The Hypoglossal Nerve (Cranial Nerve XII)

The hypoglossal nerve is the twelfth cranial nerve, and innervates all the extrinsic and intrinsic muscles of the tongue, except for the palatoglossus which is innervated by the vagus nerve. It is a nerve with a solely motor function[1]. It starts in the medulla oblongata and moves down into the jaw, where it reaches the tongue[2].

The Accessory Nerve (Cranial Nerve XI)

The eleventh cranial nerve is the accessory nerve. It is a motor nerve, responsible for innervating the sternocleidomastoid (SCM) and the trapezius muscles. The SCM is a muscle in the neck that allows rotation (looking side to side) and flexion (looking down) of the neck[1]. The trapezius muscle acts to shrug the shoulder.

The Vagus Nerve (Cranial Nerve X)

The vagus nerve is partially responsible for parasympathetic control of the heart, lungs, and digestive tract[1]. The parasympathetic nervous system is more commonly referred to as the “rest and digest” state of the body. This is on contrast to the sympathetic nervous system, which is responsible for the “fight or flight” state of the body[2]. The vagus nerve leaves the medulla oblongata and travels down the neck, chest, and finally the abdomen[1]. It comprises 80% to 90% of afferent nerves containing mainly sensory information about the body’s organs to the central nervous system (CNS)[3]. The vagus nerve doubles as a sensory and motor nerve.

A few responsibilities of the vagus nerve include controlling heart rate, sweating, movement of muscles in the mouth, including speech, and satiation following food consumption[3].

The Glossopharyngeal Nerve (Cranial Nerve IX)

The ninth cranial nerve is both a motor nerve, carrying afferent and efferent motor information, and a sensory nerve[1]. Afferent means it is traveling from somewhere in the body to the brain.This only motor function is to elevate the pharynx[2]. The sensory aspect of the glossopharyngeal nerve comes from the pharynx, tonsils, middle ear, and posterior third of the tongue[2]. The ninth cranial nerve is responsible for the carotid sinus reflex. Sensory fibers receive information from the carotid bodies to detect blood pressure in the sinus of the carotid[2]. If there is pressure applied to the carotid artery, then the body reacts by lowering its blood pressure[2].

The Vestibulocochlear Nerve (Cranial Nerve VIII)

The vestibulocochlear nerve is also known as the auditory vestibular nerve. It transmits sound and equilibrium (balance) information from the inner ear to the brain[1]. The eighth cranial nerve splits into the cochlear nerve and the vestibular nerve. This is a primarily sensory nerve[2]. The vestibulocochlear nerve allows us to sense sound, gravity, and body rotation[2]. If a person’s eighth cranial nerve is damaged they may experience a vertigo, hearing loss, or a false sense of movement[2].