Somatosensory Part 1.1 Flashcards
proprioception, pathways
Proprioception: skin stretch receptors are?
Ruffini
Joint and Fascia receptors that detect stretch of CT are?
Ruffini and Pacinian
Proprioceptive receptors mediate muscle/joint position and movement using which kinds of axons?
A-alpha, A-beta
Discriminative Touch & Proprioception:
High or Low threshold mechanoreceptors?
Rapid or Slow conduction?
Ascending pathway?
Qualitative experience or Quantitative sense?
Low threshold
Rapid AP Conduction
Dorsal Column-Lemniscal System
Quantitative sense that provides localization of the stimulus
Non-discriminative touch, pain, temp:
High or Low threshold mechanoreceptors?
Rapid or Slow conduction?
Ascending pathway?
Qualitative experience or Quantitative sense?
High threshold
Slow AP conduction
Anterolateral System
Qualitative experience of stimulus
Dorsal Column-lemniscal System Pathway:
First, Second, Third Order Neurons
First Order Neuron: A-beta, sensory; dorsal columns (cuneate and gracile fasciculi) –> synapse onto cuneate and gracile nuclei in medulla
Second Order: cuneate & gracile nuclei decussate in medulla. axons form medial lemniscus (in pons and midbrain) which synapse onto thalamus
Third Order: thalamic neurons form part of internal capsule –> primary somatosensory cortex in postcentral gyrus
True or False: Axons of low threshold mechanoreceptors innervate several segments of spinal cord before entering brain stem?
True
a touch to your knee will alert other levels of spinal cord… prepares muscles and sensitivity of reflexes so that the next move of the leg will be appropriate
Anterolateral System Modalities
non-discriminative touch, pain, temp
Anterolateral System Pathway
First Order Neurons: A-delta, C, sensory
- synapse onto second order using transmitters (NO, glutamate…)
Second Order Neurons:
- dorsal horn -> decussate -> anterolateral system
> > > dorsal horn: Rexed’s Lamina - 6 layers - neuronal groups segregated by modality
lamina l, ll - pain)
lamina lV - touch)
Third Order Neurons:
- Lateral Thalamic Neurons (from neospinothalamic tract) to Primary Somatosensory Cortex
- Medial Thalamic Neurons (from paleospinothalamic tract) to Cingulate Gyrus & Insula
The Anterolateral Pathway splits in the brain stem before it reaches the brain. What are the two tracts and what modality is it specific for?
Neospinothalamic Tract
- to lateral thalamus and somatosensory cortex
- localization of sensation
Paleospinothalamic Tract
- to reticular formation, medial thalamus and cortex
- qualitative aspect of pain, temp, and non-discriminative touch
Ex for Pain:
neo - “there’s pain there!”
paleo - “it’s an awful pain”
What is syringomyelia? And what happens as a result?
degeneration of neurons in a region (cyst forms in center of cervical grey matter) Interfering w any axons crossing the midline (decussation of anterolateral second order neurons - spinothalamic). So results in bilateral loss of pain and temp in an area.
What is the Reticular Formation?
nuclei is brainstem that governs fundamental processes for higher organisms. Old portion of the brain.
What is the Brown-Sequard Syndrome? What happens as a result?
hemisection of spinal cord cuts through dorsal and anterolateral columns on one side.
- since dorsal-lemniscal system decussates at brain stem, there is loss of ipsilateral discriminative touch
- loss of ipsilateral motor control
- since anterolateral system second order neurons can decussate below level of lesion, loss of contralateral pain and temp.
Where does decussation happen in the Anterolateral System and the Dorsal-lemniscal System?
Dorsal-lemniscal System:
second order neurons of cuneate and gracile nuclei decussate in the medulla of the brainstem!
Anterolateral System:
second order neurons in dorsal horn decussate to the anterolateral system. (not in brain stem! local)
Ipsilateral or Contralateral?
Pain, Temperature
Contralateral
