Anatomy Ventricular Flow and Dura

Brain and spinal cord buoyancy, chemical buffering

Functions of cerebrospinal fluid (CSF)

Ventricles

CSF-filled caverns and canals inside the brain

Choroid plexus

Specialized tissue in ventricles that secretes CSF

Subarachnoid space

CSF circulates through ventricles and is reabsorbed through the ___.

Interventricular foramen

Connects lateral ventricles to each other and to third ventricle

Cerebral aqueduct (mesencephalic aqueduct)

Connects third and fourth ventricles

Fourth ventricle

Continuous with central canal of spinal cord

Cerebrospinal fluid (CSF)

What are ventricles filled with?

Choroid plexus, lateral ventricles, interventricular foramen to third ventricle, cerebral aqueduct (mesencephalic aqueduct), fourth ventricle, lateral apertures, subarachnoid space (central canal of spinal cord)

CSF flow

Venules of subarachnoid space, venous sinuses of brain through arachnoid villi, lymphatic vessels

Three main routes that CSF is drained from the subarachnoid

Arachnoid villi

Invaginations in the wall of the venous sinus where CSF can be drained into

Meninges

Membranes that surround the brain

Dura mater, arachnoid membrane, pia mater

Three meninges

Protection and support for the brain and spinal cord from trauma and rapid movements; integral role to CSF and brain circulation

Functions of meninges

Dura mater

Outermost covering of brain

Has two layers that are mostly fused

Sinuses

Separations

Endosteal/periosteal layer

Inner surface of the skull bones = periosteum

Only found in brain; does not continue past foramen magnum

Meningeal layer/dura mater proper

Dense, strong fibrous material

Continuous with spinal cord dura

Also surrounds cranial nn.

Arachnoid membrane

Closely adjacent to dura mater in live animals

Collapses onto brain surface in fixed specimens

Subarachnoid space

Between arachnoid and pia mater

Contains CSF

Many blood vessels pass through this space on the way to supply the brain

Trabeculae

Delicate strands of fibrous tissue

Connect arachnoid membrane to pia mater

Spider-web appearance

Pia mater

Innermost layer

Thin layer

Adheres to brain surface; cannot be separated grossly

Extends into all sulci (grooves)

Covers third and fourth ventricles

Meningeal layer projections

Reflections or septa or folds of dura mater

Falx cerebri

Fold of dura between cerebral hemispheres

Tentorium cerebelli

Fold of dura between cerebrum and rostral cerebellum

Diaphragm sella

Surrounds infundibulum on ventral surface

Dural venous sinuses

Many associated with the edges of the dural reflections or septa

Dorsal sagittal sinus

In folds of falx cerebri

Drains blood from dorsal brain, tributaries from cerebrum —> passes blood to maxillary, internal jugular and vertebral vv.

Transverse sinus

In folds of tentorium cerebelli and bone in the occipital bone

Drains blood from cerebellar vv.

Cavernous sinus

Within diaphragm sella (around pituitary)

Drains blood from ventral brain, also venous blood from face —> potential source of infection from face to brain

Carotids/rete also pass through to cool blood —> protect brain

Hydrocephalus

Excess CSF (congenital or acquired) caused by blockage, poor absorption, or increased production

Brachycephalic breeds are at increased risk for this condition

Mental changes and seizures are common

Congenital hydrocephalus

In newborn animals, perhaps by obstruction during critical development stage; blockage of cerebral aqueduct

Acquired hydrocephalus

Any age; lesions that interfere with circulation of CSF

If it occurs after skeletal development, then skull does not enlarge when ventricles fill