CHAPTER 7: NERVOUS SYSTEM
Electrical Signals
Neurons are electrically excitable cells, meaning that they can generate, receive and transmit electrical signals. The transmission of electrical signals is the communication that allows the brain and spinal cord to regulate ALL body functions.
There are 2 types of electrical signals:
Graded Potentials: used for short distance communication
Action Potentials: used for long distance communication
The fact that neurons and muscle fibres are the only cells capable of electrical excitability is due to 2 important features of their plasma membranes: The presence of a Resting Membrane Potential (RMP) and specific types of Ion Channels.
Resting Membrane Potential (RMP)
Like most other cells in the body, the plasma membrane of excitable cells exhibit membrane potential , an electrical potential difference (voltage) across the membrane. In excitable cells this voltage is termed Resting Membrane Potential (RMP) . RMP is the difference between the inside and outside of the plasma membrane of a neuron at rest. Like a battery, if you connect the negative and positive terminals with a piece of wire, electrons flow and this is called Current . In living cells, the flow of Ions constitutes current. Graded and action potentials occur because the membranes of neurons contain many different kinds of Ion Channels that open or close in response to stimuli. The difference in charge represents current . The average neuron has an RMP of -70 millivolts (mV) . This means that the inside of the cell is 70mV more negative than the outside. The RMP exists because of a small buildup of negative ions along the inside of the cell and a buildup of positive ions on the outside of the cell. This separation of charge forms Potential Energy and is measured in millivolts (mV). The greater the
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