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Neurology Year 3 > Somatosensory System > Flashcards

Flashcards in Somatosensory System Deck (57)
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1
Q

What three broad categories is the somatosensory system divided into?

A

Exteroceptive - cutaneous senses
Proprioceptive - posture and movement
Enteroceptive - internal state of the body

2
Q

Where are first order neurones cell bodies located?

A

Dorsal root ganglia

Cranial ganglia - innovates anterior head

3
Q

Where are second order neurones cell bodies located?

A

Dorsal horn or brainstem nuclei

4
Q

Where are third order neurones cell bodies located?

A

Thalamic Nuclei

5
Q

What does threshold mean?

A

The intensity of stimuli required to excite the sensory unit.

6
Q

Low threshold receptors

A

Respond to low intensity generally non damaging stimuli
Mediate fine discriminatory touch
Thermoreception - cold to warm

7
Q

Low threshold receptors - increasing stimuli strength

A

Increased rate of firing which denotes an increased intensity. However qualitative nature doesn’t change so long as only other receptors aren’t activated
e.g pressure doesn’t become pain

8
Q

High threshold receptors

A
Respond only to high intensity potentially damaging stimuli 
Mechanoreceptors
Thermal >45
Chemical - Substances
Polymodal - at least two of the above
9
Q

Adaption

A

Allows alterations to the firing rate in response to altered intensity or fire at a constant rate regardless of changing intensity.

10
Q

Slow adapting neurones

A

e.g. stretch receptors
Fires continuously whilst deformed
Provides continual information
Amplitude of AP is still dependant on frequency

11
Q

Fast adapting neurones

A

Muscle Spindle
Number of impulses is proportional to the rate of change
Detects change in stimuli strength

12
Q

Very fast adapting

A

Respond to only very fast movement

e.g. Pacinian corpuscles and vibration

13
Q

Conduction Velocity -Group 1

A

Thick myelination and large diameter
V.fast conduction
Proprioceptors of skeletal muscles

14
Q

Conduction Velocity -Group 2

A

Moderate myelination and moderate diameter
Fast conduction
Mechanoreceptors of the skin

15
Q

Conduction Velocity -Group 3

A

Thin myelination and small diameter
Moderate conduction
Pain and Temperature

16
Q

Conduction Velocity -Group 4

A

No myelination and thin diameter
Slow conduction
Temp pain and itch

17
Q

What is a receptive field?

A

Territory in which a sensory unit can be excited

18
Q

What correlates inversely with receptive field?

A

The larger the receptive field the smaller sensory acuity, so less sensitive to touch.

19
Q

What is sensory acuity?

A

The ability to differentiate between two separate points, in this case two points of pressure pain etc

20
Q

Why is sensory acuity inversely proportional to the receptive field?

A

As increasing the receptive field decreases the innervation density.

21
Q

A patch of skin may contain overlapping receptive fields with different modalities? T/F

A

True

22
Q

Where are meissners corpuscles present?

A

Abundant in areas of very high activity, not present in hairy skin

23
Q

Meissners Corpuscles

A

Sensitive to light touch

24
Q

Where are merkels discs present?

A

Same distribution but also found in hairy skin.

25
Q

Free nerve ending distribution.

A

Ubiquitous

26
Q

List the hair end organs

A

Krause end bulbs
Ruffins endings
Paccinian Corpuscles

27
Q

Krause End bulb distribution

A

Borders of dry skin and mucous membrane

28
Q

Ruffins endings distribution

A

Within dermis and joint capsules

29
Q

Paccinian corpuscles distribution

A

Dermis and fascia

30
Q

Ruffins Endings

A

Very little adaption and respond to sustained pressure

31
Q

Pacinian corpuscle

A

Vibration

32
Q

What three forms of pain are there?

A

Nociceptive
Inflammatory
Pathological

33
Q

Nociceptive

A

Adaptive

Immediate short lived protective

34
Q

Inflammatory

A

Adaptive
Assists in healing
Persistent

35
Q

Pathological pain

A

Maladaptive
No physiological purpose
V.Persistant

36
Q

Aδ fibres

A

Mechanical or thermal

Thinly myelinated

37
Q

Aδ describe the pain they relay.

A

First or fast pain

38
Q

C fibres

A

Unmyelinated nociceptors respond to all noxious stimuli

39
Q

C Fibres the pain they relay

A

Slow or second pain

e.g. throbbing aching etc

40
Q

Which receptors are activated by thermal stimuli?

A

TRP receptors

e.g. TRPA1

41
Q

Which receptors are activated by H+ stimuli?

A

ASICs

42
Q

Which receptors are activated by ATP

A

P2x

P2Y

43
Q

Which receptors are activated by bradykinin?

A

B2 receptors

44
Q

How can some sensory C fibres have efferent action?

A

They release pro inflammatory mediators upon activation.

45
Q

What Pro inflammatory mediators released by C fibres cause neurogenic inflammation?

A

CGRP

Substance P

46
Q

Substance P

A

Vasodilation
Promotes bradykinin and histamine release
Prostaglandin formation

47
Q

CGRP

A

Induces vasodilation

48
Q

What is the affect of pro inflammatory mediators being released by sensory neurones?

A

Induces Hyperalgesia (increased pain sensitivity )

49
Q

What is the main neurotransmitter in the dorsal horn?

A

Glutamate

50
Q

What is pain?

A

The relative and subjective perception of nociception.

Highly variable between patients.

51
Q

Visceral Pain

A

Poorly localised dull throbbing

Inflammation and ischaemia of internal organs

52
Q

Viscerosomatic Pain

A

Diffuse pain progressing to sharp well localised.

Inflammatory exudate contacts somatic structure.

53
Q

What is the gate control theory?

A

If non nociceptive sensory afferents are firing at such a greater rate than the nociceptive afferents. Then the synaptic transmission within the dorsal horn to the ascending tracts of the nociceptive axons does not occur.

54
Q

List the major nociceptive tracts

A

Spinothalamic

Spinoreticular

55
Q

Where do the spinothalamic nociceptive tract project too?

A

Thalamus

56
Q

Where do the spinoreticular nociceptive tract project too?

A

Reticular nucleus

57
Q

What is the function of the spinoreticular tract?

A

Autonomic response to pain