AH! The MENINGES

There are three layers of membranes covering the Central Nervous System:

the Dura,
the Arachnoid &
the Pia mater.
- Dura Mater
- Outermost sheet
- Tough
- Compound [composed of two layers]
  - Outer layer - endosteal - controls bone
  - Inner layer - meningeal - tightly attached to outer, except when folded on itself
    - as the falx cerebri
    - as the falx cerebelli
    - as the tentorium cerebelli
    - as the diaphragma sellae, or
    - when intentionally split to form venous sinuses
- Arachnoid Mater
- Not innervated
- Non vascular
- Forms a real space with the Pia
- Pia Mater
- Covers the brain very closely
- Carries the blood vessels into the brain
- Sheaths Cranial nerves passing through the outer meningeal layers
- Contributes to the formation of CSF.

Outer layer - the DURA MATER

Blood supply

Middle meningeal artery [branch of Maxillary artery] via Foramen spinosum

Branches of the Vertebral artery from the Foramen magnum.

Nerve supply

Trigeminal nerve, V1, V2 & V3

Vagus [X].

Venous Sinuses

These are channels formed by splits in the Dura mater, often triangular in section, which function as veins to drain blood from the brain.

Venous flow tends to be:-

From anterior to posterior

From posterior in a downward direction, and also

from the midline to out

Unpaired sinuses

Superior Sagittal sinuses

Inferior Sagittal sinuses

Straight sinus

Sinus confluens

Paired sinuses

Cavernous sinus

Superior Petrosal sinuses

Inferior Petrosal sinuses

Transverse sinuses

Sigmoid sinuses

Middle layer - the ARACHNOID MATER (Like a spider's web)]

Properties

It has no blood supply and is not innervated.

Follows the Dura mater which lies outside it.

Has projections - Arachnoid granulations - which pass through the Dura into the Superior Sagittal Sinus.

Has 'Spidery' filaments from its inner surface, which connect to the Pia mater on its inside.

Main feature

It forms a real space between its inner surface and the outer surface of the Pia mater, through which the Cerebro Spinal Fluid [CSF] circulates.

The inner layer - the PIA MATER [faithful, true]

It is a delicate layer, closely applied to the outer surface of the brain, which it follows very faithfully.
It carries fine blood vessels into the brain.

Role

The Pia mater Supports the blood supply to the brain

Forms [with the Ependymal cells of the brain and the blood vessels] the Choroid Plexus.
This, in turn, makes the CSF.

MENINGEAL SPACES

There are real or potential spaces related to all of the membranes of the brain.

Extradural [potential space].

The middle meningeal artery is carried by the endosteal layer of the Dura mater. If this artery is ruptured then it may bleed into this potential extradural space and so apply pressure to the brain. Characteristics are of rapid onset, high pressures developed, often fatal.

Subdural [potential space].

Hemorrhage here is more usually venous in origin. The condition is more insidious, the pressure increase is less and slower.

Sub-arachnoid space [a real space]

The sub-arachnoid space is a real space in which the CSF circulates. Because it is a real space the volume here is much greater, thus hemorrhage here will be slower at causing fatal problems.

CerebroSpinal Fluid [for your information]

The CSF is continuously produced in cavities inside the brain called ventricles. The fluid escapes into the sub-arachnoid space from the Fourth ventricle. It circulates in the sub-arachnoid space, acting as an hydraulic shock absorber for the brain, until it is reabsorbed into the venous blood via the arachnoid granulations. It is this CSF production and reabsorption, which creates the pumping action perceived, while performing CranioSacral Therapy.

BRAIN - major subdivisions

Cerebrum - the Fore-brain

This part of the brain has a convoluted surface - which increases the surface area - which in turn provides more space for neurones.

The Ridges are called gyri
The grooves are called sulci.

Functions of the Cerebrum

It controls conscious acts [motor center]

It is the center for higher activity - e.g. thought

It receives sensory input - both general and special sensation.

Parts of the Cerebrum [there are 2 hemispheres, each with 4 lobes]

Frontal - in the anterior cranial fossa

Initiates voluntary motor activity

Contains the centers for

Speech

Memory

Intelligence

Emotion

Parietal - on the side of the cerebrum, concerned with

General sensation

Integration of senses

Temporal - in the middle cranial fossa

Concerned with hearing

Occipital - at the back of the cerebrum, above the Tentorium.

Concerned with vision

Midbrain [middle cranial fossa]

Functions

Processes visual & auditory information

Initiates involuntary motor responses

Maintains consciousness.

Pons [bridge]

Functions

Motor control

Connects Cerebellum to brainstem.

Medulla oblongata [post cranial fossa]

Functions

Connects brain & spinal cord [relay station]

center for primitive life maintenance [heart, respiration, vaso-motor function].

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