Physiological feed forward.
Type of burns
1st degree
2nd degree partial
2nd degree full
3rd degree
First degree burn
layers of skin, effects, heal time
Superficial, epidermis outer layer.
Red/pink dry painful.
No blisters eg sunburn
Skin remains a water & bacterial barrier
3 - 10 days
2nd degree partial thickness
layers of skin, effects, heal time, remedies
Epidermis + bit of Dermis.
Painful, moist (keratin layer removed), red & blistered.
1 - 2 weeks.
Good dressings (absorptive initially).
2nd degree full thickness
layers of skin, effects, heal time
epidermis + dermis.
mottled pink, red, waxy white areas with blisters; edema.
Hair follicles; sweat glands may remain intact.
Loss sensation (Tactile receptors lost).
1 month
loss sensation and scarring.
3rd degree burn
Epidermis, Dermis, Hypodermis, bit of bone.
Waxy white to deep red or black.
Hard dry & leathery.
No pain in areas as sensory nerve endings destroyed.
cms of skin graft
weeks to regenerate + scarring
Potential complications of burns
dehydration & hypovolemic shock
infection / sepsis
hypothermia
hyperkalmia (increase ECF K+)
hypermetabolism
- cortisol, catecholamines, increased thermogenesis.
Gastrointestinal Stress ulcers (curling ulcers)
- stress, cortisol, gastric ischemia.
respiratory dysfunction
renal failure
- hypotension, rhabdomyolysis
Nerve free endings respond to Painful stimulus -
Pain receptors in skin
Sharp pain conducted by? -
Dull aching persistent pain conducted by?
Aδ myelinated fibres eg needle prick
unmyelinated C fibres
