Autonomic &Somatic Nervous Systems.

Autonomic &
Somatic Nervous Systems.
By
Syed Abdul Naveed.
M.Pharm (Pharmacology).
.
1

which consists of
The Nervous System
is divided into
that make up
which is divided into
Sensory nerves
Motor nerves
Autonomic nervous
system
Central nervous
system
Somatic nervous
system
Peripheral nervous
system
Sympathetic
nervous system
Parasympathetic
nervous system
Enteric nervous
system
2

Autonomic nervous system
• The autonomic nervous system is the subdivision of the
peripheral nervous system that regulates body activities that are
generally not under conscious control (or) responsible for
control of involuntary or visceral body functions.
• The A.N.S composed of efferent neurons that innervates smooth
muscle of the viscera, cardiac muscle ,vasculators & the exocrine
gland ,cardiac output, blood flow & glandular secretion.
3

Autonomic nervous system
Divisions of the autonomic nervous system:
• Parasympathetic division
• Sympathetic division
Serve most of the same organs but cause opposing or antagonistic
effects.
• Parasysmpathetic: routine maintenance “rest &digest”.
• Sympathetic: mobilization & increased metabolism “fight, flight or
fright”.
• Efferent (Motor) Nerve : Carry impulses from cns (brain and spinal
cord) to muscle or organ (peripheral tissues).
• Afferent (Sensory)Nerve :Neuron which transmits impulses from sense
organs (bring information from periphery ) to cns
4

Introduction (efferent neurons)
• Efferent (motor)neuron carrier nerve impulse from CNS to the effector organ by
way of two types of efferant neurons.
• First nerve is called Preganglionic neuron
and its cell body is located in the CNS.
• Preganglionic neurons emerge in the brain stem or spinal cord and makes a
synaptic connection in the ganglia.
• The ganglia function as a relay station between a preganglionic neuron and second
nerve cell (postganglionic neuron)
• The postganglionic neuron has a cell body originating in the ganglia and terminates
on effector organ.
5

Introduction to somatic motor neurons
• Somatic efferent neurons are involved in the voluntary contol of
function such as contraction of the skeletal muscle.
• Input from sense organs & out put to skeletal muscle.
6

Autonomic and Somatic Motor Systems
Autonomic motor system
Chain of two motor neurons
•Preganglionic neuron
•Postganglionic neuron
Conduction is slower due to thinly or unmyelinated axons
Somatic motor system
One motor neuron extends from the CNS to skeletal muscle
Axons are well myelinated, conduct impulses rapidly
7

Sympathetic Nervous system
(fight, flight or fright)
• Also called thoracolumbar system: all its neurons are in lateral horn of gray matter from
T1-L2
• Preganglionic neuron of the sympathetic system comes from thoracic and lumbar region of
the spinal cord and they synapse in the two cord like chain of ganglia that run parallel on
each side of the spinal cord.
• Preganglion neurons are short ,. Postganglion neuros are long
• Axons of the postganglionic neuron extended from these ganglion to the tissue that they
innervate and regulate.
• The adrenal medulla (large synaptic ganglion receives preganglion fiber from the
sympathetic system.
• The adrenal medulla in response to stimulation secreates epinephrine also know as
adrenaline, and lesser amount of norepinephrine in to the blood.
8

Motor Fiber
Ach NE
Ganglion
Ach
Ach
Ach
Ach
EPI/NE
Ach Ach
Somatic
Sympathetic
Sympathetic
Sympathetic
Para-sympathetic
Postganglionic Fiber;
Adrenergic
Adrenal Gland
Skeletal
Muscle
Smooth
Muscle
Cardiac Cells
Gland Cells
Sweat
Glands
Smooth
Muscle
Cardiac Cells
Gland Cells
Ganglion
Ganglion
Neurotransmitter released by preganglionic axons
•Acetylcholine for both branches (cholinergic)
Neurotransmitter released by postganglionic axons
•Sympathetic – most release norepinephrine (adrenergic)
•Parasympathetic – release acetylcholine 9

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
10

Sympathetic Division of the ANS
11

The Role of the Adrenal Medulla in the
Sympathetic Division
• Adrenalin (also called epinephrine) is produced in
the medulla of the adrenal glands.
•The adrenal glands are located on the top of each
kidney.
•The sympathetic nervous system stimulates the
adrenal gland (an effector) to release the hormone
adrenalin or epinephrine into the bloodstream.
•Adrenalin is a modified amino acid hormone.
The target tissue for adrenalin is mainly cardiac
and skeletal muscle.
•Adrenalin increases heart rate and blood pressure
providing more oxygen to working muscles.
• It also increases blood sugar levels providing
more energy to cardiac and skeletal muscles.
12

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
13

Parasympathetic neurons
(Rest and Digest)
 Allow body to function under Rest and digest
 Pre-ganglionic fiber rises from the cranium(cranium fibers)
[III , VII, IX, X]and from sacral region of the spinal cord and
synapse in ganglia near or on the effector organ.
 Cranial outflow
 III –oculomotor nerve(- pupils constrict)
 VII -facial nerve –( tears, nasal mucus
 IX -gloss-pharyngeal nerve(parotid salivary gland)
 X –vagus nerve(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-S4): form pelvic splanchnic nerves
 Innervates organs of the pelvis and lower abdomen
 Supply 2nd half of large intestine
 Supply all the pelvic (genitourinary) organs
 Preganglionic fibers are long
 Postganglionic fibers are short , with a ganglia
close or with in the organ.
14

Summary of parasympathetic neurons
and synapses
Preganglionic neurons
• Long
• Synapse with postganglionic neurons at ganglia.
• Release acetylcholine (ACH) to activate nicotinic receptors on postganglionic
neurons
Postganglionic neurons
• Short
• Synapse on the target organ
• Release acetylcholine (ACH) to activate muscarinic receptors on the target
organ
15

INNERVATION BY THE A.N.S
DUAL INNERVATION
• Most organs in the body are
innervated by both divisions of the
a.n.s.
• Despite this dual innervation one
system usually predominates in
controlling the activity of a given
organ.
Ex: In the heart vagus nerve is the
predominant factor for controlling
rate.
ORGAN RECIVING ONLY
SYMPATHETIC INNERVATION
• The adrenal medulla pilomotor
muscle and sweat glands.
• The control of blood pressure is also
mainly a sympathetic activity with
essential no participation by the
parasympathetic system
17

Enteric neurons
• It is third division of ANS
• It is collection of nerve fibers that innervates the GIT, Pancreas and Gall
Bladder
• This system function independently of the CNS and control the motility
exocrine and endocrine secretion and micro-circulation of the GIT.
• It is modulated by both sympathetic and parasympathetic nervous system.
20

Neurotransmitter in sympathetic and
parasympathetic nervous system
21

DIFFERENCES BETWEEN SNS&PNS
SNS PNS
ORIGIN DORSO-LUMBAR(T1 TO L2 OR L3) CRANOI SACRAL(III,VII,IX,X AND
S2-S4)
DISTRIBUTION WIDE LIMITED
GANGLIA AWAY FROM ORGANS ON/ CLOSE TO THE ORGANS
POST GANGLIONIC FIBRES LONG SHORT
PRE:POST FIBRES RATIO 1:20 TO 1:100 1:1 TO 1:2
TRANSMITTER NE (MAJOR)
Ach (MINOR)
Ach
STABILITY OF TRANSMITTER NA STABLE Ach (RAPIDLY DESTROYS)
IMP FUNCTION TACKLING STRESS &
EMERGENCY
ASSIMILATION OF FOOD
,CONSERVATION OF ENERGY
22

Adrenergic Receptors
 α1-receptors: vasoconstriction, relaxation
of gastrointestinal smooth muscle, salivary
secretion and hepatic glycogenolysis
 α2-receptors: inhibition of transmitter
release (including noradrenalin and
acetylcholine release from autonomic
nerves), platelet aggregation, contraction of
vascular smooth muscle, inhibition of insulin
release
 β1-receptors: increased cardiac rate and
force
 β2-receptors: bronchi dilatation,
vasodilatation, relaxation of visceral smooth
muscle, hepatic glycogenolysis and muscle
tremor
 β3-receptors: lipolysis. 23

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.
Nicotinic receptor
• 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.
Muscarinic receptor
• 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

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.
• 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 26

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
27

synapse
• The junction between two neurons is called a synapse.
• An action potential cannot cross the synaptic cleft between neurons, and
instead the nerve impulse is carried by chemicals called
neurotransmitters.
• These chemicals are made by the cell that is sending the impulse (the pre-synaptic
neuron) and stored in synaptic vesicles at the end of the axon.
• The cell that is receiving the nerve impulse (the post-synaptic neuron) has
chemical-gated ion channels in its membrane, called neuroreceptors.
• These have specific binding sites for the neurotransmitters 28

1. At the end of the pre-synaptic neuron there are voltage-gated calcium channels. When an action
potential reaches the synapse these channels open, causing calcium ions to flow into the cell.
2. These calcium ions cause the synaptic vesicles to fuse with the cell membrane, releasing their
contents (the neurotransmitter chemicals) by exocytosis.
3. The neurotransmitters diffuse across the synaptic cleft.
4. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane, causing the
channels to open. In the example shown these are sodium channels, so sodium ions flow in.
5. This causes a depolarisation of the post-synaptic cell membrane, which may initiate an action
potential.
6. The neurotransmitter is broken down by a specific enzyme in the synaptic cleft; for example the
enzyme acetylcholinesterase breaks down the neurotransmitter acetylcholine. The breakdown
products are absorbed by the pre-synaptic neuron by endocytosis and used to re-synthesis more
neurotransmitter, using energy from the mitochondria. This stops the synapse being permanently
on.
29

General Features of Peripheral
Autonomic Neurotransmission
Membrane Depolarization of
Pre- or Postganglionic Fiber
Calcium Entry into
Varicosity
Exocytosis of NT
Depolarization of Postganglionic
Fiber or Response of
Effector Cell
Activation of NT
Receptors
Diffusion of NT Across
Neuroeffector Junction
or Synapse
Nerve Impulse
30

SYNTHESIS OF NOREPINEPHRINE
 Nor epinephrine (NE) is the primary
neurotransmitter
 For postganglionic sympathetic adrenergic
nerve.
It is synthesized inside the nerve axon,
stored within vesicles, then released by the
nerve
when an action potential travels down the
nerve.
Synthesis of NE:
The amino acid tyrosine is transported
into the sympathetic nerve axon.
Tyrosine (Tyr) is converted to DOPA
by tyrosine hydroxylase,
(rate-limiting step for NE synthesis).
DOPA is converted to dopamine (DA)
by DOPA decarboxylase.
Dopamine is transported into vesicles then
converted to norepinephrine (NE) by dopamine
β-hydroxylase (DBH); transport into the vesicle
can by blocked by the drug reserpine.
31

An action potential traveling down the axon depolarizes the membrane and causes calcium
to enter the axon.
Increased intracellular calcium causes the vesicles to migrate to the axonal membrane and
fuse with the membrane, which permits the NE to diffuse out of the vesicle into the
extracellular (junctional) space. DBH, and depending on the nerve other secondary
neurotransmitters (e.g., ATP), is released along with the NE.
The NE binds to the postjunctional receptor and stimulates the effector organ response
32

Synthesis of epinephrine
 Epinephrine is synthesized from norepinephrine within the adrenal medulla,
which are small glands associated with the kidneys.
 Preganglionic fibers sympathetic adrenergic nerves synapse within the adrenals.
Activation of these fibers releases acetylcholine, which binds to postjunctional
nicotinic receptors in the tissue.
 This leads to stimulation of NE synthesis within adenomedullary cells, but unlike
sympathetic neurons, there is an additional enzyme (phenyl ethanolamine-N-methyltransferase
) that adds a methyl group to the NE molecule to form
epinephrine.
 The epinephrine is released into the blood perfusing the glands and carried
throughout the body.
33

Synthesis of acetylcholine
Acetylcholine Synthesis
• Acetyl-CoA is synthesized from
pyruvate by mitochondria within
cholinergic nerves.
• This acetyl-CoA combines with
choline that is transported into the
nerve axon to form acetylcholine
(ACh).
• The enzyme responsible for this is
choline acetyltransferase.
• The newly formed ACh is then
transported into vesicles for storage
and subsequent release similar to
what occurs for NE.
• After ACh is released, it is rapidly
degraded within the synapse by
acetylcholineesterase, to form
acetate and choline.
34

COTRANSMISSION
Release of More Than One
Neurotransmitter from the Same
Nerve Terminal
Cotransmitter B
Cotransmitter A
Synergistic or Opposite Actions
35

Many Examples of NANC Neurotransmitters
36

Many Examples of NANC Neurotransmitters
37

MODULATION OF NEUROTRANSMISSION
Modulation of
Neurotransmisson
Presynaptic/
Prejunctional
Modulation
Postsynaptic/
Postjunctional
Modulation
Presynaptic/
Prejunctional
Inhibition
Presynaptic/
Prejunctional
Facilitation
Postsynaptic/
Postjunctional
Inhibition
Postsynaptic/
Postjunctional
Facilitation
38

MODULATION OF NEUROTRANSMISSION
From Nerve
Terminal Being
Modulated
(e.g.,
Autoinhibitory
Feedback)
From
Postsynaptic/
Postjunctional
Site (e.g., Trans-synaptic/
Transjunctional
Inhibitory
Feedback)
From
Nearby
Nerve
Terminal
(Cross-talk)
From
Remote
Site via
Circulation
(e.g., Renin
Release)
Sources of
Modulators of
Neurotransmission
39

Neuromodulation and presynaptic interactions
• As well as functioning directly as neurotransmitters, chemical
mediators may regulate:
• - presynaptic transmitter release
• - neuronal excitability.
• Both are examples of neuromodulation and generally involve second
messenger regulation of membrane ion channels.
• Presynaptic receptors may inhibit or increase transmitter release, the
former being more important.
• Inhibitory presynaptic autoreceptors occur on noradrenergic and
cholinergic neurons, causing each transmitter to inhibit its own
release (autoinhibitory feedback).
• Many endogenous mediators (e.g. GABA, prostaglandins, opioid and
other peptides), as well as the transmitters themselves, exert
presynaptic control (mainly inhibitory) over autonomic transmitter
release.
40

Mechanisms of Neuromodulation
41

SOMATIC NERVOUS SYSTEM
• The somatic nervous system, or voluntary nervous system, is part of
the peripheral nervous system that regulates body movement through
control of skeletal (voluntary) muscles and also relates the organism
with the environment through the reception of external stimuli, such
as through the senses of vision, hearing, taste, and smell.
• The somatic nervous system controls such voluntary actions as walking
and smiling through the use of efferent motor nerves, in contrast with
the function of the autonomic nervous system, which largely acts
independent of conscious control in innervating cardiac muscle and
exocrine and endocrine glands.
• It is the somatic nervous system that allows individuals to receive
sensory information and consciously react to environmental changes.
42

Overview of somatic nervous system
• The somatic nervous system consists of cranial and spinal nerves that innervate skeletal muscle
tissue and are more under voluntary control (as well as the sensory receptors).
• The somatic nervous system includes all the neurons connected with muscles ,skin , and sense
organs.
• The somatic nervous system processes sensory information and controls all voluntary muscular
systems within the body, with the exception of reflex arcs.
• The somatic nervous system consists of efferent nerves responsible for sending brain signals for
muscle contraction.
• In humans, there are 31 pairs of spinal nerves and 12 pairs of cranial nerves.
• The 31 pairs of spinal nerves emanate from different areas of the spinal cord and each spinal nerve
has a ventral root and a dorsal root.
• The ventral root has motor (efferent) fibers that transmit messages from the central nervous
system to the effectors, with the cell bodies of the efferent fibers found in the spinal cord gray
matter.
• The dorsal root has sensory (afferent) fibers that carry information from the sensory receptors to
the spinal cord
• The 12 pairs of cranial nerves transmit information on the senses of sight, smell, balance, taste,
and hearing from special sensory receptors.
• They also transmit information from general sensory receptors in the body, largely from the head.
This information is received and processed by the central nervous system and then the response
travels via the cranial nerves to the skeletal muscles to control movements in the face and throat,
such as swallowing and smiling .
43

Motor Pathway of Somatic Nervous System
Somatic division:
•Cell bodies of motor neurons reside in CNS (brain or spinal cord)
•Their axons (sheathed in spinal nerves) extend all the way to their skeletal
muscles
44

Nerve Signal Transmission
•The nerve signals in the efferent somatic nervous system involves a
sequence that begins in the upper cell bodies of motor neurons (upper
motor neurons) within the precentral gyrus (primary motor cortex).
•Stimuli from the precentral gyrus are transmitted from upper motor
neurons and down the corticospinal tract, via axons to control skeletal
(voluntary) muscles.
•These stimuli are conveyed from upper motor neurons through the ventral
horn of the spinal cord, and across synapses to be received by the sensory
receptors of alpha motor neuron (large lower motor neurons) of the
brainstem and spinal cord.
•Upper motor neurons release a neurotransmitter, acetylcholine, from their
axon terminal knobs, which are received by nicotinic receptors of the alpha
motor neurons.
•In turn, alpha motor neurons relay the stimuli received down their axons
via the ventral root of the spinal cord. These signals then proceed to the
neuromuscular junctions of skeletal muscles.
•From there, acetylcholine is released from the axon terminal knobs of
alpha motor neurons and received by postsynaptic receptors (Nicotinic
acetylcholine receptors) of muscles, thereby relaying the stimulus to
contract muscle fibers
45

Sensory neurons
• General visceral sensory neurons monitor:
– Stretch, temperature, chemical changes, and irritation
• Cell bodies are located in the dorsal root ganglia
1. Pain Receptors.
2. Thermo receptor
3. Mechanoreceptor
4. Chemoreceptor
5. Photoreceptor
6. Hearing and balance
46

Pain Receptors
• Throughout body; except
brain
• Respond to chemical
released by damaged cells
• Important to recognize
– Danger
– Injury
– Disease
Thermoreceptors
• In skin, body core,
hypothalamus
• Detect variations in body
temperature
47

Mechanoreceptors
• Skin, skeletal muscle, and
inner ears
• Sensitive to
– Touch
– Pressure
– Stretching of muscles
– Sound
– motion
Chemo receptors
• Chemoreceptors pick up
chemical reception in nose
and mouth
• Smell – olfactory bulb
• Taste – taste buds
– Salty
– Bitter
– Sour
– Sweet
48

Photoreceptors
• Eyes
• Sensitive to Light
Vision
• Cornea
– Helps focus light
– Filled with aqueous humor
• Iris
– Back of cornea
– Colored part of eye
• Pupil
– Tiny muscles regulate the size
– Regulates amount of light
• Lens
– Small muscles change its shape to
focus on object near and far away
– Behind lens eye filled with vitreous
humor
• Retina
– Has photoreceptors
– No photoreceptors where optic nerve
passes through the back of the eye;
blind spot
– Two types
1. Rods – black and white
2. Cones – color
49

Hearing and Balance
Hearing
• Ear
• Two Functions
– Hearing
– Detecting Positional change
to movement.
• Cochlea
• Hammer, Anvil, Stirrup
• Tymapnum
• Auditory canal
• Sound
Balance
• Semicircular Canals
– 3 canals that form half circles
– Filled with fluid and hairs that
detect motion of head in
relation to gravity
50

Differences Between somatic & Autonomic Nervous System
Differences Somatic Autonomic
No of neurons in efferent path
1 2
way
Neurotransmitter / receptor
at neuron target synapse
Ach/nicotinic Ach/ Muscarinic (or) N.E/ Alpha
or beta
Target tissue Skeletal muscle Smooth & cardiac muscle, some
endocrine & exocrine
Glands , some adipose tissue.
Neurotransmitter released
from
Axon terminals Varicosities & axon terminals
Effects on target tissue Excitatory only,
Muscle contracts.
Excitory or inhibitory.
Peripheral components found
outside the cns
Axons only Preganglionic axons, ganglia,
postganglionic neurons.
Summary of functions Posture & movement Visceral functions , including
Movement in internal organs &
secretion , control of
metabolisium. 51

References
GOODMAN & GILMAN'S THE PHARMACOLOGICAL
BASIS OF THERAPEUTICS (11th Ed.) .
PHARMACOLOGY BY H.P.RANG, M.M.DALE(6th Ed.).
ESSENTIALS OF MEDICAL PHARMACOLOGY BY
KD.TRIPATHI(5th Ed.)
LIPPINCOTT’S ILLUSTRATED REVIEWS
PHARMACOLOGY.
52

Autonomic &Somatic Nervous Systems.

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