Editing Scalp (section)

==Structure==
[[File:Gray1196.png|thumb|right|Diagrammatic section of scalp]]
[[File:Blausen 0110 BrainLayers.png|thumb|Illustration of the scalp and meninges]]
===Layers===
The scalp is usually described as having five layers, which can be remembered using the [[mnemonic]] 'SCALP':
* S: [[Skin]]. The skin of the scalp contains numerous [[hair follicle]]s and sebaceous glands.
* C: [[Connective tissue]]. A dense subcutaneous layer of [[fat]] and fibrous tissue that lies beneath the skin, containing the nerves and vessels of the scalp.
* A: [[galea aponeurotica|Aponeurosis]]. The epicranial aponeurosis or galea aponeurotica is a tough layer of dense fibrous tissue which anchors the above layers in place. It runs from the [[frontalis muscle]] anteriorly to the [[occipitalis]] posteriorly.
* L: [[Loose areolar connective tissue]]. This layer has a gel-like consistency, and allows the more superficial layers of the scalp to shift about in relation to the pericranium. It is constituted of more [[Matrix (biology)|matrix]] than fibers. It contains {{Clarify|text=random [[collagen I]] bundles, [[collagen III]]|date=February 2024}} and is rich in [[glycosaminoglycans]] (GAGs). In [[craniofacial surgery]] and [[neurosurgery]] this layer provides an easy plane of separation between the upper three layers and the pericranium. In [[scalping]] the scalp is also torn off through this layer. The layer is sometimes referred to as the "danger zone" because infectious agents can easily spread through it to [[emissary veins]] which drain into the [[skull|cranium]]. 
* P: Pericranium. This is the [[periosteum]] of the skull bones, a membrane that provides nutrition to the bone and the capacity for repair. During surgery it can be lifted from the bone to allow the removal of windows of bone ([[craniotomy]]).

===Blood supply===
The blood supply of the scalp is via five pairs of arteries, three from the [[external carotid]] and two from the [[internal carotid]]:
* internal carotid
** the [[supratrochlear artery]] to the midline forehead. The supratrochlear artery is a branch of the ophthalmic branch of the internal carotid artery.
** the [[supraorbital artery]] to the lateral forehead and scalp as far up as the vertex. The supraorbital artery is a branch of the ophthalmic branch of the internal carotid artery.
* external carotid
** the [[superficial temporal artery]] gives off frontal and parietal branches to supply much of the scalp
** the [[occipital artery]] which runs posteriorly to supply much of the posterior aspect of the scalp
** the [[posterior auricular artery]], a branch of the external carotid artery, ascends behind the auricle to supply the scalp above and behind the auricle.
Because the walls of the blood vessels are firmly attached to the fibrous tissue of the superficial fascial layer, cut ends of vessels here do not readily retract; even a small scalp wound may bleed profusely.

'''Venous drainage'''
The veins of the scalp accompany the arteries and thus have similar names, e.g. Supratrochlear and supraorbital veins, which unite at the medial angle of the eye, and form the angular vein, which further continues as the facial vein.

The superficial temporal vein descends in front of the tragus, enters the parotid gland, and then joins the maxillary vein to form the retromandibular vein. The anterior part of it unites with the facial vein to form the common facial vein, which drains into jugular vein, and ultimately to the subclavian vein. The occipital vein terminates to the sub-occipital plexus.

There are other veins, like the emissary vein and frontal diploic vein, which also contribute to the venous drainage.

===Nerve supply===
Innervation is the connection of nerves to the scalp: the sensory and motor nerves innervating the scalp. The scalp is innervated by the following:
* [[Supratrochlear nerve]] and the [[supraorbital nerve]] from the [[ophthalmic division]] of the [[trigeminal nerve]]
* [[Greater occipital nerve]] (C2) posteriorly up to the vertex
* [[Lesser occipital nerve]] (C2) behind the ear
* [[Zygomaticotemporal nerve]] from the [[maxillary nerve|maxillary division]] of the [[trigeminal nerve]] supplying the hairless temple
* [[Auriculotemporal nerve]] from the [[mandibular division]] of the [[trigeminal nerve]]

The innervation of scalp can be remembered using the mnemonic 'Z-GLASS' for '''Z'''ygomaticotemporal nerve, '''G'''reater occipital nerve, '''L'''esser occipital nerve, '''A'''uriculotemporal nerve, '''S'''upratrochlear nerve, and '''S'''upraorbital nerve.

The motor innervation of the scalp, specifically, the [[occipitofrontalis]] muscle, is split into two main factions: the frontal belly or [[frontalis muscle]] is supplied by the [[temporal branch of facial nerve]], while the occipital belly or [[occipitalis]] is supplied by the [[posterior auricular nerve|posterior auricular branch of facial nerve]].

===Lymphatic drainage===
Lymphatic channels from the posterior half of the scalp drain to occipital and posterior auricular nodes. Lymphatic channels from the anterior half drain to the parotid nodes. The lymph eventually reaches the submandibular and deep cervical nodes.