Ch.13.2 -Protection and Support of the Brain

Production and Circulation of Cerebrospinal Fluid.

(a) A midsagittal section identifies the sites where cerebrospinal fluid (CSF) is formed and the pathway of its circulation toward the arachnoid villi. (b) CSF flows from the arachnoid villi into the dural venous sinuses.

The tentorium cerebelli

A horizontally oriented fold of dura mater that separates both the occipital and temporal lobes of the cerebrum from the cerebellum. It is named for the fact that it forms a dural "tent" over the cerebellum. The transverse sinuses are within its posterior border, whereas the straight sinus is within its midsagittal region.

cerebral aqueduct

A narrow canal that passes through the midbrain and connects the third ventricle with the tetrahedron-shaped fourth ventricle.

falx cerebelli

A sickle-shaped, vertical partition Divides the left and right cerebellar hemispheres. A tiny occipital sinus is within its posterior vertical border.

Name the cerebellar structure A

Arbor vitae

Cerebrospinal fluid (CSF) performs several important functions:

Buoyancy. The brain floats within the CSF, thereby reducing its apparent weight by more than 95%; this prevents the brain from being crushed under its own weight. Without CSF to support it, portions of the brain would sink through the foramen magnum. Protection. CSF provides a liquid cushion to protect delicate neural structures from sudden movements. When you try to walk quickly in a swimming pool, your movements are slowed as the water acts as a "movement buffer." CSF likewise helps slow movements of the brain if the skull or body moves suddenly and forcefully. Environmental stability. CSF transports nutrients and chemical messengers to the brain and removes waste products from the brain. Additionally, CSF protects nervous tissue from chemical fluctuations that would disrupt neuron function. The waste products and excess CSF are eventually transported into the venous circulation.

Ventricles

Cavities or expansions within the brain that are derived from the neural canal (the lumen of the embryonic neural tube). All of the ventricles are lined with ependymal cells and contain cerebrospinal fluid. The ventricles are connected with one another as well as with the central canal of the spinal cord.

The cranial meninges layers from deepest to most superficial.

Deepest (closest to brain) pia mater arachnoid mater dura mater Most Superfical (farthest from the brain)

Name the cerebellar structure B

Folia

Astrocytes

Form the outermost portion of the BBB. Acts as a gatekeeper to control which materials pass from the blood into the brain.

Ventricles

Formed from the embryonic neural canal. They contain cerebrospinal fluid (CSF) which transports nutrients, chemical messengers, and waste products.

Name the cerebellar structure C

Gray Matter

Subarachnoid space

Immediately deep to the arachnoid mater. Contains cerebrospinal fluid. The arachnoid trabeculae extend through this space from the arachnoid to the underlying pia mater.

fourth ventricle

Located between the pons, medulla oblongata, and cerebellum. It opens to the subarachnoid space via paired lateral apertures and a single median aperture. Narrows at its inferior end before it merges with the slender central canal of the spinal cord.

choroid plexus

Location where cerebrospinal fluid is initially formed A region of specialized tissue in each ventricle. Composed of a layer of glial cells called ependymal cells and the blood capillaries that lie within the pia mater.

Tentorial notch (or tentorial incisure),

The anterior surface of the tentorium cerebelli has a gap, or opening, called the tentorial notch (or tentorial incisure), to allow for the passage of the brainstem.

The (3) functions of the cranial meninges

The cranial meninges are three connective tissue layers that: Separate and support the soft tissue of the brain from the bones of the cranium Enclose and protect some of the blood vessels that supply the brain Contain and help circulate cerebrospinal fluid.

(2) Potential spaces associated with the dura mater

The dura mater and the bones of the skull may be separated by an epidural space, which contains the arteries and veins that nourish the meninges and bones of the cranium. The subdural space is positioned between the arachnoid mater and the overlying dura mater.

Falx cerebri

The largest of the (4) dural septa. Large, sickle-shaped, vertical fold of dura mater Located in the midsagittal plane & projects into the longitudinal fissure between the left & right cerebral hemispheres. Anteriorly, its inferior portion attaches to the crista galli of the ethmoid bone; Posteriorly, its inferior portion attaches to the internal occipital crest. Located within the superior and inferior margins of this dural septum are two dural venous sinuses: the superior sagittal sinus & the inferior sagittal sinus,

(2) Layers of the dura mater

The meningeal layer The periosteal layer

Dural venous sinuses

The meningeal layer is usually fused to the periosteal layer, except in specific areas where these two layers are separate and form large, blood-filled spaces called dural venous sinuses. (A sinus is a modified vein). Dural venous sinuses are typically triangular in cross section, and unlike most other veins, they do not have valves to regulate venous blood flow. The dural venous sinuses drain blood from the brain.

Cranial Dural Septa

The meningeal layer of the dura mater extends as flat partitions into the cranial cavity at four locations. Collectively, these double layers of dura mater are called cranial dural septa. These membranous partitions separate specific parts of the brain and provide additional stabilization and support to the brain.

The pia mater (meninges)

The pia mater is the innermost of the cranial meninges. It is a thin layer of delicate areolar connective tissue that tightly adheres to the brain and follows every contour of the brain surface.

dura mater

The strongest (dura = tough) thick, outermost layer of the meninges surrounding and protecting the brain and spinal cord

Cerebrospinal fluid (CSF)

a clear, colorless liquid that circulates within the ventricles and subarachnoid space. CSF bathes the exposed surfaces of the central nervous system and completely surrounds it.

What is A?

arachnoid mater

The subdural space is positioned between the:

arachnoid mater and the overlying dura mater.

Arachnoid trabeculae.

arachnoid means "resembling a spider web," it is partially composed of a delicate web of collagen and elastic fibers The arachnoid trabeculae extend through subarachnoid space from the arachnoid to the underlying pia mater. Both the arachnoid trabeculae and cerebrospinal fluid support cerebral arteries and veins within the subarachnoid space.

Cells called ______________ act as "gatekeepers" that permit materials to pass to the neurons of the brain from the capillaries.

astrocytes

(4) Cranial dural septa:

falx cerebri tentorium cerebelli falx cerebelli diaphragma sellae

There are ______ ventricles within the brain

four

The meningeal layer of the dura mater

immediately superficial to the arachnoid.

Each lateral ventricle is connected with the third ventricle through an opening called the ______ ______.

interventricular foramen

The arachnoid mater, also called the arachnoid membrane (meninges)

lies external to the pia mater. arachnoid means "resembling a spider web," it is partially composed of a delicate web of collagen and elastic fibers, termed the arachnoid trabeculae. Immediately deep to the arachnoid mater is the subarachnoid space, which contains cerebrospinal fluid. The arachnoid trabeculae extend through this space from the arachnoid to the underlying pia mater. Both the arachnoid trabeculae and cerebrospinal fluid support cerebral arteries and veins within the subarachnoid space.

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Two lateral ventricles are in the cerebrum, separated by a thin medial partition called the _________ __________.

septum pellucidum

The epidural space contains

the arteries and veins that nourish the meninges and bones of the cranium.

Blood-brain barrier missing in three distinct locations in the CNS

the choroid plexus, hypothalamus, and pineal gland

The periosteal layer of the dura mater

the more superficial layer of the dura mater, forms the periosteum on the internal surface of the cranial bones.

Within the diencephalon is a smaller, thinner ventricle called the ________ ________.

third ventricle