Week 8 Flashcards
(68 cards)
Somatosensory system unique in 2 ways
- receptor organ is the skin-largest sensory organ in body
2. sensations produced are quite varied
4 distinct somatic sensations
- fine touch
- proprioception sensations
- pain
- temperature
pain receptor sub-types (nociceptors)
- mechanical
- thermal
- polymodal (combo of mechanical and thermal)
Important shared nociceptor quality of neurons
all have bare nerve endings
Receptor types are different in:
- morphology of peripheral ending
- sensitivity to stimulus energy
- diameter of axon
- whether axon has myelin or not
sensitivities of morphology of peripheral ending
the closer to the surface the more sensitive to fine touch
the deeper, the more sensitive to pressure
nerve endings types that fire only at beginning of stimulus
meissner corpuscle
&
pacinian corpuscle
nerve endings types that fire during entire stimulus
merkel cells
&
ruffini endings
order of cell types from fine touch to pressure
- meissner corpuscle (closest to surface)
- Merkel cells
- pacinian corpuscle
- ruffini endings (deepest)
Diameter of axon significance (generally)
larger the axon, the faster the signal travels
C-fibers
smallest diameter of axon
*for slow burning pain
A-delta fibers
medium seized diameter
*for sharp pain
A-Beta fibers
largest diameter
*for subcutaneous mechanoreceptors
TRPA1 channels
sensitive to chemical and mechanical stimuli
-mediate painful sensations
3 somatosensory CNS pathways
- anterolateral system (pain)
- Dorsal Column Medial Lemniscal system (touch)
- Spino-Cerebellar Tract
Cross sites of dorsal column path vs anterolateral
- Dorsal colum medial lemniscal pathway crosses at medulla (important for touch)
- anterolateral crosses immediately at the spinal cord (important for pain)
Spinal cord Graymatter areas of dorsal column medial lemniscal system (horns and layers)
- dorsal horn (layers I-V) *sensory
- Intermediate horn (layers VI & VII)
- Ventral horn *motor (layers VIII & IX)
- layer X around central canal
6 notable nuclei of spinal cord gray matter & corresponding layers
- posterior marginal (layer 1)
- substantia gelatinosa (layer 2, some 3)
- Nucleus proprius (layers 3, 4, 5, 6)
- Clarke’s nucleus (layer 8)
- interomediolateral nuclei (layer 7)
- motor nuclei (layer 9)
spinal cord white matter divisions
- dorsal columns
- lateral columns
- ventral columns
Dorsal root
swelling, collection of cell bodies of sensory neurons (dorsal root ganglion)
ventral root
axons from motor neurons from gray matter
Dorsal Colum Medial Lemniscal system pathway (summary)
- pseudo-unipolar neurons synapse at dorsal horn
- dorsal horn synapses at dorsal column nuclei
- dorsal column nuclei cross via medial lemniscus
- ->synapses at VPL & P of thalamus - Thalamus synapses at Primary somatosensory (SI)
- SI synapses at SII and Parietal cortex
1st order neurons of Dorsal column system
receptor cells with somas in dorsal root ganglia
1st order neuron 3 possible courses
- enter dorsal column and ascend to more rostral CNS areas
- synapse in dorsal horn
- synapse in ventral horn (for reflexes)