Anatomy
3 questionsWhich of the following structures is not derived from the ectoderm?
Which muscle stabilizes the clavicle during movement of the shoulder?
The thoracic duct crosses from the right to the left at the level of
NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs
Question 181: Which of the following structures is not derived from the ectoderm?
- A. Brain
- B. Retina
- C. Eustachian tube (Correct Answer)
- D. Lens
Explanation: ***Eustachian tube*** - The **Eustachian tube** (auditory tube) is derived from the **endoderm**, specifically from the first pharyngeal pouch. - It connects the nasopharynx to the middle ear and is responsible for equalizing pressure [1]. *Lens* - The **lens** of the eye develops from the surface ectoderm through an invagination called the **lens placode**. - This ectodermal origin is crucial for its transparency and refractive properties. *Brain* - The **brain** is a primary derivative of the ectoderm, specifically the **neural tube**, which forms from the neural plate during neurulation. - This ectodermal origin gives rise to the entire central nervous system. *Retina* - The **retina** of the eye, along with the optic nerve, develops from the **neuroectoderm** (a part of the neural tube). - Its ectodermal origin is essential for its light-sensing function.
Question 182: Which muscle stabilizes the clavicle during movement of the shoulder?
- A. Pectoralis major
- B. Latissimus dorsi
- C. Subclavius (Correct Answer)
- D. Serratus anterior
Explanation: ***Subclavius*** - The **subclavius muscle** originates from the first rib and inserts into the inferior surface of the clavicle, acting to **depress the clavicle** and prevent its displacement, thus enhancing shoulder stability during movement. - It plays a crucial role in protecting the underlying **neurovascular structures** (brachial plexus and subclavian vessels) from external trauma to the shoulder. *Pectoralis major* - This large, fan-shaped muscle primarily functions in **adduction, medial rotation, and flexion of the humerus** at the shoulder joint [1]. - It does not directly stabilize the clavicle but rather acts on the arm. *Latissimus dorsi* - The **latissimus dorsi** is a broad muscle of the back responsible for **extension, adduction, and internal rotation of the humerus** [1]. - Its actions are mainly on the humerus and it does not directly stabilize the clavicle. *Serratus anterior* - The **serratus anterior** muscle primarily **protracts and rotates the scapula**, keeping it pressed against the thoracic wall. - While it's essential for **scapular stability** and overhead arm movements, it does not directly stabilize the clavicle.
Question 183: The thoracic duct crosses from the right to the left at the level of
- A. T12 vertebra
- B. T2 vertebra
- C. T4-T5 vertebra (Correct Answer)
- D. T6 vertebra
Explanation: ***T4-T5 vertebra*** - The **thoracic duct** crosses from the right to the left side of the vertebral column at the level of the **T4-T5 vertebrae**, specifically just above the root of the left lung. - This crossover is an important anatomical landmark as it signifies the duct's ascent towards the neck to drain into the left subclavian vein. *T12 vertebra* - The **thoracic duct** originates from the **cisterna chyli** at the level of the L1 or L2 vertebra and ascends into the thorax at or below the T12 vertebra, it does not cross over at this level. - This level primarily marks its entry into the thoracic cavity, not its main crossover point. *T6 vertebra* - While the **thoracic duct** is present in the thorax at this level, it does not undergo its characteristic crossover from right to left at the T6 vertebra. - The duct continues its ascent along the right side of the vertebral column before moving across. *T2 vertebra* - By the level of the T2 vertebra, the **thoracic duct** has already crossed to the left side of the vertebral column and is ascending towards its termination in the neck. - The crossover event occurs more inferiorly, at the T4-T5 level.
Dental
1 questionsStability of alveoli is maintained by:
NEET-PG 2012 - Dental NEET-PG Practice Questions and MCQs
Question 181: Stability of alveoli is maintained by:
- A. Negative intrapleural pressure
- B. Residual air in alveoli
- C. Compliance of the lungs
- D. Reduced surface tension by surfactant (Correct Answer)
Explanation: ***Reduced surface tension by surfactant*** - **Surfactant** (a mixture of lipoproteins) reduces the **surface tension** at the air-liquid interface within the alveoli, preventing their collapse at the end of expiration. - This reduction in surface tension helps to maintain the **stability** and patency of the smaller alveoli, preventing them from emptying into larger ones. *Compliance of the lungs* - **Compliance** refers to the distensibility of the lungs and chest wall, indicating how easily they can be stretched. - While pulmonary compliance is important for easy breathing, it does not directly maintain the stability of individual alveoli in preventing their collapse. *Negative intrapleural pressure* - **Negative intrapleural pressure** helps to keep the lungs expanded by creating a vacuum between the visceral and parietal pleura, pulling the lungs outwards. - This pressure prevents the lung as a whole from collapsing but does not directly prevent the collapse of individual alveoli due to surface tension. *Residual air in alveoli* - **Residual volume** is the amount of air remaining in the lungs after a maximal exhalation. - While residual air prevents the complete collapse of the lungs, it is surface tension reduction by surfactant that specifically maintains the stability of individual alveoli against collapse forces.
Physiology
6 questionsMechanism by which Ach decreases heart rate is by:
Damage to the striatum primarily affects which type of memory?
Salty taste is due to?
What is the primary factor that determines the resting membrane potential in a nerve fiber?
Which substrate is both secreted and filtered by the kidneys?
Motilin secretion is decreased in which of the following states?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 181: Mechanism by which Ach decreases heart rate is by:
- A. Prolongation of action potential duration
- B. Reduction in calcium influx
- C. Inhibition of sympathetic activity
- D. Delayed diastolic depolarization (Correct Answer)
Explanation: ***Delayed diastolic depolarization*** - Acetylcholine (ACh) binding to muscarinic receptors on nodal cells increases **potassium permeability**, leading to a more negative maximal diastolic potential. - This slows the rate of **spontaneous depolarization** (pacemaker potential), thereby delaying the point at which the threshold for an action potential is reached and reducing heart rate. *Prolongation of action potential duration* - ACh typically **shortens** the action potential duration in atrial and nodal cells by increasing potassium efflux, which hyperpolarizes the cell and hastens repolarization. - A prolonged action potential duration would generally lead to a **slower heart rate** by increasing the refractory period, but this is achieved through different ionic mechanisms and is not the primary mechanism of ACh. *Reduction in calcium influx* - While ACh does reduce the inward **calcium current (ICa)** in nodal cells, contributing to a slower heart rate and weaker contractility, this effect primarily influences the upstroke and peak of the action potential. - The more **fundamentally important mechanism** for heart rate reduction is the impact on the pacemaker potential's slope, which is governed by altered ion conductances, predominantly potassium. *Inhibition of sympathetic activity* - ACh acts directly on **muscarinic receptors** on cardiac cells to decrease heart rate, which is a parasympathetic effect. - It does not directly inhibit sympathetic nerve activity but rather **counteracts sympathetic effects** by directly modulating cardiac cell physiology.
Question 182: Damage to the striatum primarily affects which type of memory?
- A. Memory of how to perform tasks (Correct Answer)
- B. Memory for recent events
- C. Memory for past experiences
- D. Memory for facts and events
Explanation: ***Memory of how to perform tasks*** - The **striatum**, a component of the **basal ganglia**, is crucial for **procedural memory**, which is the memory of how to perform skills and habitual tasks. - Damage to this area can impair the ability to learn new motor skills or execute previously learned ones, even if the person remembers the task explicitly. *Memory for recent events* - This type of memory, often referred to as **episodic memory**, relies heavily on the **hippocampus** and medial temporal lobe structures. - Damage to the striatum typically does not directly affect the recall of recent events or experiences. *Memory for past experiences* - **Autobiographical memory**, which includes past experiences, primarily involves widespread cortical networks, particularly in the **temporal and frontal lobes**. - While broad brain damage can affect this, the striatum's primary role is not in the storage or retrieval of experiential memories. *Memory for facts and events* - This describes **declarative memory**, which is subdivided into **semantic memory** (facts) and **episodic memory** (events). - These are largely mediated by the **hippocampus**, **medial temporal lobes**, and various cortical areas, not primarily the striatum.
Question 183: Salty taste is due to?
- A. Sodium ion channels (Correct Answer)
- B. Calcium ion channels
- C. G-protein coupled receptors
- D. Proton channels
Explanation: ***Sodium ion channels*** - The sensation of **salty taste** is primarily mediated by the direct influx of **sodium ions (Na+)** into taste receptor cells. - This influx leads to **depolarization** of the cell membrane, triggering neurotransmitter release and signaling to the brain. *Calcium ion channels* - While calcium ions are crucial for various cellular processes, including **neurotransmitter release**, they are not the primary initiators of the salty taste transduction pathway. - Calcium channels are more directly involved in the sensation of **umami** and **sweet tastes**, often via G-protein coupled receptors. *G-protein coupled receptors* - **G-protein coupled receptors (GPCRs)** are responsible for the transduction of **sweet, bitter, and umami tastes**. - They are not involved in the direct detection of **saline compounds**, which operate through ion channels. *Proton channels* - **Proton channels (H+)** are primarily involved in the sensation of **sour taste**. - The influx of protons causes intracellular acidification, leading to cell depolarization.
Question 184: What is the primary factor that determines the resting membrane potential in a nerve fiber?
- A. Is equal to the resting potential of cardiac muscle fibers.
- B. Can be accurately measured using intracellular electrodes.
- C. Increases with elevated extracellular potassium concentration.
- D. Is primarily determined by the equilibrium potential of potassium ions. (Correct Answer)
Explanation: ***Is primarily determined by the equilibrium potential of potassium ions*** - The **resting membrane potential** of a nerve fiber is predominantly set by the efflux of **potassium ions** through leak channels, bringing the membrane potential close to potassium's equilibrium potential. - The high permeability of the nerve membrane to **potassium** at rest means that K+ movement is the most significant factor influencing the potential. *Is equal to the resting potential of cardiac muscle fibers* - **Cardiac muscle fibers** have a distinct resting potential (around -80 to -90 mV) influenced by different ion channels and regulatory mechanisms compared to nerve fibers (around -70 mV). - While both involve potassium currents, their specific conductances and the contribution of other ions differ significantly. *Can be accurately measured using intracellular electrodes* - While **intracellular electrodes** are indeed used to measure the resting membrane potential, this statement describes a measurement method, not the *primary factor* that determines the potential itself. - The method of measurement does not explain the underlying biophysical mechanisms that establish the potential. *Increases with elevated extracellular potassium concentration* - An **elevated extracellular potassium concentration** would make the resting membrane potential *less negative* (depolarize) rather than "increase" it in the typical sense of a more positive value. - This is because a higher external K+ reduces the concentration gradient for potassium efflux, bringing the membrane potential closer to zero.
Question 185: Which substrate is both secreted and filtered by the kidneys?
- A. Glucose
- B. Urea
- C. Uric Acid (Correct Answer)
- D. Na+
Explanation: ***Uric Acid*** - **Uric acid** is freely **filtered** at the glomerulus. - It undergoes both **secretion** and reabsorption in the renal tubules, making it a substrate that is both secreted and filtered. *Glucose* - **Glucose** is freely **filtered** at the glomerulus but is almost completely **reabsorbed** in the proximal tubule under normal physiological conditions. - It is not actively secreted by the renal tubules. *Urea* - **Urea** is freely **filtered** at the glomerulus. - It undergoes **reabsorption** (especially in the medullary collecting duct) and some facilitated diffusion, but significant active secretion is not its primary handling mechanism. *Na+* - **Sodium (Na+)** is freely **filtered** at the glomerulus in large quantities. - Its renal handling is dominated by extensive **reabsorption** throughout the nephron, which is crucial for fluid balance and blood pressure regulation, with no active secretion.
Question 186: Motilin secretion is decreased in which of the following states?
- A. Thirsty
- B. Starving
- C. Ingested meal (Correct Answer)
- D. Interdigestive state
Explanation: ***Ingested meal*** - Motilin secretion is **decreased after a meal** due to the presence of food in the small intestine, which stimulates other gastrointestinal hormones and neuronal reflexes that inhibit motilin release. - The primary role of motilin is to stimulate **gastric and intestinal motility** during fasting, clearing residual food and preventing bacterial overgrowth, making its activity counterproductive during digestion. *Thirsty* - **Thirst** is primarily regulated by antidiuretic hormone (ADH) and the renin-angiotensin-aldosterone system, and it does not directly impact motilin secretion. - Motilin's main function is related to gut motility, largely independent of the body's hydration status. *Starving* - Motilin levels tend to be **higher during fasting or starvation**, as it plays a crucial role in initiating the **migrating motor complex (MMC)**, which sweeps undigested material through the gastrointestinal tract. - This activity prevents bacterial overgrowth and prepares the gut for the next meal; thus, its secretion is increased, not decreased. *Interdigestive state* - The **interdigestive state** refers to the period between meals, which is synonymous with a fasting or starving state. - During this period, motilin secretion is **increased** to stimulate the **migrating motor complex (MMC)**, which is essential for gut cleansing.