Nervous Tissue:The neuron Tissue consists of two kinds of cells. They are: Nerve cells are Neurons. And Glial cells.
Neurons cannot undergo mitasis whereas glial cells can undergo mitasis.
I. Neurons:



Neuron is the structural and functinal unit of nervous tissue. Neurons are irritable. They are ectodermal in origin. They cannot undergo mitosis. A multipolar neuron consists of a cell body and two types of cell processes – Dendroites and Axon
1. Cell body:
• The anterior expanded portion of neuron is cellbody.
• Cell body is also knwn as perikaryon or soma or cyton.
• It contains the nucleus with a prominant nucleus.
• The cytoplasm contains

Nissl bodies( rough EPR and ribosomes)
Golgi complex
Microtubules and
Pigments such as lipofuscin
• Centismes are absent from neurons.
• Cellbody is covered by Neurilemma

2. Dendrites:
• Dendrites are usually short cytoplamic processes.
• They devide like the branches of a tree.
• They conduct the impulse to the cellbody.

3. Axon:
• The axon is a single long and cylindrical cytoplasmic process.
• Axon originates from a short cone shaped region of perikaryon called the axon –hillock
• The plasma membrane of axon is called Axolemma, its cytoplasm is known as Axoplasm.
• The axon terminates on other neurons by small branches called the terminal arborization. These branches end in small swellings called Terminal boutons.
• The axon is specialized in conducting nerve impulses away from cell body to the other nerve cells
• In myelinated nerve fibres the axolemma is coverred by myelin sheath.
• Gaps in the myelin sheath are called the Nodes of Ranvier. The distance between two nodes is called an internode.
• Internode consists of alternatively arranged Schwancell.

4. Synapse:
• Synapse is the functional gap between two successive neurons.
• It is formed by an axon terminal (presynaptic terminal), dendrite of another nerve cell (post synaptic terminal), and a thin intercellular space called synaptic cleft.
• The presynaptic terminal always contains synaptic vesicles with neurotranmitters and numerous mitochondria.
• Most synapses transmit information to the next neuron by releasing chemical neurotransmitters.

5. Glial cells ( glia- glue):



Glial cells surround the neurons furnish a microenvironment suitable for neurnal activity.
1. Glial cells of central nervous system (CNS):

• Oligodendrites- produce the myelin sheath
• Astrocytes- Star shaped cells with radiating process. They form the blood brain barrie
• Ependymal cells – These are the colunmar epithelial cells covering the ventricles of brain and central of Spinal cord.
• Microglia cells-These are small,mesodermal,elongated cells. These are Phagocytic. Derived from precursor cells in the bone marrow.

Neurons refers to the nerve cells.
Nerve fibre refers to the Axon.
Types of Neurons:
Based on their processes.
1. Multipolar neurons: One axiom, two or mre dendrites. Most neurons are multipolar. E.g. Motor neurons, Inter neurons.
2. Bipolar neurons: one axiom and ne dentrite. E.g. Found in Retina eye. Inner ear and olfactory membrane.
3. Unipolar neurons : have single process. Pseudo unipolar neurons. Found in dorsal rot genglia f the spiral nerves.

Based on their function:
1. Motor neurons: control effector organs such as muscle fibres, exocrine and endocrine glands.
2. sensory neurons:involved in the reception of sensory stimuli from the environment.
3. Inner neurons: connect sensory and motor neurons

Types of nerve fibres:
• Myelinated/Medullated fibres: Axons surrounded by myelin sheath.
• Unmyelinated/ Non medullated fibres: Axons without myelin sheath.


About balarangaiahnarapuram

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