14.1 Overview of the BrainMajor LandmarksDirectional TermsRostral: towards the nose or toward the foreheadCaudal: Toward the tail or toward the spinal cordThree Major PortionsCerebrum: 83% of the brain’s volume and consists of a pair of half globes called cerebral hemispheresEach hemisphere is marked with gyri and sulciLongitudinal Fissure: separate left and right hemispheresCorpus Callosum: thick bundle of nerve fibersCerebellum: occupies the posterior cranial fossa inferior to the cerebrumTransverse cerebral fissure: separates cerebellum from cerebrum10% of the volume but 50% of the nervesBrainstem: all of the brain except for the cerebrum and cerebellumIncludes:Diencephalon, midbrain, pons, and medulla oblongataBrainstem ends at foramen magnumGray and White MatterGray Matter: forms cortex (surface layer) over cerebrum and cerebellumWhite Matter: surrounds deeper matter called nucleiLies deep into gray matterComposed of tracts (bundles of axons)Embryonic DevelopmentNervous system develops from ectodermFirst three weeks: neural plate forms and sinks to form neural groove with neural folds at each end26 days: neural tube formsFusion of neural foldsNeural tubes then forms neural crestGives rise to two inner meninges; most of PNS, and some structures in different systems4 week: forebrain, midbrain, and hindbrain are exhibited5 week:forebrain divides into telencephalon (becomes cerebral hemispheres) and diencephalon (optic vesicles)midbrain undivided: new name mesencephalonhindbrain divides into metencephalon (becomes pons and cerebellum) and myelencephalon (becomes medulla oblongata)14.2: Meninges, Ventricles, Cerebrospinal Fluid, and Blood SupplyVentricles and Cerebrospinal Fluid:Four Ventricles: internal chambersTwo lateral ventricles: form arc in each cerebral hemisphereThird Ventricle: narrow median space inferior to corpus callosumConnected to lateral ventricles by interventricular foramenFour Ventricle: small triangular chamber between bons and cerebellumConnected to third ventricle by cerebral aqueductForms central canal through medulla oblongataChoroid Plexus: spongy mass of blood capillaries on walls of each ventricleEpendyma: lines ventricles and canals and covers choroid plexus and produces cerebral spinal fluidCerebral Spinal Fluid: Liquid that fills ventricles and canals of the CNS and bathes external surfaces40% formed in subarachnoid space external to the brain; 30% by general ependymal lining; 30% by choroid plexusproduction begins with filtering blood plasmamore sodium and chloride, but less potassium, calcium, and glucose than plasmaFlows because own pulse; beating of ependymal cilia; or rhythm from heart beatCSF escapes through 3 poresMedian aperture and 2 lateral aperturesReabsorbed by arachnoid granulations (protrude through dura mater into sagittal sinus)Three PurposesBuoyancy: same density as brain so there’s no floating or sinking1,500 g without CSF; 50 g with CSFProtection: protects from brain striking the skull when joltedConcussions and shaking baby syndromeChemical Stability: rinses metabolic wastes from the nervous tissue and regulates chemical environmentBlood Supply and Blood BarrierBrain receives 15% of the blood; consumes 20% of oxygen and glucoseBecause of high demand for ATPBlood is source of antibodies, marcrophages; bacterial toxinsBrain Barrier System: regulates what can get from bloodstream into tissue fluid of brainHighly permeable to water, glucose, oxygen, carbon dioxide, alcohol affeineObstacle for medicationsCVO’s in 3rd and 4th ventricles allow for invasion of HIVBlood-Brain Barrier: protects entry of blood capillaries in brain tissueContains tight junctions between endothelial cells that form on capillary wallsBlood-CSF Barrier: protects choroid plexus by tight junctions between ependymal cells14.3: The Hindbrain and MidbrainMedulla Oblongata: begins at foramen magnum and extends 3 cmPyramids: pair of ridges on anterior surface separated by anterior median fissureOlive: bulge lateral to pyramidsGracile and Cuneate Fasciculi: two pairs of ridges posteriorly on medullaNerves connecting brain and spinal cord run through medullaAscending fibers end in gracile and cuneate nuclei and synapse with second order fibers that form medial lemniscus; second order fibers rise to thalamus synapsing to third order fibersCorticospinal Tracts: largest group of descending fibers filling the pyramidsCarry motor signalsInferior Olivary Nucleus: major relay center for signals going from many levels of the brain and spinal cord to the cerebellumCardiac Center: regulates rate and force of the heart beatVasomotor Center: regulates blood pressure by dilating and constricting blood vesselsTwo Respiratory Centers: regulate rhythm and depth of breathingPons:Connected to cerebellum by cerebellar pedunclesContinuations of reticular formation, medial lemniscus, tectospinal tractDominated by white matterCranial nerves V to VIII begin or end hereMidbrain (mesencephalon): short segment of the brainstem that connects the hindbrain and forebraincontains the cerebral aqueduct, continuations of the medial lemniscus and reticular formation, and the motor nuclei of two cranial nervesTectum: part of midbrain posterior to cerebral aqueducts that acts as a roofFour bulges: Corpora QuadrigeminaSuperior Colliculi: upper pair that functions in visual attention, visual tracking, and reflexes like blinking, focusing, dilation, and turning eyesInferior Colliculi: lower pair that receive signals from the inner ear and relay them to other parts of the brain like thalamusCerebral Peduncles:Three partsTegmentum: dominated by red nucleus collaborates in fine motor controlSubstantia Nigra: dark gray to black nucleus pigmented with melaninMotor center that relays inhibitory signals to the thalamus and basal nuclei to prevent unwanted body movementDegeneration can lead to Parkinson’sCerebral crus: bundle of nerves that connect the cerebrum to the pons and carry corticospinal fluidCentral (periaqueductal) gray matterReticular Formation: loose web of gray matter that runs vertically through all levels of the brain stemFunctions:Somatic Motor Control: reticulospinal tracts adjust muscle tension to maintain tone, balance, and posture during movementRelays signals from eyes and ears for motor coordinationCardiovascular controlPain Modulation: a route that pain signals from lower body reach cerebral cortexOrigin of descending analgesics pathwaysSleep and Consciousness: controls what