Somatosensory system

Question 1

Describe meissner corpsucles

Answer 1

• In the dermal papillae of the skin
• Respond to light touch and temperature
• Vibrations of 30-50Hz

Question 2

Describe hair follicles

Answer 2

• Located in the epithelia

- Respond to many types of modalities which move the hair follicles

Question 3

What are primary afferent neurons classified by?

Answer 3

Conduction velocity which reflects diameter

Question 4

What do the 3rd order neurons in the somatosensory system do?

Answer 4

Reverse topology so lower body neurons synapse on the more medial cortex

Question 5

What is the occupied size of each body part in the cortex proportional to to?

Answer 5

• Importance
• Density of input (number of neurons)
• More of cortex dedicated to areas with small receptive fields

Question 6

What sensory receptors have both rapidly and slowly adapting subtypes?

Answer 6

Hair follicles

Question 7

Describe tactile discs

Answer 7

• Located in the epidermis

- Respond to light touch, texture and temperature

Question 8

What are the dorsal column nuclei?

Answer 8

• In the brainstem

- Cuneate and gracile nucleus

Question 9

Describe pacinian corpsucles

Answer 9

• In the dermis, joint capsules, viscera
• Respond to deep pressure and tickle
• Vibrations of 250-350Hz

Question 10

What is special about the cortical map?

Answer 10

• It has plasticity
• If you stimulate an area more it will take over more of the cortical map in expense to neighboring areas
• Vice versa

Question 11

Describe ruffini corpsucles

Answer 11

• Located in the dermis, joint capsules and subcutaneous tissue
• Respond to heavy touch, skin stretch and joint movement

Question 12

What are sensory modalities?

Answer 12

• What we perceive after a stimulus

Eg. hot, cold, rough, smooth, pain, pressure, tickle

Question 13

As well as the brain, where else in the body is the body mapped?

Answer 13

• Thalamus

- Dorsal column nucleus

Question 14

How are the somatosensory projections organised?

Answer 14

• Topographically, spatial relations are maintained throughout space
• This reflects the topographic projection in the brain, producing a map of the body in the cortex

Question 15

What neurons are classed as ‘lower body’?

Answer 15

Below T6

Question 16

What pathway do the lower body 1st order neurons follow and where do they synapse?

Answer 16

The medial pathway and synapse in the gracile nucleus

Question 17

What are 3 slowly adapting sensory receptors?

Answer 17

1) Ruffini corpsucles
2) Tactile discs
3) Free nerve endings

Question 18

What is the spinothalamic tract?

Answer 18

Carries pain and temperature signals to the thalamus

Question 19

Where are different sensory modalities localised?

Answer 19

Along the sagital axis of the cortex

Question 20

Where are the areas of the body mapped in the cortex?

Answer 20

In the primary somatosensory cortex (post central gyrus)

Question 21

What are the 2 rapidly adapting sensory receptors?

Answer 21

1) Meissner corpsucle (tactile)

2) Pacinian corpsucle (lamellated)

Question 22

What is the relationship between dermatomes, dorsal root ganglions and spinal segments?

Why?

Answer 22

• One dermatomes is innovated by one dorsal root ganglion
• One to one correspondance with spinal segments
• Dermatomes deriving from somites
• In the embryo one somite per dorsal root ganglion

Question 23

What do the 2nd order neurons do?

Answer 23

• Relay signals from the spinal cord to the thalamus

- Cross the midline (commissural)

Question 24

What pathway do the upper body 1st order neurons follow and where do they synapse?

Answer 24

The lateral pathway and synapse in the cuneate nucleus

Question 25

What is the medial lemniscal tract?

Answer 25

Carries mechanoreceptive and proprioceptive signals to the thalamus

Question 26

What does the size of a receptive field depend upon?

Answer 26

Positon in the body

Question 27

What is the somatosensory system?

Answer 27

The part of the peripheral nervous system which innovates the skin, joints and skeletal muscle

Question 28

Describe free nerve endings

Answer 28

• Widespread, located in epithelia and connective tissue

- Respond to pain and temperature

Question 29

What are primary afferent neurons from the skin designated by?

Answer 29

Letters
A = fastest/fattest
(broken down into greek letters)
C = slowest

Question 30

What do the 3rd order neurons do?

Answer 30

Carry signals from the thalamus to the cortex

Question 31

What do the 2nd order neurons in the somatosensory system do?

Answer 31

• Cross the midline and and ascend in the medial lemniscus pathway
• Topology reversed

Question 32

What are primary afferent neurons from the muscle designated by?

Answer 32

Roman numerals
I = Largest
IV = Slowest

Question 33

How is sensory information organised in the body?

Answer 33

• Cell bodies of sensory neurons are grouped in the dorsal root ganglion
• Projections are organised into layers in the dorsal horn
• Each layer is a specific receptor and a specific sensory modality
• Spatially organised and remain this way as it is carried into the brain

Question 34

What do the 1st order neurons do?

Answer 34

Detect stimuli and transmit it to the spinal cord

Question 35

What are the two proprioceptors?

Answer 35

• Muscle spindles

- Golgi tendon organs