Autonomic Innervation — MCQs
The aortic hiatus is formed by the right and left crura of the diaphragm. Which of the following structures does NOT pass through the aortic hiatus?
Damage to pneumotaxic center along with vagus nerve causes which type of respiration?
TRUE statement regarding nerve supply of adrenal gland:
Long thoracic nerve arises from which nerve roots?
Which of the following fiber types is classically categorized as Group B nerve fibers?
Which of the following structures in the central nervous system contains major autonomic reflex centers?
Anisocoria in Horner's syndrome is due to
The primary effect of vagal stimulation on the heart is
A 32-year-old lady presents with shoulder tip pain. She is diagnosed with Pancoast tumor and presents with miosis. What is the most likely associated diagnosis?
Which nerve primarily supplies the cervical esophagus?
Autonomic Innervation Indian Medical PG Practice Questions and MCQs
Question 1: The aortic hiatus is formed by the right and left crura of the diaphragm. Which of the following structures does NOT pass through the aortic hiatus?
- A. Thoracic duct
- B. Left vagus nerve
- C. Left gastric vein (Correct Answer)
- D. Azygos vein
Explanation: ***Left gastric vein*** - The **left gastric vein** is part of the **portal venous system** and drains into the portal vein. - It **does NOT pass through the diaphragm** via the aortic hiatus or any other diaphragmatic opening. - It has **no anatomical relationship** with the aortic hiatus, making it the best answer to this question. *Thoracic duct* - The **thoracic duct** is the largest lymphatic vessel in the body and **passes through the aortic hiatus** along with the aorta. - It ascends through the aortic hiatus at the **T12 vertebral level** to eventually drain into the left subclavian vein. - It lies posterior to the aorta as it traverses the hiatus. *Left vagus nerve* - The **left vagus nerve** does NOT pass through the aortic hiatus, but it **does pass through the esophageal hiatus** at the T10 level. - It contributes to the **anterior vagal trunk** as it enters the abdomen with the esophagus. - While this structure doesn't pass through the aortic hiatus, it does traverse the diaphragm through a different opening, making it a less definitive answer than the left gastric vein. *Azygos vein* - The **azygos vein** typically **passes through the aortic hiatus** alongside the aorta and thoracic duct. - It may occasionally pass through a separate opening in the right crus of the diaphragm. - It collects deoxygenated blood from the posterior walls of the thorax and abdomen before draining into the superior vena cava.
Question 2: Damage to pneumotaxic center along with vagus nerve causes which type of respiration?
- A. Cheyne-Stokes breathing
- B. Deep and slow breathing
- C. Shallow and rapid breathing
- D. Apneustic breathing (Correct Answer)
Explanation: ***Apneustic breathing*** - Damage to the **pneumotaxic center** prevents the normal inhibition of inspiration, leading to **prolonged inspiratory gasps**. - **Vagal nerve damage** further removes the inhibitory feedback from the lungs, exacerbating the inspiratory "holds" characteristic of apneustic breathing. *Cheyne-Stokes breathing* - This pattern is characterized by a **crescendo-decrescendo pattern** of breathing, interspersed with periods of **apnea**. - It is often associated with conditions like **heart failure**, stroke, or severe neurological damage, not specifically the pneumotaxic center and vagus nerve. *Deep and slow breathing* - This pattern can be seen in conditions like **Kussmaul breathing** (due to metabolic acidosis) or as a compensatory mechanism. - It does not directly result from the combined damage of the **pneumotaxic center** and the **vagus nerve**. *Shallow and rapid breathing* - This pattern is commonly seen in restrictive lung diseases, anxiety, or pain, where tidal volume is decreased and respiratory rate increased. - It does not reflect the **prolonged inspiration** that would result from a compromised pneumotaxic center and vagal input.
Question 3: TRUE statement regarding nerve supply of adrenal gland:
- A. Adrenal cortex has no nerve supply
- B. Adrenal medulla has no nerve supply
- C. Release of catecholamines is not affected by nerve supply
- D. Preganglionic fibres from lower thoracic spinal segments bypass sympathetic chain (Correct Answer)
Explanation: ***Preganglionic fibres from lower thoracic & upper lumbar spinal segments bypass sympathetic chain*** - The adrenal medulla is innervated by **preganglionic sympathetic fibers** originating from the **T5-T11 spinal cord segments**, which travel through the splanchnic nerves and synapse directly on chromaffin cells, effectively bypassing the sympathetic chain ganglia [1], [2]. - This direct innervation allows for a **rapid, systemic catecholamine release** in response to stress. *Adrenal cortex has no nerve supply* - The **adrenal cortex** receives some **autonomic innervation**, primarily sympathetic, though it is less dense and its direct role in steroidogenesis is not fully understood. - While hormonal signals are primary for cortical regulation, nerve fibers are present and may modulate blood flow or cellular activity. *Adrenal medulla has no nerve supply* - The **adrenal medulla** is a modified sympathetic ganglion whose **chromaffin cells** are directly innervated by **preganglionic sympathetic fibers** [1], [2]. - This direct neural input is crucial for its rapid response in releasing **catecholamines** into the bloodstream. *Release of catecholamines is not affected by nerve supply* - The release of **catecholamines** (epinephrine and norepinephrine) from the **adrenal medulla** is directly and primarily controlled by **preganglionic sympathetic innervation** [1], [2]. - Without this nerve supply, the stress-induced release of these hormones would be severely impaired, highlighting the critical role of neural input.
Question 4: Long thoracic nerve arises from which nerve roots?
- A. C6 C7 T1
- B. C7 T1 T2
- C. C5 C6 C7 (Correct Answer)
- D. C5 C6 C7 T1
Explanation: ***C5 C6 C7*** - The long thoracic nerve is formed from the **anterior rami** of the fifth, sixth, and seventh **cervical nerves (C5, C6, C7)**. - This nerve uniquely descends posterior to the **brachial plexus** and innervates the **serratus anterior muscle**. *C6 C7 T1* - While these roots contribute to other brachial plexus nerves, the **long thoracic nerve** specifically excludes T1. - T1 is more commonly associated with the **lower trunk** of the brachial plexus and nerves like the **ulnar nerve**. *C7 T1 T2* - The long thoracic nerve arises primarily from **cervical roots** and does not typically include T2. - **T2 involvement** in neural innervation of the upper limb is less common for the main nerves. *C5, C6, C7, T1* - The inclusion of T1 in this option makes it incorrect for the **long thoracic nerve**. - The T1 root contributes to other nerves of the **brachial plexus**, not the long thoracic nerve.
Question 5: Which of the following fiber types is classically categorized as Group B nerve fibers?
- A. Sympathetic postganglionic
- B. Parasympathetic preganglionic
- C. Parasympathetic post ganglionic
- D. Sympathetic preganglionic (Correct Answer)
Explanation: ***Sympathetic preganglionic*** - **Group B nerve fibers** are **myelinated preganglionic autonomic fibers** with intermediate diameter (3-15 μm) and moderate conduction velocity (3-15 m/s) - Both **sympathetic and parasympathetic preganglionic fibers** are classified as Group B fibers - **Sympathetic preganglionic** neurons are the classical example, originating from T1-L2 spinal segments and synapsing in paravertebral or prevertebral ganglia *Sympathetic postganglionic* - These are **unmyelinated Group C fibers** with slow conduction velocity (0.5-2 m/s) - They extend from ganglia to target organs *Parasympathetic preganglionic* - These are also **Group B fibers** (myelinated preganglionic) - However, **sympathetic preganglionic** is the more commonly cited classical example in standard classifications - They originate from cranial nerves (III, VII, IX, X) and sacral segments (S2-S4) *Parasympathetic postganglionic* - These are **unmyelinated Group C fibers** with the slowest conduction velocities - Short fibers extending from ganglia near or within target organs to effector cells
Question 6: Which of the following structures in the central nervous system contains major autonomic reflex centers?
- A. Medulla oblongata (Correct Answer)
- B. Thalamus
- C. Cerebellum
- D. Hypothalamus
Explanation: ***Medulla oblongata*** - The **medulla oblongata** contains the most critical **vital autonomic reflex centers** including the cardiovascular center (regulating heart rate and blood pressure), respiratory center (controlling breathing rhythm), and vasomotor center - It also houses reflex centers for coughing, sneezing, swallowing, and vomiting - These are **immediate, life-sustaining reflexes** that operate without higher center input *Hypothalamus* - The **hypothalamus** is indeed a major autonomic control center and the **highest level integrator** of autonomic function - However, it functions more as a **regulatory and integrative center** rather than a direct reflex center - It modulates autonomic responses through connections with brainstem centers like the medulla *Cerebellum* - The **cerebellum** is primarily responsible for motor coordination, balance, and posture control - While it may influence some autonomic functions indirectly, it does not contain autonomic reflex centers *Thalamus* - The **thalamus** serves as a relay station for sensory information and plays a role in consciousness and alertness - It is not involved in autonomic reflex pathways
Question 7: Anisocoria in Horner's syndrome is due to
- A. Disruption of the oculosympathetic pathway (Correct Answer)
- B. Disruption of the oculoparasympathetic pathway
- C. Disruption of the oculomotor nerve
- D. Disruption of the abducens nerve
Explanation: ***Disruption of the oculosympathetic pathway*** - Horner's syndrome results from a lesion interrupting the **oculosympathetic pathway**, leading to classic symptoms of **miosis**, **ptosis**, and **anhidrosis** [1]. - The **miosis** (constricted pupil) specifically arises from the unopposed action of the **parasympathetic innervation** to the pupil dilatory muscles when sympathetic innervation is disrupted. *Disruption of the oculoparasympathetic pathway* - Disruption of the oculoparasympathetic pathway would result in **mydriasis** (dilated pupil), not miosis as seen in Horner's syndrome [2]. - This pathway is responsible for stimulating the **pupillary constrictor muscles**, and its disruption would lead to an inability to constrict the pupil [3]. *Disruption of the oculomotor nerve* - The **oculomotor nerve** (CN III) carries parasympathetic fibers to the eye, and its disruption typically causes a **fixed and dilated pupil** due to unopposed sympathetic action [3]. - Oculomotor nerve palsy also presents with **ptosis** and **down-and-out deviation** of the eye, which are not characteristic of isolated Horner's syndrome [1], [4]. *Disruption of the abducens nerve* - The **abducens nerve** (CN VI) solely innervates the **lateral rectus muscle**, responsible for abducting the eye. - Disruption of the abducens nerve causes **diplopia** and an inability to abduct the affected eye, with no direct impact on pupil size.
Question 8: The primary effect of vagal stimulation on the heart is
- A. Increased P-R interval in ECG
- B. Decreased force of heart contraction
- C. Decreased cardiac output
- D. Decreased heart rate (Correct Answer)
Explanation: ***Decreased heart rate*** - **Vagal stimulation** releases **acetylcholine**, which activates muscarinic receptors on the sinoatrial (SA) node, leading to a decrease in its firing rate and thus a slower heart rate. - This parasympathetic effect primarily targets the **SA node** and **AV node**, influencing chronotropy (heart rate) more significantly than inotropy (contractility). *Increased P-R interval in ECG* - While vagal stimulation does slow **AV node conduction**, increasing the P-R interval, this is a more specific electrophysiological effect rather than the primary overall physiological outcome of vagal stimulation on the heart. - The most direct and immediate consequence of vagal nerve activity is the slowing of the heart's rhythm, which manifests as a **decreased heart rate**. *Decreased force of heart contraction* - The **vagus nerve** has a relatively weak effect on ventricular contractility, as parasympathetic innervation is far less dense in the ventricles compared to the atria and nodal tissues. - Therefore, a significant **decrease in the force of contraction** is not a primary or direct result of typical vagal stimulation in a healthy heart. *Decreased cardiac output* - While a markedly decreased heart rate *could* lead to a decreased cardiac output (CO = HR x SV), this is not the most direct or immediate physiological effect of vagal stimulation. - The primary action is on the heart rate, and changes in cardiac output would be a **secondary consequence** depending on the extent of bradycardia and compensatory mechanisms.
Question 9: A 32-year-old lady presents with shoulder tip pain. She is diagnosed with Pancoast tumor and presents with miosis. What is the most likely associated diagnosis?
- A. Upper trunk of brachial plexus injury
- B. Thoracic outlet syndrome
- C. Horner syndrome (Correct Answer)
- D. Aberrant right subclavian artery
Explanation: Horner syndrome - The presence of miosis (constricted pupil) in a patient with a Pancoast tumor is a classic sign of Horner syndrome. - Pancoast tumors are apical lung tumors that can invade the sympathetic chain, leading to the triad of ptosis, miosis, and anhidrosis. Upper trunk of brachial plexus injury - While Pancoast tumors can involve the brachial plexus, an injury to the upper trunk (C5-C6) typically causes symptoms like weakness in shoulder abduction and external rotation, and sensory loss over the lateral arm. - It does not directly explain miosis unless the sympathetic chain is also involved, which is characteristic of Horner syndrome. Thoracic outlet syndrome - This syndrome involves compression of the neurovascular structures as they exit the thoracic outlet, often causing pain, paresthesias, and weakness in the arm and hand. - It does not directly account for the symptom of miosis, which points to sympathetic nerve involvement. Aberrant right subclavian artery - An aberrant right subclavian artery is a congenital anomaly where the right subclavian artery arises from the distal aortic arch, often causing dysphagia lusoria or being asymptomatic. - It has no direct association with Pancoast tumors or the development of miosis.
Question 10: Which nerve primarily supplies the cervical esophagus?
- A. Vagus (Correct Answer)
- B. Left recurrent laryngeal nerve
- C. Right recurrent laryngeal nerve
- D. Phrenic nerve
Explanation: ***Vagus*** - The **vagus nerve** (cranial nerve X) provides parasympathetic innervation to the entire esophagus, including the cervical portion, through its branches. - For the **cervical esophagus** specifically, the vagus nerve supplies it via the **recurrent laryngeal nerve branches**, which provide motor innervation to the striated muscle in this region. - The vagus is considered the primary nerve because the recurrent laryngeal nerves are its direct branches, and the vagus coordinates overall esophageal function throughout its length. *Left recurrent laryngeal nerve* - The **left recurrent laryngeal nerve** is a branch of the vagus nerve that provides motor innervation to both the intrinsic muscles of the **larynx** and the **cervical esophagus**. - While it does directly supply the cervical esophagus with motor fibers, it is anatomically a branch of the vagus nerve rather than an independent primary supply. - In this context, the parent nerve (vagus) is considered the primary supply. *Right recurrent laryngeal nerve* - The **right recurrent laryngeal nerve** is also a branch of the vagus nerve that supplies both the laryngeal muscles and contributes to **cervical esophageal innervation**. - Like the left recurrent laryngeal nerve, it is a branch rather than the primary nerve source. - Both recurrent laryngeal nerves work as vagal branches to innervate the cervical esophagus. *Phrenic nerve* - The **phrenic nerve** (arising from C3-C5) primarily innervates the **diaphragm**, controlling respiration. - It does not supply the cervical esophagus and has no role in esophageal motility.
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