NEET-PG 2015 - Physiology Practice Questions

Q: Vibrations are detected by which types of receptors?

Rapidly adapting. ***Rapidly adapting*** - **Rapidly adapting mechanoreceptors**, such as **Pacinian corpuscles** and **Meissner's corpuscles**, are highly sensitive to changes in pressure and movement. - They fire at the **onset and offset of a stimulus**, making them ideal for detecting vibrations, which are rhythmic changes in pressure. *Slowly adapting* - **Slowly adapting mechanoreceptors**, such as **Merkel cells** and **Ruffini endings**, are responsible for sustained pressure and touch. - They continue to fire as long as the stimulus is present, making them less suited for detecting transient vibratory stimuli. *Non-adapting* - The human body does not typically have **truly non-adapting** sensory receptors; most receptors show some form of adaptation to continuous stimuli. - This term is not standard in the classification of mechanoreceptors based on their adaptation rates. *None of the above* - This option is incorrect because rapidly adapting receptors are indeed responsible for detecting vibrations.

Q: Which of the following receptors is stimulated by sustained pressure?

Ruffini's end organ. ***Ruffini's end organ*** - These are **slowly adapting mechanoreceptors** located deep in the dermis and subcutaneous tissue. - They are responsible for detecting **sustained pressure**, stretch, and position sense. *Merkel's disc* - These are **slowly adapting mechanoreceptors** found in the basal epidermis. - They are crucial for sensing **light touch** and **two-point discrimination**. *Hair cells* - These are **mechanoreceptors** primarily found in the inner ear, responsible for hearing and balance. - They are not involved in the perception of somatosensory stimuli like pressure on the skin. *Meissner Corpuscles* - These are **rapidly adapting mechanoreceptors** located in the dermal papillae, close to the skin surface. - They are primarily involved in detecting **light touch** and **discriminative touch**, especially changes in texture.

Q: Which of the following statements is true regarding smooth muscle contraction?

Phosphorylation of myosin is essential for contraction.. **Phosphorylation of myosin is essential for contraction.** - In **smooth muscle**, the **myosin light chain (MLC)** must be phosphorylated by **myosin light chain kinase (MLCK)** to enable interaction with actin and initiate contraction. - This phosphorylation causes a conformational change in the **myosin head**, increasing its ATPase activity and allowing cross-bridge cycling. *Calmodulin plays no role in smooth muscle contraction.* - **Calmodulin (CaM)** is crucial for smooth muscle contraction, as it binds **calcium ions (Ca²⁺)** forming a Ca²⁺-CaM complex. - This complex then activates **myosin light chain kinase (MLCK)**, which phosphorylates myosin, triggering contraction. *None of the options.* - This statement is incorrect because one of the provided options, "Phosphorylation of myosin is essential for contraction," is indeed true. *Troponin plays a significant role in smooth muscle contraction.* - Unlike **striated muscle (skeletal and cardiac)**, **smooth muscle** does not contain **troponin**. - Regulation of smooth muscle contraction is primarily **calcium-calmodulin-dependent**, with roles for **MLCK** and **MLCP**, rather than troponin.

Q: Maximum density of muscle spindle is found in?

Lumbricals. ***Lumbricals*** - **Lumbricals** are small, intricate muscles in the hand, responsible for fine motor control and precise movements like grasping and manipulating objects. - The high density of **muscle spindles** in lumbricals allows for extremely accurate feedback on muscle length and tension, crucial for **proprioception** and delicate tasks. *Calf muscle* - **Calf muscles** (gastrocnemius and soleus) are large muscles primarily involved in powerful movements like walking and running. - While they do contain muscle spindles for proprioception, their density is lower compared to muscles involved in fine motor control. *Quadriceps muscle* - The **quadriceps femoris** is a large muscle group in the thigh responsible for knee extension and powerful leg movements. - They contain muscle spindles to monitor muscle stretch, but not with the extreme density seen in muscles with fine motor functions. *Triceps* - The **triceps brachii** is a large muscle on the back of the upper arm, primarily responsible for elbow extension. - It has a moderate density of muscle spindles, sufficient for coordinating arm movements but not as high as muscles designed for precision.

Q: During the sympathetic fight-or-flight response, what is the primary cardiovascular effect of epinephrine and norepinephrine on skeletal muscle vasculature?

Increased blood flow to muscles. ***Increased blood flow to muscles*** - **Epinephrine** and **norepinephrine** cause **vasodilation** in skeletal muscle arterioles, shunting blood toward tissues critical for immediate physical action. - This response ensures that muscles have adequate **oxygen** and **nutrients** to support intense activity, enabling a quick escape or confrontation. *Increased blood flow to the skin* - During fight-or-flight, the body prioritizes essential organs, causing **vasoconstriction** in the skin to redirect blood flow away from non-essential areas. - This redirection helps to conserve blood and reduce potential blood loss from surface injuries. *Bronchoconstriction* - **Epinephrine** and **norepinephrine** actually cause **bronchodilation**, leading to the relaxation of airway smooth muscles. - This effect increases the diameter of the airways, allowing more air to enter and exit the lungs, thereby enhancing **oxygen intake** and carbon dioxide expulsion. *Decreased heart rate* - The primary effect of **epinephrine** and **norepinephrine** is to **increase heart rate** and myocardial contractility. - This cardiac acceleration enhances **cardiac output**, ensuring rapid and efficient delivery of oxygenated blood throughout the body to meet the demands of stress.

Q: EPSP is due to?

Sodium ion influx. ***Sodium ion influx*** - An **Excitatory Postsynaptic Potential (EPSP)** is caused primarily by the binding of an **excitatory neurotransmitter** to its receptor, leading to the opening of **ligand-gated ion channels** permeable to sodium (Na+) ions. - The **influx of positively charged sodium ions** into the postsynaptic neuron causes a **depolarization** of the membrane potential, making it more likely to reach the threshold for an action potential. *Potassium ion influx* - **Potassium (K+) influx** is not the primary mechanism for generating an EPSP; instead, **potassium efflux** (movement out of the cell) is typically involved in **repolarization** after an action potential or in generating **Inhibitory Postsynaptic Potentials (IPSPs)**. - The movement of K+ into the cell would make the membrane potential more negative, leading to **hyperpolarization** or preventing depolarization. *Sodium ion efflux* - **Sodium (Na+) efflux** is mediated by the **Na+/K+ pump** and is crucial for maintaining the resting membrane potential, but it does **not directly cause an EPSP**. - Pumping Na+ out of the cell would **hyperpolarize** the cell or oppose depolarization, making an action potential less likely. *Calcium ion influx* - While **calcium (Ca2+) influx** is vital for many neuronal processes, including **neurotransmitter release** from the presynaptic terminal, it is **not the primary ionic basis** for generating an EPSP in the postsynaptic neuron itself. - Significant Ca2+ influx can occur during an **action potential** or lead to intracellular signaling, but it's not the main depolarizing current responsible for an EPSP.

Q: Which of the following statements about ENaC is incorrect?

Composed of 2 homologous subunits. ***Composed of 2 homologous subunits*** - ENaC (Epithelial Sodium Channel) is a **heterotrimeric complex** composed of **three distinct subunits**: α, β, and γ. - The functional channel typically has a stoichiometry of 2α:1β:1γ, forming a heterotrimer. - These subunits share sequence homology but are **non-identical proteins**, not just two homologous subunits. - A fourth related subunit (δ) exists and can substitute for α in some tissues, but the classical ENaC is a three-subunit channel. *Epithelial channel* - ENaC is indeed an **epithelial channel** responsible for critical **sodium reabsorption** in various epithelia. - It plays a vital role in regulating **fluid and electrolyte balance** across tight epithelial layers. *Present in kidney and GIT* - ENaC is abundantly expressed in the **distal nephron of the kidney**, specifically in the collecting duct, where it mediates fine-tuning of sodium reabsorption. - It is also present in the **lower gastrointestinal tract (colon)**, contributing to sodium absorption, and in the airways and salivary glands. *Inhibited by amiloride* - **Amiloride** is a well-known **potassium-sparing diuretic** that specifically acts by blocking ENaC. - This inhibition reduces sodium reabsorption and, consequently, water reabsorption, leading to increased diuresis.

Q: What is one of the specific functions of the primary motor cortex located on the anterior edge of the pre-central gyrus?

Control of voluntary movement. ***Control of voluntary movement*** - The **primary motor cortex (M1)**, located in the **precentral gyrus**, is critically involved in generating neural impulses that control the execution of **voluntary movements**. - It plays a key role in **planning and executing complex, skilled movements**, especially of the distal musculature. *Increase extensor muscle tone* - While motor pathways influence muscle tone, the primary motor cortex's most specific role is not simply increasing extensor tone; rather, it coordinates a wide range of movements involving both flexors and extensors. - **Spasticity** or increased muscle tone (often extensor) is more commonly associated with damage to the **corticospinal tracts (upper motor neuron lesions)**, which *prevents* the fine-tuning inhibitory control from the cortex. *Perception of pain* - **Pain perception** is primarily processed in the **somatosensory cortex** (postcentral gyrus), limbic system, and insula, not the primary motor cortex. - The primary motor cortex is responsible for **motor output**, not sensory interpretation. *Inhibition of stretch reflex* - While descending motor pathways can modulate spinal reflexes, the direct and primary function of the primary motor cortex is not the specific inhibition of the stretch reflex. - The **gamma motor system** and other spinal interneurons are more directly involved in modulating the sensitivity of the stretch reflex.

Q: Which part of the sympathetic nervous system is responsible for secreting catecholamines?

Adrenal medulla. ***Adrenal medulla*** - The adrenal medulla acts as a modified **sympathetic ganglion**, directly innervated by **preganglionic sympathetic fibers**. - Upon stimulation, it releases a high concentration of **epinephrine** (adrenaline) and a smaller amount of **norepinephrine** (noradrenaline) into the bloodstream, acting as hormones. *Cardiac ganglion* - **Cardiac ganglia** are parasympathetic ganglia located in the heart, involved in regulating heart rate and contractility via acetylcholine release. - They do not secrete **catecholamines** but rather act as relay stations for parasympathetic innervation. *Cervical sympathetic chain* - The **cervical sympathetic chain** primarily innervates structures in the head, neck, and upper limbs, influencing functions like pupils, salivary glands, and sweat glands. - While it contains sympathetic neurons, its primary role is not the systemic release of **catecholamines** into the bloodstream. *Thoracic sympathetic chain* - The **thoracic sympathetic chain** provides sympathetic innervation to organs in the thoracic and abdominal cavities, influencing heart rate, bronchodilation, and visceral blood flow. - Like other sympathetic ganglia, it releases norepinephrine at target organ synapses, but it does not serve as a major endocrine gland for systemic catecholamine release.

Q: What is the typical resting membrane potential (RMP) of smooth muscle cells?

-60 mV. ***-60 mV*** - Smooth muscle cells typically have a **resting membrane potential of -55 to -60 mV**, which is **less negative** compared to skeletal muscle (-90 mV) or neurons (-70 mV). - This relatively depolarized RMP allows them to be **more easily excited** and enables **spontaneous slow wave depolarizations** and pacemaker activity in some smooth muscle types. - The less negative potential is due to higher resting permeability to Na+ and Ca2+ compared to skeletal muscle. *-90 mV* - This is the typical resting membrane potential for **skeletal muscle cells** and **large myelinated nerve fibers**. - Such a highly negative RMP provides a **larger buffer against accidental excitation** and ensures precise voluntary control. - This value is maintained by high K+ permeability and active Na+/K+ ATPase activity. *-70 mV* - This is the characteristic resting membrane potential of **most neurons**, allowing for efficient generation and propagation of action potentials. - It represents a balance between depolarizing and hyperpolarizing influences, optimal for neuronal signaling. - This is more negative than smooth muscle but less negative than skeletal muscle. *-40 mV* - This value is **too depolarized** to be a stable resting potential for smooth muscle and would be **near threshold potential**. - At -40 mV, voltage-gated calcium channels would be significantly activated, causing sustained contraction rather than a resting state. - This might represent a **partially depolarized state** or the RMP of specialized pacemaker cells like cardiac SA node cells, but **not typical smooth muscle**.

Question 1

Vibrations are detected by which types of receptors?

Accepted Answer

Rapidly adapting

Answer

Slowly adapting

Answer

Non-adapting

Answer

None of the above

Question 2

Which of the following receptors is stimulated by sustained pressure?

Accepted Answer

Ruffini's end organ

Answer

Merkel's disc

Answer

Hair cells

Answer

Meissner Corpuscles

Question 3

Which of the following statements is true regarding smooth muscle contraction?

Accepted Answer

Phosphorylation of myosin is essential for contraction.

Answer

None of the options.

Answer

Calmodulin plays no role in smooth muscle contraction.

Answer

Troponin plays a significant role in smooth muscle contraction.

Question 4

Maximum density of muscle spindle is found in?

Accepted Answer

Lumbricals

Answer

Calf muscle

Answer

Triceps

Answer

Quadriceps muscle

Question 5

During the sympathetic fight-or-flight response, what is the primary cardiovascular effect of epinephrine and norepinephrine on skeletal muscle vasculature?

Accepted Answer

Increased blood flow to muscles

Answer

Increased blood flow to the skin

Answer

Bronchoconstriction

Answer

Decreased heart rate

Question 6

EPSP is due to?

Accepted Answer

Sodium ion influx

Answer

Potassium ion influx

Answer

Sodium ion efflux

Answer

Calcium ion influx

Question 7

Which of the following statements about ENaC is incorrect?

Accepted Answer

Composed of 2 homologous subunits

Answer

Present in kidney and GIT

Answer

Epithelial channel

Answer

Inhibited by amiloride

Question 8

What is one of the specific functions of the primary motor cortex located on the anterior edge of the pre-central gyrus?

Accepted Answer

Control of voluntary movement

Answer

Increase extensor muscle tone

Answer

Perception of pain

Answer

Inhibition of stretch reflex

Question 9

Which part of the sympathetic nervous system is responsible for secreting catecholamines?

Accepted Answer

Adrenal medulla

Answer

Cardiac ganglion

Answer

Cervical sympathetic chain

Answer

Thoracic sympathetic chain

Question 10

What is the typical resting membrane potential (RMP) of smooth muscle cells?

Accepted Answer

-60 mV

Answer

-90 mV

Answer

-70 mV

Answer

-40 mV

NEET-PG 2015 — Physiology