Nervous Tissue

Nervous tissue is an essential part of our bodies, helping us respond to the world around us. It plays a key role in sending and receiving messages throughout the body, keeping us safe and active.

In animals, there are four main types of tissues:

1. Connective tissue

2. Epithelial tissue

3. Muscular tissue

4. Nervous tissue

Here, we will focus on nervous tissue in detail, which is especially important for nervous tissue class 9 studies. Let us learn about its structure, location, characteristics, nervous tissue function, and nervous tissue types.

Explanation of Nervous Tissue

Nervous tissue makes up the major parts of the Central Nervous System (CNS), which includes the brain and spinal cord, and the Peripheral Nervous System (PNS), which comprises branching nerves that connect various organs and tissues to the CNS.

• It primarily consists of neurons (nerve cells) and glial cells.

• Neurons transmit signals (electrochemical impulses) throughout the body.

• Glial cells support and nourish neurons, remove debris, and provide insulation.

This tissue is specialised for quick signal transmission. When a neuron is stimulated, it sends out an electrical impulse that travels rapidly, ensuring swift communication within the body.

Structure of Nervous Tissue

Nervous tissue is composed of distinct cells known as neurons and several types of glial cells. A typical neuron has three main parts:

1. Cell Body (Soma)

• Contains the nucleus, cytoplasm, and other organelles.

• Responsible for the basic metabolic processes of the cell.

2. Dendrites

• Short, branching extensions that receive signals from other neurons or sensory receptors.

• Carry incoming information toward the cell body.

3. Axon

• A long, slender projection that carries impulses away from the cell body.

• Ends in axon terminals, which form specialised junctions (synapses) with target cells (other neurons, muscle cells, or gland cells).

Information Flow in a Neuron

Signals travel in a single direction:

• Dendrites → Cell Body → Axon → Synapse → Target Cell

Glial cells (e.g., astrocytes, oligodendrocytes, Schwann cells, microglia) perform various supporting functions such as:

• Providing nutrients to neurons

• Maintaining the chemical environment

• Forming insulating layers (myelin sheath) around axons

• Cleaning up debris

Location of Nervous Tissue

Nervous tissue is found in:

• The brain and spinal cord, which form the CNS.

• The nerves that branch out into every region of the body, forming the PNS.

These nerves extend to the muscles, glands, and sensory organs, allowing us to sense and respond to the environment.

Nervous Tissue Diagram

A simplified representation of a neuron typically includes:

• A central cell body with a nucleus

• Several branching dendrites

• A single elongated axon that may be covered with a myelin sheath

• Axon terminals at the end for communication

Characteristics of Nervous Tissue

• Composed of two main cell types: neurons and glial cells

• Responsible for receiving and transmitting signals (electrochemical impulses)

• Neurons can live for a very long time but generally cannot divide or replace themselves once fully mature

• Includes special junctions called synapses where chemical messengers (neurotransmitters) carry signals

• Highly specialised, ensuring rapid communication and response to internal and external stimuli

Nervous Tissue Function

What is the nervous tissue function? It is crucial for:

1. Signal Transmission

• Neurons generate, conduct, and transfer nerve impulses using chemical neurotransmitters.

2. Coordination and Control

• The brain and spinal cord integrate information, making decisions and directing responses.

3. Response to Stimuli

• Sensory inputs trigger signals that travel to the CNS, which then organises appropriate motor outputs.

4. Memory and Cognition

• Neurons in certain regions can store information (although their regeneration is very limited).

5. Support and Protection

• Glial cells provide nutrition, protection, and structural support to neurons.

Nervous Tissue Types

There are generally two major nervous tissue types:

1. Neurons (Nerve Cells)

• Specialised in generating and transmitting impulses.

2. Neuroglia (Glial Cells)

• Support neurons by providing insulation, nutrients, and protection.

When you study nervous tissue class 9 textbooks may further classify neurons based on their structure or function:

• Sensory (Afferent) Neurons – Carry impulses from sense organs to the CNS.

• Motor (Efferent) Neurons – Carry impulses from the CNS to muscles or glands.

• Interneurons – Connect sensory and motor neurons within the CNS.

Although we often refer to these as “types,” some sources may highlight 4 types of nervous tissue by grouping neurons and glial cells in different ways. For simplicity, remember that neurons and glial cells are the foundational cellular components of all nervous tissue.

Different Types of Nerves

Nerves are bundles of axons enclosed within protective layers. Based on their functions, nerves can be broadly classified into:

1. Motor Nerves

• Carry signals from the brain and spinal cord to muscles and glands.

• Enable actions like walking, talking, and moving away from danger.

• Damage can lead to weakness or loss of muscle function.

2. Sensory Nerves

• Conduct impulses from sensory receptors (skin, muscles, internal organs) to the CNS.

• Help detect pain, temperature, pressure, and more.

• Damage may cause numbness, tingling, or hypersensitivity.

3. Autonomic Nerves

• Regulate involuntary actions such as heart rate, digestion, and glandular secretions.

• Subdivided into:

• Sympathetic Nervous System – Prepares the body for fight-or-flight responses (e.g., increases heart rate).

• Parasympathetic Nervous System – Conserves energy and aids digestion, excretion, etc.

4. Cranial Nerves

• Twelve pairs emerging directly from the brain.

• Involved in functions like smell, vision, facial movements, tongue movements, and salivation.

• Listed from front to back: Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Spinal Accessory, and Hypoglossal.

Additional Concepts to Improve Learning

Mnemonic for Cranial Nerves

Here is a simple mnemonic to remember the 12 cranial nerves:

• On Old Olympus Towering Top A Friendly Viking Grew Vines And Hops

• O: Olfactory

• O: Optic

• O: Oculomotor

• T: Trochlear

• T: Trigeminal

• A: Abducens

• F: Facial

• V: Vestibulocochlear

• G: Glossopharyngeal

• V: Vagus

• A: Spinal Accessory (often just Accessory)

• H: Hypoglossal

Quick Quiz (with Answers)

1. Question: Which cells in nervous tissue support neurons by providing nourishment and insulation?
A: Glial cells

2. Question: Which part of a neuron receives signals from other neurons?
A: Dendrites

3. Question: Name the long projection of a neuron that transmits impulses away from the cell body.
A: Axon

4. Question: How many pairs of cranial nerves are there in humans?
A: Twelve

5. Question: Which type of nerves control involuntary functions like digestion?
A: Autonomic nerves

Feel free to test yourself and reinforce your understanding of nervous tissue.

Related Topics

• Human Nervous System

• Muscular Tissue

• Difference Between Plant and Animal Tissues