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Neuron Function
描述
Neurons are electrically excitable cells that process and transmit information through electrical and chemical signals. A neuron consists of a cell body, branched dendrites to receive sensory information, and a long singular axon to transmit motor information. Signals travel from the axon of one neuron to the dendrite of another via a synapse. Neurons maintain a voltage gradient across their membrane using metabolically driven ion pumps and ion channels for charge-carrying ions, including sodium (Na+), potassium (K+), chloride (Cl?), and calcium (Ca2+). The resting membrane potential (charge) of a neuron is about -70 mV because there is an accumulation of more sodium ions outside the neuron compared to the number of potassium ions inside. If the membrane potential changes by a large enough amount, an electrochemical pulse called an action potential is generated. Stimuli such as pressure, stretch, and chemical transmitters can activate a neuron by causing specific ion-channels to open, changing the membrane potential. During this period, called depolarization, the sodium channels open to allow sodium to rush into the cell which results in the membrane potential to increase. Once the interior of the neuron becomes more positively charged, the sodium channels close and the potassium channels open to allow potassium to move out of the cell to try and restore the resting membrane potential (this stage is called repolarization). There is a period of hyperpolarization after this step because the potassium channels are slow to close, thus allowing more potassium outside the cell than necessary. The resting potential is restored after the sodium-potassium pump works to exchange three sodium ions out per two potassium ions in across the plasma membrane. The action potential travels along the axon and upon reaching the end, causes neurotransmitters such as serotonin, dopamine, or norepinephrine to be released into the synapse. These neurotransmitters diffuse across the synapse and bind to receptors on the target cell, thus propagating the signal.