What are the main 5 layers of the scalp?
- Skin with hair follicles
- Connective Tissue layer (Dense)
- Loose connective tissue
Describe the anatomical borders of the “scalp”
From the external occipital protuberance (EOP) posteriorly and to the supraorbital margins in front (includes the forehead)
Laterally: extends to the temporal bones on both sides to the levels of the zygomatic arches.
Describe the first (most superficial) connective tissue layer and its main features
A dense layer with lots of fat, nerves and vessels (neurovascular layer)
The layer also has fibrous septa that hold the arteries and vessels open and restrict them from allowing clotting to take place.
Why would a laceration to the scalp tend to bleed profusely?
This very rich vascular supply (see diagram layer) contains anastomoses between internal and external carotid arteries.
The vessels of the scalp (dense CT layer) spiral onto the scalp from the perimeter makes t difficult to compress edges due to his pull. - Local occlusion/pressure requires circumferential application
Describe the loose connective tissue layer of the scalp
Allows for movement of scalp on the skull. It has a spiderweb like appearance making it a good medium for spread of infection from infected cut in the scalp. (common site for infection localisation).
The emissary veins also come from the dense CT layer and they have the potential to spread internal to the skull - meningitis (and encephalitis once heads to the pia)
What is the pericranium?
Pericranium (the periosteum of the skull) – it is firmly anchored to the scalp.
Why is the dura sometimes described as having two layers? Describe them
The outer layer is the periosteal or endosteal layer because it is closest to the periostium and adheres very firmly to the skull.
Inner layer is referred to as the meningeal layer (is the true dura), which adheres firmly to the underlying arachnoid space.
This two layer is not very prominent, only in the case of the venous sinuses that occur between the two “layers”
Of what muscle/s does the aponeurosis layer of the scalp belong to?
The occiptofrontalis muscle, which has two bellies: one posteriorly (occipitalis) and one anteriorly (frontalis) forming the centrally placed aponeurosis.
Why do most scalp wounds gape widely?
Because of the set up of the centrally placed aponeurosis, the bellies pull in opposite directions to widely open the wound.
Describe the layering [4 layers] of the face from superficial to deep (to bone)
- Subcutaneous connective tissue - neurovascular plane
- Muscles of facial expression
- Periosteium on external surface of facial bones
What are four major rules about the muscles of the face?
- They all arise from bone or fascia
- They all attach to the skin of the face
- They all surround a facial orifice (eyes, nose or mouth)
- They are divided into a muscles that encircle orifices (sphincters) or radiate out (dilators
What are the major groups of muscles in the face?
The frontalis muscle is also a muscle of facial expression, what is the major movement?
Elevation and depression (movement) of the forehead
What is the embryological source of the muscles of facial expression?
What nerve innervates their motor control?
Muscles of facial expression are from the 4th pharyngeal arch and they are supplied by CNVII (facial)
Describe the dermatomal innervation of the face and scalp
Anterior to the ears: cutaneously supply from CN V (Trigeminal nerve - the three divisions)
Posterior to the ears (back of the scalp) from C2
The front and side of the neck (cervical collar distribution) are supplied by C3
Where does the trigeminal ganglion sit?
At the apex of the petrous part of the cranial bone (wedge) in the middle cranial fossa. From here, the three divisions head to their target distributions.
What are the two main arterial vessels that supply the face and scalp?
Rich vascular supply with overlap between internal and external carotid arteries. Anastomoses between branches of internal carotid artery (black) and internal carotid artery (red).
Describe the distribution of arterial supply of the internal carotid artery to the face
The internal carotid comes off the common carotid and passes through the through the carotid canal and branches to give off the opthalmic artery supplying the eye balls and the central area of the forehead. They also give off the Supraorbital branches directly above the eye and supratrochlear branches above the nose
Describe the distribution of the arterial supply of the external carotid artery to the face
The external carotid in the neck branches anteriorly off the common carotid and forms the facial artery, which crosses the inferior border of the mandible to get onto the face. It has a very tortuous course and heads to the medial angle of the eye, as it does it gives branches to upper and lower lip, nose and cheek.
Describe the distribution of the arterial supply of the external carotid artery to the rest of the scalp
Branches off the external carotid artery supplies the rest of the scalp.
- The superficial temporal artery passes over the zygomatic arch and supplies the side of the scalp
- Posterior branch called the posterior auricular artery is then given off for behind the ear
- Most posteriorly are the occipital arteries for the occipital region.
Each of the arteries has a vein accompanying them. Describe the venous drainage of the face
The facial vein is the major venous drainage from the face. It runs posterior and slightly more superficial to the artery. It is straighter than the artery.
What is the risk of infection spread from the skin to the brain through the anterior part of the face?
There is potential for venous drainage through the emissary veins and diploic veins of the face into the venous sinuses. Through to the cavernous sinus.
Describe lymphatic drainage from the face and scalp 
All lymphatic vessels of the face and scalp drain into a ring of nodes around the base of the skull.
- Mastoid (over the mastoid process) also called posterior auricular
- Parotid and pre-auricular
They are superficial nodes draining all the structures of the face and scalp and from this ring, the lymphatics drain into the deep cervical nodes.
What is the parotid gland?
Where is its location?
A serous salivary gland
- Below the zygomatic arch
- Above the angle of the mandible
- In front of the ear
- Behind one of the muscles of mastication (masseter muscle).
- The parotid gland sits superficial to the styloid process of the temporal bone.
The parotid gland is wrapped in a dense layer of parotid fascia. What is the implication of this in the case of inflammation of the gland (eg. mumps)
Parotid infections are intensly painful as the fascia has no give in it for a swelling and inflamed gland (the pressure rises and causes pain)
Where does the parotid duct emerge from and where does it go?
Parotid duct emerges from the front of the gland on the masseter muscle and disappearing at the anterior border of it, piercing buccinator and entering the oral cavity opposite the second upper molar.
There are  structures that sit within the parotid gland. What are they in order from superficial to deep?
- Facial nerve plexus
- Retromandibular vein
- Terminal branches of the external carotid artery
What are the  terminal branches of the facial nerve?
Describe the extracranial course of the facial nerve from its exit point to the terminal branches
- Exits from the stylomastoid foramen (between the styloid and mastoid processes of the temporal bone)
- It gives a branch to occipitalis muscle (forehead)
- Creates a plexus (within the substance of the parotid gland) – enters the posteromedial surface of the parotid
- Terminal branches emerging from the anterior border of the gland heading to the forehead and the platisma muscle in the neck.
Describe the retromandibular vein
It is a vein that runs through the parotid gland and it sits behind mandible and is formed by union of the superficial temporal vein and the maxillary vein
Describe the formation of the terminal branches of the external carotid artery in the parotid gland
External carotid artery enters the substance of parotid gland from below and here it divides into 2 terminal branches:
- Superficial temporal artery (to lateral side of the scalp)
- Maxillary artery deeply placed for deeper structures
What is the important branch that is coming off the maxillary artery?
The middle meningeal artery is given off the maxillary artery and through spinosum into the scalp
What is Bell’s Palsy?
Any injury to facial nerve results in partial or complete paralysis of muscles of facial expression.
- Drooping of lower eyelid and angle of the mouth
- Cheek tends to fall away from teeth and mouth
- Flattening of the nasolabal fold
Bell’s Palsy is hemiparalysis of the face; most common cause is no known cause (may be post viral)