Nervous system

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Our physical bodies are electro-chemical.  Electrical signalling through the nervous system, and chemical signals through the blood (hormones).  The effectiveness of the nerve signals also depend on chemicals called neurotransmitters.  Hormones are used to bring about slow changes in the body – such as growth and pregnancy.  Transmission of signals through the nerve pathways is used for quick movements.

Cranial nerves

First a quick recap of the cranial nerves and their connectivity back to the brain.  The diagram below accounts for all the cranial nerves (12 or 13) except the tenth “X”, the Vagus Nerve.  Connections to the rest of the physical body is via the Vagus Nerve and the spinal cord.

cranial nerves

Autonomic nervous system

Most of the internal organs operate under control of the autonomic nervous system.  The sympathetic being the “fight and flight“, and the parasympathetic being the “rest and digest“.  Most of the internal body organs are connected to both – the parasympathetic through the vagus nerve, and the sympathetic through the spine.  In simple term, the sympathetic is “on”, and the parasympathetic is “off”.  This allows the organs to be activated to digest a meal, or to be switched off when reacting to a stressful situation or strenuous physical activity.  A more detailed diagram of the nerve pathways is shown below.

nervous system

See also the Full Brain diagram.