USMLE STEP 1 NEUROLOGY Questions and Answers with Complete Solutions 2024

USMLE STEP 1 NEURO LOGY Questions and Answers with Complete Solutions 2024 The notochord induces what to differentiate into what? - ANS✓✓Induces overlying ECTODERM to differentiate into NEUROECTODERM and form NUERAL PLATE Neural plate then gives rise to? - ANS✓✓Neural tube and neural crest cells Notochord becomes what? - ANS✓✓Nucleus pulposus of the intervertebral disks in adults Alar Plate - ANS✓✓Dorsal [Sensory] Same orientation as spinal cord Basal Plate - ANS✓✓Ventral [Motor] Same orientation as the spinal cord How does FGF affect chordin and noggin? - ANS✓✓FGF regulates chordin and noggin to down regulate BMP which leads to neural plate induction Three Primary Vesicles - ANS✓✓1. Forebrain [Prosencephalon] 2. Midbrain [Mesencephalon] 3. Hindbrain [Rhombencphaln] The Forebrain gives rise to: - ANS✓✓1. Telencephalon [Cerebral hemispheres, lateral ventricles] 2. Diencephalon [Thalamus, Third Ventricle] The Midbrain gives rise to: - ANS✓✓1. Mesencephalon [Midbrain, aqueduct] The Hindbrain gives rise to: - ANS✓✓1. Metencephalon [Pons, cerebellum, upper part of the fourth ventricle] 2. Myelencephalon [Medulla, Lower part of the fourth ventricle] CNS/PNS Origins - ANS✓✓Neuroectoderm = CNS neurons, ependymal cell [Inner lining of ventricles, makes CSF], oligodendrocytes, astrocytes Neural crest cells = PNS, schwann cells Mesoderm = Microglia [Like Macrophages, originate from Mesoderm] Neural tube defects - ANS✓✓NEUROPORES fail to fuse [4th week] → Persistent connection between amniotic cavity and spinal canal Associated with: 1. Low folate levels before conception and during pregnancy 2. ↑ a -fetoprotein levels [AFP] in amniotic and maternal serum 3. ↑ AChE in amniotic fluid [Helpful confirmatory test] -- Fetal AChe in CSF transudates across defect into amniotic fluid Spina bifida occulta - ANS✓✓Failure of bony spinal canal to close, NO STRUCTURAL HERNIATION Usually seen at lower vertebral levels DURA INTACT Associated w/ tuft of hair or skin dimple at level of bony defect NORMAL AFP Meningocele - ANS✓✓Meninges [BUT NO NEURAL TISSUES] herniates through bony defect Meningomyelocele - ANS✓✓Meninges and neural tissue herniate through bony defect Associated w/ Arnold -Chiari Type II Malformation Anencephaly - ANS✓✓Malformation of the ANTERIOR NEURAL TUBE → 1. No forebrain 2. Open calvarium Clinical Findings: 1. ↑ a -fetoprotein levels [AFP] 2. Polyhydramnios [No swallowing center in brain] 3. Associated w/ MATERNAL TYPE I DIABETES 4. Maternal folate supplementation ↓ risk Holoprosencephaly - ANS✓✓Failure of LEFT AND RIGHT HEMISPHERES TO SEPARATE Usually occurs during the 5th and 6th week May be related to mutations in the SONIC HEDGEHOG signaling pathway Moderate form = Cleft lip/palate Severe form = Cyclopia Seen in: 1. PATAU SYNDROME 2. FETAL ALCOHOL SYNDROME Chiari Type II Malformation - ANS✓✓Posterior fossa malformation Significant HERNIATION of the CEREBELLAR TONSILS and VERMIS through FORAMEN MAGNUM with AQUEDUCTAL STENOSIS and HYDROCEPHALUS Patients often present w/: 1. Lumbosacral meningomyelocele 2. Paralysis below the defect Dandy -Walker Malformation - ANS✓✓AGENESIS of CEREBELLAR VERMIS with CYSTIC ENLARGEMENT of the 4th ventricle Fills enlarged posterior fossa Associated w/: 1. Hydrocephalus 2. Spina bifida Syringomyelia - ANS✓✓Cystic cavity [Syrinx] within SPINAL CORD If central canal = Hydromyelia Crossing anterior spinal commissural fibers are typically damaged CAPE -LIKE BILATERAL LOSS OF PAIN and TEMPERATURE in the UPPER EXTREMITIES Fine touch sensation is preserved Associated w/: 1. Arnold Chiari malformation 2. Trauma 3. Tumor Most common C8 -T1 [CERVICAL ENLARGEMENT] Arnold Chiari Type I Malformation - ANS✓✓CEREBELLAR TONSILLAR ECTOPIA > 3 -5 mm Congenital Usually asymptomatic in childhood Manifests w/ HEADACHE and CEREBELLAR SYMPTOMS Which arches form the anterior 2/3rds of the tongue - ANS✓✓1st and 2nd brachial arches -- Sensation via CN V -- Taste via CN VII Which arches form the posterior 1/3rd of the tongue - ANS✓✓3rd and 4th brachial arches --Sensation and taste via CN IX -- Extreme posterior vagus Motor innervation of the tongue - ANS✓✓CN XII [Hypoglossal nerve] to: 1. Hyoglossus = Retracts and depresses tongue