Corticospinal tracts

Corticospinal tracts US Medical PG Question 1: A 25-year-old man comes to the physician for severe back pain. He describes the pain as shooting and stabbing. On a 10-point scale, he rates the pain as a 9 to 10. The pain started after he lifted a heavy box at work; he works at a supermarket and recently switched from being a cashier to a storekeeper. The patient appears to be in severe distress. Vital signs are within normal limits. On physical examination, the spine is nontender without paravertebral muscle spasms. Range of motion is normal. A straight-leg raise test is negative. After the physical examination has been completed, the patient asks for a letter to his employer attesting to his inability to work as a storekeeper. Which of the following is the most appropriate response?

• A. “Yes. Since work may worsen your condition, I would prefer that you stay home a few days. I will write a letter to your employer to explain the situation.”
• B. You say you are in severe pain. However, the physical examination findings do not suggest a physical problem that can be addressed with medications or surgery. I'd like to meet on a regular basis to see how you're doing.
• C. I understand that you are uncomfortable, but the findings do not match the severity of your symptoms. Let's talk about the recent changes at your job. (Correct Answer)
• D. The physical exam findings do not match your symptoms, which suggests a psychological problem. I would be happy to refer you to a mental health professional.
• E. The physical exam findings suggest a psychological rather than a physical problem. But there is a good chance that we can address it with cognitive-behavioral therapy.

Corticospinal tracts Explanation: ***"I understand that you are uncomfortable, but the findings do not match the severity of your symptoms. Let's talk about the recent changes at your job."*** - This response acknowledges the patient's reported discomfort while gently highlighting the **discrepancy between symptoms and objective findings**, which is crucial in cases of suspected **somatoform or functional pain**. - It also opens communication about potential **psychosocial stressors** related to his job change, which could be contributing to his symptoms, without dismissing his pain or making a premature diagnosis. *"You say you are in severe pain. However, the physical examination findings do not suggest a physical problem that can be addressed with medications or surgery. I'd like to meet on a regular basis to see how you're doing."* - While this option correctly identifies the lack of physical findings, it can be perceived as dismissive of the patient's pain, potentially damaging the **physician-patient relationship**. - Suggesting regular meetings without a clear plan for addressing his immediate concerns or exploring underlying issues might not be the most effective initial approach. *“Yes. Since work may worsen your condition, I would prefer that you stay home a few days. I will write a letter to your employer to explain the situation.”* - This response would **validate the patient's claim of severe pain** without objective evidence, potentially reinforcing illness behavior and avoiding addressing the underlying issue. - Providing a doctor's note for inability to work without a clear diagnostic basis or understanding of the pain's origin is **medically inappropriate** and could set a precedent for future such requests. *"The physical exam findings do not match your symptoms, which suggests a psychological problem. I would be happy to refer you to a mental health professional."* - Directly labeling the problem as "psychological" can be **stigmatizing and alienating** to the patient, leading to distrust and resistance to care. - While a psychological component might be present, immediately referring to mental health without further exploration of the patient's situation or current stressors is premature and lacks empathy. *"The physical exam findings suggest a psychological rather than a physical problem. But there is a good chance that we can address it with cognitive-behavioral therapy."* - Similar to the previous option, explicitly stating a "psychological problem" can be **stigmatizing**. - Jumping directly to recommending **cognitive-behavioral therapy (CBT)** without a comprehensive discussion and patient buy-in is premature and may lead to non-compliance.

Corticospinal tracts US Medical PG Question 2: A 78-year-old woman is accompanied by her family for a routine visit to her primary care provider. The family states that 5 months prior, the patient had a stroke and is currently undergoing physical therapy. Today, her temperature is 98.2°F (36.8°C), blood pressure is 112/72 mmHg, pulse is 64/min, and respirations are 12/min. On exam, she is alert and oriented with no deficits in speech. Additionally, her strength and sensation are symmetric and preserved bilaterally. However, on further neurologic testing, she appears to have some difficulty with balance and a propensity to fall to her right side. Which of the following deficits does the patient also likely have?

• A. Hemiballismus
• B. Hemispatial neglect
• C. Intention tremor
• D. Contralateral eye deviation
• E. Truncal ataxia (Correct Answer)

Corticospinal tracts Explanation: ***Truncal ataxia*** - This patient's symptoms of **difficulty with balance** and a **propensity to fall to her right side** are highly suggestive of truncal ataxia. - While she had a stroke, her preserved speech, symmetric strength and sensation, and alertness rule out typical hemiparesis or aphasia, pointing towards a **cerebellar lesion** affecting balance and coordination. *Hemiballismus* - This condition involves **flailing, high-amplitude, involuntary movements** typically affecting one side of the body. - The patient's description of balance issues and falling, without mention of such specific movements, makes hemiballismus less likely. *Hemispatial neglect* - Characterized by the **inability to attend to one side of the environment**, usually the left side following a right parietal stroke. - The patient's presentation does not describe an indifference to one side of her visual or personal space. *Intention tremor* - An **intention tremor** is a tremor that worsens during purposeful movement towards a target. - While it can be associated with cerebellar dysfunction, the primary deficit described is imbalance and falling to one side, not specifically a tremor. *Contralateral eye deviation* - This typically occurs in acute stroke scenarios as part of a **gaze preference**, where the eyes deviate towards the side of the lesion (or away from the hemiparesis). - The patient is 5 months post-stroke and is alert with no acute focal deficits, making acute eye deviation unlikely as a chronic presenting symptom here.

Corticospinal tracts US Medical PG Question 3: An epidemiologist is evaluating the efficacy of Noxbinle in preventing HCC deaths at the population level. A clinical trial shows that over 5 years, the mortality rate from HCC was 25% in the control group and 15% in patients treated with Noxbinle 100 mg daily. Based on this data, how many patients need to be treated with Noxbinle 100 mg to prevent, on average, one death from HCC?

• A. 20
• B. 73
• C. 10 (Correct Answer)
• D. 50
• E. 100

Corticospinal tracts Explanation: ***10*** - The **number needed to treat (NNT)** is calculated by first finding the **absolute risk reduction (ARR)**. - **ARR** = Risk in control group - Risk in treatment group = 25% - 15% = **10%** (or 0.10). - **NNT = 1 / ARR** = 1 / 0.10 = **10 patients**. - This means that **10 patients must be treated with Noxbinle to prevent one death from HCC** over 5 years. *20* - This would result from an ARR of 5% (1/0.05 = 20), which is not supported by the data. - May arise from miscalculating the risk difference or incorrectly halving the actual ARR. *73* - This value does not correspond to any standard calculation of NNT from the given mortality rates. - May result from confusion with other epidemiological measures or calculation error. *50* - This would correspond to an ARR of 2% (1/0.02 = 50), which significantly underestimates the actual risk reduction. - Could result from incorrectly calculating the difference as a proportion rather than absolute percentage points. *100* - This would correspond to an ARR of 1% (1/0.01 = 100), grossly underestimating the treatment benefit. - May result from confusing ARR with relative risk reduction or other calculation errors.

Corticospinal tracts US Medical PG Question 4: A 40-year-old man is brought to the emergency department after sustaining multiple lacerations during a bar fight. The patient’s wife says that he has been showing worsening aggression and has been involved in a lot of arguments and fights for the past 2 years. The patient has no significant past medical or psychiatric history and currently takes no medications. The patient cannot provide any relevant family history since he was adopted as an infant. His vitals are within normal limits. On physical examination, the patient looks apathetic and grimaces repeatedly. Suddenly, his arms start to swing by his side in an uncontrolled manner. Which area of the brain is most likely affected in this patient?

• A. Cerebral cortex
• B. Caudate nucleus (Correct Answer)
• C. Cerebellum
• D. Medulla oblongata
• E. Substantia nigra

Corticospinal tracts Explanation: **Caudate nucleus** - The patient exhibits features like **worsening aggression**, **apathy**, and **uncontrolled, sudden movements** of the limbs, which are characteristic of Huntington's disease, a condition primarily affecting the **caudate nucleus**. - **Huntington's disease** is an autosomal dominant neurodegenerative disorder linked to a trinucleotide repeat expansion (CAG) on chromosome 4, leading to atrophy of the **caudate and putamen**. *Cerebral cortex* - While damage to the cerebral cortex can cause personality changes and motor deficits, the specific combination of **choreiform movements** and progressive cognitive/behavioral decline seen here is more indicative of a basal ganglia disorder like Huntington's. - Cortical lesions more commonly present with **focal neurological deficits** such as hemiparesis, aphasia, or sensory loss, which are not the primary features described. *Cerebellum* - Damage to the cerebellum typically results in **ataxia**, **dysmetria**, **intention tremor**, and problems with balance and coordination. - The patient's **uncontrolled, sudden limb movements** are characteristic of chorea, not cerebellar dysfunction. *Medulla oblongata* - The medulla oblongata is crucial for vital autonomic functions such as **breathing, heart rate, and blood pressure regulation**. - Lesions in this area would likely cause life-threatening symptoms, including **respiratory failure** or severe cardiovascular instability, which are not present in this patient. *Substantia nigra* - Damage or degeneration of the substantia nigra is primarily associated with **Parkinson's disease**, leading to symptoms like **bradykinesia**, **rigidity**, **resting tremor**, and **postural instability**. - The patient's **hyperkinetic movements** (choreiform movements) are opposite to the hypokinetic presentation of Parkinson's disease.

Corticospinal tracts US Medical PG Question 5: A 21-year-old man was involved in a motor vehicle accident and died. At autopsy, the patient demonstrated abnormally increased mobility at the neck. A section of cervical spinal cord at C6 was removed and processed into slides. Which of the following gross anatomic features is most likely true of this spinal cord level?

• A. Cuneate and gracilis fasciculi are present (Correct Answer)
• B. Least amount of white matter
• C. Prominent lateral horns
• D. Absence of gray matter enlargement
• E. Involvement with parasympathetic nervous system

Corticospinal tracts Explanation: **Cuneate and gracilis fasciculi are present** - At the **C6 level** of the spinal cord, both the **fasciculus gracilis** (carrying information from the lower body) and the **fasciculus cuneatus** (carrying information from the upper body) are present in the dorsal column. - The fasciculus cuneatus typically appears at **T6 and above**, making it visible at C6. *Least amount of white matter* - The cervical spinal cord, particularly at C6, contains a **significant amount of white matter** because it carries all ascending and descending tracts to and from the brain, including those for the upper and lower limbs. - The **sacral segments** typically have the least amount of white matter due to fewer tracts remaining. *Prominent lateral horns* - **Lateral horns** are characteristic of the **thoracic and upper lumbar (T1-L2/L3)** spinal cord segments, where they house preganglionic sympathetic neurons. - They are generally **absent or poorly developed** in the cervical spinal cord. *Absence of gray matter enlargement* - The **cervical enlargement** of the spinal cord, particularly pronounced from C4 to T1, contains an increased amount of gray matter to accommodate the innervation of the **upper limbs**. - Therefore, the C6 level would show **significant gray matter enlargement**. *Involvement with parasympathetic nervous system* - The **parasympathetic nervous system** exits the spinal cord at the **sacral levels (S2-S4)** and as cranial nerves, not primarily from the cervical spinal cord through distinct horns. - The cervical spinal cord is primarily associated with **somatic motor and sensory pathways** for the neck, shoulders, and upper limbs, and receives some sympathetic input, but is not where parasympathetic outflow predominantly originates.

Corticospinal tracts US Medical PG Question 6: A 80-year-old man is brought to the emergency department with complaints that he "can't control his left leg". His symptoms started a few hours ago. He was outside taking a walk with his wife when suddenly his leg shot out and kicked her. His past medical history is notable for diabetes, hypertension, and a myocardial infarction 5 years ago. He smokes 1-2 cigarettes/day. He does not use alcohol or illicit drugs. On exam, the patient has intermittent wide, flinging movements that affect his proximal left arm and left leg. Which of the following parts of his brain is most likely damaged?

• A. Ventral posterior thalamic nucleus
• B. Left internal capsule
• C. Right subthalamic nucleus (Correct Answer)
• D. Left subthalamic nucleus
• E. Right internal capsule

Corticospinal tracts Explanation: ***Right subthalamic nucleus*** - The patient's symptoms of sudden, uncontrolled, wide-flinging movements, affecting the contralateral (left) side of the body, are characteristic of **hemiballism**. - **Hemiballism** is almost exclusively caused by a lesion in the **contralateral subthalamic nucleus (STN)**, or its afferent/efferent connections, most commonly due to a **lacunar infarct**. *Ventral posterior thalamic nucleus* - Damage to the **ventral posterior thalamic nucleus** primarily causes **sensory deficits**, such as loss of touch, pain, and temperature sensation, on the contralateral side of the body. - While it can be involved in motor control, it does not typically cause the characteristic flinging movements seen in hemiballism. *Left internal capsule* - A lesion in the **left internal capsule** would result in contralateral (right-sided) motor and sensory deficits, including **hemiparesis** or **hemiplegia**, but not the ballistic, uncontrollable movements described. - The internal capsule carries major motor and sensory pathways to and from the cerebral cortex. *Left subthalamic nucleus* - Damage to the **left subthalamic nucleus** would cause hemiballism on the **contralateral (right) side** of the body. - The patient's symptoms are on the left side, indicating a lesion in the right subthalamic nucleus. *Right internal capsule* - A lesion in the **right internal capsule** would primarily cause contralateral (left-sided) motor and sensory deficits, such as **hemiparesis** or **hemiplegia**. - While it affects the contralateral side as described in the patient, it would typically present as weakness rather than uncontrolled flinging movements.

Corticospinal tracts US Medical PG Question 7: You are currently employed as a clinical researcher working on clinical trials of a new drug to be used for the treatment of Parkinson's disease. Currently, you have already determined the safe clinical dose of the drug in a healthy patient. You are in the phase of drug development where the drug is studied in patients with the target disease to determine its efficacy. Which of the following phases is this new drug currently in?

• A. Phase 4
• B. Phase 1
• C. Phase 2 (Correct Answer)
• D. Phase 0
• E. Phase 3

Corticospinal tracts Explanation: ***Phase 2*** - **Phase 2 trials** involve studying the drug in patients with the target disease to assess its **efficacy** and further evaluate safety, typically involving a few hundred patients. - The question describes a stage after safe dosing in healthy patients (Phase 1) and before large-scale efficacy confirmation (Phase 3), focusing on efficacy in the target population. *Phase 4* - **Phase 4 trials** occur **after a drug has been approved** and marketed, monitoring long-term effects, optimal use, and rare side effects in a diverse patient population. - This phase is conducted post-market approval, whereas the question describes a drug still in development prior to approval. *Phase 1* - **Phase 1 trials** primarily focus on determining the **safety and dosage** of a new drug in a **small group of healthy volunteers** (or sometimes patients with advanced disease if the drug is highly toxic). - The question states that the safe clinical dose in a healthy patient has already been determined, indicating that Phase 1 has been completed. *Phase 0* - **Phase 0 trials** are exploratory, very early-stage studies designed to confirm that the drug reaches the target and acts as intended, typically involving a very small number of doses and participants. - These trials are conducted much earlier in the development process, preceding the determination of safe clinical doses and large-scale efficacy studies. *Phase 3* - **Phase 3 trials** are large-scale studies involving hundreds to thousands of patients to confirm **efficacy**, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug to be used safely. - While Phase 3 does assess efficacy, it follows Phase 2 and is typically conducted on a much larger scale before submitting for regulatory approval.

Corticospinal tracts US Medical PG Question 8: A 61-year-old man is brought to the emergency department by his son after collapsing to the ground while at home. His son immediately performed cardiopulmonary resuscitation and later the patient underwent successful defibrillation after being evaluated by the emergency medical technician. The patient has a medical history of hypertension, hyperlipidemia, and type II diabetes mellitus. He has smoked one-half pack of cigarettes for approximately 30 years. The patient was admitted to the cardiac intensive care unit, and after a few days developed acute onset right upper extremity weakness. His temperature is 99°F (37.2°C), blood pressure is 145/91 mmHg, pulse is 102/min and irregularly irregular, and respirations are 16/min. On physical examination, the patient is alert and orientated to person, place, and time. His language is fluent and he is able to name, repeat, and read. His strength is 5/5 throughout except in the right hand, wrist, and arm, which is 2/5. Based on this patient's clinical presentation, the affected neuronal fibers decussate at which level of the central nervous system?

• A. Caudal medulla (Correct Answer)
• B. Pons
• C. Spinal cord
• D. Primary motor cortex
• E. Thalamus

Corticospinal tracts Explanation: ***Caudal medulla*** - The patient's **acute right upper extremity weakness** following a cardiac event suggests a **stroke** affecting the left motor pathways. - The **pyramidal decussation**, where the vast majority of the **corticospinal tracts** cross to the contralateral side, occurs in the **caudal medulla**. *Pons* - While the corticospinal tracts pass through the pons, they generally do not decussate at this level. - Lesions in the pons often present with **ipsilateral cranial nerve** deficits and **contralateral body weakness**. *Spinal cord* - Only a small percentage (about 10-15%) of the corticospinal fibers decussate in the spinal cord, and these form the **anterior corticospinal tract**, mainly supplying axial muscles. - Significant contralateral upper extremity weakness implies a lesion higher up, before the spinal cord. *Primary motor cortex* - Lesions in the primary motor cortex would cause contralateral weakness, but the decussation itself occurs in the brainstem, not the cortex. - The motor cortex is where the motor commands originate, not where they cross over. *Thalamus* - The thalamus is a major **sensory relay station** and also plays a role in motor control, but it is not the site of decussation for the corticospinal tracts. - Thalamic lesions typically cause **sensory deficits** (e.g., contralateral hemianesthesia) and sometimes ataxia or dyskinesias.

Corticospinal tracts US Medical PG Question 9: Arrange in sequence the structures involved in the direct pathway (1=Striatum, 2=GPi, 3=Thalamus, 4=Cortex output, 5=Cortex input):-

• A. 1,3,4,2,5
• B. 5,1,2,3,4 (Correct Answer)
• C. 1,2,3,4,5
• D. 5,4,2,3,1
• E. 5,1,3,2,4

Corticospinal tracts Explanation: ***5,1,2,3,4*** - The direct pathway of the basal ganglia begins with the **cortex** (5) sending excitatory signals to the **striatum** (1). - The striatum then inhibits the **internal globus pallidus (GPi)** (2), which disinhibits the **thalamus** (3), leading to excitation of the **cortex** (4). - This is the correct sequence: **Cortex input → Striatum → GPi → Thalamus → Cortex output**. *1,3,4,2,5* - This sequence is incorrect as it starts with the striatum instead of cortical input. - The direct pathway does not begin with striatal activity; the cortex must first activate the striatum. *1,2,3,4,5* - This order is incorrect because it implies the pathway starts at the striatum rather than the cortex. - The cortex should be the starting point (5) and the ending point (4) of the motor loop. *5,4,2,3,1* - This sequence is incorrect as it places cortex output (4) before the striatum receives input. - This reverses the functional flow and does not follow the **disinhibitory mechanism** of the direct pathway. *5,1,3,2,4* - This sequence incorrectly places the thalamus (3) before the GPi (2). - In the direct pathway, the striatum must first inhibit the GPi before the thalamus can be disinhibited.

Corticospinal tracts US Medical PG Question 10: A 12-year-old boy is brought to his orthopedic surgeon for evaluation of leg pain and positioning. Specifically, over the past several months he has been complaining of thigh pain and has more difficulty sitting in his wheelchair. His medical history is significant for spastic quadriplegic cerebral palsy since birth and has undergone a number of surgeries for contractures in his extremities. At this visit his legs are found to be scissored such that they cross each other at the knees and are difficult to separate. Surgery is performed and the boy is placed into a cast that keeps his legs abducted to prevent scissoring. Overactivity of the muscles innervated by which of the following nerves is most consistent with this patient's deformity?

• A. Nerve to the iliopsoas
• B. Sciatic nerve
• C. Femoral nerve
• D. Superior gluteal nerve
• E. Obturator nerve (Correct Answer)

Corticospinal tracts Explanation: ***Obturator*** - The **obturator nerve** innervates the **adductor muscles** of the thigh (adductor longus, brevis, magnus, gracilis, and obturator externus). - **Overactivity** of these muscles leads to thigh adduction, causing the characteristic **"scissoring" gait** seen in some patients with cerebral palsy. *Nerve to the iliopsoas* - The **iliopsoas muscle** is a primary **hip flexor**, important for activities like sitting and standing. - While involvement of hip flexors can cause contractures, it would manifest as difficulty extending the hip, not a scissoring deformity. *Sciatic nerve* - The **sciatic nerve** innervates the **hamstring muscles** (semitendinosus, semimembranosus, biceps femoris) and most muscles of the leg and foot. - Its overactivity or spasticity would primarily affect knee flexion and foot movements, not hip adduction or scissoring. *Femoral nerve* - The **femoral nerve** innervates the **quadriceps femoris muscles** (rectus femoris, vastus lateralis, medialis, intermedius) and the sartorius. - Overactivity would lead to strong knee extension and hip flexion, not the adducted and scissored leg position described. *Superior gluteal nerve* - The **superior gluteal nerve** innervates the **gluteus medius**, **gluteus minimus**, and **tensor fasciae latae** muscles, which are primarily hip abductors and internal rotators. - Overactivity of these muscles would cause hip abduction, which is the opposite of the scissoring deformity.

Corticospinal tracts Flashcard 1 of 8

Question: The UMNs of the motor cortex that receive input from the VL nucleus (thalamus) send descending axons via the contralateral _____ tract

Answer: corticospinal

Corticospinal tracts Flashcard 2 of 8

Question: corticospinal tract (CST)

Answer: motor innervation

Extra Information: caudal medulla Number 5

Corticospinal tracts Flashcard 3 of 8

Question: The axons of upper motoneurons of peripheral nerves are found in the _____ tract

Answer: corticospinal

Extra Information:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/neuroanatomy/videos/spinal-cord-tracts?index=2] https://onlinemeded.org/spa/neuroscience/brainstem/acquire?ref=anki 

Corticospinal tracts Flashcard 4 of 8

Question: Corticobulbar fibers arise in the _____ cortex

Answer: primary motor

Extra Information:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/neuroanatomy/videos/spinal-cord-tracts?index=6] https://onlinemeded.org/spa/neuroscience/cranial-nerves/acquire?ref=anki 

Corticospinal tracts Flashcard 5 of 8

Question: ID Tracts: _____

Answer: Corticospinal and Corticobulbar tracts

Extra Information:  https://onlinemeded.org/spa/neuroscience/brainstem/acquire?ref=anki Netters: Other: 

Corticospinal tracts Flashcard 6 of 8

Question: Corticobulbar fibers arise in the _____ cortex

Answer: primary motor

Corticospinal tracts Flashcard 7 of 8

Question: The corticospinal tract is located _____ (medially or laterally) throughout the brainstem

Answer: medially

Corticospinal tracts Flashcard 8 of 8

Question: Neurons of the red nucleus (midbrain) that receive input from the emboliform and globose nuclei send descending axons via the contralateral _____ tract

Answer: rubrospinal