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Physiology III
Spinal Cord And Peripheral Nerves

(Haines, Ch. 9, pp 130-136, 139-14 1)


Posterior (Dorsal) Horn
Posterior projection (2) of gray matter of spinal cord.
Dorsal horn is composed of laminae I to VI.
The most distinct structure in the dorsal horn substantia gelatinosa (lamina II)
Input from sensory neurons
Sensory functions
Small in levels C1 to C3
Prominent in cervical (C4 to T1) and lumbosacral (L1 to S2)
Small in thoracic levels
Reaches almost to the posterolateral sulcus
Lateral Horn
Present in the thoracic and superior lumbar segments of the cord.
Visceral motor zones
Anterior (Ventral) Horn
Anterior projection (2) of gray matter of spinal cord.
Front of the canal
Contains the cells of origin of the fibers of the ventral roots, including alpha and gamma motor neurons ("lower" motor neurons).
Cervical Enlargement
C4 to T1 and L1 to S2, prominent dorsal and ventral horns because of extensive sensory input from, and motor outflow to, the arms and legs.
Lumbar Enlargement
As above, extensive sensory input from and motor outflow to, arms and legs.
Posterior Columns
Collectively the fasciculus gracilis and the fasciculus cuneatus.
also called post funiculus or tract. Located btw post median septum and medial edge of dorsal horn. Cervical areas it is the gracile and cuneate fasciculus or the dorsal column carrying discriminative touch. It travels on the ipsilateral side and carries sensory info.
Lateral Columns
or funiculus. White matter btw posterolateral and anterolateral sulci. Contains imp ascending and descending tracts most imp are lateral corticospinal tract and the ALS. Axons are coming from the motor cortex.
Anterior Columns
located btw anterolat sulcus and ventral medial fissure small area is called also the ant funiculus. It contains reticulospinal and vestibulospinal fibers portion of the ALS, ant corticospinal tract and composite bundle called medial longitudinal fasciculus. This moves info in two different direction.
Dorsal Columns
also called the post column, funiculus or tract. The gracile and cuneate fibers come in and travel side by side up this column and innervate the nuclei located in the medulla and then send axons in to the medial lemniscus to synapse in the thalamus.
Dorsal Column Nuclei
Located in lower medulla, neurons where ascending fibers in the gracile and cuneate fasciculi terminate.
Anterolateral System
Ascending tracts.
Located in the ventrolateral area of the spinal cord composite bundle. This system encompasses those regions of the white matter that were classically divided into anterior and lateral spinothalmic tracts. The ALS contains spinothalmic, spinomesencephalic (spinotectal, spinoperiaqueductal), spinohypothalmic, and spinoreticular fibers.
The fibers of the ALS originate primarily from dorsal horn cells, some also arise from neurons in the ventral horn. Those fibers that coalesce to form the ALS cross in the ventral white commissure, ascending one to two levels as they do.
In general, fibers of the ALS convey nociceptive, thermal, and touch information.
ALS is somatotopically organized; lower portions of the body are represented dorsolaterally and upper levels are represented ventromedially.
Corticospinal Tract
Descending tract.
Arise from the cerebral cortex and descend through the brainstem.
At the medulla-spinal cord junction, most cross to form the lateral corticospinal tract, but some remain uncrossed as the anterior corticospinal tract.
Lateral corticospinal fibers are somatotopically arranged.
Important function of this tract is to influence spinal motor neurons, especially those controlling fine movements of the distal musculature.
Anterior (Ventral) Root
Constitute motor outflow tracts from the spinal cord.
Carry the large-diameter alpha motor neuron axons to the extrafusal striated fibers; the smaller gamma motor neuron axons, which supply the intrafusal muscle of the muscle spindles; and a few afferent, small-diameter axons that arise from cells in the dorsal root ganglia and convey sensory information from the thoracic and abdominal viscera.
Posterior (Dorsal) Root
this exits from the cord near the dorsal horn. The dorsal root ganglia are equal to nuclei in the CNS.
Cauda Equina
Dorsal and ventral roots from spinal segments L2 to Coc1 located in the lumbar cistern extending caudally from the caudal end of the spinal cord.
The dorsal and ventral nerve roots from spinal segments L2 to Coc1 as they sweep caudally. Collectively, these roots form the cauda equina. (Haines pg. 132).

The vertebral column grows inferiorly more rapidly than does the spinal cord, forcing the lower spinal nerve roots to "chase" their exit points inferiorly through the vertebral canal. (Marieb pg. 438).

(L. cauda, tail; equus, horse): The lumbar and sacral nerve roots within the lumbar cistern as they descend to emerge from their respective intervertebral and sacral foramina. (Internet Glossary)
Area of skin supplied by nerve roots.
Segmental sensory innervation of the body surface, "skin slices"
The strip of skin that is innervated by the peripheral cutaneous branches of a given spinal nerve.
The peripheral distribution of the afferent nerves associated with each spinal level delineating segmental patterns.
The area of skin innervated by the cutaneous branches of a single spinal nerve. All spinal nerves except C1 participate in dermatomes (Marieb pg. 483)

Last Updated 04/10/00 12:27:15 PM
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