ACA is the anterior cerebral artery making up the front part of the circle of Willis. This artery supplies blood to the lower limb motor and sensory cortices. An occlusion of the ACA leads to contralateral paralysis and paresthesia of the affected lower limb.
The anterior communicating artery (Acomm) is located in the anterior part of the circle of Willis and bridges the right and left anterior cerebral arteries (ACAs). This is a common site of berry aneurysms leading to impingement of the cranial nerves affecting eyesight.
The internal carotid arteries (ICA) are supplied by the common carotid arteries and are one source of blood supply to the brain. There is one ICA bilaterally, located in the neck and head. They contribute to the circle of Willis and respectively branch into an anterior cerebral artery (ACA) and middle cerebral artery (MCA). The ICAs are also connected to the posterior cerebral arteries (PCA) by a posterior communicating artery (Pcomm).
The middle cerebral arteries are not part of the circle of Willis, but they originate from the internal carotid arteries (ICA). There is one middle cerebral artery bilaterally. The MCAs supply blood to the upper limb and face motor and sensory cortices. MCA occlusion leading to stroke can result in contralateral paralysis and paresthesia of corresponding upper limb and face.
The posterior communicating artery is part of the circle of Willis and connects an internal carotid artery to a posterior cerebral artery bilaterally. Like the AComm, this is a common site for berry aneurysm leading to CN III palsy. CN III palsy can lead to ptosis, pupillary dilation, and the classic "down and out" eyes.
The posterior cerebral arteries (PCAs) originate from the basilar artery and are at the posterior part of the circle of Willis. They supply blood to the occipital (visual) cortex. A stroke occurring due to PCA occlusion can lead to contralateral hemianopia with macular sparing.
The basilar artery originates from the confluence of two vertebral arteries between the medulla and the pons. The basilar artery (and its constituent arteries) supply the medulla and pons. The basilar artery terminates in the posterior cerebral arteries (PCAs). This is often considered the most posterior aspect of the circle of Willis.
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