⬅ Home
18# Autonomic Nervous System
1. Which neurons form the efferent limb of the autonomic nervous system?
Only postganglionic neurons
Only preganglionic neurons
Preganglionic and postganglionic neurons
Somatic motor neurons
Explanation:
Autonomic efferent pathways consist of a two-neuron chain: preganglionic and postganglionic neurons.
2. A major reason for the rapid and widespread action of the ANS is:
Fast conduction velocity
Large diameter fibers
Presence of reflex arcs
Divergence of preganglionic fibers
Explanation:
One preganglionic neuron can synapse with many postganglionic neurons, causing widespread effects.
3. Which fibers are long and myelinated?
Parasympathetic preganglionic
Parasympathetic postganglionic
Sympathetic postganglionic
Visceral afferent fibers
Explanation:
Parasympathetic preganglionic fibers are long and myelinated.
4. Which effect is characteristic of sympathetic activation?
Bronchoconstriction
Pupillary dilation
Increased peristalsis
Bladder contraction
Explanation:
Sympathetic stimulation causes mydriasis (pupil dilation).
5. Sympathetic preganglionic neurons originate from which spinal segments?
C1–C8
L4–S4
T1–L2 (or L3)
S2–S4
Explanation:
Sympathetic outflow originates from the lateral gray columns of T1–L2/3 segments.
6. White rami communicantes carry:
Preganglionic sympathetic fibers
Postganglionic sympathetic fibers
Parasympathetic fibers
Visceral afferent fibers only
Explanation:
White rami communicantes contain myelinated preganglionic sympathetic fibers.
7. Which structure receives preganglionic fibers that secrete epinephrine directly?
Celiac ganglion
Superior mesenteric ganglion
Renal plexus
Suprarenal medulla
Explanation:
Preganglionic fibers synapse directly on adrenal medullary cells, which act as modified neurons.
8. The greater splanchnic nerve is formed from which thoracic ganglia?
T1–T4
T5–T9
T10–T11
T12 only
Explanation:
The greater splanchnic nerve arises from T5–T9 sympathetic ganglia.
9. Visceral pain afferents from sympathetic pathways have their cell bodies in:
Autonomic ganglia
Anterior horn
Posterior root ganglia
Hypothalamus
Explanation:
Visceral afferent cell bodies are located in posterior (dorsal) root ganglia.
10. The ganglion impar is located at:
Upper thorax
Celiac region
L5 level
Termination of sympathetic trunks
Explanation:
The two sympathetic trunks unite inferiorly to form the ganglion impar.
11. Parasympathetic activity produces which effect?
Bronchoconstriction
Pupil dilation
Reduced glandular secretion
Closure of sphincters
Explanation:
Parasympathetic system causes bronchial smooth muscle contraction.
12. Which cranial nerve carries parasympathetic fibers from the dorsal motor nucleus?
CN III
CN VII
CN IX
CN X
Explanation:
The vagus nerve (CN X) originates from the dorsal motor nucleus.
13. Pelvic splanchnic nerves originate from which spinal segments?
L1–L3
S2–S4
T12–L2
S1–S3
Explanation:
Pelvic splanchnic nerves arise from S2–S4 segments.
14. Which plexus controls gut motility?
Meissner plexus
Submucosal plexus
Auerbach (myenteric) plexus
Celiac plexus
Explanation:
The myenteric (Auerbach) plexus controls gut wall movements.
15. Which autonomic plexus supplies pelvic viscera?
Celiac plexus
Superior mesenteric plexus
Inferior mesenteric plexus
Inferior hypogastric plexus
Explanation:
Pelvic organs are innervated by the inferior hypogastric plexus.
16. Parasympathetic ganglia are typically located:
Within or near target organs
Along the vertebral column
In the dorsal root ganglia
Near the spinal cord
Explanation:
Parasympathetic ganglia lie close to or within the walls of viscera.
17. Which transmitter is released by most sympathetic postganglionic fibers?
Acetylcholine
Dopamine
Norepinephrine
Serotonin
Explanation:
Most sympathetic postganglionic fibers release norepinephrine.
18. The submucosal (Meissner) plexus mainly controls:
Gut motility
Glandular secretion
Visceral pain
Sphincter tone
Explanation:
Meissner plexus regulates glandular secretion and mucosal blood flow.
19. Sympathetic innervation to the stomach synapses in which ganglia?
Inferior mesenteric
Hypogastric
Pelvic
Celiac and superior mesenteric
Explanation:
Sympathetic fibers synapse in celiac and superior mesenteric ganglia.
20. Parasympathetic innervation of the descending colon arises from:
Pelvic splanchnic nerves
Vagus nerve
Lumbar splanchnic nerves
Celiac plexus
Explanation:
Hindgut parasympathetic supply is via pelvic splanchnic nerves (S2–S4).
21. Which structure lacks parasympathetic innervation?
Intestinal smooth muscle
Arrector pili muscle
Bronchial smooth muscle
Bladder wall
Explanation:
Arrector pili muscle is supplied only by sympathetic fibers.
22. Gray rami communicantes contain:
Myelinated preganglionic fibers
Visceral afferents
Unmyelinated postganglionic fibers
Parasympathetic fibers
Explanation:
Gray rami carry unmyelinated postganglionic sympathetic fibers to spinal nerves.