Lecture 3

Question 1

what do free nerve endings mainly respond to

Answer 1

• temperature
• pain
• some movement and pressure
• some to itch
• some wrap around hair follicles acting as light touch receptors

Question 2

what is the most common receptor type in the skin?

Answer 2

free nerve endings

Question 3

what fibres make up free nerve endings?

Answer 3

mostly unmyelinated small diameter fibres but also some small diameter myelinated fibres

Question 4

what are tactile (merkel) discs?

Answer 4

free nerve endings located in the deepest layer of the epidermis

Question 5

where are tactile (merkel) discs abundant?

Answer 5

in fingertips and very small receptor fields

Question 6

what are tactile (merkel) discs sensitive to?

Answer 6

an objects physical features = fine touch, light pressure, texture, shape and edges

Question 7

where are tactile (meissner) corpuscles found?

Answer 7

papillary layer of the dermis, especially in hairless skin

Question 8

are tactile corpuscles encapsulated or not

Answer 8

yes they are encapsulated

• deformation of capsule triggers entry of Na+ ions into the nerve terminal = action potential

Question 9

what do tactile corpuscles sense?

Answer 9

• delicate “fine” or discriminative touch, sensitive to shape and textural changes in exploratory touch
• light pressure
• low frequency vibration

Question 10

where are lamellar (pacinian) corpuscles found?

Answer 10

scattered deep in the dermis and hypodermis

Question 11

what are the features of lamellar corpuscles?

what does deformation of capsule cause?

Answer 11

• single dendrite lying within concentric layers of collagen
• layers separated by gelatinous interstitial fluid
• dendrite essentially isolated from other stimuli other than deep pressure
• deformation of capsule opens pressure sensitive Na+ channels in sensory axon

Question 12

what stimulates lamellar corpuscles?

Answer 12

deep pressure (when first applied) and vibration (because rapidly adapting)

Question 13

where are bulbous corpuscles found?

Answer 13

the dermis and subcutaneous tissue

also found in joint capsules where help signal degree of joint rotation

Question 14

features of bulbous corpuscles

Answer 14

network of nerve endings intertwined with a core of collagen fibres that are continuous with those of the surrounding dermis

Question 15

what are bulbous corpuscles sensitive to?

Answer 15

sustained deep pressure and stretching or distortion of skin

Question 16

what does the sympathetic nervous system stimulate to control skin blood flow?

Answer 16

smooth muscle in the walls of arteries and pre capillary sphincters

Question 17

what does noradrenaline act on in controlling skin blood flow?

Answer 17

a1 adrenergic receptors on the vascular smooth muscle in the skin

Question 18

how does reduced skin blood flow occur?

Answer 18

• GPCRS coupled to intracellular 2nd messengers

= increased intracellular Ca2+

= increased interaction of actin and myosin

= increased contraction

= increased constriction

therefore reduced skin blood flow

Question 19

how does increased skin blood flow occur

Answer 19

• reducing SNS activation of a1 receptors

= causes relaxation (dilation) of arteries to skin

therefore increased skin blood flow

Question 20

what stimulates the eccrine sweat glands and what neurotransmitter chemical is used

Answer 20

sympathetic nervous system but uses Ach instead of NE (different to most SNS)

Question 21

what are the basic mechanisms of heat transfer

Answer 21

• radiation
• evaporation
• convention
• conduction

Question 22

what is radiation and what objects radiate?

Answer 22

causes heat loss in the form of infrared rays

any objects that aren’t absolute zero temp will radiate these rays

Question 23

what is evaporation and how does it cause heat change?

Answer 23

heat energy is lost when water evaporates from the body surface as energy is needed to do so

Question 24

what is convention and what does it maintain?

Answer 24

transfer of heat to air or water by conduction following the movement of air or water

• this maintains the gradient for heat loss from the body

Question 25

what is conduction

Answer 25

involves the transfer of heat with objects in which we contact

• significant amount conducted to air

Question 26

normal body temp range?

Answer 26

36.5-37.5 degrees

Question 27

what happens when body temperature increases?

Answer 27

• preoptic area of hypothalamus detects heat change which causes:
• decreased SNS activation of a1 on skin blood vessels = vasodilation
• increased SNS cholinergic activation of mAChRs on sweat glands = sweating
• increased respiratory rate

Question 28

what happens when body temperature falls?

Answer 28

central thermorecptors detect temp below set point which activates the heat gain centre - this responds in two ways

• increased generation of body heat (non shivering and shivering thermogenesis)
• conservation of body heat (vasomotor centre decreases blood flow to dermis = reducing loss by radiation and convention)

Question 29

what is shivering heat convention?

Answer 29

• as we get colder muscle tone increases

Question 30

what is non-shivering heat convention?

Answer 30

producing heat by other mechanisms other than shivering

• increased sympathetic nerve activity + increased circulating adrenaline
• increased cellular metabolism