Innervation of Abdominal Viscera — MCQs
Primary component of nonadrenergic noncholinergic nerve transmission in gut is:
Free nerve endings carrying nociceptive fibers are seen in:
In bladder injury, pain is referred to which of the following areas?
All are effects of the parasympathetic system on the heart except?
Primary afferent fibers secrete which nociceptive substance at the dorsal horn?
Sensations of pain from teeth and temperature are carried by
Sympathetic supply to the heart arises from which of the following spinal segments?
Inhibition of myenteric plexus results in
Sensory nerve supply of gall bladder is through -
Dermatome at the umbilicus is
Innervation of Abdominal Viscera Indian Medical PG Practice Questions and MCQs
Question 1: Primary component of nonadrenergic noncholinergic nerve transmission in gut is:
- A. VIP and Substance P
- B. VIP and CCK
- C. VIP and NO (Correct Answer)
- D. VIP and Motilin
Explanation: ***VIP and NO*** - **Vasoactive Intestinal Peptide (VIP)** and **Nitric Oxide (NO)** are the primary neurotransmitters mediating the **nonadrenergic noncholinergic (NANC) transmission** in the gut. - The NANC system is crucial for **gut motility, secretion, and relaxation of smooth muscle** beyond the actions of adrenergic and cholinergic systems. *VIP and substance* - While **VIP** is a key NANC neurotransmitter, **Substance P** primarily mediates excitatory effects, particularly in pain transmission and inflammatory responses in the gut, rather than being a primary NANC inhibitory transmitter. - Substance P is often co-released with acetylcholine or acts independently to **stimulate smooth muscle contraction** and secretion, not relaxation. *VIP and CCK* - Although **VIP** is a significant NANC neurotransmitter, **Cholecystokinin (CCK)** is a peptide hormone primarily involved in stimulating gallbladder contraction and pancreatic enzyme secretion, and it acts as a neuromodulator rather than a primary NANC neurotransmitter. - CCK plays a significant role in **digestion and satiety**, but its role in NANC transmission is not as central as NO for smooth muscle relaxation. *VIP and Motilin* - **VIP** is a critical NANC neurotransmitter, but **Motilin** is a peptide hormone that primarily stimulates **gastric and intestinal motility** during fasting (migrating motor complex). - Motilin's main function is related to cyclical contractions of the gut, and it is not considered a primary direct neurotransmitter in the NANC system.
Question 2: Free nerve endings carrying nociceptive fibers are seen in:
- A. Spleen
- B. Liver
- C. Mesentery (Correct Answer)
- D. Intestine
Explanation: ***Mesentery*** - The mesentery is **richly innervated with free nerve endings** that carry nociceptive (pain) fibers, making it highly sensitive to painful stimuli [1]. - These nerve endings respond to **stretch, traction, ischemia, and inflammation**, transmitting visceral pain signals via **sympathetic pathways** (T5-L2) [2]. - The mesentery's abundant nociceptive innervation is why **peritoneal irritation** and **mesenteric traction** during surgery cause significant pain [4]. - Free nerve endings in the mesentery are a key component of **visceral pain perception** in abdominal pathologies [1]. *Intestine* - The intestinal **mucosa and muscle layers** have relatively **few pain receptors** and are insensitive to cutting, burning, or crushing [1]. - Pain from the intestine primarily arises from the **serosal surface** (peritoneal covering) and associated mesentery, not from the intestinal wall itself [4]. - Intestinal pain is typically due to **distension, ischemia, or inflammation** affecting the serosa or mesentery [2]. *Liver* - The liver parenchyma is **devoid of pain receptors** - it has no free nerve endings for nociception [3]. - Hepatic pain originates only from **stretching of Glisson's capsule** (the fibrous covering), not from the liver tissue itself [3]. - This capsular pain may be referred to the right upper quadrant or shoulder via phrenic nerve (C3-C5) [4]. *Spleen* - The spleen has **sparse nociceptive innervation** and is relatively insensitive to pain. - Splenic pain, when present, typically results from **capsular distension or rupture**, not from the splenic parenchyma itself. - Pain from splenic pathology is often referred to the left shoulder (Kehr's sign) [4].
Question 3: In bladder injury, pain is referred to which of the following areas?
- A. Flank
- B. Upper part of thigh
- C. Lower abdominal wall (Correct Answer)
- D. Penis
Explanation: ***Correct Option: Lower abdominal wall*** - **Referred pain** from the bladder is typically felt in the **suprapubic region** of the lower abdominal wall due to shared visceral and somatic afferent innervation. - The **parietal peritoneum** overlying the bladder is innervated by somatic nerves that also supply the abdominal wall. - This convergence of visceral afferents from the bladder and somatic afferents from the abdominal wall at the spinal cord level (particularly S2-S4) results in referred pain to the suprapubic area. *Incorrect Option: Upper part of thigh* - Pain in the upper thigh is more commonly associated with conditions affecting the **hip joint**, **femoral nerve**, or **inguinal region**. - Bladder innervation does not primarily refer pain to the upper thigh. *Incorrect Option: Flank* - Flank pain is typically associated with conditions of the **kidneys** or **ureters**, such as **nephrolithiasis** or **pyelonephritis**. - The bladder's referred pain pattern does not usually extend to the flank. *Incorrect Option: Penis* - While bladder irritation can sometimes cause sensations in the penis, it is more often associated with conditions like **urethritis**, **cystitis**, or **prostatitis**. - Direct referred pain from bladder injury to the penis is less common than to the lower abdominal wall.
Question 4: All are effects of the parasympathetic system on the heart except?
- A. Negative chronotropic
- B. Negative dromotropic
- C. All are seen
- D. Negative inotropic (Correct Answer)
Explanation: ***Negative inotropic*** - While the parasympathetic system (via the **vagus nerve**) primarily affects the **sinoatrial (SA) and atrioventricular (AV) nodes** to decrease heart rate and conduction velocity, it has a **minimal direct effect on ventricular contractility** (inotropy) in humans. - The ventricles are less densely innervated by parasympathetic fibers compared to the atria, so acetylcholine's direct negative inotropic effect is **clinically insignificant** in a healthy heart. - This is the **EXCEPTION** - not a significant parasympathetic effect on the heart. *Negative chronotropic* - The parasympathetic system, primarily through **acetylcholine** acting on **muscarinic receptors** in the SA node, decreases the heart rate (chronotropy). - This slows the rate of spontaneous depolarization of pacemaker cells. - This **IS** a major parasympathetic effect. *Negative dromotropic* - Parasympathetic stimulation also slows the conduction velocity through the **AV node** (dromotropy). - This increases the PR interval on an ECG and can lead to various degrees of AV block in extreme cases. - This **IS** a major parasympathetic effect. *All are seen* - This option is incorrect because the **negative inotropic effect** is NOT a significant parasympathetic effect on the heart. - While negative chronotropic and negative dromotropic effects are prominent features of parasympathetic activity, the direct influence on ventricular contractility is minimal.
Question 5: Primary afferent fibers secrete which nociceptive substance at the dorsal horn?
- A. Substance P (Correct Answer)
- B. Acetylcholine
- C. Norepinephrine
- D. Epinephrine
Explanation: ***Substance P*** - **Substance P** is a neuropeptide released by **C fibers** and **A-delta fibers** (primary afferent nociceptors) in the dorsal horn of the spinal cord. - It acts as a **neurotransmitter** and **neuromodulator**, contributing to the transmission and amplification of pain signals. *Acetylcholine* - **Acetylcholine** is a primary neurotransmitter in the **neuromuscular junction** and the autonomic nervous system. - While it has some roles in the CNS, it is not the primary nociceptive substance secreted by afferent fibers in the dorsal horn. *Norepinephrine* - **Norepinephrine** (noradrenaline) is a neurotransmitter involved in the **fight-or-flight response** and mood regulation. - It can modulate pain, but it is not directly released by primary afferent fibers as a nociceptive substance in the dorsal horn. *Epinephrine* - **Epinephrine** (adrenaline) is a hormone and neurotransmitter primarily associated with the **sympathetic nervous system** and stress response. - It does not serve as a direct nociceptive transmitter released by primary afferent fibers in the spinal cord.
Question 6: Sensations of pain from teeth and temperature are carried by
- A. Lateral spinothalamic tract (Correct Answer)
- B. Trigeminal nerve pathway
- C. Ventral spinothalamic tract
- D. Corticospinal tract
Explanation: ***Lateral spinothalamic tract*** - The **lateral spinothalamic tract** primarily carries sensations of **pain and temperature** from the body to the brain. - This pathway is crucial for transmitting these somatosensory modalities from the periphery, including dental structures, up the spinal cord to the **thalamus** and then to the cerebral cortex. *Trigeminal nerve pathway* - The **trigeminal nerve (CN V)** is responsible for sensory innervation of the face, including teeth, and jaw motor function. - While it transmits sensory information from the teeth, its central pathway eventually synapses with the **trigeminal lemniscus** which then projects to the thalamus, rather than directly being the spinothalamic tract itself. *Ventral spinothalamic tract* - The **ventral (anterior) spinothalamic tract** primarily carries sensations of **crude touch and pressure**. - It does not significantly contribute to the transmission of pain and temperature, which are the main sensations from teeth and temperature described. *Corticospinal tract* - The **corticospinal tract** is a major **motor pathway** that originates in the cerebral cortex and descends to the spinal cord. - It is responsible for **voluntary fine motor control** of the limbs and body, having no role in carrying sensory information like pain or temperature.
Question 7: Sympathetic supply to the heart arises from which of the following spinal segments?
- A. T1 to T5 (Correct Answer)
- B. T2 to T6
- C. T3 to T7
- D. T4 to T8
Explanation: The preganglionic sympathetic fibers that innervate the heart originate from the lateral horns of the thoracic spinal segments T1 to T5. These fibers synapse in the cervical and upper thoracic sympathetic ganglia, from which postganglionic fibers extend to the heart. While there is some overlap, the primary and most significant sympathetic innervation to the heart stems predominantly from T1 to T5, making T2 to T6 a less precise answer. Including T6 would extend past the typical primary cardiac sympathetic innervation, which largely concludes at T5. This range is too caudal and largely beyond the principal segments providing sympathetic innervation to the heart. Segments T6-T8 are more involved in sympathetic supply to abdominal organs and other structures rather than direct cardiac control.
Question 8: Inhibition of myenteric plexus results in
- A. Hyperacidity
- B. Diarrhea
- C. Decreased gut motility (Correct Answer)
- D. Increased secretions
Explanation: ***Decreased gut motility*** - The **myenteric plexus** (Auerbach's plexus) is primarily responsible for regulating **gastrointestinal motility**, including peristalsis and muscle contraction. - Its inhibition would therefore lead to **reduced peristaltic movements** and **decreased gut motility**. *Hyperacidity* - **Gastric acid secretion** is mainly regulated by the vagus nerve (via acetylcholine), gastrin, and histamine, not directly by the myenteric plexus. - While gut motility can indirectly affect acid exposure, a primary and direct consequence of myenteric plexus inhibition is not hyperacidity. *Diarrhea* - **Diarrhea** is typically caused by increased gut motility, increased secretion, or decreased absorption. - Inhibition of the myenteric plexus would lead to **decreased motility**, making diarrhea an unlikely outcome. *Increased secretions* - **Gastrointestinal secretions** are largely controlled by the submucosal plexus (Meissner's plexus) and hormonal factors. - While the myenteric plexus has some indirect influence, its primary role is motility, and its inhibition would not directly lead to increased secretions.
Question 9: Sensory nerve supply of gall bladder is through -
- A. Vagus nerve (Cranial Nerve X) (Correct Answer)
- B. Celiac plexus (sympathetic fibers)
- C. Trigeminal nerve (Cranial Nerve V)
- D. Facial nerve (Cranial Nerve VII)
Explanation: ***Vagus nerve (Cranial Nerve X)*** - The **vagus nerve** provides the primary **sensory (visceral afferent) innervation** to the gallbladder, carrying information about distension, contraction, and physiological state. - These **parasympathetic sensory fibers** travel through the vagus nerve to medullary centers, monitoring gallbladder function and participating in reflex arcs. - The vagus nerve is the main pathway for **general sensory innervation** of the gallbladder as per standard anatomical texts. *Celiac plexus (sympathetic fibers)* - The **celiac plexus** contains **sympathetic afferent fibers** that primarily transmit **pain sensation** from the gallbladder, especially during inflammation or biliary colic [1]. - These pain fibers travel via sympathetic pathways to spinal segments **T8-T9**, mediating referred pain to the epigastric region and right upper quadrant [1]. - While important for pain transmission, the celiac plexus is not classified as the primary sensory nerve supply in anatomical nomenclature. *Trigeminal nerve (Cranial Nerve V)* - The **trigeminal nerve** provides **sensory innervation to the face** and motor innervation to muscles of mastication. - It has no role in innervation of abdominal viscera, including the gallbladder. *Facial nerve (Cranial Nerve VII)* - The **facial nerve** controls **facial expression muscles**, provides taste sensation to the anterior two-thirds of the tongue, and supplies parasympathetic fibers to lacrimal and salivary glands. - It does not innervate any abdominal organs.
Question 10: Dermatome at the umbilicus is
- A. T8
- B. T10 (Correct Answer)
- C. T12
- D. L1
Explanation: ***T10*** - The **umbilicus** (belly button) is consistently innervated by the **tenth thoracic (T10) dermatome** [1]. - This anatomical landmark is crucial for **neurological assessment** to pinpoint spinal cord injury levels. *T8* - The **T8 dermatome** is located superior to the umbilicus, roughly at the level of the **xiphoid process**. - Sensory deficits at this level would indicate a lesion higher than the umbilicus. *T12* - The **T12 dermatome** is found inferior to the umbilicus, typically around the **suprapubic region** or just above the inguinal ligament [1]. - A lesion affecting T12 would spare sensation at the umbilicus. *L1* - The **L1 dermatome** innervates the **inguinal region** and the upper parts of the thigh [1]. - This level is significantly lower than the umbilicus.
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