Vasculature of the CNS Cerebrospinal Fluid. Blood Supply Continuous blood supply to CNS is vital. Not stored in significant amounts. Reason why vascular.

Vasculature of the CNSCerebrospinal Fluid

Blood Supply• Continuous blood supply to CNS is vital.

• Not stored in significant amounts.

• Reason why vascular disorders of the CNS is a major class of disease:

I. The arterial supply of the CNS.

A. Anterior (carotid) and posterior (vertebral) systems.

B. Blood supply of the SC (spinal arteries)

C. Blood supply of the brainstem.

D. Blood supply of diencephalon and cerebral hemispheres.

II. Venous system

III. Blood-brain barrier

IV. Production and Function of CSF.

Arterial Supply of the CNS

A. Overview of the Major anterior and posterior systems.

1. The internal carotid arteries feed the major anterior circulation of the brain.

2. The posterior circulation (supplies the brain, bs, and some sc) originates from vertebral arteries (which join at the midline of bs to form the Basilar Artery).

Therefore, this posterior system is referred to as the vertebral-basilar system.

Arterial Supply of the CNS

These systems are not independent, but rather, have a connection:

- network on the ventral surface of diencephalon and midbrain –

known as Circle of Willis.

- Also network of interconnecting arteries on cortical surface (later).

- Very important functionally if occusion should occur.

Anterior andPosteriorSystems:An Overview

Blood Supply of the Spinal Cord

1. Branches of Vertebral system:

-anterior spinal artery.

-2 branches emerge just before the vertebral arteries join to form the basilar – and come together to travel down the ventral (anterior) surface of the sc.

2. Radicular arteries:

- from systemic circulation

- these branches form a network of communicating channels with the ant and post sp arteries.

**Colateral supply

Blood Supply of the Spinal Cord

Blood Supply of the Brainstem

• All from posterior circulation (vertebral-basilar).

• Arterial branches supply regions of tissue which appear like wedge-shaped slices in transverse sections.

Blood Supply of theBrain Stem:

Pons

RostralMedullaCerebellum: AICA

basilar PICA

MedullaMidbrain: Sup cereb

basilar

Blood Supply of the Diencephalon and Cerebral Hemispheres

• Contributions from both ant and post circulations.• Thalamus, bg, cerebral cortex all supplied by the 3

cerebral arteries.• Anterior cerebral and middle cerebral anterior

circulation (from internal carotid).• Posterior cerebral posterior circulation (from

basilar).• Circle of Willis: e.g., of network of interconnected

network of arteries (aka anastomosis).• This connction of the 2 arterial systems becomes

crucial when circulation shuts down because of occlusion.

Blood Supply of the Diencephalon and Cerebral Hemispheres

• The arterial supply of the deeper structures of the diencephalon and telencephalon:

- deepest structures supplied by most proximal branches.

e.g., part of bg supplied by a direct branch of internal carotid – anterior choridal.

Thalamus – Post serebral, post communicating, post choroidal.

Hypothalamus – ant-, post-cerebral, post-communicating.

BG –ant-choroidal, middle cerebral.

Cerebral Cortex: Different functional areas supplied by different cerebral arteries.

Blood Supply of the Diencephalon and Cerebral Hemispheres

• In following slide, note the arterial blood supply to the various parts of the cortex.

Different functionalareas of the CerebralCortex are supplied by different cerebral arteries.

Anastomotic Channels on the Surface of the Cerebral Cortex

Venous System of the Cerebrum

• Drainage of blood from the CNS into major vessels leading to the heart (systemic circ) is achieved wither directly or indirectly:

- Directly: from SC and caudal medulla.

- Indirectly: rest of the CNS.

Indirect: Veins 1st drain into dural sinuses located between the 2 layers of the dura mater.

- These serve as low pressure channels for venous blood flow back to systemic circ.

Superior, inferior sagital sinus straight sinus transverse signmoidal internal jugular veins.

Remember this figure…? Now, focus on the sinuses…

Dural Sinuses

Blood-Brain Barrier (BBB)

• The inside of vessels is isolated from the extracellular space of the CNS by special characteristics of the capillaries:

• Tight junctions between endothelial cells and foot processes of astrocytes.

• This permeability barrier is protective for the brain against toxic chemicals, but is also against rapid ionic changes in the blood which could affect neuronal excitability.

• The BBB is also important because certain other active (e.g., pinocytosis) and passive transport processes are not present in CNS endothelial cells.

• BBB isolates neural tissue from general circulation

• Incomplete barrier in the following areas– Parts of the hypothalamus– Pituitary gland– Pineal gland– Choroid plexus

Blood supply to the brain

Cerebral Spinal Fluid (CSF)

• CSF fills both the inside (ventricles) and outside (subarachnoid space) of the CNS.

• Functions:

1. Physical support for the brain.

2. Excretory function: taking place of lymphatic system in collecting H2O-soluble metabolites.

3. Channel for chemical communication within the CNS.

Production: Most CSF is produced by the choroid plexus within the ventricles.

Cerebrospinal Fluid (CSF)

• Pathway of CSF flow: fills ventricles subarachnoid space through 3 apertures:

1. Foramen of Magendie (midbrain).

2. Foramens of Lushka (lateral margins).

The CSF space connects with the bloodstream: From subarachnoid space dural sinuses and venous blood through small unidirectional valves, called arachnoid villi.

Clusters of these are visible protruding into the superior sagital sinus, called the arachnoid granulations.

Figure 14.5a, b

The Circulation of Cerebrospinal Fluid