Lecture 3 Flashcards
what do free nerve endings mainly respond to
- temperature
- pain
- some movement and pressure
- some to itch
- some wrap around hair follicles acting as light touch receptors
what is the most common receptor type in the skin?
free nerve endings
what fibres make up free nerve endings?
mostly unmyelinated small diameter fibres but also some small diameter myelinated fibres
what are tactile (merkel) discs?
free nerve endings located in the deepest layer of the epidermis
where are tactile (merkel) discs abundant?
in fingertips and very small receptor fields
what are tactile (merkel) discs sensitive to?
an objects physical features = fine touch, light pressure, texture, shape and edges
where are tactile (meissner) corpuscles found?
papillary layer of the dermis, especially in hairless skin
are tactile corpuscles encapsulated or not
yes they are encapsulated
- deformation of capsule triggers entry of Na+ ions into the nerve terminal = action potential
what do tactile corpuscles sense?
- delicate “fine” or discriminative touch, sensitive to shape and textural changes in exploratory touch
- light pressure
- low frequency vibration
where are lamellar (pacinian) corpuscles found?
scattered deep in the dermis and hypodermis
what are the features of lamellar corpuscles?
what does deformation of capsule cause?
- single dendrite lying within concentric layers of collagen
- layers separated by gelatinous interstitial fluid
- dendrite essentially isolated from other stimuli other than deep pressure
- deformation of capsule opens pressure sensitive Na+ channels in sensory axon
what stimulates lamellar corpuscles?
deep pressure (when first applied) and vibration (because rapidly adapting)
where are bulbous corpuscles found?
the dermis and subcutaneous tissue
also found in joint capsules where help signal degree of joint rotation
features of bulbous corpuscles
network of nerve endings intertwined with a core of collagen fibres that are continuous with those of the surrounding dermis
what are bulbous corpuscles sensitive to?
sustained deep pressure and stretching or distortion of skin
what does the sympathetic nervous system stimulate to control skin blood flow?
smooth muscle in the walls of arteries and pre capillary sphincters
what does noradrenaline act on in controlling skin blood flow?
a1 adrenergic receptors on the vascular smooth muscle in the skin
how does reduced skin blood flow occur?
- GPCRS coupled to intracellular 2nd messengers
= increased intracellular Ca2+
= increased interaction of actin and myosin
= increased contraction
= increased constriction
therefore reduced skin blood flow
how does increased skin blood flow occur
- reducing SNS activation of a1 receptors
= causes relaxation (dilation) of arteries to skin
therefore increased skin blood flow
what stimulates the eccrine sweat glands and what neurotransmitter chemical is used
sympathetic nervous system but uses Ach instead of NE (different to most SNS)
what are the basic mechanisms of heat transfer
- radiation
- evaporation
- convention
- conduction
what is radiation and what objects radiate?
causes heat loss in the form of infrared rays
any objects that aren’t absolute zero temp will radiate these rays
what is evaporation and how does it cause heat change?
heat energy is lost when water evaporates from the body surface as energy is needed to do so
what is convention and what does it maintain?
transfer of heat to air or water by conduction following the movement of air or water
- this maintains the gradient for heat loss from the body
what is conduction
involves the transfer of heat with objects in which we contact
- significant amount conducted to air
normal body temp range?
36.5-37.5 degrees
what happens when body temperature increases?
- preoptic area of hypothalamus detects heat change which causes:
- decreased SNS activation of a1 on skin blood vessels = vasodilation
- increased SNS cholinergic activation of mAChRs on sweat glands = sweating
- increased respiratory rate
what happens when body temperature falls?
central thermorecptors detect temp below set point which activates the heat gain centre - this responds in two ways
- increased generation of body heat (non shivering and shivering thermogenesis)
- conservation of body heat (vasomotor centre decreases blood flow to dermis = reducing loss by radiation and convention)
what is shivering heat convention?
- as we get colder muscle tone increases
what is non-shivering heat convention?
producing heat by other mechanisms other than shivering
- increased sympathetic nerve activity + increased circulating adrenaline
- increased cellular metabolism
