Development and anatomical organization of the nervous ... · Greenstein and Greenstein, Color...

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

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

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)

Central nervous system (CNS): Brain


forebrain midbrain hindbrain

Forebrain: Telencephalon, Diencephalon (Thalamus, Hypothalamus)

Midbrain: Mesencephalon (Tectum)

Hindbrain: Metencephalon (Pons, Cerebellum), Myelencephalon

(Medulla oblongata)

Brainstem: Midbrain + Hindbrain - Cerebellum

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

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)


Main axes of the CNS

(Kandel et al., Principles of Neural

Science)


The nervous system of the vertebrates: The mouse as a

model

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

Fertilized egg Blastula Gastrulagrowth invagination

Formation of the neural plate

from the ectoderm along the

axis of the embryo


Nervous system

multilayered structure of three

germ layers:

- ectoderm

- mesoderm

- endoderm


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)


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

2. Increase in differentiation and segmentation


3. Increase in complexity of the forebrain


4. Increase in the surface of the cerebral cortex


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.)


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)


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


Blood supply by four large

arteries:

- 2 Arteriae carotides

internae

- 2 Aa. vertebrales

Blood supply



Cerebrospinal fluid (CSF)


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)

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




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


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


(Campbell, Biologie)

Blood brain barrier


Blood brain barrier


Blood brain barrier


Tight junctions between endothelial cells formed under the influence of

astrocytes

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


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)


Blood brain barrier


Development and anatomical organization of the nervous ... · Greenstein and Greenstein, Color...

Documents

Transcript of Development and anatomical organization of the nervous ... · Greenstein and Greenstein, Color...