Spinal cord pathways Flashcards
Afferent tract neurons are segregated in the spinal cord based on
modality and axonal diameter
Large diameter neurons will:
Ascend within the Posterior Funiculus in the Fasciculus Cuneatus or Fasciculus Gracilis (aka Dorsal Column)
Synapse on interneurons or LMNs in the gray matter
Small diameter neurons will:
Synapse on 2nd order afferents in the spinal cord (spinothalamic tract)
Synapse on interneurons in the gray matter
Neuronal nomenclature across simple pathways follows some basic rules:
Neurons are given different names based on where they are situated along a neural circuit or pathway Afferent - Primary afferent - 2˚ [afferent] or 2nd order - 3˚ [afferent] or 3rd order
Efferent
- Upper Motor Neuron
- Lower Motor Neuron
Both primary afferents and lower motor neurons are, at least in part, the stuff that makes up spinal nerves and cranial nerves
How to understand decussation in afferent pathways: touch and pain
Both pathways decussate, but at different places within the CNS.
Both pain and basic touch pathways converge at the level of the thalamus
The 2˚ neurons synapse with the 3˚ neurons
Damage to the spinal cord fibers (tract) of the pain pathway (which are 2˚ neurons) will cause
contralateral symptoms
Damage to the spinal cord fibers (tract) of the basic touch pathway (which are primary afferents) will cause
ipsilateral symptoms
First 2 Pathways: Dorsal Columns (aka Posterior Columns, Medial Lemniscus)
Type of information in pathway: Tactile discrimination, conscious proprioception
Point of origin, receptors involved: Meissner’s corpuscles, merkel’s disks, pacinian corpuscles, ruffini’s endings in skin muscle spindles, golgi tendon organs in muscles, joints and tendons
Where primary cell bodies are located: DRG
Where 1st synapse is: Nucleus cuneatus and nucleus gracilis in caudal medulla
Where in Spinal Cord it enters, travels: Medial aspect of dorsal root into fasciculus cuneatus and fasciculus gracilis
Where/if it decussates: Internal arcuate fibers ventral to cuneatus and gracicils (Becomes “Medial Lemniscus”)
Where second synapse is: Ventral posteriolateral nucleus (VPL) of the Thalamus
Final destination: Primary somatosensory cortex (via internal capsule and corona radiata)
Fasciculi Cuneatus and Gracilis terminate in
Nuclei Cuneatus and Gracilis
Tactile, nociceptive and consicous proprioceptive info represented in the
primary somatosensory cortex
3rd Pathway: Neospinothalamic tract
Anterolateral system:
Type of information in pathway: Pain, temperature, poorly localized touch
Point of origin, receptors involved: Free nerve endings (TRP channels) in skin, viscera, muscles
Where primary cell bodies are located: DRG
Where 1st synapse is: Lamina I, II
Where in Spinal Cord it enters, travels: dorsal horn (Lissauer’s Fassciculus to ascend at least 1 segment), after 1st synapse, travels through anterior white commissure, ascends through anterolateral spinothalamic tract
Where/if it decussates: Spinal cord, after 1st synapse
Where second synapse is: Ventral posteriolateral nucleus (VPL) of the Thalamus
Final destination: Primary somatosensory cortex (via internal capsule and corona radiata)
4th Pathway: Paleoospinothalamic tract
Anterolateral system:
Type of information in pathway: Poorly localized pain
Point of origin, receptors involved: Free nerve endings (TRP channels) in skin, viscera, muscles
Where primary cell bodies are located: DRG
Where 1st synapse is: Lamina I – VI
Where in Spinal Cord it enters, travels: dorsal horn (Lissauer’s Fassciculus to ascend at least 1 segment), after 1st synapse, travels bilaterally, ascends through anterolateral spinothalamic tract
Where/if it decussates: Spinal cord, after 1st synapse
Where second synapse is: Intralaminar nuclei of the Thalamus
Final destination: Bilateral cortex, poorly localized (includes cingulate gyrus and insula)
4 Tracts makeup unconscious proprioception
Dorsal spinocerebellar
Ventral spinocerebellar
Rostral spinocerebellar (?)
Cuneocerebellar
How to understand decussation in afferent pathways: unconscious proprioception
Information regarding the positioning of muscles, bones and joints feeds into the cerebellum
This is only a 2-neuron chain (only primary and 2˚ neurons)
There is No Decussation (with one exception)
Damage anywhere along this pathway should have ipsilateral symptom presentation
5th and 6th pathways: Dorsal spinocerebellar and cuneocerebellar
Type of information in pathway: Unconscious proprioception
Point of origin, receptors involved: muscle spindles, golgi tendon organs in muscles, joints and tendons
Where primary cell bodies are located: DRG
Where 1st synapse is: Clarke’s Nucleus (aka nucleus dorsalis) of thoracic cord if dorsal spinocerebellar. Accessory cuneate nucleus in caudal medulla if cuneocerebellar
Where in Spinal Cord it enters, travels: Posterior funiculi (hitchhikes with dorsal columns)
Where/if it decussates: NONE
Where second synapse is: vermis/paravermis of the cerebellum via inferior cerebellar peduncle
Final destination: Deep cerebellar nuclei (via purkinje cells)
