Lecture 3: Skin Flashcards
What are Free Nerve Endings?
– small swellings at distal ends of axons = sensory terminals
- mostly unmyelinated (C fibers) but some small myelinated ones (As)
– Sensory Terminals have receptors that can respond tovarious painful (nociceptive), thermal and chemical stimuli.
- Some are chemically activated, some cation channels (both send signals to somato)
Where are Tactile (Merkel) discs located?
Free nerve endings located in deepest layerof epidermis
What do Merkel discs detect?
Sensitive to:
• touch and light pressure
• texture, shape and edges
• Low frequency vibration (5-15 Hz)
How do Merkel discs communicate?
Seratonin:
– Associated with large disc shaped epidermal (Merkel) cells
• Communication between the tactile epithelial cell and nerve ending possible via serotonin (5HT)
Where are Tactile (Meissner) Corpuscles located?
– Located in papillary layer of dermis, Especially in hairless skin
What are Tactile (Meissner) Corpuscles?
(Encapsulated)
• Spiralling / branching unmyelinated sensory terminals surrounded by modified Schwann cells and then by a thin oval fibrous connective tissue capsule
• Deformation of capsule triggers entry of Na+ ions into nerveterminal»_space; Action Potential
What do Tactile (Meissner) Corpuscles detect?
Delicate ‘fine’ or discriminative touch eg. braille reading
– Movement of objects over the surface of the skin
• Light pressure
• Low frequency vibration (most sensitive 10 to 50 Hertz)
Where are Lamellar (Pacinian) corpuscles found?
Found deep in dermis and hypodermis
What do Lamellar (Pacinian) corpuscles detect?
Stimulated by deep pressure (when first applied)
Also vibration because rapidly adapting. Optimal stimulation frequency is around 250Hz
What are Lamellar (Pacinian) corpuscles?
- Single sensory axon terminal lying within concentric layers of collagen fibres and specialized fibroblasts.
- Layers separated by gelatinous interstitial fluid
- isolated from stimulation apart from deep pressure (Na+ channels) rapidly adapting
Where are Bulbous (Ruffini) corpuscles located?
Located in dermis and subcutaneous tissue
What do Bulbous (Ruffini) corpuscles detect?
- Sensitive to sustained deep pressure and stretching or distortion of the skin
- Found in joints (proprioception)
- Slippage of objects in hands
What are Bulbous (Ruffini) corpuscles?
- Network of nerve endings intertwined with a coreof collagen fibres.
- continuous with those of the surrounding dermis.
- Capsule surrounds entire structure
How do we control Skin Bloodflow?
- Smooth muscle in walls of arteries and pre-capillary sphincters innervated by the sympathetic nervous system (SNS)
- Noradrenaline acts on α1 adrenergic receptors on this vascular smooth muscle in the skin
- Activation of a1 adrenergic receptors = vasoconstriction so less blood flow and vice versa
Eccrine sweat glands are innervated by?
- sympathetic nervous system - Sympathetic cholinergic i.e. release ACh ontomAChRs (GPCRs)
- Some eccrine sweat glands can also be stimulated by Adrenaline in blood acting on β receptors – (nervous sweating)
