BI213 Ch 15 Autonomic Nervous System AP 1

1. Chapter 15
Autonomic NS
Visceral
Reflexes

2. General Properties
ANS – motor nerves system that controls glands,
cardiac muscle, and smooth muscle.
AKA: visceral motor system
Target organs of the ANS are the viscera of the
thoracic and abdominal cavities.
Regulates unconscious processes that maintain
homeostasis
– BP, body temperature, respiratory airflow

3. General properties
Visceral effectors due not depend on the ANS to
function but rather the ANS is used to adjust their
activity to the body’s need. (heart)

4. Visceral Reflexes
• Unconscious, automatic responses to stimulation
of glands, cardiac or smooth muscle
1.Receptors
– detect internal stimuli -- stretch, blood chemicals, etc.
1.Afferent neurons
– connect to interneurons in the CNS
1.Efferent neurons
– carry motor signals to effectors
1.Effectors
– glands, smooth or cardiac muscle
• ANS modifies effector activity

5. Visceral Reflex to High BP (Baroreflex)
(1) High blood pressure
detected by arterial
stretch receptors
(baroreceptors)
(2) afferent neuron transmit
signal via CN IX to MO
(3) efferent signal via CN X
signals travel to the heart
(4) heart slows reducing BP

6. Divisions of ANS
• Two divisions innervate same target organs
– may have cooperative or contrasting effects on
same target organ.
1.Sympathetic division
2.Parasympathetic division

7. Sympathetic Division
• Adapts the body to physical activities
• Increase
– Heart rate
– Alertness
– Blood pressure
– Pulmonary air flow
• Reduces
– Blood flow to skin and digestive tract

8. Parasympathetic Division
Calming effect on body functions.
Plays a role in reducing energy expenditure, and
normal bodily maintenance – digestion and waste
elimination.

9. Autonomic Tone
• Background rate of activity that is a balance between the
activation sympathetic tone and parasympathetic tone.
I.e. Parasympathetic tone maintains the resting heart rate at
70-80 bpm, if the vagus nerve was cut the heart would beat
at its own intrinsic rate of 100bpm
Sympathetic tone keeps most blood vessels partially
constricted thus maintains blood pressure, it there is a loss
of tone then blood pressure could rapidly drop.
Different effect from each system depends upon the type of
neurotransmitter released and receptor used.

10. Neural Pathways
• ANS had components in both CNS and PNS.
CNS – hypothalamus, other regions of brainstem,
motor neurons in spinal cord.
PNS- peripheral ganglion, fiber travel through spinal
nerves.
Autonomic motor pathway to a target organ differ
from a somatic motor pathway.

11. Somatic Motor pathway – motor neuron (brainstem or spinal
cord) issues a myelinated axon that reaches all the way to
the skeletal muscle.
Autonomic pathway travels across two neurons that synapse
at an autonomic ganglion.
Preganglionic neuron has a soma in the brain or spinal cord &
terminate in the ganglion.
Postganglionic neuron axon continues to the target cells.

13. Before We go on (Groups)
Answer the following questions within your group.
They will be discussed in 10 minutes.
1. How does the autonomic nervous system differ
from the somatic motor system?
2. How do the general effects of the sympathetic
division differ from those of the parasympathetic
division?

14. Anatomy of Autonomic Nervous System
Sympathetic Division aka Thoracolumbar division
Preganglionic somas are located in the lateral horn of
the spinal cords at levels (T1)T2 – L1.
The axons from these somas will exit the spinal cord
by way of the spinal nerves and lead to a nearby
sympathetic chain of ganglia (paravertebral
ganglion).

17. Sympathetic Division
These chains ONLY receive input from T2-L1 regions
of the cord, they will extend up to the cervical and
down to the sacral and coccygeal regions.
Typically there are:
3 cervical ganglion (superior, middle, inferior)
11 thoracic ganglion
4 lumbar ganglion
4 sacral ganglion
1 coccygeal ganglion

18. Sympathetic Division
Each paravertebral ganglion is connected to the
spinal nerve by two branches called
communicating rami.
Communicating rami composed of:
1. White communicating ramus – white from
myelin.
2. Grey communicating ramus – color from lack
of myelin. These fibers will extend the rest of the
way to the target organ.

19. Sympathetic Division
Once preganglionic fibers leave the from the lateral
horn of the spinal cord enter the sympathetic
chain may follow any of these three courses.
1. Some end in the ganglion they enter and synapse
with a postganglionic neuron.
2. Some travel up or down the chain and synapse in
other ganglion at other levels.
3. Some pass through the chain without synapsing
and continue as Splanchnic nerves.

21. Nerve fibers leave the sympathetic
chain by one of three routes.
1. Spinal nerve route-
postganglionc fibers exit via
grey ramus, return to spinal
nerve and travel with it to
target organ.
This is the route to most sweat
glands, piloerector muscles,
and blood vessels of the skin
and skeletal muscles.

22. 2. Sympathetic nerve route
If the preganglionic fiber travels up
or down the chain to another
ganglion and synapse with a
postganglionic fiber. The
postganglionic fiber leaves by
way of a sympathetic nerve.
These nerves will extend to the
heart, lungs, esophagus, and
thoracic blood vessels.
Also they form a plexus (mesh)
around each carotid artery and
issue fibers to the head –
including sweating, salivary,
nasal glands, blood vessels,
dilators of the iris.

23. 3. Splanchnic nerve route –
Arise form T5-T12 cord level.
Once they pass through the
chain they are considered
splanchnic nerves.
Continue on to another ganglion
called collateral (prevertebral)
ganglion. Thus synapsing
with postganglionic neurons
and traveling to the target.

24. Collateral Ganglion
These ganglion contribute to a network called
abdominal aortic plexus, wrapped around the aorta.
3 major collateral ganglion in this plexus:
1. Celiac ganglion
2. superior mesenteric ganglion
3. inferior mesenteric ganglion
All located at a point where arteries of the same name
branch off the aorta; postganglionic fibers
accompany these arteries to the target organ.

27. Adrenal Glands
Location- superior poles of each kidney.
It is actually two glands in one.
1. Adrenal cortex- outer rind
2. Adrenal medulla – essentially a sympathetic
ganglion.
Adrenal medulla contains modified postganglionic
cells without dendrites or axons.
Sympathetic preganglionic neurons penetrate the
cortex and synapse with these cells.

28. Adrenal Glands
The sympathetic NS and adrenal gland are so closely
related in development and function, they could be
called sympathoadrenal system.
Once the postganglionic cells in the medulla are
stimulated the medulla secretes hormones into the
blood stream.
85% epinephrine
15% norepinephrine

29. Pre & Postganglionic relationship
Neuronal converging- each postganglionic cell
receives synapses from multiple preganglionic cells.
Neuronal diverging – each preganglionic fibers branch
and synapse with multiple post ganglionic cells.
There are about 17 postganglionic neurons for every
one preganglionic neurons in sympathetic division.

30. This means that the firing of one preganglionic
neuron can excite multiple postganglionic neurons
leading to multiple target organs = WIDE spread
effect.

31. Parasympathetic Division
Aka craniosacral division.
These nerves will travel along with certain cranial and
sacral nerves.
Preganglionic neurons are located in the:
1. midbrain
2. pons
3. medulla oblongata
4. spinal cord segments S2 – S4

32. Parasympathetic Division
The preganglionic neurons issue long preganglionic
fibers that end in terminal ganglion which are
found in or near a target organ.
If the terminal ganglion is located in the wall of the
target organ – intramural ganglion.

33. Parasympathetic Division
Preganglionic fibers leave the brainstem by way of 4
cranial nerves:
1. Oculomotor nerve (III)
2. Facial Nerve (VII)
3. Glossopharyngeal Nerve (IX)
4. Vagus Nerve (X)

34. Oculomotor Nerve (III)
Carry parasympathetic control of lens and pupil.
Preganglionic fibers terminate in the ciliary ganglion
behind the eye…
Postganglionic fibers enter eye and innervate the
ciliary muscle (thickens the lens) and pupillary
constrictor (narrows pupil).

35. Facial Nerve (VII)
Carries fibers that regulate tear, salivary and nasal
glands.
Preganglionic fibers leave pons & splits:
1. ends in the shenopalatine ganglion …
Postganglionic fibers continue to tear & nasal
glands.
2. Ends in the submandibular ganglion…
postganglionic fibers supply the salivary glands in
the floor of the mouth.

36. Glossopharyngeal Nerve (IX)
Carries fibers concerned with salivation.
Preganglionic fibers form the tympanic nerve and end
in the otic ganglion…
Postganglionic fibers follow the trigeminal nerve to
the parotid salivary gland.

37. Vagus Nerve (X)
Carries 90% of all parasympathetic preganglionic fibers.
Travels down neck and forms 3 networks:
1. Cardiac plexus –
2. Pulmonary plexus –
3. Esophageal plexus -
Supplies fibers to the heart
Fibers accompany the bronchi and blood vessels in the lungs.
Fibers that regulate swallowing

38. Vagus Nerve (X)
At the end of the esophagus, the plexuses give off
the anterior and posterior vagal trunks that
eventually pass down and through the abdominal
aortic plexus without synapsing and go to:
1. Liver
2. pancreas
3. stomach
4. small intestine
5. kidney
6. ureter
7. proximal half of the colon

39. S2 – S4 spinal levels
Preganglionic neurons when leaving the ventral rami
form the pelvic splanchnic nerves that lead to the
inferior hypogastric (pelvic) plexus.
Some of the preganglionic fibers synapse here but
most will pass through and continue on with the
pelvic nerves to the terminal ganglion.
Innervating the distal half of the colon, the rectum,
urinary bladder, and reproductive organs.

42. Enteric Nervous System
Unlike ANS, the ENS does not arise from the
brainstem or spinal cord.
It consists of about 100 million neurons embedded in
the wall of the digestive tract and has its own reflex
arc.
Regulates the motility of the esophagus, stomach,
and intestines as well as secretion of digestive
enzymes and acid.

43. Before We Go On. (Groups)
3. Explain why the sympathetic division is called the
thoracolumbar division even though its paravertebral
ganglia extend all the way from the cervical to sacral region.
4. Describe or diagram the structural relationship among the
following: preganglionic fiber, postganglionic fiber, gray
ramus, white ramus, and sympathetic ganglion.
5. Explain in anatomical terms why the parasympathetic
division affects target organs more selectively than the
sympathetic division does.
6. Trace the pathway of a parasympathetic fiber of the vagus
nerve form the medulla oblongata to the small intestine.

44. Autonomic Effects on Target organs
To understand the contrary effects of the sympathetic
and parasympathetic nerves we have to look to the
neurotransmitters that are released.
ANS has both:
Cholinergic fibers –
Adrenergic fibers -
Secrete acetylcholine (Ach)
Secrete norepinepherine (NE)

45. Sympathetic NS has a longer lasting effect due to NE.
NE – 3 fates:
1. reabsorbed by the nerve or broken down by MAO
(monoamine oxidase)
2. Diffuse into surrounding tissue and degraded by
COMT (catechol-O-methyltransferase).
3. Picked up by the blood stream, where MAO and
COMT are absent.
THUS = prolonged effect

46. ANS also secretes neuropeptides that modulate the
ACh or NE function.
Sympathetic fibers secrete:
- enkephalin
- substance P
- neuropeptide Y
- neurotensin
-gonadotropin releasing hormone
Parasympathetic fibers stimulate the endothelial cells
of blood vessels to release NO (nitric oxide) which
is a vasodilator.

47. Receptors
The reason why a division (SNS or PSNS) has an
excitatory and inhibitory effect on the same target
cell is due to the different kinds of receptors.
i.e. the parasympathetic NS contracts the wall of the
bladder but relax the urinary sphincter – both
important in expulsion of urine. (ACh release)
The receptors for ACh and NE are called:
Cholinergic receptors – ACh
Adrenergic receptors - NE

48. Cholinergic Receptors
Two classes:
1. Nicotinic receptors (NR)
2. Muscarinic receptors (MR)
NR located:
1. all post ganglionic cell in all ganglia of the ANS
2. Adrenal medulla
3. neuromuscular junctions
MR located:
1. all glands
2. smooth muscle
3. cardiac muscle that receives cholinergic
innervation

49. Cholinergic Receptors
All nicotinic receptors are excited by ACh.
Some muscarinic receptors are excited and inhibited
by ACh.
i.e. Muscarinic receptors (Ach) excites intestinal
smooth muscle but inhibits cardiac muscle.
How each receptor functions:
NR- opens ligand gated ion channels, changing
postsynaptic potential
MR- work through a variety of secondary
messengers.

50. Adrenergic Receptors (NE)
2 classes:
1. alpha (α) adrenergic receptors-
- binding is usually excitatory
NE binding to (α) receptor in blood vessels
causes vasoconstriction.
2. Beta (β) adrenergic receptors-
- binding is usually inhibitory
Arteries to the heart and skeletal muscles have
(β) receptors, thus dilating the these vessels.

54. Duel innervation
Most viscera receive fibers from both sympathetic
and parasympathetic divisions.
This means the two divisions will have an
antagonistic or cooperative effects on an organ.
i.e. Heart: Sympathetic –
Parasympathetic –
Digestion: Sympathetic –
Parasympathetic -
Speeds up
Slows down
Inhibits
Stimulates

55. The duel innervation will exert its effects on the same
effector cell, (i.e. heart) where the nerves terminate
in the same muscle cells.
Or…
Duel innervation can be when the two division
innervate different effector cells, (i.e. Iris)
Sympathetic fibers innervate the pupillary dilator &
parasympathetic fibers innervate the pupillary
constrictor.
See picture next slide

57. Cooperative effect is when two divisions act on
different effectors to produce a unified effect.
i.e. Salivary glands-
Parasympathetic stimulate serous cells to
produce a watery, enzyme rich secretion.
Sympathetic stimulate mucous glands of the
same organ to secrete mucous.
Both are necessary components of saliva.

58. Control without Dual Innervation
Dual innervation is not needed in all situations.
The most significant example is in the blood vessels.
The sympathetic fibers have a baseline
sympathetic tone which keeps the vessels partially
constricted = Vasomotor Tone.
Increase in firing = constriction of vessels
Decrease in firing = smooth muscle relaxation, blood
pressure in the vessel will dilate it.

59. Vasomotor tone is also responsible for re-routing
blood to different organs in times of stress and
emergency.

60. Before We Go On. (Groups)
7. What neurotransmitters are secreted by andrenergic and
cholinergic fibers?
8. Why do sympathetic effects last longer than
parasympathetic effects?
9. How can the sympathetic division cause smooth muscle to
relax in some organs but contract in others?
10. What are the two ways in which the sympathetic and
parasympathetic systems can affect each other when they
both innervate the same target organ? Give examples.
11. How can the sympathetic nervous system have
contrasting effects in a target organ without innervation?

61. Central Control of Autonomic Function
Output originates in the CNS, and receives input from
the cerebral cortex, hypothalamus, MO, and somatic
branch of the peripheral nervous system.
Cerebral Cortex – Emotional responses from the limbic
system influences the ANS.
Hypothalamus – contains nuclei for primitive functions.
Hunger, thirst, thermoregulation. Artificial stimulation
can activate fight or flight response (sym) or calming
effects (para).

62. Midbrain, Pons, MO – contain nuclei for the ANS,
cardiac centers, vasomotor centers, respiratory
centers, salivation, pupillary constriction and
dilation.
Spinal cord – autonomic reflexes defecation,
micturition, erection are all integrated by the spinal
cord.
The brain can consciously inhibit defecation and
micturition, but after SCI only the autonomic spinal
reflexes control the elimination.

63. Before We Go On (Groups)
12. What system in the brain connects our conscious
thoughts and feelings with the autonomic control
centers of the hypothalamus?
13. List some autonomic responses that are
controlled by nuclei in the hypothalamus?
14. What is the role of the midbrain, pons, and
medulla in autonomic control?
15. Name some visceral reflexes controlled by the
spinal cord.