Somatic Sensory System

Question 1

How can nerve endings be classified?

Answer 1

Encapsulated and unencapsulated

Question 2

Give 3 examples of encapsulated nerve endings

Answer 2

• Meissner(tactile) corpuscles
• Pacinian (lamellate) corpuscles
• Ruffini corpuscles

Question 3

What are Pacinian corpuscles involved in?

Answer 3

Deep pressure, stretch, tickle, vibration

Question 4

What are Meissner corpuscles involved in?

Answer 4

Light touch/texture

Question 5

What are Ruffini corpuscles involved in?

Answer 5

Heavy touch, joint movement

Question 6

Give 2 examples of unencapsulated nerves

Answer 6

• Merkel(tactile) discs

- Free nerve endings

Question 7

What are free nerve endings involved in?

Answer 7

In epithelia; pain, heat cold

Question 8

What are Merkel discs involved in?

Answer 8

Light touch, texture, edges, shapes

Question 9

How are primary axons classified?

Answer 9

By conduction velocity

Question 10

What is sensory information organised into and where?

Answer 10

Into layers in the spinal cord dorsal horn

Question 11

What happens in the spinal cord dorsal horn?

Answer 11

Sensory information is organised into layers

Question 12

2 tracts that information gets delivered to the brain

Answer 12

• Medial lemniscal tracts

- Spinothalamic tracts

Question 13

What kind of info do medial lemniscal tracts carry?

Answer 13

Mechanoreceptive and proprioceptive information to the thalamus

Question 14

What kind of info do spinothalamic tracts carry?

Answer 14

Pain and temperature signals to the thalamus

Question 15

What do first order neurones do?

Answer 15

Detect stimulus and transmit to spinal cord

Question 16

What do second order neurones do?

Answer 16

Relay signals to the thalamus

Question 17

What do third order neurones do?

Answer 17

Carry the signal from the thalamus to the cortex

Question 18

Which order neurones are commissural?

Answer 18

2nd order

Question 19

How are axons organised in the medial lemniscal system?

Answer 19

Topographically

Question 20

In the medial lemniscal system, what are the two pathways?

Answer 20

Lateral and medial pathways

Question 21

Medial lemniscal system: upper body

Answer 21

• Follow the lateral pathway

- Synapse on 2nd order neurones in cuneate nucleus

Question 22

Medial lemniscal system: lower body

Answer 22

• Follow the medial pathway

- Synapse on neurons in gracile nucleus

Question 23

Medial lemniscal system: What are the lateral and medial pathways together known as?

Answer 23

Dorsal column nuclei

Question 24

What happens when 2nd order neurones cross the midline and ascend in the medial lemniscus? Which order neurones reverse topology?

Answer 24

The topology is revered so that the lower body axons are more lateral
3rd order axons reverse it

Question 25

What is a dermatome?

Answer 25

A region of skin innovated by a specific sensory ganglipn

Question 26

Why do dermatomes arise?

Answer 26

Due to dermis of each region deriving from a specific somite

Question 27

What is the area of cortex dedicated to each dermatome proportional to?

Answer 27

Density of innervation in that area, not the physical size of the area

Question 28

All sensory fibre tracts cross the midline in the brainstem: true or false?

Answer 28

False, olfactory system