The nervous system is an organ system containing a network of specialized cells called neurons that coordinate our actions and transmit signals between different parts of our body.

It is helpful to consider the nervous system as a number of identifiable but inter-related parts: the Central Nervous System, consisting of the brain and spinal cord; the Peripheral Nervous System, which transmits sensations of heat, cold, pressure, pain, etc., from all over the body to the Central Nervous System {C.N.S.) and receives impulses from the C.N.S. to set the voluntary muscles in motion; the Autonomic Nervous System which relays nerve impulses to and from the organs and also the specialised sensory nerves involved in sight, hearing, taste and smell. These regions are all interconnected by means of complex neural pathways. The enteric nervous system, a subsystem of the peripheral nervous system, has the capacity, even when severed from the rest of the nervous system through its primary connection by the vagus nerve, to function independently in controlling the gastrointestinal system.

Neurons send signals to other cells as electrochemical waves travelling along thin fibres called axons, which cause chemicals called neurotransmitters to be released at junctions called synapses. A cell that receives a synaptic signal may be excited, inhibited, or otherwise modulated. Sensory neurons are activated by physical stimuli impinging on them, and send signals that inform the central nervous system of the state of the body and the external environment. Motor neurons, situated either in the central nervous system or in peripheral ganglia, connect the nervous system to muscles or other effector organs. Central neurons, which in vertebrates greatly outnumber the other types, make all of their input and output connections with other neurons. The interactions of all these types of neurons form neural circuits that generate an organism's perception of the world and determine its behavior. Along with neurons, the nervous system contains other specialized cells called glial cells (or simply glia), which provide structural and metabolic support.

The nervous system derives its name from nerves, which are cylindrical bundles of tissue that emanate from the brain and spinal cord and branch repeatedly to innervate every part of the body. Nerves are large enough to have been recognized by the ancient Egyptians, Greeks, and Romans, but their internal structure was not understood until it became possible to examine them using a microscope. A microscopic examination shows that nerves consist primarily of the axons of neurons, along with a variety of membranes that wrap around them and segregate them into fascicles. The neurons that give rise to nerves do not lie within them—their cell bodies reside within the brain, spinal cord, or peripheral ganglia.

The Central Nervous System consists of the Brain and Spinal Cord. It contains millions of neurones (nerve cells). If you slice through some fresh brain or spinal cord you will find some areas appear grey whilst other ares appear rather white. The white matter consists of axons, it appears white because it contains a lot of fatty material called myelin. The myelin sheath insulates an axon from its neighbours. This means that nerve cells can conduct electrical messages without interfering with one another. The grey matter consists of cell bodies and the branched dendrites which effectively connect them together. So this area is mainly cytoplasm of nerve cells which is why it appears white.

Both the spinal cord and the brain consist of white matter - bundles of axons each coated with a sheath of myelin and gray matter - masses of the cell bodies and dendrites - each covered with synapses. In the spinal cord, the white matter is at the surface, the gray matter inside. In the brain of mammals, this pattern is reversed. However, the brains of "lower" vertebrates like fishes and amphibians have their white matter on the outside of their brain as well as their spinal cord.

The action of essential oils and of massage on the various activities of the nervous system form a major part of aromatherapy. For example, analgesic oils relieve pain because they damp down the activity of the pain-transmitting nerve endings, antispasmodic oils have a calming effect on the nerves which trigger muscle activity, sedative oils act partly by reducing over-activity in the nervous system. There is a great deal of overlap in these properties, and many analgesic oils are also sedative and/or antispasmodic. For example, Bergamot, Camomile, Lavender and Marjoram share all three of these properties, while Eucalyptus, Peppermint and Rosemary are both analgesic and antispasmodic though not sedative. Not surprisingly, these are among the most valuable and often-used oils in aromatherapy and we call on them repeatedly for all conditions where there is pain or spasm in the voluntary muscles or internal organs.

Some other oils which combine sedative and antispasmodic effects are Clary Sage, Cypress, Juniper, Melissa, Neroli, Rose and Sandalwood. Of these, Neroli has a marked effect on the autono-|mic nerves governing the intestines, and is very helpful for nervous diarrhoea and 'butterflies in the tummy'. Sandalwood is particularly active on the nerves of the bronchial passages and is one of the best oils to calm down a cough which is caused by nervous reflex action.

Nervine oils are those which have a beneficial tonic action on the nervous system as a whole and include Camomile, Clary Sage, Juniper, Lavender, Marjoram, Melissa and Rosemary. As you can see, all of these have already been mentioned for their other actions on the nervous system.