Chapter 14: The Autonomic Nervous System

These flashcards cover the key concepts of the Autonomic Nervous System including its divisions, anatomy, neurotransmitters, receptors, and physiological effects based on the provided lecture slides.

What effectors are innervated by the Autonomic Nervous System (ANS)?

Smooth muscles, cardiac muscle, and glands.

What are two other names for the Autonomic Nervous System?

Involuntary nervous system or visceral motor system.

In terms of the number of neurons, how does the Somatic Nervous System (SNS) differ from the ANS?

The SNS uses a single neuron from the CNS to the effector, while the ANS uses a two-neuron chain.

What kind of axon does a somatic motor neuron have?

A single, thick myelinated group A axon.

What are the two neurons involved in the ANS motor pathway?

The preganglionic neuron (cell body in CNS) and the postganglionic neuron (cell body in autonomic ganglion outside CNS).

What are the fiber characteristics of a preganglionic ANS neuron?

A thin, lightly myelinated preganglionic axon.

Which neurotransmitter is released by all somatic motor neurons?

Acetylcholine ($ACh$).

Which neurotransmitter is released by all ANS preganglionic fibers?

Acetylcholine ($ACh$).

What neurotransmitter is released by most sympathetic postganglionic fibers?

Norepinephrine ($NE$).

What neurotransmitter is released by most parasympathetic postganglionic fibers?

Acetylcholine ($ACh$).

What is the effect of neurotransmitters on effectors in the SNS?

The effect is always excitatory.

How do the two divisions of the ANS maintain homeostasis?

Through dynamic antagonism, where both divisions serve the same organs but cause opposite effects.

What are the three D's that characterize the parasympathetic division?

Digestion, diuresis, and defecation.

Which division of the ANS is known as the 'fight-or-flight' system?

The sympathetic division.

What is the anatomical site of origin for the parasympathetic division?

Craniosacral; fibers originate in the brain stem and sacral spinal cord.

What is the anatomical site of origin for the sympathetic division?

Thoracolumbar; fibers originate in the thoracic and lumbar regions of the spinal cord ($T_1$ through $L_2$).

Compare the lengths of the preganglionic and postganglionic fibers in the parasympathetic division.

Long preganglionic and short postganglionic fibers.

Compare the lengths of the preganglionic and postganglionic fibers in the sympathetic division.

Short preganglionic and long postganglionic fibers.

Where are the ganglia located in the parasympathetic division?

In or near the visceral effector organs (terminal ganglia).

Where are the ganglia located in the sympathetic division?

Close to the spinal cord (sympathetic trunk ganglia or collateral ganglia).

Which four cranial nerves contain parasympathetic preganglionic fibers?

Oculomotor ($III$), Facial ($VII$), Glossopharyngeal ($IX$), and Vagus ($X$).

What percentage of all preganglionic parasympathetic fibers are accounted for by the vagus nerves?

$90\%$.

Where do the preganglionic fibers of the sacral part of the parasympathetic division originate?

In neurons of $S_2$ to $S_4$.

Which structures are innervated only by the sympathetic division?

Sweat glands, arrector pili muscles, and smooth muscles of all blood vessels.

What structure allows preganglionic sympathetic fibers to enter the sympathetic trunk ganglia?

White ramus communicans.

What are the three possible synapse pathways for a sympathetic preganglionic axon once it enters a trunk ganglion?

Synapse at the same level, synapse at a higher or lower level, or synapse in a collateral ganglion.

What is the pathway for postganglionic sympathetic axons to enter the ventral ramus of a spinal nerve?

Via the gray rami communicantes.

Which ramus communicans contains myelinated preganglionic axons?

White rami communicantes.

Which ramus communicans contains nonmyelinated postganglionic axons?

Gray rami communicantes.

What are the medullary chromaffin cells of the adrenal medulla responsible for secreting?

$80\%$ epinephrine and $20\%$ norepinephrine.

Which fibers are classified as cholinergic?

Fibers that release $ACh$, including all ANS preganglionic axons and all parasympathetic postganglionic axons.

Which fibers are classified as adrenergic?

Fibers that release $NE$, specifically almost all sympathetic postganglionic axons (except those at sweat glands).

What are the two types of cholinergic receptors?

Nicotinic receptors and Muscarinic receptors.

Where are nicotinic receptors found?

All postganglionic neurons, hormone-producing cells of the adrenal medulla, and the sarcolemma of skeletal muscle cells.

Is the effect of $ACh$ at nicotinic receptors excitatory or inhibitory?

It is always excitatory.

Where are muscarinic receptors found?

On all effector cells stimulated by postganglionic cholinergic fibers.

What are the two major classes of adrenergic receptors?

Alpha ($\alpha$) and Beta ($\beta$).

What effect does $NE$ have when binding to $\beta_1$ receptors of the heart?

Increases heart rate and force of contraction.

What drug is used to treat glaucoma by opening aqueous humor drainage pores?

Pilocarpine.

What is the clinical application of Albuterol?

It treats asthma by dilating bronchioles through binding to $\beta_2$ receptors.

What is sympathetic (vasomotor) tone?

A continual state of partial constriction of blood vessels maintained by sympathetic fibers.

What is the result of drugs that block parasympathetic responses?

Increased heart rate and fecal and urinary retention.

What is the best example of cooperative effects between the ANS divisions?

Control of external genitalia; parasympathetic causes erection and sympathetic causes ejaculation/contraction.

What is autonomic neuropathy?

Damage to autonomic nerves, often a complication of diabetes mellitus.

How does the sympathetic division respond to dropping body temperatures?

It causes blood vessels to constrict.

What metabolic effects does the sympathetic division trigger?

Increases metabolic rates, raises blood glucose levels, and mobilizes fats for fuel.

Why are sympathetic effects longer-lasting than parasympathetic effects?

$NE$ is inactivated more slowly than $ACh$, and adrenal hormones have prolonged effects.

Which part of the brain is the main integrative center of ANS activity?

Hypothalamus.

What is the clinical description of hypertension?

An overactive sympathetic vasoconstrictor response to stress.

What are the symptoms of Raynaud’s disease?

Painful, exaggerated vasoconstriction in fingers and toes, making digits turn pale and then cyanotic.