Cerebral blood supply
Cerebral blood fl ow originates from the arch
of the aorta (Figure 1). The blood supply fl ows
through the subclavian and common carotid
arteries before reaching the brain through two
pairs of vessels: the internal carotid arteries
and the vertebral arteries. The internal carotid
artery reaches the surface of the brain lateral
to the point at which the optic nerves cross (the
optic chiasma). It then separates into its terminal
branches: the anterior and the middle cerebral
arteries (Figure 1). Together, these arteries supply
the frontal, parietal and temporal lobes of the
brain, including structures such as the primary
motor and sensory cortices, and the auditory
cortex. The vertebral arteries ascend through the
vertebrae and enter the cranial cavity through the
foramen magnum. They run along the medulla
and join at the junction with the pons to form
the basilar artery. The basilar artery extends
along the length of the pons and terminates
when it branches off into a pair of posterior
cerebral arteries. Together, the vertebral and
basilar arteries supply blood to the brainstem,
cerebellum and occipital lobes (Crossman and
Neary 2005, Barker and Cicchetti 2012).
The circle of Willis sits at the base of the brain
and surrounds the optic chiasma (Figure 2).
It is formed from the posterior and anterior
circulation, which are joined by the anterior
communicating artery and a pair of posterior
communicating arteries. Its circular structure
ensures that cerebral blood supply can continue