scalp anatomy l General human anatomy revision for dental students

Scalp anatomy l General human anatomy revision for dental students

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The scalp

Definition: 

• it is the soft tissue covering the vault of the skull.

Extent: 

• it extends from the supraorbital margins to anteriorly to the highest nuchal lines and external occipital protuberance at the back of the skull and down to the superior temporal lines at the sides.

Structure:

• It consists of five layers, the first three of which are intimately bound together and move as a unit.
• The five letters of the word (SCALP) indicates its five layers:

Skin:

1. Thick, rich in hair follicles and sebaceous glands.
2. The commonest site for the formation of sebaceous cysts.

 

Connective tissue:

1. Fibro fatty layer                          
2. Fibrous septa uniting the skin to the underlying aponeurosis of the occipitofrontalis m.
3. Numerous arteries and veins found in this layer.
4. Nerves of the scalp are found in this layer.

Aponeurosis (epicranial):

• A thin, tendinous sheet uniting the occipital and frontal bellies of occipito-frontalis m.
• Attached on each side to superior temporal line.
• (The subaponeurotic space) is the potential space beneath thr epicranial aponeurosis.

Loose areolar tissue:

• Allows mobility of the aponeurosis on the underlying periosteum.
• Contains a few small arteries and some important valveless emissary veins.
• The emissary veins connects the superfascial veins of SCALP with  diploic veins of the skull bones and the intracranial venous sinuses.

 

Periosteum (pericranium):

• It is loosely attached to the bones but firmly adherent to sutures between bones.

Occipitofrontalis muscle

Origin: 

• it consists of four belies two fused frontal bellies & two separate occipital bellies, connected by a broad sheet of strong fibrous tissue called aponeurosis.
• The occipital belies arise from highest nuchal line
• The frontal bellies arise from the skin & superficial fascia

Insertion:

• The occipital & frontal bellies are attached into the aponeurosis (epicranium)

 

Nerve supply:

• Post. Auricular branch of the facial N. (CN XII) à occipital belly
• Temporal branch of the facial n. (CN XII) à Frontal belly

 

Action:

1. Occipitalis usually merely anchors (tightens) the epicranial aponeurosis. In certain individuals it can pull the scalp Posteriorly
2. Frontalis elevate the eyebrows in expressions of surprise or horror & producing wrinkles of the skin of forehead

Extent of Galea Aponeurotica

• Anterior: It begins at the coronal suture and extents over the frontal bellies till the eyebrows. A part of the fibrous tissue extends upto the root of nose as a median prolongation.

• Posterior: It blends with the occipital bellies and extends further to attach over the external occipital protuberance and highest nuchal lines on either side.

• Lateral: It extends over the temporal fascia and thins out to attach to the zygomatic arch. The superficial fascia connects the apponeurosis to the skin above while it is separated from the periosteum by the layer of loose areolar tissue.

Blood supply of the SCALP

Arteries

• It has a very rich supply of blood to nourish the hair follicles and for this reason, the smallest cut bleeds profusely
• The arteries lie in the superficial fascia i.e. connective tissue of 2^nd layer of scalp
• 10 arteries (5 on each side) enter the scalp from the its periphery & ramify in its center forming a very rich anastomosis
• 5 arteries enter the scalp on each side:

3 in front of auricle

1. Supratrochlear a. br. Of ophthalmic a.
2. Supraorbital a. br. Of ophthalmic a.
3. Superficial temporal artery à the smaller terminal br. Of ECA within parotid gland

 

 

Arteries behind auricle

1. Post auricular artery à branch Of external carotid a.(ECA)
2. Occipital artery àbranch Of ECA

 

Venous Drainage of Scalp:

• The veins accompany arteries and form an interconnecting network over the scalp. They are:

1. Supratrochlear and supraorbital veins:

• They join to form the angular vein at the medial angle of eye and further continue as the facial vein.

2. Superficial temporal vein:

• It forms the retromandibular vein after joining with maxillary vein.

3. Posterior auricular vein:

• It joins the posterior division of retromandibular vein and forms the external jugular vein.

4. Occipital vein:

• Terminates into suboccipital plexus of veins.

Emissary veins:

• These are veins that connect the intracranial dural venous sinuses to the external veins of the scalp and face. Emissary veins of scalp are:

1. Parietal and mastoid emissary veins which connects occipital vein to sagittal and sigmoid sinuses respectively.
2. Emissary vein from facial vein to cavernous sinus.

Lymphatic Drainage of Scalp:

• Scalp is drained by the following lymph nodes:

1. Pre-auricular lymph nodes:

• These drain anterior part of scalp, except an area below the center of forehead.

2. Post auricular lymph nodes:

• These drain posterior part of scalp.

3. Occipital lymph nodes:

• A part of posterior aspect of scalp is drained by these nodes also.

Applied anatomy:

• The subaponeurotic space is the potential space beneath the epicranial aponeurosis that is occupied by the loose areolar tissue of the 4^th layer of scalp

1. This space extends down beneath Orbicularis oculi into the eyelids.
2. Bleeding anywhere beneath aponeurosis may appear as “black eye” by the blood tracking down through the space

 

• Pericranium, which is the periosteum of the vault of the skull, is loosely attached to the bone (outer table) but firmly attached to the sutures where it becomes continuous with periosteum (endosteum) on the inner table of the skull bones,

1. This explains why fissure or fracture of skull bone produces a “localized hematoma” overlying that bone.