Skin Physiology Flashcards
5 diff types of receptors
- Free nerve endings (superficial)
- Tactile discs
- Tactile corpuscles
- Lamellar corpuscles
- Bulbous corpuscles (deep)
What is a characteristic of the receptors?
They respond likely to all types of stimuli but are sensitive to a particular type
What are free nerve endings?
- Most common receptor in the skin
- Branches into the epidermis
- Mostly unmyelinated small diameter fibres but also some small diameter myelinated fibres
– Usually small swellings at distal ends = sensory terminals
What do the sensory terminals have?
Receptors eg thermo, chemo and noci that respond to the different types of stimuli
What kind of channels present at the sensory terminals? What do free nerve endings mostly respond to?
Mostly ion channels but can be chemically activated eg when bitten, mast cells degranulate –> histamine release. Responds to this
Peritrichal endings i.e where free nerve endings wrap around the hair follicle to help with sensation
What are tactile (merkel) discs?
- Free nerve endings located in the deeper layers of the epidermis
- Associated with an epidermal merkel disc that relays info to the free nerve ending via 5HT (serotonin neurotrans)
What is a merkel disc also called
Tactile epithelial cell
Where are merkel disc mostly found?
In the fingertips with small receptive fields eg good 2 pt discrimination
What does the merkel disc distinguish between?
Helps to distinguish:
* Fine touch and light pressure
* texture, shape and edges
Another name for tactile corpuscles
Meissner corpuscles
Where are the tactile corpuscles located?
In the papillary lary of the dermis, just below the epidermis
Where are the meissner corpuscles found?
Hairless skin eg In the soles of feet, eyelids, nipples, external genitalia, lips, finger pads
Structure of a meissner corpuscle
Encapsulated
* Spiralling / branching unmyelinated sensory terminals
surrounded by modified Schwann cells (that just support but don’t myelinate the axons) and then by a thin oval of fibrous connective tissue capsule
What does deformation of the capsule do?
- Triggers entry of Na+ ions into nerve terminal i.e mechanical gating»_space; Action Potential
What does the tactile corpuscles sense?
Delicate ‘fine’ or discriminative touch
– Sensitive to shape and textural changes in exploratory
touch e.g. reading Braille text.
– Movement of objects over the surface of the skin
* Light pressure
* Low frequency vibration (2 to 80 Hertz)
Another name for tactile corpuscles
Pacinian corpuscles
Where are the Pacinian corpuscles found?
– Scattered deep in dermis and hypodermis
Structure of a Pacinian corpuscle
– Single dendrite lying within concentric layers of collagen
fibres and specialized fibroblasts that secretes it.
– Layers separated by gelatinous interstitial fluid
– Dendrite essentially isolated from stimuli other than deep
pressure
What does deformation of the capsule do? Pacinian
Deformation of capsule opens pressure sensitive Na+ channels in
sensory axon through pressure wave through interstital fluid
* Inner layers covering axon terminal ‘relax’ quickly so APs discontinued
(rapidly adapting)
What does the tactile corpuscles sense?
– Stimulated by deep pressure (when first applied)
– Also vibration because rapidly adapting
* Optimal stimulation frequency is around 250Hz which is similar to
frequency range of generated upon fingertips by textures comprising
features < 1 μM eg sandpaper
Another name for Bulbous corpuscles
Ruffini’s
Where are the Bulbous corpuscles found?
Located in dermis and subcutaneous tissue
Also found in joint capsules where help signal degree of joint
rotation (proprioception)
* in fingers may have role monitoring slippage of objects
across surface skin and so modulate grip
What does deformation of the capsule do? Bulbous
Network of nerve endings intertwined with a core
of collagen fibres that are continuous with those of the
surrounding dermis. Capsule surrounds entire structure, when collagen distorted, the nerve endings are activated
What does the bulbous corpuscles sense?
- Sensitive to sustained deep pressure and stretching or
distortion of the skin
– Important for signaling continuous states of deformation of
the tissues such as heavy prolonged touch and pressure
signals
What extends from the subpap plexus?
Precapillary sphincters
What is the precap sphincters made of
Smooth muscle
What happens when the smooth muscle contracts?
The diameter reduces and the blood flow also reduces