Dr. Ashfaqur Rahman MBBS, M.Phil (Anatomy)Associate Professor and Head, Anatomy Monno Medical College
INTRODUCTIONNEUROANATOMY: THE STUDY OF THE NERVOUSSYSTEM.2 body systems control all the functions ofthe body-1. Nervous system- which works very rapidly2. Endocrine system- which works more or less slowly.Nervous system is also called ‘master system of thebody’.
Functions of the nervous system:1. Reception of sensory stimuli2. Integration of sensory information3. Coordination and control of motor activities4. Assimilation and storage of experiences5. Programming of basic instincts Memory Sensory stimuli Correlation Effectors
Classification of nervous system Anatomically:Functionally/physiologically: Central nervous system (CNS)-Brain and1. Somatic nervous system (SNS) spinal cord2. Autonomic nervous system (ANS) Functions: 1. Integration, processing and coordination of sensory data 2. Giving appropriate motor commands 3. The seat for higher functions Peripheral nervous system (PNS)- peripheral nerves and associated ganglia Functions: 1. Provides sensory information to CNS 2. Carries motor commands of CNS to the effectors
CELLULAR ORGANIZATIONThe tissue forming the nervous system is callednervous tissue, which is one of the 4 basic tissues ofthe body. Essentially nervous tissue is a cellular type oftissue, composed of 2 types of cells without ICM.Composition:1. Neurons/nerve cells-Excitable, non-dividing cell2. Neuroglia/glial cells-Non-excitable, dividable cellNeuroglia are 10 times more in number than neurons. Bloodvessels are also found within nervous tissue which providenutrition to the neurons and neuroglia.
Types of the nervous tissue: White matter- The nervous tissue which appears white. It Grey matter- The nervous tissue which appears Grey. It is is white due to presence of myelin and less blood supply. It has grey due to rich blood supply and absence of myelin. It has less rich blood supply because it does not cell bodies of the of contains contain cell bodies the neuron. neuron. Composition: 1. Cell bodies of neurons Distal myelinated portion of axons 2. Dendrites and proximal/initial (non-myelinated) portion of Supporting cells-neuroglia (fibrous axons, sometimes whole axons (also non-myelinated) astrocyte, intrafascicular oligodendrocyte, microglia) 3. Supporting cells-neuroglia (Protoplasmic Blood vessels (few) (supplying the neuroglia present in astrocyte, perineuronal oligodendrocyte, microglia) the white matter)Organization of(abundant) white matter- 4. Blood vessels grey and1. Primitive organization-inner grey matter, outer white matter- e.g. Brain stem and spinal cord.2. Modified organization-outer grey matter, inner white matter- e.g. Cerebrum and cerebellum.
Neuron-Structural & functional unit of nervous system Neuron doctrine: by Ramon y Cajal- 6 tenets in 1 sentence Neuron is the anatomical, genetic, functional, polarized, pathologic and regenerative unit of nervous system. 2 parts of neuron- 1. Cell body/soma/perikaryon 2. Process/neurite 2 types of neurite- 1. Axon 2. Dendrite Axon (& dendrite) is called nerve fiber.Collection of neuron (cell body) inside CNS is called NUCLEUS.Collection of neuron (cell body) outside CNS is called GANGLION.Collection of nerve fiber inside CNS (specially within spinal cord) iscalled TRACT.Collection of nerve fiber outside CNS is called NERVE (PERIPHERALNERVE).
Classification of neurons:According to polarity (number of neurites)/morphologicalclassification:• Bipolar neurons- Functionally sensory neurons. E.g. Multipolar neurons- Functionally motor neurons. E.g.• Unipolar (pseudounipolar) neurons- Functionally sensory neurons. hornNeuronsspinal cord, pyramidal cells of Anterior E.g. cells of of olfactory cells, neurons cranial Bipolar neurons of retina,DRG, neurons of sensoryof ganglia, neuronsPurkinje cells and cochlear (spiral) cerebral cortex, of ganglion) of cerebellar vestibular (Scarpa’s mesencephalic nucleus of trigeminal nerve. interneurons, neurons of autonomic ganglia. cortex, ganglion. Most of the neurons of CNS are multipolar type.
Classification of neurons:According to function: Sensory/receptor neurons- E.g. Neurons ofMotor/effector neurons- E.g. Anterior horn cells ofInterneurons/internuncial/intercalated/central/assocspinalneurons of sensory cranial ganglia, neurons of cells DRG, cord, pyramidal cells of cerebral cortex, Purkinjeiational/connectorneurons of autonomic ganglia.this type. neurons. >99.9% neurons are of mesencephalic nucleus of trigeminal nerve, bipolar neuronsof cerebellar cortex,E.g. Column cells of spinal cord.• retina, olfactory cells, neurons of vestibularof UMN (Scarpa’s• LMNganglion) and cochlear (spiral) ganglion.• Preganglionic• Post ganglionic• Primary• Secondary• Tertiary
Classification of neurons:According to length of neurites (axons)/according to size of neuron:Golgi type I neurons- (microneurons)- E.g. Granule cells and II neurons E.g. Anterior horn cells of spinalstellate cells of cells of cerebral interneurons. They ofcord, pyramidalcerebellar cortex,cortex, Purkinje cellsact asassociational/interneurons.cerebellar cortex. They act as relay neurons.
Classification of neurons:Other types: neurons (cell bodies):Locations ofDevelopment of neurons:1. Amacrine neurons of CNS1. Within gray matter1. CNS neurons- from neural tube2. Microneuronsmatter of CNS as nuclei2. Within white (7µM)3. Paraneurons (apolar neurons) from neural crest and2. Neurons of peripheral ganglia-3. Within peripheral ganglia ectodermal placodes4. Within olfactory epithelium, retina
Structure of a neuron:Cell body• Nissle body (substance/granules)/tigroid or chromodial substance• Neurofibrils• Centrosome• Axon hillockDendrites• Dendritic spine/gemmulesAxon• Parts • Preaxon/initial segment • Axon proper • Axon terminale (terminal part) • Telodendria • Terminal boutons/synaptic knob• Axolemma• AxoplasmEndoneuriumPerineuriumEpineurium
Difference between axon and dendriteNeurolemma/neurolemma sheath/sheath of SchwannSchimidt-Lantermann incisura/fissure and segment
Nerve fibersAccording to functions: are called nerve fibers.Axons (and dendrites) of neurons1. Motor (efferent) nerve fibersClassification:2. Sensory (afferent) nerve fibersAccording to presence of myelin sheath:1. Myelinated nerve fibers2. Unmyelinated nerve fibers- unmyelinated peripheral nerves are known as fibers of Remak Periphery
Nerve fibersCombined classification:Fiber Sub CV Diameter Function Myelintype type m/s mA 70-120 12-20 Motor (extra-fugal fibers of skeletal + muscle) 40-70 5-12 Sensory (touch, pressure, vibration) + 10-50 3-6 Motor (intra-fugal fibers of skeletal + muscle) 6-30 2-5 Sensory (temperature, pain-sharp & + localized)B 3-15 <3 Motor (preganglionic autonomic fiber) +C 0.5-2.0 0.4-1.2 Motor (postganglionic autonomic fiber) _ Sensory (temperature, pain-diffuse & deep)
Receptors (SENSORY)Biological transducers responsible for reception of anysensory stimulation and conversion of this stimulation intonerve impulse to be carried by nerve fibers are calledreceptors.Receptors are sensory nerve endings specialized forreception of stimuli and transforming them in the form ofnerve impulses (ref. Vishram Singh).
Classification: • According to location- Exteroceptors (cutaneous receptors)-from superficial structures like skin, superficial fascia Interoceptors-from viscera and blood vessels Proprioceptors-from muscle and joint • Functional classification- Mechanoreceptors Thermoreceptors Nociceptors Chemoreceptors Electromagnatic receptors • Anatomical classification-
Uncapsulated Free nerve ending Epidermis, cornea, gut, dermis, fascia, Pain, temperature,receptors tendon, ligaments, touch (crude), joint capsules, bone, periosteum, pressure perichondrium, dental pulp, tympanic membrane, muscle Tactile discs of Thick (hairless) skin-epidermis Touch and pressure Merkel/Merkel’s disc Hair follicle Thin (hairy) skin-dermis Touch receptor/Peritrichial plexusEncapsulated Meissner’s tactile Dermis of thick (hairless) skin, Touch (2 point TD)receptors corpuscle external genitalia, nipple Pacinian corpuscle Dermis, S/C tissue, joint capsules, Vibration and ligaments, peritoneum, pleura, pressure external genitalia, nipple Ruffini’s corpuscle Dermis of thin (hairy) skin Stretch End bulbs of Golgi- Genital skin Mazzoni End bulbs of Krause Mucocutaneous junctions, conjunctiva Temperature (cold) Neuromuscular spindles Skeletal muscle Stretch-muscle length Golgi tendon organ Tendons Compression-muscle length
Cutaneous receptors Joint receptorsSensory modalities Type of receptors Free nerve endings Ruffini’s corpusclesPain, touch and Free nerve endingstemperature Pacinian corpuscles Merkel’s discs Golgi tendon organ Peritrichial plexusPressure and vibration Meissner’s corpuscles Pacinian corpusclesDeep pressure Ruffini’s corpuscles
Neuroglia/Glial cells• But the basic difference is tissue of nervous They represent connectivethat neuroglia are• Neuroglia (except cellular supporting element of The non-excitable,microglia), like capable of division by times more numerous than system. They are 5-10 mitosis whereas neurons neurons, develop from NS is called neuroglia. neuroectoderm. are not. neurons.
B. Neuroglia of PNS (peripheral neuroglia):(some authors regard supporting cells of PNS are not neuroglia. They regard supporting cells of CNS as neuroglia)- • Schwann cell/neurolemmal cell/neurolemmocyte • Capsular cell/satellite cell/perineuronal cell/ganglionic gliocyte/amphicyte• Others: Pituicyte, Bergman glial cell, Muller cell
• Perivascular feet, forms BBBAstrocyteAstrocyte• Cell body and process contain intermediate Outer glial limiting membrane, forms pia-glial• Most numerous glial cell membrane filament, named GFAP (gliofibrils)• Star shaped (stellate) body with numerous• Source of development- Neuroectoderm (neural Inner glial limiting membrane, forms ependyma- radiating process glial membrane tube)• Fibrous astrocyte- found in white matter, each process is long, slender, smooth, not much branched. Number of filament numerous.• Protoplasmic astrocyte- found in gray matter, each process is shorter, thicker, more branched. Number of filament fewer.
Functions of astrocytes• Phagocytosis insulator by covering synapse• Structural support-for nerve cell bodies and fibers Form electrical Absorb neurotransmitters and limit actions Act asBBB• Replacementfor + from migration of young nerve gliosishelpof neurotransmitter cells• Act asbarrier K spreadECF nutrition of nerve• Formup trophicand for in for neurons Store a excess Take glycogen substances Secrete scaffolding cell during IUL
Blood brain barrierThe composite barrier that exist between blood in theComposition:Functions:1. Nonfenestratedbrain brain circulating harmful capillary endothelium and tight junctionsvessel and neurons of from is called blood brain1. Protection of between them.barrier. substances of blood.2. Continuous basement membrane of capillary2. Selective transport of substances from blood by endothelium.3. specialized foot processsystem. bodies) of astrocytes. Perivascular transport (and cell
Blood brain barrierThe barrier is absent in:Median eminence of hypothalamusPosterior pituitaryPineal bodyArea postremaOVLTIntercolumnar tubercleSubfornical organChoroid plexus
Oligodendrocyte (oligodendroglia)Functions of oligodendrocyte • Small cell body with few delicate process (hence• Intrafascicular/perifascicular oligodendrocyte- Formation oligodendro) • and maintenance of myelin sheath (medullary sheath) No intermediate and other filaments • around nerve fibers in CNS Location:• Perineuronal satellite oligodendrocyte- Surround nerve 1. gray matter around nerve cell bodies as satellite cell cell bodiesmatter in rows biochemical environment of 2. white and influence along myelinated nerve fiber • neuron. of development- Neuroectoderm (neural tube) Source
Microglia• Smallest of all neurogliaFunctions of microglia• They are part of MPS• Normally body with wavy branching process Small cell they are inactive- resting microglia that give off• numerous spine-like projections condition- Gitter cell- Enlarge and proliferate in disease• Possessphagocytosis, act as scavenger cells of CNS, act as help in amoeboid movement when activated.• Location: gray and white matter APC• Source of development- macrophage (mesenchyme). They migrate to CNS during fetal life.
Ependymal cell• Source of development- Neuroectoderm (neural tube).• Have no basal lamina. 1. Ependymocyte- cuboidal or low columnar shaped cell, with cilia and microvilli, line ventricles of brain and central canal of spinal cord. 2. Tanycyte- line floor of the 3rd ventricle overlying median eminence of hypothalamus, possess long basal processes. 3. Choroidal epithelial cell- cover surfaces of choroid plexus. Form blood-CSF barrier.
Functions of ependymal cell1. Ependymocyte- Help in circulation of CSF by ciliary beat. Absorb CSF by microvilli.2. Tanycyte- Transport chemical substances from CSF to hypophyseal portal system and play a part in control of hormone production by anterior pituitary.3. Choroidal epithelial cell- Production and secretion CSF from choroid plexus.
Blood CSF barrierComposition:The composite barrier that exist between blood in1. Fenestrated capillary endothelium.choroid capillary and CSF within ventricles of brain isFunctions: basement membrane of capillary2. Continuouscalled blood CSFbrain fromis a weaker barrier than1. Protection of barrier. It circulating harmful endothelium.blood brain barrier.3. substances of blood. Pale cell layer.4. Continuous basement of substances from blood by2. Selective transport membrane of choroidal epithelial cell. specialized transport system5. Choroidal epithelial cell and tight junctions (performing actual barrier function) between them.
Schwann Cells (Neurolemmocytes)Derived from the neural crest.Found only in the PNSResponsible for myelination inPNSOne Schwann cell forms myelinaround a segment of oneaxon, in contrast to the ability ofoligodendrocytes to branch andsheath parts of more than oneaxon.
Satellite Cells of Ganglia/Ganglionic GliocytesDerived from the neuralcrest.Form a covering layerover the large neuronalcell bodies in PNS ganglia.The satellite cells exert atrophic or supportiverole, but the molecularbasis of their support ispoorly understood.
SynapseClassification of synapse- between two or moreSpecialized areas of contacts1.neurons. Now-a days neuromuscular junctions are Chemical synapse2.also called synapse Electrical synapse.
Chemical synapse•Synapse where transmission of impulse occursStructure cleft (neuropil area) Synaptic of chemical 20nm through chemical substances called synapse-•neurotransmitters. Synaptic delay (0.5msec)• Presynaptic neuron• Enzymes• Presynaptic• Neurotransmitters- knob (synaptic/terminal) excitatory/inhibitory feet) (bouton terminale/end•• Receptors- (transmitter) Presynaptic excitatory/inhibitory vesicle (synaptosome)•• Parts of a receptor protein- Presynaptic • binding presynaptic membrane,component • ionophore component density, release site, voltage gated Ca ++ channel • 2 types-• Postsynaptic 1. ion channel- cation membrane, postsynaptic channel/anion channel density (synaptic or activator 2. 2nd messenger• subsynaptic web) EPSP/IPSP
Neurotransmitters/NeuromediatorsChemical substances secreted by presynaptic neuron at synaptic cleft of chemicalsynapse which transmit nerve impulse to the post synaptic neuron.Classification- • Principal1. Small molecule, rapidly acting transmitters Class I Acetylcholine- Both excitatory and inhibitory neurotransmitters Class II: The Amines Acetylcholine (nicotinic) Norepinephrine- Both excitatory and inhibitory Glutamate Epinephrine- Both excitatory and inhibitory GABA Dopamine- Both excitatory and inhibitory • Neuromodulators Histamine Serotonin- Inhibitory Acetylcholine Class III: Amino acids (muscarinic) GABA- Inhibitory Glycine- Inhibitory Serotonin Glutamate- Excitatory Aspartate- Excitatory Histamine Class IV NO Adenosine2. Large molecule, slowly acting transmitters Neuropeptides (Neuropeptides)
Structure:Ganglion in shape• OvoidCollection of (cell bodies of) neuron outside CNS is• Contain collection of cell bodies of neurons- called ganglion. or bipolar in case of sensory (pseudo)unipolar ganglion, multipolar in case of motor ganglion.• Each cell body is covered by a layer of capsular/satellite cells.• Each ganglion is covered by a connective tissue capsule. Structure of autonomic ganglionConnective tissue capsuleCell bodies of post ganglionic neuronsInterneurons – SIF cellsSatellite/capsular cellsNerve fibers-Pre- and postganglionic fibersand fibers traversing the ganglion without synapse
Classification Motor ganglion (Autonomic ganglion)Sensory ganglion (Somatic ganglion) Parasympathetic ganglion•Motor ganglion (Autonomic ganglion) • Cranial ganglion (cranial parasympathetic Collateral ganglia • ganglia) Sympathetic ganglion of C5 Trigeminal ganglion • ••Lateral (paravertebral) ganglia- Ganglionated Geniculate ganglion of C7 Ciliary ganglion ••sympatheticand spiral ganglion of C8 Vestibular trunk ganglion Pterygopalatine • ••Subsidiary and inferior ganglion of C9 Superior ganglia ganglion Submandibular •• Superior and inferior ganglion of C10 Otic ganglion Collateral (prevertebral) ganglia•• Spinal Superior mesenteric or within wall of • ganglion Terminal ganglia- close to ganglion • Inferior mesenteric • viscera root ganglion ganglion Dorsal • Aorticorenal ganglion (renal) Ganglia of cardiac plexus • Superiorof pulmonaryganglion Ganglia hypogastric plexus • •Terminal ganglia- Adrenal medulla Ganglia of myenteric plexus • Ganglia of submucosal plexus • Inferior hypogastric ganglion
MyelinationCNS-By Oligodendrocyte Of spinal cord-at 4th month of IUL, sensory fibers first Of brain-at 6th month of IUL, motor fibers firstPNS-By Schwann cell
Structure of a myelinated nerve fiberOf CNS- Axon Myelin sheathOf PNS- Axon Myelin sheath Neurilemma Basement membrane Endoneurium
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