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WHERE AM I? Online Anatomy Module 1 INTRO & TERMS CELL EPITHELIUM CONNECTIVE TISSUE MUSCLE NERVOUS SYSTEM AXIAL SKELETON APPENDICULAR SKELETON MUSCLES EMBRYOLOGY 101H NERVOUS STRUCTURES & TISSUE CENTRAL Brain PERIPHERAL Cranial nerves Ganglia Peripheral nerves Cord Receptors Autonomic nerves PNS - Peripheral Nervous System NERVOUS STRUCTURES & NEURON The systems are large and very extended to reach to all parts of the body. The nerve cell/neuron forming the basis is a greatly extended cell. The principal cell extension is the axon. Neuron body Brain Cranial nerves Ganglia Peripheral nerves Cord Receptors Autonomic nerves Axon NEURON I The neuron body or soma itself extends branching processes DENDRITES, to pick up different influences over a wide area Neuron body Axon Dendrites Axon and dendrites are tubular extensions of the cell with very sensitive plasma membranes Dendrites (& soma) are sensitive to the influence of other nerve cells Axons have a membrane that is insensitive to such influences, but transmits an electrical signal NEURON II Dendrites Neuron body Axon The electrical signal that develops on the dendrites & body and propagates along the axon membrane is based on the coordinated actions of very many ion channels At the end of the axon branches, the electrical signal causes the release of chemicals from the swelling - the SYNAPSE The released chemical - the transmitter - acts on the dendritic membranes of the next neuron in the chain to cause more electrical activity NEURON III Axon Axon often branches to reach several target cells The myelin sheath is absent from the fine terminal branches of the axon The electrical signal that propagates along the axon membrane can be made to go much faster by wrapping the axon in lengths (segments) of a fatty insulator - MYELIN The myelin segments comprise a myelin sheath NEURON IV Axon The decision as to whether the axon will ‘fire’ and propagate the signal occurs right at the start of the axon at the AXON HILLOCK The axonal signal is termed the: action potential nerve impulse axon firing Marieb Fig 7.9, p 203 NEURON V Axon The axon + its myelin sheath, if present, is the NERVE FIBER NEURON VI synapse soma axon axon hillock dendrites Neuron # 1 soma = cell body preterminal axonal branches Neuron # 2 in chain NEURON VII Properties of the parts synapse influence soma axon transmissive axon hillock & long reach decisive dendrites receptive preterminal axonal branches distributive & more reach NEURON VIII Multipolar type These neurons are the majority type - multipolar - because they have several dendrites and always just one axon synapse soma axon preterminal axonal branches axon hillock dendrites Neuron # 1 Bipolar neurons have just two processes, one the axon Marieb Fig 7.8, p 202 Neuron # 2 in chain NEURON & GLIAL CELLS The electrical signal that develops on the dendrites & body and propagates along the axon membrane is based on the coordinated actions of very many ion channels ‘Space’ is filled by glial cells The ions leaving & entering the neuron go into an environment that has to be very tightly controlled. The cells that create and maintain this environment, and also feed and clean up after the neurons, are GLIAL CELLS. These glia are wrapped all around neuron bodies, dendrites, axons and synapses. Two glial cell types make the myelin sheaths: a central kind & a peripheral one NEURON & CNS GLIAL CELLS I OLIGODENDROCYTE synapse soma axon Node of Ranvier Myelin segment dendrites for fast saltatory (jumping) conduction Gap in the myelin is the Node of Ranvier NEURON & CNS GLIAL CELLS II ASTROCYTE synapse soma axon Myelin segment dendrites NEURON & PNS GLIAL CELLS I synapse SCHWANN CELL soma axon Node of Ranvier dendrites Myelin segment for fast saltatory conduction NEURON & PNS GLIAL CELLS II PNS SATELLITE CELL synapse soma axon Myelin segment dendrites axon } AXONS, MYELIN, & GLIA in cross-section myelinates more than one axon either enfolding several un-myelinated axons axon or enclosing one myelinated axon axon OLIGODENDROCYTE } SCHWANN CELLS CNS MYELINATION I OLIGODENDROCYTE } { axon Myelin lamellae appear exactly concentric, but are a spirally wrapped sheet Oligodendrocyte plasmalemma extends, adheres, & becomes the next myelin lamella 2 1 First, outer lip wraps; then, inner lip extends 3 axon Oligodendrocyte process Cytoplasm squeezed out 4 Transport of membrane proteins and lipids for membrane conversion 5 axon Myelin lamellae CNS MYELINATION II Oligodendrocyte CNS MYELINATION III OLIGODENDROCYTE } { axon Myelin lamellae appear exactly concentric, but are a spirally wrapped sheet Connection of plasmalemma to outermost myelin lamella is the OUTER MESAXON Oligodendrocyte plasmalemma extends, adheres, & becomes the next Intervening cytoplasm is resorbed, except myelin lamella for remnants at Nodes of Ranvier & clefts of Schmidt-Lantermann MYELINATED PERIPHERAL NERVE FIBER AXOLEMMA plasma membrane of axon SCHWANN CELL MYELIN In the periphery, the Schwann cell similarly membrane-wraps the axon, while coverting the wrappings to compact myelin layers/lamellae. AXON Two adjacent Schwann cells leave an uncovered gap - the Node of Ranvier MYELINATED PERIPHERAL NERVE FIBER: Reinforcement In the peripheral NS, two strengthening steps are needed: plasma membrane of axon MYELIN the construction of a basal lamina & a fine connective tissue sheath outside the Schwann cell AXOLEMMA BASAL LAMINA AXON ENDONEURIUM delicate connective tissue SCHWANN CELL MORE NERVOUS TISSUE COMPONENTS NEURONS/NERVE CELLS GLIAL CELLS BLOOD VESSELS Connective tissue WRAPPINGS The ion channels require large amounts of energy from glucose & oxygen to work the ion pumps, so blood is urgently needed So as not to interfere with the intimate neuron-glia relations, the brain & cord have only wrappings - no internal connective tissue - making them very squishy & vulnerable NERVOUS STRUCTURES: Neuron bodies Brain & Cord have trillions of nerve & glial cells; protected by layers of defense The neuron body keeps the neuron alive so the bodies are grouped for protection as well as function The grouped neuron bodies (& glial cells) in the peripheral system are GANGLIA Shown in two colors for sensory & autonomic Ganglia get some protection from the spine, holes in the skull, or being in soft protected visceral organs BRAIN SUB-DIVISIONS I The brain is subdivided into: Cerebellum Cerebral cortex = two cerebral hemispheres BRAIN IN CORONAL VIEW: layered defenses SKIN VENTRICLE filled with fluid, cushions from inside Marieb Fig 7.16 p 211 SKULL CORTEX CORTEX CEREBELLUM DURA Thick strong connective tissue stuck to skull SUBARACHNOID SPACE filled with cushioning fluid fine ‘skin’ of connective tissue on the brain - PIA PERIPHERAL NERVE - Bundles of nerve fibers The idea of mutiple protective layers extends to the connective tissue wrappings of individual axons, bundles (fascicles) of axons (fibers), and the bundles FASCICLE = bundle of nerve fibers FASCICLE Marieb Fig 7.20, p 218 PERIPHERAL NERVE - CONNECTIVE TISSUES Wrappings The idea of mutiple protective layers extends to the connective tissue wrappings of individual axons, EPINEURIUM bundles (fascicles) of axons (fibers), and the bundles FASCICLE PERINEURIUM main barrier to protect nerve fibers ENDONEURIUM around each myelinated fiber or bundle of nonmyelinated fibers in the FASCICLE fat cells for padding NERVES Brain The previous cross-section of a nerve could be here Cranial nerves Peripheral nerves Ganglia Autonomic nerves The nerve contains part of each contributing nerve cell, but not the bodies & not the synapses Protective wrappings: know the sequence outside-in SKIN SKULL DURA SUB-ARACHNOID SPACE EPINEURIUM PERINEURIUM ENDONEURIUM PIA CORTEX CORTEX CEREBELLUM FASCICLE NERVOUS TISSUE COMPONENTS NEURONS/NERVE CELLS GLIAL CELLS BLOOD VESSELS Connective tissue WRAPPINGS MORE CNS GLIAL CELLS Marieb Fig 7.3, p 197 MICROGLIAL CELL small reserve defensive macrophages of CNS CORTEX CORTEX EPENDYMAL CELLS epithelium-like to line the ventricles within the brain CEREBELLUM OLIGODENDROCYTE axon ASTROCYTE Always be aware of where the discussion is in the hierarchy of levels: molecular, organelle, cellular, tissue, organ, system, whole person, human population this is made more difficult in the nervous system because it goes everywhere, so also Whereabouts in the system am I? NERVOUS STRUCTURES: Neuron bodies The neuron body keeps the neuron alive so the bodies are grouped for protection as well as function Brain & Cord have trillions of nerve & glial cells In the brain & cord the neuron bodies are mostly segregated from the nerve fibers (axons & myelin), but to separate functions Where the neuron bodies congregate has less myelin, and is termed GREY MATTER GRAY MATTER vs WHITE MATTER Gray because of little myelin White because of many myelinated fibers This is the fresh-tissue, naked-eye appearance. Staining, e.g., of just myelin for brain atlases, can reverse the intensity BRAIN SUB-DIVISIONS I The brain is subdivided into: Cerebral cortex = two cerebral hemispheres Each fold of cortex has a core of white matter sandwiched between two layers of gray matter served by the white-matter fibers CEREBRUM one fold/gyrus I II III IV V GRAY MATTER VI } WHITE MATTER GRAY MATTER The Roman numerals indicate that the millions of neuron bodies are not all the same, & make up six distinguishable layers SPINAL CORD: White & gray matter The cord has many nerve cells, but also has many major connection pathways so white matter is predominant & on the outside WHITE MATTER GREY MATTER in a characteristic butterfly shape in the cross-section SPINAL CORD: More details Two swellings Cervical enlargement to serve arm & hand WHITE MATTER Thoracic to serve trunk & sympathetic autonomics Lumbo-sacral enlargement to serve leg & foot & pelvic viscera GREY MATTER dorsal horn - sensory intermediate / lateral grey ventral horn - motor Central canal Ventral fissure/cleft with anterior spinal artery BODY CAVITIES II Dorsal The bones of the skull are organized to form the face and a cranial cavity for the brain The vertebrae making up the spine have many surfaces for muscle to attach and stabilize and move the spine. But also, they each have a hole. As the holes line up, they create the spinal canal (cavity) for the spinal cord BRAIN SUB-DIVISIONS I The brain is subdivided into: Posterior Cerebral cortex = two cerebral hemispheres Anterior Cerebellum Brain stem Small, on midline, deep & mostly within brain (spinal cord) Marieb Fig 7.12, p 206 note additional region - diencephalon BRAIN SUB-DIVISIONS II Cerebral cortex = two cerebral hemispheres Anterior Posterior Cerebellum Brain stem Small, on midline, deep & mostly within brain Appreciate that one has left & right lateral views of the brain (Spinal cord) INNERVATION = NEURON DEPLOYMENT sensory motor CORTEX cerebellum B R A I NS We can keep this orientation, but distort the proportions a little to create a brain-&-cord framework for showing how neurons actually are deployed TE M C O R D PERIPHERAL-CENTRAL INTERDEPENDENCE The nervous system is defined by the nonnervous organs and tissues that it serves. (A live brain in a jar has only stored information to work with, and nothing to do in any effective sense.) So there in the ‘periphery’ is where we shall start The periphery to be considered first is the body wall and its limb derivatives. These defined ganglia & the cord. Sensory organs & muscles of the head came later in evolution and gave the head and brain their characteristics We shall be talking electrical connections NERVOUS STRUCTURES & TISSUE CENTRAL PERIPHERAL Brain Ganglia Peripheral nerves Cord Receptors But the central & peripheral work together so we’ll include peripheral structures CONVENTION FOR SHOWING NEURONS I Here the neuron bodies are represented with some dendrites ending/synapse axon axon neuron body Simplest schematic synapse 101H NERVOUS STRUCTURES & TISSUE CENTRAL PERIPHERAL Ganglia Peripheral nerves Receptors PNS - Peripheral Nervous System CONVENTION FOR SHOWING NEURONS II Here the neuron bodies are represented with some dendrites axon This type of ganglion neuron has no dendrites Motor synapse on muscle synapse touch receptor SOMATIC INNERVATION MOTOR SENSORY to detect external & internal changes To make muscle contract, glands secrete, etc SKIN BONE Joint capsule Tendon Muscle NEURON DEPLOYMENT making connections sensory motor Cortex Cerebellum neuron body Receptors movement Nerve touch motor endings Ganglion MOTOR & SENSORY PATHWAYS sensory motor Motor is for controlling skeletal muscle Sensory ‘knows’ what skin receptors are feeling CORTEX cerebellum B R A I N SOMA: Limb & body wall movement touch S T E Note chain of neurons M C O nerve R D MOTOR & SENSORY PATHWAYS: # of NEURONS sensory motor CORTEX cerebellum 3 B R 1 A I N 2 Note chains of neurons S T E M C O R D 2 1 Autonomic component of peripheral nerves The flow of blood to skin cerebellum & muscle needs to vary B Autonomic neurons R send axons to constrict A I N vessel width S ‘Autonomic’ - happens T E without thought M CORTEX C SOMA O nerve R D vasoconstriction Afferent & Efferent components of peripheral nerves CORTEX cerebellum Different axons are carrying signals in to the CNS & away from it B R A I N S T Afferent E M Efferent C O nerve Marieb Fig 7.6, p 200 R D INNERVATION = NEURON DEPLOYMENT sensory motor CORTEX cerebellum B R A I NS We can keep this orientation, but distort the proportions a little to create a brain-&-cord framework for showing how neurons actually are deployed TE M C O R D MEDIAN (Midline) TUBE MAN Head - modification of body wall + brain & special senses + start of two tubes re Al Soma - body wall & the limbs - - - - Viscera tubes, modified tubes, & accessory organs & his Neuron cvl - - - diaphragm u o Neuron - excitable, extended, fast influencer SOMATIC INNERVATION MOTOR SENSORY cutaneous autononomic proprioception skeletal m SKIN BONE Joint capsule Tendon Muscle INNERVATION = NEURON DEPLOYMENT sensory motor - CORTEX cerebellum CONVENTIONS B ending R A fiber I N ST neuron body E M C SOMA movement touch vasoconstriction + O nerve R D 101H NERVOUS STRUCTURES & TISSUE CENTRAL PERIPHERAL Ganglia Peripheral nerves Receptors PNS - Peripheral Nervous System Receptors & Sensory Information sensory motor Receptors of many kinds tell the brain & cord what is going in the body & outside Most of this information never reaches consciousness Tactile info from theneuron skin body is an exception Receptors movement Nerve touch motor endings vasoconstriction S A Ganglia THICK, HAIRLESS SKIN } 2 Receptors EPIDERMIS } Meissner’s corpuscle Marieb Fig 4.3, p 96 DERMIS Sweat gland Pacinian corpuscle Pacinian corpuscle RECEPTORS: Cutaneous (around 1 Peri-trichal hair follicle) Marieb Fig 7.7, p 201 2 Free endings in epidermis Merkel cell 5 6 Ruffini corpuscle encapsulated 3 Pacinian corpuscle encapsulated Meissner’s corpuscle encapsulated 4 Meissner’s corpuscle Receptors that are not inserted among the epithelial cells of the epidermis, but are in the underlying connective tissue, are mostly ‘encapsulated”, and have a typical structure Supporting glia-like cells Terminal impulsegenerating part of axon Connective tissue capsule Axon - peripheral branch of the axon of a sensory ganglion cell 1 Peri-trichal (around “TOUCH” hair follicle) RECEPTOR MODALITIES hair displacement 3 Merkel cell 2 Free endings TOUCH COLD PAIN Ruffini 6 corpuscle Pacinian corpuscle TOUCH 4 Meissner’s corpuscle TOUCH 5 CT DISPLACEMENT* VIBRATION * slowly adapting NERVOUS STRUCTURES Peripheral Central PNS CNS RECEPTORS CEREBRAL CORTEX Sens GANGLIA DIENCEPHALON MOTOR ENDINGS CEREBELLUM Auton GANGLIA BRAINSTEM PLEXUSES SPINAL CORD NERVES NEURAL RETINA PERIPHERAL NERVE - CONNECTIVE TISSUES Wrappings EPINEURIUM PERINEURIUM main barrier to protect nerve fibers FASCICLE ENDONEURIUM around each myelinated fiber or bundle of nonmyelinated fibers in the FASCICLE fat cells (Black with Osmium tetroxide showing myelin rings) vessels PERIPHERAL NERVE - H&E versus OsO4 staining Fat cells - clear & empty H&E Myelin sheaths - Black rings Nuclei - mostly Schwann cells’ Myelin sheaths - clear spaces Axons - central dots Fat cells - Black OsO4 Axons - clear Nuclei -unseen Node HISTOLOGY’S ORIENTATION PROBLEM Cerebellum Cortex Small pieces from a large complex system Where am I? How much of what is neuro present can I see? n body Making the connections mentally Receptors Nerve motor endings S A Ganglia SENSORY PATHWAY sensory CORTEX cerebellum B R A I N ST E M C O nerve touch R D crosses midline PATHWAYS OF AUTONOMIC MOTOR SYSTEM Cranial gland or eye smooth muscle Head vessels Brain stem Para V C Thor Cord Symp C P ADRENAL MEDULLA Sacral Cord Para I S C E R A CEREBRUM 1/2 one gyrus Pia mater I Molecular layer II III IV small stellate neurons V pyramidal neurons VI Apical dendrite White matter Basal dendrites PYRAMIDAL NEURON Soma Axon VISCERAL TUBE CONSTRUCTION Epithelium Lamina propria } Tunica muscularis nerve plexus Tunica adventitia or serosa vessel Tunica mucosa GUT MOTOR INNERVATION intrinsic with H & E staining, the only neural elements seen are the neuron bodies & characteristic nuclei. The plexuses of fibers are unseen. Meissner’s submucosal plexus Rare neuron bodies of plexus submucosa muscle Auerbach’s myenteric plexus Clumped neurons of A’s plexus Unmyelinated autonomic nerve neurons are multipolar, with dendrites! AUTONOMIC “unmyelinated” NERVE in H&E Small, pale, blueish, elongated; ‘purposeful’ track through pinker connective tissue or muscle Thin CT perineurium X-section Many nuclei (mostly of Schwann cells) giving, with the fibers, an undulating wavy character Once they leave the nerve, individual fibers need special methods to be seen INTRAMURAL (Parasympathetic) GANGLION like any other nervous gangion, is an aggregate of neuron bodies & associated cells added to a nerve Around the somas, the jumble Neuron somas, with large pale of nuclei belong to satellite cells, nucleus & prominent nucleolus Schwann cells, fibroblasts & capillaries Special methods are needed to show that the neurons are multipolar to receive the pre-ganglionic synapses INTRAMURAL (Parasympathetic) GANGLION Post-ganglionic SYMPATHETIC fiber Pre-gangionic PARASYMPATHETIC fiber Post-ganglionic PARASYMPATHETIC fiber Special methods are needed to show the plexus of autonomic fibers to which the gangion neurons contribute VOLUNTARY MOTOR PATHWAY I CORTEX motor cerebellum B R upper motor neuron A I N ST E M C O muscle movement nerve R D lower motor neuron Motor end-plate crosses midline MOTOR END-PLATE or NEUROMUSCULAR/MYONEURAL JUNCTION AXON SCHWANN CELL AXOLEMMA SARCOLEMMA SYNAPTIC VESICLES mitochondrion synaptic cleft secondary/ junctional folds of POST-SYNAPTIC MEMBRANE SKELETAL MUSCLE FIBER/MYOCYTE NEURON TYPES by SHAPE I synapse soma MULTIPOLAR axon axon hillock preterminal axonal branches The vast majority of neurons are multipolar: hence, other criteria for classification dendrites BIPOLAR Dendrites’ function transferred PSEUDO-UNIPOLAR receptive NEURON TYPE DEPLOYMENT sensory CORTEX motor All long-axoned, except cerebellum B R Spinal interneuron A I All shown: multi-polar S T except pseudoE unipolar M DRG cell C O nerve R D N movement touch vasoconstriction NEURON DEPLOYMENT sensory motor Appreciating how neurons are used: problems are that a neuron EXTENDS through many named strucures, and shares structures, e.g., here motor & sensory in a nerve Nerve touch NEURON DEPLOYMENT II one neuron extends through many named structures. The axon is doing the extending TRACT of Cord - cuneate DR GANGLION touch RAMUS of PERIPHERAL ROOT, dorsal spinal NERVE, e.g. median PLEXUS, nerve, e.g. e.g. brachial ventral SPINAL NERVE CUTANEOUS PLEXUS NEURON DEPLOYMENT III one neuron extends through many named structures. The axon is doing the extending 1 CUTANEOUS PLEXUS 2 PERIPHERAL NERVE, e.g. median 3 PLEXUS, e.g. brachial 4 RAMUS of spinal nerve, e.g. ventral 5 SPINAL NERVE 6 DR GANGLION 7 ROOT, dorsal } 8 CORD TRACT, cuneate SPINAL CORD Cervical enlargement to serve arm & hand WHITE MATTER Thoracic to serve trunk & sympathetic autonomics Lumbo-sacral enlargement to serve leg & foot & pelvic viscera GREY MATTER dorsal horn - sensory intermediate / lateral grey ventral horn - motor Central canal Ventral fissure with anterior spinal artery DORSAL ROOT GANGLION Pial connective tissue Clumps of sensory neurons Nerve-like Root central axon unseen H&E Satellite cells around neurons dorsal horn - sensory Bundles of myelinated fibers Hallmarks: large round neurons; separation of neurons from pale myelinated nerve bundles CNS STRUCTURES sensory motor CORTEX cerebellum B R like CNS neuron somas grouped in a NUCLEUS GREY A I N ST E M like CNS fibers grouped in a TRACT WHITE C O movement R D touch vasoconstriction CEREBELLUM one folium Pia mater Molecular layer few neurons Purkinje cells/neurons Granule layer small neurons White matter Gray matter Purkinje cell Projection/output neuron PNS STRUCTURES sensory N NE DRG AG CORTEX motor B R A I N S T E M C O Nerve endings motor Nerve R D sensory motor Autonomic ganglion DR ganglion NEURON TYPES by SHAPE I synapse soma MULTIPOLAR axon axon hillock preterminal axonal branches The vast majority of neurons are multipolar: hence, other criteria for classification dendrites BIPOLAR Dendrites’ function transferred PSEUDO-UNIPOLAR receptive RECEPTOR MODALITIES 1 Peri-trichal (around hair follicle) 2 Free endings “TOUCH” -hair displacement TOUCH COLD PAIN TOUCH 3 Merkel cell 4 Meissner’s corpuscle 5 Pacinian corpuscle 6 Ruffini corpuscle Light TOUCH VIBRATION CT DISPLACEMENT* * slowly adapting TASTE BUD Taste pore Receptor cells SS EPITHELIUM Basal cell Supporting cell Axons of VII, IX or X MUSCLE SPINDLE Intra-fusal muscle fibers Extra-fusal muscle fibers often holds several fibers of each type ORANGE vs MENINGES PEEL - DURA MATER LINING OF PEEL & SPACE ARACHNOID SKIN ON SEGMENTS PIA MATER BRAIN IN CORONAL VIEW CORTEX VENTRICLE with Choroid plexus SKULL DURA Dural Falx SUBARACHNOID SPACE Dural sinus CEREBELLUM Tentorium cerebelli BLOOD FLOWS FOR THE BRAIN Dural sinuses Cerebral veins Brain capillary network Arteries Jugular veins CSF PRODUCTION & FLOW Dural sinus CSF returns to blood: subarachnoid space to dural sinus CHOROID PLEXUS in ventricles making CSF from blood Arteries Jugular veins CSF drains to the outside of the brain from 4th ventricle CHOROID PLEXUS CUBOIDAL EPENDYMAL EPITHELIUM CAPILLARY CSF LOOSE CT BASAL LAMINA Choroid-plexus ependymal cells have tight junctions, and ion pumps to drive water & some electrolytes from blood to ventricle CSF RETURN TO BLOOD I CORTEX Dural sinus VENTRICLE with Choroid plexus SKULL DURA Dural Falx SUBARACHNOID SPACE CSF How to return CSF to blood? Dural sinus BLOOD CSF RETURN TO BLOOD II Dural sinus CORTEX VENTRICLE with Choroid plexus SKULL Site of Next Fig DURA Dural Falx SUBARACHNOID SPACE RETURN OF CSF: Arachnoid DURA dural-sinus blood DURAL SINUS here Sup sagittal sinus ARACHNOID MEMBRANE ENDOTHELIUM ARACHNOID TRABECULAE PIA ARACHNOID VILLUS protruding into sinus CORTEX SUBARACHNOID SPACE CORTEX FALX This Fig has appeared countless times without credit to its originator Lewis Weed of the Johns Hopkins U, so I am providing only his labels Weed LH. The absorption of cerebrospinal fluid into the venous system. Am J Anat 1923;31:191-221 VILLUS. Do I know you? ARACHNOID VILLUS SMALL INTESTINAL VILLUS JOINT SYNOVIAL VILLUS PLACENTAL CHORIONIC VILLUS Many sub-types CSF PRODUCTION, FLOW, & RETURN Arteries CHOROID PLEXUS in ventricles making CSF from blood CSF drains via foramina to the outside of the brain from 4th ventricle CSF returns to blood: subarachnoid space to dural sinus Dural sinus Jugular veins CSF FLOW & RETURN: Problems Arteries CSF production continues CHOROID PLEXUS in ventricles regardless OBSTRUCTIONS OF: making CSF from blood Flow between ventricles Out of 4th ventricle Dural-sinus uptake, e.g. from meningitis CSF drains via foramina to the outside of the brain from 4th ventricle CSF returns to blood: subarachnoid space to dural sinus RAISED INTRACRANIAL PRESSURE Dural sinus & Hydrocephalus in infant when cranial vault bones not joined (synostosed) Jugular veins CNS VULNERABILITIES SOFT & SQUISHY - EASILY BRUISED (no intrinsic c.t.) CONFINED IN HARD BOX shared with blood, CSF (& tumor?) URGENT NEED FOR OXYGEN & GLUCOSE for pumping ions SUSCEPTIBLE TO TOXINS that can pass the blood-brain barrier NO EFFECTIVE REPAIR of damage from trauma , raised intracranial pressure, or interrupted blood supply AXONAL TRANSPORT FAST ANTEROGRADE 100 mm/day Carries materials needed for the fast pace of electrical activities of the neuron SLOW ANTEROGRADE 4 mm/day Serves to move the infrastructure of transport, e.g., replacement of tubulin dimers, neurofilaments, mitochondria RETROGRADE 20 mm/day Brings back to the soma old materials for lysosomal destruction & trophic and survival factors derived from the target cell (neuron or muscle) e.g. Nerve Growth Factor Viruses,e.g., rabies, can also use this route WHERE AM I? Online Anatomy Module 1 ORIENTATION You are at the End CELL EPITHELIUM Caution how you exit. BACK on your BONE browser is needed MUSCLE Unfortunately there is NERVOUS SYSTEM no way that you can directly reach other AXIAL SKELETON topics listed here by APPENDICULAR SKELETON clicking on them. You get there by going back MUSCLES to the Paramedical Anatomy menu EMBRYOLOGY