NEET-PG 2012 Practice Questions

Q: Sympathetic supply to the heart arises from which of the following spinal segments?

T1 to T5. The preganglionic sympathetic fibers that innervate the heart originate from the lateral horns of the thoracic spinal segments T1 to T5. These fibers synapse in the cervical and upper thoracic sympathetic ganglia, from which postganglionic fibers extend to the heart. While there is some overlap, the primary and most significant sympathetic innervation to the heart stems predominantly from T1 to T5, making T2 to T6 a less precise answer. Including T6 would extend past the typical primary cardiac sympathetic innervation, which largely concludes at T5. This range is too caudal and largely beyond the principal segments providing sympathetic innervation to the heart. Segments T6-T8 are more involved in sympathetic supply to abdominal organs and other structures rather than direct cardiac control.

Q: Which structure is located immediately posterior to the head of the pancreas?

Portal vein. ***Portal vein*** - The **portal vein** is formed by the union of the **splenic vein** and the **superior mesenteric vein** (SMV) posterior to the **neck** of the pancreas [1]. - It then runs in a **groove on the posterior surface** of the head of the pancreas, lying anterior to the **inferior vena cava** (IVC). - Among the given options, the portal vein has the most direct posterior relationship to the head of the pancreas. *Splenic artery* - The **splenic artery** runs along the **superior border** of the pancreas, following its body and tail. - It does not lie posterior to the head of the pancreas. - It is a branch of the **celiac trunk** and supplies the spleen. *Inferior mesenteric vein* - The **inferior mesenteric vein** typically drains into the **splenic vein** or the junction of the splenic and superior mesenteric veins. - It ascends **anterior** to the left kidney and does not lie immediately posterior to the head of the pancreas. *Coeliac trunk* - The **celiac trunk** originates from the **abdominal aorta** at the level of T12-L1 vertebra. - It lies **superior and anterior** to the pancreas, giving off the splenic artery, common hepatic artery, and left gastric artery. - It is not located posterior to the head of the pancreas.

Q: Which structure do cytotrophoblasts invade during implantation?

Decidua basalis. ***Decidua basalis*** - The **cytotrophoblasts** invade the maternal **decidua basalis**, which is the portion of the **endometrium** directly underlying the implanted embryo, forming the maternal component of the **placenta**. - This invasion is crucial for establishing the **placenta** and allowing for nutrient and waste exchange between the mother and the fetus. *Decidua parietalis* - The **decidua parietalis** is the portion of the **endometrium** lining the rest of the **uterine cavity**, not directly involved in the immediate implantation site. - It plays a role later in pregnancy, fusing with the **decidua capsularis** as the **embryo** grows. *Decidua capsularis* - The **decidua capsularis** is the portion of the endometrium that overlies the implanted embryo, separating it from the uterine lumen. - It does not undergo invasion by the **cytotrophoblasts** in the same way the **decidua basalis** does. *Decidua vera* - The **decidua vera** is another term for the **decidua parietalis**, referring to the endometrial lining of the uterine cavity that is not involved in the implantation site. - It is not directly invaded by **cytotrophoblasts** during implantation.

Q: Stability of alveoli is maintained by:

Reduced surface tension by surfactant. ***Reduced surface tension by surfactant*** - **Surfactant** (a mixture of lipoproteins) reduces the **surface tension** at the air-liquid interface within the alveoli, preventing their collapse at the end of expiration. - This reduction in surface tension helps to maintain the **stability** and patency of the smaller alveoli, preventing them from emptying into larger ones. *Compliance of the lungs* - **Compliance** refers to the distensibility of the lungs and chest wall, indicating how easily they can be stretched. - While pulmonary compliance is important for easy breathing, it does not directly maintain the stability of individual alveoli in preventing their collapse. *Negative intrapleural pressure* - **Negative intrapleural pressure** helps to keep the lungs expanded by creating a vacuum between the visceral and parietal pleura, pulling the lungs outwards. - This pressure prevents the lung as a whole from collapsing but does not directly prevent the collapse of individual alveoli due to surface tension. *Residual air in alveoli* - **Residual volume** is the amount of air remaining in the lungs after a maximal exhalation. - While residual air prevents the complete collapse of the lungs, it is surface tension reduction by surfactant that specifically maintains the stability of individual alveoli against collapse forces.

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: 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.

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: 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.

Question 1

Sympathetic supply to the heart arises from which of the following spinal segments?

Accepted Answer

T1 to T5

Answer

T2 to T6

Answer

T3 to T7

Answer

T4 to T8

Question 2

Which structure is located immediately posterior to the head of the pancreas?

Accepted Answer

Portal vein

Answer

Splenic artery

Answer

Inferior mesenteric vein

Answer

Coeliac trunk

Question 3

Which structure do cytotrophoblasts invade during implantation?

Accepted Answer

Decidua basalis

Answer

Decidua capsularis

Answer

Decidua vera

Answer

Decidua parietalis

Question 4

Which statement accurately describes a characteristic of synovial joints?

Accepted Answer

Hyaline cartilage covers the articular surfaces of synovial joints.

Answer

The metacarpo-phalangeal joint is a condyloid joint.

Answer

Cartilage can sometimes divide the joint into two cavities.

Answer

Stability is inversely proportional to mobility in synovial joints.

Question 5

Stability of alveoli is maintained by:

Accepted Answer

Reduced surface tension by surfactant

Answer

Negative intrapleural pressure

Answer

Residual air in alveoli

Answer

Compliance of the lungs

Question 6

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 7

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 8

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

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

Salty taste is due to?

Accepted Answer

Sodium ion channels

Answer

Calcium ion channels

Answer

G-protein coupled receptors

Answer

Proton channels

NEET-PG 2012

Anatomy

Dental

Physiology