NEET-PG 2013 - Physiology Practice Questions

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: 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: Females have a lower RBC count compared to males due to?

Low erythropoietin. ***Low erythropoietin (relative to males)*** - The primary reason females have lower RBC counts is due to **hormonal differences**, specifically the lack of androgenic stimulation of erythropoiesis that males experience. - **Testosterone in males** directly stimulates erythropoietin production and enhances erythropoiesis, leading to higher RBC counts (males: 4.5-5.5 million/µL vs females: 4.0-5.0 million/µL). - Females have relatively lower erythropoietic drive compared to males due to the absence of significant androgenic hormones, which can be conceptualized as relatively lower erythropoietic stimulus. - This difference exists across all age groups, including pre-menarchal and post-menopausal women, confirming it is **hormonal rather than blood loss-related**. *High estrogen* - Estrogen does not significantly suppress erythropoiesis to cause lower RBC counts. - Estrogen has various effects on the hematopoietic system but is not the primary cause of the gender difference in RBC count. *Low stem cells* - Hematopoietic stem cell numbers and functionality are comparable between males and females. - There is no evidence of lower stem cell counts in females accounting for RBC differences. *Menstrual blood loss* - While menstrual blood loss can contribute to **iron deficiency anemia** in some women, it does NOT explain the baseline physiological difference in RBC counts between genders. - Most healthy menstruating women maintain normal RBC counts despite regular menstruation. - The RBC count difference exists even in pre-menarchal girls and post-menopausal women, proving menstruation is not the primary cause.

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: Which receptor is primarily stimulated in response to moderate cold temperatures?

TRPM8 Receptor (Menthol Receptor). ***TRPM8 Receptor (Menthol Receptor)*** - The **TRPM8 receptor** is a **cold-sensitive ion channel** that is primarily activated by moderate cold temperatures (around 8–28°C) and by cooling compounds like **menthol** and **eucalyptol**. - Its activation leads to an influx of cations, primarily **calcium**, causing depolarization and generation of action potentials. *Vanilloid Receptor 1 (VR1)* - Vanilloid Receptor 1, also known as **TRPV1**, is primarily activated by noxious heat (temperatures above 43°C), low pH, and capsaicin. - It plays a significant role in **pain sensation** and inflammation, not moderate cold detection. *Vanilloid Receptor 2 (VR2)* - Vanilloid Receptor 2, or **TRPV2**, is activated by even higher temperatures than TRPV1, typically above 52°C, and is also involved in the detection of **intense heat** and mechanical stimuli. - It does not respond to cold temperatures at all. *Vanilloid Receptor-Like 1 (VRL-1)* - **VRL-1**, or **TRPV3**, is a heat-sensitive channel activated by warm temperatures (above 31°C) and plays a role in the sensation of warmth and heat hyperalgesia. - It is not involved in the detection of cold stimuli.

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: Which of the following statements is true regarding post-ganglionic parasympathetic fibers?

They release acetylcholine at the target organs.. ***They release acetylcholine at the target organs.*** - Post-ganglionic parasympathetic fibers are **cholinergic**, meaning they release the neurotransmitter **acetylcholine** at their effector organs. - This action mediates the characteristic "rest and digest" responses of the parasympathetic nervous system. *They originate from the spinal cord.* - **Pre-ganglionic parasympathetic fibers** originate from the **brainstem** (cranial nerves III, VII, IX, X) and the **sacral spinal cord** (S2-S4). - Post-ganglionic fibers originate in ganglia located near or within their target organs, not the spinal cord directly. *They are part of the sympathetic nervous system.* - Post-ganglionic parasympathetic fibers are a component of the **parasympathetic nervous system**, not the sympathetic nervous system. - The sympathetic and parasympathetic systems are distinct divisions of the autonomic nervous system with generally opposing functions. *They are responsible for 'fight or flight' responses.* - The **'fight or flight' response** is characteristic of the **sympathetic nervous system**, which prepares the body for stressful situations. - The parasympathetic nervous system is responsible for **'rest and digest' functions**, promoting energy conservation and maintenance activities.

Q: What type of reflex is the righting reflex?

Vestibular reflex. ***Vestibular reflex*** - The **righting reflex** is primarily mediated by the **vestibular system** (labyrinthine apparatus), which detects changes in head position and movement in space. - This reflex helps maintain proper **head and body orientation** relative to gravity, ensuring balance and stability. - Note: Righting reflexes are actually a group of **postural reflexes** that also involve visual, neck proprioceptive, and body proprioceptive inputs, but the **vestibular (labyrinthine) component is the most important** and is often emphasized in medical education. *Cochlear reflex* - The **cochlea** is primarily involved in **hearing**, translating sound vibrations into electrical signals. - The cochlear reflex, such as the **stapedial reflex**, is an auditory protective reflex that dampens loud sounds, not involved in postural control or spatial orientation. *Spinal reflex* - A **spinal reflex** is mediated solely by the **spinal cord** without supraspinal integration (e.g., knee jerk, withdrawal reflex). - The righting reflex requires integration at the **brainstem and higher centers**, involving the vestibular nuclei, and cannot function through spinal cord alone. *None of the options* - This option is incorrect for exam purposes, as the righting reflex is conventionally taught as primarily a **vestibular-mediated postural reflex**. - The vestibular system is the key sensory component for detecting head position changes that trigger righting responses.

Q: Which part of the brain is primarily responsible for the righting reflex?

Midbrain. ***Midbrain*** - The **midbrain** plays a crucial role in regulating posture and movement, including the **righting reflex**. - It integrates sensory information from the **vestibular system**, eyes, and proprioceptors to maintain upright posture. *Pons* - The pons is primarily involved in relaying signals between the **cerebrum** and **cerebellum** and regulating respiration and sleep. - While it contributes to motor control, it is not the primary center for the righting reflex. *Spinal cord* - The spinal cord mediates **reflex arcs** and transmits sensory and motor information, but it does not independently control complex postural reflexes like the righting reflex. - It contains the circuits for basic reflexes such as the **stretch reflex** and **withdrawal reflex**. *Cortex* - The cerebral cortex is responsible for **voluntary movements**, higher cognitive functions, and conscious perception. - While it can influence posture, the righting reflex is a subcortical, involuntary process.

Q: What type of reflex is the righting reflex?

Postural reflex. ***Postural reflex*** - The **righting reflex** is a mechanism that helps an animal or human maintain or regain their upright body position or head orientation in space, which is a key component of **postural control**. - It involves complex inputs from the **vestibular system**, visual system, and proprioceptors to adjust muscle tone and body position against gravity. - Examples include **neck righting reflex**, **body righting reflex**, and **labyrinthine righting reflex**. *Stretch reflex* - A **stretch reflex** is a monosynaptic reflex that causes a muscle to contract in response to being stretched, primarily to maintain muscle length and tone. - It does not encompass the complex, multi-sensory integration required for maintaining overall body orientation. *Spinal reflex* - A **spinal reflex** is any reflex arc whose neural circuit passes through the spinal cord, and it can be either monosynaptic or polysynaptic. - While the righting reflex involves spinal cord components, it is a broader, more integrated reflex that extends beyond a simple spinal cord circuit. *Ocular reflex* - **Ocular reflexes** are involuntary eye movements or responses, such as pupillary light reflex or vestibulo-ocular reflex, that primarily control eye position or pupil size. - They do not directly relate to the maintenance of the entire body's upright posture.

Question 1

Cushing reflex is associated with all except?

Accepted Answer

Hypotension

Answer

Irregular respiration

Answer

Increased intracranial pressure

Answer

Bradycardia

Question 2

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 3

Females have a lower RBC count compared to males due to?

Accepted Answer

Low erythropoietin

Answer

High estrogen

Answer

Low stem cells

Answer

Menstrual blood loss

Question 4

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 5

Which receptor is primarily stimulated in response to moderate cold temperatures?

Accepted Answer

TRPM8 Receptor (Menthol Receptor)

Answer

Vanilloid Receptor 1 (VR1)

Answer

Vanilloid Receptor 2 (VR2)

Answer

Vanilloid Receptor-Like 1 (VRL-1)

Question 6

Spinal pathway mainly regulating fine motor activity?

Accepted Answer

Lateral corticospinal tract

Answer

Vestibulospinal tract

Answer

Anterior corticospinal tract

Answer

Reticulospinal tract

Question 7

Which of the following statements is true regarding post-ganglionic parasympathetic fibers?

Accepted Answer

They release acetylcholine at the target organs.

Answer

They originate from the spinal cord.

Answer

They are part of the sympathetic nervous system.

Answer

They are responsible for 'fight or flight' responses.

Question 8

What type of reflex is the righting reflex?

Accepted Answer

Vestibular reflex

Answer

Cochlear reflex

Answer

Spinal reflex

Answer

None of the options

Question 9

Which part of the brain is primarily responsible for the righting reflex?

Accepted Answer

Midbrain

Answer

Pons

Answer

Spinal cord

Answer

Cortex

Question 10

What type of reflex is the righting reflex?

Accepted Answer

Postural reflex

Answer

Spinal reflex

Answer

Ocular reflex

Answer

Stretch reflex

NEET-PG 2013 — Physiology