Somatosensory System

Question 1

What are the three main divisions of the somatosensory system?

Answer 1

Exteroceptive (cutaneous senses)
Proprioceptive (posture and movement)
Enteroceptive (internal body)

Question 2

Once sensory neurones reach membrane potential what occurs?

Answer 2

Action potentials are triggered

Question 3

What is the modality of a sensory unit?

Answer 3

The stimulus that the primary afferent neurones are tuned to

Question 4

What is the threshold of a sensory unit?

Answer 4

The intensity of a stimulus required to excite a sensory unit

Question 5

Give examples of low threshold units

Answer 5

Low threshold mechanoreceptors (fine discriminatory touch)

Low threshold thermoreceptors (cool/cold/warm/hot)

Question 6

Give examples of high threshold units

Answer 6

High threshold mechanoreceptors
Thermal noiceptors (extreme degrees of heat)
Chemical nociceptors
Polymodal nociceptors

Question 7

What is adaption in terms of a sensory unit?

Answer 7

When the sensory unit determines whether it should change its firing rate

Question 8

What occurs in fast adaption?

Answer 8

When a constant stimulus causes the unit to stop firing quickly

Question 9

Give an example of a sensory receptor that conducts rapidly

Answer 9

Proprioceptors of skeletal muscle

Question 10

Give an example of a sensory receptor that conducts slowly

Answer 10

Itch

Question 11

What is the receptive field of a sensory receptor?

Answer 11

The site at which a sensory unit can be excited

Question 12

What are Merkel cell-neurite complexes formed from?

Answer 12

Many expanded nerve terminals with a closely associated Merkel cell

Question 13

What are Meissner corpuscles formed from?

Answer 13

A capsule where several axons zigzag between Schwann cells

Question 14

What are Ruffini endings sensitive to?

Answer 14

Shearing forces

Question 15

What do Pacinian corpuscles detect?

Answer 15

Pressure

Question 16

Give some of the sensory receptors of hairless skin

Answer 16

Merkel-cell neurite complex
Ruffini endings
Pacinian corpuscles
Meissner corpuscles

Question 17

What does the dorsal column pathway detect?

Answer 17

Fine touch

Pressure

Question 18

What does the spinothalamic tract detect?

Answer 18

Pain

Temperature

Question 19

Within the dorsal column, sensory input to T6 and below runs in what?

Answer 19

Fasciculus gracilius

Question 20

Within the dorsal column, sensory input ot above T6 travels in what?

Answer 20

Fasciculus cuneatus

Question 21

What are the capabilities of the dorsal column pathway?

Answer 21

Stereogenosis
Vibration detection
Fine touch

Question 22

Where do central terminals of the trigeminal nerve synapse?

Answer 22

Second order neurones in chief nucleus/spinal nucleus

Question 23

What are the areas of the central sulcus (SI) called?

Answer 23

Broadmann area (1/2/3a/3b)

Question 24

The receptive fields of SI neurones form what?

Answer 24

A somatotopic map of the body surface

Question 25

Thalamic inputs to the SI terminate on which layer of the cortex?

Answer 25

Layer IV

Question 26

What happens to the area of SI representing a finger if the finger is lost?

Answer 26

After several months it responds to stimulation from adjacent digits

Question 27

What does the posterior parietal cortex (SII) do?

Answer 27

Receives and intergrates information from the SI as well as visual and auditory areas