The occipital nerves are sensory structures located at the base of the skull and upper neck, providing sensation to significant portions of the scalp. Their location makes them susceptible to irritation or compression from surrounding muscles and connective tissue. Understanding their anatomy is crucial for diagnosing common pain syndromes affecting the head and neck. These nerves originate from the uppermost part of the spinal column, specifically the second and third cervical spinal nerves (C2 and C3).
Origin and Classification of the Occipital Nerves
The occipital nerves arise from the spinal nerves exiting the upper cervical vertebrae (C2 and C3). They are categorized into three main branches based on size and origin: the Greater Occipital Nerve (GON), the Lesser Occipital Nerve (LON), and the Third Occipital Nerve (TON).
The Greater Occipital Nerve is the largest and most clinically significant, emerging primarily from the dorsal ramus of the second cervical spinal nerve (C2). The Lesser Occipital Nerve originates mainly from the ventral rami of the C2 and C3 spinal nerves, contributing to the cervical plexus. The Third Occipital Nerve is the medial branch of the dorsal ramus of the third cervical spinal nerve (C3).
Detailed Pathways of the Greater and Lesser Occipital Nerves
The physical course of the Greater Occipital Nerve (GON) is complex, involving a winding route through dense muscular layers before reaching the scalp. It initially emerges between the first and second cervical vertebrae, running backward beneath the obliquus capitis inferior muscle. The nerve then traverses the suboccipital triangle and ascends between the inferior capitis oblique and the semispinalis capitis muscles.
The GON typically pierces the semispinalis capitis muscle as it travels toward the skin. It continues to ascend and penetrates the aponeurotic fibrous layer of the trapezius muscle near its attachment to the occipital bone. This tortuous path through multiple layers of deep muscle makes the GON vulnerable to physical irritation. It eventually reaches the scalp alongside the occipital artery, crossing the superior nuchal line.
The Lesser Occipital Nerve (LON) follows a more lateral course than the GON as it ascends toward the head. After arising from the cervical plexus, the LON loops around the accessory nerve and travels superiorly along the posterior border of the sternocleidomastoid muscle. It remains relatively superficial compared to the GON, moving through the posterior triangle of the neck.
Near the cranium, the LON pierces the deep cervical fascia to transition into the subcutaneous layer of the scalp. It continues its ascent near the ear, distributing branches to the skin in that region. While the LON typically runs along the muscle’s border, anatomical variations exist where it may occasionally pierce the sternocleidomastoid muscle itself.
Primary Sensory Function
The primary function of the occipital nerves is sensory innervation, transmitting information about touch, pain, and temperature from the skin back to the brain. They cover specific, overlapping regions of the posterior scalp and upper neck. The Greater Occipital Nerve supplies the largest area, providing sensation to the central portion of the posterior scalp, often reaching the very top of the head (the vertex).
The Lesser Occipital Nerve is responsible for providing feeling to the skin of the upper neck, the area behind the ear, and adjacent parts of the posterior scalp. The Third Occipital Nerve supplies a smaller, more medial area of the lower occipital scalp and upper neck region. This nerve also provides sensory input to the C2-C3 facet joint, connecting it to deeper structures in the neck.
Anatomical Basis of Occipital Neuralgia
Occipital neuralgia is a painful condition arising from the physical irritation or compression of the occipital nerves. The Greater Occipital Nerve (GON) is especially prone to compression due to its demanding pathway through several layers of dense muscles. One of the most common sites for nerve entrapment is where the GON pierces the semispinalis capitis muscle.
Chronic muscle tension, injury, or inflammation in the neck can cause the muscle tissue or the surrounding fascia to tighten, effectively squeezing the nerve. The point where the GON pierces the tough aponeurotic tissue of the trapezius muscle is another frequent compression zone, often referred to as the trapezial tunnel. This pressure causes the characteristic shooting, stabbing, or throbbing pain that follows the nerve’s sensory distribution pattern.
The Lesser Occipital Nerve can also be compressed, typically where it emerges from behind the sternocleidomastoid muscle and pierces the deep cervical fascia. Both the GON and LON run in close proximity to the occipital artery, and tension or constriction around this vessel may also contribute to nerve irritation. Furthermore, the C2 spinal nerve root, from which the GON originates, is itself a potential site of irritation, which can be caused by conditions like arthritis in the upper cervical spine.