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Neurones

Neurones carry signals from and to each other and the motor and sensory organs. Signals are transmitted along neurones electrically as action potentials and from axon to dendrite (or end organ) as chemical messages via the synapse.

Structure

Neurones consist of a cell body, numerous dendrites, an axon and synapses.

The cell body houses the nucleus and all of the biochemical machinery for the cell's function. Besides just a few spurious exceptions, neurones have many dendrites and only one axon.

The axon is the single output of the neurone, transmitting the action potential from the axon hillock to the synapse at its distal end. Axons are commonly myelinated to improve their speed of conduction, in the PNS this is done by Schwann cells and Oligodendrocytes in the CNS.

The synapse is where the electrical signal is transduced to a chemical message sent to the dendrites of other neurones.

The dendrites are numerous and collect signals from many axons and transmit them to the cell body where they are collated and will either excite or inhibit the neurone from firing an action potential along its axon.

Nerve conduction

All cells are bound by a phospholipid bilayer cell membrane. the cell membrane houses a vast array of receptors and ion channels. The ion channels function to maintain the internal environment of the cell - pH and electrolyte concentration gradients with the interstitia.

Resting potential

The resting potential is the electrochemical gradient across the cell membrane between the cytoplasm of a cell and the interstitial fluid it resides in. Unlike it's name would suggest it is actively maintained by Na+/K+ ATPase channels in the cell membrane. These ion pumps are present in all cells and for each cycle of breaking down one ATP molecule pump three Na+ out and two K+ into the cytoplasm. This means that the majority of potasium in the body is intracellular and sodium is extracellular. The differential quantity of Na+ and K+ ions moving generates a cation deficit within the cell resulting the resting potential of -65mV.

Action potentials