Skin

Question 1

Two types of skin

Answer 1

Hairy and glabrous

Question 2

Outer layer

Answer 2

Epidermis

Question 3

Inner layer

Answer 3

Dermis

Question 4

Functions of the skin

Answer 4

Protection, prevention of body fluid evaporation, direct contact with external environment

Question 5

What are mechanoreceptors sensitive to

Answer 5

Physical distortion (bending, stretching)

Question 6

Functions of mechanoreceptors

Answer 6

Monitor skin contact, pressure in heart and blood vessels, stretching of digestive organs and urinary bladder, and force against teeth

Question 7

Structure of mechanoreceptors

Answer 7

Unmyelinated (grey matter) axon branches that are sensitive to stretching, pressure, vibration, or bending

Question 8

Largest mechanoreceptor

Answer 8

Pacinian corpuscle

Question 9

Where does the pacinian corpuscle lie

Answer 9

Deep in dermis, can be as long as 2mm and almost 1mm in diameter, each hand has around 2500 (highest density in fingers)

Question 10

Ruffini’s endings

Answer 10

Found in hairy and glabrous skin

Question 11

Meissner’s corpuscles

Answer 11

Located in fridges of glabrous skin (raised parts of fingertips)

Question 12

Structure of Merkel’s disks

Answer 12

Located within epidermis, consists of nerve terminal and flattened, non-neural epithelial cell

Question 13

Krause end bulbs

Answer 13

Lie in the border regions of dry skin and mucous membrane (around lips and genitals), nerve terminals look like knotted balls of string

Question 14

Who developed methods to record from single sensory neurons in human arm

Answer 14

Ake Vallbo (Swedish neuroscientist)

Question 15

Recording from single sensory axons in human arm

Answer 15

Can simultaneously measure sensitivity of mechanoreceptors in hand and evaluate perceptions produced by various mechanical stimuli; can map RF by moving probe around

Question 16

RF of Meissner’s corpuscles

Answer 16

Small

Question 17

RF of Merkel disks

Answer 17

Small

Question 18

RF of Pacinian corpuscles

Answer 18

Large

Question 19

RF of Ruffini’s endings

Answer 19

Large

Question 20

Rapidly adapting receptors

Answer 20

Meissner’s and Pacinian corpuscles; respond quickly at first but stop firing when stimulus continues

Question 21

Slowly adapting receptors

Answer 21

Merkel’s disks, Ruffini endings; generate a more sustained response during long stimulus

Question 22

Meissner’s corpuscles and adaptation

Answer 22

Small, rapid

Question 23

Pacinian corpuscles RF and adaptation

Answer 23

Large, rapid

Question 24

Merkel’s disks RF and adaptation

Answer 24

Small, slow

Question 25

Ruffini’s endings RF and adaptation

Answer 25

Large, slow

Question 26

How can distortion of hair result in receptor activation

Answer 26

Hair follicles contain free nerve endings (terminals of axons) which wrap or run parallel. Bending of hair causes deformation of follicle and surrounding skin tissues. Stretches, bends, or flattens nerve endings. Increase or decrease AP firing frequency

Question 27

Which mechanoreceptors are most sensitive to vibration at 200-300Hz

Answer 27

Pacinian’s corpuscles

Question 28

What mechanoreceptors are most sensitive to vibration at 50Hz

Answer 28

Meissner’s corpuscles

Question 29

Vibration and Pacinian corpuscle

Answer 29

20-70 concentric layers of connective tissue with a on terminal in middle. When capsule is compressed, energy is transferred to nerve terminal and the membrane is deformed, causing the mechanosensitive channels to open. Current flowing through creates a receptor potential (depolarising, graded). If depolarisation is large enough, AP is fired. If stimulus pressure is maintained, receptor potential dissipates. When pressure is released the events reverse.

Question 30

Mechanosensitive ion channels

Answer 30

In membrane of unmyelinated axons. Convert mechanical force to change of ionic current. Forces applied alter gating and either enhance or decrease channel opening

Question 31

Piezo2

Answer 31

Mechanosensitive channel in Merkel disks which opens in response to pressure and depolarises the cell. Depolarisation triggers synaptic release of unknown transmitter from cell, which excites nearby nerve ending. Nerve ending has second ion channel on membrane

Question 32

Why are the fingertips better at 2-point discrimination than the back

Answer 32

1) higher density of mechanoreceptors 2) enriched in receptor types that have small receptor fields (merkel disks) 3) more brain tissue 4) special neural mechanisms devoted to high-resolution discriminations

Question 33

Function of primary afferent axons

Answer 33

Bring information from the somatic sensory receptors to spinal cord or brain stem

Question 34

Entry of primary afferent axons to the spinal cord

Answer 34

Via the dorsal roots; their cell bodies lie in dorsal root ganglia

Question 35

Structure of primary afferent axons

Answer 35

Widely varying diameters, size correlated with type of sensory receptor (in order of decreasing size: Aa, Ab, Ad, C, or group I, II, III, IV)

Question 36

Aa fibres (group I)

Answer 36

13-20um diameter (largest), myelinated, 80-120 m/sec, proprioceptors of skeletal muscle

Question 37

Ab fibres (group II)

Answer 37

Myelinated, 6-12um, 35-75m/sec, mechanoreceptors of skin

Question 38

Ad fibres

Answer 38

Myelinated, 1-5um, 5-30m/sec, pain/temperature

Question 39

C fibres (group IV)

Answer 39

0.2-1.5um (smallest), unmyelinated, 0.5-2m/sec, temperature, pain, itch

Question 40

How do peripheral nerves communicate with the CNS

Answer 40

Via the spinal cord, encased in bony vertebral column

Question 41

Segmental organisation of spinal cord

Answer 41

Paired dorsal and ventral roots repeated 30 times down length of spinal cord

Question 42

Spinal segments

Answer 42

Cervical (C): 1-8 Thoracic (T): 1-12 Lumbar (L): 1-5 Sacral (S): 1-5

Question 43

Dermatome

Answer 43

Area of skin innervated by right and left dorsal roots of a single spinal segment