 Dr. Sanjay Sanyal, Professor Department Chair, we shall demonstrate the layers of the scalp from a different perspective. Reflecting the scalp, let's start with the age-old mnemonic, the layers of the scalp. S, C, A, L, P. Skin, C, connected tissue, dense. A, aponeurosis of the epicranial or the occipital frontalis muscle. L, loose areola tissue. P, periosteum or the pericranium. Let's say a few quick words about each of these layers. Let's start with the S, the skin. The skin of the scalp is very dense, it's very thick and it's richly covered with hair follicles as we all know. And it's got sebaceous layers. Let's come to the more important layer that is C, the connected tissue dense layer. The dense connected tissue layer is basically a subcutaneous tissue of the scalp itself. But the importance of this lies in the fact that it has got numerous fibres which connect the scalp very densely to the underlying neck structure that is the aponeurosis. This layer, the connected tissue dense layer acts as a glue connecting the skin to the aponeurosis. And the blood vessels which are running in this layer, they are all tightly adherent to the surrounding fibro structure. Therefore whenever there is an injury of the scalp, the blood vessels cannot contract and retract and therefore they bleed profusely. Coming to the aponeurosis. The aponeurosis is the central portion which connects the frontalis muscle in the front and the occipitalis muscle at the back. The occipitalis muscle takes origin from the superior nuclei and gets inserted onto the aponeurosis. When it contracts, it makes aponeurosis dense and therefore it increases the functionality of the frontalis muscle. The frontalis muscle takes origin from the aponeurosis and it gets inserted onto the skin of the forehead and therefore it produces horizontal wrinkles of the skin of the forehead. Now let's take a look at the lateral extension of the aponeurosis, the glia aponeurotica. For that I am going to reflect this temporal flap here. And when I reflect the temporal flap, you see this tissue. This is the lateral extension of the aponeurosis. This lateral extension, anatomy textbooks call this the superficial temporal fascia. And we see a layer of fascia under that, a tough fascia. Anatomy books call this the deep temporal fascia because this is the one which is covering the temporalis muscle. Surgical textbooks call this fascia as the temporal parietal fascia. And laterally this is attached to the zygomatic arch. The parietal fascia contains all the blood vessels to the scalp. Predominantly we can see this blood vessel. This is the superficial temporal artery which is a branch of the external carotid artery. And this is the superficial temporal vein and they are dividing into a frontal branch and a parietal branch. These blood vessels as well as a nerve called the auricular temporal nerve run in the superficial temporal parietal fascia. The deep fascia, that is the true temporal fascia, forms the roof of the temporal sposa. And it also covers the temporalis muscle but it is not part of the scalp and it is also attached to the zygomatic arch. This is the loose and irregular tissue layer where my finger is gone in. And where my assistant is putting his probe inside. This is the layer which separates the scalp proper. That is skin-connected tissue and aponeurosis. That is layers number 1, 2 and 3 from the periosteum. This loose, irregular tissue layer is literally loose layer. And we can see my finger goes very easily and it strips off the scalp from the underlying periosteum. This is also referred to as the danger layer of the scalp or the surgeon's layer of the scalp. And there are at least 4 reasons why this is referred to as the danger layer. Number 1, this layer is poorly supplied by blood vessels and therefore infection can easily settle in this layer. The second reason being the same infection can travel through the emissary veins in this layer to the intracranial venous sinuses, producing intracranial venous sinus thrombosis. The third reason is people can get a version of the scalp at this layer and how does this occur? This occurs especially when people with long hair are operating near rotating machinery. The long hair gets caught in the machinery and the whole scalp gets completely pulled away from the underlying periosteum and that occurs through this layer and that is known as the version of the scalp. Incidentally, in the 19th century, the Native Americans used to scalp their enemies through this layer and that was known as scalping in common language. And the fourth reason why this is called the danger layer is because if there is a blunt trauma to the head or the forehead, next morning the patient presents with black eye. The reason for the black eye is because any which occurs in this layer, it cannot go posteriorly because the occipitalis muscle is attached to the supineucal line. The blood cannot track laterally because this facial layer is attached to the zygomatic arch. Therefore, the only place that the blood can go is anteriorly and it tracks under the frontalis muscle and then it spreads under the skin of the eyelid because eyelid skin is very loose and it then tracks around the orbicularis oculi producing what is known as black eye or the racoon eye. So these are some of the reasons why this layer is also referred to as the danger layer of the scalp. Now let's come to the periosteum or the pericranium. The periosteum of the pericranium is not only covering the outer surface of the skull, that is the vault of the calvarium, but it also goes through the sutures and becomes there known as sutural membrane and from there it becomes continuous with the endosteum which is the periosteum lining the inner surface of the skull. This also goes through the foremen of the skull and it becomes continuous with the endosteum and the same periosteum then continues on to the base of the skull where it is densely adherent to the base of the skull. Whenever there is any fracture of the base of the skull, the endosteum tends to tear and can produce CSF leakage and can come out through the nose in the form of CSF rhinorrhea. It can come out through the ear in the form of CSF autoria. What about the arterial supply of the scalp as a whole? We will remember three arteries in front of the ear and two arteries behind the ear. The three arteries in front of the ear are starting from medial most. We have the supratrocular artery, small one, a suprorbital artery which goes right up to the vertex of the skull and then we have the superficial temporal artery which I showed you just now. This is the superficial temporal artery. So these are the three arteries which come from the front and the sides. Most clearly we have a smaller artery behind the ear which is called the posterior auricular artery and we have a bigger artery which we can see here, a branch of that, that is the occipital artery. These are all branches of the external carotid artery. These arteries not only anastomous with each other but they also anastomous with the opposite side and that is another reason why scalp injuries tend to bleed so profusely. So this is about the arterial supply. Let's come to the nerve supply of the scalp as a whole. For that we have reverted the whole scalp into four quadrants as we can see now. So let's take the anterior most portion of the anterior quadrant. It's supplied by the supra trochlear nerve which is a small nerve and the supra orbital nerve which is a long one going right up to the vertex. Then further laterally in front of the ear we have the zygometicotemporal and the auriculotemporal. Coming behind the ear we have the great auricular and the lesser occipital and we can see the lesser occipital here and then further posteriorly we have the greater occipital and the third occipital. The great auricular and lesser occipital are both C2, C3 anterior rami. The greater occipital is C2 posterior rami and the third occipital is C3 posterior rami. So this is about the nerve supply of the scalp. If a patient has any pathology in the anterior or the middle cranial fossa the pain is referred to the front of the forehead and that is known as frontal headache and that is in the distribution of CN5V1V2 that is ophthalmic and maxillary division corresponding to the distribution of the nerve supply of the front of the scalp. If a patient has a pathology in the posterior cranial fossa that pain is referred to the back of the skull that is referred to as occipital headache and that is in the distribution of the greater occipital and the third occipital namely C2 and C3. So this is all about the surgical anatomy of the layers of the scalp and their clinical correlations. Thank you very much for watching. If you have any questions or comments please put them in the comment section below. Dr. Sanjay Sanyal signing out. Have a nice day. Guys, thank you so much for watching. Make sure you like and make sure you subscribe.