C H A P T E R 2 9
Introduction to the autonomic nervous system
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the production and release of thyroid hormone, which
increases metabolism and the efficient use of energy.
Together, all of these activities prepare the body to
flee or to fight more effectively. When overstimulated,
however, they can lead to system overload and a variety
of disorders.
Adrenergic response
Sympathetic postganglionic nerves that synthesise,
store and release noradrenaline are referred to as adre
nergic nerves. Adrenergic nerves are also found within
the CNS. The chromaffin cells of the adrenal medulla
are also adrenergic because they synthesise, store and
release noradrenaline, as well as adrenaline.
Noradrenaline synthesis and storage
Noradrenaline belongs to a group of structurally related
chemicals called catecholamines that also includes
dopamine, serotonin and adrenaline. Noradrenaline is
made by the nerve cells using tyrosine, which is obtained
in the diet. Dihydroxyphenylalanine (dopa) is produced
by a nerve, using tyrosine from the diet and other
chemicals. With the help of the enzyme dopa decarb
oxylase, the dopa is converted to dopamine, which in
turn is converted to noradrenaline in adrenergic cells.
The noradrenaline is then stored in granules or storage
vesicles within the cell. These vesicles move down the
nerve axon to the terminals of the axon, where they
line up along the cell membrane. To be an adrenergic
nerve, the nerve must contain all of the enzymes and
Eye
Brain stem
and spinal cord Sympathetic
chain Nerves and
ganglia
Organs
Lacrimal gland
Parotid gland
Salivary gland
Lungs
Larynx
Heart
Stomach
Liver
Coeliac
ganglion
and plexus
Superior
mesenteric
ganglion
Inferior
mesenteric
ganglion and
plexus
Pancreas
Adrenal gland
Kidney
Intestine
Colon
Bladder
Reproductive
organs
Oculomotor n.
Facial n.
Glossopharyngeal n.
Vagus n.
Pelvic n.
1
2
3
4
5
1
2
3
4
5
FIGURE 29.2
The autonomic nervous system.
The sympathetic, or thoracolumbar, division
sends relatively short preganglionic fibres
to the chains of paravertebral ganglia and
to certain outlying ganglia. The second
cell, or postganglionic cell, sends relatively
long postganglionic fibres to the organs
it innervates. The parasympathetic,
or craniosacral, division sends long
preganglionic fibres that synapse with a
second nerve cell in ganglia located close to
or within the organs that are then innervated
by short postganglionic fibres.
