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General Information. VISCERAL MOTOR INNERVATIONMotor innervation to smooth muscle, cardiac muscle and glandsConsists of two opposing divisionsmost structures receive innervation by both divisions (= dual innervation)helps ensure stability of internal environmentinvoluntary activity (subconsciou
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1. Unit IXAUTONOMIC NERVOUS SYSTEM
2. General Information VISCERAL MOTOR INNERVATION
Motor innervation to smooth muscle, cardiac muscle and glands
Consists of two opposing divisions
most structures receive innervation by both divisions (= dual innervation)
helps ensure stability of internal environment
involuntary activity (subconscious)
3. Comparison of Somatic and Autonomic Nervous Systems
4. Divisions of theAutonomic Nervous System (ANS) Parasympathetic Division (PD) -- primarily concerned with gaining and conserving energy
“rest-repose” (resting and digesting) system
e.g., enhances digestion, slows heart rate
Sympathetic Division (SD) -- primarily concerned with responses to life-threatening situations
“fight-or-flight” system
e.g., inhibits digestion, raises heart rate
5. General Structure In both divisions, 2 motor neurons involved: preganglionic and ganglionic
preganglionic neuron - has its cell body in gray matter of brain or spinal cord
axon extends out via cranial or spinal nerve
small diameter, lightly myelinated (type B) fibers
release ACh at synapse to excite ganglionic neuron (= postsynaptic membrane)
6. General Structure (con’t) ganglionic neuron – cell body is in autonomic ganglion
axon (postganglionic axon or fiber) is type C and extends from autonomic ganglion to effector
postganglionic axon releases either
norepinephrine - released by most fibers of sympathetic division
ACh - released by fibers of parasympathetic division
action of neurotransmitter is excitatory or inhibitory depending on receptors in effector
7. Comparison of Divisions
8. Differences in Structure Between Divisions 1. Site of origin
2. Location of ganglia
3. Length of preganglionic and postganglionic fibers
9. 1. Site of Origin parasympathetic
cell bodies of preganglionic neurons are in brain stem nuclei or gray horns of sacral spinal segments
fibers of preganglionic neurons exit from brain via cranial nerves or sacral segments of spinal cord (= “craniosacral outflow”)
sympathetic
cell bodies of preganglionic neurons are in lateral gray horns of thoracic or lumbar segments
fibers of preganglionic neurons are part of thoracic and lumbar spinal nerves (= “thoracolumbar outflow”)
10. 2. Location of Ganglia and 3. Length of Fibers 2. Location of ganglia
parasympathetic division has ganglia generally near the structures they innervate
sympathetic division -- most ganglia lie close to the vertebral column
3. Length of fibers
parasympathetic division (generally) has long preganglionic fibers and short postganglionic fibers
sympathetic division has short preganglionic fibers and long postganglionic fibers
11. Comparison of Divisions
12. Parasympathetic (Craniosacral) Division preganglionic neurons
bodies in brain stem nuclei (for cranial nerves) or in gray horns of sacral spinal cord segments S2-S4 (for sacral nerves)
fibers are long
release ACh at synapse
ganglia are located near structures they innervate
terminal ganglia (= intramural ganglia)
postganglionic fibers
generally short
release ACh at neuroeffector junction with effector
Several cranial nerves (III, VII, IX and X) contain parasympathetic fibers
13. Craniosacral Division
14. Cranial Outflow: CN III 1. Oculomotor nerve (III)
nerve innervates smooth muscle that controls iris - causes pupil to constrict
innervates smooth muscle of ciliary body - causes lens to change shape for near vision
preganglionic fibers originate in midbrain
postganglionic fibers originate in ciliary ganglia
15. Cranial Outflow: CN VII 2. Facial nerves (VII)
stimulate nasal and lacrimal glands (tearing), lower salivary glands
preganglionic fibers originate in pons
postganglionic fibers originate in ganglia in face (pterygopalatine and submandibular)
16. Cranial Outflow: CN IX 3. Glossopharyngeal nerves (IX)
stimulate parotid salivary glands
preganglionic fibers originate in medulla
postganglionic fibers originate in otic ganglia within cranial cavity
17. Cranial Outflow: CN X 4. Vagus nerves
major nerves (90% of craniosacral preganglionic fibers) providing parasympathetic innervation to structures of thoracic and abdominal cavities
preganglionic fibers originate in medulla
postganglionic fibers arise from terminal (intramural) ganglia located on/in target organs.
fibers from right and left intermingle to form plexuses in thoracic cavity and abdominal cavity
18. Cranial Outflow: CN X Thoracic Plexuses
Cardiac plexus supplies innervation to heart
Pulmonary plexus supplies innervation to lungs (bronchi, bronchioles)
Esophageal plexus supplies innervation to lower esophagus (tube through which food passes on way to stomach)
19. Cranial Outflow: CN X Abdominal plexus (aortic plexus) supplies innervation to most of the digestive system (stomach, gall bladder, liver, small intestine, pancreas, proximal part of large intestine) and urinary system (kidneys)
20. Sacral Outflow preganglionic fibers arise from neurons in gray horns of sacral segments S2-S4
axons run through ventral roots of sacral spinal nerves
postganglionic fibers arise from ganglia near organ innervated
provide parasympathetic innervation to pelvic organs
distal (last part) large intestine (including rectum and anal canal)
reproductive system (including uterus, external genitalia)
urinary bladder and ureters
21. Sympathetic (Thoracolumbar) Division innervates same organs as parasympathetic - BUT also other structures not innervated by parasympathetic
sweat glands and arrector pili muscles of skin (make hairs stand up)
adrenal medulla
blood vessels
preganglionic neurons have cell bodies in lateral gray horns of thoracic or upper lumbar spinal cord segments (T1-L1)
release ACh at synapse with ganglionic neuron
22. Sympathetic (Thoracolumbar) Division postganglionic fibers arise from ganglionic neurons in ganglia close to spinal cord
chain (paravertebral) ganglia are located adjacent to vertebral column (paired)
prevertebral ganglia are located anterior to vertebral column (single)
23. Sympathetic Preganglionic Neurons preganglionic fibers leave through ventral roots of thoracic or lumbar spinal nerves only
myelinated fibers pass through white ramus communicans* to reach chain ganglion (paravertebral ganglion) lying laterally to vertebrae
paravertebral chain ganglia form sympathetic chain (run from cervical to sacral regions)
typically, 23 ganglia in each sympathetic chain
(23 pairs)
*plural is “rami communicantes”
24. Sympathetic Preganglionic Neurons (con’t) once it has reached ganglion, preganglionic fibers can:
1. synapse with ganglionic neuron in chain ganglion
2. go up or down through sympathetic trunk to synapse in chain ganglion at another level
25. Sympathetic Preganglionic Neurons (con’t) 3. pass through the chain ganglion and go out to prevertebral ganglion (anterior to vertebral column near aorta - major artery along back wall)
preganglionic fibers help form splanchnic nerves
synapse with ganglionic neurons in prevertebral ganglia
26. Sympathetic Innervation paravertebral postganglionic fibers innervate:
head - eye (dilate pupil); inhibit salivary glands, lacrimal gland, nasal glands
lungs - dilate airways and blood vessels
heart - increase rate and strength of contraction
prevertebral postganglionic fibers innervate:
GI organs - inhibitory (decreases activity in liver, stomach, intestines, etc.)
urinary system - decreases output and relaxes bladder
reproductive organs
MOST postganglionic neurons release norepi
*See Table 14.4
27. Adrenal Medulla part of endocrine system
releases hormones:
norepinephrine - 20%, vasoconstriction
epinephrine - 80%, control of heart and metabolism
arises from same embryonic tissue as peripheral nervous system
same as postganglionic fibers of SD/ANS: acts like one big postganglionic fiber only releases “NT” into blood instead of to specific effectors
stimulated by preganglionic fiber of SD
28. Physiology of Autonomic Nervous System (ANS) Fibers and Receptors For:
A. Parasympathetic Division
B. Sympathetic Division
29. Fibers and Receptors: PD/ANS postganglionic fibers are cholinergic - release acetylcholine (ACh) at effector
effectors have cholinergic receptors (bind ACh)
1. Nicotinic receptors
direct acting
always excitatory
found dendrites/cell bodies of all ganglionic neurons (both divisions)
also found in
skeletal muscle (part of somatic nervous system)
adrenal medulla (innervated by preganglionic fibers of SD)
30. Fibers and Receptors: PD/ANS 2. Muscarinic receptors
indirect acting
excitatory or inhibitory
found in:
all effectors innervated by postganglionic neurons of PD
e.g., cardiac muscle - inhibited (slows heart rate)
e.g., smooth muscle and glands of GI tract - stimulated* (increases activity)
some effectors innervated by SD
e.g., eccrine sweat glands - stimulated
e.g., blood vessels in skeletal muscle - inhibited (vasodilation)
31. Fibers and Receptors: SD/ANS most postganglionic fibers are adrenergic (release norepinephrine = NE)
1. Alpha receptors (?):
? 1 - almost all sympathetic target organs except heart
constricts peripheral blood vessels and GI sphincters
dilates pupils of eyes by acting on iris
32. Fibers and Receptors: SD/ANS ? 2 - inhibits NE release (binds to adrenergic axon terminals); stimulates blood clotting
some sympathetic postganglionic fibers that innervate sweat glands (in skin), some blood vessels (skeletal muscles, brain, external genitalia) secrete ACh and are, therefore, cholinergic
See Table 14.3, p. 524
33. Fibers and Receptors: SD/ANS 2. Beta receptors (ß):
ß1 - generally stimulate:
heart (increases rate and strength of contraction)
kidneys (stimulates renin secretion [long pathway resulting in water retention and increased blood pressure - will study in AP II])
34. Fibers and Receptors: SD/ANS 2. Beta receptors (ß):
ß2 – mainly inhibition (smooth muscle relaxation)
lungs (smooth muscle of bronchi & bronchioles)
heart blood vessels (vasodilation)
many other sympathetic organs
stimulates secretion of insulin
ß3 – brown adipose tissue - stimulates hydrolysis (lipolysis) of stored fat - thermogenesis
35. Effects of Selected Drugs Atropine - anticholinergic (blocks effects of ACh by blocking muscarinic receptors [blocks parasympathetic])
suppresses salivation and respiratory secretions
used to dilate pupils for eye exam
dilates bronchi when inhaled
36. Effects of Selected Drugs Neostigmine - anticholinesterase
prevents breakdown of ACh at neuromuscular junction with skeletal muscle, thus allowing ACh to accumulate to sufficient levels at synapse
used in treatment of myasthenia gravis (autoimmune disorder in which ACh receptors of skeletal muscle are damaged)
does not cross blood-brain barrier
37. Effects of Selected Drugs Tricyclic antidepressants
prolong activity of NE and serotonin (prevent reuptake) on postsynaptic membranes within CNS --> feel good
also anticholinergic effects (cause sleepiness)
38. Effects of Selected Drugs Ephedrine, phenylephrine
sympathomimetic (mimic sympathetic effects)
both used to treat colds, allergies
phenylephrine – used to treat shock; used to treat nasal congestion (Neo-Synephrine)
stimulate alpha-1 receptors, which inhibit nasal and lacrimal secretion through peripheral vasoconstriction
ephedrine also causes bronchodilation and increases heart rate
phenylephrine used to treat shock due to strong action on blood vessels
39. Effects of Selected Drugs Beta blockers - block ß1 receptors of cardiac muscle
reduce heart rate
treat arrhythmias (errors in heart rhythm)
Phentolamine - alpha blocker (?1) used to treat hypertension (increased blood pressure)
used when hypertension is associated with excess sympathetic activity, as in when patient is also taking sympathomimetic drugs (e.g., Ephedrine, Phenylephrine)
40. Interactions of ANS Divisions most organs receive dual innervation
exceptions include:
adrenal medulla
almost all blood vessels
eccrine sweat glands
normally, one division dominates
e.g., parasympathetic activity normally keeps heart rate lower
in “emergency”, sympathetic overrules
41. Sympathetic and Parasympathetic Tone tone arises from near constant output of sympathetic or parasympathetic impulses
sympathetic tone used to maintain vasomotor tone (partial constriction) of blood vessels
parasympathetic tone
keeps heart rate lower
maintains partial contraction of GI tract organs (stomach, intestines)
maintains partial contraction of urinary system tubes (ureters)
42. Cooperative Effects of ANS Divisions usually antagonistic, but work together to accomplish certain goals,e.g.,
parasympathetic impulses cause vasodilation of blood vessels in genitalia (essential to erection - penis/clitoris),
sympathetic impulses essential to ejaculation
43. Unique Roles of SD/ANS SD provides only innervation to:
adrenal medulla
sweat glands
arrector pili muscles
most blood vessels
thermoregulation (maintenance of body temperature) - depends on SD which directs blood flow
release of renin from kidney (important to fluid balance and blood pressure)
metabolic effects (increases metabolism)
44. Local Versus Diffuse Effects Parasympathetic - short-lived, local effects
ACh acts indirectly at muscarinic receptors (smooth and cardiac muscle and glands)
ACh quickly hydrolyzed to acetyl CoA and choline by acetylcholinesterase (enzyme)
one preganglionic fiber synapses with only one or a few postganglionic fibers
45. Local Versus Diffuse Effects Sympathetic - longer lasting, more diffuse
NE works indirectly through second messenger
takes longer, but also lasts longer
NE not hydrolyzed, but taken back up into axonal terminals of postganglionic fibers
preganglionic fibers synapse with many postganglionic fibers (divergence), often at several levels
activation of adrenal medulla results in release of epinephrine and norepinephrine
46. Control of ANS Function:Brain Stem & Spinal Cord Medulla oblongata has most direct effects
centers for heart rate, vasomotor tone, respiration
center for GI tone
Pons - respiratory center influences respiratory centers in medulla
Midbrain - reflex centers controlling pupil size
Spinal cord - reflexes for urination, defecation, erection, ejaculation
can be overridden by conscious controls
47. Control of ANS Function:Hypothalamus exerts overall control
influences motor activity through reticular formation
also forms important part of limbic system controlling emotions
contains centers (groups of neurons with related functions) for:
heart activity
blood pressure
body temperature
water balance
endocrine activity
48. Control of ANS: Cortical Controls biofeedback - learned access of parasympathetic division
learn to lower heart rate, blood pressure through use of devices that give feedback on status of some part
concentrate on thoughts that calm, relax
49. Review of Upper Control
50. Visceral Reflex Arcs Same basic elements as somatic reflex arc
receptors in visceral organs (e.g, heart, blood vessels) respond to
chemical changes, stretch, irritation
visceral sensory neurons carry impulse toward CNS
51. Referred Pain sensory neurons of visceral pain travel same pathways as somatic sensory neurons serving nearby areas
referred pain occurs when visceral stimuli are perceived as somatic (more common pathway)