The central nervous system

ANATOMY Brain The scalp is extremely vascular with blood supply coming from the external carotid arteries; anteriorly from the superficial temporal arteries which are branches of the maxillary arteries and posteriorly the occipital arteries. Since these vessels enter the scalp from the base upwards towards the vertex and since the supply is very good, provided the location of these supplying vessels is borne in mind, scalp incisions can be made almost anywhere with impunity without devascularizing the scalp. The layers of the scalp can be remembered by a mnemonic: S s kin C sub c utaneous tissue A the a poneurosis (galea) L l oose areola tissue (the scalp is reflected back by dissecting this layer) P p ericranium (periosteum) When suturing a scalp wound absorbable sutures are used to close the galea and then clips or sutures in the skin. As all the significant vessels lie within the subcutaneous tissue this two layer closures tamponades the vessels and can control all scalp edge bleeding. The skull is a complex series of connected bones. In the neonate the vault bones are only loosely attached at sutures and these join with cartilagenous fusion at 18 months. The skull reaches 90% of its adult size at approximately 7 years, and maximum size at puberty; the suture lines can be seen on skull radiographs throughout life but tend gradually to obliterate with advancing age. The skull varies in thickness in differing areas, being thickest in the parieto-occipital area and thinnest in the temporal area just above the mandibular articulation.