Nervous Tissue: Components, Structure, and Roles

Nervous Tissue

Nervous tissue cells produce responses sent to muscles and glands, leading to movements and secretions, respectively. These functions are performed through nerve impulses, which are common electrochemical signals. Nerve endings reach all body parts. Except for the simplest invertebrates, whose nervous tissue consists only of neurons, in other animals, it is also composed of a very different set of glial cells.

Neurons: Structure and Function

Neurons are the structural and functional units of the nervous system. They receive information from both the internal and external environments of an organism. Neurons have a high degree of specialization. Once mature, they cannot divide, and their numbers are definitively established from birth. In neurons, two main parts can be distinguished: a cell body and filamentous extensions that originate from it. These filamentous extensions can be of two types: dendrites and axons.

Types of Neurons by Extension:

• Monopolar: Present a unique extension, the axon. This type is not frequent.
• Pseudomonopolar: They have a unique branching extension that bifurcates into an axon and dendrites.
• Bipolar: Have two extensions: a branched dendrite and an axon.
• Multipolar: These neurons have several dendrites and a single axon.

Types of Neurons by Function:

• Sensory Neurons: Their function is to receive information from receptors and transmit it to the nerve centers for processing.
• Motor Neurons: These are the neurons that transmit signals from the central nervous system to different effector organs.
• Association Neurons (Interneurons): They connect with other neurons.

Glial Cells: Support and Protection

Glial cells are a group of nerve cells that accompany neurons and serve to ensure their nourishment and support. Unlike mature neurons, these cells can reproduce. There are various cell types:

Types of Glial Cells:

• Astrocytes: They have a star-like appearance. They are related to blood vessels and transport substances, including hormones, from the blood.
• Microglia Cells: They have an elongated shape. Their function is to capture and destroy waste products within nervous tissue.
• Oligodendrocytes: They form myelin sheaths around axons in the central nervous system of vertebrates.
• Schwann Cells: They cover the axons of several neurons in the peripheral nerves. The axons of many neurons are embedded in Schwann cells. In unmyelinated fibers, several Schwann cells wrap around the axon. In myelinated fibers, a single Schwann cell wraps repeatedly around one axon, forming the myelin sheath. Each axon contained within a myelin sheath constitutes a myelinated fiber.