Somatosensation 1

Question 1

What sensations does the somatosensory system convey?

Answer 1

• Touch
• Propriception
• Heat,cold
• Pain,itch

Question 2

What does the somatosensory system connect?

Answer 2

Connect the CNS to the body via peripheral nerves

Question 3

How many nerves do we get from the spine?

Answer 3

From the spine we get 31 nerves from each segment

Question 4

What is the CNS connected to the body via

Answer 4

The CNS is connected to the body via spinal nerves and cranial nerves

Question 5

What are the connective tissue element in peripheral nerves?

Answer 5

Connective tissue elements:

• Epineurium
• Perineurium
• Endoneurium

Question 6

What roots does the spinal cord give rise to?

Answer 6

Spinal cord gives rise to dorsal and ventral roots

Question 7

What is the spinal cord roughly divided into?

Answer 7

The spinal cord is roughly divided into incoming sensory information in its dorsal half and outgoing ventral commands in its ventral half

Question 8

What do dorsal roots contain?

Answer 8

Dorsal roots contain incoming sensory axons

Question 9

What do ventral roots contain?

Answer 9

Ventral roots contain outgoing axons

Question 10

Where do the dorsal and ventral roots unite into?

Answer 10

Dorsal and ventral root unite into the spinal nerve

Question 11

What is white matter?

Answer 11

White matter is ascending and descending axon tracts

Question 12

What is grey matter?

Answer 12

Grey matter is the cell bodies, dendrites and synapses

Question 13

Where do the dorsal root ganglia occur?

Answer 13

They occur just as the dorsal and ventral roots fuse

Question 14

What do dorsal root ganglia contain?

Answer 14

Contain the cell bodies of all the sensory neurons of the somatosensory system

Question 15

What are the 2 systems in the dorsal root ganglia?

Answer 15

Two anatomically and functionally distinct systems:

• Large fibres
• Small fibres

Question 16

Large fibres

Answer 16

• Myelinated
• Faster conduction
• Tactile and proproceptive

Question 17

Small fibres

Answer 17

• Unmyelinated

- Temperature, pain, itch, crude touch

Question 18

What does specificity of sensation depend on?

Answer 18

Specificity of sensation depends on afferent fiber type

Question 19

What are the cutaneous classes in the skin of receptors of the somatosensory system?

Answer 19

• Meissner corpuscle (RA)

- Merkel disks (SA)

Question 20

what are the deep classes in the skin of receptors of the somatosensory system?

Answer 20

• Pacinian corpuscle (RA)

- Ruffis Corpuscle (SA)

Question 21

What do dorsal root ganglions contain and what is the action potential produced proportional to?

Answer 21

The axon terminals of the dorsal root ganglion contain ion channels which are mechanically sensitive
-Action potential produced is proportional to the strength of stimuli

Question 22

What does rapidly adaptive fibers signal?

Answer 22

Rapidly adaptive fibers signal changing stimuli

Question 23

What does slowly adaptive fibers signal?

Answer 23

Slowly adaptive fibers signal ongoing stimuli

Question 24

What does the pacinian corpuscle detect?

Answer 24

Pacinian corpuscle are good at detecting vibration

Question 25

What does the ruffini corpuscles detect?

Answer 25

Ruffini corpuscles detect stretch of skin

Question 26

What is the meissner corpuscles responsible for?

Answer 26

Meissner corpuscles are responsible for sensitivity to light touch

Question 27

What are the merkel disks responsible for?

Answer 27

Merkels disk are responsible for sensitivity to light touch

Question 28

What do muscle spindles do?

Answer 28

Muscle spindles send information of changes to muscle length

Question 29

What do golgi tendon organs sense?

Answer 29

Sense muscle tension and receptors of joints

Question 30

What are the 2 types of free nerve ending fibres?

Answer 30

• A delta fibres

- C fibres

Question 31

A delta fibres

Answer 31

• Thin

- Myelinated

Question 32

C fibres

Answer 32

• Thin

- Unmyelinated

Question 33

What does the ability to localize depend on?

Answer 33

Ability to localize depends on sensory receptive fields

Question 34

What are the 2 major central pathways of the somatosensory sytem

Answer 34

• Dorsal column(Medial lemniscal system)

- Spinothalamic tract(STT, also known as anterolateral system)

Question 35

What does the dorsal column mediate?

Answer 35

Dorsal column mediated discriminative touch, vibration, proprioception

Question 36

What does the spinothalamic tract mediate?

Answer 36

Spinothalamic tract mediates coarse touch, temperature and pain

Question 37

What is the pathway of the long fiber system in the somatosensory pathway?

Answer 37

• Primary afferent enters the spinal cord in the dorsal horns
• Then it ascends in white matter columns
• Then terminated in the medulla
• The medulla contains dorsal column nuclei
• Second order neurons then receive signals from the primary afferent and then cross and ascend up the medial lemniscus all the way to the thalamus
• Third order neurons then receive signals from the thalamus and send signals to the cortex

Question 38

What is the pathway of the small fiber system in the somatosensory pathway?

Answer 38

• Small fiber system terminate in the dorsal horn and synapse with second order neurons and ascend up the anterior lateral margins
• Second order neurons go to the thalamus
• Then to the cortex by third order neurons

Question 39

The regional variation in cortical cytoarchitecture?

Answer 39

Different areas of the cortex have the same basic cell types organised in layers with the same basic organisation

Question 40

How can regional differences be identified in the cortex?

Answer 40

Regional differences can be identified on the basis of relative thickness of the different layers, cell size and density