Somethesis

Question 1

There are two broad categories of mechanoreceptors. What are they and how do they differ?

Answer 1

Slowly adapting- respond to enduring stimuli; has a strong action potential when the stimulus begins and maintains this action potential
Rapidly adapting-only expresses an action potential when the stimulus is applied

Question 2

What type of axon innervates all mechanoreceptors?

Answer 2

Large, myelinated

Question 3

Where are Meissner corpuscles found? Are they rapid or slow adapting?

Answer 3

Superficial layers of skin, generally in areas of high sensitivity; rapid

Question 4

Are Merkel cells slow or rapid adapting? How is their structure different from Meissner corpuscles?

Answer 4

Slow; has multiple receptors that are innervated by the same axon

Question 5

Where are Ruffini’s end organs found?

Answer 5

Deep layers of the skin

Question 6

Are Pacinian corpuscles slow or rapid adapting? What do they respond to? What is unique about their structure?

Answer 6

Rapid; Respond to pressure/motion; Comprised of lamellae that allow a stimulus to dissipate quickly allowing it to respond more quickly to future stimuli since the previous one has already subsided

Question 7

How would you define two point discrimination?

Answer 7

The minimum distance at which you can still distinguish two different pins as being separate

Question 8

Two point discrimination is related to the receptor density in the area as well as the receptor field (the area of skin that is directly innervated by a neuron as well as the adjacent area that is also stimulated). What is this relationship?

Answer 8

The distance needed to distinguish between two points decreases as receptor density increases and receptor field decreases

Question 9

What is somatosensory system designed to give us information about?

Answer 9

Spatiotemporal information- the idea that you could close your eyes and put and object in your hand and be able to identify it is an example of spatiotemporal

Question 10

What are the two major ascending tracts that carry somatosensory information to the cortex?

Answer 10

Anterolateral

Dorsal Column-Lemniscal

Question 11

What type of information does the dorsal column-lemniscal system detect? Does it have the ability to detect two-point discrimination?

Answer 11

Epicritic

Can detect two point discrimination

Question 12

Where do axons from the periphery that are destined for the dorsal column tract enter the spinal cord? Where do they go after entering the spinal cord?

Answer 12

Enter laterally and then synapse in the dorsal horn with the cell body. From there the nerve branches; one axon enters the dorsal column and heads up the spinal cord towards the brain while the other axon helps in local spinal control

Question 13

The dorsal columns have a somatotopic distribution. Which side of the dorsal column receives the lower extremities and which side receives the upper extremities?

Answer 13

Lower extremities are located in the medial dorsal column, while upper extremities are located in the lateral dorsal column

Question 14

Where does the dorsal column actually cross? What is the name of the nuclei?

Answer 14

Medulla- cuneate and gracile nuclei

Question 15

What happens to the receptive field when the axons from the spinal cord all synapse on the same nuclei within the medulla? Do all action potentials from the periphery make it to the medulla?

Answer 15

Receptive Field grows
Not all action potentials make is because some inhibitory interneurons are present which ensures that background stimulation is cut out

Question 16

After the axons from the dorsal column synapse and decussate at the medulla and continue to move up the brain, what are these axons known as?

Answer 16

Medial lemniscus

Question 17

True or False: the dorsal column, medial lemniscus, thalamic nuclei, and primary cortex are all somatotopically organized?

Answer 17

True

Question 18

What nucleus in the thalamus receives the information from the medial lemniscus?

Answer 18

Ventral posterior nucleus

Question 19

The ventral posterior lateral nucleus or the ventral posterior medial nucleus brings the information from the head/hands/face to the lateral or the medial aspect of the primary somatosensory cortex?

Answer 19

Ventral posterior medial nucleus brings information from the head/face/hands to the lateral portion of the primary somatosensory cortex

Question 20

Which part of SI do most thalamic fibers terminate?

Answer 20

3a and 3b

Question 21

How was the sensory homonculus discovered?

Answer 21

Probed monkeys at different sites and then found where action potentials were generated in the brain; later during neurosurgery probed certain parts of brain and asked patient where they felt sensation

Question 22

The primary somatosensory cortex contains columns. What information is contained in each of these columns?

Answer 22

All of the mechanoreceptors for a very specific area

Question 23

What experiment was used to demonstrate that the somatosensory cortex exhibits plasticity?

Answer 23

Trained monkeys to used their 3 middle fingers and spin a record repeatedly. Found that the corresponding region in the somatosensory cortex expanded at the expense of the other two fingers