The peripheral nervous system consists of the spinal nerves, cranial nerves, autonomic nervous system, and peripheral nerve fibers. The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems which generally have opposing effects on target organs. The sympathetic nervous system is responsible for the "fight or flight" response and mobilizes the body during stress through thoracolumbar outflow. The parasympathetic nervous system is responsible for "rest and digest" functions through craniosacral outflow.

1. THE PERIPHERAL
NERVOUS
SYSTEM

2. Peripheral nervous system consists of:
• 31 pairs of spinal nerves
• 12 pairs of cranial nerves
• The autonomic nervous system
• Peripheral nervous system consists of
Sensory nerve fibres
Motor nerve fibres

3. Each nerve consists of
• Numerous nerve fibres collected into bundles
• Each bundle has coverings of protective
connective tissue :
1. Endoneurium - surrounds each individual fibre
2. Perineurium – surrounds each bundle
3. Epineurium – surrounds and covers a number of
bundles of nerve fibres

5. Nerve Roots
• Anterior nerve root consists of motor nerve
fibres from neurones in the anterior column
of grey matter
• Posterior nerve root consists of sensory
fibres
• Just outside the spinal cord there is a spinal
ganglion(posterior root ganglion) consisting
of nerve cells
• Sensory nerve fibres pass through these
ganglia before entering the spinal cord.
• The area of skin supplied by each nerve is
called a dermatome.

6. • For a short distance the roots have dura and
arachnoid
• No pia
• Anterior and posterior roots join to form mixed
spinal nerve
• Outside the intervertebral foramen the
spinal nerve divides into :-
1. Ramus communicans
2. a posterior ramus
3. an anterior ramus

7. Rami and Plexuses
• The ramus communicans is part of the autonomic nervous
system
• They join preganglionic sympthetic neurones
• The posterior ramus passes backwards to supply skin and
muscles
• Tha anterior rami supply the anterior and lateral aspects of
the neck, trunk and the upper and lower limbs.
• In the cervical, lumbar and sacral rgions the anterior rami
unite near their origins to form nerwork of nerves or
plexuses, where nerve fibres are regrouped and rearranged
before proceeding to supply skin, bones muscles, and
joints

8. The plexuses
• Five pairs of large plexuses
• Cervical plexus
• Brachial plexus
• Lumbar plexus
• Sacral plexus
• Coccygeal plexus

9. 9
Cervical Plexus
• Formed by the anterior rami of the first four
cervical nerves
• It lies opposite the 1st , 2nd , 3rd and 4th
cervical vertebrae
• Supplies structures at the back and side of
the head and the skin of the front of the
neck
• Muscles of the neck
• Phrenic nerve from this nerve supplies
diaphragm

10. Brachial Plexus
• Formed by C5,6,7,8 and T1
• Situated above and behid the subclavian
vessels and in the axilla
• The plexus can be recognised to have five
parts – roots, trunks, divisions, cords and
nerves
• The nerves which arise from the plexus are :
musculocutaneous nerve, median
nerve, ulnar nerve and axillary nerve

11. Formed by the anterior rami of L1, 2.3 and 4
Situated in front of the transverse processes of the lumbar
vertebrae and behind the psoas muscle.
The main branches are : -
Iliohypogastric nerve
Ilioinguinal nerve
Genitofemoral nerve
Lateral cutaneous nerve of thigh
Femoral nerve
Obturator nerve
Lumbosacral trunk

12. Iliohypogastric, ilioinguinal nerves : supply muscles
and the skin in the area of the lower abdomen, upper
and medial aspects of the thigh and the inguinal region
Lateral cutaneous nerves of the thigh supplies the
lateral skin of thigh
Femoral nerve : extensor muscles of the thigh – and the
anterior; saphenous branch : medial skin of the leg,
ankle and foot
Obturator nerve : adductor muscles
Lumbosacral trunk : goes to sacral plexus

13. The Sacral Plexus
• Formed by by the anterior rami of the lumbosacral
trunk (L4,5) and sacral nerves (S1,2,3)
• Lies on the posterior wall of the pelvic cavity
• Branches supply the muscles and skin of the
pelvis, muscles around the hip joint
• It gives off sciatic nerve (L 4, 5 S1, 2, 3)
• Sciatic nerve : largest nerve in the body
passes through greater sciatic forameninto the
buttock then descends through the back of thigh
supplies the hamstring muscles
at the level of the middle of the femur divides into
two: -
the tibial nerve and the common peroneal nerve

14. 14
• The tibial nerve descends through the popliteal
fossa
• Supplies the skin and muscles of the leg, sole of
the foot and toes
• Common peroneal nerve winds round the neck of
the fibula
• Divides into deep peroneal (anterior tibial) and
superficial peroneal nerves
• These two supply the skin and muscles of the leg
Pudendal nerve
Supplies the external anal sphincter, the external urethral
sphincter and adjacent skin

15. The Autonomic
Nervous System
Visceral sensory
Visceral motor
&

16. 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
• Visceral motor innervates non-skeletal (non-
somatic) muscles
• Visceral sensory

17. The autonomic nervous system, or ANS, is responsible for controlling
several body responses which are under the conscious level and which
are mostly involuntary, like breathing, digestion, sexual arousal, beating
of the heart, and many other biochemical processes.
There are two distinguishable divisions:
the parasympathetic and the sympathetic nervous systems.

18. ANS innervation is divided into sympathetic nervous system and
parasympathetic nervous system divisions. The sympathetic
division has thoracolumbar “outflow”, meaning that the neurons
begin at the thoracic and lumbar (T1-L2) portions of the spinal
cord. The parasympathetic division has craniosacral “outflow”,
meaning that the neurons begin at the cranial nerves (CN 3, CN7,
CN 9, CN10) and sacral (S2-S4) spinal cord.
The ANS is unique in that it requires a sequential two-neuron
efferent pathway; the preganglionic neuron must first synapse onto
a postganglionic neuron before innervating the target organ. The
preganglionic, or first, neuron will begin at the “outflow” and will
synapse at the postganglionic, or second, neuron’s cell body. The
post ganglionic neuron will then synapse at the target organ.

19. 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
The hypothalamus is the center of the parasympathetic nervous system. It operates
through various interconnecting systems and organs. This system is responsible in
the “thinking” phase in stressful situations and is called the “Rest and Digest”
phase because your body goes back to its normal responses.
“rest &digest”
Sympathetic: mobilization & increased metabolism
This type of the autonomic nervous system is responsible in the distribution of
essential nutrients and oxygen to the various parts of the body. The ANS is
responsible for “Flight or Fight.” The body has to respond immediately because of
the urgency of some situations. “fight, flight or fright” or “fight,
flight or freeze”

21. 21
Where they come from
Parasympathetic:
craniosacral
Sympathetic:
thoracolumbar

22. 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”

23. 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

24. 24
Parasympathetic

25. 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”

26. 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…

27. 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

28. Sympathetic

29. Visceral sensory neurons
• Monitor temperature, pain, irritation, chemical changes and
stretch in the visceral organs
– Brain interprets as hunger, fullness, pain, nausea, well-being
• Receptors widely scattered – localization poor (e.g. which part
is giving you the gas pain?)
• Visceral sensory fibers run within autonomic nerves,
especially vagus and sympathetic nerves
– Sympathetic nerves carry most pain fibers from visceral organs of body
trunk
• Simplified pathway: sensory neurons to spinothalamic tract to
thalamus to cerebral cortex
• Visceral pain is induced by stretching, infection and cramping
of internal organs but seldom by cutting (e.g. cutting off a
colon polyp) or scraping them

30. Visceral sensory and autonomic neurons
participate in visceral reflex arcs
• Many are spinal reflexes such as defecation and
micturition
reflexes
• Some only
involve peripheral
neurons: spinal
cord not involved
(not shown)*
*e.g. “enteric” nervous system: 3 neuron reflex arcs entirely within the wall of the gut

31. Central control of the
Autonomic NS
Amygdala: main limbic
region for emotions
-Stimulates sympathetic
activity, especially previously
learned fear-related behavior
-Can be voluntary when decide to
recall frightful experience -
cerebral cortex acts through
amygdala
-Some people can regulate some
autonomic activities by gaining
extraordinary control over their
emotions
Hypothalamus: main
integration center
Reticular formation: most
direct influence over
autonomic function

32. SCHEMATICS
OF
ANS GANGLIA

33. • Ganglia are located close to the spinal
column (short pre- and long post-ganglionic
fibers)
• Ganglia are often interconnected
• Large ratio of post- to pre-ganglionic fiber
number
Sympathetic Nervous system

34. • The anatomy of sympathetic ans is structurally
designed to produce diffuse systemic responses by
simultaneous targetting of multiple tissues
• In addition to the routine homeostatic maintenance
of vital functions, the sympathetic nervous sytem is
designed to respond to physiological stress

35. PARASYMPATHETIC NERVOUS SYSTEM
• Ganglia are located close to or within the target
tissue (long pre- and short post-ganglionic
fibers)
• Ganglia are not interconnected
• Ratio of post- to pre-ganglionic fiber number =
1

36. PARASYMPATHETIC NERVOUS SYSTEM
• The anatomy of ans is structurally designed to
produce precise pin-point responses by targetting of
specific tissues
• In addition to the routine homeostatic maintenance of
vital functions, the parasympathetic nervous sytem is
designed to limit responses to physiological stress