1. Chapter 09 Lecture Outline
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2. I. Neural Control of Involuntary Effectors

3. Autonomic Neurons Innervate organs not under voluntary control
Effectors include:
Cardiac muscle
Smooth muscle of visceral organs and blood vessels
Glands
Part of the PNS
Neurons are motor, but there are sensory neurons from the viscera for control

4. Differences between somatic and autonomic
Somatic motor neurons have cell bodies in the spinal cord and just one neuron traveling from spinal cord to effector.
The autonomic motor system has two sets of neurons in the PNS.
The first has cell bodies in the brain or spinal cord and synapses in an autonomic ganglion
The second has cell bodies in the ganglion and synapses on the effector

5. Autonomic Neurons
Preganglionic neurons: originate in the midbrain or hindbrain or from the thoracic, lumbar, or sacral spinal cord
Postganglionic neurons: originate in ganglion
Autonomic ganglia are located in the head, neck, and abdomen as well as in chains along either side of the spinal cord

6. The ANS has pre- and postganglionic neurons
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Autonomic
ganglion
CNS
Involuntary
effector
Smooth
muscle
Preganglionic
neuron
Postganglionic
neuron

7. Visceral Effector Organs
Somewhat independent of innervation and will not atrophy if a nerve is cut (unlike skeletal muscle)
Target may become even more sensitive to stimulation; called denervation hypersensitivity
Cardiac muscle and some smooth muscle contract rhythmically without nerve stimulation. Autonomic innervation can speed up or slow down intrinsic contractions.
Autonomic motor neurons can stimulate or inhibit, depending on the organ and the receptors

8. Neurotransmitters
Somatic motor neurons release only acetylcholine which is always excitatory.
Autonomic neurons release mainly acetylcholine and norepinephrine but may be excitatory or inhibitory

9. Somatic vs. Autonomic System

10. II. Divisions of the Autonomic Nervous System

11. Sympathetic Division
Preganglionic neurons come from the thoracic and lumbar regions of the spinal cord.
Also called the thoracolumbar division
Preganglionic neurons synapse in sympathetic ganglia that run parallel to the spinal cord.
These are called the paravertebral ganglia.
These ganglia are connected, forming a sympathetic chain of ganglia.

12. Sympathetic Division, cont
Myelinated axons of the preganglionic neurons exit the spinal cord at ventral roots and diverge into white rami communicantes and then into autonomic ganglia at multiple levels.
Unmyelinated axons of the postganglionic neurons form the gray rami communicantes, which return to the spinal nerve and travel with other spinal nerves to their effectors.

13. Sympathetic Chain of Paravertebral Ganglia
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Spinal cord
Posterior (dorsal) root
Sympathetic chain of
paravertebral ganglia
Anterior (ventral) root
Rami communicantes
Sympathetic ganglion
Spinal nerve
Vertebral body
Rib

14. Convergence and Divergence
Because preganglionic neurons can branch and synapse in ganglia at any level, there is:
Divergence: One preganglionic neuron synapses on several postganglionic neurons at different levels.
Convergence: Several preganglionic neurons at different levels synapse on one postganglionic neuron.
Allows the sympathetic division to act as a single unit through mass activation and to be tonically active

15. Sympathetic Neuron Pathways
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Visceral effectors:
Smooth muscle of
blood vessels, arrector
pili muscles, and
sweat glands
1. Preganglionic axons
synapse with
postganglionic
neurons
2. Postganglionic
axons innervate
target organs
Sympathetic
chain
ganglion
Dorsal root
ganglion
Dorsal
root
Spinal
nerve
Sympathetic chain
White
ramus
Splanchnic
nerve
Ventral
root
Gray ramus
Visceral effector:
intestine
Collateral
ganglion
(celiac ganglion)
Preganglionic neuron
Spinal cord
Postganglionic neuron

16. Collateral Ganglia
Many of the sympathetic neurons that exit the spinal cord below the diaphragm do not synapse in the sympathetic chain of ganglia.
Instead, they form splanchnic nerves, which synapse in collateral ganglia.
Collateral ganglia include celiac, superior mesenteric, and inferior mesenteric ganglia.
Postganglionic neurons innervate organs of the digestive, urinary, and reproductive systems.

17. Collateral Sympathetic Ganglia
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Diaphragm
Superior mesenteric
ganglion
Celiac ganglion
Adrenal gland
Renal plexus
First lumbar
sympathetic
ganglion
Aortic plexus
Inferior mesenteric
ganglion
Pelvic sympathetic
chain

18. Adrenal Glands
The adrenal medulla secretes epinephrine and norepinephrine when stimulated by the sympathetic nervous system as a part of mass activation
Embryologically, the adrenal medulla is a modified ganglion and is innervated directly by preganglionic sympathetic neurons.

19. Summary of the Sympathetic Division

20. Parasympathetic Division
Preganglionic neurons come from the brain or sacral region of the spinal cord.
Also called the craniosacral division
They synapse on ganglia located near or in effector organs; called terminal ganglia
Preganglionic neurons do not travel with somatic neurons (as sympathetic postganglionic neurons do).
Terminal ganglia supply very short postganglionic neurons to the effectors

21. Cranial Nerves and the Parasympathetic Division
The occulomotor, facial, glosso-pharyngeal, and vagus nerves carry parasympathetic preganglionic neurons.
Occulomotor (III) nerve
Preganglionic fibers exit midbrain and synapse on the ciliary ganglion.
Postganglionic fibers innervate the ciliary muscle of the eye.

22. Cranial Nerves and the Parasympathetic Division, cont
Facial (VII) nerve: Preganglionic fibers exit the pons and synapse in:
Pterygopalatine ganglion: Postganglionic fibers synapse on nasal mucosa, pharynx, palate, and lacrimal glands.
Submandibular ganglion: Postganglionic fibers synapse on salivary glands.
Glossopharyngeal: Preganglionic fibers synapse on otic ganglion. Postganglionic fibers innervate salivary gland.

23. Cranial Nerves and the Parasympathetic Division, cont
Vagus (X) nerve: Preganglionic fibers exit medulla, branch into several plexi and nerves, and travel to ganglia within effector organs (heart, lungs, esophagus, stomach, pancreas, liver, intestines).

24. Path of the Vagus Nerve Hyoid bone Vagus nerve Thyroid cartilage
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Hyoid bone
Vagus nerve
Thyroid cartilage
of larynx
Trachea
Right
pulmonary
plexus
Right
cardiac
branch
Left pulmonary plexus
Left cardiac branch
Right
gastric nerve
Left gastric nerve
Stomach
Celiac plexus
Liver
Superior
mesenteric nerve

25. Sacral Nerves
Preganglionic nerves from the sacral region of the spinal cord provide innervation to the lower part of the large intestine, rectum, urinary and reproductive organs.
Terminal ganglia are located within these organs.

26. Summary of Parasympathetic Division

27. Comparison of the Sympathetic and Parasympathetic Divisions
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Cranial nerve III
Ciliary muscle and
pupil of eye
Midbrain
Cranial nerve VII
Hindbrain
Lacrimal gland
and nasal mucosa
Cranial nerve IX
Cranial nerve X
Submandibular
and sublingual
glands T1 T2 T3
Parotid gland T4 T5
Lung T6 T7
Sympathetic chain
ganglion
Celiac
ganglion T8
Heart
Greater splanchnic
nerve T9
T10
Liver and gallbladder
T11
Spleen
Lesser splanchnic
nerve
T12
Stomach
Pancreas L1 L2
Superior
mesenteric
ganglion
Large intestine
Small intestine
Adrenal gland
and kidney S2 S3
Inferior
mesenteric
ganglion S4
Urinary bladder
Pelvic nerves
Reproductive
organs

28. III. Functions of the Autonomic Nervous System

29. General functions Sympathetic Functions
The sympathetic division activates the body for “fight or flight” through the release of norepinephrine from postganglionic neurons and the secretion of epinephrine from the adrenal medulla.
Prepares the body for intense physical activity in emergencies by increasing heart rate and blood glucose levels and by diverting blood to skeletal muscles
Tonically regulates heart, blood vessels, and other organs

30. General functions, cont
Parasympathetic Functions
The parasympathetic division is antagonistic to the sympathetic division.
Allows the body to “rest and digest” through the release of ACh from postganglionic neurons
Slows heart rate, and increases digestive activities

31. Summary of Autonomic Functions

32. Adrenergic & Cholinergic Synaptic Transmission
Acetylcholine (ACh) is the neurotransmitter used by all preganglionic neurons (sympathetic and parasympathetic)
It is also the neurotransmitter released from most parasympathetic postganglionic neurons.
Some sympathetic postganglionic neurons (those that innervate sweat glands and skeletal muscle blood vessels) release ACh.
These synapses are called cholinergic.

33. Adrenergic Synaptic Transmission
Norepinephrine is the neurotransmitter released by most sympathetic postganglionic neurons.
These synapses are called adrenergic.

34. (dihydroxyphenylalanine)
Catecholamine Family of Molecules
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Tyrosine
(an amino acid) HO C C
NH2 H
COOH HO H H
DOPA
(dihydroxyphenylalanine) HO C C
NH2 H
COOH HO H H
Dopamine
(a neurotransmitter) HO C C
NH2 H H HO H H
Norepinephrine
(a neurotransmitter
and hormone) HO C C
NH2 O H H OH H H
Epinephrine
(major hormone of
adrenal medulla) H HO C C N O H H
CH3

35. Neurotransmitters of the Autonomic Nervous System
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Cranial
parasympathetic
nerves
Terminal
ganglion
ACh
Visceral
effectors
ACh
Paravertebral
ganglion NE
Visceral
effectors
ACh
Adrenal
medulla
ACh
Sympathetic
(thoracolumbar)
nerves
E, NE (hormones)
Circulation NE
Visceral
effectors
ACh
Sacral
parasympathetic
nerves
Collateral
ganglion
Visceral
effector
organs
ACh
ACh

36. Varicosities
Axons of postganglionic neurons have various swellings called varicosities that release neurotransmitter along the length of the axon.
They form “synapses en passant” - in passing.
Sympathetic and parasympathetic neurons innervate the same tissues but release different neurotransmitters

37. Sympathetic and Parasympathetic Release of Different Neurotransmitters
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Sympathetic
neuron
Varicosity
Synapses
en passant
Smooth muscle cell
Parasympathetic
neuron
(a)
Axon of Sympathetic
Neuron
Synaptic vesicle
with norepinephrine (NE) NE
Adrenergic
receptors
Antagonistic effects
Smooth
muscle cell
Cholinergic
receptors
ACh
Axon of Parasympathetic
Neuron
Synaptic vesicle
with acetylcholine (ACh)
(b)

38. Response to Adrenergic Stimulation
Can be epinephrine in the blood or norepinephrine from sympathetic nerves
Can stimulate or inhibit, depending on receptors
Stimulation: heart, dilatory muscles of the iris, smooth muscles of many blood vessels (causes vessel constriction)
Inhibition: Bronchioles in lungs, other blood vessels; inhibits contraction and causes dilation of these structures

39. α and β Adrenergic Receptors
Two types of α(alpha) - α1 and α2
Two types of β(beta) - β1 and β2
All act using G-proteins and second messenger systems.
β receptors use cAMP.
α receptors use a Ca2+ second messenger system.
Alpha receptors are more sensitive to norepinephrine
Beta receptors are more sensitive to blood epinephrine

40. Adrenergic effects in different organs

41. α2 Receptors Located on presynaptic axons
When stimulated, result in inhibition of norepinephrine release in the synapse
May be a negative-feedback system
Some drugs to lower blood pressure act on these α2 receptors to inhibit presynaptic neurons in the brain, inhibiting the whole sympathoadrenal system.
There are different subtypes that will give different responses

42. Drugs that mimic adrenergic responses
Agonists – drugs that promote the process stimulated by the NT
Antagonists – drugs that block the action of the NT
Many are useful in medical applications

43. Examples of Adrenergic and Cholinergic Agonists and Antagonists

44. Response to Cholinergic Stimulation
ACh released from preganglionic neurons of both the sympathetic and parasympathetic division is stimulatory.
ACh from postganglionic neurons of the parasympathetic division is usually stimulatory, but some are inhibitory, depending on receptors.
In general, sympathetic and parasympathetic effects are opposite

45. Cholinergic Receptors
Nicotinic: found in autonomic ganglia
Stimulated by Ach from preganglionic neurons
Serve as ligand-gated ion channels for Na+ & K+
Blocked by curare
Muscarinic: found in visceral organs and stimulated by release of Ach from postganglionic neurons
Five types identified; can be stimulatory or inhibitory (opening K+ or Ca2+ channels)
Use G-proteins and second messenger system
Blocked by atropine

46. Cholinergic Receptors & Responses to ACh

47. Comparison of Nicotinic & Muscarinic ACh Receptors
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Nicotinic ACh
receptors
Muscarinic ACh
receptors
Postsynaptic membrane of
• All autonomic ganglia
• All neuromuscular junctions
• Some CNS pathways
• Produces parasympathetic nerve effects in
the heart, smooth muscles, and glands
• G-protein-coupled receptors (receptors
influence ion channels by means of G-proteins)
Na+
Na+ or Ca2+
ACh
ACh
ACh
Ligand-gated channels
(ion channels are part
of receptor) β β α α γ γ K+ K+ K+
Depolarization
Hyperpolarization
Depolarization
(K+ channels
opened)
(K+ channels
closed)
Excitation
Inhibition
Excitation
Produces slower
heart rate
Causes smooth muscles of the
digestive tract to contract

48. Receptor Activity in Autonomic Regulation
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Parasympathetic division
Sympathetic division
Preganglionic
neurons
Nicotinic
ACh receptors
ACh
Postganglionic
neurons
ACh
Norepinephrine
Stimulates
muscarinic ACh
receptors
Stimulates
α1-adrenergic
receptors
Stimulates
β1-adrenergic
receptors
Stimulates β2-adrenergic
receptors
Parasympathetic
nerve effects
Vasoconstriction in
viscera and skin
Increased
heart rate and
contractility
Dilation of
bronchioles (of lung)
and blood vessels

49. Other Autonomic Neurotransmitters
Some postganglionic autonomic neurons do not release ACh or norepinephrine.
Called “nonadrenergic, noncholinergic fibers”
Proposed neurotransmitters include ATP, vasoactive intestinal peptide (VIP), and nitric oxide (NO).

50. Nonadrenergic, Noncholinergic Fibers
Important for erection of the penis.
Parasympathetic neurons innervate blood vessels, causing relaxation and vasodilation using NO.
NO can also produce smooth muscle relaxation in the stomach, intestines, urinary bladder, and the brain.

51. Organs with Dual Innervation
Most visceral organs are innervated by both sympathetic and parasympathetic neurons.
Most of the time these systems are antagonists:
Heart rate – sym increases, para decreases
Digestive functions – sym decreases, para increases
Pupil diameter – sym dilates, para constricts

52. Complementary Effects
Occur when both divisions produce similar effects on the same target
Example - Salivary gland secretion: Parasympathetic division stimulates secretion of watery saliva; sympathetic constricts blood vessels so the secretion is thicker.

53. Cooperative Effects
Occur when both divisions produce different effects that work together to promote a single action.
Example - Erection and ejaculation: Parasympathetic division causes vasodilation and erection; sympathetic causes ejaculation
Example - Urination: Parasympathetic division aids in urinary bladder contraction; sympathetic helps with bladder muscle tone to control urination.
Medications for overactive bladder block specific receptors

54. Summary of Autonomic Functions

55. Organs Without Dual Innervation
The following organs are innervated by the sympathetic division only:
Adrenal medulla
Arrector pili muscles in skin
Sweat glands in skin
Most blood vessels
Regulated by increase and decrease in sympathetic nerve activity
Important for body temperature regulation through blood vessels and sweat glands

56. Control of ANS by Higher Brain Centers
Many visceral functions are regulated by autonomic reflexes.
Sensory input is sent to brain centers (usually by the vagus nerve), which integrate the information and modify the activity of preganglionic neurons.
Medulla oblongata controls many cardiovascular, pulmonary, urinary, reproductive, and digestive functions.

57. Regulation of the Medulla
Higher brain regions regulate the medulla.
Hypothalamus: major regulatory center of the ANS – body temperature, hunger, thirst, pituitary gland
Limbic system: responsible for autonomic responses during emotional states (blushing, pallor, fainting, cold sweating, racing heart rate)
Cerebellum – motion sickness nausea, sweating, cardiovascular changes
Frontal & temporal lobes – emotion and personality

58. Aging Associated with increased levels of sympathetic activity
Increased sympathetic tone
Increased risk for hypertension and cardiovascular diseases

59. Autonomic Reflexes