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.
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)
Pigments such as lipofuscin
• Centismes are absent from neurons.
• Cellbody is covered by Neurilemma
• Dendrites are usually short cytoplamic processes.
• They devide like the branches of a tree.
• They conduct the impulse to the cellbody.
• 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.
• 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.
TYPES OF NEURONS AND NERVE FIBRES
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.