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For the real amazement, if you wish to be amazed, is this process. You start out as a single cell derived from the coupling of a sperm and an egg; this divides in two, then four, then eight, and so on, and at a certain stage there emerges a single cell which has as all its progeny the human brain. The mere existence of such a cell should be one of the great astonishments of the earth. People ought to be walking around all day, all through their waking hours calling to each other in endless wonderment, talking of nothing except that cell.
Lewis Thomas (1979)
Nervous DevelopmentThis chapter will briefly introduce the key developmental principles associated with the formation of the nervous system and the relationships it forms with other body systems.
• You should be familiar with the basic structure of the nervous system – central nervous system consisting of brain and spinal cord and peripheral nervous system comprised of cranial nerves and spinal nerves.
• You should understand the basic design of the special senses – the eye and the internal ear.
• Understand the process of neurulation and the early development of the key components of the nervous system.
• Recognize how the neural tube and neural crest contribute to the formation of the central and peripheral nervous system.
• Understand the basic development of the eye from the neural tube, optic placode, and surrounding mesenchyme.
• Understand how the internal ear emerges from the otic placode and its association with the neural tube.
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Review of Nervous System AnatomyBe comfortable with the following basic anatomy
Basic structure of the nervous systemCentral nervous system
Brain
Spinal cord
Peripheral nervous systemCranial nerves
Spinal nerves
Autonomic nervous pathways
Basic eye anatomyFibrous tunic
Sclera
Cornea
Vascular tunicChoroid coat
Ciliary body
Iris
Sensory tunicRetina
Photosensitive layer
Pigment layer
Basic internal ear anatomyBoney labyrinth
Membranous labyrinthCochlear division
Vestibular division
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N e r v o u s D e v e l o p m e n t
Origin of Nervous SystemReview of neurulationNeural plate
Neural groove
Neural fold
Body ectoderm
Neural tube
Rostral neuropore
Caudal neuropore
Neural crest
Neural canal
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Development of the Neural TubeVentricular zoneNeuroblasts
Future ependymal glioblasts
Marginal zoneFuture white matter glioblasts
Astrocytes
Oligodendrocytes
Intermediate zoneNeuroblasts from ventricular zone
Differentiate into neurons
MesenchymeMicroglial cells
Dura mater
Crest cellsPia-arachnoid mater
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N e r v o u s D e v e l o p m e n t
Development of Spinal CordLateral wall intermediate zoneAlar plate
Dorsal gray horn
Basal plateVentral gray horn
Lateral gray horn
Sulcus limitans
Roof plate
Floor plate
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Peripheral Nervous System DevelopmentEstablishing the peripheral nervous pathways
Neural Crest CellsPseudounipolar sensory neurons
Cell bodies
Relation to neural tube
Relation to somite
Relation to gut tube
Autonomic postganglionic motor neuronsSympathetic trunk migrations
Sympathetic collateral migrations
Sympathetic adrenal migrations
Parasympathetic terminal migrations
Enteric migrations
Association with smooth muscle and gland cells
Sympathetic postganglionic
Parasympathetic postganglionic
Section depicting sensory neuron growth, left S2-S4, right T1-L2
Section depicting neural crest migration, left S2-S4, right T1-L2
Section depicting postganglionic neuron growth, left S2-S4, right T1-L2
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N e r v o u s D e v e l o p m e n t
Neural Tube CellsSkeletal motor neurons
Cell bodies
Relation to somite
Autonomic preganglionic motor neuronsCell bodies
Sympathetic preganglionic
Parasympathetic preganglionic
Association with migrating neural crest cells
Section depicting preganglionic neuron growth, left S2-S4, right T1-L2
Section depicting skeletal motor neuron growth, left S2-S4, right T1-L2
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Resulting Structure of Peripheral Nervous SystemEmbryonic migrations and neuronal connections
Section depicting complete neuronal development, left S2-S4, right T1-L2
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N e r v o u s D e v e l o p m e n t
Section depicting complete neuronal development for levels C1-C8, T3-S1, and S5-Co1
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Development of the BrainBrain vesiclesThree primary vesicles
Prosencephalon
Mesencephalon
Rhombencephalon
Five secondary vesiclesTelencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
Brain flexuresVentral flexures
Midbrain flexure
Cervical flexure
Dorsal flexurePontine flexure
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N e r v o u s D e v e l o p m e n t
VentriclesTelencephalon
Lateral ventricles
DiencephalonThird ventricle
MesencephalonCerebral aqueduct
Metencephalon and myelencephalonFourth ventricle
Wall of neural tube in brainExpansion of roof plate
Shifting of alar and basal plates
Addition of new cell columns
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Cranial Nerve DevelopmentSomitic motor cranial nervesBasal plate origin
Oculormotor nerve
Trochlear nerve
Abducens nerve
Hypoglossal nerve
Pharyngeal arch cranial nervesCrest, lateral horn, and new column origin
First arch - trigeminal nerve
Second arch - facial nerve
Third arch - glossopharyngeal nerve
Fourth and sixth arches - vagus nerve
Lateral plate mesoderm nerveAccessory nerve
Special sensory cranial nervesOlfactory nerve
Optic nerve
Vestibulocochlear nerve
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N e r v o u s D e v e l o p m e n t
Arch 1 Arch 2 Arch 3 Arch 4
Arch 1 Arch 2 Arch 3 Arch 4
Neural tube, notochord, prechoral mesoderm
Neural crest
Premuscular mesoderm
Muscle migration and development
Motor neuron development
Peripheral ganglia development
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Development of Parts of the BrainMedulla
Pons and cerebellum
Midbrain
Diencephalon
Cerebrum
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N e r v o u s D e v e l o p m e n t
Development of the EyeEye components from neural tubeOptic groove and vesicle
Optic stalk
Optic cupOuter layer of optic cup
Inner layer of optic cup
Intraretinal space
Eye components from surface ectodermLens placode
Lens pit
Lens vesicle
Mesenchyme and neural crest
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Development of basic eye componentsOptic cup derivatives
Outer layer of optic cup - pigment layer of the retina
Inner layer of optic cup - neural layer of the retina
Ciliary bodyEpithelium from optic cup
Smooth muscle from mesenchyme
IrisEpithelium from optic cup
Connective tissue from neural crest
Smooth muscle from optic cup epithelium
Lens vesicle derivativesSubcapsular lens epithelium
Primary and secondary lens fibers
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N e r v o u s D e v e l o p m e n t
Mesenchymal derivativesCentral artery of the retina and hyaloid canal
Tunica vasculosa lentisLens capsule
Suspensory ligaments of lens
Anterior and posterior chambers
Choroid and sclera
Neural crest derivativesVitreous humor
Choroid and sclera
Surface ectoderm derivativesExternal corneal epithelium
Conjuntiva
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Development of the EarKey componentsOtic placode
Otic pit
Otic vesicle
Morphogenesis of the otic vesicleDorsal utricular part
Endolymphatic duct and sac
Utricle
Semicircular ductsAbsorption focus
Ampulla
Ventral saccular partSaccule
Cochlear duct
Surrounding mesenchyme