Answers and Explanations

1. Answer: D. A noncommunicating hydrocephalus results from a blockage limiting flow of CSF somewhere inside the ventricular system or its connections. The only choice indicating a blockage site inside the ventricular system is a stenosis of the aqueduct between the third and fourth ventricles caused by a pineal tumor.

2. Answer: B. Each lateral ventricle communicates with the third ventricle through a foramen of Munro. Blockage of one foramen of Munro will result in the enlargement of a single lateral ventricle.

3. Answer: B. Foot processes of astrocytes cover the outside of cerebral blood vessels and contribute to the blood-brain barrier.

4. Answer: B. A communicating hydrocephalus may be caused by disruption of flow of CSF in die subarachnoid space or by limiting its return to the venous system. The only choice indicating a problem (in this example, absorption of CSF back into the venous system) is meningitis, which might limit flow from of CSF through the arachnoid villi into the superior sagittal dura! venous sinus.

GENERAL FEATURES

The spinal cord is housed in the vertebral canal. It is continuous with the medulla below the pyramidal decussation and terminates as the conus medullaris at the second lumbar vertebra of the adult. The roots of 31 pairs of spinal nerves arise segmentally from the spinal cord.

There are eight cervical pairs of spinal nerves (CI through C8). The cervical enlargement (C5 through T1) gives rise to the rootlets that form the brachial plexus, which innervates the upper limbs.

There are 12 thoracic pairs of spinal nerves (T1 through T12). Spinal nerves emanating from thoracic levels innervate most of the trunk.

There are five lumbar pairs of spinal nerves (LI through L5). The lumbar enlargement (LI through S2) gives rise to roodets that form the lumbar and sacral plexuses, which innervate the lower limbs.

There are five sacral pairs of spinal nerves (SI through S5). Spinal nerves at the sacral level innervate part of the lower limbs and the pelvis.

There is one coccygeal pair of spinal nerves. The cauda equina consists of the dorsal and ventral roots of the lumbar, sacral, and coccygeal spinal nerves.

Inside the spinal cord, gray matter is centrally located and shaped like a butterfly. It contains neuronal cell bodies, their dendrites, and the proximal parts of axons. White matter surrounds the gray matter on all sides. White matter contains bundles of functionally similar axons called tracts or fasciculi, which ascend or descend in the spinal cord (Figures IV-4-1 and IV-4-2).

medical

Posterior (dorsal) gray horn

Lateral funiculus

Anterior (ventral) gray horn

Posterior median sulcus

Posterior intermediate sulcus

Dorsal root entry zone

Intermediate (lateral) gray horn

Dorsal "I Root Ventral J niamentS

Dorsal root ion

Spinal nerve

Anterior funiculus

Anterolateral sulcus

Figure IV-4-2. The Spinal Cord

Anterior median fissure

Anterolateral sulcus

Figure IV-4-2. The Spinal Cord

Posterior (dorsal) gray horn

Lateral funiculus

Anterior (ventral) gray horn

Posterior funiculus

Posterior median sulcus

Posterior intermediate sulcus

Dorsal root entry zone

Intermediate (lateral) gray horn

Anterior funiculus

Anterior median fissure

Dorsal "I Root Ventral J niamentS

Dorsal root ion

Spinal nerve

The gray matter is organized into a dorsal horn, a ventral horn, and an intermediate zone.

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Essentials of Human Physiology

Essentials of Human Physiology

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