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Neurology Year 3 > Somatosensory System > Flashcards

Flashcards in Somatosensory System Deck (57)
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1

What three broad categories is the somatosensory system divided into?

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

2

Where are first order neurones cell bodies located?

Dorsal root ganglia
Cranial ganglia - innovates anterior head

3

Where are second order neurones cell bodies located?

Dorsal horn or brainstem nuclei

4

Where are third order neurones cell bodies located?

Thalamic Nuclei

5

What does threshold mean?

The intensity of stimuli required to excite the sensory unit.

6

Low threshold receptors

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

7

Low threshold receptors - increasing stimuli strength

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

High threshold receptors

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

9

Adaption

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

10

Slow adapting neurones

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

11

Fast adapting neurones

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

12

Very fast adapting

Respond to only very fast movement
e.g. Pacinian corpuscles and vibration

13

Conduction Velocity -Group 1

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

14

Conduction Velocity -Group 2

Moderate myelination and moderate diameter
Fast conduction
Mechanoreceptors of the skin

15

Conduction Velocity -Group 3

Thin myelination and small diameter
Moderate conduction
Pain and Temperature

16

Conduction Velocity -Group 4

No myelination and thin diameter
Slow conduction
Temp pain and itch

17

What is a receptive field?

Territory in which a sensory unit can be excited

18

What correlates inversely with receptive field?

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

19

What is sensory acuity?

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

20

Why is sensory acuity inversely proportional to the receptive field?

As increasing the receptive field decreases the innervation density.

21

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

True

22

Where are meissners corpuscles present?

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

23

Meissners Corpuscles

Sensitive to light touch

24

Where are merkels discs present?

Same distribution but also found in hairy skin.

25

Free nerve ending distribution.

Ubiquitous

26

List the hair end organs

Krause end bulbs
Ruffins endings
Paccinian Corpuscles

27

Krause End bulb distribution

Borders of dry skin and mucous membrane

28

Ruffins endings distribution

Within dermis and joint capsules

29

Paccinian corpuscles distribution

Dermis and fascia

30

Ruffins Endings

Very little adaption and respond to sustained pressure