NEET-PG 2019 - Physiology Practice Questions

Q: True about decorticate rigidity:

Rigidity is less pronounced than decerebrate rigidity. ***Rigidity is less pronounced than decerebrate rigidity*** - **Decorticate rigidity** indicates damage above the **red nucleus**, disrupting descending inhibitory pathways from the cortex. [1] - While reflecting serious brain injury, it is generally considered a **less severe prognosis** than decerebrate rigidity because the red nucleus and some rubrospinal tract functions remain intact. *Flexion of lower limbs & extension of upper limbs* - **Decorticate rigidity** typically presents with **flexion of the upper limbs** (adduction, internal rotation, elbow flexion, wrist flexion), and **extension of the lower limbs** (adduction, extension, internal rotation) [1]. - This characteristic posture, often described as "mummy baby" or "posture of salvation," is due to uninhibited activity of the **rubrospinal tract** and the absence of cortical input [1]. *Removal of cerebral cortex and basal ganglia* - **Decorticate rigidity** results from lesions that interrupt the descending pathways **above the red nucleus** (e.g., in the cerebral hemispheres or internal capsule) [1]. - This specifically means the **cerebral cortex** is "removed" in terms of its functional input, but the basal ganglia are within the affected region. *None of the options* - This option is incorrect because the statement about decorticate rigidity being **less pronounced than decerebrate rigidity** is accurate. - The other clinical description and neurological basis are distinct from true decorticate rigidity.

Q: What is the PRIMARY vascular function of PGI2 (prostacyclin)?

Inhibits platelet aggregation and causes vasodilation. ***Inhibits platelet aggregation and causes vasodilation*** - **PGI2 (prostacyclin)** is a potent **vasodilator** that relaxes smooth muscle in blood vessels, increasing blood flow. - It also effectively **inhibits platelet aggregation**, preventing the formation of blood clots. *Promotes platelet aggregation and causes vasoconstriction* - This describes the primary actions of **thromboxane A2 (TXA2)**, not PGI2. - TXA2 is produced by platelets and plays a key role in **hemostasis** by constricting blood vessels and promoting platelet clumping. *Acts primarily as a bronchoconstrictor* - While some prostaglandins can affect bronchial tone, **PGI2's primary vascular role** is vasodilation and anti-aggregation. - **Leukotrienes** and certain **prostaglandins (e.g., PGD2, PGF2α)** are more classically associated with bronchoconstriction. *Stimulates inflammatory cell chemotaxis* - This is primarily a function of other inflammatory mediators such as **leukotriene B4 (LTB4)** and **C5a anaphylatoxin**. - While other eicosanoids can indirectly influence inflammation, **PGI2's main actions** are vascular and anti-platelet.

Q: A blood grouping test shows clumping with Anti-A serum, clumping with Anti-B serum, and no clumping in the control. What blood group does this indicate?

AB. ***AB*** - The results show **clumping with both Anti-A and Anti-B serum**, indicating the presence of both A and B antigens on the red blood cells. - The absence of clumping in the control confirms that the **agglutination with Anti-A and Anti-B is due to specific antigen-antibody reactions**, not nonspecific agglutination. - Blood group AB individuals have both A and B antigens on their RBCs and no anti-A or anti-B antibodies in their serum. *A* - Blood group A would show **clumping with Anti-A serum only** and no clumping with Anti-B serum. - This is incorrect because the sample shows clumping with both antisera. *B* - Blood group B would show **clumping with Anti-B serum only** and no clumping with Anti-A serum. - This is incorrect because the sample shows clumping with both antisera. *O* - Blood group O would show **no clumping with either Anti-A or Anti-B serum**, as it lacks both A and B antigens. - This is incorrect because the sample clearly shows clumping with both Anti-A and Anti-B sera.

Q: All are true about Decerebrate posture except:-

Flexion of upper extremity and extension of lower extremity. ***Flexion of upper extremity and extension of lower extremity*** - This description corresponds to **decorticate rigidity**, not decerebrate rigidity. - In decorticate rigidity, there is **flexion** of the **upper extremities** and **extension** of the **lower extremities**, indicating a lesion above the red nucleus. *Exaggerated gamma motor neuron discharge* - Decerebrate rigidity is characterized by an **increase in muscle tone** due to disinhibition of extensor muscles, which is mediated by increased **gamma motor neuron activity**. - This increased discharge leads to potentiation of the **stretch reflex**, contributing to the rigidity. *Extension of both upper and lower extremity* - **Decerebrate posture** is defined by **extension of all four limbs** (both upper and lower extremities). - This posture results from a lesion in the brainstem **below the red nucleus** but above the vestibular nuclei, causing disinhibition of the pontine reticular formation and vestibular nuclei, which primarily excite extensor muscles. *Reticulo spinal tract is also involved* - The **reticulospinal tracts** (both pontine and medullary) play a crucial role in regulating muscle tone and posture. - In decerebrate rigidity, the **pontine reticulospinal tract** is overactive due to loss of cortical inhibition, leading to **increased extensor tone**.

Question 1

True about decorticate rigidity:

Accepted Answer

Rigidity is less pronounced than decerebrate rigidity

Answer

Flexion of lower limbs & extension of upper limbs

Answer

Removal of cerebral cortex and basal ganglia

Answer

None of the options

Question 2

What is the PRIMARY vascular function of PGI2 (prostacyclin)?

Accepted Answer

Inhibits platelet aggregation and causes vasodilation

Answer

Promotes platelet aggregation and causes vasoconstriction

Answer

Acts primarily as a bronchoconstrictor

Answer

Stimulates inflammatory cell chemotaxis

Question 3

A blood grouping test shows clumping with Anti-A serum, clumping with Anti-B serum, and no clumping in the control. What blood group does this indicate?

Accepted Answer

AB

Answer

A

Answer

B

Answer

O

Question 4

All are true about Decerebrate posture except:-

Accepted Answer

Flexion of upper extremity and extension of lower extremity

Answer

Exaggerated gamma motor neuron discharge

Answer

Extension of both upper and lower extremity

Answer

Reticulo spinal tract is also involved

Question 5

Which one of the following is a function of PGI2?

Accepted Answer

Causes blood vessel relaxation and prevents platelet clumping

Answer

Causes blood vessel constriction and prevents platelet clumping

Answer

Causes blood vessel constriction and promotes platelet clumping

Answer

Causes blood vessel relaxation and promotes platelet clumping

NEET-PG 2019 — Physiology