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Introduction. The nervous system and the neurons. Electrical potential of nerve. Electrical signals from muscles-(Electromyogram). Electrical signals from heart-(Electrocardiogram). Electrical signals from the brain-(Electroencephalogram). Electrical signals from eye-(Elecrtrooculogram). There are two aspects of electricity and magnetism in medicine: 1. Electrical and magnetic affect generated inside body. 2. Applications of electricity and magnetism to the surface of body (cardiovascular instrumentations). Electrical and magnetic affect generated inside body serves for: Essentially all functions and activities of the body which involves electricity. For the control the operation of nerve, muscles and different organs. Controls various internal organs such as the heart, intestines, and glands. Autonomic nervous system (just to look) The basic structural unit of the nervous system is a neuron. A nerve cell specialized for the a-reception. b-interpretation. c-transmission of the electrical messages. Neuron consists of a cell body that receives electrical messages from other neurons through contacts called synapses located on the dendrites. The neuron transmits an electrical signal out word along axon Axons are ≈ 1 (m) long. The axon carries the electrical signal to muscle, gland, or other neurons. Axon terminals: Transmit electrical messages (information) from the neuron to muscles, glands or other neurons. Basic structural unit of the nervous system (neuron). Across the surface or membrane of every neuron is an electrical potential difference. This due to the presence of more negative ions on the inside of the membrane than the outside , the neuron said to be polarized . The inside of the cell is typically 60 -90 mv more negative than outside. Intracellular fluid Intracellular fluid When the neuron is stimulated a large momentary of change in the resting potential occurs at the point stimulation. This potential change called action potential propagates along axon. The action potential is the major method of transmission of signals within the body. The stimulation may be caused by various physical and chemical stimuli such as heat, light, sound, and others. The record of the potentials from muscles during rest and contraction is called EMG Resting potential across the membrane of a muscle fiber is similar to resting potential across a nerve fiber. A muscle is made up of many motor units. A motor unit consists of a single branching neuron from brain or spinal cord. • The action potential travels along an axon and is transmitted across the motor end plates into the muscle fibers causing them to contract. Latency or latent period is defined as follows: The period (interval, delay) elapsed between the presentation of a stimulus and the obvious response such as the contraction of a muscle. Surface electrode : Attached to the skin, measures the electrical signals from many motor units. Needle electrode : This is inserted under the skin, measure single motor unit activity.