Lecture 3: Skin

Question 1

What are Free Nerve Endings?

Answer 1

– 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)

Question 2

Where are Tactile (Merkel) discs located?

Answer 2

Free nerve endings located in deepest layerof epidermis

Question 3

What do Tactile (Merkel) discs detect?

Answer 3

Sensitive to:
* touch and light pressure
* texture, shape and edges
* Low frequency vibration (5-15 Hz)

Question 4

How do Tactile (Merkel) discs communicate?

Answer 4

Seratonin:
– Associated with large disc shaped epidermal (Merkel) cells
* Communication between the tactile epithelial cell and nerve ending possible via serotonin (5HT)

Question 5

Where are Tactile (Meissner) Corpuscles located?

Answer 5

– Located in papillary layer of dermis, Especially in hairless skin

Question 6

What are Tactile (Meissner) Corpuscles?

Answer 6

(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&raquo_space; Action Potential

Question 7

What do Tactile (Meissner) Corpuscles detect?

Answer 7

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)

Question 8

Where are Lamellar (Pacinian) corpuscles found?

Answer 8

Found deep in dermis and hypodermis

Question 9

What do Lamellar (Pacinian) corpuscles detect?

Answer 9

Stimulated by deep pressure (when first applied)
Also vibration because rapidly adapting. Optimal stimulation frequency is around 250Hz

Question 10

What are Lamellar (Pacinian) corpuscles?

Answer 10

• 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

Question 11

Where are Bulbous (Ruffini) corpuscles located?

Answer 11

Located in dermis and subcutaneous tissue

Question 12

What do Bulbous (Ruffini) corpuscles detect?

Answer 12

• Sensitive to sustained deep pressure and stretching or distortion of the skin
• Found in joints (proprioception)
• Slippage of objects in hands

Question 13

What are Bulbous (Ruffini) corpuscles?

Answer 13

• Network of nerve endings intertwined with a coreof collagen fibres.
• continuous with those of the surrounding dermis.
• Capsule surrounds entire structure

Question 14

How do we control Skin Bloodflow?

Answer 14

• 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

Question 15

Eccrine sweat glands are innervated by?

Answer 15

• sympathetic nervous system - Sympathetic cholinergic i.e. release ACh onto mAChRs (GPCRs)
• Some eccrine sweat glands can also be stimulated by Adrenaline in blood acting on β receptors – (nervous sweating)

Question 16

What happens when body temprature increases?

Answer 16

• Preoptic area of hypothalamus contains heat and cold sensitive neurons (central thermoreceptors)
• If too hot, decreased SNS a1 activation of blood vessels (vasodilation) (more skin bloodflow)
• Increased SNS cholinergic activation of mAChRs on sweat glands -> sweating
• respiratory rate increases and also -behavioural changes

Question 17

What are the three Heat Generating Mechanisms?

Answer 17

• Shivering
• Non-Shivering Thermogenesis (adrenaline and fat burn)
• Thyroxine (increases basal metabolic rate)

Question 18

What is shivering?

Answer 18

– Oscillatory contractions of agonist and antagonist muscle
– ATP → ADP + Pi + movement + heat

Question 19

What are Arrector Pili muscles and what do they do?

Answer 19

• Smooth muscle innervated bySNS (α1 receptors)
• Attach hair follicle to upperdermis
• Contraction pulls hairs upright and dimples skin > goosebumps (insulation)
• Also compresses sebaceous glands which lubricates skin

Question 20

Rule of 9’s

Answer 20

Head = 9%
Upper limb = 9%
Trunk = 36%
Genitalia = 1%
Lower limbs = 18%

Question 21

Potential Complications of Severe Burns

Answer 21

• Dehydration and hypovolemic shock
• Infection / Sepsis
  -Hypothermia