Anatomy and Function of the somatosensory system.

Question 1

Nociception is what?

Answer 1

Pain and temperature

Question 2

What are the nociceptor receptors?

Answer 2

Mechanoreceptors and Thermoreceptors/Chemoreceptors

Question 3

Hapsis is what? Picked up by what kind of receptors?

Answer 3

Touch, pressure and temperature. Mechanoreceptors

Question 4

What are the 5 types of hapsis mechanoreceptors and what do each detect?

Answer 4

Meissner’s corpuscles - light touch.
Pacinian corpuscles - vibration and textures.
Ruffini corpuscles - skin stretch and finger position.
Merkel’s receptors - light pressure.
Hair receptors - flutter or steady state pressure.

Question 5

DCML pathway detects what?

Answer 5

Fine touch, discriminitive touch and sense of position.

Question 6

1st order neurons’ axon projects where?

Answer 6

Dorsal horn in spinal cord.

Question 7

Cell bodies of first order neurons in DCML pathway are located where?

Answer 7

Dorsal root ganglia.

Question 8

What are the two types of tracts in the DCML pathway?

Answer 8

Fasiculus cuneatus (lateral) - upper limb - synapse in cuneate nucleus.
Fasiculus gracilis (medial) - lower limb - synapse in gracile nucleus.

Question 9

2nd order neurons of the DCML pathway decussate and synapse where?

Answer 9

Brain stem and Thalamus.

Question 10

Both tracts run parallel to what nucleus?

Answer 10

VPN in thalamus.

Question 11

3rd order neurons transmit to where?

Answer 11

Sensory cortex.

Question 12

Cell bodies of the 3rd order neurons of the DCML pathway are found where?

Answer 12

Thalamus.

Question 13

Anterolateral system detects what?

Answer 13

Crude touch, non-discriminitive touch, sense of position.

Question 14

What are the first order neurons comprised of?

Answer 14

C and Aδ fibres.

Question 15

Describe the characteristics of C-fibres.

Answer 15

Slow, prolonged therefore less intense. Synapse in the dorsal horn, laminae 1 & 2. Indirect with interneurons.

Question 16

Describe the characteristics Aδ fibres.

Answer 16

Fast, sharp localised pain, synapse in dorsal horn, laminae 1 & 4. Direct with 2nd order neurons.

Question 17

C - fibres release what?

Answer 17

Neuropeptide substance P and calcitonin gene releasing peptide - CGRP. Dilates blood vessels and causes histamine, PG and bradykinin release.

Question 18

Spinothalamic and Spinoreticular tracts are composed of what type of neurons?

Answer 18

1st, 2nd and 3rd order neurons.

Question 19

What are the differences between the spinothalamic and spinoreticular tract?

Answer 19

Spinothalamic is direct and synapses with the VPN nucleus in the thalamus. Only about 15% nociceptive fibres follow the tract.
Spinoreticular is indirect and has multiple synapses in the reticular formation before reaching the intralaminar nuclei in thalamus. Approximately 85% of nociceptive fibres follow this tract.

Question 20

Spinocerebellar tract assists with what?

Answer 20

Postural adjustments and coordination.

Question 21

Is the spinocerebellar tract ipsilateral or contralateral? And does it have 3rd order neurons?

Answer 21

Ipsilateral fibres. They have no 3rd order neurons.

Question 22

Spinocerebellar tract is composed of which 3 tracts?

Answer 22

Dorsal - lower limb
Ventral - lower limb
Cuneocerbellar - upper limb and neck.

Question 23

Damage to DCML pathway causes what?

Answer 23

Loss of discriminative fine touch, the sensation of vibration and proprioception in the ipsilateral side of the body below the lesion.

Question 24

A positive Rhomberg sign is a good sign of what?

Answer 24

DCML damage.

Question 25

What is Freidreich’s ataxia?

Answer 25

Hereditary disorder in which the spinocerebellar tracts and the DCML pathways degenerate and produce deteriorating ataxia.