UWorld Step 1 Flashcards
Blood brain barrier
Formed by tight junctions between nonfenestrated capillary endothelial cells that prevent the paracellular passage of fluid and solutes. This barrier only permits passage of substances from the blood to the brain via trans cellular movement across the endothelial plasma membrane, which is limited by diffusion or carrier-mediated transport.
Radial nerve injury - supinator canal
Injury to the radial nerve during its passage through the supinator canal may occur due to repetitive pronation/supination of the forearm, direct trauma, or subluxation of the radius. Patients typically have weakness during finger and thumb extension (“finger drop”) without wrist drop or sensory deficits.
Common peroneal nerve injury
Trauma/sustained pressure to the neck of the fibula can injure the common peroneal nerve, causing weakness on foot dorsiflexion (“foot drop”) and eversion, as well as toe extension, and impaired sensation over the lateral shin and dorsal foot, and between the first and second toes.
Femoral nerve block
A femoral nerve block at the inguinal crease will anesthetize the skin and muscles of the anterior thigh (eg, quadriceps), femur, and knee.
Down syndrome Alzheimer risk
Patients with trisomy 21 (Down syndrome) have 3 copies of the amyloid precursor protein gene located on chromosome 21. This increases amyloid-beta accumulation in the brain, placing these patients at high risk for developing early-onset Alzheimer disease
Iliohypogastric nerve injury - s/p appendectomy
The iliohypogastric nerve provides sensation to the suprapubic and gluteal regions and motor function to the anterolateral abdominal wall muscles. Abdominal surgery (eg, appendectomy) can damage the nerve and cause decreased sensation and/or burning pain at the suprapubic region.
Complete contralateral sensory loss
The ventral posterior lateral nucleus (receives input from the spinothalamic tract and dorsal columns) and ventral posterior medial nucleus (receives input from the trigeminal pathway) of the thalamus send somatosensory projections to the cortex via thalamocortical fibers. Damage to these nuclei results in complete contralateral sensory loss.
Lacunar infarcts
Lacunar infarctions are small ischemic infarcts (<15 mm in diameter) and are usually the result of small vessel occlusion (eg, due to lipohyalinosis, microatheroma formation, and hardening/thickening of the vessel wall - hypertensive arteriolar sclerosis) in the penetrating vessels supplying the deep brain structures (eg, basal ganglia, pons) and subcortical white matter (eg, internal capsule, corona radiata). Uncontrolled hypertension and diabetes mellitus are major risk factors for this condition.
Focal seizure - postcentral gyrus
The primary somatosensory cortex (postcentral gyrus) is responsible for processing all somatic sensory modalities (eg, touch, temperature/pain, vibration/proprioception) of the contralateral body. A partial (focal) seizure originating in this cortical region can result in contralateral sensory disturbance (eg, numbness, paresthesias).
Elevated levels of AFP and AChE on amniocentesis
Neural tube defects most often occur when the neural folds fail to fuse in the region of the anterior or posterior neuropores. Persistent communication between the spinal canal and the amniotic cavity allows leakage of alpha-feroprotein (AFP) and acetylcholinesterase (AChE) into the amniotic fluid, leading to elevated levels of AFP and AChE that can be detected on amniocentesis.
Changes in membrane potential
Occur in response to changes in the neuronal membrane permeability to various cellular ions. The more permeable the membrane becomes for a cellular ion, the more that ion’s equilibrium potential contributes to total membrane potential.
ACA occlusion
The anterior cerebral arteries supply the medial portions of the 2 hemispheres (frontal and parietal lobes). Occlusion can cause contralateral motor and sensory deficits of the lower extremities, behavioral changes, and urinary incontinence.
Huntington disease - histone acetylation
Hypo-acetylated histones bind tightly to DNA and prevent transcription of genes in their associated regions. Alteration of gene expression in Huntington disease occurs in part due to deacetylation of histones. This prevents the transcription of certain genes that code for neurotrophic factors, contributing to neuronal cell death.
Meyer’s loop - injury
Injury to Meyer’s loop in the temporal lobe results in contralateral superior quadrantanopia.
Acute nausea s/p chemo
Acute nausea following administration of systemic chemotherapy results from stimulation of the chemoreceptor trigger zone (CTZ), which lies in the area postrema of the dorsal medulla near the fourth ventricle.
Neuron action potential - K+ ion permeability
The action potential results from changes in the membrane permeability to K+ and Na+ ions. Depolarizations results from massive influx of Na+ through voltage-gated Na+ channels. Repolarization occurs due to closure of voltage-gated Na+ channels and opening of voltage-gated K+ channels. K+ ion permeable is highest during the repolarization phase of the action potential.
Broca aphasia
Broca (motor, nonfluent) aphasia results from damage to the inferior frontal gyrus of the dominant hemisphere. Patients are often frustrated as they understand language but cannot properly formulate the motor commands to write or form words (eg, slow, fragmented speech). Aphasia may be associated with right upper limb and face weakness due to extension of the lesion into the primary motor cortex.
PICA occlusion
Posterior inferior cerebellar artery occlusion causes lateral medullary (Wallenberg) syndrome, characterized by vertigo/nystagmus, ipsilateral cerebellar signs, loss of pain/temperature sensation in the ipsilateral face and contralateral body, bulbar weakness, and ipsilateral Horner syndrome. This condition can occur in the setting of cervical spine trauma with dissection of the vertebral artery.
CN IV palsy
The trochlear nerve innervates the superior oblique muscle, which causes the eye to intort (internally rotate) and depress with adducted. Trochlear nerve palsy is typically traumatic or idiopathic and presents with vertical diplopia that worsens when the affected eye looks down and toward the nose (eg, walking downstairs, up-close reading). Patients may compensate by tucking the chin and tilting the head away from the affected eye.
Sciatic - S1 clinical presentation
Sciatica is a nonspecific term for low back pain that radiates down the leg due to compression of the lumbosacral nerve roots (eg, from vertebral disc herniation). The S1 nerve root is commonly involved, resulting in pain/sensory loss down the posterior thigh and calf to the lateral aspect of the foot. Patients may also have weakness on thigh extension, knee flexion, and foot plantarflexion with an absent ankle jerk reflex.
Kinesin
Kinesin is a microtubule-associated, ATP-powered motor protein that facilitates the anterograde transport of neurotransmitter-containing secretory vesicles down axons to synaptic terminals.
Spontaneous deep intracerebral hemorrhage
Spontaneous deep intracerebral hemorrhage is typically caused by hypertensive vasculopathy involving the penetrating branches of the major cerebral arteries. The most frequently affected locations include the basal ganglia (putamen), cerebellar nuclei, thalamus, and pons. The basal ganglia are supplied by the lenticulostriate arteries, which are small vessel branches off the middle cerebral artery.
“Red ragged” muscle fibers
“Red ragged” muscle fibers are seen in mitochondrial diseases. Muscle fibers have this appearance because abnormal mitochondria accumulate under the sarcolemma. Mitochondrial diseases show maternal inheritance.
Musculocutaneous nerve
The musculocutaneous nerve innervates the major forearm flexors (eg, biceps brachii, brachialis) and coracobrachialis (flexes and adducts the arm) and provides sensory innervation to the lateral forearm. It is derived from the upper trunk of the brachial plexus (C5-C7) and can be injured by trauma or strenuous upper extremity exercise.
Hydrocephalus - infant
Hydrocephalus in infants presents with macrocephaly and poor feeding. Imaging studies showing enlarged ventricles are characteristic. Untreated hydrocephalus leads to spasticity due to stretching of the periventricular pyramidal tracks, development delays, and seizures.
Alzheimer disease - ACh
Alzheimer disease is characterized by decreased levels of acetylcholine in the nucleus basalis of Meynert and the hippocampus, caused by diminished activity of choline acetyltransferase.
Acoustic neuromas
Acoustic neuromas are Schwann cell-derived tumors that typically arise from the vestibular portion of the vestibulocochlear nerve and are commonly located at the cerebellopontine angle (between the cerebellum and lateral pons). Patients usually present with unilateral sensorineural hearing loss and tinnitus.
Disrupted first and second pharyngeal arches
The development of derivatives of the first (eg, trigeminal nerve, mandible, maxilla, zygoma, incus, malleus) and second (eg, facial nerve, stapes, styloid process, lesser horn of hyoid) pharyngeal arches can by disrupted in genetic disorders (eg, Treacher-Collins syndrome), resulting in hypoplasia of the mandibular and zygomatic bones.
Interscalene nerve block
Interscalene nerve block anesthetizes the brachial plexus as it passes through the scalene triangle. It is used to provide anesthesia for the shoulder and upper arm. Nearly all patients develop transient ipsilateral diaphragmatic paralysis due to involvement of the phrenic nerve roots as they pass through the interscalene sheath.
Internuclear ophthalmoplegia
Internuclear ophthalmoplegia is a disorder of conjugate horizontal gaze in which the affected eye (ipsilateral to the lesion) is unable to adduction and the contralateral eye abducts with nystagmus. Convergence and the pupillary light reflex are preserved. This typically occurs with damage to the medial longitudinal fasciculus.
ICA aneurysm
An aneurysm of the internal carotid artery can laterally impinge on the optic chiasm. This can cause ipsilateral nasal hemianopia by damaging uncrossed optic fibers from the temporal portion of the retina.
NF-1
Neurofibromatosis type I (von Recklinghausen disease) is a single-gene autosomal dominant disorder caused by mutations in the NF1 tumor suppressor gene located on chromosome 17. Patients characteristically develop numerous cutaneous neurofibromas comprised mostly of Schwann cells, which are embryologically derived from the neural crest. Other common symptoms include café-au-lait spots and Lisch nodules.
Fragile X syndrome
Fragile X syndrome, an X-linked disorder, is the most common cause of inherited intellectual disability. The pathogenesis involves an unstable expansion of trinucleotide repeats (CGG) in the fragile X retardation 1 (FMR1) gene. Key physical findings include dysmorphic facial features (eg, large jaw, protruding ears, long face) and macroorchidism.
3-5 days after ischemic brain infarct
Microfilm move to the area of ischemic infarct approximately 3-5 days after the onset of ischemia and phagocytize the fragments of neurons, myelin, and necrotic debris. A cystic space replaces the necrosis, and astrocytes form a glial scar along the periphery.
Drug binding and activating GABA-A receptors
A drug that binds to activate GABA-A receptors (or enhances their activity) will increase the conductance of chloride ions, leading to increased passive transport of chloride into the cell interior. This causes the membrane potential to become hyperpolarized (more negative than the resting membrane potential) by approaching or reaching the equilibrium potential for chloride.
Schwannomas
Schwannomas present histologically with a biphasic pattern of cellularity (Antoni A and B areas) and S-100 positivity (indicating neural crest origin). Schwannomas can arise from the peripheral nerves, nerve roots, and cranial nerves (except CN II). Acoustic neuromas are the most common type of intracranial schwannoma and are located at the cerebellopontine angle at CN VIII.
ALS
Amyotrophic lateral sclerosis (ALS) causes both upper and lower motor neuron lesions. Loss of neurons of the anterior horns of the spinal cord (LMN lesion) causes muscle weakness and atrophy. Demyelination of the lateral corticospinal tract (UMN lesion) leads to spasticity and hyperreflexia.
Parkinson disease - high-frequency deep brain stimulation
Nigrostriatal degeneration in Parkinson disease reduces activity of the thalamus and its projections to the cortex, resulting in bradykinesia and rigidity. Patients with medically intractable symptoms of Parkinson disease may benefit from high-frequency deep brain stimulation of the globus pallidus internus or subthalamic nucleus as it promotes thalamo-cortical disinhibition with improved mobility
Direct and consensual pupillary light reflex
The upper midbrain contains neural structures (eg, optic nerve, pretectal nuclei, Edinger-Westphal nuclei, oculomotor nerve) that mediate the direct and consensual pupillary light reflex.
Wallerian degeneration
Wallerian degeneration refers to the process of axonal degeneration and breakdown of the myelin sheath that occurs distal to the site of injury. Axonal regeneration does not occur in the central nervous system due to the persistence of myelin debris, secretion of neuronal inhibitory factors, and development of dense glial scarring.
Uncal herniation
Transtentorial (i.e., uncal) herniation is a complication of an ipsilateral mass lesion, such as a hemorrhage or brain tumor. The first sign of uncal herniation is a fixed and dilated pupil on the side of the lesion. Ipsilateral paralysis of oculomotor muscles (compressed as it exits the midbrain, resulting in oculomotor nerve pays with fixed dilated pupil - due to preganglionic parasympathetic fiber damage), contralateral or ipsilateral hemiparesis, and contralateral homonymous hemianopsia with macular sparing may also occur.
Ectoderm adult derivatives
All adult cells and tissues can be traced back to the 3 primary germ layers (ectoderm, mesoderm, and endoderm). The ectoderm gives rise to the surface ectoderm, neural tube, and neural crest.
Tetanospasmin
Tetanospasmin is a neuro-exotoxin released by Clostridium tetani. The toxin blocks the release of glycine and gamma-aminobutyric acid (GABA) from the spinal inhibitory interneurons that regulate the lower motor neurons. These disinhibited motor neurons cause increased activation of muscles, leading to spasms and hyperreflexia.
Normal-pressure hydrocephalus
Normal-pressure hydrocephalus is the result of decreased cerebrospinal fluid (CSF) resorption by the arachnoid granulation. The classic triad of symptoms consists of progressive gait difficulties, cognitive disturbances, and urinary incontinence. Brain imaging reveals ventricular enlargement that is out of proportion to sulci enlargement.
Optic tract lesion
A lesion in the optic tract can produce contralateral homonymous hemianopia and a relative afferent pupillary defect (Marcus Gunn pupil) in the pupil contralateral to the tract lesion.
Cystic tumor in cerebellum - child
A cystic tumor in the cerebellum of a child is most likely pilocytic astrocytoma. Biopsy will show a well-differentiated neoplasm comprised of spindle cells with hair-like glial processes that are associated with microcysts. These cells are mixed with Rosenthal fibers and granular eosinophilic bodies.
Epidural hematoma
Epidural hematoma occurs due to tear of the middle meningeal artery. It is often associated with temporal bone fracture and is located between the bone and dura mater. Clinical presentation is characterized by a “lucid interval”, followed by loss of consciousness.
Herpes encephalitis - CSF
Viral infections of the central nervous system are usually characterized by elevated protein, normal glucose, and an elevated white blood cell count with a lymphocytic predominance. Patients with herpes encephalitis also usually have elevated erythrocytes in the cerebrospinal fluid due to hemorrhagic inflammation of the temporal lobes.
Muscarinic receptor activation
Activation of muscarinic receptors by acetylcholine or cholinergic agonist results in peripheral vasodilation due to synthesis of nitric oxide in endothelial cells, which leads to vascular smooth muscle relaxation (eg, hypotension). Muscarinic receptor activation in other sites causes smooth muscle contraction.
Wilson disease
Wilson disease (hepatolenticular degeneration) is an autosomal recessive condition of excess copper leading to toxic accumulation in the liver, basal ganglia, and cornea. Chelation therapy with D-penicillamine is indicated to remove excess loosely bound serum copper.
Tetanus
Tetanus is a clinical diagnosis that should be suspected in patients who have characteristic symptoms (eg, lockjaw, muscle pain/spasms, difficulty swallowing), particularly if they are unlikely to be adequately vaccinated or have an antecedent cutaneous injury.
Alzheimer disease
Alzheimer dementia typically presents insidiously with memory loss (especially of recent events), executive dysfunction, and visuospatial impairment. Classic histopathologic findings include amyloid plaques (central amyloid beta core surrounded by dystrophic neurites) and neurofibrillary tangles (aggregated of hyperphosphorylated tau protein).
Light reflex pathway - optic nerve damage
The afferent limb of the light reflex pathway is the optic nerve; the efferent limb is the parasympathetic fibers of the oculomotor nerve. Where an optic nerve is damaged, light in that eye will cause neither pupil to constrict (the nerve can’t see the light). However, light in the contralateral eye will cause both pupils to constrict (because the motor pathways are intact).
Thiamine deficiency
Thiamine (i.e., vitamin B1) deficiency acutely leads to Wernicke encephalopathy and chronically leads to Korsakoff psychosis. The neural structure most frequently affect in patients with Wernicke encephalopathy is the mammillary body, which is part of the Papez circuit. Alcoholic or malnourished patients should receive intravenous thiamine supplementation before intravenous dextrose administration because giving dextrose without prior thiamine can precipitate a Wernicke encephalopathy.
Speed of conduction down an axon
The speed of conduction down an axon depends on 2 constants: the length constant and the time constant (ie, velocity = length/time). Myelination increases the length constant and decreases the time constant, both of which improve axonal conduction speed. Demyelination thus impairs stimulus transmission.
Opsoclonus-myoclonus
Opsoclonus-myoclonus is a paraneoplastic syndrome associated with neuroblastoma, the most common extracranial solid neoplasm in children. The tumor typically arises from the neural crest cells of the adrenal medulla and presents with an abdominal mass and elevated catecholamine breakdown products.
Cerebellar hemisphere lesion
The cerebellar hemispheres are responsible for motor planning and coordination of the ipsilateral extremities via their connections with the lateral descending motor systems. Consequently, cerebellar hemispheres lesions typically result in ipsilateral dysdiadochokinesia, limb dysmetria, and intention tremor.
Neonatal intraventricular hemorrhage
Neonatal intraventricular hemorrhage usually occurs in the fragile germinal matrix and increases in frequency with decreasing age and birth weight. It is a common complication of prematurity that can lead to long-term neurodevelopmental impairment.
Neuroleptic malignant syndrome
Neuroleptic malignant syndrome is a life-threatening adverse reaction to antipsychotic medications characterized by diffuse muscle rigidity, hyperthermia, autonomic instability, and altered sensorium. The antipsychotic should be stopped and supportive care provided, and dantrolene can be used to reduce muscle rigidity.
CN III injury - aneurysm
The oculomotor nerve (CN III) courses between the posterior cerebral and superior cerebellar arteries as it exits the midbrain in the interpeduncular space and is particularly susceptible to injury from ipsilateral posterior communicating artery aneurysms. Aneurysmal compression of CN III produces mydriasis (due to superficial parasympathetic fiber damage) with diplopia, ptosis, and “down and out” deviation of the ipsilateral eye (due to somatic efferent fiber injury).
Status epilepticus - Tx
Intravenous benzodiazepines (eg, lorazepam) are the initial drug of choice for status epilepticus. They work by enhancing the effect of gamma-aminobutyric acid (GABA) at the GABA-A receptor, leading to increased chloride influx and suppression of action potential firing.
Obturator nerve injury
The obturator nerve is the only major nerve that exits the pelvis through the obturator foramen. Nerve injury typically results from compression (eg, due to pelvic trauma, surgery, or tumor) and presents with weakness on thigh adduction and sensory loss over the distal medial thigh.
Malignant tumor parotid gland - nerve compression
The facial nerve (CN VII) exits the stylomastoid foramen and courses through the substance of the parotid gland, where it divides into its 5 terminal branches that innervate the muscles of facial expression. Malignant tumors of the parotid gland often compress and disrupt the facial nerve and its branches, causing ipsilateral face droop.
