FMGE 2018 - Physiology Practice Questions

Q: Histamine is secreted by:

Enterochromaffin-like cell (ECL cell). ***Enterochromaffin-like cell (ECL cell)*** - **Enterochromaffin-like (ECL) cells** are located in the gastric mucosa and are the primary source of histamine in the stomach. - Histamine released by ECL cells stimulates **parietal cells** to secrete hydrochloric acid. - Note: ECL cells are distinct from enterochromaffin (EC) cells, which primarily secrete serotonin. *Chief cell* - **Chief cells** primarily secrete pepsinogen, the inactive precursor of the digestive enzyme pepsin. - They also produce gastric lipase, which aids in fat digestion. *Oxyntic cell* - The term **oxyntic (or parietal) cell** refers to the same cell type responsible for secreting hydrochloric acid and intrinsic factor. - They do not directly secrete histamine; instead, their acid secretion is stimulated by histamine. *Parietal cell* - **Parietal cells** are responsible for secreting hydrochloric acid and intrinsic factor, crucial for vitamin B12 absorption. - Their acid secretion is stimulated by acetylcholine, gastrin, and **histamine** (released from ECL cells).

Q: Delivery of stimulus above threshold intensity leads to a constant amplitude of AP and is known as:

All or none law. ***All or none law*** - The **all-or-none law** states that if a stimulus reaches or exceeds the **threshold intensity**, a neuron will fire an action potential of a constant, maximal amplitude. - If the stimulus is below the threshold, no action potential will fire, meaning there is no partial or submaximal action potential. *Electrotonic potential* - **Electrotonic potentials** are subthreshold, local changes in membrane potential that decay with distance and time. - They are **graded**, meaning their amplitude is proportional to the stimulus intensity, unlike the fixed amplitude of an action potential. *Absolute refractory period* - The **absolute refractory period** is the time during an action potential when the membrane is completely unresponsive to further stimulation, no matter how strong. - This period is due to the **inactivation of voltage-gated sodium channels**, preventing another action potential from being generated. *Relative refractory period* - The **relative refractory period** is the time following the absolute refractory period when a **larger-than-normal stimulus** is required to elicit another action potential. - This occurs because some potassium channels are still open, and the membrane is hyperpolarized, making it harder to reach the threshold.

Q: The primary dopaminergic reward center in the brain is?

Ventral tegmental area. ***Ventral tegmental area*** - The **ventral tegmental area (VTA)** is a key component of the mesolimbic dopamine system, often referred to as the **reward pathway** in the brain. - It projects dopamine neurons to various areas, including the **nucleus accumbens** and prefrontal cortex, mediating feelings of pleasure and reward. *Hippocampus* - The **hippocampus** is primarily involved in **memory formation** and spatial navigation. - While it interacts with reward pathways, it is not the primary dopaminergic reward center itself. *Amygdala* - The **amygdala** is critical for processing **emotions**, particularly fear and aggression, and plays a role in emotional memory. - It modulates reward responses but is not the primary source of dopaminergic reward signaling. *Thalamus* - The **thalamus** acts as a **relay station** for sensory information, directing it to appropriate cortical areas. - It has diverse functions but is not recognized as the central dopaminergic reward area.

Q: Inverse stretch reflex is mediated :

Golgi tendon organ. ***Golgi tendon*** - The **Golgi tendon organ (GTO)** is a **proprioceptor** located at the junction of muscle fibers and tendons, sensitive to changes in muscle tension. - When muscle tension becomes excessive, the GTO is activated, inhibiting the alpha motor neurons innervating that muscle, leading to muscle relaxation, which is the **inverse stretch reflex**. *Unmyelinated C fibres* - These fibers are primarily involved in transmitting **slow, dull pain** and **temperature sensations**, but not proprioceptive reflexes. - Their conduction velocity is much slower than that required for rapid protective reflexes. *Dorsal Column* - The dorsal column-medial lemniscus pathway is responsible for transmitting **fine touch, vibration, and proprioception** to the brain, but it is an ascending sensory pathway and does not directly mediate spinal reflexes. - This pathway is involved in conscious perception, not the direct arc of a reflex. *Muscle spindle* - The **muscle spindle** is responsible for the **stretch reflex** (myotatic reflex), which causes muscle contraction in response to stretch. - It detects changes in **muscle length and rate of change of length**, which is distinct from the inverse stretch reflex mediated by the GTO.

Q: An exaggerated pain response to a normally painful stimulus is called:

Hyperalgesia. ***Hyperalgesia*** - This term describes an **increased sensitivity to pain** where a stimulus that is normally painful is perceived as even more painful than usual. - It often results from **damage to nociceptive afferent pathways** or central sensitization. *Causalgia* - This is an older term now largely replaced by complex regional pain syndrome type II (**CRPS II**), characterized by severe, burning pain following a **nerve injury**. - Unlike hyperalgesia, it specifically refers to a **syndrome of severe pain** after nerve trauma, not just an increased response to noxious stimuli. *Allodynia* - This refers to pain caused by a stimulus that **does not normally provoke pain**, such as light touch or brushing of the skin. - It differs from hyperalgesia, which is an exaggerated response to a **normally painful stimulus**. *Hypersensitivity* - This is a **general term** meaning an increased physical or allergic sensitivity to a substance or condition. - It is a **broader concept** and not as specific to pain perception as hyperalgesia or allodynia.

Q: What is needed for prothrombin to thrombin conversion?

Calcium. ***Calcium*** - **Calcium ions (Ca2+)** are absolutely essential cofactors for the conversion of **prothrombin to thrombin** in the coagulation cascade. - They are required for the formation and function of the **prothrombinase complex** (Factor Xa + Factor Va + Ca2+ + phospholipid surface). - Calcium binds to **γ-carboxyglutamic acid (Gla) residues** on prothrombin and Factor Xa, enabling them to anchor to phospholipid surfaces where the conversion occurs. - This is why **EDTA and citrate** (calcium chelators) are used as anticoagulants in blood collection tubes. *Magnesium* - **Magnesium** is an important cofactor for numerous enzymatic reactions (e.g., ATP-dependent enzymes, DNA/RNA polymerases). - However, it is **not directly involved** in the prothrombin to thrombin conversion step of the coagulation cascade. - Its primary roles are in DNA synthesis, muscle function, and nerve transmission. *Sodium* - **Sodium** is vital for maintaining fluid balance, osmotic pressure, nerve impulses, and muscle contractions. - It does **not play a direct role** as a cofactor in the prothrombinase complex or prothrombin to thrombin conversion. *Potassium* - **Potassium** is essential for maintaining cell membrane potential, nerve impulses, cardiac function, and muscle contraction. - It is **not a cofactor** for the enzymatic reactions involved in the coagulation cascade.

Question 1

Histamine is secreted by:

Accepted Answer

Enterochromaffin-like cell (ECL cell)

Answer

Chief cell

Answer

Oxyntic cell

Answer

Parietal cell

Question 2

Delivery of stimulus above threshold intensity leads to a constant amplitude of AP and is known as:

Accepted Answer

All or none law

Answer

Electrotonic potential

Answer

Absolute refractory period

Answer

Relative refractory period

Question 3

The primary dopaminergic reward center in the brain is?

Accepted Answer

Ventral tegmental area

Answer

Hippocampus

Answer

Amygdala

Answer

Thalamus

Question 4

Inverse stretch reflex is mediated :

Accepted Answer

Golgi tendon organ

Answer

Unmyelinated C fibres

Answer

Dorsal Column

Answer

Muscle spindle

Question 5

An exaggerated pain response to a normally painful stimulus is called:

Accepted Answer

Hyperalgesia

Answer

Causalgia

Answer

Allodynia

Answer

Hypersensitivity

Question 6

What is needed for prothrombin to thrombin conversion?

Accepted Answer

Calcium

Answer

Magnesium

Answer

Sodium

Answer

Potassium

FMGE 2018 — Physiology