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Question 1
Incorrect
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A mother brings her 3-month-old son for his routine check-up. She mentions that his left hand has been in a fixed 'claw-like' position since birth. Upon examination, the left forearm is found to be supinated and the left wrist and fingers are flexed. Additionally, a slight droop is observed in the right eyelid and the right pupil is constricted.
What is the probable diagnosis?Your Answer: Erb-Duchenne palsy
Correct Answer: Klumpke palsy
Explanation:Klumpke palsy is a condition that can occur due to shoulder dystocia during birth or sudden upward jerking of the hand. It results from damage to the lower trunk of the brachial plexus (C8, T1) and can cause a flattened forearm, flexed wrist, and fingers. Klumpke injury may also be associated with Horner’s syndrome, which can cause ptosis and miosis on the opposite side of the face.
Erb-Duchenne palsy is another condition that can occur due to shoulder dystocia during birth, but it results from damage to the upper trunk of the brachial plexus (C5, C6). The affected arm hangs by the side, is internally rotated, and has an extended elbow.
Radial nerve palsy can be caused by a humeral midshaft fracture and can result in wrist drop.
Median nerve palsy can have different features depending on the site of the lesion. If the lesion is in the wrist, it can cause paralysis of the thenar muscles, leading to an inability to abduct and oppose the thumb. If the lesion is in the elbow, it can cause a loss of pronation of the forearm and weak wrist flexion.
Horner’s syndrome is a condition characterized by several features, including a small pupil (miosis), drooping of the upper eyelid (ptosis), a sunken eye (enophthalmos), and loss of sweating on one side of the face (anhidrosis). The cause of Horner’s syndrome can be determined by examining additional symptoms. For example, congenital Horner’s syndrome may be identified by a difference in iris color (heterochromia), while anhidrosis may be present in central or preganglionic lesions. Pharmacologic tests, such as the use of apraclonidine drops, can also be helpful in confirming the diagnosis and identifying the location of the lesion. Central lesions may be caused by conditions such as stroke or multiple sclerosis, while postganglionic lesions may be due to factors like carotid artery dissection or cluster headaches. It is important to note that the appearance of enophthalmos in Horner’s syndrome is actually due to a narrow palpebral aperture rather than true enophthalmos.
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This question is part of the following fields:
- Neurological System
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Question 2
Incorrect
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During a challenging femoro-popliteal bypass surgery, the surgeon mistakenly applies a clamp on the femoral nerve. The clamp remains in place for a significant portion of the procedure. Upon examination after the operation, the nerve is found to be intact but shows signs of compression. What is the most probable outcome in the coming months?
Your Answer: Rapid restoration of neuronal function because the axon itself is intact
Correct Answer: Wallerian degeneration
Explanation:Despite the nerve remaining intact, a neuronal injury can lead to Wallerian degeneration and potentially the formation of neuromas.
Nerve injuries can be classified into three types: neuropraxia, axonotmesis, and neurotmesis. Neuropraxia occurs when the nerve is intact but its electrical conduction is affected. However, full recovery is possible, and autonomic function is preserved. Wallerian degeneration, which is the degeneration of axons distal to the site of injury, does not occur. Axonotmesis, on the other hand, happens when the axon is damaged, but the myelin sheath is preserved, and the connective tissue framework is not affected. Wallerian degeneration occurs in this type of injury. Lastly, neurotmesis is the most severe type of nerve injury, where there is a disruption of the axon, myelin sheath, and surrounding connective tissue. Wallerian degeneration also occurs in this type of injury.
Wallerian degeneration typically begins 24-36 hours following the injury. Axons are excitable before degeneration occurs, and the myelin sheath degenerates and is phagocytosed by tissue macrophages. Neuronal repair may only occur physiologically where nerves are in direct contact. However, nerve regeneration may be hampered when a large defect is present, and it may not occur at all or result in the formation of a neuroma. If nerve regrowth occurs, it typically happens at a rate of 1mm per day.
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This question is part of the following fields:
- Neurological System
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Question 3
Incorrect
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A 62-year-old man comes to the emergency department with recent involuntary movements. During the examination, it is observed that he has unmanageable thrashing movements of his left arm and leg, which cannot be diverted. A CT scan reveals a fresh acute infarct.
What part of the brain has been impacted by this infarct, causing these symptoms?Your Answer: Substantia nigra
Correct Answer: Subthalamic nucleus
Explanation:Lesions of the subthalamic nucleus (STN) within the basal ganglia can result in a hemiballismus, characterized by uncontrollable thrashing movements. The STN plays a role in unconscious motor control by providing excitatory input to the globus pallidus internus (GPi), which then acts in an inhibitory way on motor outflow from the cortex. When the STN is damaged, there is less activity within the GPi and relative hyperactivity of the motor cortex, leading to excessive movements.
In contrast, lesions of the caudate nucleus within the basal ganglia can cause behavioral changes and agitation. The caudate processes motor information from the cortex and provides an excitatory input to the globus pallidus externus (GPe), which then has an excitatory input to the STN. Lesions of the caudate result in motor hyperactivity, but this manifests as a restless state rather than uncontrolled movements. The caudate also plays a role in the neural circuits underlying goal-directed behaviors, and lesions can result in personality and behavioral changes.
Lesions of the medial pons can cause hemiplegia and hemisensory loss or locked-in syndrome, depending on the level of disruption to the motor and sensory pathways. Lesions above the level of the trigeminal and facial motor nuclei can result in a full locked-in syndrome, while lesions below these nuclei result in hemiplegia and hemisensory loss but with preservation of facial sensation and movement.
Lesions of the substantia nigra result in Parkinsonism, as the dopaminergic neurons of the substantia nigra have an inhibitory effect on the outflow of the striatum. This prevents motor information from leaving the cortex, resulting in the bradykinesia characteristic of Parkinsonism.
Thalamic lesions most commonly cause hemisensory loss, as the thalamus acts as a sensory gateway that allows processing of sensory information before relaying it to the relevant primary cortex. Lesions disrupt this pathway and prevent information from reaching the cortex.
Brain lesions can be localized based on the neurological disorders or features that are present. The gross anatomy of the brain can provide clues to the location of the lesion. For example, lesions in the parietal lobe can result in sensory inattention, apraxias, astereognosis, inferior homonymous quadrantanopia, and Gerstmann’s syndrome. Lesions in the occipital lobe can cause homonymous hemianopia, cortical blindness, and visual agnosia. Temporal lobe lesions can result in Wernicke’s aphasia, superior homonymous quadrantanopia, auditory agnosia, and prosopagnosia. Lesions in the frontal lobes can cause expressive aphasia, disinhibition, perseveration, anosmia, and an inability to generate a list. Lesions in the cerebellum can result in gait and truncal ataxia, intention tremor, past pointing, dysdiadokinesis, and nystagmus.
In addition to the gross anatomy, specific areas of the brain can also provide clues to the location of a lesion. For example, lesions in the medial thalamus and mammillary bodies of the hypothalamus can result in Wernicke and Korsakoff syndrome. Lesions in the subthalamic nucleus of the basal ganglia can cause hemiballism, while lesions in the striatum (caudate nucleus) can result in Huntington chorea. Parkinson’s disease is associated with lesions in the substantia nigra of the basal ganglia, while lesions in the amygdala can cause Kluver-Bucy syndrome, which is characterized by hypersexuality, hyperorality, hyperphagia, and visual agnosia. By identifying these specific conditions, doctors can better localize brain lesions and provide appropriate treatment.
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This question is part of the following fields:
- Neurological System
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Question 4
Incorrect
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A 36-year-old patient, Sarah, arrives at the emergency department with an abrupt onset of left-sided facial weakness. The weakness impacts the entire left side of her face, including her forehead, and her corneal reflex is absent upon examination. The physician prescribes prednisolone and informs Sarah that her facial weakness should improve within a few weeks.
What is the cranial foramen through which the nerve responsible for Sarah's symptoms passes?Your Answer: Foramen ovale
Correct Answer: Internal acoustic meatus
Explanation:The correct answer is the internal acoustic meatus, through which the facial nerve (CN VII) and vestibulocochlear nerve (CN VIII) pass. Emily is likely experiencing Bell’s Palsy, which is treated with prednisolone. The foramen ovale is incorrect, as it is where the mandibular branch of the trigeminal nerve (CN V₃) passes. The foramen spinosum is also incorrect, as it is where the middle meningeal artery, middle meningeal vein, and meningeal branch of the mandibular nerve (CN V₃) pass. The jugular foramen is incorrect, as it is where the glossopharyngeal nerve (CN IX), vagus nerve (CN X), and spinal accessory nerve (CN XI) pass. The superior orbital fissure (SOF) is also incorrect, as it is where the lacrimal nerve, frontal and nasociliary branches of the ophthalmic nerve (CN V₁), trochlear nerve (CN IV), oculomotor nerve (CN III), abducens nerve (CN VI), superior ophthalmic vein, and a branch of the inferior ophthalmic vein pass.
Cranial nerves are a set of 12 nerves that emerge from the brain and control various functions of the head and neck. Each nerve has a specific function, such as smell, sight, eye movement, facial sensation, and tongue movement. Some nerves are sensory, some are motor, and some are both. A useful mnemonic to remember the order of the nerves is Some Say Marry Money But My Brother Says Big Brains Matter Most, with S representing sensory, M representing motor, and B representing both.
In addition to their specific functions, cranial nerves also play a role in various reflexes. These reflexes involve an afferent limb, which carries sensory information to the brain, and an efferent limb, which carries motor information from the brain to the muscles. Examples of cranial nerve reflexes include the corneal reflex, jaw jerk, gag reflex, carotid sinus reflex, pupillary light reflex, and lacrimation reflex. Understanding the functions and reflexes of the cranial nerves is important in diagnosing and treating neurological disorders.
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This question is part of the following fields:
- Neurological System
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Question 5
Correct
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A laceration of the wrist produces a median nerve transection in a 50-year-old patient. The wound is clean and seen immediately after injury. Collateral soft tissue damage is absent. The patient asks what the prognosis is. You indicate that the nerve should regrow at approximately:
Your Answer: 1 mm per day
Explanation:When a peripheral nerve is cut, it causes bleeding and the nerve ends retract. The axon, which is the part of the nerve that transmits signals, starts to degenerate immediately after the injury. This degeneration occurs both in the part of the nerve that is distal to the injury and in the part that is proximal to the first node of Ranvier. As the degenerated axonal fragments are removed by phagocytosis, empty spaces are left in the neurilemmal sheath where the axons used to be.
After a few days, axons from the proximal part of the nerve start to regrow. If they are able to make contact with the distal neurilemmal sheath, they can regrow at a rate of about 1 mm per day. However, if there is any trauma, fracture, infection, or separation of the neurilemmal sheath ends that prevents contact between the axons, the regrowth can be erratic and may result in the formation of a traumatic neuroma.
In cases where the nerve injury is accompanied by significant soft tissue damage and bleeding (which increases the risk of infection), some surgeons may choose to delay the reattachment of the severed nerve ends for several weeks.
Nerve injuries can be classified into three types: neuropraxia, axonotmesis, and neurotmesis. Neuropraxia occurs when the nerve is intact but its electrical conduction is affected. However, full recovery is possible, and autonomic function is preserved. Wallerian degeneration, which is the degeneration of axons distal to the site of injury, does not occur. Axonotmesis, on the other hand, happens when the axon is damaged, but the myelin sheath is preserved, and the connective tissue framework is not affected. Wallerian degeneration occurs in this type of injury. Lastly, neurotmesis is the most severe type of nerve injury, where there is a disruption of the axon, myelin sheath, and surrounding connective tissue. Wallerian degeneration also occurs in this type of injury.
Wallerian degeneration typically begins 24-36 hours following the injury. Axons are excitable before degeneration occurs, and the myelin sheath degenerates and is phagocytosed by tissue macrophages. Neuronal repair may only occur physiologically where nerves are in direct contact. However, nerve regeneration may be hampered when a large defect is present, and it may not occur at all or result in the formation of a neuroma. If nerve regrowth occurs, it typically happens at a rate of 1mm per day.
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This question is part of the following fields:
- Neurological System
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Question 6
Incorrect
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The blood-brain barrier is not easily penetrated by which of the following substances?
Your Answer: Glucose
Correct Answer: Hydrogen ions
Explanation:The blood brain barrier restricts the passage of highly dissociated compounds.
Cerebrospinal Fluid: Circulation and Composition
Cerebrospinal fluid (CSF) is a clear, colorless liquid that fills the space between the arachnoid mater and pia mater, covering the surface of the brain. The total volume of CSF in the brain is approximately 150ml, and it is produced by the ependymal cells in the choroid plexus or blood vessels. The majority of CSF is produced by the choroid plexus, accounting for 70% of the total volume. The remaining 30% is produced by blood vessels. The CSF is reabsorbed via the arachnoid granulations, which project into the venous sinuses.
The circulation of CSF starts from the lateral ventricles, which are connected to the third ventricle via the foramen of Munro. From the third ventricle, the CSF flows through the cerebral aqueduct (aqueduct of Sylvius) to reach the fourth ventricle via the foramina of Magendie and Luschka. The CSF then enters the subarachnoid space, where it circulates around the brain and spinal cord. Finally, the CSF is reabsorbed into the venous system via arachnoid granulations into the superior sagittal sinus.
The composition of CSF is essential for its proper functioning. The glucose level in CSF is between 50-80 mg/dl, while the protein level is between 15-40 mg/dl. Red blood cells are not present in CSF, and the white blood cell count is usually less than 3 cells/mm3. Understanding the circulation and composition of CSF is crucial for diagnosing and treating various neurological disorders.
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This question is part of the following fields:
- Neurological System
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Question 7
Incorrect
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A 65-year-old man comes to the emergency department after experiencing a sudden, severe headache that started one hour ago. He describes it as feeling like he was hit in the head with a hammer while he was in the shower.
During the examination, the patient has a dilated left pupil with an eye that is fixed to the lower lateral quadrant. Although he feels nauseous, there is no change in his Glasgow Coma Scale score (GCS).
Which of the following dural folds is responsible for the compression of the oculomotor nerve, resulting in the eye signs observed in this case?Your Answer:
Correct Answer: Tentorium cerebelli
Explanation:The tentorium cerebelli, which is a fold of the dura mater on both sides, separates the cerebellum from the occipital lobes. When there are expanding mass lesions, the brain can be pushed down past this fold, resulting in the compression of local structures such as the oculomotor nerve. This compression can cause abnormal eye positioning and a dilated pupil in the patient.
It is important to note that the corpus callosum is not a fold of the meninges. Instead, it is a bundle of neuronal fibers that connect the two hemispheres of the brain.
The falx cerebri, on the other hand, is a fold of the dura mater that extends inferiorly between the two hemispheres of the brain.
The arachnoid and pia mater are the middle and innermost layers of the meninges, respectively. They are not involved in the fold of the dura mater that separates the occipital lobe from the cerebellum.
The Three Layers of Meninges
The meninges are a group of membranes that cover the brain and spinal cord, providing support to the central nervous system and the blood vessels that supply it. These membranes can be divided into three distinct layers: the dura mater, arachnoid mater, and pia mater.
The outermost layer, the dura mater, is a thick fibrous double layer that is fused with the inner layer of the periosteum of the skull. It has four areas of infolding and is pierced by small areas of the underlying arachnoid to form structures called arachnoid granulations. The arachnoid mater forms a meshwork layer over the surface of the brain and spinal cord, containing both cerebrospinal fluid and vessels supplying the nervous system. The final layer, the pia mater, is a thin layer attached directly to the surface of the brain and spinal cord.
The meninges play a crucial role in protecting the brain and spinal cord from injury and disease. However, they can also be the site of serious medical conditions such as subdural and subarachnoid haemorrhages. Understanding the structure and function of the meninges is essential for diagnosing and treating these conditions.
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This question is part of the following fields:
- Neurological System
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Question 8
Incorrect
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Which one of the following is not a content of the cavernous sinus?
Your Answer:
Correct Answer: Optic nerve
Explanation:Cavernous sinus contents mnemonic: OTOM CAT
Understanding the Cavernous Sinus
The cavernous sinuses are a pair of structures located on the sphenoid bone, running from the superior orbital fissure to the petrous temporal bone. They are situated between the pituitary fossa and the sphenoid sinus on the medial side, and the temporal lobe on the lateral side. The cavernous sinuses contain several important structures, including the oculomotor, trochlear, ophthalmic, and maxillary nerves, as well as the internal carotid artery and sympathetic plexus, and the abducens nerve.
The lateral wall components of the cavernous sinuses include the oculomotor, trochlear, ophthalmic, and maxillary nerves, while the contents of the sinus run from medial to lateral and include the internal carotid artery and sympathetic plexus, and the abducens nerve. The blood supply to the cavernous sinuses comes from the ophthalmic vein, superficial cortical veins, and basilar plexus of veins posteriorly. The cavernous sinuses drain into the internal jugular vein via the superior and inferior petrosal sinuses.
In summary, the cavernous sinuses are important structures located on the sphenoid bone that contain several vital nerves and blood vessels. Understanding their location and contents is crucial for medical professionals in diagnosing and treating various conditions that may affect these structures.
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This question is part of the following fields:
- Neurological System
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Question 9
Incorrect
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A 26-year-old female patient is being evaluated by her GP a couple of weeks after recuperating from an incident. Although most of her injuries have healed, she still cannot utilize the muscles of mastication on the left side of her face. Which cranial nerve is likely to be accountable for this?
Your Answer:
Correct Answer: Left trigeminal motor nerve (CN V)
Explanation:Cranial nerves are a set of 12 nerves that emerge from the brain and control various functions of the head and neck. Each nerve has a specific function, such as smell, sight, eye movement, facial sensation, and tongue movement. Some nerves are sensory, some are motor, and some are both. A useful mnemonic to remember the order of the nerves is Some Say Marry Money But My Brother Says Big Brains Matter Most, with S representing sensory, M representing motor, and B representing both.
In addition to their specific functions, cranial nerves also play a role in various reflexes. These reflexes involve an afferent limb, which carries sensory information to the brain, and an efferent limb, which carries motor information from the brain to the muscles. Examples of cranial nerve reflexes include the corneal reflex, jaw jerk, gag reflex, carotid sinus reflex, pupillary light reflex, and lacrimation reflex. Understanding the functions and reflexes of the cranial nerves is important in diagnosing and treating neurological disorders.
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This question is part of the following fields:
- Neurological System
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Question 10
Incorrect
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A 25-year-old man is having an inguinal hernia repair done with local anaesthesia. During the surgery, the surgeon comes across a bleeding site and uses diathermy to manage it. After a minute or so, the patient reports feeling a burning pain from the heat at the surgical site. Which type of nerve fibers are responsible for transmitting this signal?
Your Answer:
Correct Answer: C fibres
Explanation:Mechanothermal stimuli are transmitted slowly through C fibres, while A α fibres transmit motor proprioception information, A β fibres transmit touch and pressure information, and B fibres are responsible for autonomic functions.
Neurons and Synaptic Signalling
Neurons are the building blocks of the nervous system and are made up of dendrites, a cell body, and axons. They can be classified by their anatomical structure, axon width, and function. Neurons communicate with each other at synapses, which consist of a presynaptic membrane, synaptic gap, and postsynaptic membrane. Neurotransmitters are small chemical messengers that diffuse across the synaptic gap and activate receptors on the postsynaptic membrane. Different neurotransmitters have different effects, with some causing excitation and others causing inhibition. The deactivation of neurotransmitters varies, with some being degraded by enzymes and others being reuptaken by cells. Understanding the mechanisms of neuronal communication is crucial for understanding the functioning of the nervous system.
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This question is part of the following fields:
- Neurological System
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