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Autonomic nervous system: an introduction
1.
2. ο Autonomic nervous system (ANS) is
concerned with the innervation of involuntary
structures e.g. heart, smooth muscle, glands
ο It is distributed throughout the central &
peripheral nervous system
3. ο It is divided into 2 types:
1. Sympathetic nervous system
2. Parasympathetic nervous system
4.
5. ο It emerges from the spinal cord between
segments T1 to L2
ο Efferent fibers
ο Afferent fibers
6.
7.
8. ο Spinal cord from T1 to L2 posses a lateral
horn or column
ο Cell bodies of sympathetic connector
neurons are located in the lateral horn
ο Axons (pre-ganglionic myelinated fibers)
leave the spinal cord in the anterior nerve
roots
ο Pass the WHITE RAMI COMMUNICANTES
to the paravertebral ganglia of the
sympathetic trunk
9.
10.
11. ο The pre-ganglionic fibers, after reaching the
sympathetic trunk may pass one of the three
possible destinations.
12. ο Pre-ganglionic fiber may terminate in the
sympathetic ganglion they have entered
ο Synapse: a site where two neurons come in
close proximity but not into anatomic continuity
ο Neurotransmitter (Acetylcholine)
ο Post-ganglionic fibers (non-myelinated) leave
the ganglion through GRAY RAMI
COMMUNICANTES to thoracic spinal nerve
ο May supply blood vessels, sweat glands,
arrector pili muscles of the skin
13.
14. ο Pre-ganglionic fibers may travel high up to
the cervical sympathetic ganglia
ο Synapse
ο Post-ganglionic fiber leaves the sympathetic
trunk as gray rami communicantes
ο May join the cervical spinal nerves
15.
16. ο Pre-ganglionic fibers of lower part of the
thoracic sympathetic trunk may travel down
to lower lumbar and sacral sympathetic trunk
ο Synapse
ο Post-ganglionic fibers leave the sympathetic
trunk as gray rami communicantes to join the
lumbar, sacral & coccygeal spinal nerves
17.
18. ο Pre-ganglionic fibers may pass through the
thoracic sympathetic trunk WITHOUT
synapsing
ο These myelinated fibers form three
SPLANCHNIC NERVES
19.
20.
21. ο Arises from 5th to 9th thoracic ganglia
ο Pierces the diaphragm
ο Synapse with cells in the ganglia of CELIAC
PLEXUS
22.
23. ο Arises from the 10th and 11th ganglia
ο Pierces the diaphragm
ο Synapse with the excitor cells in the ganglia
of lower part of celiac plexus
24.
25. ο Not always present
ο Arises from 12th thoracic ganglion
ο Pierces the diaphragm
ο Synapse with the excitor cells in the ganglia
of RENAL PLEXUS
ο The splanchnic nerves hence supply to
smooth muscle and glands of viscera
26. ο A few pre-ganglionic fibers travelling in the
greater splanchnic nerve end directly on the
cells of the supra-renal medulla
ο Therefore, the medullary cells of supra-renal
glands may be regarded as MODIFIED
SYMPATHETIC EXCITOR CELLS
27. ο The sympathetic trunks of both sides end
below by joining together to form a single
ganglion
28.
29. ο Sympathetic trunks of both sides are
ganglionated
ο They extend by the side of whole length of
vertebral column
ο 3 ganglia in neck (cervical ganglia)
ο 11 or 12 ganglia in thorax
ο 4 or 5 ganglia in lumbar region
ο 4 or 5 ganglia in pelvis
30. ο Afferent myelinated nerve fibers travel from
the viscera through the sympathetic ganglia
without synapse
ο They enter the spinal nerve via the white
rami communicantes
ο They reach their cell bodies in the posterior
root ganglion of the corresponding nerve
31. ο The central axons enter the spinal cord and
may form:
1. Afferent component of local reflex arc OR
2. Pass up to higher autonomic centers in
brain
32. ο It has 2 outflows:
1. CRANIAL OUTFLOW: carried by III,VII,IX
and X cranial nerves
2. SACRAL OUTFLOW: carried by S2, S3 and
S4 nerves
33. ο The cranial efferent preganglionic fibers
relay in the parasympathetic ganglia situated
near to the viscera being supplied
ο These ganglia are named as:
1. Ciliary ganglion
2. Pterego-palatine ganglion
3. Submandibular ganglion
4. Otic ganglion
34. ο The efferent parasympathetic fibers from sacral
outflow leave the spinal cord segments S2, S3
& S4
ο These are myelinated fibers
ο Pre-ganglionic fibers in the pelvic splanchnic
nerves relay in the ganglia in HYPOGASTRIC
PLEXUSES or in the walls of viscera
ο Post-ganglionic fibers are non-myelinated &
short as compared to sympathetic fibers
ο Supply the viscera of pelvis
35. ο Afferent MYELINATED fibers travel from the
viscera to their cell bodies located:
1. Either in the sensory ganglia of the cranial
nerves
2. Or in the posterior root ganglia of the sacro-
spinal nerves
ο Central axons then enter the CNS and take
part in the formation of:
a) Local reflex arc or
b) Pass to higher centers of ANS in brain
36. ο The nerve endings in the autonomic afferent
component may not be activated by:
1. Heat or
2. Touch
ο But these are activated by:
a) Stretch
b) Lack of oxygen
37. ο It prepares the body for an emergency e.g.
FIGHT OR FLIGHT
ο It increases heart rate
ο It causes constriction of peripheral blood
vessels
ο It raises blood pressure
38. ο It conserves and sores the energy
ο It slows the heart rate
ο It increases peristalsis of intestine
ο It opens the sphincters
ο It is the system of REST & DIGESTION