NS Practical 2 Study Guide

Sensory Tracts:• DCML (discriminative touch, proprioception, vibration)• ALS (pain, temperature, itch, crude touch)•

University of St. Augustine

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Anatomical & Clinical Review{ Two long tracts of nervous system{ Somatosensory pathways

z Posterior column-medial lemniscal systemz Anterolateral systems

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Anatomical & Clinical Review

{ Somatotopically organized

Name Alternative name Myelinated Receptors Sensory modalities

A-alpha DCML

I Yes MS, GTO Proprioception

A-Beta DCML

II Yes MS Proprioception

Meissners Ruffini

merkels

Superficial touch

pacinian hair receptors

Deep touch, vibration

A-delta ALS

III Yes Free nerve ending

Pain, temp, and itch

C fiber ALS

IV No Free nerve ending

Pain, temp, and itch

University of St. Augustine

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Posterior Column-Medial Leminiscal Pathway

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Posterior Column-Medial Leminiscal Pathway { Somatotopic organization

z MNEMONIC x 2

University of St. Augustine

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Spinothalamic Tract & Other Anterolateral Pathways{ Sensory neuron fiber type{ Axon-small diameter, little to no myelination{ Receptor{ Sensory modality{ Enter SC via medial portion of dorsal root

entry zone{ Anterolateral pathways consist of three

tracts: spinothalamic, spinoreticular, & spinomesencephalic tracts

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Spinothalamic Tract & Other Anterolateral Pathways

Tract 1st Order 2nd Order 3rd Order

DCMLPeriphery—>

Nucleus Gracilis/Cuneatus

Nucleus Gracilis/Cuneatus, decussate via internal arcuate fibers (called

medial lemniscus when exits)—> VPL Thalamus

VPL of Thalamus to primary somatosensory

cortex via posterior limb of internal capsule

ALSPeriphery—>

Gray Matter of SC lamina I &

IV

Dorsal horn Lamina I/IV, decussate in anterior

commissure—> VPL of Thalamus

VPL of Thalamus to primary somatosensory

cortex DCML

ALS

Motor Tracts (function):• Lateral Corticospinal (movement of contralateral limbs)• Rubrospinal (movement of contralateral limbs/ fast finger movements)• Anterior Corticospinal (control of bilateral axial and girdle muscles• Vestibulospinal (Medial/Lateral) (M: head and neck positioning; L: balance)• Reticulospinal (automatic posture and gait related movements)• Tectospinal (coordination of head and eye movements)

Tract Origin Decussation Termination Function

Lateral corticospinal

PMC, frontal and parietal

Pyramidal decussation (cervicomedullary jxn)

Entire cord; Lateral Intermediate Zone

(LIZ), Lateral Motor Nuclei (LMN)

Movement of contralateral limbs

Rubrospinal Red nucleus in midbrain

Ventral tegmental decussation (midbrain)

Cervical cord; (LIZ, LMN)

Movement of contralateral limbs

(fast finger movements)

Tract Origin Decussation Termination Function

Anterior CST PMC and supplemental Motor areas None Cervical and upper T/S

cord; (MIZ,MMN)Control of B axial and

girdle muscle

Vestibulospinal Medial Lateral

Medial: med and inferior vestibular nuclei

Lateral: lateral vestib. None

Medial: cervical and upper T/S

Lateral: entire cord (MIZ,MMN)

M: head and neck positioning L: balance

Reticulospinal Tract

1. Pontine reticular formation

2.Medullary reticular formation

None Entire cord; (MIZ,MMN)

Automatic posture and gait related movements

Tectospinal Tract Superior Colliculi

Dorsal tegmental

deucssation in midbrain

Cervical cord; (MIZ,MMN)

Coordination of head and eye movement

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Lateral Corticospinal Tract{ Tract descends to enter

the anterior horn to synapse on lateral LMNs

{ Left cortex controls right body musculature, and right cortex controls left musculature due to the crossing of the tract (pyramidal decussation)

A lesion to the left lateral corticospinal tract in the spinal cord would affect which side of the body?

LR

Left, because it has already crossed

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Rubrospinal Tract{ Begins in red nucleus of

midbrain and crosses to opposite side at ventral tegmental decussation

{ Descends through pons and medulla, then into lateral spinal cord to enter anterior horn and synapse with lateral LMNsz Involved in movement of

contralateral limbs{ Ends in cervical spinal

cord

Lateral Corticospinal Rubrospinal

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Medial Motor Systems{ Medial tracts project to medial anterior horn cells{ Medial ant horn cells control more proximal muscles

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Put it together…motor and sensory findings:

Spinal cord syndromes, pp.292-294

Anterior Corticospinal Vestibulospinal Reticulospinal/Tectocpsinal