Neuro Exam 1 SG M Nguyen PDF

Chapter 1 Review the different cells Central Nervous System (CNS) – brain + spinal cord Peripheral Nervous System – all nerves and their components outside of the CNS o Afferent neurons – Receive and transmit information from the environment to the CNS ▪ Afferent = sen...

Chapter 1 Review the different cells Central Nervous System (CNS) – brain + spinal cord Peripheral Nervous System – all nerves and their components outside of the CNS o Afferent neurons – Receive and transmit information from the environment to the CNS ▪ Afferent = sensory information Input from sensory organs, skin, muscles, joints, viscera o Efferent neurons – transmit info generated in the CNS to the periphery ▪ Efferent = motor information Travels to glands, smooth muscle, skeletal muscle Cellular Components of the Nervous System: Neurons – excitable cells of the nervous system o Organized in circuits or networks that encode for processing of all conscious and nonconscious info in brain + spinal cord o Signal propagation via action potentials o Neurons connect to each other via synapses ▪ Synapses have 3 components: Axon terminal of one cell Dendrite of the receiving cell Glial cell process Synaptic cleft – space between neurons o Functional Organization of Neurons ▪ Soma/perikaryon = cell body Contains cell nucleus Where all proteins, hormones, and NTs are produced ▪ Nissl substance = halo of ER around the nucleus High metabolic rate of neurons Stains intensely blue with Nissl stain ▪ Microtubules – railroad for axonal transport Anterograde transport – perikaryon along the axon to the synapse o This is how NTs are transported Retrograde transport – from synaptic terminal to the perikaryon o Critical for shuttling trophic factors e.g. neurotrophin o Neurons depend on trophic substances supplied by their peripheral targets for survival  o Some viruses (e.g. herpes virus) also depend on this transport ▪ Dendrites – where synaptic input to a neuron occurs small spines → protrusions where synaptic contacts with axons are made o Postsynaptic densities in the spines → serve as scaffolding, holds, and organizes NT receptors and ion channels ▪ Axon: Axon hillock (initial segment) – where AP begins Axon terminal – make synaptic contacts w/ other neurons ▪ o Types of Neurons: ▪ Multipolar neurons – most abundant type of neuron in CNS Dendrite branch directly off the cell body A single axon arises from the axon hillock ▪ Pseudounipolar – spinal ganglia (dorsal root ganglion) Dendritic axon that receives sensory info and sends it to spinal cord, bypassing the cell body along the way Relays sensory info to CNS without modifying the signal ▪ Bipolar – retina, olfactory epithelium Single main dendrite that receives synaptic input, conveys to cell body, and from there via an axon to next layer of cells Integrate multiple inputs and then pass that modified info onto the next neuron in the chain o Types of Synapses: ▪ Axodendritic synapses – most common synaptic contacts in CNS Between an axon and a dendrite Multipolar neurons receive thousands of axodendritic synaptic inputs Allows neuron to reach threshold and generate an AP Architecture of dendritic tree → allows for temporospatial summation ▪ Axosomatic synapses Axon contacts another neuron directly on the cell soma Less common in CNS Powerful signal much nearer to the axon hillock ▪ Axoaxonic synapses  When an axon contacts another axon Synapses are often on or near the axon hillock, causing very powerful effects Glia – support and protect neurons o Oligodendroglia – myelinating cells in the CNS ▪ 1 oligodendrocyte can myelinate multiple axons ▪ Function of myelin sheath: Provides trophic support (promotes cell survival) Protects axon Organizes distribution of ion channels ▪ Gaps in myelin sheath → nodes of Ranvier o Schwann cells – myelinating cells in the PNS ▪ 1 Schwann cell can myelinate only a single axon ▪ Function like both oligodendrocytes + astrocytes in the CNS ▪ At NMJ, Schwann cells take up excessive NT and maintain homeostasis to facilitate signal transduction o Astroglia –BBB, ion homeostasis, nutritive functions ▪ Fibrous astrocytes → white matter ▪ Protoplasmic astrocytes → gray matter ▪ Muller cells → found in retina ▪ Functions: Take up and recycle excess NT at the synapse Maintain homeostasis around neurons o E.g. take up glutamate and convert it to glutamine Blood brain barrier – astrocyte end-feet line the blood vessels in the brain, important part of BBB. o Separates blood from nervous tissue o Maintain homeostasis by shuttling excess ions into the bloodstream Tripartite synapse = presynaptic neuron, postsynaptic neuron, and astrocyte o Astrocytes release NT into synaptic cleft, strengthening the signal at that synapse o Have NT receptors and can communicate with each other through waves of intracellular Ca2+ propagated from one astrocyte to another via gap junctions Radial glia o Provide the direction and scaffolding for axon migration and targeting o Polydendrocytes – stem cell pool within the CNS; can generate both new glial cells and neurons ▪ Can receive synaptic input from neurons ▪ Direct link b/w neuronal signaling network and glial network ▪ Demyelinating disorders: Polydendrocyte recruitment as a oligodendrocyte precursor are the first step in remyelination ▪ Stem cells in PNS are more active than they are in the brain More able to replace damaged cells in PNS o Microglia – immune cells within the brain, similar to macrophages ▪ Monocyte-macrophage derived ▪ Activated through release of inflammatory molecules (cytokines) ▪ Recruited into areas of neuronal damage → phagocytose cell debris, involved in antigen presentation  o Ependymal cells – line the ventricles, separate the CSF from the neuropil (nervous tissue) ▪ Choroid plexus – produces CSF Blood-brain barrier: o 3 layers of protection: ▪ 1) Endothelial tight junctions ▪ 2) Continuous basement-membrane → strong CT ▪ 3) Astrocyte end feet processes ▪ o Homeostasis o Transport by diffusion for small lipophilic molecules, water, and gas o All other substances require active transport o Limits the drugs that can be given to treat disorders in the brain to those that can cross the BBB Action Potential: there are biophysics concepts that I did not discuss. Read the redacted paragraphs about AP Ion Movements: o Phospholipid bilayer maintains differential ion concentrations on the inside vs outside of the cell o Movement of ions generates an electrochemical gradient for each ion o Membrane potential (electrical potential) – the sum of all ion gradients o Biological membranes actively change their permeability for different ions: o Voltage-gated ion channels: regulated by membrane potential ▪ Change in membrane potential opens the channel pore  ▪ Ex: Voltage-gated Na+ channels → their opening initiates an AP ▪ o Ligand-gated ion channels: regulated by a specific molecule that binds to the channel ▪ Ex: Post-synaptic neurotransmitter receptors o Mechanically gated ion channels – mechanically opened ▪ Touch receptors in the skin ▪ Receptors in the inner ear o Thermally gated ion channels – regulated by temperature Action Potential (APs) – wave of depolarization that travels along surface of a neuron o o o Generation of an Action Potential ▪ Depolarization (more positive) Increased permeability of membrane to Na+ due to opening of Na+ channels Na+ ions flow into the neuron ▪ Threshold potential Once threshold is reached, voltage-gated Na+ channels open All-or-none response  o No variation in strength of a single impulse o Either membrane potential exceeds threshold or it does not o Once begun, an AP is self-propagating o As AP moves down an axon, repolarization occurs behind it ▪ Refractory period – undershoot phase Due to increased K+ permeability K+ ions flow out of the cell, restores negative charge inside cell Absolute refractory period – occurs during depolarization o Whenitcan’t transmit another AP Relative refractory period – when enough gates controlling Na+ channels have been reset o When threshold is higher o Stronger-than normal stimulus is required to initiate an AP ▪ Resting State Na+/K+ ATPase restores ion homeostasis at the end of AP Voltage-gated Na+ and K+ channels are closed o Types of Summation: ▪ Temporal summation – involves a single presynaptic neuron rapidly firing signals to a postsynaptic neuron ▪ Spatial summation – simultaneous signals coming from multiple presynaptic neurons being received by a single postsynaptic neuron ▪ Passive vs Active Current: o Passive Current – shuttling of charge along a neuronal process o Active current → movement of ions through ion channels o Continuous Conduction vs Saltatory Conduction: o Continuous conduction – in unmyelinated axons, passive current flows along axon and continuously opens Na+ channels (active current) that are inserted along the entire length of the axon ▪ Continuous regeneration of APs along the entire length of axons ▪ Involves the entire axon plasma membrane  ▪ o Saltatory conduction – in myelinated axons, Na+ channels are accumulated at Nodes of Ranvier ▪ Passive current is shuttled along a long segment of myelinated axons ▪ At nodes of Ranvier, change in membrane potential causes opening of Na+ channels, regenerating the AP ▪ AP jumps from node to node ▪ More rapid than continuous conduction o o Nodes of Ranvier: ▪ Sites where axon is not covered by myelin ▪ Na+ channels are concentrated here  Velocity of AP depends on velocity of both Active & Passive Current: o Increasing Passive current ▪ Depends on reducing resistance it encounters in the axon: increasing axon diameter decreasing leak current through myelination o Increasing active current: (DON’TNEEDTOKNOW) ▪ Reducing capacitance of the membrane Reduce axon diameter Myelination Summary: APs are o Unidirectional → achieved through the refractory period o Fast → decrease in both membrane capacitance (from myelin) and resistance (from increased axon diameter) helps speed the AP along o Efficient → APs are generated only at Nodes of Ranvier, not along the entire length of the axon, saving energy o Simple → all-or-none response Synaptic Transmission Electrical Synapse – movement of ions through gap junctions coupling 2 neurons (protein pore complex, connexon) o Found in areas where neurons need to be synchronized with each other o Ex: breathing center or in hormone-secreting regions of hypothalamus Chemical Synapse – composed of presynaptic terminal, synaptic cleft, postsynaptic terminal, and an astrocyte process o Communication is achieved via NTs o Charge and ions do not directly move b/w cells o Most common type of synapse in CNS Synaptic Signal Transduction (Chemical Synapse) o AP arrives at presynaptic terminal → voltage-gated Ca2+ channels open, influx of Ca2+ o NT filled vesicles fuse w/ the membrane and diffuse the NT across the synaptic cleft o NT binds to postsynaptic receptors and ion channels open o Type of ion channels determines IPSP or EPSP: ▪ Influx of Na+ → causes an EPSP (brings membrane closer to threshold) ▪ Influx of Cl- → IPSP (further away from threshold) ▪ Efflux of K+ → IPSP (further away from threshold) ▪ Temporospatial summation → synapses receiving input must be close together and receive input in the same timeframe o When a sufficient # of excitatory postsynaptic potentials come together in time and space, postsynaptic cell depolarizes sufficiently to reach threshold → an AP is generated Postsynaptic receptors are either ionotropic or metabotropic:  o Ionotropic receptors → NT receptor is coupled with an ion channel ▪ NT binds → ion channel opens ▪ Direct effect o Metabotropic receptors → NT receptor coupled w/ intracellular signaling cascades ▪ Requires second messenger to open ion channel ▪ GPCR mechanisms ▪ Indirect effect ▪ Neurotransmitters: only glutamate, GABA, acetylcholine Excitatory → influx of positive charge → depolarization Inhibitory → influx of negative charge → hyperpolarization o Glutamate – excitatory NT in CNS ▪ Binds to ionotropic glutamate receptors, causing an influx of cations into postsynaptic neurons → depolarization! NMDA receptors o Pore is blocked by Mg2+ ion unless postsynaptic membrane is depolarized o Once unblocked, permeable to Na+ and Ca2+ → depolarization AMPA receptors Kainate receptors ▪ Also bind to family of metabotropic glutamate receptors (mGluRs) ▪ Synthesized in neurons from precursor glutamine Glutamine supplied by astrocytes → produce glutamine from glutamate they take up in the synaptic cleft o GABA – inhibitory NT in CNS  ▪ Bind to ionotropic GABA receptors (GABAA and GABAC) → induce Cl- influx Accumulation of negative charge → hyperpolarization ▪ Bind to metabotropic GABA receptor (GABAB) → activates K+ channels, blocks Ca2+ channels Net loss of positive charge → hyperpolarization o Glycine – inhibitory NT in CNS ▪ About half of all inhibitory synapses in spinal cord use glycine ▪ Binds to ionotropic receptor, allows for Cl- influx o Acetylcholine (ACh) – excitatory NT in both PNS & CNS ▪ Used in: PNS (ganglia of visceral motor system) CNS (forebrain) Neuromuscular junction (NMJ) ▪ 2 types of receptors for (ACh): Nicotinic ACh receptors – ionotropic receptors, coupled w/ nonselective cation channel o PNS (ganglia of visceral motor system) o NMJ (muscle contraction) Muscarinic ACh receptors – linked to G protein-mediated pathway o CNS (Forebrain) o Hippocampus, important for memory ▪ Synthesis & Breakdown: Synthesis requires enzyme choline acetyltransferase (ChAT) ACh is made from choline (Ch) and acetyl coenzyme (acetyl CoA) in the axon terminal then filled into synaptic vessels Once released into the synaptic cleft, its rapidly broken down by enzyme acetylcholinesterase Ch is transported back into the axon and reused to make ACh Clinical Applications: read only description of multiple sclerosis Multiple Sclerosis → damage of oligodendrocytes (CNS) o Chronic neurological disease affecting young adults o Pathology: ▪ Loss of myelin sheath around axons – demyelination ▪ Loss of axons – neurodegeneration ▪ Severe inflammation in areas of demyelination ▪ Conduction block within axon  ▪ Clusters of Na+ channels are too far apart; passive current dissipates before next cluster of Na+ channels can be activated o Body Response to Conduction Block: ▪ Insert Na+ channels along demyelinated axon → nonsaltatory continuous conduction Inserted Na+ channels cause more Na+ influx into axon than normal o Na+/Ca+ exchanger can no longer maintain Na+ homeostasis → proteases activated → axon degenerates Can be successful in some cases o Continuous conductance established, APs propagate at slower pace ▪ Remyelination Polydendrocytes (oligodendrocyte precursor cells) are recruited to affected area Once polydendrocytes mature into oligodendrocytes, they begin remyelination Macrophages remove myelin debris in affected area Function restored, but not as quick or efficient o Paresthesia – abnormal sensations ▪ Cross talk between axons can occur when myelin sheath has been lost o Permanent loss of function in MS due to axonal loss & neuronal death ▪ Axonal loss due to Loss of myelin sheath Insertion of faulty Na+ channels Failure to remyelinate Guillain-Barre Syndrome → damage of Schwann Cells (PNS)  Chapter 2 Skip Development Review the orientation of the Brain Planes of Orientation: o Coronal – cuts through the brain from dorsal to ventral; perpendicular cut ▪ Likeatiaraorcorona“crown”sittingonthehead ▪ Like slices of a loaf of bread o Horizontal – cuts through the brain parallel to the ground ▪ Like slicing a hamburger bun or bagel o Sagittal – cuts through the brain from anterior to posterior ▪ Like an arrow shooting through the brain ▪ Midsagittal section → separates the 2 hemispheres o Directions: o Caudal-Rostral ▪ Rostral – “beak” Anything toward the anterior pole of the forebrain ▪ Caudal – “tail” Anything toward the inferior pole of the spinal cord o When referring to the brain/forebrain  ▪ Dorsal surface of the brain → superior surface ▪ Ventral surface of the brain → inferior surface o When referring to spinal cord and brainstem: ▪ Dorsal surface → posterior surface ▪ Ventral surface → anterior surface Gross Anatomy of the CNS Gray matter vs White matter: o Gray matter – any accumulation of neuronal cell bodies ▪ Nucleus – collection of nerve cell bodies within the CNS ▪ Ganglion – collection of nerve cell bodies within the PNS o White matter – sum of all fiber tracts, myelinated axons ▪ Tract – bundle of myelinated axons in the CNS Myelinatedaxonsresultinthe“white”appearance White matter tracts connect various parts of the brain with each other ▪ Nerve – bundle of myelinated axons in the PNS o In the brain: ▪ White matter is located centrally and surrounded by gray matter on the cortical surface layer Gray matter also found in the deep nuclei in the forebrain o In the spinal cord ▪ Gray matter located centrally and surrounded by white matter Surface Anatomy: o Gyrus = ridge o Sulcus = grooves between ridges o Fissure = deeper grooves, deeper sulcus o Major Sulci & Gyri: ▪ Longitudinal fissure → located along midsagittal plane; separates the 2 hemispheres ▪ Central sulcus → separates frontal lobe and parietal lobe ▪ Lateral or Sylvian fissure → separates the temporal lobe from the frontal and parietal lobes ▪ Parietooccipital sulcus → on medial surface of brain; separates the occipital lobe from the parietal lobe/temporal lobes ▪ Calcarine fissure → on medial surface in occipital lobe Frontal Lobe Central sulcus – separates frontal lobe & parietal lobe o Precentral gyrus (primary motor cortex) – anterior to central sulcus ▪ Voluntary motor activity ▪ Precentral gyrus lesion → contralateral paralysis o Postcentral gyrus – posterior to central sulcus; a part of parietal lobe → Primary somatosensory area Premotor cortex  o Planning and coordination of complex, coordinated movements; also involved in motor learning o Initiating motor behavior Frontal Pole = Superior frontal gyrus, Middle frontal gyrus, Inferior frontal gyrus o Inferior frontal gyrus ▪ Pars opercularis ▪ Pars triangularis ▪ Pars orbitalis Broca’s motor speech area – L hemisphere = pars opercularis + pars triangularis o Expressive or motor aspects of language o Language production o Broca’saphasia – results from damage on L side (R side damage would not produce damage) ▪ Form of expressive aphasia → struggle to form complete sentences ▪ No issue understanding speech → have awareness Remainder of frontal lobe consists of association areas known as prefrontal association areas – concerned w/ emotion, motivation, personality initiative, judgement, ability to concentrate and social inhibitions o Cingulate gyrus – modulating emotional aspects of behavior; found on medial surface o Prefrontal cortex ▪ Higher-order cognitive functions ▪ Executive functions (decision making, planning, problem-solving) ▪ Emotional regulation ▪ Social behavior and judgement ▪ Personality expression and control ▪ Working memory o Orbitofrontal cortex ▪ Emotional processing, decision-making, selecting socially appropriate behavior ▪ Schizophrenia Characterized by socially inappropriate behavior Sometimes violence ▪ o Dorsolateral prefrontal cortex ▪ Working memory, cognitive flexibility, goal-directed behavior o Frontal Eye Fields ▪ Control of voluntary eye movements, particularly saccades  ▪ o Anterior Cingulate Cortex ▪ Motivation, error detection, decision-making o Motor Association Cortex ▪ Coordination and planning of complex motor actions, integrating sensory information to guide movements o Supplementary Motor Area (SMA): ▪ Involved in planning and coordinating complex motor actions, especially those involving sequences of movements Parietal Lobe – somatosensory, language, and spatial orientation functions Central sulcus – separates it from frontal lobe Lateral fissure – separates it from temporal lobe Parietooccipital fissure – separates it from occipital lobe Parietal Lobe - Functional Anatomy: o Postcentral gyrus (primary somatosensory cortex) – posterior to central sulcus ▪ Processes sensory information related to touch, pressure, temperature, and pain from all over the body ▪ Postcentral gyrus lesion → contralateral anesthesia Inability to localize sensation Inability to separately identify 2 cutaneous stimuli placed closely together (2-point discrimination) o Superior parietal lobule ▪ Somatosensory Association Cortex – adjacent to primary somatosensory cortex Integrates sensory information Higher-level processing of signals from somatosensory cortex, thalamus, primary visual cortex, occipital lobe, primary auditory cortex are integrated Somatosensory association cortex lesion → contralateral inability to recognizecomplexobjectsoreventhesenseofone’sownbodyon side that’soppositetotheparietalinjury o Inferior parietal lobule (Primary vestibular cortex) ▪ Spatial orientation, self-motion proprioception ▪ Separated into: Supramarginal Gyrus – near the lateral sulcus o Language processing, particularly phonological processing (speech sounds) and reading  Angular Gyrus – adjacent to supramarginal gyrus and near the posterior part of the lateral sulcus o Associated with language processing and reading comprehension, as well as cross-modal integration of sensory information Insula Lobe – deep, hidden below lateral fissure; Part of cerebral cortex Involved in taste, emotion Emotional component of pain (depression) Temporal Lobe – processing auditory information, language, and certain complex functions Lateral fissure – separates it from the frontal and parietal lobes Superior temporal gyrus – runs along superior aspect of temporal lobe o Our ability to both hear and interpret what we hear is processed o Higher-level auditory processing o Language processing, sound localization o Primary auditory cortex (Heschel’s Gyrus) – within superior temporal gyrus ▪ Processes auditory information, including sound perception and discrimination o Wernicke’sArea(Lhemisphere)– in the left posterior superior temporal gyrus ▪ Language comprehension and formulation of coherent speech Middle temporal gyrus – positioned between superior and inferior temporal gyrus o Associated with various functions, including language processing, visual motion perception, and attention Inferior temporal gyrus – adjacent to fusiform face area o Object recognition o Recognition of complex visual stimuli Fusiform Face Area (FFA) – ventral part of temporal lobe o Facial recognition and processing Hippocampus – deep within the temporal lobe, part of the limbic system o Formation of new memories and spatial navigation Parahippocampal gyrus – surrounds the hippocampus  o Memory formation, spatial processing, scene recognition Deep Structures: Basal Ganglia – group of interconnecting, interacting nuclei within the forebrain, diencephalon, midbrain o Play critical role in initiation and control of voluntary movements o Components: ▪ Forebrain component of basal ganglia: Caudate nuclei Lenticular (putamen and globus pallidus) nuclei ▪ Diencephalon – subthalamic nucleus ▪ Midbrain – substantia nigra Limbic Structures – drive-related, emotional behaviors, learning, memory o Amygdala + Hippocampus (both located in temporal lobe) White Matter – deep to cerebral cortex, important in connecting various cortical areas to each other o Association Fibers – interconnect areas within one hemisphere o Commissural fibers – connect the hemispheres ▪ Corpus callosum – separates R and L hemispheres Connects regions of almost all parts of cerebral cortex of the 2 hemispheres ▪ Anterior commissure: connects structures of olfactory pathway, frontal cortex, temporal pole and parahippocampal gyri ▪ Posterior commissure – connects language processing centers of both cerebral hemispheres o Projection fibers – carry information to and from the cerebral cortex ▪ Corona radiata is the largest set of projection fibers Bundled into the internal capsule → contains all the fibers traveling among the cortex, spinal cord, and deep forebrain structures  Diencephalon – several sets of paired structures on either side of the 3 rd ventricle; everything with“thalamus”initsname o Thalamus – largest structure, 2 egg-shaped nuclear masses ▪ “gatekeeper”tothecortex ▪ Critical processing station for all sensory information (except olfactory) on its way to the cortex ▪ Key roles in processing motor information ▪ Integrating higher order cognitive and emotional information ▪ Regulation of cortical activity o Hypothalamus ▪ Structurally part of diencephalon ▪ Functionally part of limbic system ▪ Coordination, integration of endocrine, autonomic, homeostatic function o Subthalamus – part of basal ganglia ▪ Important in modulating, integrating voluntary movement and muscle tone o Brainstem – Midbrain + Hindbrain CNS division caudal to the diencephalon Conduit through which all ascending and descending info between brain and spinal cord travel Cranial nerves – provide sensory and motor information to and from the head Reticular formation nuclei – diffuse nuclei that run along midline of brainstem o Integrates cardiovascular, respiratory, cortical activity and consciousness Midbrain – most rostral area o Anterior surface – large pair of cerebral peduncles o Posterior surface – 2 pairs of nuclei: superior and inferior colliculi ▪ Superior colliculi → visual reflexes ▪ Inferior colliculi → integrating center in auditory pathway o Cerebral aqueduct – connect the 3rd and 4th ventricles, found in dorsal area of midbrain o Important Internal Structures of the midbrain: ▪ Red nucleus ▪ Substantia nigra Hindbrain – comprises pons + medulla o Pons (Basal pons) ▪ Prominent anterior or basal pons consisting of: descending, longitudinal corticospinal fibers transverse pontocerebellar fibers → carry info from pontine nuclei to opposite cerebellum thorugh the middle cerebellar peduncles, which arise off the lateral surface of the basal pons ▪ Posterior surface 4th ventricle Superior cerebellar peduncles → contain cerebellar efferent fibers o Medulla – most caudal part of brainstem, merges at its most caudal end with the spinal cord ▪ Rostral portion of medulla Pyramids – descending corticospinal fibers 4th ventricle found on posterior surface Inferior cerebellar peduncles → found on posterolateral side; carry info from spinal cord and brainstem Olives – oval swellings on lateral surface of rostral medulla ▪ Caudal portion of medulla Anterior surface → Pyramids (corticospinal fibers) Posterior surface → prominent sensory tracts o Fasciculus gracilis o Fasciculus cuneatus  Pyramids cross, forming the decussation of the pyramids, in the caudal medulla Ventricles – CSF fluid-filled cavities within the CNS Ventricles: Lateral ventricles – associated with telencephalon, one in each hemisphere o C shaped o Body o Anterior horn – deep in frontal and parietal lobes of forebrain; associated with basal ganglia, in particular the head of the caudate nucleus o Posterior horn— in occipital lobe o Inferior horn – temporal lobe Septum pellucidum – separates the lateral ventricles on the medial surface Interventricular foramen of Monro – connect each lateral ventricle with the 3rd ventricle 3rd ventricle – midline cavity between halves of the diencephalon o Thalamus and hypothalamus located on either side of 3 rd ventricle Cerebral aqueduct – connects the 3rd and 4th ventricles 4th ventricle – between cerebellum and brain stem (pons and medulla) o Continuous with the central canal of the spinal cord o One midline (foramen Magendie) and two lateral (foramen of Luschka) foramina allow CSF to flow into the subarachnoid space CSF: Fills ventricles and surrounds brain + spinal cord in the subarachnoid space Main function → support and cushion brain o Similar function to lymph system → continuous exchange b/w brain parenchyma and CSF o Periventricular neurons can secrete NTs (such as serotonin) into ventricular system Production of CSF: o Cerebrospinal fluids (CSF) secreted from ependymal cells of the choroid plexus; found in all 4 ventricles o Composition of CSF is like that of plasma, except that it has a minimal protein content o About 500 ml of CSF is produced daily Circulation of CSF o CSF moves from lateral → 3rd → 4th ventricle, pushed along by newly formed CSF o CSF flows flows out of the 4th ventricle through the 2 lateral foramina (Luschka) and 1 central foramen (Magendie) and into subarachnoid space or the central canal of the spinal cord o CSF moves through subarachnoid space until it reaches the arachnoid granulations (or villi) which protrude primarily into the superior sagittal venous sinus o Subarachnoid cisterns: ▪ Width of subarachnoid space varies b/c of irregular contours of brain ▪ Regions that contain more substantial amounts of CSF are called subarachnoid cisterns Reabsorption of CSF o CSF is reabsorbed through the arachnoid granulations into the superior sagittal venous sinus → reenters the venous circulation o Movement across arachnoid villi is passive, driven by difference in hydrostatic pressure b/w the CSF in the subarachnoid space and the venous blood in the superior sagittal venous sinus ▪ Villi act as tiny flaps so reverse flow I prevented if venous pressure exceeds CSF pressure Meninges – 3 layers of CT; Dural Venous Sinuses Dura Mater (2 layers) – connected to the skull, contains venous sinuses o Outer layer – periosteal layer o Inner layer – meningeal layer o These layers are tightly fused, but separate to form venous sinuses, into which the cerebral veins drain o Dural reflections: ▪ Falx cerebri – lies w/in the longitudinal fissure, separates the 2 cerebral hemispheres Contains: o Superior sagittal sinus – outer border o Inferior sagittal sinus – free border b/w 2 hemispheres ▪ Tentorium cerebelli – separates middle cranial fossa from the posterior cranial fossa Posterior cranial fossa (infratentorial compartment) contains cerebellum + brainstem Transverse sinus – runs along outer border of the tentorium o Venous blood drains through transverse sinus to the sigmoid sinus and from there to the internal jugular vein Straight sinus – along attachment of falx cerebri with the tentorium ▪ Falx cerebelli – separates 2 cerebellar hemispheres Occipital sinus ▪ Superior sagittal sinus, transverse sinus, occipital sinus all meet at the posterior pole of the skull at the confluence of sinuses ▪ Diaphragma sellae – covers the pituitary fossa in the base of the skull  o Innervation: ▪ Anterior and middle cranial fossae → trigeminal nerve (CNV) ▪ Posterior cranial fossa → vagus nerve (CNX) o Blood Supply: ▪ Middle meningeal artery Arachnoid mater – thinner, middle layer o Lines the dura, bridges over sulci of brain surface and cisterns of subarachnoid space o Small strands of collagenous CT, the arachnoid trabeculae, connect to pia mater o Bridging veins pierce the arachnoid to connect to the venous sinuses within the dura o Arachnoid granulations protrude into the superior sagittal sinus ▪ Responsible for reabsorption of CSF Pia Mater – thin, innermost layer o Adheres tightly to surface of brain parenchyma, following all gyri and sulci o Separates the brain from the CSF in the subarachnoid space o As vessels penetrate the brain parenchyma from the subarachnoid space, they enter through a sleeve of pia, the perivascular space, which extends until the vessel becomes a capillary Spaces between the meninges: o True epidural space – spinal cord!!! ▪ In the spinal cord, dura mater only has 1 meningeal layer ▪ Exists between meningeal layer of dura and the periosteum of the vertebrae ▪ Filled with fatty tissue + vertebral venous plexus o Epidural Space/Extradural space (potential)– b/w skull and dura mater ▪ Epidural hematoma – after traumatic injury to head w/ skull fracture to the middle meningeal artery, pressure of the arterial bleed separates the dura from the periosteum Collection of blood b/w skull + dura Develops slowly b/c it takes a lot of force to separate the dura from the skull o Subdural Space (potential) – bridging veins ▪ Subdural hematoma (shaken baby syndrome) – violent shaking of the head severs the bridging veins connecting the arachnoid to the Dural sinuses A venous hemorrhage  o Subarachnoid space (true)– contains CSF, cerebral arteries & veins ▪ Subarachnoid hemorrhage – hemorrhagic stroke or bleeding of an arterial aneurysm Tearing of cerebral arteries + veins Spinal tap shows RBCs in the CSF Hydrocephalus – “waterhead” Too much CSF is present in the brain Production, circulation, or absorption of CSF is impaired Communicating, nonobstructive hydrocephalus o Communication b/w ventricles and subarachnoid space is intact o Deficiency of absorption of CSF into the sinus ▪ Arachnoid granulations are damaged (e.g. bacterial meningitis) Noncommunicating hydrocephalus o Outflow from ventricles is obstructed o No communication b/w ventricles and subarachnoid space o CSF continues to be produced w/in ventricles, but cannot be circulated normally and be reabsorbed in arachnoid granulations o Results in enlargement of ventricles o Underlying cause – tumor or developmental anomaly Treatment: o Reestablishing normal cycle of production, circulation, reabsorption o Surgical implantation of a shunt from the ventricles to the peritoneal cavity where CSF Can be absorbed  Chapter 3 – overview of PNS Overview PNS composed of cranial + spinal nerves that link the brain and spinal cord w/ peripheral environment and visceral tissues o Cranial nerves → arise from brain + brainstem o Spinal nerves → arise from spinal cord o Peripheral nerves: o carry afferent sensory input to CNS o Carry efferent motor output from CNS → muscles for motor response Somatic vs Visceral Components: o Somatic ▪ Somatic sensory (somatic afferents) Carry information from somites (skin, skeletal muscle joints) ▪ Somatic motor (somatic efferents) Carry info to musculature derived from somites (skeletal muscle) o Visceral ▪ Visceral sensory (visceral afferents) Carry info from viscera of the body core (thoracic, abdominal, pelvic organs) ▪ Visceral motor (visceral efferents) = Autonomic nervous system Sympathetic – motor innervation to body core (viscera) and body periphery (blood vessels, sweat glands) Parasympathetic – only innervate the core (viscera) Ganglia = aggregations of nerve cell bodies outside the CNS o All sensory (BOTH somatic and visceral) have their nerve fibers in spinal ganglion o Visceral motor or autonomic nerves synapse in a peripheral ganglion The Peripheral Nerve: Organization of the peripheral nerve o Peripheral nerves are arranged in bundles called fasciculi o 3 layers of CT sheaths: ▪ Epineurium – external layer, vascular CT surrounding the nerve fascicles ▪ Perineurium – surrounds each individual fascicle ▪ Endoneurium – coats individual axons o May contain somatic and visceral sensory (afferent) fibers as well as somatic visceral motor (efferent) fibers  Classification of peripheral nerve fibers: o o Classification based on conduction velocity uses letters A,B,C ▪ A – the fastest o Classification based on axon diameter → used only for sensory fibers; uses roman numerals I, II, III, IV ▪ I – largest diameter Sensory Receptors – The only receptors to be reviewed: spindles and golgi tendon organ Proprioceptors – signal awareness of body position and movement to muscles, tendons, joints Muscle Spindles – detect muscle length/stretch, found dispersed throughout all skeletal muscles o Proprioceptive organ of skeletal muscle o Gamma reflex loop o Structure: ▪ Composed of a few intrafusal muscle fibers and nerve endings surrounded by a CT capsule Extrafusal muscle fibers – generate force needed to move bones Intrafusal muscle fibers – sensory, monitoring muscle length and changes in length; contained within the muscle spindle capsule o Up to 12 intrafusal fibers enclosed within a CT capsule o Each intrafusal fiber comprises a noncontractile portion centered b/w 2 weakly contractile regions o Muscle spindles contain 2 types of intrafusal fibers: ▪ Nuclear bag fiber – swellcentrallytoforma“bag” containing numerous clustered nuclei  ▪Nuclear chain fiber – thinner, more numerous; nuclei form achaindownthefiber’slength o Muscle spindles – Sensory Transduction ▪ Signal via 2 types of sensory nerve afferents (Group Ia and Group II) Both classes have wide, myelinated axons to maximize signal conduction velocity Type Ia → innervate the middle portion of all intrafusal fibers (primary endings) o Coil around the central (equatorial) regions of both nuclear bag and nuclear chain fibers o Form primary muscle spindle receptors Type II → innervate nuclear chain fibers (secondary endings) o Endings located at the ends of nuclear chain fibers and some nuclear bag fibers o Form secondary muscle spindle receptors o ▪ When a muscle is stretched (limb extension) → intrafusal fibers are stretched → causes distortion of nerves that wrap around them Stretching activates mechanosensitive cation channels, resulting in depolarization and increased afferent nerve firing frequency ▪Motor innervation to intrafusal fibers come from gamma motor neurons Conduct more slowly than the alpha motor neurons o Muscle Spindles – Regulation ▪ Intrafusal fibers are contractile, but do not contribute significantly to muscle force development Contractile portion serve only to shorten the fiber during muscle excitation and keep the central, sensory portion taut as muscle contracts Maintain tension → allows intrafusal fibers to continue functioning as stretch sensors through the contraction ▪ Alpha-gamma coactivation Alpha and gamma motor neurons fire simultaneously → spindle shortens in parallel with the body of the muscle when the muscle contracts  Combination of muscle spindles and their associated gamma-motor neurons constitutes a fusimotor system o Muscle Spindle Density: ▪ Muscles that require precise movement → high density of muscle spindles Extraocular muscles, finger muscles ▪ Gross motor movements → low density of muscle spindles Leg movements Golgi tendon organs – detect muscle strength, tension; found at tendon-muscle junction o Monitor the amount of tension that develops in a muscle when stretched passively or when it contracts o Structure: ▪ CT capsule filled with collagen fibers that are interwoven with group Ib sensory nerve endings ▪ Type Ib nerve afferents are myelinated to increase signal conduction rates Detect deformation of the capsule fibers resulting from tension in the tendon o Spinal Reflexes Reflex Arcs: o Sensory stimulus initiates motor response directly o Example: ▪ Withdrawal reflex triggered by touching a hot stove or stepping on a sharp object o Mediated by spinal cord, where sensory neuron synapses and activates a motor neuron  o Myotatic-stretch reflex (stretch reflex or deep-tendon reflex) – MONOSYNAPTIC o Initiatedbystretchingamuscleandcausecontractionofthesame“homon muscle o Example: ▪ Contraction of the thigh (quadriceps) muscles caused by tapping the patellar ligament Tapping the patellar ligament → stretches the quadriceps → activates spindles buried within Sensory signals carried by type Ia nerve afferents to spinal cord, where they synapse with and excite alpha-motor neurons innervating the same muscle Muscle contracts reflexively, leg extends, and foot jerks forward o Designed to resist inappropriate changes in muscle length, important for posture o Reciprocal innervation  ▪ Ia interneuron is activated by the same Ia afferent signal that caused the quads to contract ▪ Interneuron synapses w/ and inhibits the alpha-motor neurons that innervate the hamstring muscles, allowing the leg to extend w/o resistance ▪ 2 or more sets of muscles oppose each other around a joint (e.g. flexors and extensors) Activate the agonist Inhibit the antagonist Inverse myotatic reflex (Golgi tendon reflex) – POLYSYNAPTIC o Activates whenever a muscle contracts and GTOs are stretched o Type Ib afferents from GTOs synapse with Ib inhibitory interneurons upon entering spinal cord ▪ When activated, they inhibit alpha-motor output to the homonymous muscle o Excitatory interneurons simultaneously activate alpha-motor output to the heteronymous muscle o Important for fine motor control, maintaining posture o Flexion and crossed-extension reflex – POLYSYNAPTIC o Stepping on a thorn or injurious objects precipitates 2 urgent actions: ▪ 1) withdraws the foot from the source of the pain (leg flexion) ▪ 2) braces opposing limb so that weight can be transferred while still maintaining balance o 3 Stages: ▪ 1) Stimulus (pain) sensation ▪ 2) Wounded (ipsilateral) limb flexion ▪ 3) Extension of the opposing (contralateral limb)  o Chapter 5 – Spinal Cord Overview – SC Anatomy White matter vs. Gray Matter: o Spinal cord tracts located in white matter, which surrounds the gray matter containing nerve cell bodies o  o Butterfly-shaped distribution of gray matter: ▪ Anterior (ventral) horn – LMNs are located ▪ Posterior (dorsal) horn ▪ Lateral horn – visible at: Sympathetic spinal cord levels T1-L2 Parasympathetic levels S2-S4 UMNs vs LMNs: o Upper motor neurons – motor neurons in the cortex o Lower motor neurons – motor neurons in the anterior horn spinal cord, which innervate muscles Spinal cord divided into 31 segments; pair of spinal nerves associated w/ each spinal segment o 8 cervical segments – nerves (C1-C8) o 12 thoracic – (T1-T12) o 5 lumbar – (L1-L5) o 5 sacral – (S1-S5) o 1 coccygeal o Each spinal nerve contains both sensory and motor info. Sensory (afferent) info: o Sensory cell bodies lie in the dorsal root ganglion of each spinal nerve o Enters spinal cord through posterior sensory root Motor info: o Leaves spinal cord through the anterior motor roots LMNs – located in anterior horn at each spinal level Autonomic fibers o Efferent autonomic fibers: ▪ Cell bodies in lateral horn Leave the spinal cord through the anterior root o Afferent autonomic fibers ▪ Travel with somatic afferents through the posterior root Each spinal nerve is composed of: o Posterior roots (sensory) o Anterior roots (motor) o Roots come together in the intervertebral foramen, where the spinal ganglion is located o Mixed signal emerges from intervertebral foramen, it divides into” ▪ Anterior rami – supplies anterior aspect of the body  ▪ Posterior rami – supplies posterior aspect of body Surface Anatomy of the Spinal Cord: Cauda equina – posterior and anterior roots that travel through the lumbar cistern from the end of the spinal cord at L1-L2 to their respective vertebral levels o No spinal cord here; only nerve portion that exits below Spinal cord ends at the conus medullaris Is attached to dorsum of the first coccygeal segment by the filum terminale Longitudinal Fissures & Sulci o Anterior median fissure – entire anterior surface and length of spinal cord ▪ where anterior spinal artery can be found in subarachnoid space ▪ divides the anterior surface of the spinal cord in 2 halves o Anterior white fissure – deep to anterior median fissure ▪ Where some sensory and motor fibers cross the midline o Posterior median sulcus – separates posterior surface of spinal cord into 2 halves o Posterolateral sulcus – marks entry of posterior sensory rootlets of spinal cord o Anterolateral sulcus – site of exit for anterior motor rootlets o Spinal Meninges 3 layers: o Dura mater – outermost layer ▪ Single layer continuous w/ inner layer of cranial dura ▪ Dura forms the dural sac, surrounding the entire spinal cord, extends to S2 ▪ Lumbar cistern – space between L1-L2 and S2 o True epidural space – separates dura from periosteum of vertebral column ▪ Filled with fat and vertebral venous plexus  o Arachnoid mater – ballooned out against the dura o Subarachnoid space – filled with CSF, spinal blood vessels are suspended in arachnoid trabeculae in this space o Pia mater – adheres to surface of spinal cord ▪ Gives off the paired denticulate ligaments → pierce arachnoid and attach to dura Separates anterior and posterior rootlets Spinal Nerves: Dermatomes – each segment of spinal cord innervates a specific area of skin o Posterior roots o 8 cervical segments – nerves (C1-C8) → arm o 12 thoracic – (T1-T12) → torso o 5 lumbar – (L1-L5) → leg o 5 sacral – (S1-S5) → perineum o 1 coccygeal Myotome – sum of all muscle fibers supplied by a single spinal nerve o Anterior spinal roots provide motor control to the muscles Internal Structure of Spinal Cord Gray matter is localized centrally and surrounded by white matter o Gray matter – nerve cell bodies ▪ Posterior horn -- sensory neurons Discriminative touch, proprioception – do not synapse in posterior horn, but ascend in the ipsilateral posterior columns Pain, temp → enter posterior horn and then ascend or descend several spinal levels in Lissauer tract o Synapse in Lamina I and in the nucleus proprius (laminae III, IV) o Nucleus propius extend processes in the substantia gelatinosa (lamina II) ▪ Where pain modulation occurs before impulse travels to higher cortical centers ▪ Anterior horn – lower motor neurons (alpha-motor neurons) and Renshaw cells (interneurons) ▪ Lateral horn – preganglionic visceral motor cell bodies of sympathetic (T1-L2) and parasympathetic (S2-S4) are located  o Rexed Laminae – Dorsal Horn ▪ Lamina I – Lissauer’stract(dorsolateralfasciculus) Posterior horn of spinal gray matter Axons from dorsal root ganglion cells carrying pain and temp ▪ Lamina II – substantia gelantinosa (pain modulation) Posterior horn of spinal gray matter Numbs pain; personal pain dr. ▪ Lamina VII (C8-L3) – Clarke’sColumn or the nucleus thoracic or dorsalis Origin of spinocerebellar tract Most anterior part of posterior horn and lateral horn Important relay station for nonconscious proprioceptiong going to the cerebellum White Matter – neuronal axons o Consists of: ▪ Ascending tracts – sensory ▪ Descending tracts – delivering motor information to LMNs o White matter divided into 3 columns or fasciculi: 3 White matter Spinal Columns/Tracts: o Posterior (Dorsal Column): ▪ Fasciculus cuneatus – Sensory (fine touch, vibration, proprioception from ipsilateral upper limb (above T6) ▪ Fasciculus gracilis – Sensory (fine touch, vibration, proprioception) from ipsilateral lower limb (below T6) o Lateral Column – where major ascending and descending tracts are located ▪ Spinocerebellar tract – proprioception from limbs to cerebellum ▪ Lateral corticospinal tract – motor info from cortex → ipsilateral anterior horn cells Contains UMNs that synapse with the LMNs in the anterior horn Main motor tract to spinal cord, lateral corticospinal tract descends from the forebrain, having crossed in the brainstem to reach the LMNs at each spinal cord level at the anterior horn UMNs cross in the brainstem ▪ Anterolateral (spinothalamic) tract – sensory (pain, temp, crude touch) from the contralateral side of the body o Anterior (Ventral) Column: ▪ Anterior corticospinal tract – motor to ipsi- and contralateral anterior horn (mostly axial musculature) Cross over at the anterior white commissure level of the spinal cord at which they innervate the LMNs Most of innervation to trunk is bilateral Allow for maintaining posture during upright gait  o Blood Supply to Spinal Cord Comes from 2 sources o Vertebral-basilar system o Segmental arteries