NEET-PG 2013 - Physiology Practice Questions

Q: Which of the following is classified as a pain receptor?

Free nerve endings. ***Free nerve endings*** - **Free nerve endings** are the most common type of sensory receptor in the skin and are responsible for detecting **pain**, temperature, and crude touch. - They lack specialized structures and are found throughout the epidermis and dermis. *Meissner's corpuscle* - **Meissner's corpuscles** are encapsulated nerve endings that detect **light touch** and **vibration**. - They are rapidly adapting and are abundant in sensitive, hairless skin areas like fingertips and lips. *Pacinian corpuscle* - **Pacinian corpuscles** are large, encapsulated receptors that detect **deep pressure** and **vibration**. - They are rapidly adapting and respond to high-frequency stimuli. *Merkel disc* - **Merkel discs** are specialized epithelial cells associated with nerve endings that detect **sustained pressure** and **texture**. - They are slowly adapting receptors crucial for tactile discrimination.

Q: Spinal pathway mainly regulating fine motor activity?

Lateral corticospinal tract. ***Lateral corticospinal tract*** - This pathway contains **85-90% of corticospinal fibers** that cross at the medullary pyramids and descend in the **lateral funiculus** of the spinal cord - It is the **primary pathway for fine, precise, voluntary movements** of **distal extremities**, particularly the hands, fingers, feet, and toes - Enables intricate skilled movements like writing, buttoning, and fine manipulation due to direct monosynaptic connections to motor neurons - Damage results in loss of fine motor control and skilled movements *Anterior corticospinal tract* - Contains only **10-15% of corticospinal fibers** that descend uncrossed in the anterior spinal cord - Controls **bilateral movements of axial and proximal muscles** (neck, trunk, shoulders) - Not specialized for fine motor control of distal limbs *Vestibulospinal tract* - Regulates **posture and balance** by modulating extensor muscle tone - Coordinates head position and maintains upright posture - Does not control fine voluntary movements *Reticulospinal tract* - Modulates **muscle tone, posture, and locomotion** - Provides general motor control and autonomic regulation - Not specialized for precise, intricate fine motor movements

Q: What is the normal cerebral blood flow in milliliters per minute for a healthy adult?

750 ml/min. ***750 ml/min*** - The brain receives approximately **15% of the cardiac output**, which for an average adult with a cardiac output of 5 L/min (5000 ml/min) translates to about **750 ml/min**. - This flow rate is essential to meet the high metabolic demands of the brain, which consumes about **20% of the body's total oxygen**. - For reference, this corresponds to approximately **50-55 ml/100g/min** when normalized to brain tissue weight. *55 ml/min* - This value represents the **cerebral blood flow per 100 grams of brain tissue** (50-55 ml/100g/min), not the **total cerebral blood flow**. - As a total flow value, 55 ml/min would be severely **inadequate** for the entire brain (~1400g) and would lead to immediate **ischemia** and neurological dysfunction. *150 ml/min* - While higher than 55 ml/min, this rate is still **grossly insufficient** to maintain the metabolic needs of the entire adult brain. - Such a low total flow would result in widespread **cerebral hypoperfusion** and severe neurological deficits. *1000 ml/min* - Although the brain has significant blood flow, 1000 ml/min is generally **higher than the normal average** for a healthy adult at rest. - The normal range is typically **750-800 ml/min**; sustained flow at 1000 ml/min might be seen in hyperemia or certain physiological states but is not the typical baseline.

Q: What is the primary action observed in the withdrawal reflex?

Flexion. ***Flexion*** - The **withdrawal reflex** is a protective reflex that causes the affected limb to **flex** and withdraw from a painful stimulus. - This **flexion** is mediated by the contraction of flexor muscles and relaxation of extensor muscles, moving the limb away from danger. *Extension* - **Extension** is the opposite of flexion and would move the limb closer to or maintain its position relative to the painful stimulus. - This action is typically observed in the **crossed extensor reflex**, where the contralateral limb extends to support the body, not in the direct withdrawal of the stimulated limb. *Flexion followed by extension* - While **flexion** is the primary action, it is not typically followed immediately by extension within the same limb in a simple withdrawal reflex. - If a coordinated movement were to occur, such as shifting weight, the **crossed extensor reflex** would involve extension in the opposite limb. *Not applicable* - The withdrawal reflex involves a clear and defined muscle action which is **flexion**, making "not applicable" incorrect. - This reflex is a fundamental component of the nervous system's response to noxious stimuli.

Q: Which of the following substances has the same concentration in cerebrospinal fluid (CSF) and plasma?

Cl. ***Cl*** - **Chloride ions (Cl-)** have the **closest concentration** between CSF and plasma among the listed options, with a CSF-to-plasma ratio of approximately 1.1-1.15. - CSF chloride is **slightly higher** than plasma chloride (CSF: ~120-130 mEq/L; Plasma: ~100-110 mEq/L) because chloride ions freely cross the **blood-brain barrier** and help maintain **electroneutrality** in CSF due to the low protein content. - The elevated chloride compensates for the absence of negatively charged proteins in CSF, making it the **best answer** among the given options. *Glucose* - **Glucose** concentration in CSF is approximately **60-70%** of plasma glucose concentration (CSF: 50-80 mg/dL; Plasma: 70-110 mg/dL). - Transport across the **blood-brain barrier** occurs via **GLUT1 transporters**, which are tightly regulated to meet brain metabolic demands. *Ca* - **Calcium (Ca2+)** concentration in CSF is **significantly lower** than in plasma (CSF: ~2.1-2.5 mg/dL; Plasma: ~8.5-10.5 mg/dL). - Only the **ionized, unbound fraction** can cross the blood-brain barrier, as protein-bound calcium cannot pass through. *HCO3* - **Bicarbonate (HCO3-)** concentration in CSF is typically **slightly lower** than in plasma (CSF: ~20-25 mEq/L; Plasma: ~22-28 mEq/L). - Active regulation maintains **CSF pH** and CO2 buffering capacity independent of plasma bicarbonate levels.

Q: Cell bodies of orexigenic neurons are present in?

Lateral hypothalamic area. ***Lateral hypothalamic area*** - The **lateral hypothalamic area** (LHA) contains neurons that produce **orexin (hypocretin)**, a neuropeptide critical for promoting appetite and wakefulness. - Stimulation of the LHA leads to increased food seeking and consumption, earning it the moniker "**feeding center**." *Dorsal raphe* - The **dorsal raphe nucleus** is a key source of **serotonin** in the brain, involved in mood, sleep-wake cycles, and appetite regulation (often promoting satiety). - It does not primarily house orexigenic neurons that directly stimulate appetite. *Locus coerulus* - The **locus coeruleus** is the primary source of **norepinephrine** in the brain, playing a significant role in arousal, attention, and stress response. - While it modulates appetitive behaviors indirectly, its neurons are not the primary orexigenic cell bodies. *Hippocampus* - The **hippocampus** is crucial for **learning, memory formation**, and spatial navigation. - It is not directly involved in the primary neural circuits that control hunger and satiety through orexigenic neuropeptides.

Q: Cushing reflex is associated with all except?

Hypotension. ***Hypotension*** - The **Cushing reflex** is a compensatory response to increased intracranial pressure (ICP) aiming to maintain cerebral perfusion, which typically involves **hypertension**, not hypotension. - While prolonged or severe ICP can lead to decompensation and eventual hypotension, it is not a direct component of the reflex itself. *Increased intracranial pressure* - The **Cushing reflex** is triggered by an elevation in **intracranial pressure (ICP)**, as the body attempts to maintain blood flow to the brain. - This increased ICP reduces cerebral perfusion pressure, prompting a systemic response to raise mean arterial pressure. *Bradycardia* - **Bradycardia** is a classic component of the **Cushing reflex**, occurring as a compensatory response to the reflex hypertension. - The increased arterial blood pressure stimulates carotid and aortic baroreceptors, leading to a vagal response that slows the heart rate. *Irregular respiration* - **Irregular respiration** is another key component of the **Cushing reflex**, often manifesting as **Cheyne-Stokes breathing** or **ataxic breathing**. - This respiratory dysregulation is due to direct compression and dysfunction of the brainstem, specifically the medullary respiratory centers, caused by increased ICP.

Q: Which of the following does not have sympathetic noradrenergic fibers?

Sweat gland. ***Sweat gland*** - While sweat glands are innervated by the **sympathetic nervous system**, their postganglionic fibers are **cholinergic**, releasing **acetylcholine** rather than noradrenaline. - This is an important exception where sympathetic stimulation leads to acetylcholine release, causing sweating. *Blood vessels* - Most blood vessels, particularly resistance vessels such as **arterioles**, receive substantial **sympathetic noradrenergic innervation** that causes vasoconstriction. - This sympathetic tone is crucial for regulating **blood pressure** and distributing blood flow. *Heart* - The heart is richly innervated by **sympathetic noradrenergic fibers** that increase **heart rate**, **contractility**, and **conduction velocity** via beta-1 adrenergic receptors. - This makes noradrenaline a key neurotransmitter in the sympathetic regulation of cardiac function. *Eye* - The eye receives sympathetic noradrenergic innervation primarily to the **dilator pupillae muscle**, causing **mydriasis** (pupil dilation) upon activation. - These fibers also contribute to the sympathetic control of the **tarsal muscle** (Müller's muscle) in the eyelid.

Q: All should be features of a substance to measure GFR, except?

Freely reabsorbed. ***Freely reabsorbed*** - A substance used to measure GFR should **not be reabsorbed** by the kidney tubules. If it were reabsorbed, the amount excreted in the urine would be less than the amount filtered, leading to an **underestimation of GFR**. - The ideal GFR marker is **neither reabsorbed nor secreted**, ensuring that its excretion rate directly reflects the filtration rate. *Freely filtered across the glomerulus membrane* - For a substance to accurately measure GFR, it must be **freely filtered** from the blood into the Bowman's capsule, without any restriction due to its size or charge. - This ensures that its concentration in the glomerular filtrate is the same as in the plasma, allowing for a direct calculation of the filtration rate. *Not secreted by kidney* - An ideal GFR marker should **not be secreted** by the renal tubules, as active secretion would add to the amount excreted in the urine, leading to an **overestimation of GFR**. - This property, along with not being reabsorbed, ensures that the amount of the substance appearing in the urine solely reflects the amount filtered. *None of the options* - This option is incorrect because there is a definitive feature listed among the choices that is *not* a characteristic of an ideal GFR marker. The ability to be "freely reabsorbed" is a disqualifying trait.

Q: What is the normal range of renal blood flow in humans?

1 to 1.2 L/min. ***1 to 1.2 L/min*** - The **kidneys** receive a substantial portion of the **cardiac output**, typically around 20-25%, to perform their filtration and regulatory functions. - This translates to an absolute renal blood flow of approximately **1000 to 1200 mL/min**, or **1 to 1.2 liters per minute**. - This represents the normal physiological range for healthy adults at rest. *1.5 to 2 L/min* - This range is **higher than the normal physiological** renal blood flow. - While renal blood flow can be influenced by various factors, sustained flow in this range would typically be considered **above the average baseline** for healthy individuals. *2 to 2.5 L/min* - This range significantly **exceeds the typical** renal blood flow observed in healthy humans. - Such high flow rates would be **unusual** and are not representative of normal renal perfusion. *2.5 to 3 L/min* - This range represents an **extremely high** renal blood flow, far beyond what is considered normal. - Sustained perfusion at this level would be **pathological** or indicative of an experimental setting rather than a physiological state.

Question 1

Which of the following is classified as a pain receptor?

Accepted Answer

Free nerve endings

Answer

Meissner's corpuscle

Answer

Pacinian corpuscle

Answer

Merkel disc

Question 2

Spinal pathway mainly regulating fine motor activity?

Accepted Answer

Lateral corticospinal tract

Answer

Vestibulospinal tract

Answer

Anterior corticospinal tract

Answer

Reticulospinal tract

Question 3

What is the normal cerebral blood flow in milliliters per minute for a healthy adult?

Accepted Answer

750 ml/min

Answer

55 ml/min

Answer

150 ml/min

Answer

1000 ml/min

Question 4

What is the primary action observed in the withdrawal reflex?

Accepted Answer

Flexion

Answer

Extension

Answer

Flexion followed by extension

Answer

Not applicable

Question 5

Which of the following substances has the same concentration in cerebrospinal fluid (CSF) and plasma?

Accepted Answer

Cl

Answer

Glucose

Answer

Ca

Answer

HCO3

Question 6

Cell bodies of orexigenic neurons are present in?

Accepted Answer

Lateral hypothalamic area

Answer

Dorsal raphe

Answer

Locus coeruleus

Answer

Hippocampus

Question 7

Cushing reflex is associated with all except?

Accepted Answer

Hypotension

Answer

Irregular respiration

Answer

Increased intracranial pressure

Answer

Bradycardia

Question 8

Which of the following does not have sympathetic noradrenergic fibers?

Accepted Answer

Sweat gland

Answer

Heart

Answer

Eye

Answer

Blood vessels

Question 9

All should be features of a substance to measure GFR, except?

Accepted Answer

Freely reabsorbed

Answer

Not secreted by kidney

Answer

Freely filtered across the glomerulus membrane

Answer

None of the options

Question 10

What is the normal range of renal blood flow in humans?

Accepted Answer

1 to 1.2 L/min

Answer

1.5 to 2 L/min

Answer

2 to 2.5 L/min

Answer

2.5 to 3 L/min

NEET-PG 2013 — Physiology