*Meninges- Chapter 12*

Meninges

* Mening=Membrane *Singular=Menix *Fluid containing membranes that surround and protect the spinal cord and brain (CNS). *Three connective tissue membranes (dura mater, pia mater, arachnoid mater) that lie just external to the CNS organs. *Protective coverings of the CNS *The meninges- Cover and protect the CNS, protect blood vessels and enclose venous sinuses, contain cerebrospinal fluid, form partitions in the skull. *From external to internal= dura mater, arachnoid mater, pia mater. *From internal to external= pia mater, arachnoid mater, dura mater.

Dura Mater:

*"Tough Mother" *The leathery dura mater is the strongest menix. *Where it surrounds the brain it is a two layered sheet of fibrous connective tissue. *Thick outermost layer of the meninges surrounding and protecting the brain and spinal cord. *Subdivided into the periosteal and meningeal layers.

Pia Mater:

*("Gentle Mother") *Composed of delicate connective tissue and contains many tiny blood vessels. *ONLY menix that clings tightly to the brain like plastic wrap, following its every convolution. *Delicate innermost membrane enveloping the brain and spinal cord.

Encephalitis:

*Brain inflammation.

Choroid Plexus:

*Capillary beds that line the ventricles and produce CSF by filtering blood. *Hang from the roof of each ventricle form CSF. *These plexuses are frond-shaped clusters of broad, thin-walled capillaries enclosed first by pia mater and then by a layer of ependymal cells lining the ventricles *Plex=interwoven * The choroid plexuses also help cleanse the CSF by removing waste products and unnecessary solutes.

Cerebrospinal Fluid:

*Found in and around the brain and spinal cord. *Forms a liquid cushion that gives buoyancy to CNS structures. *By floating the jellylike brain, the CSF effectively reduces brain weight by 97% and prevents the delicate brain from crushing under its own weight. *Nourish the brain and spinal cord and protect it from trauma *Consistency of watery broth. *Plasmalike fluid that fills the cavities of the CNS and surrounds the CNS externally.

Meningitis:

*Inflammation of the meninges. *Serious threat to the brain because a bacterial or viral meningitis may spread to the CNS. *Diagnosed by obtaining a sample of cerebrospinal fluid via a lumbar tap and examining it for signs of infection.

Dural Septa:

*Limit excessive movement of the brain within the cranium. *Contain the: falx cerebri, falx cerebelli, and the tentorium cerebelli.

Arachnoid Mater:

*Web-like middle layer of the three meninges. *Forms a loose brain covering, never dipping into the sulci at the cerebral surface. *Separated from the dura mater by a narrow serous cavity, the subdural space, which contains a film of fluid. *Beneath the arachnoid mater is the wide subarachnoid space. *The arachnoid mater is fine and elastic, the blood vessels are poorly projected.

Hydrocephalus:

*When CSF is produced faster than it drains, it builds up in the ventricles. *The increased pressure on the delicate brain tissues causes brain damage. *When excess fluid builds up in the ventricles, it places increased pressure on the brain. *"Water on the Brain"

The four basic functions of the meninges are:

-Cover and protect the CNS -Protect blood vessels and enclose venous sinuses. -Contain cerebrospinal fluid. -Form partitions in the skull.

The average adult has about _______________ of CSF in our bodies, which is recycled and replaced how often?

150mL (half a cup); every 8 hours or so.

How much CSF then must be formed every day?

450mL (2 cups).

Cerebrospinal fluid ends up reducing the weight of the brain by _____.

97%

Meningitis is caused by what types of infections?

Bacterial or viral

Which vertebrae do doctors like to sneak in between while extracting CSF?

Cervical and thoracic.

Why is hydrocephalus fatal in adults, yet infants and small children can survive for quite some time?

For adults, the skull is rigid and cannot enlarge while infants' cranial sutures have not yet fused so the increase in pressure enlarges the head.

What can cause hydrocephalus?

Increased pressure on brain tissues ("water on the brain"). Build up of fluid in the cavities, ventricles deep within the brain. Excess fluid increases the size of the ventricles and puts pressure on the brain.

The singular form of 'meninges' is:

Menix

How is meningitis typically diagnosed?

Obtaining a sample of cerebrospinal fluid via a lumbar tap.

What separates the arachnoid layer from the pia mater?

Subarachnoid mater

What separates the dura mater from the arachnoid layer?

Subdurals Space

The textbook compares the pia mater to _______________ because of the way it clings to the actual brain tissue.

convolutions

Glial cells that form cerebrospinal fluid:

ependymal