TQ 1: The Mammalian Nervous System

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TAQ 1:
a)

b) The mammalian nervous system is split into two. The central nervous system consists of the brain and the spinal cord, which coordinates and controls the movement and activities of the body and the peripheral nervous system, made up of the somatic and autonomic system, which forms the connections between the organs and the central nervous system.
The brain and the spinal cord work together to aid the coordination of the body. The brain can be divided into three main regions: the forebrain, midbrain and hindbrain. The forebrain interprets sensory information, thought processes and memory and it also monitors the composition of the blood and temperature on the body. The midbrain acts as an important link between
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Voltage gated channels open and close in response to an electrical voltage, so they are affected by changes in electrical change around them. When a neuron is “at rest” a charge difference is maintained between the inside and the outside of the cell. This charge difference is produced and maintained largely by active transport using sodium-potassium pumps. The pumps send ions out of the cells and bring potassium ions in. While other channels allow some flow of potassium ions back out of the cell, the sodium ions cannot easily get back in to replace the lost positive charges. The overall result is that the exterior of the cell has a net positive charge and the interior has a net negative charge. The difference in charge between the interior and exterior of the cell is called the resting membrane potential. A nerve impulse begins when a stimulus disturbs the plasma membrane on a dendrite, causing sodium channels to open. Sodium ions flow into the cell lessening the charge difference at that location. If the change is enough it will cause nearby voltage-gated sodium channels to open. This allows sodium ions to flood into the cell at that location the membrane there is ‘depolarized’, with the inside of the cell having a net positive charge and the outside having a net negative charge. This affects neighboring sodium channels, which then open moving the depolarization along the membrane. This is called action potential. Changes occur behind the action potential to restore the resting membrane potential. The sodium channels close and the potassium channels open. This allows the flow of potassium ions of the cell, repolarizing the membrane so that the inside is negative and the outside positive. This is followed by the use of sodium-potassium pumps to fully restore the resting membrane potential and to

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