Histology and Cell Biology: Meninges and Cerebrospinal Fluid

Flashcards covering the histology and cell biology of the meninges, cerebrospinal fluid (CSF) dynamics, vascular lesions, and brain barriers.

What are the three sequential meninges layers surrounding the brain and spinal cord, listed from outermost to innermost?

1. Outermost layer: dura mater

2. Intermediate layer: arachnoid

3. Innermost layer: pia mater

What is the general anatomical definition and function of the meninges?

Meninges are connective tissue membranes or coverings that surround the brain and spinal cord.

What tissue type composes the dura mater layer?

It is a thick layer of dense fibrous connective tissue.

What are the two layers of the dura mater in the cranium and what are their histological components?

1. Outer Periosteal layer: formed of osteoprogenitor cells, fibroblasts, and bundles of collagen fibers (well vascularized).
2. Inner Meningeal layer: composed of fibroblasts and fine collagen fibres (small blood vessels).

How and where are venous dural sinuses formed in the cranial meninges?

They are formed where the outer periosteal layer and inner meningeal layer of the cranial dura mater separate at certain places.

How is the dura mater positioned in the spinal cord relative to the vertebrae?

In the spinal cord, the dura mater is separated from the periosteum of the vertebrae by the epidural space, which is filled with fat and a venous plexus.

What are the two main components of the arachnoid layer?

1. Flat Sheet-like membrane in contact with the dura mater.
2. Trabeculae containing cavities called subarachnoid spaces filled with cerebrospinal fluid and large blood vessels.

What are arachnoid villi and what is their functional role?

Arachnoid villi are CSF-filled protrusions covered by vascular endothelial cells lining the sinuses; they function as a site for the absorption of CSF into the blood of the venous sinuses.

What structural layer forms the glia limitans and separates the pia mater from neural tissue?

End feet (subpial feet) processes extended by protoplasmic astrocytes on the surfaces of the brain and spinal cord form the glia limitans.

How do blood vessels enter neural tissue through the pia mater?

Blood vessels penetrate neural tissue through long perivascular spaces covered by the pia mater.

What four types of meningeal and vascular lesions are depicted in this diagram?

1. Epidural hemorrhage
2. Subdural hemorrhage
3. Subarachnoidal hemorrhage
4. Intracerebral mass hemorrhage

What are the key chemical and cellular characteristics of cerebrospinal fluid (CSF)?

CSF is clear and colourless and contains no cells. It has low concentrations of protein, glucose, and $K^+$ ions, but contains large amounts of $NaCl$.

By how much does buoyancy in CSF reduce the effective weight of the brain?

Due to buoyancy, the $1500\,g$ brain weight is reduced to $50\,g$ when immersed in CSF.

What is the total volume of CSF in the human body and where is most of it contained?

The total volume is $140\,ml$, mostly contained in the subarachnoid cisternae.

What are the formation rate and daily turnover rate of CSF?

The rate of formation is $0.35\,ml/min$ (or $500\,ml/day$), with a turnover rate of three times per day for a total volume of $140\,ml$.

What is the sequential path of CSF flow from production to absorption?

1. Secreted by choroid plexus in each lateral ventricle.
2. Flows through interventricular foramina into third ventricle.
3. Choroid plexus in third ventricle adds more CSF.
4. Flows down cerebral aqueduct to fourth ventricle.
5. Choroid plexus in fourth ventricle adds more CSF.
6. Flows out two lateral apertures and one median aperture.
7. Fills subarachnoid space and bathes external surfaces of brain and spinal cord.
8. Reabsorbed at arachnoid villi into venous blood of dural venous sinuses.

What is the normal pressure range of CSF inside the cranial cavity?

The normal pressure of CSF is $5 - 15\,mm\,Hg$.

What are four causes for elevated CSF pressure leading to hydrocephalus?

1. Oversecretion of CSF (rare)
2. Malfunction of CSF resorption at the arachnoidal villi (e.g., sagittal sinus thrombosis)
3. Obstruction of CSF pathways
4. Aqueductal stenosis (most common cause)

What three structural components create the Blood-Brain Barrier (BBB)?

1. Capillary endothelial cells (continuous-type capillary with tight occluding junctions)
2. Basal lamina of the endothelium
3. Feet of astrocyte processes

What functions are performed by the Blood-Brain Barrier (BBB)?

1. Protects the CNS from fluctuating levels of electrolytes, hormones, and tissue metabolites in blood vessels.
2. Restricts passage of certain ions and substances ($K^+$, drugs, foreign proteins) from bloodstream to CNS tissues.
3. Mediates active transport of glucose, vitamins, and amino acids via specific transmembrane carrier proteins.
4. Maintains water homeostasis to prevent tissue edema.

What four components form the Blood-CSF barrier?

1. Capillary endothelial cells (continuous with occluding junctions)
2. Basal lamina of endothelial cells
3. Basal lamina of ependymal cells
4. Ependymal epithelium joined by tight junctions

What is the primary function of the Blood-CSF barrier?

It maintains the chemical stability of CSF and the difference in composition of CSF relative to blood.