Download 1 BIOL 2401 CHAPTER 15: THE AUTONOMIC NERVOUS SYSTEM

BIOL 2401
DR. WELCH
CHAPTER 15: THE AUTONOMIC NERVOUS SYSTEM (ANS)
Quick Review:
Somatic Nervous System (SNS) – somatic sensory receptors (p. 615) & special senses (sight, smell, hearing, taste & equilibrium)
A. Sensations normally consciously received.
B. Motor neurons to skeletal muscles resulting in reflex or voluntary control. List an example of skeletal muscles that cannot
contract voluntarily?
1. Excitation of muscle always results in contraction.
2. Single neuron extends from CNS to skeletal muscle; myelinated
3. Release ONLY Ach as NT. Review Chapter 11 – NMJ.
ANS - maintains internal homeostasis; responds to subconscious visceral stimuli and excites or inhibits smooth & cardiac muscle as
well as glands (endocrine & exocrine). Operates via reflex arcs. Compare & contrast SNS vs. ANS.
I. Autonomic (Visceral) Sensory Receptors – relies mostly on interceptors
A. Interceptors – sensory receptors located in b.v., visceral organs, smooth & cardiac muscle. Not normally received
consciously. Give an example of each of the following.
1. Chemoreceptors
2. Mechanoreceptors
II. Autonomic Motor Neuron – regulates viscera by exciting OR inhibiting involuntary effector tissue. Refer to Fig. 15.1 p. 583, Table
15.1 p. 584 to Compare ANS vs. SNS Motor Neurons.
 Continues to function to some extent even if nerve supply is damaged.
 Cannot consciously be altered (99% rule); review biofeedback & limbic system.
A. Two motor neuron in a series
1. Preganglionic neuron –
a. Cell body in CNS to autonomic ganglion OR CNS to chromaffin cells in adrenal medulla
b. Type B fiber; Myelinated
2. Postganglionic neuron –
a. Autonomic ganglion in PNS to visceral effector
b. Type C fiber; unmyelinated
B. Release either ACh OR Norepinephrine (NE)
C. Output either sympathetic OR parasympathetic. Most organs have dual innervation.
III. Sympathetic Division – “fight-or-flight”; increased alertness & metabolic activity. List some examples.
A. Preganglionic neuron cell bodies begin in spinal cord @ lateral horn of all thoracic, L1 & L2. Referred to as
________________ division. Pass thru IVF  anterior root  white ramus  sympathetic trunk. Only Ti-T12 & L1L2.
1. Many axon branches & may synapse with 20> postganglionic neurons = divergence enables sympathetic
innervation of almost the entire body simultaneously.
B. Sympathetic Ganglia – site of pre & post synapse. 2 major groups:
1. Sympathetic Trunk - Arranged paravertebral.
a. Cervical ganglia/ plexus – Includes superior, middle, & inferior. All innervate b.v., sweat glands & the
heart.
i. Superior (Cervical) – pineal, lacrimal, parotid, sublingual & submandibular glands; mucosa of
nose & palate. Smooth muscle of eye, sweat glands & b.v. of head
ii. Middle (Thoracic 2-4) – Heart (Cardiac Plexus), lungs, bronchi, arrector pili.
iii. Inferior (Thoracic & lumbar) – Bronchial tree (Pulmonary Plexus)
2. Prevertebral (Collateral) Ganglia – lies anterior to spine. Innervates organs inferior to diaphragm. 5 plexuses:
a. Celiac (Solar) – largest autonomic plexus; distributed to stomach, spleen, pancreas, liver, gallbladder,
kidneys, adrenal medulla, testes & ovaries.
b. Superior Mesenteric/ Aorticorenal – supplies SI & proximal LI
c. Interior Mesenteric – LI  hypogastric plexus – pelvic viscera
d. Renal – renal arteries o kidneys & ureters.
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C. Postganglionic neurons – primarily innervate organs above the diaphragm; longer than preganglionic neurons. Leaves
sympathetic trunk by:
1. Spinal Nerves  gray rami  anterior ramus of spinal nerve (gray rami communicantes  innervates visceral
effectors in skin of neck, trunk, & limbs; unmyelinated.
2. Cephalic Periarterial Nerves – ascend (ex. around carotid) to head from neck  innervated visceral effectors in
skin of face & others of head (eye, salivary glands &nasal mucosa.
3. Sympathetic Nerves – extend through thoracic cavity – heart (celiac ganglia T1-T4); bronchial tree (T2-T4)
4. Splanchnic Nerves  prevertebral ganglia to:
a. Abdominopelvic Organs –
1. Greater Splanchnic Nerve – Greater, lesser, least & lumbar  pierces diaphragm then enters:
i. Celiac ganglion (T5-T9 or 10) innervates b.v. to stomach, spleen, liver, kidneys & SI
ii. Lesser Splanchnic Nerve (T10-T11) – SI & proximal colon
iii. Least (lowest) Splanchnic Nerve (T12) – supplies kidney arterioles & ureters.
iv. Lumbar Splanchnic Nerve (L1-L4)  inferior mesenteric ganglion – supplies distal
colon & rectum;  hypoglossal plexus – supplies b.v. of distal colon, rectum, urinary
bladder, & genital organs.
b. Adrenal Medulla – extend to chromaffin cells with synapsing prior to; lack dendrites & axons. Release
catecholamine hormones into blood (80% Epinephrine, 20% NE, & trace dopamine.
IV. Parasympathetic Division – “rest-and-digest”; conserve & restore energy. List some examples.
A. Preganglionic neuron cell bodies begin in spinal cord in nuclei of CN III, VII, IX, X) and lateral horn of C2-S4. Referred to
as ________________ division.
B. Parasympathetic Ganglia/ Nerves – terminal (intermural) ganglia d/t located close to viscera. Postganglionic neuron are
shorter than sympathetic. Usually synapse with only 4-5 postganglionic neurons = localized single effector.
1. Ciliary ganglion – pass with CN III innervate smooth muscle of eyeball. Refer to Fig. 17.8 p. 646.
2. Pterygopalatine – from CN VII to nasal mucosa, palate, pharynx, & lacrimal glands.
3. Submandibular – from CN VII to submandibular & sublingual glands.
4. Otic – from CN IX to parotid glands.
5. Vagus (80%) to thorax (heart & lungs) & abdomen (liver, GB, stomach, pancreas, SI & part of LI.
6. Pelvic Splanchnic Nerves (S2-S4) – innervate smooth muscle & glands in colon, ureters, UB, & reproductive
organs.
*Refer to Table 15.3 p. 597 to compare & contrast Sympathetic vs. Parasympathetic Divisions.
V. Enteric Division – GI homeostasis; can & does function independently of CNS controlling GI, pancreas & GB by regulating motility
and secretory activity. 2 Enteric Plexuses: refer to Fig. 24.2 p. 970.
A. Myenteric Plexus – between outer longitudinal & circular layer from _________________ to the _______________.
1. Communicates with smaller plexus
B. Submucosal Plexus – between circular muscle & muscularis mucosae running from ______________ to the __________.
VI. NT & Receptors – 2 major groups: Refer to Table 15.2 p. 595.
A. Cholinergic Neurons – release Ach from synaptic vesicles by exocytosis then binds with specific receptor located on a
integral protein in the postsynaptic plasma membrane. Includes:
1. All Sympathetic & Parasympathetic preganglionic neurons
2. Sympathetic postganglionic neurons to most sweat glands
3. All Parasympathetic postganglionic neurons NOTE: All parasympathetic neurons release Ach.
4. 2 types of receptors. *Nicotine & muscarine do not active the others receptors; but ACh can.*
a. Nicotinic Receptors – named b/c nicotine mimics ACh. ACh causes ________________. Present in:
i. Both sympathetic & parasympathetic postganglionic neurons
ii. Chromaffin cells of adrenal medulla
iii. Motor end plate of NMJ
b. Muscarinic Receptors – named b/c action of mushroom poison (muscarinic) mimics ACh. ACh causes
______________________ or _________________Present in:
i. All effectors (smooth muscle, cardiac muscle & glands) innervated by parasympathetic
postganglionic axons.
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ii. Most sweat glands (sympathetic)
5. Uptake of ACh - Quickly inactivated by ______________ making effects brief.
B. Andrenergic Neurons – release NE (aka. noradrenalin) from synaptic vesicles via exocytosis causing excitation OR
inhibition. Present in:
1. Most sympathetic postganglionic neurons (except sweat glands). Effector cells can contain one type of
receptors or both. NE stimulates α receptors more strongly; epi stimulated both α & β strongly
2. 2 types of Receptors – which bind both epi (hormone) & NE (NT or hormone via chromaffin cells).
a. Alpha (α) Receptors – 2 subgroups
i. α1 – cause excitation (90% rule)
ii. α2 - cause inhibition (90% rule)
b. Beta (β) Receptors – 3 subgroups; Which condition would a beta blocker be prescribed & how does it
work?
i. β1 - cause excitation (90% rule)
ii. β2 - cause inhibition (90% rule)
iii. β3 – only present in brown adipose (thermogenesis)
3. Uptake of NE by presynaptic axon or enzyme (COMT or MAO); lingers in synaptic cleft therefore last longer.
VII. Prescription Drugs - Receptor Agonists & Antagonists
A. Agonists – bind to activate receptor by mimicking a natural NT or hormone.
1. Phenylephrine (α1) ingredient used in cold/sinus meds to constrict b.v. in nasal mucosa & reduce mucus
production.
B. Antagonist – bind to block receptor preventing a natural NT or hormone.
1. Atropine (muscarinic) – blocks ACh resulting in dilates pupils, reduces glandular secretions & relaxes smooth
muscles of GI. Used to reduce iritis, hypermotility of GI & agents that inactivate AChesterase.
2. Propranolol (Inderal) – nonselective β blocker meaning that it binds to all beta receptors blocking NE & epi.
Used to treat HTN. What are contraindications of this Rx?
3. Why would you need to prescribe Lopressor instead?
VIII. Physiology of ANS – What is autonomic tone & what regulates it? Sympathetic & Parasympathetic responses. Refer to Table
15.4 p. 598 for comparison.
A. Sympathetic Response – dominates during physical & emotional stress. What are “E” situations?
1. Note: items innervated by sympathetic division only: sweat glands, arrector pili, kidneys, spleen, most b.v. &
adrenal medulla.
B. Parasympathetic Response – conserves & stores energy (glycogen) during rest & recovery. What does the acronym
SLUDD mean? Also results in decreased HR, bronchoconstriction & constriction of the pupils.
IX. Autonomic Reflexes – play a key role in blood pressure, digestion, defecation & urination.
X. Autonomic Control – _________________ is the major control & integration center. Posterior & lateral region control
sympathetic division. Anterior & medial control parasympathetic.
A. Sensory input – olfaction & gustation (special senses) as well as temperature, osmolarity, & chemical.
1. Related to emotion thru ______________________.
B. Motor output – from hypothalamus to
1. Brain stem (CV, salivation, swallowing, & vomiting centers). What 3 structures make up the brain
stem?
2. Spinal Cord (sacral region) – defecation & urination reflex.
Review all Clinical Connections, Disorders: Homeostatic Imbalances, & Medical Terminology (back of chapter).
This is only a general outline. There may be material that has been discussed in lecture that is not included in this outline and there may be material
on this outline that has not been discussed in lecture. Any material discussed in lecture or listed in this outline is "fair game" for the test.
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