Chapter 9 Somatic Sensory System: Touch & Proprioception

Question 1

Mechanoreceptors: Merkel Cell Afferent

Answer 1

Epidermis. Fine edges. Texture and form. Sustained (slow adaptation). Smallest receptive field.

Question 2

Mechanoreceptor: Pacinian Corpuscle

Answer 2

Dermis & Subcutaneous. Vibration, tool use. Entire finger or hand receptive field. Rapid adaptation (not sustained) response. Onion layers. Deepest. Very sensitive.

Question 3

Meissner Afferent

Answer 3

Dermis. Close to skin surface. Rapid adaptation (not sustained). Motion detection, grip control. Make up 40% innervating human hand.

Question 4

Ruffini corpuscle

Answer 4

Dermis. Skin stretch. Sustained (slow adaptation)

Question 5

Dermatomes

Answer 5

Territory innervated by each spinal nerve. Segmental arrangement of somatic nerves and targets they innervate (arise from somites - embryonic tissue)

Question 6

Adequate stimulus

Answer 6

hearing: sound; retina: light;

Question 7

What disease related to dermatomes? Chicken pox for adults

Answer 7

Herpes Zoster aka shingles

Question 8

2 Point Discrimination

Answer 8

The minimal receptor distance that two neurons can each distinctly detect a sensory stimuli

Question 9

Sensitivity vs Resolution

Answer 9

Sensitivity based on how tiny the stimulus is. Resolution is ability to discriminate. The larger the resolution, the lower the sensitivity

Question 10

Free nerve endings

Answer 10

Pain receptors

Question 11

The somatosensory afferents travel in bundles in the dorsal columns known as?

Answer 11

Fasciculus gracilus (lower limbs)
Fasciculus cuneatus (upper limbs, trunk, and neck)

Question 12

Cranial Nerve Ganglia vs Dorsal Root Ganglia

Answer 12

Head Neurons vs Body Neurons that provide information from PNS to CNS.

Question 13

Other name for somatotopic map

Answer 13

Homunculus (small man)

Question 14

Why is homunculus distorted?

Answer 14

It is systematic but distorted bc it is proportional to the amount of receptors found at different parts of the body. Finger tips have more receptor density than back.

Question 15

Neurons in dorsal root ganglia are often considered?

Answer 15

Pseudounipolar. Peripheral and central components of afferent fibers are continuous (central axon and peripheral axon are continuous)

Question 16

What are distinguished features of sensory afferents?

How are they differentiated

Answer 16

1. Axon diameter (The wider the faster the conduction speed of AP; e.g. pain/temp small, muscle sensory receptors largest)
2. Receptive Field size (Spatial accuracy) - the larger the less sensitive (more branching, smaller receptive field sizes) – dense innervation like fingers have smaller receptive fields (movement)
3. Temporal Dynamics. Rapid followed by silence vs slow response and sustained discharge (size and shape)
4. Quality of somatic sensory stimulation

(1. Conduction velocity, receptive field size, dynamics, and effective stimulus features vary in parallel pathways)

Question 17

Receptive field

Answer 17

area that corresponds to a significant change in the rate of AP.
Affect the spatial accuracy

Question 18

Nocireceptors

Answer 18

pain. free nerve endings.

Question 19

Meissner Afferent

Answer 19

Dermis. Close to skin. 40%. Rapid response. Sensitive, larger receptive field, lower spatial resolution, low spatial acuity (than Merkel). Skin motion detection, grip

Question 20

Merkel Afferents

Answer 20

Epidermis. Slow response. Form and texture. Details.

Question 21

Pacinian corpuscle

Answer 21

Dermis. Deepest. Vibrations, tools. Fastest response. Sensitive, large receptive field, low spatial resolution.

Question 22

Ruffini Afferent

Answer 22

Dermis. Deep. Slow response. Conformation/motion of finger/hand. Stretch.

Question 23

Increase sensitivity, what happens to receptive field?

Answer 23

Receptive field increases, spatial resolution decreases.

Question 24

nearsighted /myopia corrective lens

Answer 24

convex (minus)

Question 25

myopia malfunction

Answer 25

eyeball is too long, lens cant flatten out enough

Question 26

hyperopia

Answer 26

farsighted. eyeball is too short, refracting system is too weak. Convex lens

Question 27

Presbyopia

Answer 27

cant see near objects bc lens loses elasticity.