A&P 001.2 - The Ventricular System

Posted by John Dalton on September 16, 2008

*As with all anatomy I suggest you search for each new term on google then click on the ‘Images’ tab at the top of the page.  Look at as many different pictures of each structure, from as many different angles as you can. Then look at it on the Visible Body. This will help you get a 3 dimensional image of the structure in your head.

The Ventricular System is a system of cavities and canals deep
within the brain and spinal cord. They have a thin membranous
lining called the Ependyma.  The whole Ventricular System is filled
with Cerebrospinal Fluid. The Ventricular System consists of
four ventricles connected by various communicating channels.

These are:

❍ Two lateral Ventricles (1st and 2nd Ventricles) located within
the two cerebral hemispheres, each of which communicates via an
inter-ventricular foramen to

❍ The third Ventricle located between the two Thalami of the brain.
The Third ventricle communicates inferiorly through the cerebral
aqueduct (aqueduct of sylvius) to

❍ The fourth Ventricle located between the Cerebellum (posteriorly)
and the Pons and Medulla (anteriorly).  The fourth Ventricle is
continuous inferiorly with the central canal passing down the
centre of the Spinal Cord.

In the roof of each of the four ventricles are located Choroid Plexi.
These are filter like structures through which Cerebrospinal Fluid
is formed as a filtrate from arterial blood.  Arterial blood enters
the Choroid Plexi from the cerebral arteries; then blood cells,
proteins and other large particles are filtered out (remaining in
the blood).  The pure colourless fluid that filters through this
Choroid Plexi into the Ventricular System is Cerebrospinal Fluid.

HOW DOES CEREBROSPINAL FLUID GET OUT OF THE VENTRICULAR SYSTEM?

In the posterior and lateral walls of the fourth ventricle are three foramina -

The Foramen of Magendie (medial aperture), posteriorly, and
Two Foramina of Luschka (lateral apertures), bilaterally.

Cerebrospinal Fluid flows throughout the Ventricular System.
It passes out through the Foramina of Magendie and Luschka
into the sub-arachnoid space where it circulates throughout
the Sub-arachnoid space around the Brain and Spinal Cord.

Cerebrospinal Fluid also seeps through the walls of the ventricles
into the nerve tissue of the Brain and Spinal Cord.  From the
sub-arachnoid space it seeps through the Pia Mater into the
tissues of the Brain and Spinal Cord. Cerebrospinal Fluid also
seeps out with the peripheral nerves of the spinal cord as they
leave the Central Nervous System and travel out to the periphery.

REABSORBTION
Cerebrospinal Fluid is eventually returned to the blood via the
Arachnoid Villi which protrude from the sub-arachnoid space
through to the Superior Sagittal Sinus of the Brain. It re-joins the
Venous blood which then drains from the Venous Sinuses via the
Internal Jugular Vein to be returned to the heart.

So the direction of flow is,

• Arterial blood is pumped into the Choroid Plexi in the roofs
  of the Ventricles where it is filtered into cerebrospinal fluid.
• The lateral ventricles drain into the Third Ventricle via
  Inter-ventricular foramina.
• The third ventricle drains into the Aqueduct of Sylvius to the
  Forth Ventricle.
• It is in the Fourth Ventricle that the cerebrospinal fluid leaves
  the ventricles and enters the sub arachnoid space via the
  foramina of Luschka and Magendie. (It also travels down the
  central canal of the spinal cord.)
• It travels throughout the sub arachnoid space.
• Some of it seeps out with the peripheral nerves and is
  reabsorbed as an extracellular fluid.
• The bulk of it is reabsorbed by the arachnoid granulations
  of the arachnoid villi. These transform it into Venous blood
  as they deposit it into the Venous sinuses, particularly the
  superior sagittal sinus.

A&P 001.1 - The Cranio Sacral Sysytem overview.

Posted by John Dalton on June 19, 2008

*As with all anatomy I suggest you search for each new term on google then click on the ‘Images’ tab at the top of the page. Look at as many different pictures of each structure, from as many different angles as you can. Then look at it on the Visible Body. This will help you get a 3 dimensional image of the structure in your head.

The cranio sacral system is a physiological system within the body.
Along with the Respiratory and Cardio-Vascular systems, it forms
one of the three primary life systems.

The Cranio Sacral System consists of -
❍ Fluids
❍ Membranes
❍ Fascia
❍ Bones

Each is a recognised anatomical structure but outside Cranio Sacral
Therapy they are not treated as one integrated system.

CEREBRO SPINAL FLUID

A clear colourless fluid which surrounds and bathes the central
nervous system, creating the environment within which the brain
and spinal cord grow, develop and function. It provides nutrition
and drainage for the brain and spinal Cord also. It is in continuous
motion, as any stagnation would undermine the brain and nervous
system.

Cerebro spinal Fluid is produced in hollow spaces at the centre of
the brain called ventricles and circulates throughout the
membrane system.

THE MEMBRANE SYSTEM

Containing the cerebrospinal fluid is a tough waterproof sack
made up of three membranous layers called the meninges which
surround the brain and spinal cord. The meninges have horizontal
infoldings in the cranium which separate the cerebrum from the
cerebellum called the Tentorium Cerebelli and a vertical infolding
called the Falx Cerebri and Falx Cerebelli which divide the right
and left hemispheres of the Cerebrum and cerebellum respectively.

THE FASCIA

Fascia is a connective tissue which forms a continuous sheath
throughout the body from the top of the head to the soles of the feet.
It envelops every organ, nerve, blood vessel, muscle and indeed every
structure throughout the body.

This continuous fascial sheath forms a close connection to the
meninges at the point where each peripheral nerve emanates from
the spinal cord. As the spinal nerves penetrate the Dura they pull
some of the Dura with them and this blends into the fascial sheath
which covers the spinal nerve on its journey. This transition point
from membrane to fascia is called the epineurium. It is one of the
ways the Cranio Sacral Rhythm is translated to the rest of the body

BONES

The meninges are closely attached to the bones of the Cranium
and also to the 2nd and 3rd Cervical Vertebrae (C2 and C3) and
to the Sacrum and Coccyx. The outer layer of the Dura is so
closely attached to the bones of the Cranium that it forms a
periosteum or inner lining to these bones.

Consequently, all the bones to which the membranes attach must
inevitably follow any motion exhibited by the membrane, expanding
and contracting in accordance with the membrane and reflecting
every pull or tension within the membrane system.