Neurobio_Mod.3_Somatosensory System_11/15/11

Front 1

What are the 2 different types of skin? Which type do we focus on?

Back 1

Skin can either be (1) glabrous (without hair), or (2) hairy. The palm and fingertips are examples of glabrous skin.
We focus on the receptors of glabrous skin.

Front 2

What are 4 mechanoreceptor types in glabrous skin? Which types are slow/rapid-adapting? Which types hall small/large receptive fields?

Back 2

The 2 corpuscles (Meissner and Pacinian) are rapidly-adapting. The Ruffini endings and Merkel disks are slow-adpating.
The Meissner and Merkel have small receptive fields. The Pacinian and Ruffini have large receptive fields.

Front 3

Which mechanoreceptors are most superficial? Which are deepest? How does this affect their function?

Back 3

The Merkel and Meissner are both most superficial, and consequently have the smallest receptive fields. The Ruffini endings and Pacinian corpuscles are deepest, and therefore havelarge receptive fields.

Front 4

What is the relationship between depth and size of receptive field?

Back 4

As depth increases, receptive field increases.

Front 5

How are the axons dedicated to discriminative touch different from the axons for pain/temperature? What is the functional significance of this?

Back 5

The axons for discriminative touch are myelinated. The axons for pain/temperature are unmyelinated. This means that the info for discriminative touch is conducted faster due to less passive decay.

Front 6

What mechanoreceptor is most involved in spatial acuity? Why does a bigger stimulus not evoke a more intense response?

Back 6

Merkel cells are best for spatial acuity. Individual Merkel cells do not have robust firing with a broad stimulus because of lateral inhibition of all neighboring Merkel cells.

Front 7

What is the difference between slow and rapidly adapting mechanoreceptors? Why is this functionally significant?

Back 7

Slowly adapting receptors fire at a constant rate as long as the stimulus is present. Rapidly adapting cells fire once when the stimulus appears, and again when the stimulus is removed? This is significant because it allows for different kinds of tactile information to be transmitted.

Front 8

What kinds of cells code for gradual changes in pressure? What is the physiological basis for this phenomenon?

Back 8

Meissner corpuscles and pacinian corpuscles (i.e. cells with corpuscles) can code for gradual changes in the pressure of a single stimulus. They can do this because the corpuscle acts as a buffer that distributes the intensity of a stimulus across a larger range of possible pressures, each of which is coded for by a specific action potential intensity.

Front 9

What is the physiological basis of rapidly adapting receptors? Is it an intrinsic property of the axon? What experiment demonstrated this?

Back 9

The physiological basis of the rapidly adapting cells is the corpuscle. When the corpuscle is removed the axon reacts the same as a slowly adapting receptor.

Front 10

What is an emergent property of corpuscled receptors? What factors affect this? What are the profiles for meissner and pacinian corpuscles? What type of stimulus do we say they are each sensitive for?

Back 10

An emergent property of corpuscled cells is that they respond best to certain frequencies of tactile stimulation. This response frequency further varies with the amount of skin indentation that is made by the tactile stimulus.
The meissner is best activated by a low frequency, high-indentation stimulus. The pacinian is best activation by high-frequency, low-indentation stimuli. This is counter-intuitive because the pacinian is deeper. The meissner is described as being attuned to "flutter", and the pacinian to "vibration".

Front 11

What kinds of stimuli activate the Merkel and Ruffini cells?

Back 11

The Merkel cells are activated by pressure, and the ruffini cells are activated by stretching.

Front 12

Which mechanoreceptors are most abundant on the distal parts of the fingers (i.e. the fingertips)?

Back 12

All except Ruffini endings are more abundant on the dital parts of the fingers, but the most superficial receptors (meissner and merkel) are especially abundant. This is because they have the smallest receptive fields.

Front 13

What is the two-point discrimination task? What does it measure?

Back 13

The two-point discrimination task is a measure of tactile spatial acuity. The smaller the distance between two points that can be distinguished is indicative of its acuity.

Front 14

What is the consequence of lateral inhibition?

Back 14

Lateral inhibition produces sharper, more localized (and presumably more useful) signals.

Front 15

What is the relationship between two-point discrimination and lateral inhibition? Explain.

Back 15

As the degree of lateral inhibition increases, the ability to discriminate between two point stimuli increases. This is because greater lateral inhibition produces a sharper, more localized signal.

Front 16

Where are the two enlargements of the spinal cord? What do these correspond to?

Back 16

The two enlargement are at the cervical and lumbar levels. These correspond to the extra innervation to the arms and legs, respectively.

Front 17

What is the dermatome? What is true about the distribution of dermatome? Why is this significant?

Back 17

Dermatome is the region of skin that projects to a single dorsal root ganglion. Because the different dermatomes overlap, that means that damage to any one dorsal root ganglion will not result in much somatosensory deficit.

Front 18

What is the relationship between dermatomes and sensitivity on the two-point discrimination task?

Back 18

The dermatomes in the cervical level have greater acuity on the two-point discrimination task than the dermatomes of the thoracic level. This is because there are more receptors in the cervical dermatome, thus the cervical bulge.

Front 19

Describe the differences between the somatosensory and pain pathways in the spinal cord.

Back 19

Information from both pathways eventually reaches the contralateral side of the brain. However,they differ in where the decussation occurs:

1. somatosensory pathway- info goes up the ipsilateral side, and decussates in the pons.

2. Pain pathway- info decussates at the level of the dorsal root ganglion from which it entered, and then simply ascends up the contralateral side of the spinal cord

Front 20

Describe a spinal cord injury that would differentially affect somatosensory vs. pain/temp. perception.

Back 20

Damage to the dorsal side of the right lumbar spinal cord would result in the ability to feel somatosensory info from the left side, but inability to feel pain/temp info from the left side.

Front 21

What are the four different afferent fibers, in order of decreasing diameter? What variable correlates with fiber diameter?

Which two are for pain? What kinds of pain does each correspond to?

Back 21

A-alpha fibers (proprioception), A-beta fibers (mechanoreceptors), A-delta fibers (pain: immediate sharp), and C-fibers (pain: delayed aching). As fiber diameter increases, speed of conduction increases.

Front 22

What are mediators? What are the two types of mediators? What is the ultimate result of the action of mediators?

Back 22

Mediators are molecules that contribute to the body's response to injury. The two types of injury are activators and sensitizers. The ultimate result of the induction of mediators is changes in gene expression.

Front 23

Where does incoming tactile/pain/temperature information converge? What phenomenon does this account for?

Back 23

All the somatosensory/pain/temperature info converges in the dorsal horn of the spinal cord. Some of the cells receive pain info from multiple areas; this explains the existence of referred pain (e.g. feeling arm pain when the source of the pain is your heart.

Front 24

Ask Dr. Brumberg to explain page 8, slide 4)

Back 24

Ask Dr. Brumberg to explain page 8, slide 4)

Front 25

How does the Weil stain affect tissue?

Back 25

The Weil stain makes axons black and cell bodies white, the inversion of how these things are typically colored.

Front 26

At the level of the medulla, is the incoming somatosensory fibers ipsilateral or contralateral? What about the pons, thalamus, and cortex? What is the point of decussation called?

Back 26

At the level of the medulla, the incoming somatosensory information is still ipsilateral. At the level of the pons, thalamus and cortex, the fibers have already decussated and it's contralateral. The point of decussation is called the medial lemniscus.

Front 27

What area do all sensory modalities except one converge onto? What is the exception?

Back 27

All sensory modalities converge on the thalamus. The exception is olfaction.

Front 28

How are slowly-adapting and rapidly-adapting inputs organized in the cortex?

Back 28

Slowly-adapting and rapidly-adapting inputs are segregated in the cortex into different columns.

Front 29

What do the barrels in the rodent somatosensory cortex correspond to? Why does this make them a good model for plasticity?

Back 29

The barrels correspond to individual whiskers on the contralateral face. This model system is ideal for studying plasticity because removal or stimulation of a whisker has observable consequences on the neighboring barrels.

Front 30

What does "Monocular deprivation Induced plasticity" refer to? What researchers are associated with this phenomenon?

Back 30

"Monocular deprivation Induced plasticity" refers to the failure of the blinded hemisphere to develop normal ocular dominance columns, while the control (un-deprived) hemisphere developed normal columns. This experiment, done by blinding kittens, is associated with Hubel and Weisel.

Front 31

Give three examples of plasticity?

Back 31

Removing appendages from owl monkeys results in the adjacent areas expanding to occupy empty area. Phantom limbs are the brains way of accounting for regions of the body that do not exist anymore, leading to phantom sensations. Musicians have expanded somatotopic maps in the side of the brain that control the playing hand than the opposite hemisphere.