Nervous Tissue

Nervous tissue consists of nerve cells, or neurons, which are specialized for the generation and conduction of electrical events, and of supporting cells, which provide the neurons with anatomical and functional support. Supporting cells in the brain and spinal cord are referred to as neuroglial cells, or often simply as glial cells.

Each neuron consists of three parts: (1) a cell body, (2) dendrites, and (3) an axon (fig. 1.10). The cell body contains the nucleus and serves as the metabolic center of the cell. The dendrites (literally, "branches") are highly branched cytoplasmic extensions of the cell body that receive input from other neurons or from receptor cells. The axon is a single cytoplasmic extension of the cell body that can be quite long (up to a few feet in length). It is specialized for conducting nerve impulses from the cell body to another neuron or to an effector (muscle or gland) cell.

The supporting cells do not conduct impulses but instead serve to bind neurons together, modify the extracellular environment of the nervous system, and influence the nourishment and electrical activity of neurons. Supporting cells are about five times more abundant than neurons in the nervous system and, unlike neurons, maintain a limited ability to divide by mitosis throughout life.

Neurons and supporting cells are discussed in detail in chapter 7.

12

Chapter One

Table 1.3 Summary of Epithelial Membranes

Type Structure and Function

Location

Simple Epithelia

Simple squamous epithelium Simple cuboidal epithelium Simple columnar epithelium Simple ciliated columnar epithelium Pseudostratified ciliated columnar epithelium

Stratified Epithelia

Single layer of cells; function varies with type

Single layer of flattened, tightly bound cells; diffusion and filtration

Single layer of cube-shaped cells; excretion, secretion, or absorption Single layer of nonciliated, tall, column-shaped cells;

protection, secretion, and absorption Single layer of ciliated, column-shaped cells;

transportive role through ciliary motion Single layer of ciliated, irregularly shaped cells; many goblet cells; protection, secretion, ciliary movement

Two or more layers of cells; function varies with type

Covering visceral organs; linings of body cavities, tubes, and ducts Capillary walls; pulmonary alveoli of lungs; covering visceral organs; linings of body cavities Surface of ovaries; linings of kidney tubules, salivary ducts, and pancreatic ducts Lining of most of digestive tract

Lining of uterine tubes

Lining of respiratory passageways

Epidermal layer of skin; linings of body openings, ducts, and urinary bladder

Stratified squamous epithelium (keratinized)

Numerous layers containing keratin, with outer layers flattened and dead; protection

Epidermis of skin

Stratified squamous epithelium (nonkeratinized)

Numerous layers lacking keratin, with outer layers moistened and alive; protection and pliability

Linings of oral and nasal cavities, vagina, and anal canal

Stratified cuboidal epithelium

Usually two layers of cube-shaped cells; strengthening of luminal walls

Large ducts of sweat glands, salivary glands, and pancreas

Transitional epithelium

Numerous layers of rounded, nonkeratinized cells; distension

Walls of ureters, part of urethra, and urinary bladder

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Essentials of Human Physiology

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Responses

  • bungo
    Are the outer layers alive on stratified squamous epithelium?
    8 years ago

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