Somatosensation I

Question 1

What types of sensations does somatosensation convey?

Answer 1

Touch, proprioception, heat/cold and pain/itch

Question 2

What is proprioception?

Answer 2

awareness of body position

Question 3

What are the two subsystems of somatosensation?

Answer 3

Tactile sensation and pain and temperature sensation

Question 4

What is an epineurium?

Answer 4

Connective tissue ensheathing the whole nerve

Question 5

What are dorsal root ganglion cells?

Answer 5

The sensory receptors of the somatosensory system

Question 6

What are the two systems of the dorsal root ganglion cells?

Answer 6

Large and small fibres

Question 7

What are the features of the large dorsal root ganglion fibres?

Answer 7

Large diameter, myelinated and fast conduction

Question 8

What are the features of the small dorsal root ganglion fibres?

Answer 8

Small diameter, thinly myelinated or unmyelinated and medium or slow conducting

Question 9

What does the quality of sensation depend on?

Answer 9

Afferent fibre type

Question 10

What are the types of receptors in the somatosensory system (and with which system are they used)?

Answer 10

A-alpha afferents (proprioception), A-beta afferents (tactile afferents) and free nerve endings

Question 11

What are the features of A-alpha afferents?

Answer 11

Large diameter, myelinated, fastest conducting and includes muscle spindles

Question 12

What are the features of A-beta afferents?

Answer 12

Large diameter, myelinated, second fastest conducting and includes superficial and deep classes

Question 13

What are examples of superficial A-beta afferents?

Answer 13

Meissners corpuscules and merkels discs

Question 14

What are meissners corpuscules good at?

Answer 14

Detecting changes

Question 15

What are merkels discs good at?

Answer 15

Very specific touch

Question 16

What are examples of deep A-beta afferents?

Answer 16

Ruffini corpuscules and pacinian corpuscules

Question 17

What are the features of free nerve endings?

Answer 17

Low resolution tactile, temperature and pain

Question 18

What are the features of A- delta fibres?

Answer 18

Small diameter, thinly myelinated and moderate conduction velocity

Question 19

What are the features of C-fibres?

Answer 19

Small diameter, unmyelinated and slow conducting

Question 20

What is a muscle spindle?

Answer 20

Specialised muscle fibres embedded within contractile muscle fibres of a voluntary muscle

Question 21

What attaches to muscle spindles?

Answer 21

Group I and II afferent axons

Question 22

What is a golgi tendon organ?

Answer 22

Specialised sensory endings near the joint of a muscle to its tendon that senses tension in a muscle

Question 23

How is a receptive field measured?

Answer 23

The amount of indentation needed to produce a threshold response

Question 24

What are the two major central pathways of the somatosensory system?

Answer 24

Dorsal column-medial lemniscal (DCML) systems
Spinothalamic tract (STT)

Question 25

What does the dorsal column medial lemniscal system mediate?

Answer 25

Discriminative touch, vibration and proprioception

Question 26

Where does the DCML system accept inputs from?

Answer 26

A-alpha and A-beta afferent fibres

Question 27

What does the spinothalamic tract mediate?

Answer 27

Coarse touch, temperature and pain

Question 28

Where does the STT accept inputs from?

Answer 28

A-delta and C fibres

Question 29

What is the STT pathway?

Answer 29

Spinal cord -> medulla -> midbrain -> ventral posterior nuclear complex of the thalamus

Question 30

What is the DCML pathway?

Answer 30

Spinal cord -> cunate nucleus -> medial lemniscus -> midbrain -> ventral posterior nuclear complex of the thalamus

Question 31

What is the ventral posterior complex the route for?

Answer 31

Tactile and proprioceptive information to reach the thalamus

Question 32

What is the ventral posterior nucleus divided into?

Answer 32

Lateral and medial

Question 33

What does the VPM receive?

Answer 33

Sensory information from the face

Question 34

What does the VPL receive?

Answer 34

Sensory information from the rest of the body

Question 35

What do the VPM and VPL generally target?

Answer 35

Primary somatic sensory cortex (brodmann areas 1, 2 and 3)

Question 36

How thick is the cerebral cortex?

Answer 36

1-2mm

Question 37

How many neurons does the cerebral cortex contain?

Answer 37

100,000 neurons per cubic millimetre

Question 38

What are some cytoarchitectural differences between brodmann areas?

Answer 38

Relative thickness of layers, cell size and density

Question 39

How many brodmann areas are there?

Answer 39

>50

Question 40

Where does the primary somatosensory cortex project to?

Answer 40

Secondary somatosensory cortex and other parietal areas