posted by admin on Jul 5

The brain is enclosed in a container of bone (the skull) which in turn is covered by a fibrous structure and skin (the scalp). The scalp is attached by muscles to the forehead and the bone of the neck so that tensing these muscles causes stretching of the scalp. Beneath the skin there are numerous blood vessels-arteries-taking blood from the heart and veins returning blood to it. The scalp arteries arise from the large carotid artery which divides in the neck into two branches. One of these, the external carotid artery, sends blood to the outside of the skull and also to the coverings of the brain (meninges) within the skull, whilst the other branch, the internal carotid artery, enters the skull to join with vessels originating from the vertebral artery. The blood supply to the brain is from branches of the left and right internal carotid arteries which, with the vertebral arteries, form a communication round the base of the brain (the circle of Willis). From this circle, branches go to the front, centre, and back of the brain sending out a network of ever finer vessels which dive deep into the substance of the brain.Veins drain the blood from the brain and channel it into a series of large veins (venous sinuses) closely attached to the brain coverings. From these, the blood travels either by way of the jugular veins, or by communications through the skull, to join with blood draining from the scalp to return eventually to the heart.

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