Page 887 - Textbook of Pathology, 6th Edition

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Chapter 30 The Nervous System
Chapter 30

CENTRAL NERVOUS SYSTEM dendrites (Fig. 30.1,A). The cell body (or perikaryon) is the
main constituent of the neuron from which an axon and
NORMAL STRUCTURE numerous dendritic processes extend. The cell bodies may
be arranged in layers as in the cerebral cortex, or may be
The skull and the vertebrae form a rigid compartment aggregated as in the basal ganglia. The cell body possesses a
encasing the delicate brain and spinal cord. The average large, round, centrally-placed nucleus having finely granular
weight of the brain is about 1400 gm in men and 1250 gm in nuclear chromatin and a prominent nucleolus. The cytoplasm
women. The two main divisions of the brain— the cerebrum contains polygonal, basophilic structures called Nissl
and the cerebellum, are quite distinct in structure. The brain substance. It consists of aggregates of RNA, sheaves of rough
does not have lymphatic drainage. There are 2 types of tissues endoplasmic reticulum and intervening groups of free
in the nervous system: ribosomes. Besides Nissl substance, other special features of
1. Neuroectodermal tissues which include neurons (nerve the cytoplasm of neuronal cell body are the presence of
cells) and neuroglia, and together form the predominant microtubules, synaptic vesicles and neurofilaments which
constituent of the CNS. are a form of intermediate filaments specific to neurons.
2. Mesodermal tissues are microglia, dura mater, the lepto- Lipofuscin may be present due to ageing. Neuromelanin is
meninges (pia-arachnoid), blood vessels and their found in neurons in the substantia nigra and pigmented CHAPTER 30
accompanying mesenchymal cells. nucleus of the pons.
The predominant tissues comprising the nervous system Neurons respond to injury in a variety of ways depen-
and their general response to injury are briefly considered ding upon the etiologic agent and the pathologic processes.
below:
These include central chromatolysis, atrophy and
1. NEURONS. The neurons are highly specialised cells of degeneration of neurons and axons, and intraneuronal
the body which are incapable of dividing after the first few storage of substances.
weeks of birth. Thus, brain damage involving the neurons is Neuropil is the term used for the fibrillar network formed
irreversible. Neurons vary considerably in size and shape. by processess of all the neuronal cells.
Their size may range from the small granular cells of the
cerebellum to large Betz cells of the motor cortex. Some 2. NEUROGLIA. The neuroglia provides supportive matrix The Nervous System
neurons are round, others oval or fusiform but the prototype and maintenance to the neurons. It includes 3 types of cells:
of cortical neuron is pyramidal in shape. A neuron consists astrocytes, oligodendrocytes and ependymal cells
of 3 main parts: the cell body, an axon and numerous (Fig. 30.1,B). Neuroglia is generally referred to as glia; the

Figure 30.1 Cells comprising the nervous system.