Lecture on autonomic nervous system for undergraduate medical students

2.  Autonomic nervous system (ANS) is
concerned with the innervation of involuntary
structures e.g. heart, smooth muscle, glands
 It is distributed throughout the central &
peripheral nervous system

3.  It is divided into 2 types:
1. Sympathetic nervous system
2. Parasympathetic nervous system

5.  It emerges from the spinal cord between
segments T1 to L2
 Efferent fibers
 Afferent fibers

8.  Spinal cord from T1 to L2 posses a lateral
horn or column
 Cell bodies of sympathetic connector
neurons are located in the lateral horn
 Axons (pre-ganglionic myelinated fibers)
leave the spinal cord in the anterior nerve
roots
 Pass the WHITE RAMI COMMUNICANTES
to the paravertebral ganglia of the
sympathetic trunk

11.  The pre-ganglionic fibers, after reaching the
sympathetic trunk may pass one of the three
possible destinations.

12.  Pre-ganglionic fiber may terminate in the
sympathetic ganglion they have entered
 Synapse: a site where two neurons come in
close proximity but not into anatomic continuity
 Neurotransmitter (Acetylcholine)
 Post-ganglionic fibers (non-myelinated) leave
the ganglion through GRAY RAMI
COMMUNICANTES to thoracic spinal nerve
 May supply blood vessels, sweat glands,
arrector pili muscles of the skin

14.  Pre-ganglionic fibers may travel high up to
the cervical sympathetic ganglia
 Synapse
 Post-ganglionic fiber leaves the sympathetic
trunk as gray rami communicantes
 May join the cervical spinal nerves

16.  Pre-ganglionic fibers of lower part of the
thoracic sympathetic trunk may travel down
to lower lumbar and sacral sympathetic trunk
 Synapse
 Post-ganglionic fibers leave the sympathetic
trunk as gray rami communicantes to join the
lumbar, sacral & coccygeal spinal nerves

18.  Pre-ganglionic fibers may pass through the
thoracic sympathetic trunk WITHOUT
synapsing
 These myelinated fibers form three
SPLANCHNIC NERVES

21.  Arises from 5th to 9th thoracic ganglia
 Pierces the diaphragm
 Synapse with cells in the ganglia of CELIAC
PLEXUS

23.  Arises from the 10th and 11th ganglia
 Pierces the diaphragm
 Synapse with the excitor cells in the ganglia
of lower part of celiac plexus

25.  Not always present
 Arises from 12th thoracic ganglion
 Pierces the diaphragm
 Synapse with the excitor cells in the ganglia
of RENAL PLEXUS
 The splanchnic nerves hence supply to
smooth muscle and glands of viscera

26.  A few pre-ganglionic fibers travelling in the
greater splanchnic nerve end directly on the
cells of the supra-renal medulla
 Therefore, the medullary cells of supra-renal
glands may be regarded as MODIFIED
SYMPATHETIC EXCITOR CELLS

27.  The sympathetic trunks of both sides end
below by joining together to form a single
ganglion

29.  Sympathetic trunks of both sides are
ganglionated
 They extend by the side of whole length of
vertebral column
 3 ganglia in neck (cervical ganglia)
 11 or 12 ganglia in thorax
 4 or 5 ganglia in lumbar region
 4 or 5 ganglia in pelvis

30.  Afferent myelinated nerve fibers travel from
the viscera through the sympathetic ganglia
without synapse
 They enter the spinal nerve via the white
rami communicantes
 They reach their cell bodies in the posterior
root ganglion of the corresponding nerve

31.  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.  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.  The cranial efferent preganglionic fibers
relay in the parasympathetic ganglia situated
near to the viscera being supplied
 These ganglia are named as:
1. Ciliary ganglion
2. Pterego-palatine ganglion
3. Submandibular ganglion
4. Otic ganglion

34.  The efferent parasympathetic fibers from sacral
outflow leave the spinal cord segments S2, S3
& S4
 These are myelinated fibers
 Pre-ganglionic fibers in the pelvic splanchnic
nerves relay in the ganglia in HYPOGASTRIC
PLEXUSES or in the walls of viscera
 Post-ganglionic fibers are non-myelinated &
short as compared to sympathetic fibers
 Supply the viscera of pelvis

35.  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
 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.  The nerve endings in the autonomic afferent
component may not be activated by:
1. Heat or
2. Touch
 But these are activated by:
a) Stretch
b) Lack of oxygen

37.  It prepares the body for an emergency e.g.
FIGHT OR FLIGHT
 It increases heart rate
 It causes constriction of peripheral blood
vessels
 It raises blood pressure

38.  It conserves and sores the energy
 It slows the heart rate
 It increases peristalsis of intestine
 It opens the sphincters
 It is the system of REST & DIGESTION

43. The end