Anatomy and Function of the somatosensory system. Flashcards
Nociception is what?
Pain and temperature
What are the nociceptor receptors?
Mechanoreceptors and Thermoreceptors/Chemoreceptors
Hapsis is what? Picked up by what kind of receptors?
Touch, pressure and temperature. Mechanoreceptors
What are the 5 types of hapsis mechanoreceptors and what do each detect?
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.
DCML pathway detects what?
Fine touch, discriminitive touch and sense of position.
1st order neurons’ axon projects where?
Dorsal horn in spinal cord.
Cell bodies of first order neurons in DCML pathway are located where?
Dorsal root ganglia.
What are the two types of tracts in the DCML pathway?
Fasiculus cuneatus (lateral) - upper limb - synapse in cuneate nucleus. Fasiculus gracilis (medial) - lower limb - synapse in gracile nucleus.
2nd order neurons of the DCML pathway decussate and synapse where?
Brain stem and Thalamus.
Both tracts run parallel to what nucleus?
VPN in thalamus.
3rd order neurons transmit to where?
Sensory cortex.
Cell bodies of the 3rd order neurons of the DCML pathway are found where?
Thalamus.
Anterolateral system detects what?
Crude touch, non-discriminitive touch, sense of position.
What are the first order neurons comprised of?
C and Aδ fibres.
Describe the characteristics of C-fibres.
Slow, prolonged therefore less intense. Synapse in the dorsal horn, laminae 1 & 2. Indirect with interneurons.
Describe the characteristics Aδ fibres.
Fast, sharp localised pain, synapse in dorsal horn, laminae 1 & 4. Direct with 2nd order neurons.
C - fibres release what?
Neuropeptide substance P and calcitonin gene releasing peptide - CGRP. Dilates blood vessels and causes histamine, PG and bradykinin release.
Spinothalamic and Spinoreticular tracts are composed of what type of neurons?
1st, 2nd and 3rd order neurons.
What are the differences between the spinothalamic and spinoreticular tract?
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.
Spinocerebellar tract assists with what?
Postural adjustments and coordination.
Is the spinocerebellar tract ipsilateral or contralateral? And does it have 3rd order neurons?
Ipsilateral fibres. They have no 3rd order neurons.
Spinocerebellar tract is composed of which 3 tracts?
Dorsal - lower limb
Ventral - lower limb
Cuneocerbellar - upper limb and neck.
Damage to DCML pathway causes what?
Loss of discriminative fine touch, the sensation of vibration and proprioception in the ipsilateral side of the body below the lesion.
A positive Rhomberg sign is a good sign of what?
DCML damage.
What is Freidreich’s ataxia?
Hereditary disorder in which the spinocerebellar tracts and the DCML pathways degenerate and produce deteriorating ataxia.
