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Next SlideShares. Download Now Download to read offline and view in fullscreen. Download Now Download Download to read offline. Ascending and descending tracts of spinal cord Download Now Download Download to read offline. Amruta Rajamanya Follow. Sleep and its disorders. Antibody mediated encephalitis ppt. Updates in ms. Limbic system final. Corpus callosum with disconnection syndromes. Pons anatomy and syndromes. What to Upload to SlideShare. Related Books Free with a 30 day trial from Scribd.
Jen Gunter. Related Audiobooks Free with a 30 day trial from Scribd. Gundry, MD. Permission to Dream Chris Gardner. Single On Purpose: Redefine Everything. Find Yourself First. John Kim. Suraj Jadhav , Krishna Saraswat. Anusree Sreedharan. Mamta Gupta. Alfarid Shahid Ali. Devi Priya. Ramniwas Sah. Its shape and boundaries vary along the length of the cord. Lamina VII neurons receive information from Rexed lamina II to VI as well as visceral afferent fibers, and they serve as an intermediary relay in transmission of visceral motor neurons impulses.
The dorsal nucleus of Clarke forms a prominent round oval cell column from C8 to L3. The large cells give rise to uncrossed nerve fibers of the dorsal spinocerebellar tract DSCT.
Cells in the lateral horn of the cord in segments T1 and L3 give rise to preganglionic sympathetic fibers to innervate postganglionic cells located in the sympathetic ganglia outside the cord. Lateral horn neurons at segments S2 to S4 give rise to preganglionic neurons of the sacral parasympathetic fibers to innervate postganglionic cells located in peripheral ganglia. Rexed lamina VIII — Includes an area at the base of the ventral horn, but its shape differs at various cord levels.
In the cord enlargements, the lamina occupies only the medial part of the ventral horn, where descending vestibulospinal and reticulospinal fibers terminate. The neurons of lamina VIII modulate motor activity, most probably via g motor neurons which innervate the intrafusal muscle fibers. Its size and shape differ at various cord levels.
Rexed lamina X — Neurons in Rexed lamina X surround the central canal and occupy the commissural lateral area of the gray commissure, which also contains decussating axons.
In summary, laminae I-IV are concerned with exteroceptive sensations, whereas laminae V and VI are concerned primarily with proprioceptive sensation and act as a relay between the periphery to the midbrain and the cerebellum.
All visceral motor neurons are located in lamina VII and innervate neurons in autonomic ganglia. Surrounding the gray matter is white matter containing myelinated and unmyelinated nerve fibers. These fibers conduct information up ascending or down descending the cord. The white matter is divided into the dorsal or posterior column or funiculus , lateral column and ventral or anterior column Figure 3. The anterior white commissure resides in the center of the spinal cord, and it contains crossing nerve fibers that belong to the spinothalamic tracts, spinocerebellar tracts, and anterior corticospinal tracts.
Three general nerve fiber types can be distinguished in the spinal cord white matter: 1 long ascending nerve fibers originally from the column cells, which make synaptic connections to neurons in various brainstem nuclei, cerebellum and dorsal thalamus, 2 long descending nerve fibers originating from the cerebral cortex and various brainstem nuclei to synapse within the different Rexed layers in the spinal cord gray matter, and 3 shorter nerve fibers interconnecting various spinal cord levels such as the fibers responsible for the coordination of flexor reflexes.
Ascending tracts are found in all columns whereas descending tracts are found only in the lateral and the anterior columns. Four different terms are often used to describe bundles of axons such as those found in the white matter: funiculus, fasciculus, tract, and pathway. Funiculus is a morphological term to describe a large group of nerve fibers which are located in a given area e. Within a funiculus, groups of fibers from diverse origins, which share common features, are sometimes arranged in smaller bundles of axons called fasciculus, e.
Fasciculus is primarily a morphological term whereas tracts and pathways are also terms applied to nerve fiber bundles which have a functional connotation. A tract is a group of nerve fibers which usually has the same origin, destination, and course and also has similar functions. The tract name is derived from their origin and their termination i.
A pathway usually refers to the entire neuronal circuit responsible for a specific function, and it includes all the nuclei and tracts which are associated with that function. For example, the spinothalamic pathway includes the cell bodies of origin in the dorsal root ganglia , their axons as they project through the dorsal roots, synapses in the spinal cord, and projections of second and third order neurons across the white commissure, which ascend to the thalamus in the spinothalamic tracts.
Ascending tracts Figure 3. The ascending tracts transmit sensory information from the sensory receptors to higher levels of the CNS.
The ascending gracile and cuneate fasciculi occupying the dorsal column, and sometimes are named the dorsal funiculus. These fibers carry information related to tactile, two point discrimination of simultaneously applied pressure, vibration, position, and movement sense and conscious proprioception.
In the lateral column funiculus , the neospinothalamic tract or lateral spinothalamic tract is located more anteriorly and laterally, and carries pain, temperature and crude touch information from somatic and visceral structures.
Nearby laterally, the dorsal and ventral spinocerebellar tracts carry unconscious proprioception information from muscles and joints of the lower extremity to the cerebellum. In the ventral column funiculus there are four prominent tracts: 1 the paleospinothalamic tract or anterior spinothalamic tract is located which carry pain, temperature, and information associated with touch to the brain stem nuclei and to the diencephalon, 2 the spinoolivary tract carries information from Golgi tendon organs to the cerebellum, 3 the spinoreticular tract, and 4 the spinotectal tract.
Intersegmental nerve fibers traveling for several segments 2 to 4 and are located as a thin layer around the gray matter is known as fasciculus proprius, spinospinal or archispinothalamic tract. It carries pain information to the brain stem and diencephalon. Descending tracts Figure 3. The descending tracts originate from different cortical areas and from brain stem nuclei.
The descending pathway carry information associated with maintenance of motor activities such as posture, balance, muscle tone, and visceral and somatic reflex activity. These include the lateral corticospinal tract and the rubrospinal tracts located in the lateral column funiculus. These tracts carry information associated with voluntary movement.
Other tracts such as the reticulospinal vestibulospinal and the anterior corticospinal tract mediate balance and postural movements Figure 3. Lissauer's tract, which is wedged between the dorsal horn and the surface of the spinal cord carry the descending fibers of the dorsolateral funiculus DFL , which regulate incoming pain sensation at the spinal level, and intersegmental fibers.
Additional details about ascending and descending tracts are described in the next few chapters. Information from the skin, skeletal muscle and joints is relayed to the spinal cord by sensory cells located in the dorsal root ganglia.
The dorsal root fibers are the axons originated from the primary sensory dorsal root ganglion cells. Each ascending dorsal root axon, before reaching the spinal cord, bifurcates into ascending and descending branches entering several segments below and above their own segment.
The ascending dorsal root fibers and the descending ventral root fibers from and to discrete body areas form a spinal nerve Figure 3. There are 31 paired spinal nerves. The dorsal root fibers segregate into lateral and medial divisions. The lateral division contains most of the unmyelinated and small myelinated axons carrying pain and temperature information to be terminated in the Rexed laminae I, II, and IV of the gray matter.
In entering the spinal cord, all fibers send collaterals to different Rexed lamina. Axons entering the cord in the sacral region are found in the dorsal column near the midline and comprise the fasciculus gracilis, whereas axons that enter at higher levels are added in lateral positions and comprise the fasciculus cuneatus Figure 3. Ventral root fibers are the axons of motor and visceral efferent fibers and emerge from poorly defined ventral lateral sulcus as ventral rootlets.
The ventral rootlets from discrete spinal cord section unite and form the ventral root, which contain motor nerve axons from motor and visceral motor neurons. The visceral neurons send preganglionic fibers to innervate the visceral organs. All these fibers join the dorsal root fibers distal to the dorsal root ganglion to form the spinal nerve Figure 3. The spinal nerve roots are formed by the union of dorsal and ventral roots within the intervertebral foramen, resulting in a mixed nerve joined together and forming the spinal nerve Figure 3.
Spinal nerve rami include the dorsal primary nerves ramus , which innervates the skin and muscles of the back, and the ventral primary nerves ramus , which innervates the ventral lateral muscles and skin of the trunk, extremities and visceral organs.
The ventral and dorsal roots also provide the anchorage and fixation of the spinal cord to the vertebral cauda. The arterial blood supply to the spinal cord in the upper cervical regions is derived from two branches of the vertebral arteries, the anterior spinal artery and the posterior spinal arteries Figure 3.
At the level of medulla, the paired anterior spinal arteries join to form a single artery that lies in the anterior median fissure of the spinal cord. The posterior spinal arteries are paired and form an anastomotic chain over the posterior aspect of the spinal cord.
A plexus of small arteries, the arterial vasocorona, on the surface of the cord constitutes an anastomotic connection between the anterior and posterior spinal arteries.
This arrangement provides uninterrupted blood supplies along the entire length of the spinal cord. At spinal cord regions below upper cervical levels, the anterior and posterior spinal arteries narrow and form an anastomotic network with radicular arteries. The radicular arteries supply most of the lower levels of the spinal cord.
There are approximately 6 to 8 pairs of radicular arteries supplying the anterior and posterior spinal cord Figure 3. Contains the cell bodies of postganglionic sympathetic efferent neurons. In the laminar somatotopic organization of the dorsal columns, the most lateral fibers represent:. The fibers entering at the lumbar region are located in the lateral portion of the dorsal columns.
Syringomyelia syndrome results from lesions in the anterior spinal white commissure that results in losing pain and temperature sensation at the level of the lesion. Occupies the lumbar cistern B. Has twelve 12 cervical segments C. Contains the cell bodies of postganglionic sympathetic efferent neurons D. Ends at the conus medullaris E. Has no arachnoid membrane. The spinal cord The spinal cord does not occupy the lumbar cistern. The spinal cord has seven 7 cervical segments.
Postganglionic neurons are located in the periphery, not in the spinal cord. Arachnoid membrane covers the spinal cord. Corticospinal B. Ventral spinothalamic C. Ventral spinocerebellar D. Anterior spinocerebellar E. Dorsal spinocerebellar. Which of the following tracts crosses at the spinal cord level of entry?
From these tracts, only the lateral spinothalamic tract crosses at the entry level. Vertebral arteries B. Posterior spinal arteries C. Anterior spinal artery D. Basilar artery E. Posterior communicating artery. The blood supply for the corticospinal tract is derived from the: A. The anterior spinal artery supplies the corticospinal tract and the other tracts in this region.
Sacral region B. Thoracic region C. Lumbar region D. Cervical region E. Coccygeal region. In the laminar somatotopic organization of the dorsal columns, the most lateral fibers represent: A. Dorsal root ganglia B. Fibers decussating in the spinal white commissure C. Fibers of the anterior spinal thalamic tract D. Ventral root ganglia E. Fibers of the dorsal spinocerebellar tract. Syringomyelia syndrome occurs with selective spinal lesions in the: A. Neurons in the laminae II B. Motor neurons C.
Somatic efferent neurons D. Internuncial neurons E. Commissural neurons. Spinal root neurons are: A. The axons of the spinal root neurons are the somatic efferent fibers. Has no arachnoid membrane The spinal cord Dorsal spinocerebellar Which of the following tracts crosses at the spinal cord level of entry? Posterior communicating artery The blood supply for the corticospinal tract is derived from the: A. Coccygeal region In the laminar somatotopic organization of the dorsal columns, the most lateral fibers represent: A.
Fibers of the dorsal spinocerebellar tract Syringomyelia syndrome occurs with selective spinal lesions in the: A. Commissural neurons Spinal root neurons are: A.
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