Sympathetic nerve cells. Light micrograph of a section through a sympathetic nerve ganglion. Sympathetic ganglia are collections of nerve cell bodies found on either side of the spinal cord. They contain nerve fibres that originate in the central nervous system, known as preganglionic fibres, and fibres that connect to effector organs, such as muscles, known as postganglionic fibres. The preganglionic fibres are thicker as they are surrounded by a myelin sheath; a layer of connective tissue that increases impulse speed. The sympathetic nervous system controls the body's fight-or-flight response to stress. Magnification: x7 when printed at 10 centimetres wide.
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