Somatosensory System Flashcards Preview

2.4.1. Nervous System > Somatosensory System > Flashcards

Flashcards in Somatosensory System Deck (21):
1

Define sensation

A physical feeling from stimulation of a sense organ

2

How are the senses classified?

Special = CN: hearing, taste, sight, smell

General = 1) somatic (body wall, skin, mucosa) 2) visceral

3

What are the modalities of the senses?

Somatic = pain, temp, pressure, stretch, vibration, joint position, 2-point discrimination

Each modality has diff qualities associated with it (temp: hot, cold)

4

How are the modalities determined?

By the type of receptor being activated

5

How is the quality of the modality determined?

How the receptor is activated

6

Describe the basic layout of the somatosensory system

Primary sensory neurone – 1st order sensory neurone in the dorsal root ganglion – enters spinal cord

(Properties of the sensory neurone and the receptor determine the modality)

Synapses with 2nd order neurone

2nd order neurone sends axon decussates the midline and up to the thalamus

Synapses with 3rd order neurone in the thalamus

3rd order neurone projects to the cortex

7

Give some examples of cutaneous receptors in the skin

Pacininian corpuscles

Ruffini endings

8

Outline how the generator potential is produced

Mechanoreceptors get physical deformation = open ion channels = Na rushes in

Small deformation = small Na (and vis-versa)

If deformation is large enough = large Na influx = AP generated

9

Your perception of the strength of the stimulus is proportional to what?

The frequency of APs along the first order neurone

10

How are the receptors from which the generator potential is produced classed?

Tonic receptors – slowly adapting (pain) = AP frequency remain firing at a very high rate

Phasic receptors – rapidly adapting (pressure) = AP frequency slow down though adaption

11

Discuss acuity

The larger the receptive field = poorer acuity

Acuity is inversely proportional to the size of the receptive field

Lateral inhibition increase acuity

12

What clinical response occurs from the overlapping of primary receptive fields?

Means dermatome boundaries are not clear lines

13

Explain lateral inhibition

Associated with every 1st order neurone are inhibitory neurones

Excitatory AP stimulate the inhibitory neurones to send inhibitory signals to the neighbouring axons

Localising the epicentre of sensation

14

Where are the locations of the somatosensory neurones?

1st order = dorsal root ganglion

2nd order = grey matter in the cord, brainstem- decussates

3rd order = thalamus (projects to cortex)

15

Outline the dorsal-column medial lemniscus pathway

Light touch, 2-point discrimination, vibration, joint position sense

Medial to lateral = sacral, lumbar, thoracic, cervical = to stop crossing over

Lumbar 1st order synapse in medulla grey mater - gracile nucleus 2nd order dips down decussates, synapse in thalamus with 3rd order neurone - project medially

Cervical 1st order synapse in medulla grey mater - cuneate nucleus 2nd order dips down decussates, synapse in thalamus with 3rd order neurone - project laterally

White mater pathway created by 2nd order neurones = medial lemniscus

16

What are the internal arcuate fibres?

Axons of second-order sensory neurones that compose the gracile and cuneate nuclei of the medulla oblongata

17

Which nucleus handles touch, vibration, 2-point discrimination, joint position from T6 downwards?

Gracile nucleus

18

Outline the spinothalamic pathway

Pain, crude touch, temp

Medial to lateral = cervical, thoracic, lumbar, sacral

Lumbar 1st order neurone synapses at entry level, dorsal horn 2nd order neurone decussates, anterior-lateral spinothalamic tract, to thalamus, synapse with 3rd order neurone – project medially

Cervical 1st order neurone synapses at entry level, dorsal horn 2nd order neurone decussates, anterior-lateral spinothalamic tract, to thalamus, synapse with 3rd order neurone – project laterally

19

Why does rubbing a painful area alleviate pain?

Activation of mechanoreceptors = activation of A-beta neurones that project into the dorsal horn = exciting inhibitory enkephalinergic interneurones = inhibits 2nd order pain neurone = switching off pain transmission

20

Which fibres carry pain?

C fibres – slow conducting

21

Outline the inhibitory pain pathway created by hypnosis

Excitatory cortical neurones project down to midbrain

2nd neurone sits in periaqueductal grey (midbrain), projects down to medulla

Excites nucleus raphe magnus (reticular formation) project down the cord

Excites inhibitory enkaphalinergic interneurones

Inhibit 2nd order sensory neurones