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Physiology 2041 > 3. Somatosensory System > Flashcards

3. Somatosensory System Flashcards

1
Q

Subdivisions of somatosensory system

A

Proprioceptive
Enteroceptive
Exteroceptive

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2
Q

Exteroceptive division

A

Division is responsible for providing information about contact of the skin with objects in the external world, and a variety of cutaneous mechanoceptive, nociceptive (pain), and thermal receptors

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3
Q

Enteroceptive

A

Division has receptors for monitoring the internal state of the body and includes mechanoreceptors that detect distention of the gut or fullness of the bladder.

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4
Q

Proprioceptive

A

Division provides information about body and limb position and movement and relies primarily on receptors found in the joints, muscles, and tendons.

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5
Q

Mechanoreceptors

A

Touch, pressure, vibration and stretch

Location: skin, muscle, tendons, blood vessels, inner ear

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6
Q

Thermoreceptors

A

Cold, warm

Skin

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7
Q

Nociceptors

A

Stimuli causing tissue damage

Skin

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8
Q

Why are sensations of temperature and pain often grouped together

A

The sensations of pain and temperature are related and often grouped together because they are mediated by overlapping sets of receptors, share some common molecular mechanisms, and are conveyed by the same types of fibers in the PNS and the same pathways in the CNS.

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9
Q

Types of nerve fibers in somatosensory system

A

Group I/II. A-alpha and A-beta fibers

Group III. A-delta fiber

Group IV. C fiber

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10
Q

Group I/II. A-alpha fibers and A-beta fibres

A

Myelinated
Large diameter
Proprioception, light touch

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11
Q

Group III. A-delta fibers

A

Lightly myelinated
Medium diameter
Nociception
(mechanical, thermal, chemical)

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12
Q

Group IV. C fiber

A 
Unmyelinated
Small diamater
Innocuous temeprature, itch
Nociception
(mechanical, thermal, chemical)
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13
Q

Types of mechanoreceptors

A 
Pacinian corpuscle
Meissner's corpuscle
Hair follicles
Ruffini's corpuscle
Merkel's receptors
Tactile discs
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14
Q

Pacinian corpuscle: location, adaptation, sensation encoded

A

Hairy/nonhairy skin; intramuscular
Very rapidly
Vibration, tapping

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15
Q

Meissner’s corpuscle: location, adaptation, sensation encoded

A

Nonhairy skin
Rapidly
Point discrimination, tapping, flutter

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16
Q

Hair follicles: location, adaptation, sensation encoded

A

Hairy skin
Rapidly
Velocity, direction of movement

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17
Q

Ruffini’s corpuscle: location, adaptation, sensation encoded

A

Hairy/nonhairy skin
Slowly
Strech, joint rotation

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18
Q

Merkel’s receptors

A

Nonhairy skin
Slowly
Vertical indentation of skin, light touch

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19
Q

Tactile discs

A

Hairy skin
Slowly
Vertical indentation of skin

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20
Q

Thermoreceptors

A

Respond slowly to temperature change
Slowly adapting receptors
Two types: warm receptors and cold receptors

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21
Q

What receptors are activated by extreme heat or cold?

A

Nociceptors not thermoreceptors

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22
Q

What channels are associated with thermosensation

A

TRP channels, which change to allow ions to flow through. They are associated with thermosensations. Humans have 6.

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23
Q

Why does spicy food make you feel hot? Why does mint make you feel cool?

A

Capsaicin in spicy food activated TRPV1; methol in mint activates TRPM8.

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24
Q

Do cold and warm receptors overlap

A

Yes, they have large windows

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25
Q

Describe structure of TRP channels

A

6 TM domains

A hole channel between 5th and 6th subunit, which triggers AP

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26
Q

6 subfamilies of thermoreceptors

A 
TRPV4
TRPV3
TRPV2
TRPV1
TRPM8
TRP A1
Each activated at different temperatures.
React to light and mechanical stimuli, chemicals and natural compounds.
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27
Q

Nociceptors

A

Respond to noxious stimuli (mechanical, thermal, and chemical) that cause tissue damage.

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28
Q

Two classes of nociceptors

A
  1. Thermal or mechanical

2. Polymodal

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29
Q

Thermal or mechanical nociceptors

A

Fast conducted A-delta nerve fibers; respond to mechanical or thermal stimuli such as sharp, pricking pain

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30
Q

Polymodeal nociceptors

A

Slow-conducting C fibers; respond to high-intensity mechanical, chemical, and thermal stimuli

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31
Q

Two phases of pain

A
  1. Fast/first pain

2. Slow/second pain

32
Q

Hyperalgesia

A

An amplified response to a noxious stimulus (sensitization of pain)
Ex: hot water sensitizes pain caused by a paper cut

33
Q

Allodynia

A

A painful response to a normally innocuous stimulus (elicitation of painful sensations by stimuli that do not normally provoke pain)
Ex: wearing a shirt (innocuous) can be painful when skin is sensitized by sunburn

34
Q

Inflammatory soup

A

Caused by tissue damage: Peptides (bradykinin), lipids (prostaglandins), neurotransmiters (serotonin 5-HT, substance P, and ATP), H+, cacitonin, gener-related protein (CGRP) and neurotrophins (NGF).

35
Q

Thermal nociceptors

A

Coldness: TRPM8, TRPA1

Extreme heat: TRPV1 (TRPV2(

36
Q

Chemical nociceptors

A

TRPV1 (capsaicin, H+, toxins)
TRPA1 (Acrolein)
ASICs (H+)

37
Q

Mechanical nociceptors

A

DEG/ENaC (degenerin/epithelial Na+ channel) family, TRPA1, TRPV4

38
Q

Location of somatosensory innervation of the body

A

Primary sensory neurons located in the dorsal root ganglion

39
Q

Location of somatosensory innervation of the face

A

Primary sensory neurons located in the trigerminal ganglion

40
Q

A common disease that illustrates the dermatomal organization of the dorsal roots

A

Shingles (herpes zoster virus): the rash is confined to one side of the body in a dermatomal distribution

41
Q

No. of spinal nerves

A

31

42
Q

How many of the spinal nerves are dermatomes

A

Only 30, C1 nerve is not dermatome (sends directly to the brain not the spinal cord)

43
Q

Dermatome

A

An area of the skin supplied by nerves from a single spinal root

44
Q

Two somatosensory pathways

A
  1. Dorsal column-medial lemniscus system

2. Anterolateral (spinothalamic) system

45
Q

Dorsal column-medial lemniscus system

A

fine touch, pressure, vibration, proprioception, and two-point discrimination

46
Q

Anterolateral (spinothalamic) system

A

pain, temperature, and crude touch

47
Q

Why is decussation level clinically important

A

Because damage to the pathway below this level will produce loss of sensation on the same, or ipsilateral, side of the lesion, whereas lesions about this level will produce contralateral deficits

48
Q

Order of neurons in somatosensory pathways

A

1st order neuron: primary afferent neuron
2nd order neuron: in the spinal cord (anterolateral system) or in the brain stem (dorsal column system); decussation.
3rd order neuron: in the somatosensory nuclei of the thalamus
4th order neuron: in the somatosensory cortex

49
Q

Dorsal Column-Medial Lemniscus Pathway - order

A

1st order neuron: large myelinated axons (Group I/II)
2nd order neuron: in the nucleus gracilis and the nucleus cuneatus (Medulla of the brain stem); decussation
3rd order neuron: in the ventral posterior lateral (VPL) nucleus of the thalamus
4th order neuron: in the somatosensory cortex

50
Q

Dorsal Column-Medial Lemniscus Pathway - sensations

A

fine-touch, pressure, two-point discrimination, and vibratory sensations

51
Q

Graphesthesia

A

The ability to recognize letters or numbers traced on the skin

52
Q

Anterolateral/Spinothalamic Pathways - order

A

1st order neuron: small lightly myelinated and unmyelinated axons (Group III/IV)
2nd order neuron: in the spinal cord; decussation
3rd order neuron: in the ventral posteroinferior (VPI) nucleus of the thalamus
4th order neuron: in the somatosensory cortex

53
Q

Anterolateral/Spinothalamic Pathways - sensations

A

pain, temperature and crude touch

54
Q

What pathway is damaged if you lose the ability to identify objects by their shape and texture but not pain and temperature sensation?

A

The dorsal column pathway

55
Q

Structural and functional difference between the two pathways?

A

Type of nerve fibers; site of decussation; sensations processed.

56
Q

Somatosensory homunculus

A

Homunculus represents each part of the body in proportion to its number of sensory neural connections but not its actual size.

57
Q

Pain

A

an unpleasant feeling caused by noxious stimuli; a protective mechanism

58
Q

Type of nerve fibers that supply nociceptors

A

A-delta fibres

C fibres

59
Q

Fast/first pain

A

Transmitted via faster Adelta fibers
Rapid onset and offset
Precisely localized (e.g. pin prick)
Serves as a warning signal

60
Q

Slow/second pain

A

Transmitted via slower C fibers
More prolonged and less intense
Poorly localized (e.g. burn)
Involves a more complex emotional process

61
Q

Site of Nociceptive pain

A

PNS only

62
Q

Site of inflammatory pain

A

PNS and CNS

63
Q

Site of neuropathic pain

A

PNS and CNS

64
Q

Classes of pain that involve TRP channels

A

Nociceptive and inflammatory, maybe neuropathic

65
Q

Classes of pain that involve nociceptors AND non-nociceptors for sensing pain

A

Inflammatory and neuropathic

66
Q

Clinical settings of classes of pain

A

Nociceptive: acute trauma
Inflammatory: post-operative, arthritis, etc
Neuropathic: PNS and CNS lesions, diabetic neuropathy, spinal cord injury

67
Q

Function of classes of pain

A 
Nociceptive = protective
Inflammatory = healing/repair
Neuropathic = pathological
68
Q

What type of pain for trigeminal neuralgia that is caused by mechanical damage to the trigeminal ganglion by an artery? How to treat it?

A

Neuropathic pain; surgical displacement of the artery.

69
Q

What is the gate control theory of pain?

A

Innocuous stimuli are able to suppress pain.

70
Q

What is the mechanism of the gate control theory of pain?

A

Mechanism: activation of inhibitory interneurons by innocuous stimuli applied to Aβ fibres results in an inhibition of pain signals transmitted via C fibres to the CNS.

71
Q

Referred pain

A

Referred pain: used for the sensation of pain that is experienced at a site other than the injured tissue
Visceral origin
Example: ischemic heart pain is referred to the left arm

72
Q

Dermatomal rule

A

Pain is referred to a structure, which is developed from the same dermatome from which the pain producing structure is developed.
Example:
The ischemic heart pain is referred to left arm because the heart and inner aspect of left arm originate from the same dermatome.

73
Q

Why morphine can relieve pain? How to treat morphine overdose?

A

Morphine activates the endogenous analgesia system. Naloxone can reverses morphine’s effect.

74
Q

Endogenous analgesia system

A

The centrifugal control of somatosensation.
Opioids (enkephalin, endorphins, dynorphin)
Drugs: naloxone (antagonist), morphine (agonist)
Serotonin/catecholamines

75
Q

Role of serotonin/catecholamine in centrifugal control of somatosensation

A

Can inhibit the interneurons or interact with the opiods system

Physiology 2041 (6 decks)

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