Transcript VascCSF4

Vasculature of the CNS
Cerebrospinal 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 and
Posterior
Systems:
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 (vertebralbasilar).
• Arterial branches supply regions of tissue
which appear like wedge-shaped slices in
transverse sections.
Blood Supply of the
Brain Stem:
Pons
Rostral
Medulla
Cerebellum: AICA
basilar
PICA
Medulla
Midbrain: 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 functional
areas of the Cerebral
Cortex 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.
Blood supply to the brain
• BBB isolates neural tissue from general
circulation
• Incomplete barrier in the following areas
–
–
–
–
Parts of the hypothalamus
Pituitary gland
Pineal gland
Choroid plexus
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.
The Circulation of Cerebrospinal Fluid
Figure 14.5a, b