1. Protection of the Central Nervous System
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2. Protection of the Central Nervous System
Physical Protection:
Bone: Skull and vertebral column
Membranes: Skin/Scalp, Meninges
Watery Cushion: Cerebrospinal fluid (CSF)
Chemical Protection:
Blood-brain barrier
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3. Meninges 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

4. Figure 7.17a Meninges of the brain.
Skin of scalp
Periosteum
Bone of skull
Periosteal
Dura mater
Meningeal
Superior sagittal sinus
Arachnoid mater
Subdural space
Pia mater
Arachnoid villus
Subarachnoid space
Blood vessel
Falx cerebri (in longitudinal fissure only)
(a)

5. Cerebrospinal Fluid (CSF)
Unique to the CNS
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
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6. Figure 7.18a Ventricles and location of the cerebrospinal fluid.
Lateral ventricle
Anterior horn
Septum pellucidum
Interventricular foramen
Inferior horn
Third ventricle
Lateral aperture
Cerebral aqueduct
Fourth ventricle
Central canal
(a) Anterior view

7. Figure 7.18b Ventricles and location of the cerebrospinal fluid.
Lateral ventricle
Anterior horn
Posterior horn
Interventricular foramen
Inferior horn
Third ventricle
Median aperture
Cerebral aqueduct
Fourth ventricle
Lateral aperture
Central canal
(b) Left lateral view

8. Figure 7.18c Ventricles and location of the cerebrospinal fluid.4
Superior sagittal sinus
Arachnoid villus
Choroid plexus
Subarachnoid space
Arachnoid mater
Corpus callosum
Meningeal dura mater
Periosteal dura mater 1
Interventricular foramen
Right lateral ventricle (deep to cut)
Third ventricle 3
Choroid plexus of fourth ventricle
Cerebral aqueduct
Lateral aperture
CSF is produced by the choroid plexus of each ventricle. 1
Fourth ventricle 2
Median aperture
CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures.
Some CSF flows through the central canal of the spinal cord. 2
Central canal of spinal cord
(c) CSF circulation
CSF flows through the subarachnoid space. 3 4
CSF is absorbed into the dural venous sinuses via the arachnoid villi.

9. Meningitis Inflammation of the meninges
>Cause is 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

10. Cerebral Circulation Circle of Willis
Arrangement of blood vessels supplying arterial blood to brain tissue
Originate from carotid arteries in neck
Wastes in blood are returned, in conjunction with wastes of CSF, by way of venous return through the jugular veins

11. The Circle of Willis

12. Blood-Brain Barrier The least permeable capillaries of the body
-Bound together by tight junctions
-allows diffusion of 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
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