Sensory innervation of the scalp is from two major sources, cranial nerves or cervical nerves, depending on whether it is anterior or posterior to the ears and the vertex of the head (Fig. 8.73), The occipitofrontalis muscle is innervated by branches of the facial nerve [VII].
Anterior to the ears and the vertex
Branches of the trigeminal nerve [V] supply the scalp anterior to the ears and the vertex of the head (Fig. 8.73). These branches are the supratrochlear, supra-orbital, zygomaticotemporal, and auriculotemporal nerves:
The supratrochlear nerve exits the orbit, passes through the frontalis muscle, continues superiorly across the front of the forehead, and supplies the front of the forehead near the midline.
The supra-orbital nerve exits the orbit through the supra-orbital notch or foramen, passes through the frontalis muscle, and continues superiorly across the scalp as far back as the vertex of the head.
The zygomaticotemporal nerve exits the skull through a foramen in the zygomatic bone and supplies the scalp over a small anterior area of the temple.
The auriculotemporal nerve exits from the skull, deep to the parotid gland, passes just anterior to the ear, continues superiorly anterior to the ear until nearly reaching the vertex of the head, and supplies the scalp over the temporal region and anterior to the ear to near the vertex.
Posterior to the ears and the vertex
Posterior to the ears and vertex, sensory innervation of the scalp is by cervical nerves, specifically branches from spinal cord levels C2 and C3 (Fig. 8.73). These branches are the great auricular, the lesser occipital, the greater occipital, and the third occipital nerves:
The great auricular nerve is a branch of the cervical plexus, arises from the anterior rami of the C2 and C3 spinal nerves, ascends on the surface of the sternocleidomastoid muscle, and innervates a small area of the scalp just posterior to the ear.
The lesser occipital nerve is also a branch of the cervical plexus, arises from the anterior ramus of the C2 spinal nerve, ascends on the posterior border of the sternocleidomastoid muscle, and supplies an area of the scalp posterior and superior to the ear.
The greater occipital nerve is a branch of the posterior ramus of the C2 spinal nerve, emerges just inferior to the obliquus capitis inferior muscle, ascends superficial to the suboccipital triangle, pierces the semispinalis capitis and trapezius muscles, and then spreads out to supply a large part of the posterior scalp as far superiorly as the vertex.
The third occipital nerve is a branch of the posterior ramus of the C3 spinal nerve, pierces the semispinalis capitis and trapezius muscles, and supplies a small area of the lower part of the scalp.
Arteries supplying the scalp (Fig. 8.74) are branches of either the external carotid artery or the ophthalmic artery, which is a branch of the internal carotid artery.
Branches from the ophthalmic artery
The supratrochlear and supra-orbital arteries supply the anterior and superior aspects of the scalp. They branch from the ophthalmic artery while it is in the orbit, continue through the orbit, and exit onto the forehead in association with the supratrochlear and supra-orbital nerves. Like the nerves, the arteries ascend across the forehead to supply the scalp as far posteriorly as the vertex of the head.
Branches from the external carotid artery
Three branches of the external carotid artery supply the largest part of the scalp—the superficial temporal, posterior auricular, and occipital arteries supply the lateral and posterior aspects of the scalp (Fig. 8.74):
The smallest branch (the posterior auricular artery) leaves the posterior aspect of the external carotid artery, passes through deeper structures, and emerges to supply an area of the scalp posterior to the ear.