• the branches of the spinal nerves;

• the disorders of the spinal nerves;

• the parts of the autonomic nervous system;

• The functions of the autonomic nervous system.

Text 1. Spinal Cord

The spinal cord occupies the spinal canal, but not all of it in the lower part. In adult the cord ends in the region just below the area to which the last rib attaches (between the first and the second lumbar vertebrae).

The spinal cord consists of gray matter (nerve cell bodies) and a larger area surrounding this gray part that consists of white matter (nerve fibers). The structure of the spinal cord is shown in Fig. 20-1.

You can see that the gray matter has the form of the letter H or a butterfly (метелика). The functions of the spinal cord may be divided into three categories:

• reflex activities;

• conduction of sensory impulses (to the brain);

• conduction of motor impulses (from the brain).

All the nervous activities are taking place through the reflex arcs. The reflex arc consists of five components: the receptor, the afferent pathway, the nervous center, the efferent pathway and the effector.

The diseases of the spinal cord are: poliomyelitis (an infectious disease, which commonly occurs in children; polio virus enters the body through the nose and throat; the virus destroys

dorsal root /. gangliorTy^

ventral - horn

cell-body

the motor nerve cells in the spinal cord; the preventive medicine is the oral Sabin vaccine), paraplegia (the loss of sensation and motion in the lower part of the body), tumors that grow from within the cord or that compress the cord from outside.

spinal nerve

Text 2. Spinal Nerves

Look at Fig. 19-1. There are

31 Pairs of spinal nerves, each pair is numbered according to the level of the spinal cord from which it arises. Each spinal nerve has small posterior divisions and rather large anterior divisions.

The larger anterior branches

form networks called plexuses, which innervate (іннервують) different parts of the body.

The three main plexuses are described as follows:

1. The cervical plexus supplies motor impulses to the muscles of the neck and receives sensory impulses from the neck and the back of the head. The phrenic nerve, which activates the diaphragm, arises from this plexus.

2. The brachial ['braskial] plexus sends numerous branches to the shoulder, arm, forearm, wrist and hand. The radial nerve emerges from the brachial plexus.

3. The lumbosacral [^Amba'seikral] plexus supplies nerves to the lower extremities. The largest of these branches is the sciatic [sai'aetik] nerve, which leaves the dorsal part of the pelvis, passes the glutaeus maximus muscle and then to the thigh, and lower leg, and foot.

The disorders of the spinal nerves are:

- neuritis (inflammation of a nerve);

• sciatica [sai'astkka] (kind of neuritis characterized by severe pain along the sciatic nerve);

• herpes zoster (known as shingles) is characterized by numerous blisters along the course of certain nerves (the cause is the chickenpox virus).

Text 3. Autonomic Nervous System

Look at Fig. 20-2. The autonomic nervous system is the motor (efferent) division of the visceral (involuntary) nervous system. It has many ganglia that serve as relay stations. In these ganglia each message is transferred at a synapse from the first neuron to the second one from there to the muscle or gland cell. This differs from the voluntary (somatic) nervous system, in which each motor nerve fiber extends all the way from the spinal cord to the skeletal muscle with no intervening synapse.

The autonomic nervous system has sympathetic pathways and parasympathetic pathways.

The sympathetic pathways begin in the spinal cord with cell bodies in the thoracolumbar area and then their nerve fibers extend to ganglia where they form a synapse with a second set of neurons, whose fibers extend to the glands and involuntary muscle tissues. These second neurons act on the effectors by releasing the neurotransmitter epinephrine (adrenaline), so the sympathetic system can also be called adrenergic [aedri пз:дзік].

The parasympathetic pathways begin in the craniosacral areas, with fibers arising from cell bodies of midbrain, medulla, and sacral part of the spinal cord, and stimulate the visceral tissues. The neurons of this part of the nervous system release the neurotransmitter acetylcholine, so it is called cholinergic [кт)1і'пз:дзік].

The autonomic nervous system regulates the action of the glands, the smooth muscles of hollow organs, and the heart. The sympathetic part tends to act as an accelerator for the organs needed to meet a stressful situation.

The parasympathetic part normally acts as a balance for the sympathetic system once a crisis has passed.

The autonomic nervous system, together with the endocrine system, regulates our responses to stress.

Exercise 3. Write out all terms of Greek origin form Texts 1, 2, 3.

Exercise 4. Define the following terms.

Plexus, ganglia, autonomic nervous system, somatic nervous system, neuritis, neuron, herpes zoster, synapse, nervous system.

Exercise 5. Differentiate between the sympathetic and parasympathetic nervous systems.