Somatosensory System I- Introduction

Question 1

What are the modalities that the sensory system mediates?

Answer 1

1. Discriminative Touch
2. Proprioception
3. Nociception
4. Temperature Sense
5. Light Touch

Question 2

Define Discriminative Touch

Answer 2

The ability to recognize the shape, size, and texture of objects and their movement across the skin. Includes vibratory sense and pressure.

Question 3

What is Conscious Proprioception and what are its categories?

Answer 3

The sense of static position and movement of the limbs and body.

• Limb Position Sense: The sense of the stationary position of the limbs.
• Kinesthesia: The sense of limb movement.

Question 4

What does unconscious proprioception refer to?

Answer 4

Proprioceptive information that is conveyed from the spinal cord to the cerebellum for the modulation of movements.

Question 5

Define nociception?

Answer 5

the signaling of tissue damage or chemical irritation, typically perceived as pain or itch.

Question 6

define Temperature Sense

Answer 6

the sense of warmth or cold

Question 7

define light touch

Answer 7

the sense of cutaneous touch or light pressure. Absence produces little, if any disturbance in tactile sensibility.

Question 8

What class of neurons do all modalities share?

Answer 8

Dorsal root ganglion neurons (pseudounipolar)

Question 9

What are the two regions of dorsal root ganglions?

Answer 9

1. Receptors

2. Fibers (Axons)

Question 10

What does the structure of a receptor determine?

Answer 10

the sensory function of each dorsal root ganglion

Question 11

Describe the structure of a dorsal root ganglion receptor.

Answer 11

Most of them have specialized CT capsules surrounding the nerve terminal, when they become deformed in particular ways, this excites the dorsal root ganglion neuron

Question 12

What do Mechanoreceptors in the skin do?

Answer 12

Mediate touch

Question 13

Receptive fields are smaller in what part of the skin? Why is it important?

Answer 13

Smaller in the superficial part of the skin

-important for tactile discrimination

Question 14

Receptive fields are larger in what part of the skin? Why is it important?

Answer 14

Larger in the deep layer of the skin

-important for detecting global properties of objects

Question 15

RA receptors sense what?

Answer 15

The motion of the objects (speed and duration).

-Have lower thresholds, so they detect minute vibrations

Question 16

SA receptors sense what?

Answer 16

• Signal the pressure and shape of objects
• Higher thresholds, that require more salient bumps or edges to activate. Once stimulated, have a clearer image of contours.

Question 17

The spatial characteristics of objects are signaled by what?

Answer 17

Populations of mechanoreceptors

Question 18

What do Mechanoreceptors in muscles and joints do, and what are examples?

Answer 18

Mediate proprioception

-Muscle spindles, golgi tendon organs, joint receptors

Question 19

What do Nociceptors do?

Answer 19

Mediate Pain

-Serve an important protective function, warning of injury that should be avoided or treated.

Question 20

What types of pain are there?

Answer 20

1. Acute vs. Chronic

2. Nociceptive vs. Neuropathic

Question 21

Nociceptive pain has what 2 levels?

Answer 21

1. Sharp, Localized

2. Second- Dull/Burning, Diffiuse

Question 22

What are the 3 types of Nociceptors?

Answer 22

1. Mechanical
2. Thermal
3. Polymodal

Question 23

What effective stimuli does the Mechanical receptors cause?

Answer 23

Intensive pressure applied to the skin. Evokes sensations of sharp or pricking pain.

Question 24

What effective stimuli do thermal receptors cause?

Answer 24

Extreme temperatures (too hot or too cold).

Question 25

What effective stimuli do polymodal receptors cause?

Answer 25

High intensity mechanical, thermal (both hot and cold), or chemical stimuli. Evokes sensations of slow, burning pain.

Question 26

Describe Thermoreceptors

Answer 26

Mediate temperature

-Show a graded response to changes in temperature

Question 27

What are the types of thermal sensation?

Answer 27

• Cold
• Cool
• Warm
• Hot

Question 28

What does the code for skin temperature involve?

Answer 28

Comparing the relative activity of the different populations of thermal receptors.

Question 29

How are fibers classified?

Answer 29

1. Based on conduction velocity in mixed peripheral nerves

2. Fiber diameter in cutaneous nerves

Question 30

Proprioceptors and mechanoreceptors are innervated by what type of fibers?

Answer 30

-Large-diameter myelinated axons with fast conduction velocities

Question 31

Nociceptors and thermoreceptors are innervated by what type of fibers?

Answer 31

-Small myelinated or unmyelinated axons with slow conduction velocities.

Question 32

The sensory specialization of dorsal root ganglion neurons are preserved where?

Answer 32

In the central nervous system through distinct ascending pathways for various modalities.

Question 33

Describe the neural pathways of the somatosensory system.

Answer 33

-Comprised of 3 neurons (periphery to the highest levels of CNS

Question 34

Where are the cell bodies of 1st order neurons?

Answer 34

Dorsal root or cranial nerve ganglia

Question 35

Where are the cell bodies of the 2nd order neurons?

Answer 35

Lie in the nuclei in the spinal cord and brainstem

Question 36

Where are the cell bodies of the 3rd order neurons?

Answer 36

Lie in the thalamus