somato-sensory system

Question 1

sensory receptors with encapsulated nerve endings

Answer 1

meissner (or tactile) corpuscles

pacinian (or lamellated)
corpuscles

ruffini corpuscles

Question 2

sensory receptors with unencapsulated nerve endings

Answer 2

merkel (or tackle) discs

free nerve endings

Question 3

‘encapulsated nerve endings’

Answer 3

means they can filter out frequencies

to give specific frequencies

Question 4

meissner corpuscles location

Answer 4

dermal papillae of skin esp hands, palms, eyelids, lips, tongue ec

Question 5

modality of messier corpuscles

Answer 5

light touch, texture (movement)
sensitive to 30-50 Hz
rapidly adapting

Question 6

pancinian corpuscles location

Answer 6

dermis
joint capsules
viscera

Question 7

pancinian corpuscles modality

Answer 7

deep pressure
stretch
 tickle 
vibration 
sensity to 150-350 Hz
rapidly adapting

Question 8

ruffini corpuscles location

Answer 8

dermis
subcutaneous tissue
joint capsules

Question 9

ruffini corpuslces modality

Answer 9

heaving touch, pressure, skin stretch
joint movements
slowing adapting

Question 10

merkel discs location

Answer 10

superficial skin (epidermis)

Question 11

merkel discs modality

Answer 11

light touch, texture , edges shapes

slowing adapting

Question 12

free nerve ending locations

Answer 12

widespread in epithelia and connective tissue

Question 13

free nerve ending modality

Answer 13

pain, heat and cold

Question 14

hair follicles location

Answer 14

widespread in epithelia

Question 15

hair follicles modality

Answer 15

varied according to type

both rapid and slowly adapting subtypes

Question 16

different classes of machine receptor response

Answer 16

phasic and tonic

Question 17

tonic

Answer 17

slowing adapting
continue to response as long as the stimulus is present (info about persistence of stimulus)

e.g. ruffini corp

Question 18

phasic

Answer 18

rapidly adapting five info about changes in the stimulus

e.g. pacinian corp

Question 19

primary afferent axon subtypes are classified according to….

Answer 19

conduction velocity

which broadly reflects diameter (faster=longer diameter)

Question 20

axons coming from the skin are designated by

Answer 20

letters ( A, B, C)
a= fastest/largest
c=slowest/smallest

A group further broken down by greek character

alpha, beta delta
a= fastest
d=slowest

Question 21

axons coming from muscles designated by …

Answer 21

roman numerals

I II III IV

I = largest
IV= smallest

Question 22

pain fibres are ….. than proprioceptors

Answer 22

slower

evolutionarily important- ability to stand, feedback has to be very fast

Question 23

how is sensory info organised

Answer 23

The cell bodies of sensory neurons are grouped in the Dorsal root ganglion and their projections are organised to different layers of the dorsal horn

Question 24

two main routes that send info from all sensory subtypes to brain

Answer 24

1) medial lemniscal tracts

2) spinothalamic tracts

Question 25

medial lemniscal tract

Answer 25

carry mechanoreceptive and proropceptive signals to the thalamus

Question 26

spinothalamic tract

Answer 26

carries pain and temp signals to the thalamus

Question 27

Typically, sensory information travels through 3 neurons to reach higher centres:

Answer 27

First-order neurons detect the stimulus and transmit to spinal cord via Dorsal Root Ganglion

Second-order neurons relay the signal from spinal cord to the thalamus, the “gateway” to the cortex

Third-order carry the signal from the thalamus to the cortex

Question 28

commissural

Answer 28

cross the midline to the contralateral side

Question 29

in both medial lemniscal tracts and spin thalamic tracts 2nd order axons do what?

Answer 29

cross the midline i.e. are commissural

Question 30

in the medial lemiscal system, 1st order neurones from the upper body…..

Answer 30

follow lateral pathway and synapse on 2nd order neurones in the cuneate nucleus (in medulla)

Question 31

in the medial lemiscal system, 1st order neurones from the lower body…. (below vertebra T6)

Answer 31

follow the more medial pathway and synapse on neurons in the gracile nucleus

Question 32

the doors column nuclei

Answer 32

the cuneate and the gracile nucleus

Question 33

2nd order axons in the medial lemiscal system

Answer 33

cross the midline

and the topology is reversed relative to the midline so that lower body axons are more lateral on reaching the thalamus

Question 34

3rd order axons in the medial lemiscal system

Answer 34

again reverse the topoglofy so that lower body axons synapse on the more medial cortical neurones

Question 35

medial ness and laternal ness of axons

Answer 35

1st ordeR: upper= lateral
                 lower = medial
2nd order: upper= medial
                   lower= lateral
3rd order: upper=lateral
                  lower = medial

Question 36

somatopoic order in the brain is not simply lower vs upper body axons, the maps is very fine which reflects…..

Answer 36

the fact that each dorsal root ganglion innervate a specific domain of the body called a dermatone

Question 37

dermatome

Answer 37

area of the skin that is mainly supplied by a single spinal nerve

Question 38

dermatomes arise from

Answer 38

embryonic somite (which are repeating structures that give rise to the underlying musculature and skeleton)

each DRG is associated with a specific somite and subsequently innervates the tissues surrounding that somite

Question 39

receptive fields

Answer 39

an axon splits into multiple endings and extend over a n area

Question 40

fingers receptive fields

Answer 40

small (high discrimination)

cortex more dedicated to these areas

Question 41

receptive fields in legs

Answer 41

large (low discrimination)

Question 42

receptive field size

Answer 42

In these regions, although the number of receptors (nerve endings) may be similar, the number of endings from different neurons per unit area is higher, therefore the amount of derived information is also higher

Question 43

largest receptive fields

Answer 43

upper arm, thigh, calf

Question 44

what factor effects the velocity of propagation of the action potential

Answer 44

AXONAL DIAMETER

The influx of sodium that occurs during an action potential causes depolarisation of the axon membrane that lies just ahead of it. As this region reaches threshold, voltage-gated sodium channels open and the action potential is propagated along the axon. The influx of positive charge associated with the inward sodium current has two paths that it can take, it can flow down the inside of the axon or it can cross the axonal membrane. The more charge that flows down the inside of the axon the faster the propagation of the action potential. Therefore, axons with a wider diameter provide more opportunity for the current to flow down the centre of the axon, rather than across the membrane, giving large diameter axons a faster conduction velocity.