Nervous Tissue

Nervous tissue is made up of two kinds of cell: neurons (nerve cells), and neuroglia. The neuron is the structural and functional unit of the nervous system — it is the cell specialised for generating and conducting nerve impulses, and it is what brings about quick communication within the body. Neuroglial cells, by contrast, are non-nervous cells that support the neurons and fill the spaces between them; unlike neurons, neuroglial cells retain the ability to divide and regenerate. Neurons themselves cannot regenerate, because they lack a centriole. There is no intercellular matrix in nervous tissue, unlike in connective tissue.

A neuron shows two defining physiological properties: excitability, meaning it can change the electrical (action) potential of its membrane in response to an external stimulus, and conductivity, meaning it can then carry that change as a wave of electrical impulse along its length, from its dendron end to its axon end.

Structurally, a neuron is made up of a cyton (cell body), containing granular cytoplasm called neuroplasm and a centrally placed nucleus. The neuroplasm contains mitochondria, Golgi apparatus, rough endoplasmic reticulum, and RNA-containing granules called Nissl's granules. From the cyton arise two kinds of cell processes:

• Dendrons — short, branching processes whose finer branches are called dendrites; these carry impulses toward the cyton.
• Axon — a single, elongated, cylindrical process, bounded by a membrane called the axolemma and filled with cytoplasm called axoplasm, which contains large numbers of mitochondria and fine filaments called neurofibrils. …