LOM TBL 1 NEURO PDF

Meninges & Ventricular Choroid plexus (network of capillaries) is the main source of CSF and actively regulates in constituents Hydrocephalus Dilation of one or more parts of the ventricular system and/or subarachnoid space due to the ABNORMAL COLLECTION OF...

Meninges & Ventricular Choroid plexus (network of capillaries) is the main source of CSF and actively regulates in constituents Hydrocephalus Dilation of one or more parts of the ventricular system and/or subarachnoid space due to the ABNORMAL COLLECTION OF CSF Noncommunicating (Obstructive) hydrocephalus - Obstruction of CSF flow within the ventricular system (interventricular foramen, cerebral aqueduct) or from ventricular to subarachnoid space (medial and lateral apertures of 4th v) - This causes an enlargement of ventricles PROXIMAL to the obstruction - The most common cause of the obstruction of the cerebral aqueduct (enlargement of the 3rd ventricle?) - Can there be an obstruction between multiple sites of ventricular system Communicating hydrocephalus - Caused by impaired CSF reabsorption in arachnoid granulations (usually secondary to subarachnoid hemorrhage) or rarely by excess CSF production - (all?)Ventricles and subarachnoid space are dilated Normal pressure hydrocephalus - Seen in elderly - Clinical triad: gait difficulties, urinary incontinence, mental decline (dementia) ***cant walk, cant pee, cant think - CSF pressure is not elevated; unknown mechanism (thought to be communicating w impaired CSF reabsorption) Blood Brain Barrier and Blood-CSF Barrier Large molecules cant pass from blood to extracellular fluid of CNS due to existence of blood brain barrier Components of the BBB - Endothelial cells with tight junctions between then - Astrocytes with perivascular end-feet - Capillary basement membrane **BBB prevents entry of blood-borne foreign substances into the brain tissue, BUT problem when the goal is to deliver drugs into the CNS Large molecules cant pass from blood to CSF either due to the: blood-CSF barrier *pls explain more about the blood-CSF barrier In the choroid plexus, tight junctions do not exist between endothelial cells lining the capillary wall; the capillary endothelium is fenestrated (large molecules can pass from blood through this cap endothelium of choroid plexus) **the blood brain barrier protects most of the blood vessels in the brain but some areas lack BBB (circumventricular organs) that are centered around the ventricles in the brain - Their functions require access into the bloodstream Arterial Supply of the CNS Internal Carotid Begins at bifurcation of common carotid 4 parts: Cervical (origin to base of skull) Petrous (petrous part of temporal bone, with the carotid canal) Cavernous (within cavernous sinus) Cerebral (exit cavernous sinus - become anterior & middle cerebral arteries) Br. of CEREBRAL part of internal carotid artery - Ophthalmic artery - Anterior choroidal artery - Posterior communicating artery - Anterior cerebral artery - Middle cerebral artery Branches of internal carotid (cerebral part) Ophthalmic artery Enters orbit with optic nerve via the optic canal Supplies: orbit, nasal cavity, paranasal sinuses, scalp Anterior choroidal artery Runs posteriorly, inferior to the optic tract Supplies: choroid plexus in inferior horn of lateral ventricle, structures along medial aspect of temporal lobe (uncus, hippocampus, amygdala), tail of caudate, globus pallidus, inferior part of internal capsule, optic tract, lateral portions of thalamus Posterior communicating artery Extends from internal carotid to proximal part of posterior cerebral artery Connects the anterior (carotid) and posterior (vertebro-basilar) circulations Anterior cerebral artery (ACA) Joined by anterior communicating artery A1 segment: Extends from origin of ACA to anterior communicating artery - passes anteriorly and medially above the optic nerve **the cortical branches of ACA supply: Medial surface of cerebral hemisphere (frontal to parietooccipital) **includes parts of primary motor cortex and primary somatosensory cortex **they control movement and receive general sensory info from contralateral L.L Most of corpus callosum Medial part of inferior surface of frontal lobe (inc. olfactory bulb and tract) Distal br supply a strip of cortex on lateral side Middle cerebral artery (MCA) Larger terminal branch of the internal carotid artery Runs laterally, goes into lateral sulcus towards insula where it divides into superior and inferior trunks M1 segment: Extends from origin of MCA to its bifurcation into superior and inferior trunks Distal to bifurcation, MCA is divided into M2 and M4 segments Cortical branches of MCA supply: Lateral part of inferior surface of frontal lobe Insula Most of lateral surface of cerebral hemisphere, except its peripheral rim (supplied by br of anterior and posterior cerebral arteries) Superior trunk of MCA supplies: Most of primary motor cortex and primary somatosensory cortex → control movements and receive general sensory info from contralateral face and upper limb, motor speech (Broca’s area), frontal eye field (controls conjugate eye movements to opposite side) Inferior trunk of MCA supplies: Primary auditory cortex (transverse temporal gyri) Sensory speech (Wernicke’s area) Vertebral artery O: 1st part of subclavian artery Divided into 4 parts: 1st - Prevertebral : runs superiorly and posteiroly to transverse foramen of C6 2nd - Cervical : ascends through transverse foramina of C6 to C1 3rd - Atlantic : lies in groove of sup. surface of post arch of atlas 4th - Intracranial : pierces atlanto-occipital membrane, dura mater and arachnoid and ascends into cranial cavity (within subarachnoid space) via foramen magnum In posterior cranial fossa, runs superiorly and medially, anterior to rootlets of hypoglossal nerve, and at the medullopontine sulcus joins vertebral artery of opposite side to form basilar artery Br of the 4th part - Posterior inferior cerebellar artery - Posterior spinal artery - Anterior spinal artery Branches of 4th part Posterior inferior cerebellar artery (PICA) Largest br of vertebral artery - curves around medulla to reach inferior cerebellar surface Supplies posterolateral part of medulla, choroid plexus of 4th ventricle and posterior and medial parts of inferior surface of cerebellum Posterior spinal artery Anterior spinal artery Supplies anteromedial part of medulla and anterior ⅔ of spinal cord Arterial supply of Medulla Basilar Artery Runs in basilar sulcus of pons from medullopontine sulcus to pons-midbrain junction, where it terminates by dividing into 2 posterior cerebral arteries Branches - Pontine arteries - Anterior inferior cerebellar artery - Labyrinthine (internal auditory) artery - Superior cerebellar artery - Posterior cerebral artery Pontine arteries Anterior inferior cerebellar artery Supplies anterior and lateral parts of inferior surface of cerebellum, lower part of middle cerebellar peduncle, choroid plexus of 4th ventricle, and send slender twigs to upper medulla and lower pons Labyrinthine artery Enters internal acoustic meatus with cranial nerves VII and VIII to supply internal ear Superior cerebellar artery Passes laterally, just inferior to oculomotor nerve Wraps around brainstem, under tentorium cerebelli to supply superior surface of cerebellum, including most of cerebellar nuclei Its proximal part gives branches to upper pons, upper part of middle cerebellar peduncle, superior cerebellar peduncle, and inferior colliculus of midbrain Arterial Supply of Pons  Posterior cerebral artery (PCA) Passes laterally, just above oculomotor nerve → continues around midbrain and joins medial aspect of temporal lobe Cortical branches of PCA supply: Inferior and medial surfaces of temporal and occipital lobe → this includes primary visual cortex Splenium of corpus callosum Distal branches supply a strip of cortex on lateral surface Cerebral Arterial Circle (of Willis) Consists of larger cerebral vessels and their interconnections on the ventral surface of the brain Components: - Internal carotid artery - Anterior communicating artery - Posterior communicating - Posterior cerebral artery - Anterior cerebral artery **may serve as potential vascular shunt, assisting in development of collateral circulation if one of the proximal vessels is occluded  Perforating (central) branches - Small arteries that originate from the large arteries on the base of the brain to supply deeply located structures of the cerebral hemispheres and diencephalon and pats of the midbrain Groups: - Anteromedial - Anterolateral - Posteromedial - Posterolateral anteromedial O: A1 segment of ACA and anterior communicating artery Supply: optic chiasm and anterior part of hypothalamus anterolateral O: M1 segment of MCA (lenticulostriate arteries) and a few may come from A1 segment of ACA Supply: most of caudate, putamen, globus pallidus, and interal capsule **lenticulostriate arteries are the most common site of intra-cerebral hemorrhage in HTN ppl posteromedial O: posterior communicating artery and P1 segment of posterior cerebral artery Supply: middle and posterior regions of hypothalamus, subthalamus, anterior part of thalamus and medial parts of midbrain posterolateral O: P2 segment of posterior cerebral artery Supply: posterior part of thalamus, choroid plexus of lateral and 3rd ventricles and posterior and lateral midbrain Arterial supply of spinal cord Spinal cord is supplied by 1 anterior and 2 posterior spinal arteries Blood received by spinal arteries from vertebral arteries is sufficient only to supply upper cervical segments of spinal cord Spinal arteries are reinforced at intervals by spinal branches of segmental arteries - Spinal br enter vertebral canal via intervertebral foramina and give off anterior and posterior radicular arteries and anterior and posterior spinal medullary arteries Anterior and posterior radicular arteries supply ventral and dorsal roots of spinal nerves and are present at ALL spinal cord levels Anterior and posterior spinal medullary arteries reinforce anterior and posterior spinal arteries and are NOT present at all spinal cord levels Largest spinal medullary artery (Adamkiewicz) joins anterior spinal artery in upper lumbar region, most frequently on left side → may provide entire arterial supply to lumbosacral spinal cord Branches of anterior spinal artery supply anteior ⅔ of spinal cord → anterior horn, intermediate zone of gray matter, basal part of posterior horn, anterior and lateral funiculi Branches of posterior spinal artery supply posterior ⅓ of spinal cord → posterior horn and posterior funinculus  Somatosensory System 1-17, 23-27 General senses - Touch (discriminative & non-discriminative)*** - Vibration - Proprioception (limb position & motion) - Pain - Temperature Discriminative touch, vibration, and proprioception are carried by: DORSAL COLUMN-MEDIAL LEMNISCUS pathway Non-discriminative touch, pain, and temperature are carried by: ANTEROLATERAL system (spinothalamic tract) LARGE DIAMETER, MYELINATED FIBERS (Aα, A𝛽) form the MEDIAL DIVISION OF DORSAL ROOT - These transmit the discriminative touch, proprioception and vibration - This info carried by: dorsal colum-medial lemniscus system SMALL DIAMETER MYELINATED (Aδ) UNMYELINATED FIBERS (C) form the LATERAL DIVISION OF DORSAL ROOT - These transmit non-discriminative touch, pain, and temperature - This info carried by: anterolateral system (spinothalamic tract)  General Arrangement of the Somatosensory Pathways to the Cerebral Cortex AFFERENT → SENSORY (signals of touch to brain) EFFERENT → MOTOR (signals from brain to react) Consists of 3 neurons 1st order neuron (sensory, unipolar, pseudo-unipolar) Location: sensory ganglion (dorsal root ganglia or spinal nerves, trigeminal ganglion) 2nd order neuron Location: nucleus of spinal cord or brainstem *the axon crosses to opposite side and then ascends to the thalamus 3rd order neuron Location: thalamus (VPL or VPM nuclei) *projects to cerebral cortex which is the primary somatosensory cortex Dorsal Column-Medial Lemniscus Pathway Carries discriminative touch, vibration and proprioception from trunk and limbs *central branches of the 1st order neurons enter the spinal cord via medial division of dorsal roots then divide into short local branch and a long ascending branch - Short local branch: ends in gray matter of spinal cord (reflex connections) - Long ascending branch: ascends in ipsilateral column *Long ascending branches entering dorsal column below midthoracic levels are more medially located and form gracile fasciculus *Long ascending branches entering dorsal column above midthoracic levels are more laterally located and form cuneate fasciculus The ascending fibers of gracile and cuneate fasciculi synapse with 2nd order neurons that are located in gracile and cuneate nuclei (lower medulla) Axons of the 2nd order neurons run anteriorly in lower medulla as internal arcuate fibers, cross midline in sensory decussation, and ascend to thalamus in medial leminscus Axons of 3rd order neurons pass through posterior limb of internal capsule and terminate in primary somatosesory cortex (postcentral gyrus & posterior paracentral lobule - areas 3,1,2 of Brodmann) Whole pathway = somatotopically organzied (info from diff parts of body is carried by diff parts of pathway) Anterolateral System (spinothalamic tract) Carries nondiscriminative touch, pain, and temperature info from trunk and limbs There are: direct & indirect pathways Direct spinothalamic pathway: - Aka: neospinothalamic pathway - Carries FAST pain (SHARP,WELL-LOCALIZED) 1st order neurons - sensory neurons located in dorsal root ganglia of spinal nerves; their central branches (Aẟ fibers) enter spinal cord via lateral division of dorsal roots of spinal nerves and synapse w 2nd order neurons 2nd order neurons - located in dorsal horn of spinal cord (mainly laminae I and V); their axons decussate in anterior white commissure and ascend to thalamus in contralateral anterolateral system *takes 2-3 spinal cord segments for decussating fibers to join anterolateral system *spinal cord lesions involving anterolateral system cause contralateral loss of pain and temp sensations beginning 2 or 3 segments below the level of lesion 3rd order neurons - located in VPL nucleus of thalamus Their axons ascend to cerebral cortex via posterior limb of interal capsule and terminate in primary somatosensory cortex (POSTCENTRAL GYRUS & POSTERIOR PARACENTRAL LOBULE) Indirect spinothalamic pathway: - Aka: paleospinothalamic pathway - Carries SLOW pain (DULL, BURNING, ACHE) Info carried into spinal cord by C fibers Info does not travel directly from spinal cord to thalamus, but indirectly via brainstem reticular formation consisting of spinoreticular and reticulothalamic fibers Other fibers in anterolateral: Spinomesencephalic fibers → extend from spinal cord to periaqueductal gray matter of midbrain and play a role in intrinsic pain control mechanisms Hypothalamus and limbic system structures receive pain info directly or indirectly → important for emotional and autonomic responses to nociceptive stimuli Primary Somatosensory Cortex (SI) Location: postcentral gyrus and posterior paracentral lobule (Brodmann 3, 1, 2) Contains somatotopic representation of contralateral body in an upside down fashion (“little man”) The size of cortical area associated w a particular region of the body DEPENDS ON SENSITIVITY of body region and NOT THE SIZE OF THE REGION - Hands and lips have high density of receptors = large cortical representation - Back has small density of receptors = small cortical representation Lesions affecting the primary somatosensory cortex cause impairment of fine aspects of somatic sensations (they cant judge the exact location or the intensity of the stimulus) There is also a deficit in sense of position and movement of the body parts, but DOES NOT ABOLISH TACTILE SENSATION OR SENSATION OF PAIN *they can still feel pain Supplied by: MCA and ACA Vacular lesions in MCA = sensory loss in contralateral upper limb and face Vascular lesions in ACA = sensory loss in contralateral lower limb