Lecture 3 Flashcards
What is the most common skin receptor?
Free nerve endings
What are sensory terminals on free nerve endings?
Small swellings at distal ends
What stimuli do free nerve ending mainly respond to?
Pain and temp
- some also respond to itch ( histamine)
- some wrap around hair follicles and act as light touch receptors and detect bending of hairs
What are tactile (Merkel) disks?
Free nerve endings located in the deepest layer of the epidermis associated with large disc shaped epidermal (Merkel) cells between which communication occurs via serotonin (5HT)
What skin receptors are abundant in fingertips
tactile (Merkel) disks
What size receptive fields do tactile (Merkel) disks?
Very small
Where are tactile corpuscles located?
IN the papillary layer of the der4mis especially in hairless thick skin
What are tactile corpuscles?
Spiralling/ branching unmyelinated sensory terminals surrounded by modified Schwann cells and then by a thin oval fibrous connective tissue capsule.
How are tactile corpuscles triggered?
Deformation of the capsule
What are tactile corpuscles sensitive to? (3)
Fine or discriminative touch
Shape and textural changes
Light pressure and low frequency vibration
Where are Lamellar corpuscles located?
Scattered deep in the dermis and hypodermis
What are lamellar corpuscles?
Single dendrites lying within concentric layers of collagen fibres and specialised fibroblasts. The layers are separated by gelatinous interstitial fluid
What are lamellar corpuscles sensitive to?
Deep pressure
Where are bulbous corpuscles located?
Dermis and subcutaneous tissue
What are bulbous corpuscles?
A network of nerve endings intertwined with a core of collagen fibres that are continuous with those of the surrounding dermis. A capsule surrounds the entire structure
What are bulbous corpuscles sensitive to?
Sustained deep pressure
Stretching or distortion of the skin
Where are bulbous corpuscles found not in skin?
joint capsules to signal degree of joint rotation( proprioception)
Where in the body is there a high density of bulbous corpuscles and why?
- around fingernails
- monitoring slippage of objects across surface skin
What are eccrine sweat glands triggered by?
Sympathetic nervous system- adrenaline
What are the skin responses when body temp increases?
- decreased SNS activation on skin blood vessels leads to vasodilation
- increased SNS cholinergic activation of sweat glands leads to sweating
- increased respiratory rate
- behavioural changes ( seek shade, drink water)
What are skin responses when body temp falls?
- central thermoreceptors detect temp below set point and activates heat gain centre
- increased generation of body heat by non shivering and shivering thermogenesis
- increased constriction of blood vessels in dermis
- countercurrent exchange
- infants can use brown fat to produce heat- bypassing ATP
What is shivering?
Involves increased tone of skeletal muscles. When tone rises above critical level, shivering begins due to oscillate contractions of agonist and antagonist muscles mediated by muscle spindles (stretch receptors)
What is non shivering thermogenesis?
Increased sympathetic nerve activity and increased circulating adrenaline/noradrenaline from adrenal medulla. Increased cellular metabolism
Name the three heat generation mechanisms?
- shivering
- non shivering thermogenesis
- thyroxine
What method is used to work out % of total body surface area involved in burns for fluid replacement?
Rule of 9s
What are the potential complications of severe burns?
- dehydration
- infection/ sepsis
- hypothermia
