Protection of the Central Nervous System pages 247-251

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 © 2015 Pearson Education, Inc.

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

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)

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 © 2015 Pearson Education, Inc.

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

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

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.

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

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

The Circle of Willis

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 © 2015 Pearson Education, Inc.