ACA is the anterior cerebral artery that makes up the front part of the circle of Willis. This artery supplies blood to the motor and sensory cortex that controls the lower limbs. Therefore, stroke due to the ACA would lead to contralateral paralysis and loss of sensation in the lower limbs.
The anterior communicating artery (Acomm) is located in the anterior part of the circle of Willis. It bridges the right and left anterior cerebral arteries (ACA). This is a common site of berry aneurysm, which can impinge on the cranial nerves leading to visual field defects. The lesions are typically aneurysms rather than strokes.
The internal carotid arteries (ICA) arise from the common carotid arteries and are one source of blood supply to the head. There is one ICA on each side of the neck and head. They are part of the circle of Willis and each branch into an anterior cerebral artery (ACA) and middle cerebral artery (MCA). The ICAs are also connected to the posterior cerebral arteries (PCA) by the posterior communicating artery (Pcomm).
The middle cerebral arteries are not part of the circle of Willis, yet they originate from the internal carotid arteries (ICA). There is one middle cerebral artery on each side. The MCAs supply blood to the motor and sensory parts of the cortex that control the upper limb and face. MCA occlusion leading to stroke can result in contralateral paralysis and loss of sensation in the upper limbs and face.
Posterior communicating artery is the part of the circle of Willis that connects the internal carotid artery to the posterior cerebral artery. Like the AComm, this is a common site for berry aneurysm, which can cause CNIII palsy. CNIII palsy can lead to ptosis and pupil dilation, and the classic "down and out" eyes.
The posterior cerebral arteries (PCA) arise 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 arises from the confluence of the two vertebral arteries. This occurs between the medulla and the pons. The basilar artery (and the smaller vessels that arise from it) supply the medulla and pons. The basilar artery leads to the posterior cerebral arteries (PCA). This is often considered the most posterior aspect of the circle of Willis.
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