Somatosensory Physiology

Question 0

What happens if you damage peripheral or central components of the somatosensory system ?

Answer 0

Neuropathy
Neuralgia
Phantom pain

Question 1

What is the fundamental function of the somatosensory system ?

Answer 1

Provide communication between us and the outside world

Question 2

What are primary afferents ?

Answer 2

Axons carrying info to he spinal cord from somatic receptors
- enter via the spinal nerve and dorsal roots

Question 3

What are motor efferents ?

Answer 3

Axons carrying info from the spinal cord to the periphery

- leave the spinal cord via the ventral roots and spinal nerve

Question 4

What are dermatomes ?

Answer 4

Subdivisions of the body surface

Each one represents area of the skin innervated by left and right dorsal roots of single spinal segment

Question 5

Dermatome boundaries are overlapping. What are the advantages/disadvantages of this ?

Answer 5

Advantage - means if you lose some sensory input then it is not completely lost from that area
Disadvantage - difficult to determine exactly where pain is felt

Question 6

What are the 4 classes of somatosensory receptors ?

Answer 6

Tactile
Nociceptice
Proprioception
Thermal

Question 7

What a Meissners corpuscles ?

Answer 7

Cutaneous receptor
Looping axonal terminal intertwined with supporting cells 
Low threshold mechanoreceptor
Just below epidermis 
Detect low freq 30-50Hz
Detect rough texture and movement

Question 8

What are merkels disks ?

Answer 8

Cutaneous receptors
Low threshold mechoreceptors
Dome structure on top of an axon terminal
Located in epidermal/dermal border
Detects form, shape, rough edges and texture

Question 9

What are pacinian corpuscles ?

Answer 9

Cutaneous receptors
Low threshold Mechanoreceptor
Sensory axon surrounded by fluid filled capsule
Located in deep dermis
Detects high freq vibrations of 250-350Hz
Detects fine texture and movement

Question 10

What are ruffinis endings !?

Answer 10

Cutaneous receptors
Low threshold mechanoreceptor a
Nerve terminals intertwined with collagen fibres
In deep dermis
Detect stretching indentation and lateral movements of skin

Question 11

What are the rapidly activity cutaneous mechanoreceptors ?

Answer 11

Pacinians and Meissners

Important for motor feedback during motor tasks

Question 12

What are the slowly activity cutaneous mechanoreceptors ?

Answer 12

Ruffinis and merkels disks

Question 13

Which mechanoreceptors are characteristic of discrete receptive fields of the hand and which have more broad receptive zones ?

Answer 13

Discrete zones= Meissners and merkels

Broad zones= pacinian and ruffinis

Question 14

What is human 2 point discrimination thresholds ?

Answer 14

Different parts of ten body pick up different mechanical thresholds
High sensitivity= fingertips and face
Low sensitivity= torso and limbs

Question 15

What are the theories of mechanotransduction ?

Answer 15

Pressure sensitive sodium channels 
Transduction by
- stretch activation 
- tethering 
- indirect gated

Question 16

What are the example channels involved in mechanotransduction ?

Answer 16

DEG/ENaC
TRPN and TRPA
TRPV

Question 17

What happens when capsaicin binds to VR1 ?

Answer 17

Causes influx of calcium

Question 18

What receptor family is involved in thermoregulation ?

Answer 18

Trp

Question 19

Which receptors are activated by menthol and capsaicin ?

Answer 19

Menthol = trpm8
Capsaicin= trpv1

Question 20

What fibres are associated with nociceptors ??

Answer 20

Unmyelinated c fibres

Thinly myelinated a-delta fibres

Question 21

What does muscle spindle and Golgi tendon organ detect ?

Answer 21

Muscle spindle - changes in muscle length

Golgi tendon organ - changes in muscle tension

Question 22

What are the properties of group 1(a-alpha) afferents ?

Answer 22

13-20 micrometer diameter
80-120m/sec conduction
Proprioceptors of skeletal muscle

Question 23

What are the properties of group 2(a-beta) afferents ?

Answer 23

6-12 micrometer diameter
35-75m/sec conduction
Mechanoreceptors of skin

Question 24

What are the properties of a-delta afferents ?

Answer 24

1-5 micrometer diameter
5-30m/sec conduction
Pain and temperature

Question 25

What are the properties of c afferents ?

Answer 25

0.2-1.5micrometer diameter
0.5-2 m/sec conduction
Pain, temperature and itch

Question 26

Which laminae do each of the afferent fibres terminate in ?

Answer 26

A-alpha- 6-9 - can directly innervate motor neurons in laminae 9
A-beta- 3-6
A-delta- 1 and 2
C- 1 and 2

Question 27

What info is carried in the dorsal colun medial lemniscus pathways ?

Answer 27

Gracilis- lower body and legs- everything caudal to t6
Cuneatus - upper body and arms- everything rostral to t6
Carry innocuous inputs from skin receptors

Question 28

How many areas did Brodmann subdivide the cortex into ?

Answer 28

47

Question 29

Where is s1 and what does it do ?

Answer 29

Post central gyrus - areas 1, 2, 3a, 3b

Receives string somatosensory inputs from thalamus

Question 30

Where is s2 and what does it do ?

Answer 30

Adjacent to s1 along lateral sulcus
Important in sensory and motor integration
Receives inputs from corpus callosum to form joined up body image

Question 31

Where are the association area and what do they do ?

Answer 31

Areas 5 and 7 of postural parietal cortex

Integrate multimodal senses

Question 32

What is asteroagnosia ?

Answer 32

Inability to identify objects on the basis of touch alone

Question 33

What is neglect syndrome ?

Answer 33

Body part or visual field is disregarded