Lecture 18; Somatosensory receptor cells, receptors, primary afferents

Question 1

What are some characteristics of receptor cells?

Answer 1

Rapidly or slowly adapting

Small or large receptive fields

Question 2

What are somatic sensations?

Answer 2

touch

pain,

temperature,

body position

Question 3

List examples of receptor cells?

Answer 3

Exteroceptors
 Interoceptors
 Proprioceptors
 Mechanoreceptors
 Thermoreceptors
 Nociceptors
 Encapsulated nerve endings
 Free nerve endings

Question 4

What do encapsulated receptor cells consist of? (1)

Answer 4

Meissner’s corpuscles – sensitive to tactile
stimulation, small RFs and rapidly adapting.
Pacinian corpuscles – sensitive to vibrations,
large RFs, rapidly adapting.
Merkels discs – sensitive to slow deformation
of skin, small RFs, slowly adapting.

Question 5

What do encapsulated receptor cells consist of? (2)

Answer 5

Ruffini cylinders – sensitive to tactile stimulation,
large RFs, slowly adapting.
Dogiel body, 
Golgi-Mazzoni body, 
Endbulbs of Krause,
Genital corpuscle etc.

Question 6

What are nocioceptors?

Answer 6

signal painful stimulation

Question 7

What are the 4 major types of touch mechanoreceptors?

Answer 7

1. Merkel discs
2. Meissner corpuscles
3. Ruffini cylinders
4. Pacinian corpuscles.

Question 8

How do the 4 major types of touch mechanoreceptors differ?

Answer 8

in regard to 5 features;

1. location in the skin
2. physical appearance
3. speed of adaptation
4. size of their receptive fields
5. tuning to stimulus

Question 9

What is the Meisner corpuscle?

Answer 9

is composed of flattened cells located in the dermis, near the epidermis. A single nerve fiber winds its way through these cells.

Question 10

What is the Merkel Disc?

Answer 10

is a disk-shaped receptor that is located near the epidermis and dermis border.

Question 11

What is the Ruffani cylinder?

Answer 11

is located in the dermis and has many branched fibers inside a cylindrical capsule.

Question 12

What is the Pacinian Corpuscle?

Answer 12

is a layered, onion-like capsule surrounding a nerve fiber.
It is located deep in the dermis, in the subcutaneous fat. They are also found in the intestines and joints as proprioceptors.

Question 13

What is two point discrimination?

Answer 13

is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one.

Question 14

What are proprioceptors?

Answer 14

are located in skeletal muscles, tendons, ligaments
and joints.

They are sensitive to muscle stretch, muscle tone and position of joints

Question 15

What do proprioceptors consist of?

Answer 15

Free nerve endings

Pacinian and paciniform endings

Muscle spindles

Golgi tendons

Question 16

What is reflexive behavioural circuits in muscle spindles and golgi tendons?

Answer 16

Sensors in the tendon, the Golgi tendon organ, are activated upon stretch of the tendon, which requires considerable force.

These sensors synapse on interneurons in the spinal cord that inhibit further activity of the motor neurons innervating the muscle. This relaxation of the muscle prevents damage from excess force.

Question 17

Who was Thomas Graham Brown?

Answer 17

he was the first to propose a half-centre model of motor neurons in which two groups of spinal neurons that are both reciprocally organized and mutually inhibiting are capable of producing basic rhythmic movement

Question 18

Explain Henrik Ehrsson’s out of body experience?

Answer 18

subject is shown their peripheral view, in which the camera they see out of is prodded and so is their chest

Question 19

What does TRP stand for?

Answer 19

Transient Receptor Potential (TRP) channels

of sensory afferents

Question 20

In persistent injury what do central and peripheral pain pathways exhibit?

Answer 20

exhibit tremendous plasticity, producing

hypersensivity (hyperalgesia/allodynia)

Question 21

What are the stimuli that lead to tissue damage but also activate nociceptors?

Answer 21

Strong mechanical stimulation
Extreme temperature
Oxygen deprivation
Exposure to certain chemicals

Question 22

What are nociceptors described as?

Answer 22

Nociceptors are polimodal or they respond exclusively to thermal stimuli or some chemicals.
They are usually C fibres and lightly myelinated delta fibres.
There are also molecular pain receptors.

Question 23

What does damaged tissue leak?

Answer 23

Damaged tissue leaks several chemicals: ATP and K+ , but also proteases (like kininogen to form bradykinin).

Bee venom causes histamine release from mast cells, which in turn sensitizes nociceptors.

Histamine causes blood capillaries to become leaky…hence causing redness and swell.

Question 24

What is Hyperalgesia?

Answer 24

Primary (mechanical and heat stimuli) and secondary hyperalgesia (mechanical stimuli only)
Peripheral and central hyperalgesia

Sensitizing chemicals: bradykinin, substance P and prostaglandins

Question 25

List the primary afferent axons?

Answer 25

Aα, Aβ, Ad, C

Question 26

What fibres are involved in slow pain?

Answer 26

C fibres
1um in diameter
1 sec to travel to brain

Question 27

What fibres are involved in fast pain?

Answer 27

Ad fibres
mylinated
5um in diameter
30 msec to travel to brain