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Introduction to the cranial nerves
Cranial nerve pathways
Anatomy of the olfactory (CN I) and optic (CN II) nerves
Anatomy of the oculomotor (CN III), trochlear (CN IV) and abducens (CN VI) nerves
Anatomy of the trigeminal nerve (CN V)
Anatomy of the facial nerve (CN VII)
Anatomy of the vestibulocochlear nerve (CN VIII)
Anatomy of the glossopharyngeal nerve (CN IX)
Anatomy of the vagus nerve (CN X)
Anatomy of the spinal accessory (CN XI) and hypoglossal (CN XII) nerves
Anatomy clinical correlates: Olfactory (CN I) and optic (CN II) nerves
Anatomy clinical correlates: Oculomotor (CN III), trochlear (CN IV) and abducens (CN VI) nerves
Anatomy clinical correlates: Trigeminal nerve (CN V)
Anatomy clinical correlates: Facial (CN VII) and vestibulocochlear (CN VIII) nerves
Anatomy clinical correlates: Glossopharyngeal (CN IX), vagus (X), spinal accessory (CN XI) and hypoglossal (CN XII) nerves
The spinal accessory nerve, or the eleventh cranial nerve, and the hypoglossal nerve, or the twelfth cranial nerve, are two purely motor cranial nerves that innervate muscles in the neck, as well as the tongue.
Specifically, the spinal accessory nerve provides somatic motor innervation to the sternocleidomastoid and trapezius muscles, while the hypoglossal nerve provides somatic motor innervation to almost all the muscles of the tongue.
Let’s start with the spinal accessory nerve. The somatic motor pathway of the spinal accessory nerve starts in the cerebral cortex. Then, the axons travel to the spinal accessory nucleus, which is located in the cervical spinal cord, specifically in the posterolateral aspect of the anterior horn.
The axons travel through the rootlets from the first five or six cervical segments of the spinal cord and form the spinal accessory nerve. The spinal accessory nerve ascends through the foramen magnum, enters the posterior cranial fossa, and then exits through the jugular foramen.
It continues its journey down along the internal carotid artery and runs deep to the sternocleidomastoid muscle, which it supplies. Then, it emerges from the sternocleidomastoid muscle through its posterior border, and continues inferiorly in the posterior triangle of the neck to reach and supply the trapezius muscle through multiple branches.
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