Nervous system

1. ChapterChapter :8:8
NervousNervous SystemSystem
PartPart :3:3
((AutonomicAutonomic NervousNervous SystemSystem))
Presented by: Prof.Mirza Anwar BaigPresented by: Prof.Mirza Anwar Baig
Anjuman-I-Islam's Kalsekar Technical CampusAnjuman-I-Islam's Kalsekar Technical Campus
School of Pharmacy,New Pavel,NaviSchool of Pharmacy,New Pavel,Navi
Mumbai,MaharashtraMumbai,Maharashtra
11

2. Autonomic Nervous
System (ANS)
• The ANS consists of motor neurons
that:
– Innervate smooth and cardiac muscle
and glands
– Make adjustments to ensure optimal
support for body activities
– Operate via subconscious control
– Have viscera as most of their
effectors
2

3. ANS Versus Somatic
Nervous System (SNS)
• The ANS differs from the SNS in
the following three areas
– Effectors
– Efferent pathways
– Target organ responses
3

4. Effectors
• The effectors of the SNS are
skeletal muscles
• The effectors of the ANS are
cardiac muscle, smooth muscle,
and glands
4

5. Efferent Pathways
• Heavily myelinated axons of the
somatic motor neurons extend
from the CNS to the effector
• Axons of the ANS are a two-neuron
chain
– The preganglionic (first) neuron has a
lightly myelinated axon
– The ganglionic (second) neuron
extends to an effector organ
5

6. Neurotransmitter Effects
• All somatic motor neurons release
Acetylcholine (ACh), which has an
excitatory effect
• In the ANS:
– Preganglionic fibers release ACh
– Postganglionic fibers release norepinephrine
or ACh and the effect is either stimulatory or
inhibitory
– ANS effect on the target organ is dependent
upon the neurotransmitter released and the
receptor type of the effector
6

7. Comparison of Somatic and
Autonomic Systems
7

8. 8
Diagram contrasts somatic (lower) and
autonomic (upper):
autonomic
somatic
this dorsal
root
ganglion is
sensory

9. 9
Where they come from
Parasympathetic:
craniosacral
Sympathetic:
thoracolumbar

10. 10
Parasympathetic nervous system
“rest & digest”
 Also called the craniosacral system because all
its preganglionic neurons are in the brain stem or
sacral levels of the spinal cord
Cranial nerves III,VII, IX and X
In lateral horn of gray matter from S2/ S4
 Only innervate internal organs (not skin)
 Acetylcholine is neurotransmitter at end organ
as well as at preganglionic synapse: “cholinergic”

11. 11
Parasympathetic continued
 Cranial outflow
III - pupils constrict
VII - tears, nasal mucus, saliva
IX – parotid salivary gland
X (Vagus n) – visceral organs of thorax & abdomen:
Stimulates digestive glands
Increases motility of smooth muscle of
digestive tract
Decreases heart rate
Causes bronchial constriction
 Sacral outflow (S2-4): form pelvic splanchnic nerves
Supply 2nd half of large intestine
Supply all the pelvic (genitourinary) organs

12. 12
Sympathetic nervous system
“fight, flight or fright”
 Also called thoracolumbar system: all its neurons
are in lateral horn of gray matter from T1-L2
 Lead to every part of the body (unlike parasymp.)
Easy to remember that when nervous, you sweat;
when afraid, hair stands on end; when excited
blood pressure rises (vasoconstriction): these
sympathetic only
Also causes: dry mouth, pupils to dilate, increased
heart & respiratory rates to increase O2 to
skeletal muscles, and liver to release glucose
 Norepinephrine (aka noradrenaline) is
neurotransmitter released by most postganglionic
fibers (acetylcholine in preganglionic): “adrenergic”

13. 13
Sympathetic nervous system
continued
 Regardless of target, all
begin same
 Preganglionic axons exit
spinal cord through ventral
root and enter spinal nerve
 Exit spinal nerve via
communicating ramus
 Enter sympathetic
trunk/chain where
postganglionic neurons are
 Has three options…

14. Options of preganglionic axons
in sympathetic trunk
1. Synapse on postganglionic neuron in chain
ganglion then return to spinal nerve and
follow its branch to the skin
2. Ascend or descend within sympathetic trunk,
synapse with a posganglionic neuron within a
chain ganglion, and return to spinal nerve at
that level and follow branches to skin
3. Enter sympathetic chain, pass through
without synapsing, form a splanchnic
nerve that passes toward thoracic or
abdominal organs
 These synapse in prevertebral ganglion
in front of aorta
 Postganglionic axons follow arteries to
organs
14

15. 15
Synapse in chain ganglia
at same level or different level

16. 16
Pass through ganglia and synapse in
prevertebral ganglion

17. 17
Summary

18. Interactions of the Autonomic
Divisions
• Most visceral organs are innervated by
both sympathetic and parasympathetic
fibers
• This results in dynamic antagonisms
that precisely control visceral activity
• Sympathetic fibers increase heart and
respiratory rates, and inhibit digestion
and elimination
• Parasympathetic fibers decrease heart
and respiratory rates, and allow for
digestion and the discarding of wastes18

19. Role of the
Parasympathetic Division
• Concerned with keeping body energy
use low
• Involves the D activities – digestion,
defecation, and diuresis
• Its activity is illustrated in a person who
relaxes after a meal
– Blood pressure, heart rate, and respiratory
rates are low
– Gastrointestinal tract activity is high
– The skin is warm and the pupils are
constricted
19

20. Role of the Sympathetic
Division
• The sympathetic division is the “fight-or-flight”
system
• Involves E activities – exercise, excitement,
emergency, and embarrassment
• Promotes adjustments during exercise – blood
flow to organs is reduced, flow to muscles is
increased
• Its activity is illustrated by a person who is
threatened
– Heart rate increases, and breathing is rapid and deep
– The skin is cold and sweaty, and the pupils dilate
20

21. Visceral Reflexes
Figure 14.721

22. Cholinergic Receptors
• The two types of receptors that
bind ACh are nicotinic and
muscarinic
• These are named after drugs that
bind to them and mimic ACh
effects
22

23. Nicotinic Receptors
• Nicotinic receptors are found on:
– Motor end plates (somatic targets)
– All ganglionic neurons of both
sympathetic and parasympathetic
divisions
– The hormone-producing cells of the
adrenal medulla
• The effect of ACh binding to
nicotinic receptors is always
stimulatory
23

24. Muscarinic Receptors
• Muscarinic receptors occur on all
effector cells stimulated by
postganglionic cholinergic fibers
• The effect of ACh binding:
– Can be either inhibitory or excitatory
– Depends on the receptor type of the
target organ
24

25. Adrenergic Receptors
• The two types of adrenergic receptors
are alpha and beta
• Each type has two or three subclasses
(α1, α2, β1, β2 , β3)
• Effects of NE binding to:
– α receptors is generally stimulatory
– β receptors is generally inhibitory
• A notable exception – NE binding to β
receptors of the heart is stimulatory
25

26. Dual Innervation
• Most of viscera receive nerve fibers from
both parasympathetic and sympathetic
divisions
• Both divisions do not normally innervate
an organ equally
26

27. Dual Innervation
• Antagonistic effects
– oppose each other
– exerted through dual innervation of same
effector
• heart rate decreases (parasympathetic)
• heart rate increases (sympathetic)
– exerted because each division innervates
different cells
• pupillary dilator muscle (sympathetic) dilates
pupil
• constrictor pupillae (parasympathetic) constricts
pupil
27

28. Dual Innervation of the Iris
28

29. Dual Innervation
• Cooperative effects seen when 2 divisions act on
different effectors to produce a unified effect
– parasympathetics increase salivary serous cell
secretion
– sympathetics increase salivary mucous cell
secretion
• ANS cooperation is best seen in control of the external
genitalia
– Parasympathetic fibers cause vasodilation and are
responsible for erection of the penis and clitoris
– Sympathetic fibers cause ejaculation of semen in
males and reflex peristalsis in females
29

30. Without Dual Innervation
• Some effectors receive only sympathetic
– adrenal medulla, arrector pili muscles, sweat
glands and many blood vessels
• Sympathetic tone
– a baseline firing frequency
– vasomotor tone provides partial constriction
• increase in firing frequency = vasoconstriction
• decrease in firing frequency = vasodilation
• can shift blood flow from one organ to another as
needed
– sympathetic stimulation increases blood to skeletal and
cardiac muscles -- reduced blood to skin30

31. Sympathetic and Vasomotor Tone
Sympathetic division
prioritizes blood
vessels to skeletal
muscles and heart in
times of emergency.
Blood vessels to
skin vasoconstrict
to minimize
bleeding if injury
occurs during
stress or exercise. 31

32. 32

33. 33

34. Regulation of ANS
• Autonomic reflexes control most of activity of
visceral organs, glands, and blood vessels.
• Autonomic reflex activity influenced by
hypothalamus and higher brain centers, but it is
the hypothalamus that has overall control of the
ANS.
• Sympathetic and parasympathetic divisions
influence activities of enteric (gut) nervous system
through autonomic reflexes. These involve the CNS.
• But, the enteric nervous system can function
independently of CNS through local reflexes. E.g.,
when wall of digestive tract is stretched, sensory
neurons send information to enteric plexus and
then motor responses sent to smooth muscle of gut
wall and the muscle contracts.
34

35. Levels of ANS Control
• The hypothalamus is the main
integration center of ANS activity
• Subconscious cerebral input via
limbic lobe connections influences
hypothalamic function
• Other controls come from the
cerebral cortex, the reticular
formation, and the spinal cord
35

36. Hypothalamic Control
• Centers of the hypothalamus
control:
– Heart activity and blood pressure
– Body temperature, water balance,
and endocrine activity
– Emotional stages (rage, pleasure) and
biological drives (hunger, thirst, sex)
– Reactions to fear and the “fight-or-
flight” system
36

37. Levels of ANS Control
Figure 14.937