Nervous Tissue Anatomy and Function

Study Notes

Nervous tissue is one of the basic tissues of the body, dividing anatomically into the central nervous system (brain and spinal cord) and peripheral nervous system (nerves and ganglia).
Histologically, it divides into nerve cells (neurons) and neuroglia.

A nerve cell (neuron) is the structural and functional unit of nervous tissue, consisting of a cell body (perikaryon), nerve processes (axon and dendrites), and cell inclusions.

The cell body contains a large, rounded central pale nucleus with a prominent nucleolus.
Cytoplasm contains RER, scattered basophilic bodies (Nissl's granules), Golgi apparatus, mitochondria, lysosomes, SER, neurotubules, and neurofilaments.
The mature nerve cell has no centrosome, so it cannot divide.

Dendrites are multiple, short, and thick processes branching along their course.
They have irregular surfaces and diameters.
Dendrites conduct nerve impulses towards the cell body and contain all organelles except Golgi, including Nissl granules.

The axon is a single, thin, and long process of the cell body.
It has a regular surface and diameter.
The axon branches at its terminal end, forming axon terminals.
Its cytoplasm contains most organelles, but no Golgi or Nissl granules.
The axon may be covered by a myelin sheath and transmits nerve impulses away from the cell body.

Unipolar neurons have one process, found in invertebrates.
Pseudo-unipolar neurons have one process that divides into two branches, found in cells of spinal ganglia.
Bipolar neurons have a fusiform cell body with two processes, one acting as an axon and the other as a dendrite, found in the olfactory epithelium, retina, and inner ear.
Multipolar neurons can be:
- Stellate neurons with multiple short dendrites and a single long axon, found in sympathetic ganglia and anterior horn cells.
- Pyramidal neurons with a pyramidal shape, multiple dendrites, and a single axon, found in the cerebral cortex.
- Pyriform neurons with a flask shape, multiple dendrites, and a single axon, found in Purkinje cells of the cerebellum.

A ganglion is a collection of nerve cell bodies outside the central nervous system.

Cerebro-spinal ganglia:
- Located in cranial and spinal sensory nerves.
- Structure: thick CT capsule surrounds each ganglion, with pseudo-unipolar neurons arranged in groups or rows, surrounded by satellite cells, and thickly myelinated nerve fibers.
- Synapses: absent.
Autonomic ganglia:
- Located along sympathetic and parasympathetic nerves.
- Structure: thin capsule, with stellate multipolar neurons, surrounded by few satellite cells, and unmyelinated nerve fibers.
- Synapses: present.