There are two main types of nervous tissue in animals: neurons and neuroglia (also known as glial cells).
Neurons
Neurons are the fundamental units of the nervous system, responsible for transmitting electrical and chemical signals throughout the body. They allow animals to sense, think, and react to their environment. Key features of neurons include:
- Function: Transmit electrical and chemical signals (nerve impulses).
- Structure: Typically composed of three main parts:
- Cell Body (Soma): Contains the nucleus and other organelles.
- Dendrites: Branch-like extensions that receive signals from other neurons or sensory receptors.
- Axon: A long, slender projection that transmits signals away from the cell body to other neurons, muscles, or glands.
Neuroglia (Glial Cells)
Neuroglia, or glial cells, provide support, insulation, and protection for neurons. They are much more numerous than neurons and play crucial roles in maintaining the health and function of the nervous system. There are several types of glial cells, each with specialized functions:
- Astrocytes: The most abundant glial cells in the central nervous system (CNS). They provide structural support, regulate the chemical environment around neurons, and form the blood-brain barrier.
- Oligodendrocytes: Found in the CNS, these cells form myelin sheaths around the axons of neurons, which insulate the axons and speed up the transmission of nerve impulses.
- Microglia: Act as the immune cells of the CNS, removing debris and pathogens through phagocytosis.
- Ependymal Cells: Line the ventricles of the brain and the central canal of the spinal cord. They help circulate cerebrospinal fluid (CSF).
- Schwann Cells: Similar to oligodendrocytes, but found in the peripheral nervous system (PNS). They form myelin sheaths around axons in the PNS.
- Satellite Cells: Surround neuron cell bodies in ganglia of the PNS. They provide support and regulate the environment around neurons.
| Cell Type | Location | Function |
|---|---|---|
| Astrocytes | CNS | Support, regulate chemical environment, form blood-brain barrier |
| Oligodendrocytes | CNS | Form myelin sheaths around axons |
| Microglia | CNS | Immune defense, remove debris |
| Ependymal Cells | CNS | Line ventricles, circulate cerebrospinal fluid |
| Schwann Cells | PNS | Form myelin sheaths around axons |
| Satellite Cells | PNS | Support neuron cell bodies in ganglia, regulate the environment around neurons |
In summary, nervous tissue is composed of neurons, which transmit signals, and neuroglia, which support and protect neurons. Both cell types are essential for the proper functioning of the nervous system.
