NEET-PG 2012 - Physiology Practice Questions

Q: When the tension in a muscle fibre is maximum, its length is called?

Optimum length. ***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.

Q: What is the effect of acetylcholine on the Lower Esophageal Sphincter (LES)?

Causes contraction. ***Correct Option: Causes contraction*** - Acetylcholine acts on **M3 muscarinic receptors** on LES smooth muscle cells to cause **contraction** - This is part of the **excitatory cholinergic pathway** that maintains LES tone and prevents gastroesophageal reflux - Acetylcholine is released from **excitatory motor neurons** in the myenteric plexus *Incorrect: Causes relaxation* - LES relaxation during swallowing is mediated by **nitric oxide (NO)** and **vasoactive intestinal peptide (VIP)**, NOT acetylcholine - These inhibitory neurotransmitters are released from separate **inhibitory motor neurons** - The relaxation response during swallowing is due to activation of the inhibitory pathway, which suppresses cholinergic tone *Incorrect: No effect on LES* - Acetylcholine has a significant effect on the LES - It is one of the key neurotransmitters maintaining basal LES tone - Loss of cholinergic input can lead to decreased LES pressure *Incorrect: Contraction followed by relaxation* - Acetylcholine itself causes only contraction - The swallowing reflex involves coordinated activation of inhibitory (NO/VIP) and suppression of excitatory (acetylcholine) pathways - The sequence of events is neural, not a biphasic response to acetylcholine alone

Q: Salty taste is due to?

Sodium ion channels. ***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.

Q: Osmolarity is defined as?

Number of osmoles per litre. ***Number of osmoles per litre*** - **Osmolarity** is a measure of the **solute concentration** in a solution, specifically the number of **osmoles of solute per liter of solution**. - It is often used in clinical settings to assess the **concentration of dissolved particles** in bodily fluids like plasma. *Number of osmoles per kg* - This definition describes **osmolality**, which measures the concentration of a solution as the **number of osmoles of solute per kilogram of solvent**. - While related, osmolarity and osmolality are distinct terms, with osmolality being less affected by temperature and pressure changes. *Weight of solute per litre of solution* - This definition describes a **mass concentration** (e.g., g/L), but it does not account for the **number of osmotically active particles**. - Different solutes can have the same weight but varying numbers of particles (e.g., 1 mol of glucose vs. 1 mol of NaCl dissociates into 2 particles). *Weight of solvent per litre of solution* - This statement incorrectly relates to solvent quantity rather than solute concentration and is not a standard definition for osmolarity or any related osmotic property. - The focus of osmolarity is on the concentration of the **dissolved particles (solute)**, not the weight of the solvent.

Q: Transpulmonary pressure is the difference between:

Pressure in alveoli and intrapleural pressure. ***Pressure in alveoli and intrapleural pressure*** - Transpulmonary pressure is the **pressure gradient** across the lung wall, which is essential for maintaining alveolar inflation. - It is calculated as the **alveolar pressure minus the intrapleural pressure**. *The pressure in the bronchus and atmospheric pressure* - This difference would represent the pressure driving airflow through the **bronchial tree**, not the pressure across the lung wall itself. - It's a measure relevant to **airway resistance**, not lung distension. *The difference between atmospheric pressure and intrapleural pressure* - This difference is related to the **intrathoracic pressure**, which influences venous return and cardiac function, but not directly the distension of the lungs. - It does not account for the **alveolar pressure**, which is the primary internal pressure expanding the lung. *The difference between atmospheric pressure and intraalveolar pressure* - This difference is the **driving pressure for airflow** into or out of the lungs. - It represents the pressure gradient that causes air to move between the **atmosphere and the alveoli** during inspiration and expiration.

Q: Which of the following statements regarding the lower esophageal sphincter is TRUE?

It relaxes in response to swallowing.. ***It relaxes in response to swallowing.*** - The **lower esophageal sphincter (LES)** normally maintains high resting tone to prevent gastroesophageal reflux but **relaxes completely during swallowing** to allow passage of food into the stomach. - This relaxation (called **receptive relaxation**) is mediated by **vagal nerve stimulation** through release of nitric oxide (NO) and vasoactive intestinal peptide (VIP). - The relaxation occurs **before the peristaltic wave arrives**, allowing coordinated transit of the bolus. *It remains contracted during swallowing to prevent regurgitation.* - This is **incorrect** - the LES must **relax during swallowing** to allow food passage into the stomach. - Failure of LES relaxation during swallowing is the pathophysiology of **achalasia**, leading to dysphagia. - The LES only maintains contraction between swallows to prevent reflux. *Its tone is primarily influenced by the myogenic properties of the smooth muscle.* - While the LES contains smooth muscle with intrinsic myogenic properties, its tone is **predominantly regulated by neural and hormonal factors**. - **Neural control:** Vagal cholinergic pathways (increase tone), non-adrenergic non-cholinergic (NANC) pathways with NO and VIP (decrease tone). - **Hormonal factors:** Gastrin increases tone, while progesterone, CCK, and secretin decrease tone. *It contracts in response to gastric distension.* - This is **incorrect** - gastric distension actually triggers **transient LES relaxations (TLESRs)**, which are the primary mechanism of physiological reflux. - TLESRs are vagally mediated reflex responses that allow venting of gastric air. - Increased LES contraction in response to gastric distension would be counterproductive.

Q: Which of the following is NOT a location where multi-unit smooth muscle is present?

Gut. ***Gut*** - The gut primarily contains **unitary (single-unit) smooth muscle**, characterized by cells connected by **gap junctions** that allow for synchronized contractions (e.g., peristalsis). - This type of smooth muscle exhibits **spontaneous rhythmic contractions** due to pacemaker cells, and its activity is modulated by neural and hormonal inputs rather than requiring individual innervation of each cell. - Multi-unit smooth muscle is **NOT present** in the gut. *Blood vessels* - Many larger blood vessels (e.g., large arteries) contain **multi-unit smooth muscle**, which allows for **fine, graded control** over vascular tone and blood flow. - Each muscle cell is typically **innervated individually**, enabling precise regulation of contraction strength. *Iris* - The iris contains **multi-unit smooth muscle** (e.g., sphincter pupillae and dilator pupillae muscles) which control pupil size. - These muscles require **individual innervation** to allow for very fine and precise movements in response to light intensity changes. *Ciliary muscle* - The ciliary muscle of the eye contains **multi-unit smooth muscle**, which controls the shape of the lens for accommodation (focusing). - These muscle fibers are **individually innervated** to allow precise control of lens curvature for near and far vision.

Question 1

A man slept with his head over his forearm. The next morning, he complains of tingling and numbness over the forearm. If this were primarily due to hypoxia affecting nerve fibers, which of the following statements about nerve fiber sensitivity to hypoxia is correct?

Accepted Answer

B fibers are most sensitive to hypoxia, followed by A fibers, and C fibers are least sensitive.

Answer

All nerve fibers are equally sensitive to hypoxia.

Answer

C fibers are most sensitive to hypoxia, followed by B fibers, and A fibers are least sensitive.

Answer

A fibers are most sensitive to hypoxia, followed by B fibers, and C fibers are least sensitive.

Question 2

When the tension in a muscle fibre is maximum, its length is called?

Accepted Answer

Optimum length

Answer

None of the options

Answer

Initial length

Answer

Equilibrium length

Question 3

What is the effect of acetylcholine on the Lower Esophageal Sphincter (LES)?

Accepted Answer

Causes contraction

Answer

Causes relaxation

Answer

No effect on LES

Answer

Contraction followed by relaxation

Question 4

Salty taste is due to?

Accepted Answer

Sodium ion channels

Answer

Calcium ion channels

Answer

G-protein coupled receptors

Answer

Proton channels

Question 5

What is the Bohr effect in relation to hemoglobin's affinity for oxygen?

Accepted Answer

Decrease in O2 affinity of hemoglobin when the pH of blood falls

Answer

Decrease in CO2 affinity of hemoglobin when the pH of blood falls

Answer

Decrease in O2 affinity of hemoglobin when the pH of blood rises

Answer

Decrease in CO2 affinity of hemoglobin when the pH of blood rises

Question 6

Osmolarity is defined as?

Accepted Answer

Number of osmoles per litre

Answer

Number of osmoles per kg

Answer

Weight of solute per litre of solution

Answer

Weight of solvent per litre of solution

Question 7

Transpulmonary pressure is the difference between:

Accepted Answer

Pressure in alveoli and intrapleural pressure

Answer

The pressure in the bronchus and atmospheric pressure

Answer

The difference between atmospheric pressure and intrapleural pressure

Answer

The difference between atmospheric pressure and intraalveolar pressure

Question 8

Which of the following factors increases stroke volume?

Accepted Answer

Increased end-diastolic volume and decreased end-systolic volume

Answer

Increased end-diastolic and end-systolic volumes

Answer

Decreased end-diastolic and end-systolic volumes

Answer

Decreased end-diastolic volume and increased end-systolic volume

Question 9

Which of the following statements regarding the lower esophageal sphincter is TRUE?

Accepted Answer

It relaxes in response to swallowing.

Answer

It remains contracted during swallowing to prevent regurgitation.

Answer

Its tone is primarily influenced by the myogenic properties of the smooth muscle.

Answer

It contracts in response to gastric distension.

Question 10

Which of the following is NOT a location where multi-unit smooth muscle is present?

Accepted Answer

Gut

Answer

Blood vessels

Answer

Iris

Answer

Ciliary muscle

NEET-PG 2012 — Physiology