Cell Membrane And The Cell Body

917 Words Sep 3rd, 2015 4 Pages
Neurons are made up of four regions, the cell body, dendrites, axons and presynaptic terminal. The cell body (soma) contains the nucleus of a neuron and the endoplasmic reticulum. Extending out from the cell body are processes called dendrites and axons. These processes conduct nerve impulses. Dendrites conduct impulses toward the cell body while axons conduct impulses away from the cell body. A fatty sheath called myelin sheath encases axons. It is the greatly expanded plasma membrane of an accessory cell called the Schwann cell where the sheath of one Schwann cell meets the next. The axolemma is the portion of the cell membrane surrounding the axon of a neuron and is responsible for maintaining the membrane potential of the neuron. A single neuron, especially one in the central nervous system may have thousands of other neurons synapsing on it. Some of these release activating (depolarizing) neurotransmitters; others release inhibitory (hyperpolarizing) neurotransmitters.
An inactive or resting neuron actively pumps sodium out of the cell and potassium into the cell to maintain equilibrium. However, the plasma membrane is more permeable to potassium than to sodium, which results in some potassium to diffuse out of the neurons. Large, negatively charged proteins such as phosphate and sulfate cannot diffuse out of the neuron. This results in a net excess of positively charged ions outside the neuron membrane and net excess of negatively charged ions inside the neuron.
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