The document summarizes the structure and function of the nervous system. It describes how the nervous system is divided into the central nervous system (CNS) and peripheral nervous system. The peripheral nervous system is further divided into the efferent and afferent divisions. The efferent division carries signals from the CNS to peripheral tissues and is divided into the somatic and autonomic systems. The autonomic system regulates vital functions unconsciously through the neurotransmitters acetylcholine and norepinephrine. Acetylcholine and norepinephrine are synthesized, stored, released, and terminated through specific mechanisms to control organs and physiological processes.
2. The nervous system is divided into two anatomical divisions:
1. The central nervous system (CNS), which is composed of the
brain and spinal cord,
2. The peripheral nervous system, which includes neurons
located outside the brain and spinal cord that is, any nerves
that enter or leave the CNS.
3.
4.
5. The peripheral nervous system is subdivided into the
1. EFFERENT DIVISION, the neurons of which carry signals
away from the brain and spinal cord to the peripheral tissues,
2. AFFERENT DIVISION, the neurons of which bring
information from the periphery to the CNS.
6.
7. • The efferent portion of the peripheral nervous system
is further divided into two major functional
subdivisions, the somatic and the autonomic systems.
• The SOMATIC efferent neurons are involved in the
voluntary control of functions such as contraction of
the skeletal muscles essential for locomotion.
• On the other hand, the AUTONOMIC system
regulates the everyday requirements of vital bodily
functions without the conscious participation of the
mind.
8. • All neurons are distinct anatomic units, and no structural
continuity exists between most neurons.
• Communication between nerve cells and between nerve
cells and effector organs occurs through the release of
specific chemical signals, called neurotransmitters, from
the nerve terminals. This release is triggered by the arrival
of the action potential at the nerve ending, leading to
depolarization.
• The neurotransmitters rapidly diffuse across the synaptic
cleft or space (synapse) between neurons and combine
with specific receptors on the postsynaptic (target) cell.
9. • An important traditional classification of autonomic nerves is
based on the primary transmitter molecules—acetylcholine or
norepinephrine—released from their terminals and varicosities.
A large number of peripheral ANS fibers synthesize and release
acetylcholine; they are cholinergic fibers; that is, they work by
releasing acetylcholine.
10. • Acetylcholine (ACh) is the primary transmitter in all
autonomic ganglia and at the synapses between
parasympathetic postganglionic neurons and their
effector cells.
• It is the transmitter at postganglionic sympathetic
neurons to the thermoregulatory sweat glands.
• It is also the primary transmitter at the somatic (voluntary)
skeletal muscle neuromuscular junction.
11. • 1. Synthesis and storage—Acetylcholine is synthesized
in the nerve terminal by the enzyme choline
acetyltransferase (ChAT) from acetyl-CoA (produced in
mitochondria) and choline (transported across the cell
membrane).
• Acetylcholine is actively transported into its vesicles for
storage by the vesicle-associated transporter, VAT. This
process can be inhibited by another research drug,
vesamicol.
12. • Release of acetylcholine—Release of transmitter stores
from vesicles in the nerve ending requires the entry of
calcium through calcium channels and triggering of an
interaction between SNARE (soluble N-ethylmaleimide-
sensitive-factor attachment protein receptor) proteins.
13. • Termination of action of acetylcholine—The action of
acetylcholine in the synapse is normally terminated by
metabolism to acetate and choline by the enzyme
acetylcholinesterase in the synaptic cleft.
14.
15. • Norepinephrine (NE) is the primary transmitter at the
sympathetic postganglionic neuron-effector cell synapses
in most tissues.
• Dopamine may be a vasodilator transmitter in renal blood
vessels, but norepinephrine is a vasoconstrictor of these
vessels.
16. • Synthesis and storage—After transport across the cell
membrane, tyrosine is hydroxylated by tyrosine hydroxylase
to DOPA , decarboxylated to dopamine, and hydroxylated to
norepinephrine.
• Tyrosine hydroxylase can be inhibited by metyrosine.
• Norepinephrine and dopamine are transported into vesicles by
the vesicular monoamine transporter (VMAT) and are stored
there.
• Monoamine oxidase (MAO) inactivates a portion of the
dopamine and norepinephrine in the cytoplasm. Therefore,
MAO inhibitors may increase the stores of these transmitters
.
• VMAT can be inhibited by reserpine, resulting in depletion of
transmitter stores.
17.
18. • Release and termination of action—Dopamine and
norepinephrine are released from their nerve endings by
the same calcium-dependent mechanism responsible for
acetylcholine release.
• Lack receptors for botulinum.
19. • Termination occurs via diffusion and reuptake
(especially uptake-1, by the norepinephrine transporter,
NET, or the dopamine transporter, DAT) reduce their
concentration in the synaptic cleft and stop their action.
• Outside the cleft, these transmitters can be
metabolized—by MAO and catechol-O-
methyltransferase (COMT)—and the products of these
enzymatic reactions are excreted.
20. • Drugs that block norepinephrine synthesis (eg,
metyrosine) or catecholamine storage (eg, reserpine) or
release (eg, guanethidine) were used in treatment of
several diseases (eg, hypertension) because they block
sympathetic but not parasympathetic functions.
25. • These sites include the CNS centers; the ganglia; the
postganglionic nerve terminals; the effector cell
receptors; and the mechanisms responsible for
transmitter synthesis, storage, release, and termination of
action
26. • A. Local Integration: Mainly provided through
mechanism of negative feedback.
• This effect is mediated by α2 receptors located on the
presynaptic nerve membrane.
• B. Systemic Reflexes: System reflexes regulate blood
pressure, gastrointestinal motility, bladder tone, airway
smooth muscle, and other processes.
• The control of blood pressure—by the baroreceptor
neural reflex and the renin-angiotensin-aldosterone
hormonal response.
27. • C. Complex Organ Control: The Eye
• The pupil, is under reciprocal control by the SANS (via α
receptors on the pupillary dilator muscle) and the PANS
(via muscarinic receptors on the pupillary constrictor).
• The ciliary muscle, which controls accommodation, is
under primary control of muscarinic receptors innervated
by the PANS, with insignificant contributions from the
SANS.
