ANS introduction in Pharmacology

1. PRESENTED BY:
AMAN SHARMA
M.SC(MEDICINE)
PHARMACOLOGY STUDENT
RUHS-CMS,JAIPUR

2. Nervous System
Two main divisions
I. CNS
• Brain & spinal cord
II. PNS
1. Afferent (sensory)
2. Efferent (motor)
• Somatic & ANS

3. CENTRAL NERVOUS SYSTEM (CNS)
• Brain and spinal cord:
• receives and processes incoming sensory information and
responds by sending out signals that initiate or modify a
Process
PERIPHERAL NERVOUS SYSTEM (PNS)
Includes all the neurons and ganglia found outside the CNS
Afferent: sensory input to CNS
• Afferent neurons carry sensory input from the periphery to the
CNS and modify motor output through the reflex arc.
Efferent: motor output from CNS
• Efferent neurons carry motor signals from the CNS to the
peripheral areas of the body.

4. Efferent Division
The efferent portion of the PNS is further divided into two major
functional subdivisions,
1. Somatic (SNS):
• one motor neuron innervates the skeletal muscles and control
voluntary (consciously) functions; movement, respiration and
posture.
2. Autonomous nervous system (ANS):
• The ANS is the major involuntary portion of the NS
• is responsible for automatic, unconscious bodily function, such as
• control of HR and BP and both GIT and GUT functions.

7. Autonomic Nervous System
 It is a division of the peripheral nervous system that supplies smooth muscle
and glands, and thus influence the function of internal organs.
 The autonomic nervous system is a control system that acts largely
unconsciously and regulates bodily functions such as the heart rate,
digestion, respiratory rate, pupillary response and urination etc.
 This system is the primary mechanism in control of the fight-or-flight
response.

8. Parasympathetic Division–
also called
the craniosacral division
 The preganglionic fibers arise
from the cranial nerve nuclei III,
VII, IX, and X and sacral region
(usually S2-S4) of the spinal cord,
and synapse in ganglia close to the
effector organ.
 Thus, in contrast to the
sympathetic system, the
preganglionic fibers are long, and
the postganglionic ones are short.
Sympathetic Division –
also called
the thoracolumbar
division
 The preganglionic fibers arise
from the thoracic (T1-T12)
and lumbar (L1-L5) regions
of the spinal cord, and they
synapse in paravertebral
ganglia close and parallel to
the vertebral column.
Postganglionic axons lead to
an effector organ.
CENTRAL ROOTS OF ORIGIN

10. DIFFERENCES BET WEEN SYMPATHETIC AND
PARASYMPATHETIC NERVOUS SYSTEM

11. LOCATION OF GANGLIA
• Both the PANS and SANS have
relay station, or ganglia, between
the CNS and the end organ, but the
somatic system does not;
• The ANS, carries nerve impulses
by
• a preganglionic fiber that leaves
the CNS,
• a postganglionic fiber that
innervates the effector.

12. GENERAL OUTLAY OF EFFERENT NERVOUS SYSTEM:

13. ADRENAL MEDULLA
The adrenal medulla,
• like the sympathetic ganglia, receives preganglionic fibers
from the sympathetic system.
• Lacking the axons,
• in response to stimulation by Ach, influences other organs by
secreting the epinephrine and lesser amounts of nor-
epinepherine into the blood.

14. • Is normally active, even at rest; however, it assumes a
dominant role when the body becomes stressed (trauma, fear,
hypoglycemia cold or exercise).
• Fight or Flight – Protective mechanisms designed to help
person cope with the stress or get away from it.
• For example, if you sense danger: Your heart rate increase,
BP rises, eyes dilates, blood sugar rises, bronchioles expand,
and blood flow shift from skin to skeletal muscles.
FUNCTIONS OF THE SYMPATHETIC
NERVOUS SYSTEM

15. 1. Rest and digest: maintains essential body functions; digestive
process and elimination of wastes.
2. Save energy.
3. Dilation of blood vessels in skin.
4. Decrease heart rate (bradycardia).
5. Increase secretion of digestive enzymes.
6. Constriction of smooth muscle of bronchi.
7. Increase in sweat glands.
8. Contraction of smooth muscles of urinary bladder.
FUNCTIONS OF THE PARASYMPATHETIC
NERVOUS SYSTEM

16. • All preganglionic fibers of both sympathetic and
parasympathetic divisions.
• All parasympathetic postganglionic.
• Few sympathetic postganglionic fibers (sweat gland).
• All Somatic (non autonomic) fibers to skeletal muscle
THE CHOLINERGIC NEURON

17. • Most sympathetic postganglionic fibers release
norepinephrine; are noradrenergic or simply
adrenergic.
• Some peripheral sympathetic fibers release dopamine
(dopaminergic).
• The adrenal medulla, a modified sympathetic
ganglion, receives sympathetic preganglionic fibers
and releases epinephrine (~85%) and to a lesser
amount norepinephrine (15%) into the blood.
THE ADRENERGIC NEURON

18. • Parasympathetic – cholinergic receptors:
– muscarinic (M1 to M5)
– and nicotinic receptors
• Sympathetic – adrenergic receptors:
– alpha (α1, α 2),
– beta (β1 to β 3),
– and dopamine (D1 to D5) receptors.
RECEPTOR TYPES

22. NEUROHUMORAL TRANSMISSION
Neurohumoral transmission implies that nerves transmit their message across
synapses and neuroeffector junctions by the release of humoral (chemical)
messengers.
 Elliot (1905)- Suggest that sympathetic nerves functioned by the release of
an adrenaline like substance.
 Dixon (1907)-Propose that vagus released a muscarinic like chemical.
 Otto loewi (1921)-Provided direct proof of humoral transmission by perfusing
two frog hearts in series.
 Von Euler(1946)-the sympathetic transmitter was eventually shown to be noe
adrenaline.

23. To be considered as a postjunctionally acting neurohumoral transmitter a
substance must fulfill the following criteria:
 It should be present in the presynaptic neurone (usually along with enzymes
synthesizing it).
 It should be released in the medium following nerve stimulation.
 Its application should produce responses identical to those produced by
nerve stimulation.
 Its effects should be antagonized or potentiated by other substances which
similarly alter effects of nerve stimulation.

24. STEPS IN NEUROHUMORAL TRANSMISSION
I. Impulse conduction
II. Transmitter release
III. Transmitter action on postjunctional membrane
IV. Postjunctional activity
V. Termination of transmitter action

25. I. Impulse Conduction
A. Polarization(Resting potential)
 A neuron at resting is electrically charged but not conducting, the potential difference
measured at this stage is called resting potential which is about -70mV.
 Due to difference in concentration of ions, Na+ ion tends to diffuse into the axoplasm
and K+ tends to diffuse outside the axoplasm.
 The membrane of neuron at resting is more permeable to K+ ion than Na+.So K+
leaves the neuron faster than Na+ enter the neuron.

26. B. Depolarization (Action potential)
 When a stimulus is applied in the resting neuron, it opens the Na+ channel. Now
the permeability of Na+ ion suddenly increases at the point of stimulus causing
depolarization.
 The diffusion of Na+ increases by 10 times from outside to inside. As a result the
axoplasm become positively charges, which is exact opposite to polarized state, so
called as depolarized state or reverse polarized state.
 The depolarization of the membrane stimulates the adjacent voltage channel, so
the action potential passes as a wave along the length of neuron.

27. C. Repolarization
 When the concentration of Na+ ion inside axoplasm increases, the permeability to
Na+ decreases and the Na+ channel starts to close.
 The Na-K pump activates, so that Na+ are pumped out and K+ inside until the original
resting potential is restored. The process is known as repolarization and it starts from
the same from where depolarization starts.

28. II. Transmitter Release
 The transmitter (excitatory or inhibitory) is stored in prejunctional nerve endings within
synaptic vesicles.
 The release process can be modulated by the transmitter itself and by other agents
through activation of specific receptor located on prejunctional membrane.
 e.g. noradrenaline(NA) release is inhibited by NA (a2 receptor)
 dopamine,adenosine,prostaglandins and enkephalins while isoprenalin(b2 receptor)
and angiotensin(AT1 receptor) increase NA release.
 Similarly, a2 and muscarinic agonists inhibit acetylcholine(ACh) release at autonomic
neuroeffector sites

29. III.Transmitter action on postjuctional membrane
The released transmitter combines with specific receptors on the postjunctional
membrane and depending on its nature induces:
EPSP(Excitatory postsynaptic potential)
Increase in permeability to cations Na+ or Ca+2 influx causes depolarization followed
by K+ efflux.These ionic movements are passive.
IPSP(Inhibitory postsynaptic potential)
Increase in permeability to anion Cl- moves in and tend to hyperpolarize the
membrane an IPSP is generated.

31. IV. Postjunctional Activity
 A suprathreshold EPSP generates a propagated postjunctional AP which results in
nerve impulse (in neurone) , contraction (in muscle) or secretion (in glands).
 An IPSP stabilizes the postjunctional membrane and resist depolarizing stimuli.
V. Termination of transmitter action
 Its combination with the receptor, the transmitter either locally degraded(e.g. ACh) or
is partly taken back into the prejunctional neurone by active reuptake and partly
diffuses away(NA).
 Specific carrier proteins like norepinephrine transporter(NET) ,dopamine
transporter(DAT),serotonin transporter (SERT) are expressed on the axonal
membrane for this purpose.
 The rate of termination of transmitter action governs the rate at which responses can
be transmitted across a junction (1 to 1000/sec).
 Aminoacid transmitters (glutamate,GABA) are also partly taken up by active transport
into neuronal and neighbouring glial cells, but no active reuptake of peptide
neurotransmitters(VIP,NPY,Enkephalins etc.) occurs.

32. COTRANSMISSION
 On stimulation most peripheral and central neurones have been shown to release
more than one active substance.
 In the ANS, besides the primary transmitters Ach and NA, neurones have been found
to elaborate purines (ATP, adenosine), peptides (vasoactive intestinal peptide or VIP,
neuropeptide-Y or NPY, substance P, enkephalins, somatostatin, etc.), nitric oxide
(NO) and prostaglandin as cotransmitters.
 In most autonomic cholinergic neurones VIP is associated with ACh, while ATP is
associated with both ACh and NA.
 Vascular adrenergic nerves contain NPY which causes long lasting vasoconstriction.
 On being released by nerve impulse the cotransmitter may serve to regulate the
presynaptic release of the primary transmitter or postsynaptic sensitivity to it
(neuromodulator role).
 The cotransmitter may also serve as an alternative transmitter in its own right or exert
a trophic influence on the synaptic structures.

33. THANK YOU!