Outline the general organization of the nervous system:

The nervous system is composed of cells called neurons. These cells are often very elongated and can carry messages at high speed in the form of electrical impulses. The nervous system is divided into two main parts: the central nervous system (CNS), and the peripheral nervous system (PNS). The organs of the CNS, the brain and the spinal cord, are located within and protected by, respectively, the skull and the vertebral column. The PNS is composed of nerves that branch from the CNS and connect the CNS to the rest of the body. The CNS receives impulses from the nerves of the PNS and interprets them, and transmits the corresponding signals back to the origin through the PNS, thus controlling the functions of the entire body.

Explain the ion movements caused by a nerve impulse:

The ion movements caused by a nerve impulse happen in 4 different stages.

Stage 1: An action potential in one part of a neuron causes an action potential to develop in the next section of the neuron. This is due to diffusion of sodium ions between the region with an action potential and the region with a resting potential. These ion movements, local currents, reduce the resting potential. If the potential rises above the threshold level, voltage-gated channels open.

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Stage 2: Sodium channels open very quickly and sodium ions diffuse into the neuron down the concentration gradient. This reduces the membrane potential and causes more sodium channels to open. The entry of positively charged sodium ions causes the inside of the neuron to develop a net positive charge compared to the outside – the potential across the membrane is reversed, aka depolarization.

Stage 3: Potassium channels open after a short delay. Potassium ions diffuse out of the neuron down the concentration gradient through the opened channels. The exit of positively charged potassium ions cause the inside of the ...

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