Nerves messages 370

Complete vertebrates (late Cambrian) As above plus myelinated neurons use of zinc enzymes in glial cells Free zinc in nerve messages NO/haem chemistry in glial cells ... 

The neurochemical basis for these effects has also heen studied in some detail. Researchers have learned that MDMA (and its phenyl-ethylamine cousins) interferes with the normal function of at least two neurotransmitters in the brain, serotonin and dopamine. Under normal circumstances, nerve messages are transmitted through the CNS when an axon on one neuron releases a neurotransmitter, such as serotonin or dopamine, which travels across the synapse between two neurons and is taken up at a receptor site in the second neuron. 

The chemical that crosses the synaptic cleft and causes the transmission of the nerve message in an adjacent neuron or the stimulation of an effector cell (muscle or gland). 

Both calcium-45 and calcium-47 can be used to study how calcium is used in the body. A doctor may think that a person s body is not using calcium properly in making bones or regulating nerve messages. The doctor can use calcium-45 or calcium-47 to find out more about this problem. The radioactive isotope is injected into the person s bloodstream. Then its path can be followed by the radiation it gives off The doctor can then tell if the calcium is being used normally in the body. 

Sodium is also involved in sending nerve messages to and from cells. These impulses control the way muscles move. Again, an excess or lack of sodium can result in abnormal nerve and muscle behavior. Sodium is also needed to control the digestion of foods in the stomach and intestines. 

Everything important that happens in the body is directly related to electrons being moved from place to place to make things happen. Electron transfer is the basis for all oxidation and reduction reactions, including cellular respiration—the making of energy. Electrolytes are the top enzyme activators and are essential to the movement of nerve messages in the body and protection of the heart muscle and blood vessels. 

Section (4) refers to the restrictions imposed on cation movement by membranes. The relative ease of movement of potassium through a nerve membrane at rest generates a potassium potential. Imposition of a perturbation upon the membrane changes its properties so that it is more permeable to sodium, and the activated membrane shows a sodium potential of reversed sign to the potassium potential. Thereupon a self-propagating spike of depolarization which is rapidly followed by recovery to the rest state fiows along the nerve cell and is the nerve message. 

A bone is classified according to shape as flat, long, short, or irregular. A living bone consists of three layers the periosteum, the hard cortical bone, and the bone marrow or cancellous bone. The periosteum is a thin coUagenous layer, filled with nerves and blood vessels, that suppHes nutrients and removes cell wastes. Because of the extensive nerve supply, normal periosteum is very sensitive. When a bone is broken, the injured nerves send electrochemical neural messages relaying pain to the brain. 

We need to point additionally to the evolution of special organs, glands, which have stored chemical message systems to help coordinate activities and are associated with nerves and the brain (Figure 8.6 and Table 8.3). Glands are advantageous in organisation as chemical substations connected to different remote parts of the... 

Animals with nerves as in (6) but with new uses of Na, K, Cl and Ca ions in currents carrying messages. Central control of nerves led to brains and greater reach to use the environment in external devices by animals (some three hundred million years ago). 

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