Dermis 3 Flashcards
What are the types of receptors
Free nerve endings Tactile (merkel) discs Tactile (meissner) corpuscles Lamellar (pacinian) corpuscles Bulbus (ruffini) corpuscles
Describe free nerve endings
Can be un/myelinated.
Small swellings at distal end (receptors) that have receptors that function as cation channels.
What do free nerve endings mainly respond to
Temperature
Painful stimuli (myelinated initial sharp pain unmyelinated slower aching pain)
Itch (chemical - histamine)
Light touch receptors (peritrichial - around hair follicles)
Describe Tactile (Merkel) discs
Free nerve endings in deepest layer of epidermis.
Associated with large disc shaped (Merkel) cells
Very small receptive fields - abundant in fingertips
What do Tactile (Merkel) discs mainly respond to
Sensitive physical features; Texture, shape and edges
Fine touch and light pressure
Describe Tactile (Meissner) corpuscles
Papillary layers of dermis (hairless skin)
Modified Schwann cells (not myelin forming) surrounded by a thin fibrous connective tissue capsule - deformation triggers Na+ channels
What do Tactile (Meissner) corpuscles mainly respond to
Delicate ‘fine’ or discriminative touch - shape/textural changes
Light pressures
Low frequency vibrations (2-80 Hz)
Describe Lamellar (Pacinian) corpuscles
Deep in dermis and hypodermis
Single dendrite surrounded by concentric layers of collagen fibres and fibroblasts
Layers separated by gelatinous interstitial fluid
Deformation opens Na+ channels - rapidly adapting
What do Lamellar (Pacinian) corpuscles mainly respond to
Deep pressure (when first applied) Vibration - as rapidly adapting (250Hz optimal)
Describe Bulbous (Ruffini) corpuscles
Dermis and subcutaneous tissue
Network of nerve endings intertwined with core of collagen fibres (continuous with dermis) - capsule surrounds structure
What do Bulbous (Ruffini) corpuscles mainly respond to
Deep pressure and stretching or distortion points of the skin
Signals continuous states of deformation - heavy prolonged touch and pressure
Degree of joint rotation (Proprioception)
Finger nails - slippage/grip
How is blood flow controlled
Precapillary sphincter muscles around artery controlled by sympathetic nervous system
How does the sympathetic nervous system effect blood flow
Noradrenaline - GPCRs coupled to receptors (2nd messenger system) opens Ca+ channels and constricts blood vessels lowering blood flow to dermis layer of skin
What does changing blood flow do
Helps control thermoregulation and blood pressure
What are the forms of thermoregulation
Radiation
Conduction
Convection
Evaporation
Describe radiation
Anything not at absolute 0 looses heat. When an object is colder than it’s surroundings it can gain heat from them
Describe conduction
When in contact with object or air/water. Gradient for heat exchange - Heat moves from higher to lower. When there is no gradient there is no loss of heat
Describe Convection
Transfer of heat to air/water. When we heat a layer around our skin and it moves we will then loose more heat heating up the next layer and it continues
Describe evaporation
Heat loss - Best when external temperature is high. Loose the heat required to evaporate the water from our skin. In hot climates this is our only way of loosing heat.
How do sweat glands work during thermoregulation
Sympathetic nervous system - ACh neurotransmitter
Some Beta receptors can also be activated by adrenaline (Why we sweat when nervous and excited)
How do we detect a change in core body temp
Central thermoreceptors - In Preoptic area of Hypothalamus
What happens when body temp goes above ‘set point’
Vasodilation - Reduce sympathetic nerve stimulation
Sweating - Increase SNS activity on sweat glands
Behavioural changes - Increased respiratory rate (Increases air flow and evaporation)
How can we use our blood vessels to increase body temp
Counter current exchange - Warm blood from arteries transfers heat to cold blood from vein
Increases SNS to constrict blood flow to dermis
How does shivering help increase body temp
Shivering - Increase tone of skeletal muscle , creating oscillatory contractions of agonist/antagonist (Mediated by stretch receptors
What are the other non-shivering ways of increasing body temp
Increase SN activity and increase circulating adrenaline/noradrenaline
Increased cellular metabolism
‘Uncoupling’ of oxidative phosphorylation - produce heat instead of ATP (Adipose tissue - lypolysis)
How does thyroxin help increase the bodies temp
Increase BMR which increases heat
May take several weeks exposure to cold before thyroxin secretion levels increase
Describe the arrector pili muscles
Smooth muscle
Controlled by SNS (alpha 1 receptors)
Attaches hair follicle to upper dermis
What does the arrector pili muscle do
When contacted pulls hair upright and dimples skin (Goosebumps)
Compresses sebaceous glands (lubricate skin)
Example of physiological feed forward - skin detects temp and sends message to hypothalamus causing a shiver and activating pili (before core body temp changes)
Describe characteristics of a 1st degree burn
Superficial - outer layers of epidermis
Red/pink, dry, painful
Skin remains water and bacterial barrier
(e.g. mild sunburn)
Describe characteristics of a 2nd degree burn
Epidermis & varying amounts of dermis
Red, Painful, moist and blistered
Deeper: Whiteish waxy looking areas. Some tactile receptors may be lost. Loss of Waterproof effect and damage to blood vessels.
Dressing needed to treat
Describe characteristics of a 3rd degree burn
Full thickness (into subcutaneous tissue - may involve muscle and bone)
Waxy white to deep red or black
Hard, dry, leathery
No pain as sensory nerve endings destroyed
Loss of Waterproof effect and damage to blood vessels
Often skin grafting required to treat
