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Protection of the Central Nervous
Systempages 247-251
© 2015 Pearson Education, Inc.
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)
© 2015 Pearson Education, Inc.
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
© 2015 Pearson Education, Inc.
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.
© 2015 Pearson Education, Inc.
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