Central and peripheral nervous system histology US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Central and peripheral nervous system histology. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Central and peripheral nervous system histology US Medical PG Question 1: A 32-year-old woman presents with a 3-month history of intermittent blurred vision and problems walking. The patient states that she often feels “pins and needles” in her legs that cause her problems when she’s walking. The patient is afebrile, and her vital signs are within normal limits. An autoimmune disorder is suspected. Which of the following findings would most likely be present in this patient?
- A. Damaged myelin sheath and myelin-producing cells (Correct Answer)
- B. Absence of interneurons
- C. Destruction of blood-brain barrier
- D. Degeneration of anterior horn cells
- E. Decreased cerebrospinal fluid due to destruction of cells
Central and peripheral nervous system histology Explanation: ***Damaged myelin sheath and myelin-producing cells***
- The patient's symptoms of intermittent **blurred vision** (optic neuritis), **problems walking** (ataxia, spasticity), and **paresthesias** ("pins and needles") are classical presentations of Multiple Sclerosis (MS).
- MS is characterized by multifocal areas of inflammation and **demyelination** in the central nervous system, where the **myelin sheath** surrounding axons is damaged, and the **oligodendrocytes** (myelin-producing cells) are attacked.
- This demyelination disrupts saltatory conduction, leading to the varied and intermittent neurological symptoms.
*Absence of interneurons*
- The absence of **interneurons** is typically associated with conditions like **spinal muscular atrophy** or certain **neuropathies**, which present with different clinical features (e.g., muscle weakness, atrophy) than those described.
- While interneurons are crucial for neuronal communication, their absence doesn't explain the *intermittent* and multifocal symptoms seen in this case.
*Destruction of blood-brain barrier*
- While **blood-brain barrier (BBB) breakdown** does occur in MS, it is a *consequence* of the inflammatory process rather than the primary *pathological finding* that directly explains the neurological symptoms.
- BBB destruction allows inflammatory cells to enter the CNS, contributing to demyelination, but the core issue remains the myelin damage itself.
*Degeneration of anterior horn cells*
- **Anterior horn cell degeneration** is the hallmark of **amyotrophic lateral sclerosis (ALS)** and **spinal muscular atrophy**, presenting with progressive muscle weakness, atrophy, and fasciculations.
- These conditions lack the sensory symptoms (paresthesias) and visual disturbances seen in this patient, and typically show a progressive rather than intermittent course.
*Decreased cerebrospinal fluid due to destruction of cells*
- **Decreased CSF volume** is not a characteristic feature of MS; in fact, CSF analysis often shows increased protein and **oligoclonal bands**.
- The destruction of cells in MS primarily affects myelin and oligodendrocytes, not cells responsible for CSF production or volume regulation.
Central and peripheral nervous system histology US Medical PG Question 2: Which receptor type mediates the slow phase of synaptic transmission in autonomic ganglia?
- A. Muscarinic (M3)
- B. Muscarinic (M2)
- C. Muscarinic (M1) (Correct Answer)
- D. Nicotinic (N2)
Central and peripheral nervous system histology Explanation: ***Muscarinic (M1)***
- **M1 receptors** are **Gq-protein coupled receptors** that activate phospholipase C, leading to increased intracellular calcium and diacylglycerol, which mediates the slow excitatory postsynaptic potential in autonomic ganglia.
- This activation results in a **slow depolarization** that prolongs the excitability of ganglionic neurons after the initial fast synaptic transmission.
*Muscarinic (M3)*
- **M3 receptors** are primarily found on **smooth muscle**, glands, and endothelium, mediating contraction, secretion, and vasodilation, respectively.
- While also **Gq-protein coupled**, their role in autonomic ganglia is not the main mediator of the slow phase of synaptic transmission.
*Muscarinic (M2)*
- **M2 receptors** are **Gi-protein coupled receptors** mainly found in the heart, mediating decreased heart rate and contractility.
- In autonomic ganglia, M2 receptors could have a modulatory role, but they are not responsible for the slow excitatory phase of synaptic transmission.
*Nicotinic (N2)*
- **Nicotinic N2 receptors** (also known as **NN or neuronal nicotinic receptors**) mediate the **fast excitatory postsynaptic potential** (EPSP) in autonomic ganglia by opening ion channels.
- This leads to rapid depolarization and action potential generation, which is distinct from the **slower, prolonged phase** of transmission.
Central and peripheral nervous system histology US Medical PG Question 3: An investigator is studying cellular repair mechanisms in various tissues. One of the samples being reviewed is from the anterior horn of the spinal cord of a patient who was involved in a snowboard accident. Pathologic examination of the biopsy specimen shows dispersion of the Nissl bodies, swelling of the neuronal body, and a displacement of the nucleus to the periphery in numerous cells. Which of the following is the most likely explanation for the observed findings?
- A. Neurodegenerative changes
- B. Neuronal aging
- C. Central chromatolysis (Correct Answer)
- D. Reactive astrogliosis
- E. Wallerian degeneration
Central and peripheral nervous system histology Explanation: ***Central chromatolysis***
- This process is a **response to axonal injury**, where the neuron undergoes characteristic morphological changes to prepare for regeneration.
- Key features include **dispersion of Nissl bodies**, **neuronal swelling**, and **nucleus displacement to the periphery**, all indicative of an attempt at cellular repair.
*Neurodegenerative changes*
- These typically involve **neuronal loss** and accumulation of **abnormal protein deposits**, rather than an attempt at cellular repair.
- The observed features (swelling, Nissl body dispersion) are part of an acute injury response, not chronic degeneration.
*Neuronal aging*
- Though aging neurons can accumulate **lipofuscin** and show some atrophy, they do not typically present with the acute, dramatic changes of cell body swelling and peripheral nucleus displacement described.
- Aging is a slow, progressive process, distinct from an acute response to injury from an accident.
*Reactive astrogliosis*
- This refers to the **proliferation and hypertrophy of astrocytes** in response to CNS injury.
- While it's a component of the injury response, it describes glial cell changes, not the neuronal body changes observed in the question.
*Wallerian degeneration*
- This process describes the **degeneration of the axon distal to the site of injury**, as well as the myelin sheath.
- It does not characterize the **changes occurring within the neuronal cell body** (soma), which are the focus of the question.
Central and peripheral nervous system histology US Medical PG Question 4: A 57-year-old man is brought to the emergency department by his wife 20 minutes after having had a seizure. He has had recurrent headaches and dizziness for the past 2 weeks. An MRI of the brain shows multiple, round, well-demarcated lesions in the brain parenchyma at the junction between gray and white matter. This patient's brain lesions are most likely comprised of cells that originate from which of the following organs?
- A. Kidney
- B. Skin
- C. Lung (Correct Answer)
- D. Thyroid
- E. Prostate
Central and peripheral nervous system histology Explanation: ***Lung (Correct Answer)***
- **Lung cancer** is the most common cause of **brain metastases** in adults, accounting for approximately **50% of all cases**
- The clinical presentation—seizure, headaches, dizziness, and **multiple, round, well-demarcated lesions at the gray-white matter junction**—is classic for metastatic lung cancer
- Both **small cell and non-small cell lung cancers** have high propensity for hematogenous spread to the brain
- The watershed areas at the gray-white junction are common sites due to lodging of tumor emboli in terminal arterioles
*Kidney (Incorrect)*
- **Renal cell carcinoma (RCC)** can metastasize to the brain but accounts for only **5-10% of brain metastases**
- While RCC metastases can appear similar on imaging, lung cancer is statistically more likely given its higher prevalence
- RCC metastases are often **highly vascular and may hemorrhage**, which is not mentioned in this case
*Skin (Incorrect)*
- **Melanoma** has the **highest propensity per case** to metastasize to the brain among all cancers
- However, the **overall incidence of melanoma is much lower** than lung cancer, making it a less probable primary source
- Melanoma brain metastases often present as **hemorrhagic lesions** and would typically have skin findings or history
*Thyroid (Incorrect)*
- **Thyroid cancer** rarely metastasizes to the brain (accounts for <1% of brain metastases)
- Brain metastases from thyroid cancer typically occur in **advanced papillary or follicular carcinoma** or in **anaplastic thyroid cancer**
- More common metastatic sites for thyroid cancer are lung and bone
*Prostate (Incorrect)*
- **Prostate cancer very rarely metastasizes to the brain** (<1% of cases)
- Prostate cancer preferentially metastasizes to **bone (especially axial skeleton), lymph nodes, and liver**
- Brain metastases from prostate cancer suggest extremely advanced, aggressive disease and are exceptionally uncommon
Central and peripheral nervous system histology US Medical PG Question 5: A researcher is studying the brains of patients who recently died from stroke-related causes. One specimen has a large thrombus in an area of the brain that is important in relaying many modalities of sensory information from the periphery to the sensory cortex. Which of the following embryologic structures gave rise to the part of the brain in question?
- A. Metencephalon
- B. Diencephalon (Correct Answer)
- C. Mesencephalon
- D. Telencephalon
- E. Myelencephalon
Central and peripheral nervous system histology Explanation: ***Diencephalon***
- The **thalamus**, a key relay center for sensory information to the cerebral cortex, develops from the diencephalon.
- A thrombus in this area would severely impair the transmission of **sensory modalities** from the periphery.
*Metencephalon*
- The metencephalon gives rise to the **pons** and the **cerebellum**.
- These structures are primarily involved in motor control, coordination, and respiratory regulation, not direct sensory relay to the cortex.
*Mesencephalon*
- The mesencephalon develops into the **midbrain**.
- The midbrain contains structures involved in visual and auditory reflexes, and motor control, but not the primary sensory relay described.
*Myelencephalon*
- The myelencephalon gives rise to the **medulla oblongata**.
- The medulla is crucial for vital autonomic functions (e.g., breathing, heart rate) and connects the brain to the spinal cord.
*Telencephalon*
- The telencephalon develops into the **cerebral hemispheres** (cerebral cortex, basal ganglia, hippocampus).
- While it processes sensory information, it is not the primary relay center from the periphery; that role belongs to the thalamus.
Central and peripheral nervous system histology US Medical PG Question 6: A 26-year-old man presents to his primary doctor with one week of increasing weakness. He reports that he first noticed difficulty walking while attending his sister's graduation last week, and yesterday he had difficulty taking his coffee cup out of the microwave. He remembers having nausea and vomiting a few weeks prior, but other than that has no significant medical history. On exam, he has decreased reflexes in his bilateral upper and lower extremities, with intact sensation. If a lumbar puncture is performed, which of the following results are most likely?
- A. High lymphocytes, high protein, low glucose, high opening pressure
- B. Normal cell count, high protein, normal glucose, normal opening pressure (Correct Answer)
- C. High neutrophils, high protein, low glucose, high opening pressure
- D. Normal cell count, normal protein, normal glucose, normal opening pressure
- E. High lymphocytes, normal protein, normal glucose, normal opening pressure
Central and peripheral nervous system histology Explanation: ***Normal cell count, high protein, normal glucose, normal opening pressure***
- This patient's presentation with **ascending paralysis** following a viral illness (nausea and vomiting a few weeks prior) is highly suggestive of **Guillain-Barré Syndrome (GBS)**.
- The classic cerebrospinal fluid (CSF) finding in GBS is **albuminocytologic dissociation**, characterized by a **normal white blood cell count** but **elevated protein levels** due to inflammation of nerve roots and increased permeability of the blood-nerve barrier.
*High lymphocytes, high protein, low glucose, high opening pressure*
- This CSF profile, particularly **low glucose** and **high lymphocytes**, is more characteristic of **bacterial meningitis** or certain **viral encephalitides**, which do not fit the clinical picture of ascending paralysis and intact sensation.
- While GBS can have high protein, the presence of low glucose points away from GBS.
*High neutrophils, high protein, low glucose, high opening pressure*
- This CSF profile strongly suggests **acute bacterial meningitis**, characterized by a prominent **neutrophilic pleocytosis**, low glucose, and high protein, which is not consistent with the patient's symptoms of progressive weakness.
- The patient's presentation is a subacute progressive weakness, not an acute infectious process affecting the CNS.
*Normal cell count, normal protein, normal glucose, normal opening pressure*
- A completely normal CSF profile would make the diagnosis of GBS less likely, as **elevated CSF protein** is a hallmark of the condition due to nerve root inflammation.
- While GBS can sometimes have normal CSF early in the disease, in the context of progressing weakness, elevated protein is expected.
*High lymphocytes, normal protein, normal glucose, normal opening pressure*
- This CSF profile with **high lymphocytes** and otherwise normal parameters might indicate a **viral meningioencephalitis** or other lymphocytic inflammatory conditions, but it does not align with the characteristic **elevated protein** seen in GBS.
- The absence of elevated protein despite significant neurological symptoms makes this less likely for GBS.
Central and peripheral nervous system histology US Medical PG Question 7: A 26-year-old woman presents to the obstetrics ward to deliver her baby. The obstetrician establishes a pudendal nerve block via intravaginal injection of lidocaine near the tip of the ischial spine. From which of the following nerve roots does the pudendal nerve originate?
- A. L4-L5
- B. S2-S4 (Correct Answer)
- C. L3-L4
- D. L5-S2
- E. L5-S1
Central and peripheral nervous system histology Explanation: ***S2-S4***
- The **pudendal nerve** originates from the **sacral plexus**, specifically from the ventral rami of spinal nerves **S2, S3, and S4**.
- Its origin from these segments is crucial for its function in innervating structures of the **perineum**, **external genitalia**, and the **anal and urethral sphincters**, making it highly relevant for procedures like **pudendal nerve blocks** during childbirth.
*L4-L5*
- Nerve roots **L4-L5** contribute significantly to the **lumbar plexus** and subsequently to nerves like the **femoral nerve** and portions of the **sciatic nerve**.
- These roots are primarily involved in innervating the **lower limbs** (e.g., quadriceps, tibialis anterior) and are not the primary origin of the pudendal nerve.
*L3-L4*
- The **L3-L4** nerve roots are also part of the **lumbar plexus**, chiefly contributing to the **femoral nerve**.
- They are essential for motor innervation of the **anterior thigh muscles** and sensation in this area, distinct from the pudendal nerve's role in the perineum.
*L5-S2*
- While **S2** is part of the pudendal nerve's origin, the inclusion of **L5** and **S1** primarily characterizes the origin of the **sciatic nerve** (which is formed by L4-S3) and its branches, such as the common fibular and tibial nerves.
- These roots are primarily concerned with the **posterior thigh** and **leg innervation**, not the perineum, which differentiates it from the pudendal nerve.
*L5-S1*
- The nerve roots **L5-S1** are key components of the **lumbosacral plexus** and contribute significantly to the **sciatic nerve**, particularly its innervation of the **hamstrings** and certain lower leg muscles.
- This origin does not align with the known roots of the **pudendal nerve** which stems from S2-S4.
Central and peripheral nervous system histology US Medical PG Question 8: A 21-year-old G3P2 woman presents to her obstetrician at 6 weeks gestation for routine prenatal care. Her past medical history includes obesity and gestational diabetes. She has had two spontaneous vaginal deliveries at term. One infant was macrosomic with hypoglycemia, but otherwise, she has had no complications. Her physician informs her that she must start taking a multivitamin with folic acid daily. The defect that folic acid supplementation protects against arises in tissue that is derived from which germ cell layer?
- A. Mesoderm
- B. Notochord
- C. Endoderm
- D. Mesenchyme
- E. Ectoderm (Correct Answer)
Central and peripheral nervous system histology Explanation: ***Ectoderm***
- Folic acid supplementation primarily prevents **neural tube defects**, such as **spina bifida** and **anencephaly**.
- The **neural tube**, which forms the brain and spinal cord, is derived from the **ectoderm**.
*Mesoderm*
- The **mesoderm** gives rise to structures like muscle, bone, connective tissue, and the cardiovascular system.
- Defects in mesodermal development are not primarily prevented by folic acid supplementation.
*Notochord*
- The **notochord** is a transient embryonic structure that induces the formation of the neural plate from the ectoderm.
- While critical for nervous system development, it is not a germ cell layer itself, and defects in its development are not directly prevented by folic acid.
*Endoderm*
- The **endoderm** forms the lining of the gastrointestinal and respiratory tracts, as well as glands like the thyroid and pancreas.
- Anomalies of these internal organs are not the primary target of folic acid supplementation.
*Mesenchyme*
- **Mesenchyme** is embryonic connective tissue, largely derived from the mesoderm, but can also come from neural crest (ectoderm).
- It differentiates into connective tissues, blood, and lymphatic vessels; neural tube defects are not considered mesenchymal in origin.
Central and peripheral nervous system histology US Medical PG Question 9: A 33-year-old man is brought to the emergency department 20 minutes after he fell from the roof of his house. On arrival, he is unresponsive to verbal and painful stimuli. His pulse is 72/min and blood pressure is 132/86 mm Hg. A CT scan of the head shows a fracture in the anterior cranial fossa and a 1-cm laceration in the left anterior orbital gyrus. If the patient survives, which of the following would ultimately be the most common cell type at the injured region of the frontal lobe?
- A. Microglia
- B. Oligodendrocytes
- C. Neurons
- D. Schwann cells
- E. Astrocytes (Correct Answer)
Central and peripheral nervous system histology Explanation: ***Astrocytes***
- Following **neuronal injury**, astrocytes proliferate rapidly and form a **glial scar** around the damaged area to isolate it and prevent further spread of damage.
- This process, known as **astrogliosis**, leads to astrocytes becoming the most abundant cell type in the chronically injured region of the central nervous system.
*Microglia*
- **Microglia** are the brain's resident immune cells and are primarily involved in **phagocytosis** of cellular debris and pathogens after injury.
- While they are activated and proliferate early after injury, they typically do not become the most common cell type in the *chronically injured* region.
*Oligodendrocytes*
- **Oligodendrocytes** are responsible for forming the **myelin sheath** around axons in the central nervous system.
- They are often damaged during acute brain injury and do not typically proliferate to become the most common cell type in the scar tissue.
*Neurons*
- **Neurons** are the primary cells affected by acute brain injury, and many are irrecoverably lost at the site of trauma.
- The adult central nervous system has very limited capacity for neurogenesis, so neurons do not regenerate or become the most common cell type after injury.
*Schwann cells*
- **Schwann cells** are responsible for myelinating axons in the **peripheral nervous system (PNS)**.
- They are not found in the central nervous system (CNS) region of brain injury and therefore would not be involved in the repair or scarring process there.
Central and peripheral nervous system histology US Medical PG Question 10: A 23-year-old man comes to the physician for evaluation of decreased hearing, dizziness, and ringing in his right ear for the past 6 months. Physical examination shows multiple soft, yellow plaques and papules on his arms, chest, and back. There is sensorineural hearing loss and weakness of facial muscles bilaterally. His gait is unsteady. An MRI of the brain shows a 3-cm mass near the right internal auditory meatus and a 2-cm mass at the left cerebellopontine angle. The abnormal cells in these masses are most likely derived from which of the following embryological structures?
- A. Surface ectoderm
- B. Neural tube
- C. Neural crest (Correct Answer)
- D. Notochord
- E. Mesoderm
Central and peripheral nervous system histology Explanation: ***Neural crest***
- The patient's symptoms (bilateral sensorineural hearing loss, facial weakness, unsteady gait, central masses) along with cutaneous lesions (soft, yellow plaques) are highly suggestive of **Neurofibromatosis type 2 (NF2)**.
- NF2 is characterized by **vestibular schwannomas** (acoustic neuromas) and other CNS tumors, which are derived from **Schwann cells**. Schwann cells, along with melanocytes and other peripheral nervous system components, originate from the **neural crest**.
*Surface ectoderm*
- The surface ectoderm forms structures such as the **epidermis**, hair, nails, and anterior pituitary.
- While the skin lesions are present, the primary tumors (schwannomas) are not derived from the surface ectoderm.
*Neural tube*
- The neural tube gives rise to the **central nervous system** (brain and spinal cord) and motor neurons.
- While the tumors affect the brain and cranial nerves, the specific cell type forming schwannomas (Schwann cells) does not originate directly from the neural tube.
*Notochord*
- The notochord induces the formation of the neural tube and eventually degenerates, contributing to the **nucleus pulposus** of the intervertebral discs.
- It is not involved in the pathogenesis or cellular origin of schwannomas.
*Mesoderm*
- The mesoderm gives rise to connective tissues, blood, bone, muscle, and most internal organs.
- While some tumors can have mesodermal origins, schwannomas are neuroectodermal in origin.
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