Electricity within the body lect.8
:Lecture objectives 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).
Introduction: There are two aspects of electricity and magnetism in medicine: Electrical and magnetic affect generated inside body. 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.
The nervous system and the neurons
The nervous system can be divided in two parts: 1-Central nervous system consists of the a-brain b-spinal cord c-nerve fibers (neurons) transmits sensory information to brain or spinal cord and from brain or spinal cord to appropriate muscles and glands.
2-Aoutonomic nervous system: Controls various internal organs such as the heart, intestines, and glands. Autonomic nervous system (just to look)
Neuron: 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).
ELECTRICAL POTENTIALS OF NERVES 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.
The potential difference is called the resting potential of the neuron The potential difference is called the resting potential of the neuron. the typical concentrations of various ions inside and outside the membrane of an axon. 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.
ELECTRICAL SIGNALS OF THE MUSCLE(the electromyogram): 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.
The Electromyogram (EMG) electrodes : 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.