Neurons and Glial Cells — MCQs
Absolute refractoriness of a neuron is due to?
Some cells secrete chemicals into the extracellular fluid that act on cells in the same tissue. Which of the following refers to this type of regulation?
Ventricles are lined by?
Which of the following structures in the heart are known for their rapid conduction of electrical impulses?
What is the mechanism of action of local anesthetics?
A child undergoes prophylactic irradiation as preparation for bone marrow transplantation (BMT) for treatment of acute lymphoblastic leukemia (ALL). Which of the following cell types will be least affected by the radiation?
All the following features are seen in neurons from dorsal root ganglia, EXCEPT:
Which condition is associated with defects in pre-mRNA splicing and SMN protein dysfunction?
Identify the cell type marked in the cerebellum.
What is the primary function of oligodendrocytes in the central nervous system?
Neurons and Glial Cells Indian Medical PG Practice Questions and MCQs
Question 1: Absolute refractoriness of a neuron is due to?
- A. Hyperpolarization of Cl channels
- B. Opening of rectifier K+ channels
- C. Closure of activated Na channels
- D. Inactivation of Na channels (Correct Answer)
Explanation: ***Inactivation of Na channels*** - During the **absolute refractory period**, voltage-gated **Na+ channels** enter an inactivated state, making them unresponsive to further stimulation. - This inactivation prevents another action potential from being generated, regardless of the stimulus intensity, ensuring unidirectional propagation. *Hyperpolarization of Cl channels* - While **Cl- channels** can cause hyperpolarization, this typically leads to **inhibition** rather than absolute refractoriness. - Their activity doesn't directly prevent the generation of a new action potential by blocking Na+ channel function. *Opening of rectifier K+ channels* - The opening of **rectifier K+ channels** is involved in **repolarization** and the **relative refractory period**, by increasing K+ efflux. - While it contributes to making the neuron less excitable, it doesn't cause the absolute inability to fire associated with Na+ channel inactivation. *Closure of activated Na channels* - The **closure of activated Na+ channels** occurs as part of the repolarization process, but the critical mechanism for absolute refractoriness is their transition into an **inactivated state**, not simply closure. - **Inactivation** locks the channels in a non-responsive configuration, whereas simple closure would allow them to reopen quickly with sufficient depolarization.
Question 2: Some cells secrete chemicals into the extracellular fluid that act on cells in the same tissue. Which of the following refers to this type of regulation?
- A. Neural
- B. Endocrine
- C. Neuroendocrine
- D. Paracrine (Correct Answer)
Explanation: ***Paracrine*** - **Paracrine signaling** involves chemical messengers, or **paracrine factors**, that act on **neighboring cells** within the **same tissue** without entering the bloodstream. - This type of regulation is crucial for local communication and coordination, such as in wound healing or immune responses. *Neural* - **Neural regulation** involves communication via **neurons** that transmit **electrical signals** (action potentials) and release **neurotransmitters** at synapses. - Neurotransmitters act on target cells, which can be distant from the neuron, for rapid and precise responses throughout the body. *Endocrine* - **Endocrine regulation** involves glands that secrete **hormones** directly into the **bloodstream**, which then travel to distant target cells in other tissues or organs. - This form of signaling leads to widespread and long-lasting effects, such as growth regulation or metabolic control. *Neuroendocrine* - **Neuroendocrine regulation** is a hybrid system where specialized **neurons** (neurosecretory cells) release **hormones** into the **bloodstream**, rather than releasing neurotransmitters into a synapse. - An example is the hypothalamus secreting ADH and oxytocin, which act on distant target organs.
Question 3: Ventricles are lined by?
- A. Schwann cells
- B. Oligodendrocytes
- C. Ependymal cells (Correct Answer)
- D. Astrocytes
Explanation: Ependymal cells - Ependymal cells are a type of glial cell that form the epithelial lining of the ventricles of the brain and the central canal of the spinal cord [3]. - They possess cilia that help circulate the cerebrospinal fluid (CSF) and microvilli involved in CSF absorption. Schwann cells - Schwann cells are responsible for forming the myelin sheath around axons in the peripheral nervous system (PNS) [4]. - They do not line the ventricles, which are part of the central nervous system [2]. Oligodendrocytes - Oligodendrocytes are glial cells that form the myelin sheath around axons in the central nervous system (CNS) [1], [4]. - While they are CNS cells, their primary function is myelination, not lining the ventricular system [1]. Astrocytes - Astrocytes are the most abundant and diverse glial cells in the CNS, providing structural support, metabolic regulation, and forming the blood-brain barrier. - They are found throughout the brain parenchyma but do not directly line the ventricular cavities.
Question 4: Which of the following structures in the heart are known for their rapid conduction of electrical impulses?
- A. Sinoatrial (SA) node
- B. Atrioventricular (AV) node
- C. His bundle
- D. Purkinje fibers (Correct Answer)
Explanation: ***Correct: Purkinje fibers*** - **Purkinje fibers** have the **fastest conduction velocity** among all cardiac tissues, approximately **4 m/s** - These specialized myocardial fibers ensure **rapid and synchronized depolarization of the ventricles**, allowing for efficient and coordinated ventricular contraction - Their rapid conduction is essential for simultaneous contraction of ventricular myocardium from apex to base *Incorrect: Sinoatrial (SA) node* - The SA node is the natural **pacemaker** of the heart, initiating electrical impulses at a rate that determines heart rate - However, its conduction velocity is **very slow** (~0.05 m/s), much slower than Purkinje fibers - Its role is impulse generation, not rapid conduction *Incorrect: Atrioventricular (AV) node* - The AV node has the **slowest conduction velocity** in the heart (~0.05 m/s) - It **delays electrical impulses** from the atria to the ventricles (AV delay ~0.1 seconds) - This delay allows for **complete ventricular filling** before ventricular contraction begins *Incorrect: His bundle* - The bundle of His transmits impulses from the AV node to the bundle branches - While faster than the AV node (~1-1.5 m/s), it is still **significantly slower than Purkinje fibers** - Its conduction velocity is intermediate between the AV node and Purkinje fibers
Question 5: What is the mechanism of action of local anesthetics?
- A. Block chloride channels
- B. Block calcium channels
- C. Block sodium channels (Correct Answer)
- D. Block potassium channels
Explanation: ***Block sodium channels*** - Local anesthetics work by **reversibly binding** to the alpha subunit of **voltage-gated sodium channels** on the neuronal membrane. - This binding prevents the influx of sodium ions, thereby inhibiting the **depolarization** of the neuron and **propagation of action potentials**. *Block chloride channels* - **Chloride channels** are primarily involved in **hyperpolarization** or stabilization of the resting membrane potential, and their blockade is not the primary mechanism of local anesthesia. - Drugs like **benzodiazepines** modulate GABA-gated chloride channels for their anxiolytic and sedative effects. *Block calcium channels* - **Calcium channels** are important for neurotransmitter release and muscle contraction, but their blockade is not the way local anesthetics exert their effects. - **Calcium channel blockers** are used in cardiovascular medicine (e.g., diltiazem, verapamil) to reduce heart rate and blood pressure. *Block potassium channels* - **Potassium channels** are crucial for repolarization of the neuronal membrane and maintaining the resting potential. - While some toxins block potassium channels, it is not the principal mechanism by which **local anesthetics** achieve their nerve blocking effect.
Question 6: A child undergoes prophylactic irradiation as preparation for bone marrow transplantation (BMT) for treatment of acute lymphoblastic leukemia (ALL). Which of the following cell types will be least affected by the radiation?
- A. Spermatogonia
- B. Bone marrow
- C. Intestinal epithelial cells
- D. Neurons (Correct Answer)
Explanation: ***Neurons*** - **Neurons** are highly differentiated cells with very low rates of cell division in adults. As radiation primarily targets rapidly dividing cells [4], **neurons are least susceptible** to radiation damage. - While high doses of radiation can eventually damage neurons, their **radioresistance** is significantly higher compared to rapidly proliferating tissues. *Spermatogonia* - **Spermatogonia** are germ cells that undergo continuous and rapid division to produce sperm, making them **highly sensitive to radiation** [2]. - Radiation exposure can lead to **sterility** due to the destruction of these rapidly dividing cells [2]. *Bone marrow* - The **bone marrow** contains hematopoietic stem cells that are responsible for the continuous production of blood cells, involving **rapid cell division** [3]. - It is one of the most **radiosensitive tissues** [1], and radiation exposure can lead to **myelosuppression** and pancytopenia. *Intestinal epithelial cells* - **Intestinal epithelial cells** have a high turnover rate due to their constant shedding and replacement [5], making them **very sensitive to radiation** [1]. - Radiation damage to these cells can cause **mucositis, nausea, vomiting, and diarrhea**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 112-113. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 113-114. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 112-113. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Central Nervous System Synapse, pp. 436-437. [5] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 79-80.
Question 7: All the following features are seen in neurons from dorsal root ganglia, EXCEPT:
- A. They are multipolar (Correct Answer)
- B. They are derived from neural crest cells
- C. They have eccentrically located nuclei
- D. They contain lipofuscin granules
Explanation: ***They are multipolar*** - Dorsal root ganglia (DRG) neurons are typically **pseudounipolar**, meaning they have a single process that branches into two (peripheral and central) rather than multiple dendrites and an axon [1]. - **Multipolar neurons** are characteristic of motor neurons and interneurons in the central nervous system, not DRG sensory neurons [1]. *They contain lipofuscin granules* - **Lipofuscin granules** are common in long-lived, post-mitotic cells like neurons and are considered "wear and tear" pigments, accumulating with age. - Their presence in DRG neurons is a normal finding and reflects the neuron's metabolic activity over time. *They have eccentrically located nuclei* - While not universally present in all DRG neurons, an **eccentrically located nucleus** is a common histological feature of certain types of DRG neurons, particularly larger ones. - This feature helps distinguish them from other neuron types and can be accentuated by the large amount of cytoplasm in these cells. *They are derived from neural crest cells* - All sensory neurons of the DRG, along with other components like Schwann cells and sympathetic ganglia, originate from **neural crest cells**. - This developmental origin is a fundamental characteristic of DRG neurons, distinguishing them from CNS neurons derived from the neural tube.
Question 8: Which condition is associated with defects in pre-mRNA splicing and SMN protein dysfunction?
- A. Sickle cell disease
- B. Huntington's disease
- C. Spinal muscular atrophy (Correct Answer)
- D. α-Thalassemia
Explanation: ***Spinal muscular atrophy*** - **Spinal muscular atrophy (SMA)** is primarily caused by mutations in the **SMN1 gene**, leading to insufficient production of the **survival motor neuron (SMN) protein**. - Without adequate SMN protein, defects occur in the **pre-mRNA splicing** of motor neuron genes, leading to the degeneration of **alpha motor neurons** in the spinal cord. *Sickle cell disease* - **Sickle cell disease** is an inherited **hemoglobinopathy** caused by a point mutation in the beta-globin gene, leading to the production of abnormal **hemoglobin S**. - This condition does not involve defects in pre-mRNA splicing or SMN protein dysfunction, but rather the **polymerization of hemoglobin S** under low oxygen conditions. *Huntington's disease* - **Huntington's disease** (formerly called Huntington chorea) is a neurodegenerative disorder caused by an **expanded CAG trinucleotide repeat** in the huntingtin gene. - Huntington's disease involves protein misfolding and aggregation, but not primary defects in pre-mRNA splicing or SMN protein dysfunction. *α-Thalassemia* - **α-Thalassemia** is a group of inherited blood disorders characterized by reduced or absent production of **alpha-globin chains**, typically due to **gene deletions** on chromosome 16. - This condition affects the assembly of hemoglobin and does not involve pre-mRNA splicing defects or SMN protein dysfunction.
Question 9: Identify the cell type marked in the cerebellum.
- A. Basket cells
- B. Granule cells
- C. Golgi cells
- D. Purkinje cells (Correct Answer)
Explanation: ***Purkinje cells*** - These are **large, flask-shaped neurons** with extensive dendritic trees, forming a single layer in the cerebellar cortex. - The image clearly shows these characteristic large, pear-shaped cell bodies with a surrounding paler area (Purkinje layer), distinguishing them from the smaller, more numerous cells in the granular layer below. *Basket cells* - These are **inhibitory interneurons** located within the **molecular layer** of the cerebellum, superficial to the Purkinje cells. - They are typically smaller than Purkinje cells and send axons that form a "basket" around the somata of Purkinje cells, which is not what is highlighted here. *Granule cells* - These are the **smallest and most numerous neurons** in the brain, found in the **granular layer** of the cerebellum, deep to the Purkinje cells. - They appear as small, densely packed, dark nuclei in the image, distinct from the larger, paler cells indicated by the arrow. *Golgi cells* - These are inhibitory interneurons located in the **granular layer** of the cerebellum, below the Purkinje cell layer. - While larger than granule cells, they are generally smaller and less distinct than Purkinje cells, and their morphology does not match the prominent cells pointed out by the arrow.
Question 10: What is the primary function of oligodendrocytes in the central nervous system?
- A. Myelination of axons in the CNS (Correct Answer)
- B. Form the blood-brain barrier
- C. Act as immune cells in the CNS
- D. Support and maintain neuronal health
Explanation: ***Myelinates the CNS*** - Oligodendrocytes are responsible for the **myelination of axons in the central nervous system (CNS)**, which enhances the speed of electrical signal transmission [1]. - They can myelinate multiple axons simultaneously, providing **support and insulation** to neuronal fibers [1]. *Nutrition of nervous tissue* - While oligodendrocytes contribute to the overall health of nervous tissue, their primary role is not **nutrition** but rather **myelination**. - Neurons and other glial cells, like astrocytes, are more involved in **metabolic support** and nutrition. *Behave like macrophages* - Oligodendrocytes do not function like macrophages; instead, their primary role is myelination, while **microglia** serve as the immune cells in the CNS. - Macrophages are involved in phagocytosis and immune defense, which is not characteristic of oligodendrocytes. *Lining the cavities of the CVS* - This description pertains more to the role of **endothelial cells** or **ependymal cells** rather than oligodendrocytes. - Oligodendrocytes are not involved in lining cavities, particularly in the cardiovascular system (CVS). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1255-1256.
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