NERVOUS TISSUE• Each neurone consists of a cell body and its

processes, one axon and many dendrites.• Neurones are commonly referred to simply

as nerve cells.• Bundles of axons bound together are called

nerves.• Neurones cannot divide and for survival

they need a continuous supply of oxygen and glucose. Unlike many other cells, neurones can synthesise chemical energy (ATP) only from glucose.

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Properties of neurones• Neurones have the characteristics of irritability and conductivity.

• Irritability is the ability to initiate nerve impulses in response to stimuli from:

• outside the body, e.g. touch, light waves

• inside the body, e.g. a change in the concentration of carbon dioxide in the blood alters respiration; a thought may result in voluntary movement.

• In the body this stimulation may be described as partly electrical and partly chemical — electrical in that motor neurones and sensory nerve endings initiate nerve impulses, and chemical in the transmission of impulses between one neurone and the next or between a neurone and an effector organ.

• Conductivity means the ability to transmit an impulse.

Parts of Neuron1. Cell body 2.Dendrites 3.Axon

Cell Body: Vary in size & shape; contains nucleus surrounded by cytoplasm, contains lysosomes, mitochondria, Golgi complex & clusters of ER-Nissl bodies

Dendrites: receiving portions of neuron; usually short, tapering & highly branched. Contains Nissl bodies, mitochondria.

Axons• Each nerve cell has only one axon, carrying

nerve impulses away from the cell body. They are usually longer than the dendrites, sometimes as long as 100 cm.

• Structure of an axon

• axolemma -The membrane of the axon, it encloses the cytoplasmic extension of the cell body.

•Large axons and those of peripheral nerves are surrounded by a myelin sheath. This consists of a series of Schwann cells arranged along the length of the axon. Each one is wrapped around the axon so that it is covered by a number of concentric layers of Schwann cell plasma membrane. Between the layers of plasma membrane there is a small amount of fatty substance called myelin.

Cytoplasm

Myelinated Non-myelinated

• Postganglionic fibres and some small fibres in the central nervous system are non-myelinated.

• In this type a number of axons are embedded in Schwann cell plasma membranes .The adjacent Schwann cells are in close association and there is no exposed axolemma. The speed of transmission of nerve impulses is significantly slower in non-myelinated fibres.

Axon Terminal- Each axon finely divides in many branches

Synaptic end-bulb- Each terminal swell into it. Contains many tiny sacs-Synaptic vesicles

Neurotransmitter- Chemical in synaptic vesicles e.g. acetylcholine, dopamine

One axon may have 1-3 neurotransmitters