1. Topic: Organization ,
Subdivisions and
Innervations of Autonomic
Nervous System
Zulcaif Ahmad

2. ORGANIZATION OF NERVOUS SYSTEM

3. BRIEF INTRODUCTION TO NERVOUS SYSTEM
• The nervous system is divided into anatomical divisions : CNS
which is composed of composed of the brain and spinal cord,
and PNS which includes neurons located outside the brain and
spinal cord i.e. any nerve that enter or leaves the CNS
• The peripheral nervous system is further subdivided into the
efferent divisions , the neurons of which carry signals away
from the brain and spinal cord to the peripheral tissues, and
the afferent division, the neurons of which bring information
from periphery to the CNS.

4. WHAT IS AUTONOMIC SYSTEM?
• The autonomic nervous system (ANS) is largely autonomous
(independent) in that its activities are not under direct
conscious control .
• It is concerned with visceral functions-cardiac output, blood
flow to various organs, digestion, etc- that are necessary for
life.

5. Autonomic nervous system and
endocrine system
• The autonomic nervous system, along with the
endocrine system coordinates the regulation and
integration of bodily functions.
• The endocrine system sends signals to target
tissues by varying the levels of blood borne
hormones.
• In contrast, the nervous system exerts its
influence by the rapid transmission of electrical
impulses over nerve fibers that terminate at
effector cells, which specifically respond to the
release of neuromediator substances

6. Autonomic drugs
• Drugs that produce their primary therapeutic
effect by mimicking or altering the functions
of the autonomic nervous system are called
autonomic drugs.
• These autonomic agents act either by
stimulating portions of the autonomic nervous
system or by blocking the action of the
autonomic nerves.

7. ANATOMY OF THE AUTONOMIC
NERVOUS SYSTEM

8. 1.EFFERENT NEURONS
• The ANS carries nerve impulses from the CNS to the
effector organs by way of two types of efferent neurons
• The first nerve cell is called a preganglionic neuron, and its
cell body is located within the CNS . Preganglionic neurons
emerge from the brainstem or spinal cord and make a
synaptic connection in ganglia(an aggregation of nerve cell
bodies located in the peripheral nervous system).
• These ganglia function as relay stations between a
preganglionic neuron and a second nerve cell, the
postganglionic neuron . The latter neuron has a cell body
originating in the ganglion .It is generally nonmyelinated
and terminates on effector organs, such as smooth muscles
of the viscera, cardiac muscle and the exocrine glands

10. AFFERENT NEURONS
• The afferent neurons of the ANS are important
in the reflex regulation of this system
• For example:
• By sensing pressure in the carotid sinus and
aortic arch and in signaling the CNS to
influence the efferent branch of the system to
respond.

12. Sympathetic neurons
• Anatomically, the sympathetic and parasympathetic neurons originate in
the CNS and emerge from two different spinal cord regions.
• The preganglionic neurons of the sympathetic system come from thoracic
and lumbar regions (T1 and L2) of the spinal cord , and they synapse into
two cord like chains of ganglia that run close to and parallel on each side
of the spinal cord.
• Axons of the postganglionic neuron extend from these ganglia to the
tissues that they innervate and regulate.
• The sympathetic nervous system is also called thoracolumbar division
because of its origin.
• In most cases, the preganglionic endings of sympathetic nervous system
are highly branched enabling one preganglionic neuron to interact with
many postganglionic neurons.
• This arrangement enables them to activate numerous effector organs.

14. Parasympathetic nervous system
• The parasympathetic preganglionic fibers arise
from cranial nerves 3 (oculomotor), 7(facial), 9
(glossopharyngeal) and vagus as well as from
the sacral regions (S2 and S4) of the spinal
cord and synapse in ganglia near or on the
effector organ.
• They are also called as craniosacral division

16. Enteric neurons
• The enteric nervous is the third division of the
ANS.
• It is a collection of nerve fibers that innervate the
gastro intestinal (GI) tract, pancreas, gallbladder.
• It constitutes the “BRAIN OF THE GUT”
• This system functions independetly of the CNS
and controls the motility ,exocrine and endocrine
secretions, and microcirculation of the GI tract.

19. Innervations

20. 1.Dual innervations
• Most organs in the body are innervated by both divisions of
the ANS.
• Thus , vagal parasympathetic innervation slows the heart
rate, and sympathetic innervation increases the heart rate.
• Despite this dual innervation, one system usually
predominates in the controlling the activity of a given organ
• For example
• In the heart the vagus nerve is the predominant factor for
controlling rate
• This type of antagonism is considered to be dynamic and is
fine-tuned at any given time to control homeostatic organ
functions

21. 2.Organ receiving only sympathetic
innervation
• Although most tissues receive dual
innervation, some effector organs, such as the
adrenal medulla, kidney , pillomotor muscles,
and the sweat glands, receive innervation
from the sympathetic system.
• The control of blood pressure is also mainly
sympathetic activity, with essentially no
participation by the parasympathetic system.

22. Receptors ???
• A receptor is a molecule most often found on
the surface of a cell, which receives chemical
signals originating externally from the cell.
Through binding to a receptor, these signals
direct a cell to do something—for example to
divide or die, or to allow certain molecules to
enter or exit.

23. Autonomic Nervous System Receptors
• There are two types of autonomic neurons:
• cholinergic
• adrenergic.

24. Cholinergic Neurons and Receptors
• They release Ach.
• They are all the sympathetic and parasympathetic
neurons, sympathetic postganglionic neurons that
innervate most sweat glands, and all
parasympathetic postganglionic neurons.
• ACh from synaptic clefts in presynaptic neurons >
binds specific cholinergic receptors in postsynaptic
neurons.
• There are two types of cholinergic receptors: nicotinic
receptors and muscarinic receptors.

25. Adrenergic Receptors
• Adrenergic receptors bind both hormones nor
epinephrine and epinephrine.
• There are two types of receptors: alpha and beta.
• They are further classified as alpha1 (excitation),
alpha2 (inhibition), beta1 (excitation), beta2
(inhibition), and beta3 (present on brown fat;
activation causes heat production).

26. Agonists and Antagonists
• Agonists activate receptors, mimicking the
effect of a natural neurotransmitter or
hormone.
• Antagonists deactivate receptors.

27. SYMPATHETIC RECEPTORS
• The major receptor types are alpha and beta
• These are subdivided into alpha-1, alpha-2, beta-1 and beta-2
• Alpha-1 type is found in the smooth muscle of most arterioles
and in sphincter muscles of the GI tract and bladder. Alpha-2
type is found in presynaptic nerves and parts of the GI tract.
• Beta-1 type is the dominant type in the heart. Beta-2 type is
found in the bronchioles of the lung, the wall muscles of the
bladder and other locations.

28. Parasympathetic receptors
• Types of muscarinic receptors
• The five main types of muscarinic receptors:
• The M1 muscarinic receptors are located in the neural system.
• The M2 muscarinic receptors are located in the heart
• The M3 muscarinic receptors are located at many places in the body, such
as the endothelial cells of blood vessels, as well as the lungs
• The M4 muscarinic receptors: Postganglionic cholinergic nerves, possible
CNS effects
• The M5 muscarinic receptors: Possible effects on the CNS
• Types of nicotinic receptors
• In vertebrates, nicotinic receptors are broadly classified into two subtypes
based on their primary sites of expression: muscle-type nicotinic receptors
and neuronal-type nicotinic receptors.

29. EFFECT OF
SYMPATHETIC ACTIVITY PARASYMPATHETIC ACTIVITY
Organ Action Receptor Action Receptor
1.Eye
Radial muscle contracts a1
Circular muscle contracts M3
Ciliary muscle relaxes b contracts M3
2.Heart
Sinoatrial node accelerates B1,b2 decelerates M2
Ectopic pacemakers accelerates B1,b2

30. contractility increases B1,b2 decreases M2
3.Blood vessels
Skin,splanchnic contracts a
vessels
Skeletal muscle relaxes b2
vessels
4.Bronchiolar relaxes b2 contracts M3
smooth muscle
5.Gastro intestinal
tract
Smooth muscle
walls relaxes A2,b2 contracts M3
sphincter contracts a1 relaxes M3
MYENTERIC PLEXUS Activates m1
6.Genitourinary
smooth muscle
Bladder wall relaxes b2 contracts M3

31. 7.Skin
Pilomotor contracts a
smooth muscle
Sweat glands
Thermoregulat increases M
ory
Apocrine(stress increases a
)
8.Metabolic
functions
liver gluconeogenesi B2,a
s
liver glycogenolysis B2,a
kidney Rennin release b1

32. Autonomic
nerve endings
Sympathetic Decrease NE M
release
Parasympath Decrease Ach a
etic release

33. Summary of differences
SYMPATHETIC PARASYMPATHETIC
Sites of origin Thoracic and lumbar brain and sacral areas
region of the spinal cord of spinal cord
(thoracolumbar) (craniosacral)
Length of fibers Short preganglionic Long preganglionic
Long postganglionic Short postganglionic
Location of ganglia Close to spinal cord Within or near effector
organs
Preganglionic fiber Extensive Minimal
branching
Distribution Wide Limited
Type of response Diffuse Discrete