MIT 9.14 Class 9adspace.mit.edu/bitstream/handle/1721.1/97100/9-14-spring-2009/... · Visceral...

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


neural crest • Sympathetic innervation pattern (thoracico-

lumbar system) • Cf. parasympathetic innervation (cranio-sacral



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


Sympathetic Innervation

Brodal) (P.



lumbar system) • Parasympathetic innervation (cranio-sacral



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


Autonomic nervous system

• Overview of functions • Schematic overview • Formation of sympathetic ganglia from the


lumbar system) • Parasympathetic innervation (cranio-sacral


• 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)


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




a. Spinal cord

b. Hindbrain (rhombencephalon




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


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


The mesoderm below the head region becomes segmented:

Somites, 2-day chick embryo

(Photo from Wolpert, 2002, p. 22)


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


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


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


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


MIT OpenCourseWare http://ocw.mit.edu

9.14 Brain Structure and Its Origins 9200Spring

. shttp://ocw.mit.edu/termrials or our Terms of Use, visit: on about citing these mateFor informati

http://ocw.mit.edu/terms

http://ocw.mit.edu

MIT 9.14 Class 9adspace.mit.edu/bitstream/handle/1721.1/97100/9-14-spring-2009/... · Visceral...

Documents

Transcript of MIT 9.14 Class 9adspace.mit.edu/bitstream/handle/1721.1/97100/9-14-spring-2009/... · Visceral...