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A sketch of the central nervous system and its origins
G. E. Schneider 2009Part 5: Differentiation of the brain vesicles
MIT 9.14 Class 9a
Autonomic nervous system structures
Autonomic nervous system • Overview of functions • Schematic overview • Formation of sympathetic ganglia from the
neural crest (REVIEW) • Sympathetic innervation pattern (thoracico-
lumbar system) • Cf. parasympathetic innervation (cranio-sacral
system); dual innervation of smooth muscles and glands.
• Chemical mediation at synapses: discovery by Otto Loewi in 1921.
Closure of neural tube; formation ofsympathetic ganglia
Neural plate Ectoderm Notochord
Neural groove
Neural tube and neural crest
Roof plate Alar plate
Basal plate Floor plate
Autonomic nervous system • Overview of functions • Schematic overview • Formation of sympathetic ganglia from the
neural crest • Sympathetic innervation pattern (thoracico-
lumbar system) • Cf. parasympathetic innervation (cranio-sacral
system); dual innervation of smooth muscles and glands.
• Chemical mediation at synapses: discovery by Otto Loewi in 1921.
Internal structure of spinal cord:Note the lateral horn
INTERNAL STRUCTURE OF THE SPINAL CORD
Dorsal RootFibers
Fasc.Gracilis
Nuc cornucommissuralis PosteriorSubstantia Gelatinosa
Nuc. Posteromarginalis
Zone of LissauerLat. Corticospinal Tr.
Nuc. Proprius Cornu DorsalisNuc. ReticularisNuc. Dorsalis (of Clarke)
Ant. Spinocerebellar Tr.Lat. Spinothalamic Tr.
Nuc. Motorii LateralisFasc. Proprius
Ant. Spinothalamic Tr.Vestibulospinal Tr.
Nuc. Motorii MedialisVentral Root Fibers
Internal Structure
Spinal Cord Segment C1
Segment C5
Segment C8
Segment T2
Segment T10
Segment L1
Segment L4
Segment S4
III
IIIIV
V
VI
VII
VIIIIX
IXIX
IX
X M
Figure by MIT OpenCourseWare.
xxxxx
xxxxx
xx
Smooth muscle: Glands; intestinal tract; blood vessels, erector pili (hairs); sweat glands.
Cardiac muscle
Dorsal root ganglion
Spinal nerve
Prevertebral ganglion, e.g., celiac
Paravertebral ganglion
Descending reticulospinal fibers
To striated muscles
Sympathetic nervous system axons, schematic section of spinal cord, thoracic level
Figure by MIT OpenCourseWare.
Sympathetic Innervation
Brodal) (P.
Autonomic nervous system • Overview of functions • Schematic overview • Formation of sympathetic ganglia from the
neural crest • Sympathetic innervation pattern (thoracico-
lumbar system) • Parasympathetic innervation (cranio-sacral
system); dual innervation of smooth muscles and glands.
• Chemical mediation at synapses: discovery by Otto Loewi in 1921.
Vagus nerve (10th cranial nerve)
Parasympathetic Innervation
(P. Brodal)
MESENCEPHALONVisceral Efferent OculomotorNucleus (Edinger-Westphal)
Oculomotor Nerve
Superior Salivary Nucleus
MEDULLAOBLONGATA
MEDULLAOBLONGATA
MEDULLASPINALIS(S3 - S4)
Pupillary SphinCiliary Muscle
Lacrimal Gland
Nasal & Palatal
Submandibular Sublingual Gla
Parotid Gland
PharynxEsophagusTrachea, BroncLungs
HeartStomachSmall IntestineLarge IntestineLiver, PancreasGallbladderLarge Intestine(Lower)RectumBladderGenitals
Ciliary Ganglion
Maxillary NerveIntermediateNerve
GreaterPetrosal Nerve Pterygopalatine
Ganglion
Facial Nerve
Dorsal MotorVagus Nucleus
Glossopha-RyngealNerve
ChordaTympani
Mandibular Nerve
Lingual Nerve
SubmandibularGanglion
Auriculo-Temporal Nerve
Otic GanglionTympanicNerve
Vagus Nerve
Ganglia &Plexuses
Pelvic NerveSympathetic Trunk
cter Muscle
Gland
Glandnd
hi
Figure by MIT OpenCourseWare.
Autonomic nervous system
• Overview of functions • Schematic overview • Formation of sympathetic ganglia from the
neural crest • Sympathetic innervation pattern (thoracico-
lumbar system) • Parasympathetic innervation (cranio-sacral
system); dual innervation of smooth muscles and glands.
• Chemical mediation at synapses: discovered by Otto Loewi in 1921 (REVIEW)
Autonomic pathways with
neurotransmittersshowing accelerator & decelerator nerves
of the heart
An advance in PNS anatomy in the late part of the 20th century:
The enteric nervous systemThe “little brain” in the gut: A semi-autonomous network that may contain as many neurons as the entire spinal cord.
In the wall of the intestine, this network contains multiple plexi:•Myenteric plexus (the outer plexus) •Submucous plexus (the middle plexus) •Villous plexus (inner plexus) •Periglandular plexus (inner plexus)
Innervation by vagus nerve
Cf. Cardiac Ganglion: Does the heart have a brain?
Various neurotransmitters are used in this system.
Levels of autonomic control
• The enteric nervous system shows autonomy at the lowest level, in control of the alimentary tract.
• Within the CNS, there are lower levels of control of the internal environment capable of some autonomy.
• Temperature regulation is a good example. – For this function, each higher level adds more
refinement.
Levels of control in the ANS: the temperature regulation systems
• Temperature is regulated by mechanisms operating at all levels: – spinal, – hindbrain, – midbrain, – hypothalamus of the ‘tweenbrain.
• Each higher level adds refinements: for endothermic animals, this means speed and a narrower range of target temperatures.
• See reviews by Evelyn Satinoff.
• For other functions, there is probably a similar hierarchy.
A sketch of the central nervous system and its origins
G. E. Schneider 2009Part 5: Differentiation of the brain vesicles
MIT 9.14 Class 9b
Differentiation of the brain vesicles: Introduction to hindbrain and segmentation
The encephalon* (brain)
• Hindbrain (rhombencephalon)• Midbrain (mesencephalon) • Forebrain (prosencephalon)
– ‘Tweenbrain (diencephalon) – Endbrain (telencephalon)
* “In the head”
The embryonic neural tube above the spinal cord
What are the "flexures" in the neural tube?(See, e.g., Nauta & Feirtag, pp 162-163)
The flexures of the developing neural tube’s rostral end, human
(From Nauta & Feirtag)
Figure by MIT OpenCourseWare.
Origin of the term “rhombencephalon”
What happens to the roof plate where the pontine flexure (bend) forms? (See, e.g., Nauta & Feirtag, p. 162)
Basic subdivisions,
c yonibrembe: tuneural
Where is the s?rhombu?tWhat is i
ents Studer:Remindd and narstde undshoul
re!gufi sih towkn
a. Spinal cord
b. Hindbrain (rhombencephalon)
c. Midbrain (mesencephalon)
d. ‘Tweenbrain (diencephalon)
e. Endbrain (telencephalon)
a. Spinal cord
b. Hindbrain (rhombencephalon
c. Midbrain (mesencephalon)
d. ‘Tweenbrain (diencephalon)
e. Endbrain (telencephalon)
a. Spinal cord
b. Hindbrain (rhombencephalon
c. Midbrain (mesencephalon)
d. ‘Tweenbrain (diencephalon)
e. Endbrain (telencephalon)
Forebrain
(prosencephalon)
Terminology:
What is the obex? Find it in the previous picture.
The hindbrain (rhombencephalon)topics
• Basic structural organization compared with spinal cord
• Basic functions • Cell groupings; origins • Sensory channels and the trigeminal nerve • The "distortions" in the basic organization
Basic organization:"a glamorized spinal cord"
• Alar and basal plates; widened roof plate (with widened ventricle – the 4th ventricle)
• No more law of roots; some cranial nerves are "mixed nerves" containing both sensory and motor components.
Cell groupings
Secondary sensory nuclei (cell groups) in the alar plate Motor nuclei (groups of motor neurons)
in the basal plate
• The arrangement can be understood as a simple modification of spinal cord organization.
Motor neuron cell groups
Embyonic spinal cord & hindbrain compared
Embryonic spinal cord (in cross section) Alar plate
Basal plate Ventricular zone Intermediate zone Marginal zone
Sulcus limitans
Alar plate
Basal plate
Embryonic hindbrain Secondary sensory cell groups in intermediate zone of alar plate
in intermediate zone of basal plate
Hindbrain functions• Routine maintenance: the support services area of the
CNS, for centralized control of spinal functions – Vital functions (control of breathing, blood pressure & heart
rate, & other visceral regulation) – Motor coordination (cerebellum, vestibular system) – Fixed Action Pattern generators: swallowing, vomiting,
eyeblink, grooming, smiling, frowning, righting, etc.– Widespread modulation of brain activity: sleep & waking;
arousal effects [See following illustrations] • Role in mammalian higher functions: movement
control for functions of more rostral brain systems– for speech (tongue, lip, breath control) – for emotional displays, especially in facial expressions – for eye movements
Neurons of the reticular formation
• “Isodendritic” core of the brainstem (Ramon-Moliner & Nauta)
• Neuropil segments • Axons with very wide distributions
• Contrast: isodendritic & idiodendritic
Dendritic orientation of reticular formation neurons in hindbrain, forming a series of neuropil segments:
Collaterals of pyramidal tract axons have similar distributions.For contrast, cells of the hypoglossal nucleus are also shown
Golgi stain, parasagittal section of hindbrain, young rat. From Scheibel & Scheibel, 1958
Figure removed due to copyright restrictions.
Neuron of hindbrain reticular formation: Axon has ascending and descending branches, each with widespread distribution of terminations
2-day old rat, Rapid Golgi stain, from Scheibel & Scheibel, 1958
Figure removed due to copyright restrictions.
Notes on hindbrain origins: definitions• Segmentation above the segments of the spinal cord: The
somitomeres & branchial arches in the mesoderm, and the rhombomeres of the CNS
• See Nauta & Feirtag, ch.11, p. 170, on the “branchial motor column” -- in addition to the somatic and visceral motor columns.
Visceral motor column
Somatic motor column
Branchial motor column
Sulcus limitans
Alar plate
Basal plate Reticular formation
Three segmented systems, 3-day chick embryo:somites, branchial arches, rhombomeres
Branchial arches of the mesoderm, innervated by the Trigeminal Motor & the Facial Nucleus and by Nucleus Ambiguus.
(Functions of Nuc. Ambiguus: swallowing and vocalization)
The branchial arches in humans form jaws, the auditory ossicles, the hyoid, and the pharyngeal skeleton including thyroid cartilage.
Wolpert, 2002 Fig. 4.24
s2
s10Limb Bud
Branchial Arches
b1b2b3b4
MidBrainr1
r2r3
r4r5
r6r7
r8
Rhombomeresof Hindbrain
Somites
s20
Figure by MIT OpenCourseWare.
The mesoderm below the head region becomes segmented:
Somites, 2-day chick embryo
(Photo from Wolpert, 2002, p. 22)
Figure removed due to copyright restrictions.
Somites, 2-day chick embryoPlease see:
. 2nd ed.Principles of DevelopmentWolpert, Lewis, et al. Oxford, UK: Oxford University Press, 2002, p. 22. ISBN: 0198792913.
Hox gene expression in the mouse embryo after neurulation
Genes underlying segmentationtopics
• Ancient origins of segmentation along the A-P axis, with corresponding nervous system differentiation
• The homeobox genes: What are they? • Examples of gene expression patterns
Homeobox genes in Drosophila, and
Figure by MIT OpenCourseWare.
uses of moemomoso chr in 4oupsgrgous o paral13
E 9.5 mouse embryos, immunostained using antibodies specific For the protein products of the indicated Hox genes. (Wolpert, 2002, fig. 4.11)
Figure removed due to copyright restrictions.Please see:Figure 4.11 from Wolpert, Lewis, et al. Principles of Development. 2nd ed.Oxford, UK: Oxford University Press, 2002. ISBN: 0198792913.
Hox gene expression along the antero-posterior axis of the mouse mesoderm
Hox gene expression along the antero-posterior axis of the mouse mesoderm
(Wolpert, 2002, fig. 4.12)
c5c6
c8c9
b1
b4
b5
b9b7
d3d4
d8
d9d10d11
d12d13
a1
a4
a5
a6a7
a10
a11
CervicalThoracicLumbar
Vertebral regions
Anterior
Anterior marginsof expression
SacralCaudal
Hox genes
Posterior
Figure by MIT OpenCourseWare.
Rhombomeres: the 8 segments of the rhombencephalon
(Scanning e.m. photo from Allman, 2000)
Figure removed due to copyright restrictions..Evolving BrainsAllman, John Morgan. "Scanning Electron Microscope Photo." In
New York, NY: Scientific American Library: Distributed by W.H. Freeman and Co., 1999.ISBN: 0716750767.
Gene Expressionand
Rhombomeres
(Lumsden & Krumlauf ’96)
r1r2
r2
r3
r3
r4
r4
r5
r5
r6
r6
r7
KreislerKrox-20
Sek-1Sek-2Sek-3Sek-4
EbkElk-LElf-2
Elk-L3Hoxa-1Hoxb-1Hoxa-2Hoxb-2Hoxa-3Hoxb-3Hoxd-3Hoxd-4Hoxb-4Hoxa-4
Fgf-3FollistatinCRABP-1
RAR αRAR β
Figure by MIT OpenCourseWare.
The hindbrain neuromeres (= rhombomeres): A) Expression of transcription factor genes; B) Fate of embryonic precursor cells injected before and after rhombomere formation
From Striedter (2005), p. 79
A) Gene Expression boundaries B) Lineage restriction boundaries
r1
r2
r3
r4
r5
r6
r7
hox
d4ho
x b2
hox
b3ho
x b1
krox
20
Figure by MIT OpenCourseWare.
MIT OpenCourseWare http://ocw.mit.edu
9.14 Brain Structure and Its Origins 9200Spring
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