1/1/2016

Introduction

• Protection of the brain – Bone (skull) The Nervous System – Membranes (meninges) – Watery cushion (cerebrospinal fluid) – Blood-brain barrier (astrocytes) Meninges CSF

The Meninges The Meninges

• Series of membranes • Three layers • Cover and protect the CNS – Dura mater • Anchor and cushion the brain – Arachnoid mater – • Contain cerebrospinal fluid (CSF) Pia mater

The Meninges

• Dura mater – “Tough mother” Skin of scalp Periosteum – Strongest meninx Bone of skull Periosteal Dura – Fibrous connective tissue Meningeal mater Superior Arachnoid mater – sagittal sinus Pia mater Limit excessive movement of the brain Subdural Arachnoid villus – space Blood vessel Forms partitions in the skull Subarachnoid Falx cerebri space (in longitudinal fissure only)

Figure 12.24

1 1/1/2016

Superior The Meninges sagittal sinus Falx cerebri • Arachnoid mater – “Spider mother” Straight sinus – Middle layer with weblike extensions Crista galli – Separated from the dura mater by the subdural space of the Tentorium ethmoid cerebelli – Subarachnoid space contains CSF and blood vessels bone Falx Pituitary cerebelli gland

(a) Dural septa

Figure 12.25a

The Meninges

• Pia mater – “Gentle mother” – Connected to the dura mater by projections from the arachnoid mater – Layer of delicate vascularized connective tissue – Clings tightly to the brain

T Meningitis TT121212 Ligamentum flavumflavumflavum L • LL555 Lumbar puncture Inflammation of meninges needle entering subarachnoid • May be bacterial or viral spacespacespace LLL444 • Diagnosed by obtaining CSF sample via lumbar tap SupraSupraSupra-Supra --- spinousspinousspinous ligament

LLL555 FilumFilumFilum terminale

SSS111 InterInterInter-Inter --- Cauda equina vertebral Arachnoid DuraDuraDura in subarachnoid discdiscdisc mattermattermatter matermatermater spacespacespace

Figure 12.30

2 1/1/2016

Cerebrospinal Fluid (CSF) Cerebrospinal Fluid (CSF)

• Solution that bathes the CNS • Functions • Composition – Gives buoyancy to the CNS organs – Watery solution • Reduces brain’s effective weight by 97%! • Modified plasma (less protein, different ion – Protects the CNS from blows & other trauma concentrations) – Nourishes the brain & carries chemical signals – Constant volume (about 150 ml) • About 500 ml formed daily • Replaced every 8 hours or so

Cerebrospinal Fluid (CSF)

• Choroid plexuses Ependymal cells – Produce CSF at a constant rate Capillary Section – Hang from the roof of each ventricle of choroid Connective plexus – Clusters of capillaries enclosed by pia mater & a tissue of pia mater layer of ependymal cells

Wastes and Cavity of CSF forms as a filtrate unnecessary containing glucose, oxygen, solutes absorbed ventricle vitamins, and ions (Na +, Cl –, Mg 2+ , etc.) (b) CSF formation by choroid plexuses

Figure 12.26b

SuperiorSuperiorSuperior sagittal sinus 4 ChoroidChoroidChoroid plexus Arachnoid villus InterventricularInterventricular foramenforamenforamen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep(deep toto cut)cut) Choroid plexus 3 of fourth ventricle Third ventricle 1 CSF is produced by the Cerebral aqueduct choroid plexus of each Lateral aperture ventricle. Fourth ventricle 2 CSF flows through the ventricles and into the Median aperture 2 Median aperture subarachnoid space via the Central canal median and lateral apertures. of spinal cord Some CSF flows through the central canal of the spinal cord. 3 (a) CSF circulation CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi.

Figure 12.26a

3 1/1/2016

Cerebrospinal Fluid (CSF) Cerebrospinal Fluid (CSF)

• Hydrocephalus • Hydrocephalus – Due to blockage or overproduction of CSF – Due to blockage or overproduction of CSF – Internal hydrocephalus – Infants • CSF accumulates in the ventricles, expanding them outward • Head enlarges because skull bones have not yet fused – External hydrocephalus – Adults • CSF accumulates in the subarachnoid space, compressing the • brain Accumulating fluid compresses blood vessels and soft nervous tissue, causing brain damage

Cerebrospinal Fluid (CSF)

• Hydrocephalus – Treatment • 6/10 will die without treatment • Shunts are placed to divert excess fluid to other areas of the body

4