Spinal Cord Sensory Pathways

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Stimuli received by the body are..

transduced into action potentials by various types of sensory receptors that are located throughout the body in the skin, muscles, tendons, joint capsules, viscera and special sense organs.

The types of stimuli that reach the spinal cord may be perceived as...

pain, temperatures, proprioception, two point discrimination, touch, light touch, vibration, pressure, and stretch. All of these stimuli reach consciousness.

In order for conscious perception to be achieved....

the information must reach relay nuclei in the thalamus

The specific thalamic relay nucleus for...

ALL conscience sensory modalities conveyed by the spinal cord is the ventral posterior lateral (VPL) thalamic nucleus.

In order to localize the origin of a stimulus to a specific anatomic site, the VPL...

must relay information to the primary somatosensory cortex.

The primary somatosensory cortex is located..

in the postcentral gyrus which is Brodmann's areas 3, 2, 1.

Not all sensory modalities reach the conscience level. Some axon fiber tracts...

of the spinal cord synapse directly in the cerebellum. There are the spinocerebellar tracts.

Dorsal root ganglia are the home...

of first order afferent cell bodies for all somatosensory and viscerosensory modalities carried by the spinal nerves.

ALL transduced stimuli travel..

toward the spinal cord along peripheral processes of pseudounipolar cells in dorsal root ganglia (DRG). There are NO synapses in the DRG's.

The axonal transmission continues along

the central processes of DRG cells, which enter the spinal cord via dorsal rootlets at the posterolateral sulcus.

Some of these central processes...

synapse with second order neurons in the dorsal horn of the spinal cord while others travel in the dorsal funiculus before they synapse with secondary neurons in the caudal medulla

What are the three conscious sensory pathways?

1) Lateral Spinothalamic pathway
2) Anterior Spinothalamic pathway
3) Dorsal Column/Medial Lemniscal Pathway

The lateral spinothalamic pathway conveys...

conscious pain and temperature and some crude touch.

The primary neurons in the lateral spinothalamic pathway are in...

DRG.

In the lateral spinothalamic pathway, what happens?

Small unmyelinated central processes of the primary neurons enter the spinal cord via dorsal rootlets at the posterolateral sulcus.

Pain and Temperature fibers travel is what tract?

Lissauer's tract

Pain and Temperature fibers travel in Lissaur's tract where they may do one of two thing: name 1)

1) Some fibers or collaterals may proceed into and synapse in lamina's I and II with secondary neurons at the spinal cord segment levels of entry.

Pain and Temperature fibers travel in Lissaur's tract where they may do one of two thing: name 2)

Other fibers may travel up or down the cord for several segments before synapsing in lamina's I and II at different cord segments.

Synapses in lamina I...

are with with neurons what are located in lamina I.

Synapses in lamina II (substantia gelatinosa) is with...

dendrites mostly of neurons located in lamina's IV and V.

The lateral spinothalanic pathway is....

primarily a crossed pathway.

What forms the lateral spinothalamic tract?

The fibers from secondary neurons in lamina's I, IV, and V project across the midline through the anterior white commissure to the contralateral ventrolateral funiculus.

The secondary fibers of the spinothalamic tract travel..

superiorly in an anterolateral position in the lateral funiculus just medial to the peripherally located anterior (ventral) spinocerebellar tract.

How is the lateral spinothalamic tract organized?

somatotopically organized

Within the lateral spinothalamic tract, fibers that carry

pain and temperature from sacral levels are located most laterally.

What fibers are located most medially in the lateral spinothalamic pathway?

cervical pain and temperature fibers.

In the lateral spinothalamic pathway: in the sacral cord

only sacral pain and temperature fibers within sacral spinal nerves that serve the lower extremities are present. They get in the "first row" laterally.

In the spinothalamic pathway, somatotopically organized secondary fibers...

travel through the lateral regions of the tegmentum of the medulla, pons, and mid brain before they synapse with tertiary neurons in the ventral posterior nucleus (VPL) of the thalamus.

In the spinothalamic pathway, the axon fibers from tertiary thalamic neurons project...

through the posterior limb of the internal capsule to the primary somatosensory cortex - the post central gyrus (Brodmann' areas 3, 1, 2).

When discussing the lateral spinothalamic pathway, the post gyrus is arranged such that...

the most inferior region of the postcentral gyrus receives sensory information from the head and neck while the superior and midsaggital regions receive sensory information from the lower extremity. This defines the sensory homunculus.

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