Chapter 14: The Autonomic Nervous System

Question 1

Autonomic Nervous System:

Answer 1

• The system of motor neurons that innervates smooth and cardiac muscle.
• Also called the involuntary nervous system or the general visceral motor system.

Question 2

Somatic Nervous System:

Answer 2

Deals primarily with the body’s external environment.o Motor neuron cell bodies in the CNS axons in spinal/cranial nerves extend to skeletal muscles they activate.
o Somatic Motor Fibers: Thick, heavily myelinated group A fibers that conduct nerve impulses rapidly.
o Releases ACh- which gives an excitatory/stimulating effect.

Question 3

Somatic Nervous System Input:

Answer 3

(afferent) Comes from somatic sensory neurons; skin, special &general senses.

Question 4

Somatic Nervous System Output:

Answer 4

(efferent) somatic motor neurons primarily innervate body wall; Skeletal muscles, joint. Produces conscious voluntary movement. Voluntary nervous system.

Question 5

Structures and Details about the ANS:

Answer 5

o Deals primarily with the body’s internal environment.
o ANS Input: (afferent) comes from autonomic sensory neurons in blood vessels & internal body organs (viscera).
o ANS Output: (efferent) commands (motor control): smooth muscle; cardiac muscle; glands; adipose tissue.
o Uses two-neuron efferent motor chain.
• Preganglionic Neuron: (In CNS), motor neuron cell body is in brain/spinal cord; has a thin, lightly myelinated preganglionic axon.
• Postganglionic (ganglionic) neuron: Cell Body in autonomic ganglion outside the CNS has nonmyelinated postganglionic axon that extends to effector organ.
o Releases Norepinephrine (sympathetic) or ACh (parasympathetic). Stimulatory or inhibitory depending on type of receptors.

Question 6

The 2 Divisions of the ANS:

Answer 6

o	Parasympathetic: 
•	Promotes maintenance functions.
•	Conserves body energy
•	Rest & Digest
o	Sympathetic: 
•	Mobilizes body during activity.
•	“Fight or Flight” 
•	Occurs during situations of exercise, excitement, emergency, or embarrassment.

Question 7

Dual Innervation:

Answer 7

• One division stimulates certain smooth muscles to contract or a gland to secrete; the other division inhibits this action.
• Both sympathetic and parasympathetic systems are simultaneously active, each branch keeping the other in homeostatic balance.
• Over- or Under- activation of either branch can disrupt homeostasis.

Question 8

Dual Innervation in Smooth Muscle of Iris(EYES):

Answer 8

o Parasympathetic: Causes constriction of the pupils.

o Sympathetic: Causes dilation of the pupils.

Question 9

Dual Innervation in Smooth Muscle of Bronchioles of Lungs:

Answer 9

o Parasympathetic: Causes Bronchoconstriction.

o Sympathetic: Causes Bronchodilation.

Question 10

How is Homeostasis Maintained in the ANS?

Answer 10

Due to the dynamic antagonism between the two divisions of the ANS.

Question 11

Parasympathetic Nervous System Effects:

Answer 11

o SLUDD: Salivation, Lacrimation, Urination, Digestive Functions, Defacation
o Favors body functions that can calm, conserve& restore body energy.
o Reduces activities or functions that consume energy.
o Decrease heart rate, decrease Blood pressure, bronchoconstriction, constriction of pupils, increased digestive motility, increased digestive secretion, increased feces formation & defecation, increased urine formation, store glycogen, contract ciliary muscles of eye for close-up vision.

Question 12

Sympathetic Nervous System Effects:

Answer 12

o “e” situations: Emergency, Exercise, Excitement, Escape.
o Favors body functions that can support vigorous physical activity.
o Reduces non-essential activities or functions that favor energy storage.
o Increased heart rate& increased force of contraction of heart, increased blood pressure, bronchodilation, dilates pupils, stimulate sweat glands, piloerection, decreases digestive tract motility & secretions, decreases urine formation.

Question 13

Origin of Parasympathetic Fibers in the ANS:

Answer 13

Craniosacral- Originate in the brain and spinal cord.

Question 14

Origin of Sympathetic Fibers in the ANS:

Answer 14

Thoracolumbar- Originate in the thoracic and Lumbar regions of the spinal cord.

Question 15

Length of Fibers in the Parasympathetic Division of ANS:

Answer 15

o Has long, slightly myelinated preganglionic
o Typically non-branching, sometimes very few with little divergence.
o Short, unmyelinated postganglionic fibers that are sometimes located in the wall of the target organ.

Question 16

Length of Fibers in the Sympathetic Division of ANS:

Answer 16

o Has short, slightly myelinated preganglionic fibers
o Typically with diffuse branching, and can synapse on as many as 20 Postganglionic somas.
o Long, unmyelinated postganglionic fibers that extend to target organs.

Question 17

Ganglia Location in the Parasympathetic Division of ANS:

Answer 17

o Located in visceral effector organs.
o Preganglionic fibers spring from brain stem and sacral region.
o Axons extend from CNS nearly all way to innervate structures.
o Soma of preganglionic neuron is either in the nuclei of cranial nerves in the brainstem( Cranial Nerves: III, VII, IX, X) or in lateral gray areas of S2-S4 of spinal cord.
o Axons synapse with postganglionic neurons.
o Ganglia are very close to target tissues, referred to as terminal or intramural ganglia.

Question 18

Ganglia Location in the Sympathetic Division of ANS:

Answer 18

o Located close to the spinal cord.
o Innervate more organs.
o Supplies visceral organs in internal body cavities.
o Supplies visceral structures in superficial (somatic) part of body.
o Some glands & smooth muscle structures in soma(sweat glands, and arrector pili. require autonomic innervation.
o Innervates smooth muscles in walls of all arteries & veins (deep and superficial).
o Thoracolumbar division.
o Soma/cell body of preganglionic neuron in lateral gray horn of T1-L2 in spinal cord. Forms lateral gray horns.
o Ganglia are usually close to vertebral column.

Question 19

Sympathetic Nervous System Structures:

Answer 19

o Sympathetic Chains: Chains of connected ganglia that extend from the neck to the pelvis.
o Located anterior and lateral to vertebral column (2 chains).
o Rami Communicantes: Communicate with spinal nerves via these.
o White Rami Communicans: Myelinated sympathetic preganglionic axons that connect ventral ramus of a spinal nerve to the sympathetic trunk.
o Gray Rami Communicans: unmyelinated sympathetic postganglionic axons that allow the axon to travel back to the spinal nerve.
o Sympathetic Ganglia: Are collections of cell bodies (somas) of postganglionic neurons.
• 3 Cervical
• 11-12 Thoracic
• 4-5 Lumbar
• 4-5 Sacral
• 1 Coccygeal

Question 20

Sympathetic Nervous System Pathways:

1) Preganglionic Axons

Answer 20

o Preganglionic axons: leave spinal cord via ventral roots, then leave spinal nerve via a white ramus communicans to enter the sympathetic chain(trunk).
o Some preganglionic neurons synapse at the same level, other synapse at higher or lower levels. (Most diverge and synapse at multiple levels)

Question 21

Sympathetic Nervous System Pathways:

2) Trunk Ganglion

Answer 21

o Once a preganglionic reaches a trunk ganglion, the preganglionic and postganglionic neurons can take one of three pathways : 1) Synapse at the same level; in the same trunk ganglion. 2) Synapse at a higher or lower level; preganglionic axon ascends/descends sympathetic trunk to another ganglion. 3) Preganglionic neurons that serve structures in the abdominopelvic cavity don’t synapse in the sympathetic chain, they pass through the sympathetic chain without synapsing and travel by way of splanchnic nerves to collateral prevertebral ganglia.

Question 22

Sympathetic Nervous System Pathways:

3) Collateral Ganglia

Answer 22

o Collateral ganglia aren’t paired. They’re located anterior to the vertebral column amid the abdominopelvic plexuses; Celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion.

Question 23

Sympathetic Nervous System Pathways:

4) Sympathetic Chain

Answer 23

o When the preganglionic neuron synapses on a postganglionic soma in the sympathetic chain, the post ganglionic axon has options: 1) It can leave the sympathetic chain and return to a spinal nerve via a gray ramus communicans. This usually happens in the effector in the body wall. 2) The axon of the postganglionic neuron can leave the sympathetic chain via “new” nerves called sympathetic nerves to serve effectors in the thoracic cavity.

Question 24

Sympathetic Nervous System Pathways:

5) Abdominopelvic cavity

Answer 24

o When the preganglionic neuron synapses on a postganglionic soma in the collateral ganglia, the postganglionic axon will leave the collateral ganglion to serve various organs in the abdominopelvic cavity: Postganglionic axons from the celiac ganglion innervate; stomach, spleen, liver, pancreas, kidneys, small part of small intestine. Postganglionic axons from superior mesenteric ganglion innervate; small intestine, proximal ½ large intestine. Postganglionic axons from inferior mesenteric ganglion innerate; Distal ½ large intestine, urinary bladder, reproductive organs.

Question 25

Sympathetic Nervous System Pathways:

Exceptions

Answer 25

o Some preganglionic neurons are an exception to these choice, they leave the spinal cord via the ventral roots of T5, and travel to sympathetic chain. They don’t synapse in the sympathetic chain, they pass through the sympathetic chain and travel to the celiac ganglion. Then they keep going until they synapse directly on the adrenal medulla. Norepinephrine and epinephrine catecolamines are then released.

Question 26

Visceral ANS Reflexes:

Answer 26

o Visceral reflex arcs have same components as somatic reflex arcs (chemical changes, stretch, and irritation of viscera), but visceral reflex arc has two neurons in motor pathway (preganglionic and postganglionic)
o Visceral pain afferents travel along same pathways as somatic pain fibers, contributing to phenomenon of referred pain.

Question 27

Neurotransmitters:

Cholinergic Fibers

Answer 27

• Release NT ACh
• All ANS preganglionic axons
• All parasympathetic postganglionic axons at effector synapse
o 2 Types: Nicotinic and Muscarinic
o Named after drugs that bind to them and mimic ACh effects.
o Nicotinic:
• Found on Sarcolemma of skeletal muscle cells at NMJ.
• All postganglionic neurons (sympathetic and parasympathetic)
• Hormone-producing cells of adrenal medulla
• Effect: ACh at nicotinic receptors is always excitatory/stimulatory
• Opens ion channels, depolarizing postsynaptic cell
o Muscarinic:
• Found on all effector cells stimulated by postganglionic cholinergic fibers
• Effect of ACh at muscarinic receptors can either be inhibitory or excitatory depending on receptor type of target organ.

Question 28

Neurotransmitters:

Adrenergic Fibers

Answer 28

• Release NT NE
• Most sympathetic postganglionic axons
• EXCEPTION: sympathetic postganglionic fibers secrete ACh at sweat glands.
• B1: Heart, kidneys, and adipose tissue. Increases heart rate and force of contraction; stimulates kidneys to release renin.
• B2: Lungs and most other sympathetic target organs; abundant on blood vessels serving the heart, live, and skeletal muscle. Effects mostly inhibitory; dilates blood vessels and bronchioles, release smooth muscle walls of digestive and urinary visceral organs, relaxes uterus.
• B3: Adipose tissue. Stimulates lipolysis by fat cells.
• A1: Most important blood vessels serving skin, mucosae, abdominal viscera, kidneys and salivary glands, also virtually all sympathetic target organs except heart. Constricts blood vessels and visceral organ sphincters, and dilates pupils of eyes.
• A2: Membrane of adrenergic axon terminals; pancreas; blood platelets. Inhibits NE release from adrenergic terminals; inhibits insulin secretion by pancreas, promote blood clotting.

Question 29

Drugs Dealing with Conditions of the ANS:

Answer 29

o Atropine: Anticholinergic; blocks muscarinic ACh receptors. Used to prevent salivation during surgery, and to dilate pupils for examination.
o Neostigmine: Inhibits acetylcholinesterase that breaks down ACh. Used to treat myasthenia gravis.
o Over-The-Counter drugs for colds, allergies, and nasal congestion: Stimulate a-Adrenergic receptors
o Beta-Blockers: Drugs that attach to B2 receptors to dilate lung bronchioles in asthmatic; other uses.

Question 30

Interactions of the Autonomic Divisions:

Answer 30

o Most visceral organs have dual innervation.
o Dynamic antagonism allows for precise control of visceral activity
o Sympathetic division increases heart and respiratory rates, and inhibits digestion and eliminations.
o Parasympathetic division decreases heart and respiratory rates, and allows for digestion and discarding of wastes.