NEET-PG 2012

1213 Questions — Page 27 of 122

Anatomy

4 questions

Q261

What is the outer layer of the blastocyst called?

Q262

Which of the following is an operculated sulcus ?

Q263

Risorius is a muscle of?

Q264

From which ribs does the spleen extend?

NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs

Question 261: What is the outer layer of the blastocyst called?

A. Embryo proper
B. Trophoblast (Correct Answer)
C. Primitive streak
D. Yolk sac

Explanation: ***Trophoblast*** - The **trophoblast** is the outer layer of cells of the blastocyst, which goes on to form the **placenta** and other extraembryonic tissues [1]. - It plays a crucial role in the **implantation** of the blastocyst into the uterine wall and in producing hormones [1]. *Primitive streak* - The **primitive streak** is a structure that forms during **gastrulation**, much later than the initial blastocyst stage. - It establishes the **anterior-posterior axis** and initiates the formation of the three germ layers. *Yolk sac* - The **yolk sac** is an extraembryonic membrane that forms within the blastocyst cavity, but it is not the outermost layer of the entire structure. - It is involved in early **nutrient transfer** and **blood cell formation** before the placenta is fully functional. *Embryo proper* - The **embryo proper**, derived from the **inner cell mass (ICM)**, is the part of the blastocyst that will develop into the actual embryo [2]. - It is located *inside* the trophoblast layer, not forming the outer boundary of the blastocyst [2].

Question 262: Which of the following is an operculated sulcus ?

A. Lunate
B. Calcarine
C. Central
D. Sylvian fissure (lateral sulcus) (Correct Answer)

Explanation: ***Sylvian fissure (lateral sulcus)*** - The **lateral sulcus**, also known as the Sylvian fissure, is a deep groove on the lateral surface of the brain that **separates the frontal and parietal lobes from the temporal lobe**. - It is considered an **operculated sulcus** because its banks contain the insula, which is a buried part of the cerebral cortex covered by the surrounding cortical folds called opercula. *Calcarine* - The **calcarine sulcus** is located on the medial surface of the occipital lobe, forming the primary visual cortex, and is not an operculated sulcus. - It delineates the **upper and lower banks of the visual cortex** and does not involve overlying cortical structures. *Lunate* - The **lunate sulcus** is found on the posterior part of the occipital lobe and is not typically described as an operculated sulcus. - It represents a boundary in the visual cortex, but its banks do not hide a buried cortical region like the insula. *Central* - The **central sulcus** (Rolandic fissure) separates the frontal lobe from the parietal lobe and is a prominent sulcus, but it is not operculated. - Its banks contain the **precentral gyrus** (primary motor cortex) and **postcentral gyrus** (primary somatosensory cortex) directly facing each other.

Question 263: Risorius is a muscle of?

A. Mastication
B. Deglutition
C. Facial expression (Correct Answer)
D. Eye movement

Explanation: Facial expression - The **risorius muscle** retracts the **corner of the mouth** laterally, contributing to smiling or grimacing. - It falls under the category of **mimetic muscles**, all of which are innervated by the **facial nerve (cranial nerve VII)**. *Mastication* - Muscles of mastication, such as the **masseter**, **temporalis**, and **pterygoids**, are primarily involved in **chewing** and moving the mandible. - These muscles are innervated by the **trigeminal nerve (cranial nerve V)**, not the facial nerve. *Deglutition* - Deglutition refers to the process of **swallowing**, involving muscles of the **pharynx** and **larynx**. - Examples include the **palatoglossus**, **stylopharyngeus**, and **superior pharyngeal constrictor**. *Eye movement* - Muscles responsible for eye movement are the **extrinsic ocular muscles**, such as the **recti** and **oblique muscles** [1]. - These muscles are innervated by the **oculomotor (III)**, **trochlear (IV)**, and **abducens (VI)** cranial nerves. *Note: No provided references mention the risorius muscle, mimetic muscles, or muscles of mastication; citations are applied only to supported sub-topics.*

Question 264: From which ribs does the spleen extend?

A. 5th to 9th rib
B. 2nd to 5th rib
C. 11th to 12th rib
D. 9th to 11th rib (Correct Answer)

Explanation: ***9th to 11th rib*** - The **spleen** is located in the **left upper quadrant** of the abdomen, deep to the 9th, 10th, and 11th ribs. - Its protected position beneath these ribs makes it vulnerable to injury from trauma to the left lower chest or upper abdomen. *5th to 9th rib* - This range primarily covers the location of the **heart** and the upper part of the **lungs**. - While the spleen is superior to other abdominal organs, it does not extend as high as the 5th rib. *2nd to 5th rib* - This region is mainly associated with the **upper lobes of the lungs** and the **superior mediastinum**. - The spleen is an abdominal organ and is situated much lower in the thoracic cavity. *11th to 12th rib* - This range is too low and posterior for the typical position of the spleen, especially for its superior border. - The 12th rib primarily overlies the **kidneys** and the more inferior aspects of the diaphragm.

Biochemistry

1 questions

Q261

What cofactor is required for the proper functioning of glucose-6-phosphate dehydrogenase?

Internal Medicine

1 questions

Q261

Progressive distal-to-proximal motor recovery following nerve regeneration is most characteristic of which type of nerve injury?

Physiology

4 questions

Q261

What is the fixed length of a myosin filament?

Q262

What happens to the concentration of inulin as fluid passes through the Proximal Convoluted Tubule (PCT)?

Q263

Gastric secretions are essential for absorption of -

Q264

What is the difference between the amount of Oxygen consumed and Carbon Dioxide produced per minute at rest?

NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs

Question 261: What is the fixed length of a myosin filament?

A. 0.16 nm
B. 1.6 micrometers (Correct Answer)
C. 16 nm
D. 1.6 mm

Explanation: ***1.6 micrometers*** - Myosin filaments, also known as **thick filaments**, are integral components of muscle contraction and have a characteristic fixed length. This length is precisely **1.6 micrometers** in mammalian skeletal muscle. - This consistent length is crucial for the **sliding filament model** of muscle contraction, ensuring proper overlap with actin filaments and efficient force generation. *0.16 nm* - This value is significantly too small; **nanometers (nm)** are typically used for atomic or molecular distances, not for entire protein filaments like myosin. - A myosin filament is composed of hundreds of myosin molecules, making its overall length much larger than a fraction of a nanometer. *16 nm* - While nanometers are used for molecular structures, 16 nm is still too small for a myosin filament. The entire filament is roughly **100 times larger** than this value. - This dimension might be more appropriate for the diameter of a single myosin molecule's head region, but not the entire filament's length. *1.6 mm* - This value is significantly too large; **millimeters (mm)** are visible to the naked eye and represent macroscopic objects. - Muscle filaments are microscopic structures, and a length of 1.6 mm would imply they are many times longer than an entire muscle cell.

Question 262: What happens to the concentration of inulin as fluid passes through the Proximal Convoluted Tubule (PCT)?

A. Concentration of inulin increases (Correct Answer)
B. Concentration of urea remains constant
C. Concentration of HCO3- increases
D. Concentration of Na+ decreases

Explanation: ***Concentration of inulin increases*** - Inulin is **freely filtered** at the glomerulus and is neither reabsorbed nor secreted along the renal tubule, making it an excellent marker for **glomerular filtration rate (GFR)**. - As water is reabsorbed from the PCT, the volume of tubular fluid decreases, causing the concentration of **unreabsorbed solutes**, like inulin, to increase. *Concentration of urea remains constant* - Urea is **reabsorbed** along the tubule, though passively; its concentration typically **increases** initially in the PCT due to water reabsorption, but then decreases as some is reabsorbed. - The statement is incorrect because urea concentration changes significantly throughout the nephron, particularly increasing as water is reabsorbed and then decreasing with some reabsorption. *Concentration of HCO3- increases* - The majority (approximately 80-90%) of **bicarbonate (HCO3-)** is reabsorbed in the PCT, primarily through its conversion to CO2 within the tubular lumen and then back to HCO3- intracellularly. - Therefore, the concentration of HCO3- in the tubular fluid actually **decreases** significantly as fluid passes through the PCT. *Concentration of Na+ decreases* - **Sodium (Na+)** is actively reabsorbed along the entire nephron, with about 65-70% reabsorbed in the PCT. - While Na+ is reabsorbed, water follows passively, so its concentration in the tubular fluid remains relatively **iso-osmotic** with plasma, meaning its concentration does not significantly decrease as fluid passes through the PCT, remaining fairly constant.

Question 263: Gastric secretions are essential for absorption of -

A. Cobalamin (Correct Answer)
B. Fat
C. Thiamine
D. Folic acid

Explanation: ***Cobalamin*** - **Intrinsic factor**, secreted by gastric parietal cells, is crucial for the absorption of **vitamin B12 (cobalamin)** in the terminal ileum [1]. - Without sufficient intrinsic factor, **pernicious anemia** can develop due to impaired B12 absorption [2]. *Fat* - Fat digestion primarily occurs in the **small intestine** with the help of **bile salts** and **pancreatic lipases**. - While gastric lipase begins some fat digestion, it's not essential for overall fat absorption. *Thiamine* - **Thiamine (vitamin B1)** is absorbed in the jejunum and ileum, primarily via **active transport** and passive diffusion. - Gastric secretions do not play a direct, essential role in its absorption. *Folic acid* - **Folic acid** is absorbed in the **duodenum and jejunum** as monoglutamates after being deconjugated from polyglutamate forms. - This process is not directly dependent on gastric secretions [2].

Question 264: What is the difference between the amount of Oxygen consumed and Carbon Dioxide produced per minute at rest?

A. 20 ml/min
B. 50 ml/min (Correct Answer)
C. 75 ml/min
D. 100 ml/min

Explanation: ***50 ml/min*** - The body typically consumes about **250 ml/min of oxygen** at rest and produces approximately **200 ml/min of carbon dioxide**. - The difference between oxygen consumed and carbon dioxide produced is therefore **50 ml/min** (250 - 200 = 50). - This difference exists because the **respiratory quotient (RQ)** is approximately **0.8** (200/250), meaning less CO2 is produced than O2 consumed on a molar basis. *20 ml/min* - This value is **too low** and underestimates the physiological difference between oxygen consumption and carbon dioxide production. - With typical O2 consumption of 250 ml/min and RQ of 0.8, the difference cannot be this small. *75 ml/min* - This value represents an **overestimation** of the difference between oxygen consumption and carbon dioxide production under normal resting conditions. - This would imply an RQ of approximately 0.7, which is lower than the typical mixed diet RQ of 0.8. *100 ml/min* - This value is a significant **overestimation** of the physiological difference. - This would suggest an RQ of 0.6, which is not physiologically normal for resting conditions on a mixed diet.