NEET-PG 2012 - Physiology Practice Questions

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: Diurnal variation of ACTH depends on ?

Suprachiasmatic nucleus. ***Suprachiasmatic nucleus*** - The **suprachiasmatic nucleus (SCN)** acts as the body's **master circadian clock**, synchronizing various physiological rhythms, including the **diurnal variation of ACTH** secretion. - It receives light input from the **retina** and projects to other brain regions to regulate the timing of hormone release. *Supraoptic nucleus* - The **supraoptic nucleus (SON)** is primarily involved in the production of **vasopressin (ADH)** and **oxytocin**, which are released by the posterior pituitary. - It does not directly control the diurnal rhythm of ACTH. *Ventrolateral nucleus* - The **ventrolateral preoptic area (VLPO)** is a key region for **sleep regulation**, promoting sleep by inhibiting wake-promoting neurotransmitters. - While it contributes to sleep-wake cycles, it is not the primary regulator of ACTH's diurnal variation. *Thalamus* - The **thalamus** is a major relay center for sensory information and plays a role in consciousness, sleep, and alertness. - It does not directly control the **circadian rhythm of ACTH secretion**.

Q: Nonshivering thermogenesis in adults is due to:

Brown fat between the shoulders. ***Brown fat between the shoulders*** - In adults, the primary **effector tissue** for **non-shivering thermogenesis** is **brown adipose tissue (BAT)**, with major depots located between the shoulders, around the neck, and along the spine. - **BAT** contains specialized mitochondria with **uncoupling protein 1 (UCP1)** that uncouples oxidative phosphorylation, generating heat instead of ATP. - This is the tissue where non-shivering thermogenesis actually occurs, making it the direct answer to what non-shivering thermogenesis is "due to." *Noradrenaline* - **Noradrenaline** is the key neurotransmitter that **activates brown fat** via **β3-adrenergic receptors** to initiate non-shivering thermogenesis. - While noradrenaline is the **trigger/stimulus**, the actual heat production occurs in brown adipose tissue. - Noradrenaline itself does not produce heat directly; it acts as the signal that activates the thermogenic machinery in BAT. *Thyroid hormone* - **Thyroid hormone** increases **basal metabolic rate** and can potentiate the thermogenic response by upregulating UCP1 expression in brown fat. - Its role is **permissive and long-term** rather than being the immediate effector of acute non-shivering thermogenesis. - It modulates overall cellular metabolism but is not the primary mechanism for rapid heat generation in cold exposure. *Muscle metabolism* - **Muscle contraction** during shivering generates heat through increased ATP hydrolysis, which is **shivering thermogenesis**. - **Non-shivering thermogenesis** specifically refers to heat production **without muscle contraction**, making muscle metabolism the mechanism for shivering, not non-shivering, thermogenesis.

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.

Q: What happens to the pressure in the calf compartment during the heel touch phase of walking?

Increases compared to resting pressure. ***Increases compared to resting pressure*** - During **heel strike (initial contact)**, the calf muscles (**gastrocnemius and soleus**) contract eccentrically to control ankle dorsiflexion and decelerate the foot - Simultaneous **weight bearing** and **muscle contraction** within the confined fascial compartment lead to increased intramuscular pressure - This is a well-documented phenomenon in gait biomechanics and exercise physiology *Decreases compared to resting pressure* - Incorrect: Muscle activation and weight bearing during initial contact inherently increase compartment pressure - Pressure decrease occurs during swing phase when the limb is unloaded and muscles are relaxed *First increases and then decreases* - While pressure varies throughout the complete gait cycle, the **heel touch phase specifically** is characterized by an initial pressure increase - The brief duration of heel strike does not typically show a biphasic pressure pattern within this single phase *Remains the same as resting pressure* - Incorrect: Active weight bearing and eccentric muscle contraction during heel strike necessarily elevate intramuscular pressure above resting levels - Resting pressure only occurs when the limb is unloaded and muscles are inactive

Q: Mechanism by which Ach decreases heart rate is by:

Delayed diastolic depolarization. ***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.

Q: Damage to the striatum primarily affects which type of memory?

Memory of how to perform tasks. ***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.

Q: Which part of the brain is responsible for setting posture before planned movement?

Supplementary motor cortex. ***Supplementary motor cortex*** - The **supplementary motor cortex (SMA)** is responsible for **anticipatory postural adjustments** that occur before voluntary movements - It plays a key role in **internal generation and planning of complex motor sequences** - SMA activation precedes movement, ensuring **postural stability and coordination** - Essential for **bilateral coordination** and **motor programming** *Premotor cortex* - The **premotor cortex** is primarily involved in **externally guided movements** and selection of movements based on sensory cues - While it participates in motor planning, it is more focused on **sensory-motor integration** rather than anticipatory postural control *Motor cortex* - The **primary motor cortex** executes voluntary movements by sending signals directly to spinal motor neurons - Responsible for **fine motor control** and determining the **force and direction** of muscle contractions - Functions in **movement execution** rather than preparatory postural adjustments *Frontal eye fields* - The **frontal eye fields** control **voluntary saccadic eye movements** and visual attention - Not involved in trunk or limb **postural preparation** for planned movements

Q: Lesion of preoptic nucleus of hypothalamus is associated with which of the following conditions?

Hyperthermia. ***Hyperthermia*** - The **preoptic nucleus** of the anterior hypothalamus is the primary **heat-loss center** containing warm-sensitive neurons. - Lesion of this area impairs **heat dissipation mechanisms** (sweating, cutaneous vasodilation), preventing the body from lowering its temperature. - Results in **hyperthermia** - a pathological elevation of core body temperature due to failure of heat dissipation, not a change in set point. - This is the **most specific and clinically accurate** term for this condition. *Impaired thermoregulation* - While technically true, this is too **broad and non-specific**. - Impaired thermoregulation could refer to inability to either increase or decrease temperature. - In medical terminology, we use more specific terms like "hyperthermia" to describe the actual clinical condition. *Increased body temperature* - This is a **general descriptive term** rather than a specific clinical diagnosis. - While the body temperature is indeed increased, **hyperthermia** is the precise medical term that indicates the mechanism (impaired heat dissipation). - Less specific than "hyperthermia" for exam purposes. *Normal thermoregulation* - Clearly incorrect - a lesion in the primary thermoregulatory center would **abolish normal temperature control**. - The preoptic nucleus is essential for detecting and responding to temperature changes.

Question 1

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 2

Diurnal variation of ACTH depends on ?

Accepted Answer

Suprachiasmatic nucleus

Answer

Supraoptic nucleus

Answer

Ventrolateral nucleus

Answer

Thalamus

Question 3

Nonshivering thermogenesis in adults is due to:

Accepted Answer

Brown fat between the shoulders

Answer

Muscle metabolism

Answer

Thyroid hormone

Answer

Noradrenaline

Question 4

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

Question 5

What happens to the pressure in the calf compartment during the heel touch phase of walking?

Accepted Answer

Increases compared to resting pressure

Answer

Decreases compared to resting pressure

Answer

First increases and then decreases

Answer

Remains the same as resting pressure

Question 6

Which one of the following is the CORRECT statement regarding coronary blood flow?

Accepted Answer

Coronary blood flow is directly related to perfusion pressure and inversely related to resistance

Answer

Coronary blood flow is inversely related to perfusion pressure and directly related to resistance

Answer

Coronary blood flow is directly related to perfusion pressure and also to resistance

Answer

Coronary blood flow is inversely related to both pressure and resistance

Question 7

Mechanism by which Ach decreases heart rate is by:

Accepted Answer

Delayed diastolic depolarization

Answer

Prolongation of action potential duration

Answer

Reduction in calcium influx

Answer

Inhibition of sympathetic activity

Question 8

Damage to the striatum primarily affects which type of memory?

Accepted Answer

Memory of how to perform tasks

Answer

Memory for recent events

Answer

Memory for past experiences

Answer

Memory for facts and events

Question 9

Which part of the brain is responsible for setting posture before planned movement?

Accepted Answer

Supplementary motor cortex

Answer

Motor cortex

Answer

Frontal eye fields

Answer

Premotor cortex

Question 10

Lesion of preoptic nucleus of hypothalamus is associated with which of the following conditions?

Accepted Answer

Hyperthermia

Answer

Impaired thermoregulation

Answer

Increased body temperature

Answer

Normal thermoregulation

NEET-PG 2012 — Physiology