Download An Overview on the Physiologic Anatomy of the Autonomic Nervous

An Overview on the Physiologic
Anatomy of the Autonomic
Nervous System
Rabiu AbduSSALAM Magaji, Ph.D.
Bayero University, Kano, Nigeria.
IBRO-SfN-NAS Teaching Tools Workshop in Neuroscience,
Fayoum Egypt, 2-6th December, 2009
Target Audience
9First Year Medical Students
Objectives
Students should be able to list:
9The divisions of the ANS
9Structure of the ANS
9Functions of the ANS
DIVISIONS OF THE NERVOUS SYSTEM
THE AUTONOMIC NERVOUS SYSTEM
¾The autonomic nervous
system (ANS) regulates
physiologic processes
without conscious control.
¾The ANS consists of
two sets of nerve bodies:
preganglionic and
postganglionic fibers.
¾The two major divisions
of the ANS are the
sympathetic and
parasympathetic
systems.
Anatomy of the Autonomic Nervous System
Sympathetic:
9The preganglionic cell bodies of
the sympathetic system are located
in the intermediolateral horn of the
spinal cord between T1 and L2 or
L3.
9The sympathetic ganglia are
adjacent to the spine and consist of
the vertebral (sympathetic chain)
and prevertebral ganglia
9Long fibers run from these ganglia
to effector organs, including the
smooth muscle of blood vessels,
viscera, lungs, scalp (piloerector
muscles), and pupils; the heart; and
glands
(sweat,
salivary,
and
digestive).
Parasympathetic
™The preganglionic cell bodies of
the parasympathetic system are
located in the nuclei of the brain
stem and sacral portion of the
spinal cord (S2-S4).
™These preganglionic fibers exit
the brain stem with the 3rd, 7th, 9th,
and 10th cranial nerves.
™Parasympathetic ganglia are located
in the blood vessels of the head, neck,
and thoracoabdominal viscera; lacrimal
and salivary glands; smooth muscle of
viscera and glands.
™Postganglionic parasympathetic
fibers are relatively short (only
about 1 or 2 mm long) thereby
producing specific, localized
responses in the effector organs.
Inputs to the Autonomic Nervous System
¾ The ANS receives input
from parts of the CNS
that process and
integrate stimuli from the
body and external
environment.
¾ These parts include the
hypothalamus, nucleus
of the solitary tract,
reticular formation,
amygdala, hippocampus,
and olfactory cortex.
Neurotransmitters of the ANS
Two most common neurotransmitters released by
neurons of the ANS are acetylcholine (cholinergic)
and norepinephrine/noradrenaline (adrenergic).
Acetylcholine:
All preganglionic nerve fibers
All postganglionic fibers of the parasympathetic
system
Sympathetic postganglionic fibers innervating
sweat glands
Adrenaline:
In most sympathetic postganglionic fibers
Receptors of the ANS Neurotransmitters
™ Cholinergic receptors: nicotinic or
muscarinic.
™ Adrenergic receptors: alpha (α) and beta
(β), with α being more abundant.
™The adrenergic receptors are further
divided into (α1, α2, β1 and β2)
according to some factors.
Functions of the ANS
9 The two divisions of the ANS are dominant under different
conditions.
9 The sympathetic system is activated during emergency
“fight-or-flight” reactions and during exercise.
9 The parasympathetic system is predominant during quiet
conditions (“rest and digest”). As such, the physiological
effects caused by each system are quite predictable.
9 In other words, all of the changes in organ and tissue
function induced by the sympathetic system work together to
support strenuous physical activity and the changes induced
by the parasympathetic system are appropriate for when the
body is resting.
Summary
ANS as a division of the NS is
concerned with the control of visceral
functions.
Sympathetic and parasympathetic
divisions of the ANS are anatomically
and physiologically distinct.
Both the two divisions work together to
make the ANS functions possible.