Lectures 4-5 NROSCI 1011
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This 13 page Class Notes was uploaded by Alexis Gray on Monday September 14, 2015. The Class Notes belongs to NROSCI 1011 at University of Pittsburgh taught by Susan Sesack in Summer 2015. Since its upload, it has received 23 views. For similar materials see Functional Neuroanatomy in Neuroscience at University of Pittsburgh.
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Functional Neuroanatomy NROSCI 1011 Neuroembryology Urge and urge and urge Always the procreant urge 0f the world Out of the dimness opposite equals advance Always substance and increase always sex Always a knit of identity always distinction Always a breed of life Walt Whitman Leaves of Grass Zona pellucida General Features of Neural Development An egg is released by the ovary during Uterus ovulation and is fertilized by sperm in the fallopian tubes 2cell stage First cleavage Oviduct 39 OOOO39 a is formed day 5 that implants into the uterine wall The dividing cells reposition 39 and become unequal gastrulation Which a marks the beginning of differentiation Cells in the zygote divide until a blastocyst 39 Early stage of implantation whereby cells become fated to different tissue types BLASTUE H ST POI L t The outer cells become the placenta The Sigig 39 O inner cell mass becomes the embryo and TU IiP D tEm 513m EB FEM fetus Stem cells before the blastocyst are WESTE aquot l I gal totipotent and can become any tissue in O OO the body Stem cells of the inner cell Embaryqniemm cell mass are pluripotent and can become ES mm any tissue except the placenta 1 39 Skin Spina39m rdv Tailends 7 l OO O Chur lgnlc VII CHE PNS Heme LIVEr 3km Elli Amniotic fluid i Stalk H Muiliipeient stem cells Digestive I tract quot Heart 39 u O O O Ch ri ni Some blastocyst cells invaginate caus1ng three distinct germ layers to form in the embryo The E ectoderm outer becomes the skin and nervous system The mesoderm middle becomes the body a OOOOEOOOOOOOOOOOOEOOOO structure ie skeleton muscle and connective tissue and ehdoderm inner becomes the internal organs y m Ectoderma a Mesoderm The head process in the early ectoderrn is induced to thicken by the notochord in the underlying mesoderrn The thickened ectoderrn forms the neural plate which starts to role up and is surrounded by the neural folds Through the process of neurulation these structures become respectively the neural tube early CNS and neural crest early PNS Neurulation begins with the thickening of the neural plate and ends with the closure of the neural tube at the neuropores V The formation of the neural tube creates a midline axis the neural groove Structures close to this are considered medial in position while structures further away are lateral A EQHLY NEuaum Neural plate Neural fold GEES Longitudinal SECUQW sectian r quot N r l r 39 39 RH b i H aura pate g g FFF Notoohoro x Mesooerrn Endoderm Ectooerm Neural tolrzl Neural crest Neuralcrestcells v Motoehoro Neural tube Migrating 3 p neural crest cells Figure 1316 Neurulation Formation ot the Future Nervous Sys tem Ea to The events of neurulation or neural tube torrnation are easier to envision by considering the upper surtaoe at an Neural tube embryo out in half to a The neural plate on the embryos dorsal surtaoe rolls inward forming first a neural crest and then a fused neural tube E Neurulation creates a thicker anterior or cephalic head end Which Will become the brain and a thinner posterior or tail end that Will become the spinal cord The neural tube remains open at these neuropores for several weeks The anterior neuropore then closes at 24 days While the posterior neuropore closes at 26 days After fertilization Neural tube defects Failure of the neural tube to close at the anterior neuropore causes anencephaly an no la enkephalos brain Gr Failure of the neural tube to close at the posterior neuropore causes spina bifida Adjacent to the developing neural tube are segmented collections of tmesodermal cell called somites They Will make up the skeleton muscles and connective tissue and each somite Will eventually develop connections With individual spinal cord segments This segmented organization of the PNS re ects our evolution from simpler segmented organisms Neural plate Ectoderm Neural groove Neural tube Neural crest Spinal cord white matter Spinal cord Central canal gray matterxf Iquot Brain Spinal cord Features of the Neural Tube and Neural Crest Cells of the neural crest give rise to sensory neurons of the PNS and postganglionic autonomic motor neurons They also give rise to Schwann cells and meningeal cells Cells of the neural tube give rise to somatic motor neurons preganglionic autonomic motor neurons and all interneurons They also give rise to astrocytes and Oligodendrocytes Cells from the neural crest give rise to the PNS Cells from the neural tube gives rise to the CNS Multipolar postganglionic motor neurons of ANS Pia mater cells Bipolar sensory neurons AraChnold cells Chromaffin cells of adrenal medulla Schwann cells Neural Crest Pseudounipolar sensory neurons Neu rat Tu 39 Somatic skeletaI Motor neurons Multipolar preganglionic motor neurons of ANS Oligodendrocytes Astrocytes Interneurons functioning in motor control All other interneurons Interneurons functioning in sensory processing Neuronal Outgrowth Migrating Neurons develop from the neuroepithelium in the ependymal layer lining the central canal of the neural tube Migrating neurons are guided to their appropriate positions by the fibers of radial glial cells When their job is done the radial glia will differentiate intoastrocytes NEURON MIGRATION A cross sectional view of the occipital lobe which processes vision of a threemonthold monkey fetus brain center shows immature neurons migrating along glial bers from the inner to the outer surface These neurons make transient connections with other neurons before reaching their destination A single migrating neuron shown about 2500 times its actual size right uses a glial ber as a guiding scaffold To move it needs adhesion molecules which recognize the pathway and contractile proteins to propel it along Radial glial fibers Outer surface Migrating neuron Migratin w zona 39 Inner surface Farthest out The early neural tube consists of three layers or zones the ependymal mantle and marginal zones In the spinal cord neuronal migration ends in the mantle layer which will become gray matter in the adult Cells that will become motor neurons will send their axons out through the marginal layer Cells that will become sensory neurons whose soma lie outside the cord E will send their axons through the marginal layer into the mantle layer Hence in the spinal cord white matter marginal layer develops external to gray matter mantle layer In the brain neuronal migration continues into the marginal layer In the cerebellar and cerebral cortices migrating neurons form additional sublayers within the marginal zone The inner part of the marginal layer contains the descending axons of these cells and will become white matter The gray matter develops external to white matter exactly opposite to the spinal cord E B CORD QR Migrating neuroblasts MEDULLA 7 area quot 3 a a 5 a g r Zr y yew a a emit a F za 39 o a 0quot 63 pixvr egg a bug 523 V Central canal and lts 43 57 n 453 39 r aetiT af u 2 1 ut t ezz rz J Ependymal Mantle zone Marginal zone zone gray matter white matter Pia mater J External limiting Pial membrane cell Developing neural tube Migrating A neurohiast Mi ratin neuroblasts C CEREBELLUM g g 7 7 macr 5 36363 eve 355 1 9 7 4e 7 Ef e 55 raggegae 4 33 r r 333 ne er11 39 i V i 3945 T 1 39 i 391 7 I Ependymal Mantle Future Granular Ependymal Mantle Marginal zone zone white and Golgi a zone Zone zone matter cell layer l39 Internal limiting d N 39 membran quot y E I Pia mater e cell layer Molecular Purkin layer D CEREBRUM Migrating neuroblasts Margmal zone 7139 3963 ea f a awn x was quot39Q iia i 39 3 Gaga a on 4 H a ml H H I quotau39 All Pia mater o39 a a c9 gig 36 t 7 hquot 0 lt59 Q e t r Ependymal Mantle Future E 3 zone zone White E 395 7 e x u matter 5 g 3 a 39E 5 Q gt A u E E x 7 i Marginal zone FIGURE 16 Differentiation of the walls of the neural tube A Section of 5week human neural tube showing three zones ependymal mantle marginal B Section of 3month spinal cord and medulla showing retention of the original tripartite organization CD Sections of 3month cerebellum and cerebrum showing modi cation of tripartite structure caused by the migration of neuroblasts to speci c regions of the marginal zone After Crelin 1974 The neural tube at 46 weeks develops a limiting groove the sulcus limitans which divides the upper dorsal alar plate from the lower ventral basal plate The alar plate contains interneurons that receive input from the axons of sensory neurons the cell bodies of the sensory neurons are derived from the neural crest and lie outside the neural tube The basal plate contains the cell bodies of motor neurons The sulcus limitans and its division of sensory dorsal and motor ventral structures continues into the brainstem but not the diencephalon ventral basal motor efferent dorsal alar sensory afferent Receives AIar plate afferent Root plate Mantle layer Marginal layer Sl nals Central Dorsalroot 7 g canal li fi39tgi ganglion Basal plate 7 Neural crest A FlOOT lplale NeurTSjeItrhehal r r quot Central FIGURE AA The alar and basal plates evolve into sensory and motor regions respectively The line that divides the two areas the sulcus limitans is an important referential landmark that Basal late extends from the spinal cord through the mesencephalon A week 6 By the sixth week Dorsal root B p the sensory ganglion developing from the neural crest sends axons into the alar plate sensory region of the CNS while at the same time motor neurons in the basal plate extend ax ons out of the CNS B The sensory ganglion extends peripheral axons that meet motor axons leaving the CNS loined they form a spinal nerve that contains both afferent sen sory and efferent motor components C Dorsal horn Outgrowing motor 39 39 neurons Central Trunk of s inal nerve p Ventral horn Ventral root motor Development of the Brain The expansion of the brain in the developing embryo is called encephalization At 4 weeks there are three prominent bulges or vesicles that will form major divisions the prosencephalon mesencephalon and rhombencephalon Forward Middle Hindbrain At 5 weeks the prosencephalon and rhombencephalon divide further to create a total of ve 395 vesicles telencephalon cerebral cortex and basal ganglia diencephalon thalamus and hypothalamus mesencephalon metencephalon pons and cerebellum and myelencephalon medulla The optic vesicle rudimentary eye and retina emerges from the diencephalon The retinal sensory neurons are developed from the neural tube only sensory neurons not from neural crest The infundibulum connects the pituitary gland to the diencephalon The rhinencephalon rhin nose buds off the telencephalon and will form the olfactory bulb in the adult At 7 weeks the brain shows the developmentof the rhinencephalon A Three vesicle stage B Fivevesicle stage Telencephalon Prosencephalon Lateral VentrICie Diencephalon Forebrain Mesencephalon Neural retina Rhombencephalon 0 Lens Mesencephalon gtMidbrain Third ventricle mldbram Cerebral aqueduct Metencephalon pons and I Caudal neural tube cerebellum Hmdbra39n Fourth ventricle Myelencephalon medulla Spinal cord Central canal C P onUne Ce hailC egure exure Cervrcal Cephalic Cervrcal flexure flexure tlexure Figure 522 Successive stages in the development of the neural tube A Threevesicle stage At early stages of development only early structures and the mature nervous system are summa three brain vesicles are present rized in Table 52 1 B Five vesicle stage At later stages two additional vesicles C The positions of the cephalic pontine and cervical flexures form one in the area of the forebrain 1a and lb and the other in the hindbrain 3a and 3b The relationships between these Within the developing vesicles are cavities that Will become the ventricles that circulate cerebrospinal uid lateral telencephalon third diencephalon cerebral aqueduct mesencephalon fourth met and myelencephalon central canal spinal cord The embryo develops in a curved position With three bends or exures cervical between the hindbrain and spinal cord cephalic between the midbrain and hindbrain and Wwithin the hindbrain Only the cephalic exure persists in the adult brain causing it to have a curved longitudinal axis The basal plate is the source of motor neurons After the mesencephalon there are no more motor neurons and thus the basal plate ends The sulcus limitans divides alar and basal plates Where the basal plate ends the sulcus limitans ends A shallower groove the hypothalamic sulcus lies within the di and telencephalon and divides dorsal structures with sensory function from ventral structures with motor function alar plate metencephalon By 3 months the telencephalon starts to grow more than the other vesicles eventually mesencephalon E surrounding them in a backwards twisted C shape The ventricles undergo expansion and elaboration with the rest of the structures diencephalon To increase surface area and fit more cells the sulcus limitans myelencephalon Hypothalamic sulcus O asal plate cortex folds in on itself producing many 39 fund39bu39um Basal plate ends at the convolutions and a nearly adultlike pattern mesencephalon and at birth te39encepha39on diencephalon junction Excessive alcohol consumption during the 25 days 40 days 50 days 100 days later phases of encephalization leads to microcephaly and mental retardation which characterizes fetal alcohol syndrome Cells that have already migrated to their adult positions continue to develop through the growth of dendrites axons and synaptic connections These processes continue until puberty when synapses begin to decline through a process known as pruning 5 months 6 months 7 months 8 months 9 months Functional Neuroanatomy NROSCI 1011 Gross Structure Spinal Cord Dorsal Rostral Caudal Ventral Orientation in the Nervous System There are several important anatomical terms denoting 7 r position and orientation They are simple for quadrupeds whose nervous systems have a straight longitudinal axis Dorsal Back Up Superior Ventral Belly Down Inferior PM W Rostral Nose In front Anterior 39 Caudal Tail Behind Posterior anteriOr posterior For humans persistence of the cephalic exure gives the nervous system a bent longitudinal axis with quot v 39 the spinal cord and brainstem lying along a anterior postcri or inferior different part of the axis from higher brain centers Dorsal Structures above the midbrain are horizontal to the ground 53121111 Caudal structures below the midbrain are perpendicular to the ground Rostra39 mm i I s f 1 Ventral Above the midbrain Below the midbrain quot 39 Anterior rostral ventral infgriorl Posterior caudal dorsal Arrows I Superior dorsal rostral are ShlftS 90dg to left Inferior ventral caudal coronal Xi gi r 533212110 planes A Horizontal H Caudal Planes for Viewing the Nervous System The nervous system can be sectioned in different perpendicular planes A horizontal plane is parallel to the longitudinal axis of the nervous system and cuts from side to side and front to back In the brain it is horizontal to ground in the spinal cord it is vertical to ground A coronal plane is perpendicular to the longitudinal axis of the nervous system and cuts from side to side and top to bottom In the brain it is vertical to ground in the spinal cord it is horizontal to ground A sagittal plane L sagitta arrow is parallel to the longitudinal axis and the midline of the nervous system It cuts from top to bottom and front to back A midsagittal section divides the brain into two hemispheres Anything lateral to the midline is parasagittal General Features of the Spinal Cord Neuronal migration during development of the spinal cord leads to an inner core of gray matter former mantle zone surrounded by an outer layer of White matter former marginal zone containing the axons of cells projecting out ie motor neurons or projecting in ie sensory neurons The sulcus limitans divides Ependymal zone Dorsal horn the spmal cord mto adorsal Dorsalfumculus Lateramniculus Sulcus limitans Alar plate sensory alar plate and a ventral motor basal plate This division persists in the adult gray matter Which is H shaped and has columns With dorsal and ventral halves a sensory Mantle zone Basal plate 39 Marginal zone Ventral funiculus Ventral horn Lateral horn l5 der1ved from the alar plate a Dorsal ramus Dorsal root Dorsal root Gray ramus ganglion communicans anterior horn derived from the basal plate The centrally directed axons of the sensory neurons make up the dorsal roots and terminate in the dorsal horn the soma of sensory Ventrammus spinal Ventralroot wmteragnus neurons are clustered in the communicans Fi 2 2 Develo ment of the Spinal Cord dorsal rOOt gangha AgThe walls of he neural tube rapidly increase in To Prtvmeb a thickness through cell proliferation Sulcus limitans in ganghon dicates the boundary between the basal and alar plates I l B The basal plates develop into ventral and lateral l V MOtOr neurons haVe thelr horns whereas the alar plates form the dorsal horns S m thtec soma 1n the ventral horn 1 trinfgangnon l l and their axons 1n the ventral roots A spinal nerve contains the peripherally directed axons of sensory and motor neurons and is formed by the merger of dorsal and ventral roots just as they exit the spinal column through the IE intervertebral foramen L fora to pierce The major branches rami L ramus branch of the spinal nerves contain both sensory and motor bers The thinner dorsal ramus innervates structures along the back or dorsal surface the thicker ventral ramus innervates structures on the front or ventral surface The thoracic and upper lumbar ie trunk regions of the cord contain a small intermediate lateral horn that contains the cell bodies of preganglionic motor neurons of the autonomic nervous system Their axons exit the ventral roots travel through spinal nerves and synapse on postganglionic motor neurons that innervate the smooth muscles of internal organs There are 31 pairs of spinal nerves each originating from a single 2 6 spinal segment and named for the vertebrae from which they 3 g emerge cervical neck Cl8 thoracic breast plate Tl12 cmmh 4 I lumbar loin LlS sacral sacred bone 815 and coccygeal ewes cuckoo s beak CXl 7 The dorsal and ventral roots extend the length of the spinal column 2 The spinal cord itself ends between the LlL2 vertebrae because of j l the more rapid growth of the vertebral column vs the spinal cord 2 during development In lower parts of the spinal column gholracic individual spinal cord segments lie well above the vertebrae where was 9 their dorsal and ventral roots eXit The dorsal and ventral roots that m exit the spinal column at lower levels stretch to form the cauda Termination oi spinal cord Cauda aquina amp equina surrounded by the cerebrospinal uid lled lumbar cistern This is the region from which spinal taps are drawnIn the newborn the lumbar cistern lies below the L3L4 vertebrae 3a Lumbar nerves Spinal cord 1st lumbar vertebra FIGURE 216 Cerebrospinal fluid is drawn from the lumbar cistern in a spinal tap Adapted from House Pansky and Siegel 1979 A The needle is inserted into the subarachnoid space ofthe lumbar cistern B Because the spinal cord ends rostral to the insertion point of the needle it remains undamaged during the spinal tap In this drawing of the caudal portion of the vertebral column and spinal cord the meninges have been omitted to better show the spinal rootlets in Pia mate the lumbar cistern over slpinal cord HQ Dura mater j Arachnoid j mater Dorsal root Q 4 ganglion D cistern FIGURE 215 The vertebral column grows longer than the spinal cord A side view and the detailed organization of the lumbrosacral spinal cord and vertebral column are shown at three stages of development Adapted from Pansky 1982 A Fetus at 3 months B Fetus at the end of 5 months C Newborn Cytoarchitecture of the Spinal Cord The composition cytoarchitecture of the spinal cord gray matter varies at different levels segments Neurons with similar size shape and function are clustered into longitudinal columns of gray matter that appear like layers in the coronal plane These Rexed39s laminae are the equivalent of spinal cord nuclei Layers I VI lie in the dorsal horn Neurons here process and relay sensory information Layers VIII and IX of the ventral horn contain somatic motor neurons Layer VII represents the intermediate lateral horn and contains preganglionic autonomic motor neurons Layer X surrounds the central canal Dorsal column The outer white matter contains myelinated axons that transmit information between the spinal cord and higher centers and 333 between different spinal segments These white matter bundles run the length of the spinal cord and are called columns funiculi the largest are subdivided into fasciculi They also form tracts named for Ventral column their points of origin and termination I VI Dorsal horn VII Intermediate zone VIII IX Ventral horn descending 7 The amount of White matter increases at upper levels of the quot cord ascending I The number of myelinated fibers ascending the cord he an carrying sensory information to higher brain centersbecomes greater at higher levels The number of myelinated fibers descending the cord ie carrying motor commands from higher centers becomes smaller at lower levels Hence the proportion of white to gray matter is higher at cervical levels than at sacral levels of the spinal cord The amount of gray matter increases at the cervical and lumbar enlargements The relative volume of gray matter also changes In both cervical and lumbar divisions of the spinal cord the gray matter bulges outward Lower cervical segments supply sensory and motor innervation to the arms while the lumbar segments supply the legs Thus where there are extremities there is more gray matter especially in the ventral horn In the thoracic and uppermost lumbar segments of the cord there are visible intermediate lateral horns containing the preganglionic motor neurons of the Cewica autonomic nervous system The lateral horns are most visible in thoracic segments because the ventral horns are quite small here Cervical 4 Cervical cord l l Individual spinal cord sections can be recognized as follows cervical largest size largest proportion of white matter large amount of gray matter for arms Thoracic 2 thoracic intermediate size intermediate Lateral hem high proportion of white matter very small gray matter especially the ventral horns prominent lateral horns lumbar intermediate size intermediate low proportion of white matter large igigrrgiizli39column amount of gray matter for legs sacral smallest size smallest proportion of white matter intermediate amount of gray matter Cervical 78 Thoracic cord Ventral horn Lumbar cord i Sacral cord Filum terminale 1 G Thoracic 12 Clarke39s nucleus Lumbar 5 Sacral 3 Sacral 4