Structure and Functions of Nervous Tissues

Structure and Functions of Nervous Tissues

NERVOUS TISSUES

What is nervous tissue?

Nervous tissue or nerve tissue:

Is the main tissue component of the two parts of the nervous system; the brain and spinal cord of the central nervous system (CNS), and the branching peripheral nerves of the peripheral nervous system (PNS), which regulates and controls bodily functions and activity.

Nervous tissue is distributed throughout the body as an integrated communicating network

Components of Nervous Tissue

Structurally, nerve tissue consists of two classes of cell types.

Neurons, the nervous tissue is made up of billions of cells called neurons that are specialized to respond to stimuli and to transmit a signal to activate other cells.

Glial cells or neuroglia, non-excitable supporting cells, participate in neural activity, neural nutritional and defence processes of the central nervous system.

A Typical Neuron Consist of:

Cell body, which has many radiating processes called dendrites, which are specialized to receive signals from other neurons.

Axon, a single long process, which is capable of generating a nerve impulse and conducting it over a long distance to stimulate other neurons in the CNS, or muscular or secretory cells elsewhere in the body.

Neurons usually receive information through dendrites; the information is integrated in the cell body and transmitted onwards via axons.

Types of Neuron

Unipolar neurons, these neurons have single processes, the axon arising from the cell body.

Unipolar neurons have no dendrites.

Bipolar neurons, have two processes (both axons) emerging directly and oppositely from the cell body.

Bipolar neurons are found in the cochlear and vestibular ganglia as well as retina and olfactory mucosa.

• Multipolar neurons, has one axon and many dozens of dendrites.

Most neurons in the CNS are multipolar ( +all motor neurones) Pseudo unipolar neurons, has a single short process (an axon) with a T-shaped branching, one branch extending towards the CNS, and the other extending to a periphery ending.

In typical pseudo unipolar neurons, both branches are axons on both structural and electrophysiological grounds.

Classification of Neurons according to their Functional Roles

Motor neurons are involved in stimulating muscles or glands (effector organs) in the periphery.

Sensory neurons, sensory neurons receive sensory stimuli from the environment or from tissues and organs of the body.

Interneurons, maintain connection between neurons in the CNS, forming complex function chains or circuits.

Neuroglia and their Functions

What is neuroglia?

Neuroglia (Glial Cells) :

These are supporting cells found in the central nervous system and peripheral nervous system There are six types of supporting cells Four are found in the CNS and two are found in the PNS Neuroglia found in central nervous system are :

I.Astrocytes

Star-shaped, abundant, and versatile Guide the migration of developing neurons, they are found in large numbers adjacent to blood vessels They form a blood-brain barrier (BBB), i.e. the blood is separated from neurones by capillary wall and a layer of astrocytes foot process

II.Microglia

• Specialized immune cells that act as the macrophages of the CNS
• They derived from monocytes

III.Ependymal Cells

These cells form the epithelial lining of the ventricles of the brain and the central canal of the spinal cord IV. Oligodendrocytes,

These are found in clusters around cell bodies They form and maintain the myelin, having the same functions as schwann cells in peripheral nerves These cells have clinical importance as most tumours of the brain are arising from them

Glia Cells Found in the Peripheral Nervous System

V.Satellite cells, surround clusters of neuronal cell bodies in the PNS, they are of unknown function VI.Schwann cells, form myelin sheaths around the larger nerve fibers in the PNS, they are for neuronal regeneration

Key points

The nervous system is composed of neurons (nerve cells) and neuroglia (protective and supporting cells) Neurons are sensitive to stimuli, convert stimuli into electrical signals called action potentials (nerve impulses), and conduct nerve impulses.

Neuroglia (Glial Cells) are supporting cells found in the central nervous system and peripheral nervous system

evaluation

• What is nervous tissue?
• What are the components of nervous tissue?
• What are the types of neuron types?
• What are the types of neuroglia and their functions?

What are the function of neuroglia?