Autonomic Nervous System (ANS) & Review – Week 13

These flashcards review key structural, functional, and clinical concepts of the autonomic nervous system (ANS), contrasting sympathetic and parasympathetic divisions, neurotransmitter pathways, anatomical ganglia, autonomic plexuses, visceral reflexes, pharmacology, and related clinical syndromes.

What structures does the autonomic nervous system (ANS) primarily control and regulate?

Smooth muscle, cardiac muscle, and glands.

How many neurons are in a typical ANS motor pathway, and where are their cell bodies located?

Two; the pre-ganglionic neuron’s cell body is in the brainstem or spinal cord, and the post-ganglionic neuron’s cell body is in a ganglion outside the CNS.

What is the key difference in neuron number between the somatic motor system and the autonomic motor system?

Somatic uses a single motor neuron to the effector; autonomic uses a two-neuron chain (pre- and post-ganglionic).

Which division of the ANS innervates the skin (sweat glands, arrector pili, cutaneous blood vessels)?

The sympathetic division.

From which spinal cord levels do sympathetic pre-ganglionic cell bodies arise?

Thoracic (T1–T12) and lumbar (L1–L2) segments.

Describe the relative lengths of sympathetic pre- and post-ganglionic fibers.

Sympathetic pre-ganglionic fibers are short; post-ganglionic fibers are long.

What neurotransmitter is released by ALL pre-ganglionic autonomic neurons (both sympathetic and parasympathetic)?

Acetylcholine (ACh).

What is the usual neurotransmitter released by sympathetic post-ganglionic neurons at most target organs?

Norepinephrine (NE).

Which sympathetic pathway uses ACh at both the pre- and post-ganglionic synapses?

The pathway to sweat glands (ACh → ACh).

What endocrine organ acts as a modified sympathetic ganglion, releasing epinephrine into the bloodstream?

The adrenal medulla.

How many paired sympathetic (paravertebral) ganglia exist in the sympathetic trunk?

Twenty-three paired ganglia, plus one unpaired coccygeal ganglion.

Through which structure do sympathetic pre-ganglionic fibers ENTER the sympathetic trunk?

White rami communicantes.

Through which structure do sympathetic post-ganglionic fibers LEAVE the sympathetic trunk to re-enter spinal nerves?

Gray rami communicantes.

Name the three major pre-vertebral (collateral) sympathetic ganglia associated with abdominal aortic branches.

Celiac, superior mesenteric, and inferior mesenteric ganglia.

Which cranial nerves carry parasympathetic fibers from the brainstem?

Cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal), and X (vagus).

From which spinal cord segments do sacral parasympathetic pre-ganglionic neurons arise?

Segments S2–S4 (pelvic splanchnic nerves).

Compare the lengths of parasympathetic pre- and post-ganglionic fibers.

Parasympathetic pre-ganglionic fibers are long, and post-ganglionic fibers are short (often within or near the target organ).

What general bodily state is promoted by the parasympathetic division?

“Rest and digest” (conservation of energy, digestion, and maintenance functions).

What general bodily state is promoted by the sympathetic division?

“Fight or flight” (preparation for physical activity and emergencies).

What forms an autonomic plexus?

A mix of sympathetic post-ganglionic axons, parasympathetic pre-ganglionic axons, and visceral sensory fibers.

List two major autonomic plexuses found in the thorax.

Cardiac plexus and pulmonary plexus.

What is a visceral reflex, and what neurons are involved in its efferent limb?

An unconscious, automatic, stereotyped response of visceral effectors; the efferent limb uses pre-ganglionic and post-ganglionic autonomic neurons.

What is the pharmacologic action of muscarinic antagonists?

They competitively inhibit post-ganglionic parasympathetic (muscarinic) ACh receptors (anticholinergic effect).

Give three clinical signs of muscarinic antagonist (anticholinergic) overdose.

Dry mouth, dilated pupils with photophobia, increased heart rate (others include hyperthermia, GI ileus, urinary retention).

What triad of symptoms characterizes Horner’s syndrome due to sympathetic trunk damage?

Ptosis (drooping eyelid), miosis (constricted pupil), and anhidrosis (loss of sweating) on the affected side of the face.