KICK THE BOARDS USMLE STEP 1NEUROANATOMY Prepared by Dr. Irfan Mir KICK THE BOARDS USMLE STEP 1 NEUROLOGY Prepared by Dr. IRFAN MIR1 NEUROLOGY BRAIN -- Cerebrum ----------------------------------------Telencephalon ---------------------- Cerebral cortex Cerebellum ---------------- Cerebellar cortexDiencephalons -- ThalamusSubcortical WM Brain stem ---- Mid brainCerebellar nucleiHypothalamus Commissures PonsEpithalamus Basal ganglia Medulla oblongata Subthalamus * Ectoderm of embryonic disc form Neural plate which folds and become Neural tube, where group of cellsmigrate to form Neural crest . (middle of the neural tube close first and ends close later). * CNS derived from Neural tube where as PNS derived from Neural crest cells. * Alar plate give rise to sensory neuronwhere asBasal plate give rise to motor neuron in CNS. * Nissl substance found in neuronal cell body (not in axon or hillock) consist of polysomes & Endoplasmic reticulum Protein syn. * Adenohypophysis also called Rathke's pouch (derived from ectoderm diverticulum of primitive mouth cavity) , its remnant give rise to Craniopharyngiomawhereas Neurohypophysis develop from neuro ectoderm of the neuraltube. * In newborn spinal cord (conus medullaris) ends at L3 vertebrae where as in adults it ends at its resting level of L1. * The receptive part of the neuron is Dendrite where as conducting part is Axon. * Microglia are microphages where as Macroglia are Astrocytes & Oligodendrocytes which have capacity to regenerate in CNS. * Single Oligodendrocyte myelinate many axons in CNS, it predominate in WM & are capable of regeneration,where as single Schwann cells myelinate single axon in peripheral nervous sys and is also capable ofregeneration. * Astrocyte provide structural support to CNS tissue & participate in reuptake of NT, regulate electrolyte balance &repair it may cause glial scaring due to chronic repair.* Small gaps in myelin where axons exposed to ECF is called Node of Ranvier (| in Na+channels). * Myelin has high electrical resistance and low capacitance and act as insulator. (remember smallest axons are 4unmyelinated) * In myelinated axon current jumps from node to node (fast) term Saltatory. ( because Myelin part of axon doesnot contain Na+ channels ). * The pathways ascend, descend, and decussate (cross).* Gray matter consist of neuronal bodies whereas Laminas are nerve cells present only in Gray matter of spinalcord.* White matter is composed of myelinated & unmyelinated nerve fiber (tracts). * Fasciculi is the pathway b/w group of neuron in CNSvs. Funiculi is pathway in spinal cord also called columns. * Horizontal neuronal connection are called Commissures. * Efferent are involve in motor function where as Afferent are involve in sensory function. * Ventral is Anterior whereas Dorsal is posterior. * Rostral is forward (nose side) and Caudal is tail. * Medial is toward middle where as Median is midplane (midsagital). * Failure of Neural tube to close at Cranial end (Ant neuropore) results into Anencephaly where as failure of Neuraltube to close at Caudal end (post neuropore) results into Spinabifida. (Spinabifida occulta is mild form in whichtuft of hair often seen. when meninges comes out of the sac it called Meningiocele or Spinabifida cystica.If saccontain brain tissuecalled Myelomeningiocele . Its most severe form is Rachischisis in which neural tissue is visibleexternally). * IfMeningiomyelocele is high in the vertebral column, the clinical picture may resembles complete orincomplete transection of the cord or symptoms of combined root and cord defect may resemble Syringomylia.The Tx is surgical closure. Some time Hydrocephalus occur after surgery specially if defect is large. * Alpha feto protein (AFP) in amniotic fluid indicates Down $where as AFP level indicates Anencephaly. ------------------------------------------------------------------------ KICK THE BOARDS USMLE STEP 1 NEUROLOGY Prepared by Dr. IRFAN MIR2 * Hypoglycemia depress brain metabolism confusion, marked sweating, hunger, convulsion or coma. (repeatedbouts of hypoglycemia may results in permanent brain damage).* Resting potential of neuronal cell membrane is - 70mV. * Guillian Barre $ is acute demyelinating dis of neuron usually in periphery marked + in conduction velocity (90%complete recovery occur). where asMultiple Sclerosis is demyelinating dis of CNS functional recovery occur dueto | in Na+ channel in the region which is formerly covered by myelin. ( Remember Na+channels are normallypresent only at Node of Ranvier in myelinated axon ). * Phosphorylation of protein called Synapsins cross link the hormones containing vesicle to cytoskeleton thusimmobilize it. This immobilization permit fusion of vesicle in presynaptic mem results into neurotransmitter relase. ------------------------------------------------------------------------ NEUROTRANSMITTERS : 1. Ach present in Caudate Nuc, Putamen, Basal Nuc of Meynert, Portion of Limbic Sys, Motor Nuclei of Cranial nerve, Autonomicganglia and neuromuscular junction. 2. nor EN present in Locus ceruleus and Lateral Tagamentum. 3. Dopamine present in Hypothalamus, midbrain and Negro straital sys. It is inhibitory and use cAMP mech.4. Serotinin present in Pineal gland, Nucleus Raphe Magnus in Pons, and Parasympathetic neuron in guts. 5. GABA present in Cerebral cortex, Cerebellum, Hippocampus, & straitonegral sys. It is inhibitory & use IP3 - DAGmechanism. 6. Glutamic acid present in Cerebral Cortex, Cerebellum, Hippocampus, brainstem and Spinal cord. 7. Glycine present in spinal cord. It is inhibitory NT. 8. Substance P is a neurotransmitter use by pain fibers. 9. Endorphin, Enkephalin binds opiate receptor to kill pain. Glutamic acid decarboxylase form GABA from L- Glutamic acid in CNS and Retina.Baclofen is GABABreceptor agonist. ------------------------------------------------------------------------ * Myotonia -- In which Na+ channel fail to close after single stimulus Inappropriate sustained muscle contraction. * Myasthenia Gravis -- Ab against postsynaptic ACh receptors. Edrophonium (Anticholinesterase) use for Dx. * Myasthenic $ (Eaton Lambert $): Ab against presynaptic Ca++ channels occur with resultant interference of AChrelease. (Myasthenic $ is paraneoplastic disorder often seen in context ofsystemic neoplasm sp those of lung and breast). * Pineal Gland Tumor can compress Cerebral AqueductHydrocephalus. (other signs are vertical gaze palsy, loss of pupillary reflex) * Hypothalamic LesionEndocrine abnormalities, Optic tract compression, sensory and motor dysfunction. * Subcortical WM abnormality (Leukodystrophy) is common in infant and children than adult. * Subcortical Gray Matter abnormality ( Basal Ganglia )Variety of movement disorder eg. Parkinson and Huntington dis. * Cerebral Cortex LesionAphasia (impairment of language), Hemi inattention or Neglect $, Gerstmann $,Seizures. * Lesion in Grey Matter interfere with function of neuronal body or synapse produce -ve and +ve manifestation where as Lesion in White Matter interfere with axonal conduction results into Disconnecting $ &-ve manifestation. * Negative manifestation shows loss of function where as positive manifestation results from inappropriateexcitation.* Wallen Berg $ results from infarction of lateral medulla due to occlusion of Posterior inferior cerebellar artery Loss of pain & temp over ipsilateral face, & contralateral torso & body. Ataxia, Ptosis, Miosis, Vertigo, Hoarseness,nauzea, & dysphasia also occur. * Multiple sclerosis is common b/w age 20 - 45 yrs and it is rarely present in elderly.* Carcinoma of prostate and breast commonly metastasize to vertebral column. * The C1 lack Dorsal root and vertebral disc. * The Nerve Root exit above the corresponding vertebral body till C7 than below than corresponding vertebralKICK THE BOARDS USMLE STEP 1 NEUROLOGY Prepared by Dr. IRFAN MIR3 body. The ventral and the dorsal root converge to become a spinal nerve on each side at each segment. * Ventral Root carries Efferent o and motoneuron to muscle. * Dorsal Root carries Afferent (except C1) & it is sensory in function , some visceral afferent enter the cord throughventral root. * Ventral Root carries -- o Motoneuron to extrafusal straited muscle and motoneuron to intrafusal spindle muscle, Few small diameter afferent that arise in Dorsal root from thoracic and abdominal visceraalso end up in ventral root.* Dorsal Root Carries -- efferent fibers Except C1. Ia comes from muscle spindle & participate in spinal reflexes. A beta come from mechano receptors of skin and joint. C unmyelinated and A deltamyelinated convey pain and temp. * o motoneuron, motoneuron, B, C are Efferent (motor). (B are preganglionic autonomic fiber and C are post ganglionic autonomic fiber) * Ia, Ib, A beta, Delta and IV (C) are Efferent (sensory). (Ib use in spinal reflexes, comes from Golgi tendon organ) * Reflex is subconscious stimuliresponse mechanism. * o Motoneuron responsible for muscle contraction by extrafusal muscle fiber, where as motoneuron maintain postural muscle tone by intrafusal fibers. * Renshaw cells are interneuron project inhibitory stimulus to o motoneuron to prevent its over activity. * Golgi tendon organ are stretch receptors activates by stretching or contraction of muscles. These have Ibafferent fiber from tendon organ. It ends on interneuron and mediate inverse stretch reflex which prevent overactivity of o motoneuron.* Flexor Reflex represent withdrawal mechanism that removes extremity from harmful stimulus. * Cutting o motoneuron fiber results into flaccidity or little tone. * Transection of spinal cord in chronic phase results into hyperactivity of stretch reflex below the level of lesion andcause spasticity due to loss of descending modulatory influence. The spasticity can be treated by Baclofen(GABAB agonist). ---------------------------------------------------------------------- * Visceral Efferent fibers ----------------- Sympathetic -------------- T1 to T12 and L1 to L2. Parasympathetic --------- CN III, VII, IX, X and S2 to S4. * Dermotomes are sensory (distributing) component of spinal cord. ( Remember C1 have no vertebral disc, ganglia or dermotome). C5 to T1 ---------- is confined to arm. T4 ------------------- to nipple. T10 ----------------- to umbilicus. * Myotomes are axonal innervations of skeletal muscle. ---------------------------------------------------------------------- * Dorsal Column System is sensory system consist of 2nd order neuron. * Dorsal Column System -- Fibers ascend ipsilateral spinal cord & Decussate in medulla sense fine touch,proprioception & two point discrimination. Fibers Decussate when enter in spinal cord and ascend contralaterally -- it sense pain, temp and crude touch. * Upper motor neuron lesion -- Spastic paralysis (paresis), little or no muscular atrophy, hyperactive deep tendon reflex, Extensor planter reflex (Babinski sign). Typically find in strokes. * Lower motor neuron lesion -- Flaccid paralysis, muscle atrophy, diminish or absent deep tendon reflexes,fasiculation, and fibrillation present. * UMN signs are common in stroke, tumor and infections. * Dorsal root ganglia exceptionally lie with in the sacrum. * Meningiomas and Neurofibromas are often located in the intradural extramedullary component. * Ant spinal artery arise from vertebral artery and it becomes ant medial spinal artery below T4. Redicular arterysupplies T1 - L1 some of them (not all) arise from intercostal arteries from aorta. * Posterolateral spinal artery also arise from vertebral artery. KICK THE BOARDS USMLE STEP 1 NEUROLOGY Prepared by Dr. IRFAN MIR4 * Posterior spinal artery and sulcal artery supplies T1 - L1. ( post spinal artery to dorsal column and sulcal artery toventral and lateral column) * Thoracic Kyphosis (Dowager's Hump) become severe in old age. * Lumbar puncture is contraindicated in | IC pressure, tumor ( brain herniation), epidural abscess. * Manometric Pressure of spinal cord is normally 70 - 200 mmHg (average 125 mmHg). * During Lumbar puncture if pressure is normal initially than falls after 7 - 10 mL of drawing CSF indicateSubarachinoid blockade above the puncture site. * After Lumbar puncture complications are severe headache relieved by lying down, infection, Epiduralhematoma, Uncal herniation and Cerebellar tonsil prolapse. * Spinal shock results from acute transection or severe injury to spinal cord or from sudden loss of stimulation fromhigher center due to over dose of spinal anesthesia. It is usually transient and may disappear in 3 - 6 weeksfollowed by period of | reflex response. * Reticular formation of the brain stem tegmentum is vitally important because it control respiration, cardiovascularsystem, state of consciousness, sleep and alertness. ----------------------------------------------------------------------- DESCENDING TRACT(VENTRAL COLUMN TRACT) : Associated with motor function (efferent) & comprise of 6 major tracts. 1. Corticospinal Tract :Arise from motor and premotor cortex (area 4 & 6). It is involve in fine motor function. * >85% of axon decussate in medulla and descend through lateral corticospinal tract. * 10 % descend down through Ant corticospinal tract & decussate in spinal cord (do notdecussate in medulla). *