Protection of the Central Nervous

Systempages 247-251

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Physical Protection: Bone: Skull and vertebral column Membranes: Skin/Scalp, Meninges Watery Cushion: Cerebrospinal fluid (CSF)

Chemical Protection: Blood-brain barrier

Protection of the Central Nervous System

Thin connective tissue layers (superficial to deep)

Dura Mater: double-layered, toughest◦ Has inner folds between fissures

Arachnoid Mater: web-like, villi reabsorb CSF

Pia Mater: delicate, attaches directly to brain/cord

Meninges

Figure 7.17a Meninges of the brain.

Skin of scalpPeriosteum

Bone of skull

PeriostealMeningeal

Duramater

Arachnoid mater

Pia mater

Arachnoid villusBloodvesselFalx cerebri(in longitudinalfissure only)

Superiorsagittal sinusSubduralspace

Subarachnoidspace

(a)

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Similar to blood plasma composition◦ -Proteins and sugars

Formed by the choroid plexus of lateral and 4th ventricles◦ –capillaries in the ventricles of the brain

Circulates in:◦ -Arachnoid space ◦ -Ventricles◦ -Central canal of the spinal cord

Arachnoid villi reabsorb CSF into venous blood

Cerebrospinal Fluid (CSF)

Figure 7.18a Ventricles and location of the cerebrospinal fluid.

Septumpellucidum

Inferiorhorn

Lateralaperture

Lateral ventricle

Anterior horn

Interventricularforamen

Third ventricle

Cerebral aqueduct

Fourth ventricle

Central canal

(a) Anterior view

Figure 7.18b Ventricles and location of the cerebrospinal fluid.

Lateral ventricle

Anterior horn

Interventricularforamen

Third ventricle

Cerebral aqueduct

Fourth ventricle

Central canal

Posteriorhorn

Inferior horn

Medianaperture

Lateralaperture

(b) Left lateral view

Figure 7.18c Ventricles and location of the cerebrospinal fluid.

1

2

3

4

1

2

3

4

Superiorsagittal sinus

Choroid plexus

Corpuscallosum

Interventricularforamen

Third ventricle

Arachnoid villus

Subarachnoid spaceArachnoid mater

Meningeal dura mater

Periosteal dura mater

Right lateral ventricle(deep to cut)

Choroid plexusof fourth ventricle

Cerebral aqueductLateral aperture

Fourth ventricle

Median aperture

Central canalof spinal cord

CSF is produced by the choroid plexus of each ventricle.

CSF flows through theventricles and into thesubarachnoid space via themedian and lateral apertures.Some CSF flows through thecentral canal of the spinal cord.

CSF flows through thesubarachnoid space.

CSF is absorbed into thedural venous sinuses viathe arachnoid villi.

(c) CSF circulation

Inflammation of the meninges Can be bacterial or viral (most common) CSF is sampled for presence of pathogen Bacterial Causes:

◦ Strep◦ Pneumonia◦ Listeria

Viral Causes:◦ Enteroviruses◦ Mumps/Measles/Influenza◦ West Nile

Meningitis

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Hydrocephalus◦ CSF accumulates and exerts pressure on the brain

if not allowed to drain

◦ Possible in infants - skull bones have not yet fused◦ In adults, can result in brain damage

Hydrocephalus in a Newborn

Figure 7.19 Hydrocephalus in a newborn.

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The least permeable capillaries of the body -Bound together by tight junctions -allows water, glucose, essential amino acids

Keeps out potentially harmful substances: -metabolic wastes (urea, useless proteins) -some drugs -potassium ions

Useless against some substances including: -Fats/fat-soluble molecules -Respiratory gases -Alcohol/Nicotine -Anesthesia

Blood-Brain Barrier