Touch

Question 1

Merkel disc density in fingertips:

Answer 1

70 per cmsq.

Question 2

Meissner’s corpuscles density in fingertips:

Answer 2

150 per cmsq.

Question 3

Pacinian corpuscles density in fingertips:

Answer 3

20-70 per cmsq.

Question 4

Ruffini endings density in fingertips:

Answer 4

1-2 per cmsq.

Question 5

Why are Pacinian corpuscles and Ruffini endings large?

Answer 5

Allows them to be more sensitive to mechanical displacement.

Question 6

RA receptors detect:

Answer 6

Motion and vibration.

Question 7

(RA) Meissner’s corpuscles tuned to what frequencies?

Answer 7

30-50Hz.

Question 8

(RA) Pacinian corpuscles tuned to what frequency?

Answer 8

<500Hz.

Question 9

Meissner’s corpuscle structure:

Answer 9

Stack of flattened, fluid-filled cells ecapsulating RA fibre.

Question 10

Pacinian corpuscle structure:

Answer 10

Concentric, fluid-filled connective tissue lamellae encapsulating RA fibre.

Question 11

How do Meissner’s and Pacinian corpuscles do rapid adaptation?

Answer 11

Fibres inside linked to stretch-sensitive ion channels which response to rapid deformation of capsule, firing at the start and end of stimulation.

Question 12

SA receptors detect:

Answer 12

Object pressure and form.

Question 13

Merkel’s discs sensitive to what? Makes them well suited for…

Answer 13

Sustained pressure and indentation. Picking up fine details such as reading braille.

Question 14

Merkel discs’ structure:

Answer 14

specialised, disc-shaped cells closely associated w/ epidermal later of skin.

Question 15

Ruffini endings sensitive to:

Answer 15

Stimulation that stretches skin along its long axis.

Question 16

Ruffini endings structure:

Answer 16

Elongated fusiform structures that enclose collagen fibrils extending from the subcutaneous tissue to folds in the skin at joints.

Question 17

What may Ruffini endings play a role in.

Answer 17

Stereognosis and proprioception.

Question 18

Complementary roles, SA receptors provide … for … , while RA receptors alert the system to ….

Answer 18

A steady baseline for monitoring constant stimuli, alert the system to changes or new inputs.

Question 19

In terms of complementary roles, when holding an object what are the roles for both RA and SA receptors?

Answer 19

SA: continuously assess grip strength and texture. RA: detect slippage or adjustments.

Question 20

Why is parallel processing via diff. receptors useful?

Answer 20

Allows brain to process many object features at once, assisting speed of identification.

Question 21

Describe the DCMLS.

Answer 21

Sensory neurons terminate in DC nuclei. 2nd order neurons cross the midline in the medulla synapsing in the gracile (lower) or cuneate (upper) nucleus, then ascend contralaterally to thalamus, terminate in ventral posterolateral.

Question 22

Where is S1? What does it consist of?

Answer 22

Parietal lobe. Postcentral gyrus and posterior paracentral lobule.

Question 23

Why is contralateral projection important>

Answer 23

Ensures tactile sensations processed in conjunction with movements controlled by the opposite hemisphere.

Question 24

What shows that crude touch exists, and ascends via the anterolateral system?

Answer 24

Advanced syphillis, hardening of dorsal columns, touch but no localisation.

Question 25

What shows that there is a role for touch in movement?

Answer 25

Somatosensory losses accompanied by motor deficits: clumsy movements, dystonia.

Question 26

Mountcastle discovered vertical columns in S1 .... wide, spanning all 6 layers.

Answer 26

300-600um.

Question 27

Neurons within columns receive inputs from same what?

Answer 27

Locality and class of touch receptor.

Question 28

Columns provide what?

Answer 28

Anatomical structure that organisies sensory inputs to convey information about location and modality.

Question 29

Columns within S1 arranged topographically such that...

Answer 29

Complete representation of each body part in each area of S1.

Question 30

Cortical map corresponds roughly to...

Answer 30

Spinal dermatomes.

Question 31

What body parts overrepresented in homunculus?

Answer 31

Hands, feet, tongue. (in humands and monkeys more cortical colmns devoted to fingers than entire trunk).

Question 32

Cortical magnification. Closely correlated with ...

Answer 32

The innervation density and thus the spatial acuity of the touch receptors in an area of skin.

Question 33

How may S1 topographical organisation lead to phantom limbs?

Answer 33

Hand area is very close to the face.

Question 34

Central pathways integrate responses of thousands of neurons through ... , this allows what?

Answer 34

Neural convergence. This allows representation of global features of objects.

Question 35

Example of increase in RF size up the pathway:

Answer 35

MD and MC RF tiny spots on fingertip, those of cortical neurons the entire fingertip.

Question 36

Why are RFs progessively larger than in areas 3a and b in areas 1, 2 and 5?

Answer 36

3a and b input. Convergent inputs from neurons in area 3b that are stimulated together when hand is used. Area 5 has bilateral RFs, respond to touch at mirror image locations on both hands.

Question 37

Neurons in areas 1 and 2 have Rfs that include ..., and thus fire at higher rates when..., as such signalling the ..., explaining why area 2 lesion leads to...

Answer 37

More than one finger, and thus fire at higher rates when several fingers touch simultaneously. As such signal the size and shape of objects held in hand. Explaining why area 2 lesion leads to deficit in size and shape differentiation.

Question 38

Large RFs enable...

Answer 38

Integration of fragmented info from touch receptors.

Question 39

What evidence highlights how active touch is different to passive?

Answer 39

Steinmetz et al (2000) used multiple electrode arrays to find that most neuron pairs in SII cortex fired synchronously and that the degree of synchrony was affected by the monkey's attentional state.

Question 40

Experimental ablation of S1 areas in monkeys. Lesions to 3b lead to...

Answer 40

Deficits in touch from particular body part.

Question 41

Experimental ablation of S1 areas in monkeys. Lesions to 1 lead to...

Answer 41

Deficits in texture assesment.

Question 42

Experimental ablation of S1 areas in monkeys. Lesions to 2 lead to...

Answer 42

Deficit in size and shape differentiation.

Question 43

How do sensory receptors do lateral inhibition to increase resolution?

Answer 43

Neuron stimulated most sends out collaterals which contact GABAergic interneurons that inhibits neurons either side of it.

Question 44

Somatotopic mapping: individual digits can be discriminated (X), and even along the phalanges of a single finger exhibit topographical distinction (X).

Answer 44

Kolasinski et al (2016). Sanchez-Panchuelo et al (2012).

Question 45

Lesions to S1 can cause:

Answer 45

Agraphesthesia (loss of vibration). Hemisypesthesia (loss of fine touch).

Question 46

What fibres may be involved in thermoception?

Answer 46

Adelta fibres.