Anatomy
1 questionsAll the following features are seen in neurons from dorsal root ganglia, EXCEPT:
NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs
Question 311: All the following features are seen in neurons from dorsal root ganglia, EXCEPT:
- A. They are multipolar (Correct Answer)
- B. They are derived from neural crest cells
- C. They have eccentrically located nuclei
- D. They contain lipofuscin granules
Explanation: ***They are multipolar*** - Dorsal root ganglia (DRG) neurons are typically **pseudounipolar**, meaning they have a single process that branches into two (peripheral and central) rather than multiple dendrites and an axon [1]. - **Multipolar neurons** are characteristic of motor neurons and interneurons in the central nervous system, not DRG sensory neurons [1]. *They contain lipofuscin granules* - **Lipofuscin granules** are common in long-lived, post-mitotic cells like neurons and are considered "wear and tear" pigments, accumulating with age. - Their presence in DRG neurons is a normal finding and reflects the neuron's metabolic activity over time. *They have eccentrically located nuclei* - While not universally present in all DRG neurons, an **eccentrically located nucleus** is a common histological feature of certain types of DRG neurons, particularly larger ones. - This feature helps distinguish them from other neuron types and can be accentuated by the large amount of cytoplasm in these cells. *They are derived from neural crest cells* - All sensory neurons of the DRG, along with other components like Schwann cells and sympathetic ganglia, originate from **neural crest cells**. - This developmental origin is a fundamental characteristic of DRG neurons, distinguishing them from CNS neurons derived from the neural tube.
Physiology
9 questionsWhat is the definition of preload in the context of cardiac physiology?
Neurotransmitter involved in nigrostriatal pathway is?
What is a key difference between smooth muscle and skeletal muscle physiology?
When the tension in a muscle fibre is maximum, its length is called?
Which of the following is the MOST accurate statement about CSF?
What triggers the cephalic phase of gastric secretion?
Which of the following statements about gastric secretion is true?
Ptyalin is secreted by?
What is the body's first physiological response to hypoglycemia?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 311: What is the definition of preload in the context of cardiac physiology?
- A. Volume of blood in the ventricles at the end of systole
- B. Volume of blood in the ventricles at the end of diastole (Correct Answer)
- C. Amount of blood pumped by the heart per beat
- D. Resistance to blood flow in the arteries
Explanation: ***Volume of blood in the ventricles at the end of diastole*** - Preload represents the **initial stretching** of the cardiac myocytes prior to contraction, largely determined by the **volume of blood filling the ventricles** at the end of relaxation (diastole). - This **end-diastolic volume** directly correlates with the ventricular muscle fiber length at the start of systole, influencing the force of contraction according to the **Frank-Starling mechanism**. *Volume of blood in the ventricles at the end of systole* - This describes the **end-systolic volume**, which is the amount of blood remaining in the ventricle after it has contracted and ejected blood. - End-systolic volume is a determinant of the **ejection fraction** but does not define preload. *Amount of blood pumped by the heart per beat* - This refers to the **stroke volume**—the volume of blood ejected from the left ventricle with each heartbeat. - While preload influences stroke volume, stroke volume itself is not the definition of preload. *Resistance to blood flow in the arteries* - This describes **afterload**, which is the pressure or resistance the ventricle must overcome to eject blood during systole. - Afterload primarily affects the *force* needed for contraction, rather than the initial stretch or filling volume of the heart.
Question 312: Neurotransmitter involved in nigrostriatal pathway is?
- A. Acetylcholine
- B. Serotonin
- C. Dopamine (Correct Answer)
- D. Norepinephrine
Explanation: ***Dopamine*** - The **nigrostriatal pathway** is a major dopaminergic pathway in the brain, originating in the **substantia nigra pars compacta** and projecting to the striatum. - It is crucial for the control of voluntary movement, and its degeneration is a hallmark of **Parkinson's disease**. *Serotonin* - Serotonin (5-HT) is primarily involved in mood, sleep, appetite, and cognition, and is not the primary neurotransmitter of the **nigrostriatal pathway**. - Serotonergic pathways originate in the **raphe nuclei** and project widely throughout the brain. *Acetylcholine* - Acetylcholine is a key neurotransmitter in the periphery (neuromuscular junction, autonomic nervous system) and in the central nervous system, involved in learning and memory. - Cholinergic neurons in the **basal forebrain** project to the cortex and hippocampus, but acetylcholine is not the neurotransmitter of the **nigrostriatal pathway**. *Norepinephrine* - Norepinephrine (noradrenaline) is involved in arousal, attention, and the fight-or-flight response, with pathways originating in the **locus coeruleus**. - While it plays a role in modulating motor circuits, it is not the main neurotransmitter of the **nigrostriatal pathway**.
Question 313: What is a key difference between smooth muscle and skeletal muscle physiology?
- A. Calcium is required for contraction.
- B. Troponin is absent in smooth muscle. (Correct Answer)
- C. Myosin is essential for contraction.
- D. Potassium is required for contraction.
Explanation: ***Troponin is absent in smooth muscle.*** * Smooth muscle contraction is regulated by **calcium-calmodulin complex** and subsequent activation of **myosin light chain kinase (MLCK)**, in contrast to skeletal muscle's reliance on the troponin-tropomyosin system. * **Troponin** is a calcium-binding protein found in skeletal and cardiac muscle, which plays a critical role in regulating muscle contraction by initiating the movement of tropomyosin, thereby exposing myosin-binding sites on actin. *Calcium is required for contraction.* * While calcium is indeed required for contraction in both smooth and skeletal muscle, the **mechanism of its action** differs, making this statement insufficiently discriminative as a *key difference*. * In both muscle types, an increase in intracellular **calcium** initiates the contractile process, but the downstream signaling pathways diverge significantly. *Myosin is essential for contraction.* * **Myosin** is a fundamental motor protein essential for contraction in *all* muscle types, including skeletal, cardiac, and smooth muscle. * This statement highlights a similarity, not a key difference, as **actin-myosin cross-bridge cycling** is the basis of force generation in all muscle tissues. *Potassium is required for contraction.* * **Potassium ions** are crucial for maintaining the resting membrane potential and for repolarization following an action potential, which is necessary for muscle excitability, but they do not directly trigger muscle contraction. * The influx of calcium (or release from intracellular stores) is the direct trigger for contraction, not potassium.
Question 314: When the tension in a muscle fibre is maximum, its length is called?
- A. None of the options
- B. Initial length
- C. Equilibrium length
- D. Optimum length (Correct Answer)
Explanation: ***Optimum length*** - This is the muscle length at which the **maximum number of cross-bridges** can form between actin and myosin filaments. - At this length, the sarcomere allows for the **greatest overlap** of thick and thin filaments without excessive stretching or compression, leading to peak tension generation. *Equilibrium length* - This term usually refers to the **resting length** of a muscle fiber when no external forces are acting upon it. - At equilibrium, the tension generated by the muscle may not necessarily be at its maximum. *Initial length* - This is a general term that refers to the **starting length** of a muscle fiber before it contracts or is stretched. - It does not specifically denote the length at which maximum tension is achieved. *None of the options* - This option is incorrect because **optimum length** accurately describes the muscle length yielding maximum tension.
Question 315: Which of the following is the MOST accurate statement about CSF?
- A. Formed by the choroid plexus in the ventricles. (Correct Answer)
- B. Normally contains no neutrophils
- C. pH is less than that of plasma
- D. Removal of CSF during dural tap can cause a headache due to the change in pressure.
Explanation: ***Formed by the choroid plexus in the ventricles.*** * The **choroid plexus**, located in the ventricles of the brain, is primarily responsible for the production of **cerebrospinal fluid (CSF)**. * Specialized epithelial cells of the choroid plexus filter blood plasma to produce CSF, which then circulates through the central nervous system. *Normally contains no neutrophils* * Normal CSF should contain **virtually no neutrophils**; their presence typically indicates an inflammatory or infectious process, such as **bacterial meningitis**. * While normal CSF doesn't have neutrophils, this option isn't as broadly accurate as the choroid plexus statement because the presence of other cell types like lymphocytes in small numbers is normal. *pH is less than that of plasma* * The pH of CSF is typically **slightly lower than that of plasma** (around 7.31 compared to 7.40), but the statement "less than" is broad and the degree of difference can be variable and is a less defining characteristic than its formation site. * This slight difference in pH is important for regulating **respiration** through chemoreceptors, but it's not the most accurate or fundamental statement about CSF properties. *Removal of CSF during dural tap can cause a headache due to the change in pressure.* * A **post-dural puncture headache** (PDPH) is a well-known complication of a dural tap (lumbar puncture), caused by the leakage of CSF from the puncture site, leading to **intracranial hypotension**, not simply a change in pressure. * This decrease in CSF volume and pressure causes a traction on pain-sensitive structures within the cranium, resulting in a headache that is typically **worse when upright** and relieved by lying down.
Question 316: What triggers the cephalic phase of gastric secretion?
- A. On food entering stomach
- B. On food entering intestine
- C. On seeing food (Correct Answer)
- D. On stress
Explanation: ***On seeing food*** - The **cephalic phase** of gastric secretion is initiated by sensory input such as the sight, smell, taste, or even the thought of food. - This phase is mediated by the **vagus nerve**, stimulating gastric acid and enzyme secretion in anticipation of food arrival. *On food entering stomach* - This describes the initiation of the **gastric phase** of digestion, where mechanical stretch and chemical presence of food in the stomach stimulate further secretions. - The gastric phase primarily involves local reflexes and hormonal mechanisms (like **gastrin** release), rather than purely sensory input from the head. *On food entering intestine* - This marks the beginning of the **intestinal phase** of digestion, which involves both stimulatory and inhibitory signals for gastric secretion. - The primary role of the intestinal phase is to regulate the rate at which chyme enters the small intestine and to coordinate bile and pancreatic enzyme release. *On stress* - While stress can impact digestive function, it typically affects the **autonomic nervous system** in a generalized way, often leading to inhibition of digestion or altered motility. - Stress does not specifically trigger the cephalic phase of gastric secretion, which is a physiological response linked to nutrient anticipation.
Question 317: Which of the following statements about gastric secretion is true?
- A. Inhibited by curare
- B. Stimulated by nor adrenaline
- C. Increased by stomach distention (Correct Answer)
- D. Stimulated by an increase in tonic activity
Explanation: ***Increased by stomach distention*** - **Stomach distention** activates local reflexes and the **vagovagal reflex**, leading to the release of **acetylcholine** and **gastrin**, which stimulate gastric acid secretion during the gastric phase. - This is a physiological response that prepares the stomach for digestion of incoming food. *Inhibited by curare* - **Curare** is a **nicotinic acetylcholine receptor antagonist** that primarily affects neuromuscular junctions, causing muscle paralysis. - It does not directly inhibit the primary mechanisms of gastric acid secretion, which are largely mediated by **muscarinic acetylcholine receptors**, histamine, and gastrin. *Stimulated by nor adrenaline* - **Noradrenaline** (norepinephrine) is a neurotransmitter of the **sympathetic nervous system**, which generally **inhibits** gastric motility and secretion. - Activation of alpha-2 adrenergic receptors can decrease gastric acid secretion. *Stimulated by an increase in tonic activity* - This statement is vague; "tonic activity" can refer to various physiological processes. If it refers to **sympathetic nervous system** tonic activity, it would **inhibit** gastric secretion. - If it implies increased vagal tone (parasympathetic activity), then secretion would be stimulated, but the phrasing is not precise enough to be unequivocally true for gastric secretion in general.
Question 318: Ptyalin is secreted by?
- A. Gastric gland
- B. Salivary gland (Correct Answer)
- C. Duodenal gland
- D. Pancreatic gland
Explanation: ***Salivary gland*** - **Ptyalin**, also known as **salivary amylase**, is an enzyme produced by the salivary glands. - Its primary role is to initiate the **digestion of carbohydrates** (starches) in the mouth. *Gastric gland* - Gastric glands primarily secrete **hydrochloric acid** and **pepsinogen**, involved in protein digestion. - They do not produce ptyalin or enzymes for carbohydrate digestion. *Duodenal gland* - Duodenal glands (Brunner's glands) secrete alkaline mucus to protect the duodenum from acidic chyme. - They are not involved in the production of carbohydrate-digesting enzymes like ptyalin. *Pancreatic gland* - The pancreas produces **pancreatic amylase**, which continues starch digestion in the small intestine. - While it secretes an amylase, it is distinct from salivary amylase (ptyalin) and released into the duodenum, not the mouth.
Question 319: What is the body's first physiological response to hypoglycemia?
- A. Decreased insulin (Correct Answer)
- B. Increased glucagon
- C. Increased cortisol
- D. Increased norepinephrine
Explanation: ***Decreased insulin*** - **Decreased insulin secretion** is the body's **first and earliest** physiological response to falling blood glucose levels, occurring at approximately **80-85 mg/dL**. - This represents the **primary defense mechanism** against hypoglycemia - by reducing insulin release from pancreatic beta cells, the body removes the most potent glucose-lowering stimulus. - This allows blood glucose to stabilize before it drops further, and occurs **before** any active counterregulatory hormones are released. - This is a critical **first-line defense** that prevents the need for more aggressive counterregulatory responses. *Increased glucagon* - **Glucagon** is the **second line of defense** against hypoglycemia, with secretion increasing at glucose levels around **65-70 mg/dL**. - While glucagon is the most important **active counterregulatory hormone** (stimulating glycogenolysis and gluconeogenesis), it is not the *first* response. - The temporal sequence is: insulin suppression occurs first, followed by glucagon release if glucose continues to fall. *Increased cortisol* - **Cortisol** is a late counterregulatory hormone, responding to more severe or prolonged hypoglycemia (glucose <65 mg/dL). - It promotes gluconeogenesis and reduces peripheral glucose utilization over hours, not minutes. - Along with growth hormone, cortisol provides sustained glucose elevation but is not an early response. *Increased norepinephrine* - **Norepinephrine** (and epinephrine) are part of the sympathetic/adrenomedullary response to hypoglycemia at approximately **65-70 mg/dL**. - These catecholamines provide important counterregulation but are activated after insulin suppression has already occurred. - They contribute to both glucose mobilization and the symptomatic (adrenergic) response to hypoglycemia.