Lecture 1: Cutaneous Sensation - Receptors And Primary Afferents

Question 1

What organ does cutaneous sensation refer to?

Answer 1

Skin.

Question 2

Do Afferents sensory neurons enter the spinal cord via the dorsal or ventral root?

Answer 2

Dorsal root.

Question 3

Which group of cutaneous receptors respond to distortion (touch and hair movement)?

Answer 3

Low threshold mechanoreceptors.

Question 4

Which group of cutaneous receptors respond to non-damaging temperatures?

Answer 4

Thermoreceptors.

Question 5

Which group of cutaneous receptors respond to stimuli that cause pain and potential tissue damage?

Answer 5

Nociceptors.

Question 6

Which group of cutaneous receptors respond to itch-inducting stimuli?

Answer 6

Itch receptors.

Question 7

Which group of cutaneous receptors may be a subset of nociceptors?

Answer 7

Itch receptors. Because they also respond to painful stimuli.

Question 8

What are the specialised endings of low threshold mechanoreceptors?

Answer 8

Merkel’s disks
Ruffini endings
Meissner’s corpuscles
Pacinian corpuscles

Question 9

Apart from specialised endings, there is another type of low threshold mechanoreceptor, what is it?

Answer 9

Hair follicle afferents.

Question 10

Nociceptors, thermoreceptors and itch receptors all have what in common?

Answer 10

They all terminate as free nerve endings in the skin.

Question 11

Which specialised ending of low threshold mechanoreceptors are fast with a small receptive field size?

Answer 11

Meissner’s corpuscles

Question 12

Which specialised ending of low threshold mechanoreceptors are fast and have a large receptive field size?

Answer 12

Pacinian corpuscles.

Question 13

Which specialised ending of low threshold mechanoreceptors are slow and have a small receptive field size?

Answer 13

Merkel’s disks.

Question 14

Which specialised ending of low threshold mechanoreceptors are slow and have a large receptive field size?

Answer 14

Ruffini’s endings.

Question 15

Do slowly adapting receptors detect displacement or movement?

Answer 15

Displacement. Rapidly adapting receptors detect movement.

Question 16

Which specialised ending has “onion skin” of connective tissue surrounding the terminal part of the axon? And what property does it aid?

Answer 16

Pacinian corpuscle. It gives the receptor it’s rapidly adapting property.

Question 17

What range of temperatures do thermoreceptors detect?

Answer 17

10 degrees C to 45 degrees C. Outside this range it gets painful and nociceptors are responsible for detection.

Question 18

What are polymodal nociceptors?

Answer 18

Nociceptors that respond to different types of stimuli (mechanical thermal and chemical).

Question 19

What are “silent nociceptors”?

Answer 19

Nociceptors that only respond when sensitised (e.g. after tissue injury).

Question 20

Piezo2 is an example of what? Is it a small or large protein?

Answer 20

Mechanosensitive ion channel. It is a very large protein with >30 transmembrane domains.

Question 21

Which channels are used in thermal transduction? Give an example.

Answer 21

Transient receptor potential channels that signal various temperatures. Eg. TRPV1 which responds to temps of >43 degrees C.

Question 22

TRPM channels or TRPV channels are associated with hot or cold temperatures?

Answer 22

TRPM - cold

TRPV - hot

Question 23

Where do primary afferents have their cell body?

Answer 23

In the dorsal root ganglion.

Question 24

What are the two types of primary afferents?

Answer 24

Myelinated (A fibres - can be A beta or A delta) and Unmyelinated (C fibres).

Question 25

Are there more myelinated or unmyelinated primary afferent cutaneous nerves?

Answer 25

Unmyelinated fibres outnumber myelinated fibres 4:1.

Question 26

Which primary afferents correspond to:
A beta fibres,
A delta fibres,
C fibres?

Answer 26

A beta fibres = large myelinated
A delta fibres = small myelinated
C fibres = unmyelinated

Question 27

Most low threshold mechanoreceptors are large myelinated (A beta), small myelinated (A delta) or unmyelinated (C)?

Answer 27

Large myelinated (A beta).

Question 28

Most nociceptors, thermoreceptors and itch receptors are what in terms of myelin?

Answer 28

Small myelinated (A delta) or unmyelinated (C).

Question 29

What type of pain do C nociceptors pick up?

Answer 29

Slow pain, dull, poorly localised.

Question 30

Which afferents send a branch up the dorsal columns to the medulla?

Answer 30

A beta afferents.

A delta and C fibres only give local branches to the dorsal horn.

Question 31

The grey matter of the spinal cord is divided into what?

Answer 31

Laminae of Rexed.

Question 32

Which afferents end mainly in the superficial dorsal horn (laminae I and II of Rexed)?

Answer 32

A delta and C afferents.
Large (A beta) afferents branch deeper in the dorsal horn (laminae III - VI of Rexed) and have an ascending branch in the dorsal columns.

Question 33

What neurotransmitter do all primary afferents use?

Answer 33

Glutamate.

Question 34

Neuropeptides (e.g. substance P) are also released by which type of afferents?

Answer 34

Nociceptive afferents.