Ventral Root
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 α motor nerve axons innervate the extrafusal muscle fibers while the small γ motor neuron axons innervate the intrafusal muscle fibers located within the muscle spindles. 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 3.10).
Spinal Nerve Roots
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 3.10). 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.
Blood Supply of the Spinal Cord
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 3.12). 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 are branches of the cervical, trunk, intercostal & iliac 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 3.12).
Test Your Knowledge
The spinal cord...
A. 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...
A. Occupies the lumbar cistern This answer is INCORRECT.
The spinal cord does not occupy 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...
A. Occupies the lumbar cistern
B. Has twelve (12) cervical segments This answer is INCORRECT.
The spinal cord has seven (7) 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...
A. Occupies the lumbar cistern
B. Has twelve (12) cervical segments
C. Contains the cell bodies of postganglionic sympathetic efferent neurons This answer is INCORRECT.
Postganglionic neurons are located in the periphery, not in the spinal cord.
D. Ends at the conus medullaris
E. Has no arachnoid membrane
The spinal cord...
A. 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 This answer is CORRECT!
E. Has no arachnoid membrane
The spinal cord...
A. 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 This answer is INCORRECT.
Arachnoid membrane covers the spinal cord.
Which of the following tracts crosses at the spinal cord level of entry?
A. 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?
A. Corticospinal This answer is INCORRECT.
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?
A. Corticospinal
B. Ventral spinothalamic This answer is CORRECT!
From these tracts, only the lateral spinothalamic tract crosses at the entry level.
C. Ventral spinocerebellar
D. Anterior spinocerebellar
E. Dorsal spinocerebellar
Which of the following tracts crosses at the spinal cord level of entry?
A. Corticospinal
B. Ventral spinothalamic
C. Ventral spinocerebellar This answer is INCORRECT.
D. Anterior spinocerebellar
E. Dorsal spinocerebellar
Which of the following tracts crosses at the spinal cord level of entry?
A. Corticospinal
B. Ventral spinothalamic
C. Ventral spinocerebellar
D. Anterior spinocerebellar This answer is INCORRECT.
E. Dorsal spinocerebellar
Which of the following tracts crosses at the spinal cord level of entry?
A. Corticospinal
B. Ventral spinothalamic
C. Ventral spinocerebellar
D. Anterior spinocerebellar
E. Dorsal spinocerebellar This answer is INCORRECT.
The blood supply for the corticospinal tract is derived from the:
A. 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. Vertebral arteries This answer is INCORRECT.
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. Vertebral arteries
B. Posterior spinal arteries This answer is INCORRECT.
C. Anterior spinal artery
D. Basilar artery
E. Posterior communicating artery
The blood supply for the corticospinal tract is derived from the:
A. Vertebral arteries
B. Posterior spinal arteries
C. Anterior spinal artery This answer is CORRECT!
The anterior spinal artery supplies the corticospinal tract and the other tracts in this region.
D. Basilar artery
E. Posterior communicating artery
The blood supply for the corticospinal tract is derived from the:
A. Vertebral arteries
B. Posterior spinal arteries
C. Anterior spinal artery
D. Basilar artery This answer is INCORRECT.
E. Posterior communicating artery
The blood supply for the corticospinal tract is derived from the:
A. Vertebral arteries
B. Posterior spinal arteries
C. Anterior spinal artery
D. Basilar artery
E. Posterior communicating artery This answer is INCORRECT.
In the laminar somatopic organization of the dorsal columns, the most lateral fibers represent:
A. Sacral region
B. Thoracic region
C. Lumbar region
D. Cervical region
E. Coccygeal region
In the laminar somatopic organization of the dorsal columns, the most lateral fibers represent:
A. Sacral region This answer is INCORRECT.
B. Thoracic region
C. Lumbar region
D. Cervical region
E. Coccygeal region
In the laminar somatopic organization of the dorsal columns, the most lateral fibers represent:
A. Sacral region
B. Thoracic region This answer is INCORRECT.
C. Lumbar region
D. Cervical region
E. Coccygeal region
In the laminar somatopic organization of the dorsal columns, the most lateral fibers represent:
A. Sacral region
B. Thoracic region
C. Lumbar region This answer is INCORRECT.
D. Cervical region
E. Coccygeal region
In the laminar somatopic organization of the dorsal columns, the most lateral fibers represent:
A. Sacral region
B. Thoracic region
C. Lumbar region
D. Cervical region This answer is CORRECT!
The fibers entering at the lumbar region are located in the lateral portion of the dorsal columns.
E. Coccygeal region
In the laminar somatopic organization of the dorsal columns, the most lateral fibers represent:
A. Sacral region
B. Thoracic region
C. Lumbar region
D. Cervical region
E. Coccygeal region This answer is INCORRECT.
Syringomyelia syndrome occurs with selective spinal lesions in the:
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. Dorsal root ganglia This answer is INCORRECT.
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. Dorsal root ganglia
B. Fibers decussating in the spinal white commissure This answer is CORRECT!
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.
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. Dorsal root ganglia
B. Fibers decussating in the spinal white commissure
C. Fibers of the anterior spinal thalamic tract This answer is INCORRECT.
D. Ventral root ganglia
E. Fibers of the dorsal spinocerebellar tract
Syringomyelia syndrome occurs with selective spinal lesions in the:
A. Dorsal root ganglia
B. Fibers decussating in the spinal white commissure
C. Fibers of the anterior spinal thalamic tract
D. Ventral root ganglia This answer is INCORRECT.
E. Fibers of the dorsal spinocerebellar tract
Syringomyelia syndrome occurs with selective spinal lesions in the:
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 This answer is INCORRECT.
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons
C. Somatic efferent neurons
D. Internuncial neurons
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II This answer is INCORRECT.
B. Motor neurons
C. Somatic efferent neurons
D. Internuncial neurons
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons This answer is INCORRECT.
C. Somatic efferent neurons
D. Internuncial neurons
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons
C. Somatic efferent neurons This answer is CORRECT!
The axons of the spinal root neurons are the somatic efferent fibers.
D. Internuncial neurons
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons
C. Somatic efferent neurons
D. Internuncial neurons This answer is INCORRECT.
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons
C. Somatic efferent neurons
D. Internuncial neurons
E. Commissural neurons This answer is INCORRECT.
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