Nervous tissues | General | Structure of a Motor Neuron | Classification of Neurons | Funtions of Nerve Tissue | General All living cells have the ability to react to stimuli. Nervous tissue is specialised to react to stimuli and to conduct impulses to various organs in the body which bring about a response to the stimulus. Nerve tissue (as in the brain, spinal cord and peripheral nerves that branch throughout the body) are all made up of specialised nerve cells called neurons. Neurons are easily stimulated and transmit impulses very rapidly. A nerve is made up of many nerve cell fibres (neurons) bound together by connective tissue. A sheath of dense connective tissue, the epineurium surrounds the nerve. This sheath penetrates the nerve to form the perineurium which surrounds bundles of nerve fibres. blood vessels of various sizes can be seen in the epineurium. The endoneurium, which consists of a thin layer of loose connective tissue, surrounds the individual nerve fibres. Although the system forms a unit it can be divided into the following parts: the central nervous system (CNS) which consists of the brain and spinal cord, the nervous system consists of the nerves outside the CNS which connect the brain and spinal cord to the organs and muscles of the body and the automatic or involuntary nervous system consists of nerve centres and fibres inside as well as outside the central nervous system. There are three main types of neurons, which are classified according their function: Those that conduct impulses from the sensory organs to the central nervous system (brain and spinal cord) are called sensory (or afferent) neurons; those that conduct impulses from the central nervous system to the effector organs (such as muscles and glands) are called motor (or efferent) neurons. Interneurons (also known as connector neurons or association neurons) are those that connect sensory neurons to motor neurons. Structure of a Motor Neuron A motor neuron has many processes (cytoplasmic extensions), called dendtrites, which enter a large, grey cell body at one end. A single process, the axon, leaves at the other end, extending towards the dendrites of the next neuron or to form a motor endplate in a muscle. Dendrites are usually short and divided while the axons are very long and does not branched freely. The impulses are transmitted through the motor neuron in one direction, i.e. into the cell body by the dendrites and away from the cell body by the axon . The cell body is enclosed by a cell (plasma) membrane and has a central nucleus. Granules, called Nissl, bodies are found in the cytoplasm of the cell body. Within the cell body, extremely fine neurofibrils extend from the dendrites into the axon.
Posted on: Thu, 05 Sep 2013 10:18:27 +0000
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