development and anatomical organization of the nervous ... · greenstein and greenstein, color...
TRANSCRIPT
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Contents:
The nervous system of the vertebrates
1. Main components
2. The mouse as a model
3. Brain and spinal cord
3.1 Evolution and development
3.2 Principles of organization
3.3 Blood and liquor system
Literature:
Dudel et al., Neurowissenschaft (Springer)
Reichert, Neurobiologie (Thieme)
Kandel et al., Principles of Neural Science (McGraw Hill)
Kahle, Taschenatlas der Anatomie, Band 3: Nervensystem und
Sinnesorgane (Thieme)
Greenstein and Greenstein, Color Atlas of Neuroscience (Thieme)
Development and anatomical organization of the
nervous system II
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Increase in centralization and cephalization:
In humans, the majority of the neurons are located in the brain and about
99,999% of the nerve cells are interneurons
The nervous system of the vertebrates
Sensory
InputMotor
outputIntegration
Sensory
inputMotor
outputIntegration
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The nervous system of the vertebrates: Main components
PNS: Groups of neurons (ganglia) and peripheral nerve tracks
- somatic part
- autonomous (vegetative) part - sympathic part
- parasympathic part
(Campbell et al.,
Biologie)
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Central nervous system (CNS): Brain
The nervous system of the vertebrates: Main components
forebrain midbrain hindbrain
Forebrain: Telencephalon, Diencephalon (Thalamus, Hypothalamus)
Midbrain: Mesencephalon (Tectum)
Hindbrain: Metencephalon (Pons, Cerebellum), Myelencephalon
(Medulla oblongata)
Brainstem: Midbrain + Hindbrain - Cerebellum
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CNS: Spinal cord
- Segmented organization (31 paired
spinal nerves in 4 major regions),
- H-like structure: gray and surrounding
white matter
- Divided into dorsal and ventral horn and
dorsal, lateral, and ventral
columns(Kandel et al., Principles of Neural
Science)
Evolution and development
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Somatic nervous system:
Signals to skeletal muscle in response
to external stimuli
Autonomous (vegetative) nervous
system: signals that affect the inner
milieu (energy metabolism and
homeostasis)
Two subunits:
Sympathicus: Increase in energy
consumption, organism is prepared for
action ("fight and flight")
Parasympathicus: reduction of energy
consumption, recovery ("rest and
digest")
Peripheral nervous system (PNS)
(Kahle, Taschenatlas der Anatomie Band 3)
The nervous system of the vertebrates: Main components
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Main axes of the CNS
(Kandel et al., Principles of Neural
Science)
The nervous system of the vertebrates: Main components
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The nervous system of the vertebrates: The mouse as a
model
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The nervous system of the vertebrates: The mouse as a
model
> 99% of all genes have homolog in humans (a gene inherited in
two species by a common ancestor) → disease model
Diverse genetic tools: (conditional) transgenic, knockout, knock-in mouse
models
Complete genome information (2002)
Limitations:
- Rats are a better model for high blood pressure and atherosclerosis
- Rabbits are physiologically more similar to humans
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Fertilized egg Blastula Gastrulagrowth invagination
Formation of the neural plate
from the ectoderm along the
axis of the embryo
Evolution and development
Nervous system
multilayered structure of three
germ layers:
- ectoderm
- mesoderm
- endoderm
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Evolution and development
Central nervous system (CNS)
Dorsally positioned tube-like
nerve strand (produced by invagination of the
neural plate)
Posterior part
→ spinal cord
Anterior part
→Vesicles
→Brain(Segmental structure,
present in both hemispheres
of the brain)
(Kahle, Taschenatlas der Anatomie Band 3)
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Principles of organization
Mammal Body weight Brain weightRelative brain
weight
elephant
greenland whale
mouse
man
gorilla
cat
2047 kg
62250 kg
21 g
60-72 kg
95,5 kg
4-5 kg
4048 g
2490 g
0,4 g
1300-1500 g
425 g
27,3-32 g
0,2%
0,004%
1,9%
2-2,3%
0,46%
0,64-0,68%
(R. Nickel, A. Schummer, E. Seiferle, Lehrbuch
der Anatomie der Haustiere Bd. 4, Parey)
1. Increase in the relative size of the brain
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2. Increase in differentiation and segmentation
Principles of organization
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3. Increase in complexity of the forebrain
Principles of organization
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4. Increase in the surface of the cerebral cortex
Principles of organization
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5. Separation in gray and white matter
Functionality of the CNS requires optimization of two competing
requirements:
- high interconnectivity
- short conduction delays
→ Solution: Segregation between gray and white matter:
- High connectivity in small regions („local connections“) (maximal number of
cells: about 10,000 neurons with tolerable delay (ms range) → gray matter
- Fast connections with high conduction speed („global wiring“) → white matter
(Lit.: Wen, Q., and Chlovskii, D.B. (2005) Segregation of the brain into gray and white
matter: a design minimizing conduction delays. PLOS Computational Biol. 1: e78-
e87.)
Principles of organization
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6.Serial organization and orderly connections
- Serial organization
(relays); information is
transformed at every step
- Pathways that link the
components (tracts, „Bahnen“)
- Pathways cross to the other side
(contralateral side) of the body at
a certain anatomical level
- Projections occur in an orderly
fashion thus producing neural
maps (somatotopy)
(Kandel et al., Principles of Neural
Science)
Principles of organization
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Total of 700 km of veins
→ Large surface (180 cm2/g brain):
→ Efficient gas exchange (O2, CO2)
Blood supply
Brain is highly vulnerable – anoxia and ischemia within the range of
seconds cause neurologic symptoms and within the range of minutes
irreversible damage of neurons (stroke)
Blood and liquor system
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(Kahle, Taschenatlas der Anatomie Band 3)
Blood supply by four large
arteries:
- 2 Arteriae carotides
internae
- 2 Aa. vertebrales
Blood supply
Blood and liquor system
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(Kahle, Taschenatlas der Anatomie Band 3)
Cerebrospinal fluid (CSF)
Blood and liquor system
CNS is surrounded by Liquor
cerebrospinalis including the four
ventricles (about 140 ml) →
provides cushion and buoyancy
(Reduction of brain weight
from 1400 g to 45 g)
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Liquor cerebrospinalis is present in the subarachnoid space
Secreted by the choroid plexus in the lateral ventricles
Absorbed through the arachnoid membranes (purple;
„Spinngewebshaut“) and transported through the arachnoid
granules into the venous sinuses → provides a one-way system
to remove harmful metabolites (turnover 3 times/24 hrs.)
Composition of the
CSF may be
altered during
disease →
diagnostic tool
(Kahle, Taschenatlas der Anatomie Band 3)
Cerebrospinal fluid (CSF)
Blood and liquor system
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Cerebrospinal fluid (CSF)
Blood and liquor system
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1st Goldmann-Experiment (Edwin Goldmann, 1909):
IV (intravenous) Trypan blue injection → No staining of brain and spinal cord
(Saunders et al., The rights and wrongs of
blood-brain permeability studies“
Frontiers in Neuroscience, 2014)
Blood brain barrier
Blood and liquor system
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2nd Goldmann experiment: Trypan blue injection into liquor room →
only brain and spinal cord stain → blood-liquor barrier
Blood brain barrier is present already
early during embryonal
development
Blood brain barrier
Blood and liquor system
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(Campbell, Biologie)
Blood brain barrier
Blood and liquor system
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Blood brain barrier
Blood and liquor system
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Blood brain barrier
Blood and liquor system
Tight junctions between endothelial cells formed under the influence of
astrocytes
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1. Water-soluble substances do not
pass through the blood-brain
barrier
2. Lipid-soluble substances pass
through the blood-brain barrier
Blood brain barrier
Blood and liquor system
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Disease: Hydrocephalus (accumulation
of CSF) – genetic defect or caused
by infection H. occlusus: blockage of foramina
H. aresorptivus: decreased resorption by
arachnoid membranes
H. hypersecretorius: increased production
Foramen interventriculare
(Monroi)
(Kahle, Taschenatlas der Anatomie Band 3)
Blood brain barrier
Blood and liquor system