Vertebrates all have a dorsal hollow nerve cord. It forms on the dorsal side of the embryo as the neural tube. The brain and the spinal cord derive from that neural tube. The neural tube closes early in embryogenesis and failure to close can result in a baby who is anencephalic (without a brain) or who has spina bifida, an opening somewhere along the spinal cord. The child is paralyzed from the opening down. Folate, one of the vitamins, is known to reduce the risk of such an anomaly. Folate is also good for your heart and everyone is advised to take it. However, women of childbearing age should be taking it all the time or eating foods that are rich in it. If a person has already had a child with a neural tube defect (NTD) the mother is advised to take 4 mg/day of folate (or folic acid) at least three months before and three months after conception in future pregnancies. Hispanics have a higher incidence of NTDs than other ethnic groups.

The vertebrate nervous system is anatomically divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is composed of the brain and the spinal cord which contain inter neurons. The PNS is composed of the sensory and motor neurons that come from the receptors and go to the effectors. There are 12 cranial nerves connected to the brain. Some are sensory, some motor and some mixed. There are 31 pairs of spinal nerves which are connected to the spinal column. They are both sensory and motor nerves.

The (motor) neurons of the peripheral nervous system are divided functionally into the somatic and autonomic subdivisions. The somatic subdivision refers to those cranial and spinal nerves that carry messages to voluntary skeletal muscles. The autonomic nervous system is that part of the peripheral nervous system that is not under voluntary control. The autonomic nerves are those cranial and spinal nerves that carry messages to the smooth muscle of the organs (uterus, stomach, etc.), heart, most glands and other internal organs. In the voluntary system, the motor neurons originate in the spinal cord and run uninterrupted to the effector. In the autonomic, an additional motor neuron is inserted.

An additional functional separation exists within the autonomic system. It consists of the sympathetic and parasympathetic motor nerves. All organs are innervated by both types of nerves. The sympathetic and parasympathetic work antagonistically but result in fine tuning the body needs. At times one takes precedence over the other.

The parasympathetic consists of some of the cranial nerves from the brain (e.g., the vagus nerve, 10^th cranial nerve) and some from the sacral region of the spinal cord. Acetylcholine is the chemical transmitter at the parasympathetic synapses. Its function is to stimulate digestion, slow the heart and lower the blood supply to skeletal muscles. The parasympathetic signals a "vegetative" state. After a full meal, the parasympathetic takes over and the blood is diverted to the digestive tract and away from the skeletal muscles and brain.

The sympathetic consists of nerves from the thoracic and lumbar regions of the spinal cord and the nerves form a chain of ganglia immediately outside the vertebral column, "the sympathetic chain," composed of cell bodies (nuclei) of additional motor neurons. (The parasympathetic system also has ganglia but they are close to the target organ and far from the CNS.)When the sympathetic signals are predominating, the body assumes a "fight or flight" response. If something scares you, the sympathetic takes over and causes a release of adrenalin (epinephrine) so that the blood goes to the skeletal muscles and heart and away from the digestive tract. The sympathetic system also stimulates the adrenal gland, thus even more adrenalin is released to help the body fight or flee. Epinephrine is both neurotransmitter and a hormone.

When you take the final in this class, do not eat too much beforehand or your blood will go to your stomach and not to your brain! As you read the exam the photoreceptors in your retina will be stimulating the sensory neurons of your optic nerve (a cranial nerve which is part of your PNS). The optic nerve endings will stimulate the inter neurons of your brain which in turn will stimulate others (we hope) to remember the answers to the questions. When you have the answer, the inter neurons of the brain and spinal cord will stimulate the motor neurons in the somatic subdivision of your PNS and they, in turn, will stimulate the muscles (effector cells) of your arm and fingers to write the right answers!! Whew!! Good luck.

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