DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

SOMATIC SYSTEM
177
Various
levels
of
spinal cord
Motor neuron
ACh
Skeletal
(striated)
muscle
Nicotinic
Receptors
N m
N m
AUTONOMIC SYSTEM
Parasympathetic
Cranial
and
spinal
ACh
N n
Ganglion
ACh
Muscarinic
Receptors
M
CHAPTER 8
Sympathetic
Thoracic
and
lumbar
Adrenal
medulla
N n
ACh
N n
ACh
Epi/NE
(80%/20%)
Ganglion
Sympathetic
cholinergic fiber
ACh
M
Sweat
glands
Figure 8–2. Schematic representation of the somatic motor nerves and the efferent nerves of the autonomic nervous system. The principal
neurotransmitters, acetylcholine(ACh) and norepinephrine (NE), are shown in red. The receptors for these transmitters, nicotinic (N)
and muscarinic (M) cholinergic receptors, α and β adrenergic receptors, are shown in green. The somatic nerves innervate skeletal
muscle directly without a ganglionic relay. The autonomic nerves innervate smooth muscles, cardiac tissue and glands. Both parasympathetic
and sympathetic systems have ganglia where ACh is the transmitter of the preganglionic fibers; ACh acts on nicotinic receptors
on the postganglionic nerves. ACh is also the neurotransmitter at cells of the adrenal medulla, where it acts on nicotinic ACh
receptors to cause release of the catecholamines epinephrine (Epi) and NE into the circulation. Epi represents ~80% of the released catecholamines.
ACh is the predominant neurotransmitter of postganglionic parasympathetic nerves and acts on muscarinic receptors. NE
is the principal neurotransmitter of postganglionic sympathetic nerves, acting on α or β adrenergic receptors. Note that somatic nerves
form a specialized synaptic junction, termed the motor end plate. Autonomic nerves form a more diffuse pattern with multiple synaptic
sites. The ganglia in the parasympathetic system are near or within the organ being innervated with generally a one-to-one relationship
between pre- and post-ganglionic fibers. In the sympathetic system the ganglia are generally far from the effector cells (e.g., within
the sympathetic chain ganglia). Preganglionic sympathetic fibers may make contact with a large number of postganglionic fibers.
M
NE
α/β
Smooth
muscle,
cardiac
tissue,
secretory
glands
Adrenergic
Receptors
α/β
Muscarinic
Receptors
(sweat glands)
M
NEUROTRANSMISSION: THE AUTONOMIC AND SOMATIC MOTOR NERVOUS SYSTEMS
components of instinctive reactions to the external environment
are lost; and other serious deficiencies in the
protective forces of the body are discernible.
The sympathetic system normally is continuously
active; the degree of activity varies from moment to
moment and from organ to organ. In this manner,
adjustments to a constantly changing environment are
accomplished. The sympatho-adrenal system also can
discharge as a unit. This occurs particularly during rage
and fright, when sympathetically innervated structures