lecture 3 - skin physiology

Question 1

What is the most common type of receptor in the skin?

Answer 1

Free nerve endings

Question 2

Are the majority of free nerve endings in the skin myelinated or unmyelinated?

Answer 2

Majority unmyelinated with small diameter

Question 3

What is the name for a small swelling at the distal end of a free nerve ending?

Answer 3

Sensory terminal

Question 4

What is the sensory terminal of a free nerve ending?

Answer 4

A swelling at the distal end that acts as a receptor with cation channels

Question 5

How do free nerve endings generate nerve signals?

Answer 5

They have cation channels that when opened lead to a local depolarisation and subsequent action potential.

Question 6

What stimuli do free nerve endings predominantly respond to?

Answer 6

Temperature, pain, some movement/pressure, itch,

Question 7

How do free nerve endings detect itchiness?

Answer 7

They responded to histamines

Question 8

How do free nerve endings detect light touch from hairs bending?

Answer 8

Nerve endings wrap around hair follicles.

Question 9

What is the name for a free nerve ending that wraps around a hair follicle to detect bending of the hair?

Answer 9

Peritrichial ending

Question 10

What are the 5 types of touch receptors on the skin?

Answer 10

Free nerve endings, Tactile (Merkel) discs, tactile (Meissen) corpuscles, lamella (pacinian) corpuscles. bulbous corpuscles (Ruffini’s endings)

Question 11

What is the alternative name for tactile discs?

Answer 11

Merkel discs

Question 12

Where are tactile/merkel discs found?

Answer 12

Free nerve endings located in deepest layer of the epidermis

Question 13

What are merkel cells?

Answer 13

Large disc shaped epidermal cells involved in sensory perception of tactile discs

Question 14

How do merkel cells communicate?

Answer 14

Via serotonin (5HT) neurotransmitters

Question 15

Where are tactile/merkel discs most abundant, and how does this reflect their function?

Answer 15

In fingertips and small receptive fields, as they are good for 2 point discrimination.

Question 16

What are tactile/merkel discs sensitive to?

Answer 16

An object’s physical features: texture, shape, edges. Fine touch and light pressure

Question 17

What is the alternative name for tactile corpuscles?

Answer 17

Meissner corpuscles

Question 18

Where are tactile/meissner corpuscles located?

Answer 18

In the papillary layer of the dermis, especially in hairless skin (finger pads, lips, eyelids, external genitalia, soles of feet, nipples)

Question 19

What is the structure of a tactile/meissner corpuscle?

Answer 19

Spiralling/branching unmyelinated sensory terminals surrounded by modified schwann cells then by a thin oval capsule of fibrous connective tissue.

Question 20

Are the sensory terminals of tactile/meissner corpuscles myelinated or unmyelinated?

Answer 20

Unmyelinated - but they are surrounded by modified schwann cells

Question 21

How are action potentials generated by tactile/meissner corpuscles?

Answer 21

Deformation of the capsule triggers entry of Na+ into a nerve terminal, triggering an action potential.

Question 22

What type of sensation are tactile/meissner corpuscles used for?

Answer 22

Fine, discriminative touch. Sensitive to shape and texture. used for exploratory touch, e.g. braille. Detect light pressure and low frequency vibration (2-80 Hz)

Question 23

What frequency range of vibration can be detected by tactile/meissner corpuscles?

Answer 23

2 to 80 hertz

Question 24

What is the alternative term for lamellar corpuscles?

Answer 24

Pacinian corpuscles

Question 25

Where are lamellar/pacinian corpuscles located?

Answer 25

Scattered deep in the dermis and hypodermis

Question 26

What is the structure of a lamellar/pacinian corpuscle?

Answer 26

Single dendrite lying within concentric layers of collagen fibres and specialised fibroblasts, with layers separated by gelatinous interstitial fluid

Question 27

What are the layers of collagen and fibroblasts of a lamellar/pacinian corpuscle separated by?

Answer 27

Gelatinous interstitial fluid

Question 28

Why are lamellar/pacinian corpuscles only activated by deep pressure?

Answer 28

They are located deep in the skin, and the dendrites is isolated from light pressure by the collagen capsule.

Question 29

How are lamellar/pacinian corpuscles rapidly adapting?

Answer 29

Inner layers of the capsule that cover the axon terminal ‘relax’ quickly so that Action Potenials are discontinued.

Question 30

What is the optimal stimulation frequency of a lamellar/pacinian corpuscle?

Answer 30

approximately 250Hz.

Question 31

The optimal stimulation frequency (250Hz) of lamellar/pacinian corpuscles is generated by fingertip interaction with features of what size?

Answer 31

less than 1 micrometer

Question 32

What is the alternative name for bulbous corpuscles?

Answer 32

Ruffini’s endings

Question 33

Where are bulbous corpuscles located?

Answer 33

The dermis and subcutaneous tissue (hypodermis)

Question 34

What is the structure of bulbous corpuscles?

Answer 34

Network of nerve endings that are continuous with those of the surrounding dermis. Surrounded by collagen capsule that transmits distortion

Question 35

What stimulation are bulbous corpuscles sensitive to?

Answer 35

Sustained deep pressure, stretching/distortion of the skin - prolonged touch

Question 36

What type of touch receptor is found within the joint capsule and is responsible for proprioception of joint rotation?

Answer 36

Bulbous corpuscles/Ruffini’s endings

Question 37

What is the role of bulbous corpuscles in joint capsules?

Answer 37

Help in proprioception - signal the degree at which a joint has rotated

Question 38

Why is there a high density of bulbous corpuscles around the fingernails?

Answer 38

Monitoring of slippage of objects and modulation of grip.

Question 39

How is blood flow to the skin mechanically regulated?

Answer 39

Smooth muscles in walls of arteries and pre-capillary sphincters are contracted/relaxed via innervation by the sympathetic nervous system

Question 40

What neurotransmitter is involved with triggering vascular smooth muscle contractions in the skin to regulate blood flow?

Answer 40

Noradrenaline, which acts on a1 (alpha 1) adrenergic receptors on the vascular smooth muscle in the skin

Question 41

What receptors does noradrenaline act on to produce contraction of vascular smooth muscle in the skin?

Answer 41

a1 (alpha 1) adrenergic receptors

Question 42

What is the process of vascular smooth muscle contraction, after a neurotransmitter signal have been received?

Answer 42

GPCRs (G-protein coupled receptors) are coupled to intracellular 2nd messengers, leading to an increase in intracellualr Ca2+, thereby facilitating contraction/vasoconstriction

Question 43

How is vasodilation facilitated by the skin, in terms of negative feedback?

Answer 43

Reduced sympathetic nervous system activity reduces contraction of vascular smooth muscle in the skin, increasing skin blood flow.

Question 44

What are the 2 key factors influenced by skin blood flow?

Answer 44

Thermoregulation, blood pressure

Question 45

What are the 4 heat transfer mechanisms?

Answer 45

Radiation, evaporation, convection, conduction

Question 46

What is conduction, in terms of body temperature regulation?

Answer 46

The transfer of heat between a hot/cold object and the skin

Question 47

What is evaporation, in terms of body temperature regulation?

Answer 47

Transfer of heat from skin to water, allowing it to evaporate. e.g. sweating

Question 48

What is convection, in terms of body temperature regulation?

Answer 48

Transfer of heat from skin to the surrounding air. The warmed air rises away from the skin and is replaced by cool air which is in turn warmed.

Question 49

What is radiation, in terms of body temperature regulation?

Answer 49

Transfer of heat to or from the body via infrared radiation

Question 50

How are eccrine sweat glands predominantly controlled?

Answer 50

They are innervated by the sympathetic nervous system

Question 51

What type of synapses do eccrine sweat glands receive?

Answer 51

Sympathetic cholinergic

Question 52

How do sympathetic cholinergic synapses trigger eccrine sweat glands?

Answer 52

Acetylcholine (ACh) is released onto mACHRs (muscarinic acetylcholine receptors)/GPCRs in the cell membrane.

Question 53

How are eccrine sweat glands triggered hormonally?

Answer 53

Some glands can be stimulated by adrenaline in the blood, which acts on beta receptors causing ‘nervous sweating’

Question 54

What causes ‘nervous sweating’?

Answer 54

Adrenaline in blood acting on beta receptors on eccrine sweat glands

Question 55

Where does ‘nervous sweating’ usually occur on the body?

Answer 55

Palms and soles, axilla (armpit)

Question 56

What is the axilla?

Answer 56

The armpit

Question 57

What part of the brain detects body temperature?

Answer 57

The pre optic area of the hypothalamus, which contains central thermoreceptors

Question 58

What are mAChRs?

Answer 58

muscarinic acetylcholine receptors

Question 59

What are GPCRs?

Answer 59

G protein coupled receptors

Question 60

What are central thermoreceptors?

Answer 60

Heat and cold sensitive neurons found in the pre optic area of the hypothalamus

Question 61

How is the body’s heat loss centre activated?

Answer 61

If the hypothalamus detects the blood temperature exceeding the set point

Question 62

When the heat loss centre is activated, what happens to the skin blood flow?

Answer 62

Less SNS activation of alpha 1 receptors on skin blood vessels leads to vasodilation

Question 63

When the heat loss centre is activated, what happens to sweat production?

Answer 63

Increased SNS cholinergic activation of mAChRs on eccrine sweat glands.

Question 64

What happens to respiratory rate when the heat loss centre is activated?

Answer 64

Increased respiratory rate

Question 65

What mechanisms are activated by the heat loss centre (4)?

Answer 65

Vasodilation, sweating, increased respiratory rate, behavioural changes

Question 66

What activates the heat gain centre?

Answer 66

Central thermoreceptors detect blood temperature going below set point, and activate the hypothalamus

Question 67

What are key heat generation mechanisms (3)?

Answer 67

Shivering, non-shivering thermogenesis, increased thyroxine release

Question 68

How is shivering initiated?

Answer 68

Skeletal muscle tone is increases until it rises above a critical level, causing oscillatory contractions of agonist and antagonist muscles mediated by muscle spindles/stretch receptors

Question 69

What is non-shivering thermogenesis?

Answer 69

Increased sympathetic nerve activity, releasing noradrenaline/adrenaline from the adrenal medulla to increase cellular metabolism

Question 70

What cellular processes does non-shivering thermogenesis induce?

Answer 70

Increased cellular metabolism - e.g. glyocgenolyis in liver and muscle.

Question 71

What hormones increase cellular metabolism in non-shivering thermogenesis?

Answer 71

Adrenaline and noradrenaline

Question 72

What is the role of thyroxine in heat generation?

Answer 72

Increased thyroxine/T4 is released as a result of TRH and TSH release. This increases the basal metabolic rate.

Question 73

What is thyroxine?

Answer 73

T4 thyroid hormone.

Question 74

What is the long term heat generation mechanism?

Answer 74

Thyroxine release - increases metabolic rate after lengthy exposure to cold .

Question 75

What are the arrector pili muscles activated by?

Answer 75

They are smooth muscle, activated by SNS at alpha 1 receptors.

Question 76

What do the arrector pili muscles attach?

Answer 76

Hair follicle to upper dermis

Question 77

How do arrector pili muscles affect sebaceous glands?

Answer 77

They compress them, allowing them to release sebum to lubricate the skin

Question 78

How are the arrector pili muscles involved in thermoregulation?

Answer 78

They causes goosebumps which allow the hairs to trap a layer of warm air around the skin, preventing heat loss.

Question 79

What does fluid replacement in burn victims depend on?

Answer 79

The percentage of total body surface that is involved.

Question 80

What rule is used in burn fluid replacement?

Answer 80

‘Rule of 9’s’ (in adults)

Question 81

In burn fluid replacement, what percentage of the body is given by the head?

Answer 81

9%

Question 82

In burn fluid replacement, what percentage of the body is given by the upper limbs?

Answer 82

9% each

Question 83

In burn fluid replacement, what percentage of the body is given by the trunk (front and back)?

Answer 83

36%

Question 84

In burn fluid replacement, what percentage of the body is given by the genitalia?

Answer 84

1%

Question 85

In burn fluid replacement, what percentage of the body is given by the lower limbs?

Answer 85

18% each

Question 86

What are the complications of severe burns that are directly related to skin function?

Answer 86

Dehydration/hypovolemic shock, infection/sepsis, hypothermia

Question 87

What complications of severe burns are not directly related to skin function?

Answer 87

Electrolyte imbalances, hypermetabolism, gastrointestinal ulceration, renal failure, respiratory dysfunction

Question 88

What is an example of an electrolyte imbalance caused by severe burns?

Answer 88

Hyperkalaemia (high K+ conc.)