Myelin

Myelin ensheathes the nerve fibers in a spiral lamellar fashion, promoting a faster and more effective conduction of nervous impulses along the nerve fibers. It is produced by the oligodendrocytes during development of the brain and spinal cord and maintained by them after completion of myelination (Fig. 2.10). The major chemical components of myelin are lipids, which constitute about 70 to 85 . The sphingolipids and cholesterol are the most important of these. The remaining 15 to 30 of myelin...

Astrocytic Tumors

Astrocytic tumors constitute the largest group of intracranial tumors in both adults and children. Their locations, gross and histologic features, biologic behavior, and genetic alterations vary greatly. The WHO distinguishes four grades of astrocytic tumors based on their histologic characteristics (Table 11.5). Astrocytic Tumors (Grades 2, 3, and 4) Diffuse astrocytoma grade 2, anaplastic astrocytoma grade 3, and glioblastoma grade 4 constitute the largest group of primary intracranial tumors...

Ischemic Stroke Cerebral Infarction

The brain requires a constant and adequate blood flow to supply oxygen and glucose essential for its high energy metabolism. A constant blood flow is assured by an autoregulatory mechanism of arteries and arterioles they constrict in response to rising systemic blood pressure and dilate in response to falling systemic blood pressure. This mechanism operates while the arterial pressure remains between 50 and 160 mm Hg. One- Atherosclerosis of cerebral arteries. A. Severe atheromatosis of basal...

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Is depleted of neurons, becomes spongy, and displays a dense astrofibrosis. The white matter is variably devoid of myelin, which is replaced by astrogliosis. Astrocytes in the cerebral cortex and oligodendrocytes in the white matter may display argyrophilic and tau-immunoreactive cytoplasmic inclusions. Dementia with Parkinsonism Linked to Chromosome 17 Clinical features. This is a familial dementia inherited in an autosomal dominant pattern The interest of the disease lies in its association...

Intracranial Hemorrhages

Intracranial hemorrhages may occur in the epidural, subdural, and subarachnoid compartments and within the brain parenchyma. Epidural hematoma EDH occurs in 2 of severe head injuries. An epidural hematoma forms between the inner table of the calvarium and the dura, usually in the frontotemporal region Fig. 12.1 . It is commonly an arterial bleed that results from tearing of meningeal arteries, often of the middle meningeal artery, by a linear fracture across its cranial groove. In children, it...

Spinal and Spinal Cord Defects

Vertebral Defects

Dysraphic disorders of the spine and spinal cord comprise a broad spectrum of malformations, ranging from total absence of the cord to asymptomatic bony defects and cord anomalies. Familial occurrences are common. The clinical manifestations vary from mild motor and sensory deficits to paraplegia with severe sensory impairment and loss of sphincter control. Amyelia, total absence of the spinal cord occurs with anencephaly see Fig. 13.2 . The cord is replaced with a mixture of fibrous tissue,...