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2.3. Blood Supply
Blood Supply to the CNS
The brain and spinal cord require a constant supply of oxygen- and glucose-rich blood at a constant pressure in order to function properly. In the healthy human, the brain and spinal cord have certain protective features that ensure this is always the case. Without oxygen, irreversible brain damage can occur within five minutes.
Blood Supply to the Brain
The brain has a dual blood supply. This means it is supplied by two pairs of arteries. These arteries are the left and right internal carotid arteries and the left and right vertebral arteries.
The left and right internal carotid arteries are branches of the common carotid artery (this is the artery in your neck that you press on when taking your pulse). The internal carotid artery enters the skull through a canal and provides much of the blood supply to the front and middle portions of the brain. When in the skull, the internal carotid divides into the anterior cerebral artery, the middle cerebral artery and the posterior communicating artery.
The left and right vertebral arteries are branches of the subclavian artery on each side. These arteries enter the skull through the foramen magnum (the large hole in the base of the skull through which the spinal cord connects to the medulla). The left and right vertebral arteries then join up to form the basilar artery. The basilar artery then divides again to form the posterior cerebral arteries.
Together, the branches of the internal carotid arteries and the vertebral arteries supply the entire brain with blood. At the base of the brain, all of these arterial branches actually link together, forming an arterial ring (or ‘anastomosis’) called the circle of Willis. This arterial circle, in theory, provides an emergency blood supply when required; if one branch gets blocked, the other branches that contribute to the arterial circle will compensate for it. Figure 2.3.1. shows the circle of Willis and other important arteries. Note that the circle of Willis consists of the:
The left and right internal carotid arteries are branches of the common carotid artery (this is the artery in your neck that you press on when taking your pulse). The internal carotid artery enters the skull through a canal and provides much of the blood supply to the front and middle portions of the brain. When in the skull, the internal carotid divides into the anterior cerebral artery, the middle cerebral artery and the posterior communicating artery.
The left and right vertebral arteries are branches of the subclavian artery on each side. These arteries enter the skull through the foramen magnum (the large hole in the base of the skull through which the spinal cord connects to the medulla). The left and right vertebral arteries then join up to form the basilar artery. The basilar artery then divides again to form the posterior cerebral arteries.
Together, the branches of the internal carotid arteries and the vertebral arteries supply the entire brain with blood. At the base of the brain, all of these arterial branches actually link together, forming an arterial ring (or ‘anastomosis’) called the circle of Willis. This arterial circle, in theory, provides an emergency blood supply when required; if one branch gets blocked, the other branches that contribute to the arterial circle will compensate for it. Figure 2.3.1. shows the circle of Willis and other important arteries. Note that the circle of Willis consists of the:
- 2x Anterior cerebral arteries
- 1x Anterior communicating artery
- 2x Internal carotid arteries
- 2x Posterior communicating arteries
- 2x Posterior cerebral arteries
- 1x Basilar artery
Blood Supply to the Spinal Cord
The blood supply to the spinal cord is illustrated in Figure 2.3.2. The anterior spinal artery runs along the anterior aspect of the spinal cord, just in front of the ventral median fissure. It gives off branches that supply much of the grey matter in the spinal cord. There are also two posterior spinal arteries, one on each side, and these give off branches that supply the posterior aspect of the spinal cord (in particular, the DCML tracts, that we identified in Section 2.2. Overview of the Spinal Cord).
Overall, these three spinal arteries can’t provide enough blood for the entire spinal cord, so the intercostal arteries and lumbar arteries also help out by supplying segmental arteries. These segmental arteries give off anterior and posterior radicular arteries, which supply that extra little bit of required blood to the spinal cord. The radicular arteries also give off smaller arteries that run around the outside of the spinal cord, forming an anastomotic network called the vasocorona.
Overall, these three spinal arteries can’t provide enough blood for the entire spinal cord, so the intercostal arteries and lumbar arteries also help out by supplying segmental arteries. These segmental arteries give off anterior and posterior radicular arteries, which supply that extra little bit of required blood to the spinal cord. The radicular arteries also give off smaller arteries that run around the outside of the spinal cord, forming an anastomotic network called the vasocorona.
Clinical Top Tip:
PCA Blockage
A blockage of the posterior cerebral artery with a blood clot can lead to severe nervous system deficits. The posterior cerebral artery supplies two key structures: the hippocampus and the primary visual cortex. The hippocampus is required for forming memories and the primary visual cortex is required for understanding images from the retina (see Section 2.1. Overview of the Brain). As such, a blockage in the posterior cerebral artery which is not treated quickly can lead to memory and visual problems. Structure, function and disease pathology are intricately linked.
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