There are 12 cranial nerves in our body that are responsible for supplying various parts to communicate signals from the brain. Based on the function and location, cranial nerves can have sensory, motor, or a combined supply.
Mixed cranial nerves are a group of cranial nerves that consist of sensory and motor nerve fibers. There are four such nerves in our peripheral nervous system namely the Trigeminal nerve (CN V), Facial nerve (CN VII) Glossopharyngeal nerve (CN IX), and Vagus nerve (CN X).
Let’s take a look at each of the four mixed cranial nerves to explore their functions and locations better.
Trigeminal nerve (CN V)
The trigeminal nerve (CN V) is a mixed cranial nerve containing both, general sensory (afferent) fibers and somatic motor (efferent) fibers. The fibers start from the nuclei present in the brainstem and spinal cord.
The spinal cord has the following nuclei for the trigeminal nerve which are referred to as the principal sensory nucleus of the trigeminal nerve, the mesencephalic nucleus of the trigeminal nerve, the motor nucleus of the trigeminal nerve, and the spinal nucleus of the trigeminal nerve. CN V forms a trigeminal ganglion close to the apex of the petrous portion of the temporal bone.
Arising from the trigeminal ganglion, the trigeminal nerve branches into three divisions.
- Ophthalmic nerve (CN V1)
- Maxillary nerve (CN V2)
- Mandibular nerve (CN V3)
Ophthalmic division leaves the skull through the superior orbital fissure, maxillary division exits via the foramen rotundum in the base of the skull, and the mandibular nerve leaves via through the foramen ovale.
The sensory branch of the fifth cranial nerve transmits information about pain, touch sensations, pressure, and temperature from the anterior two-thirds of the brain, including the face.
The smaller muscular component supplies the skeletal muscles that are derived from the first pharyngeal arch such as the mylohyoid muscles, tensor tympani in the ear, tensor veli palatini in the pharynx, anterior belly of the digastric muscle, and the mastication muscles (the masseter, temporalis, medial and lateral pterygoid muscles).
Because of its notable size, the trigeminal nerve can be easily noticed where it emerges in the brainstem from the pons close to the middle cerebral peduncle.
Here’s an insight into the three divisions of the trigeminal nerve.
Ophthalmic Division (CN V1)
The ophthalmic division of the trigeminal nerve (CN V1) transmits sensory signals from receptors on the: forehead (upper part of the face), scalp, cornea, upper eyelid, dorsal surface of the nose, and the mucous membranes that line the nasal and frontal sinuses.
The information signals then travel along the nerve fibers which enter the skull through the superior orbital fissure accompanied by other cranial nerves such as the oculomotor, trochlear, and abducens nerves.
Maxillary Division (CN V2)
The maxillary division of the fifth cranial nerve (CN V2) transmits sensory signals from receptors located on the following structures.
- Upper Teeth
- Lateral Surface Of The Nose
- Hard Palate
- Upper Cheek
- Mucous Membranes Of The Upper Teeth
- Roof Of The Mouth
Signals that are initiated by these receptors then travel down the nerve fibers and go into the skull through the foramen rotundum.
Mandibular Division (CN V3)
The mandibular branch of the trigeminal nerve (CN V3) sends sensory signals from receptors located on the following structures.
- Lower jaw and teeth
- External ear
- Parts of the posterior cheek
- The floor of the mouth.
- Anterior two-thirds of the tongue
It also supplies motor branches to the muscles of mastication along with a few other muscles present in the lower face. These nerve fibers enter the skull through the foramen ovale.
Facial Nerve (CN VII)
The facial nerve is responsible for the following functions.
- Moving muscles that help in facial expressions as well as those that move your jaw
- Providing taste sensation for most of the tongue
- Supplying glands present in the head or neck area, for example, the salivary glands and tear-producing glands
- Communicating sensations present in the outer parts of the ear
The facial nerve carries both, general and special sensory fibers. It starts from the brainstem as two separate branches. There is a larger primary motor root that runs along with a smaller intermediate nerve that carries sensory and parasympathetic nerve fibers.
The motor root starts from the motor nucleus of the facial nerve, while the sensory fibers stem from the nuclei of the solitary tract, the superior salivatory nucleus, and the spinal nucleus of the trigeminal nerve.
The two divisions of the facial nerve exit the cranial cavity via the internal acoustic meatus and then travel through the facial canal. Once they reach this space, they join together and leave the cranium through a space known as the stylomastoid foramen.
The facial nerve innervates several muscles of facial expression and also salivary glands via its major branches that are listed below.
- Cervical branches
Sensory branches that reach the middle ear, nasal cavity, soft palate produce the general visceral afferent limb of the eye.
Anterior two-thirds of the tongue is supplied by special visceral afferents whereas the general somatic afferents supply the external auditory meatus. Motor fibers from the facial nerve supply the lacrimal, submandibular, sublingual, nasal, palatine glands.
Glossopharyngeal Nerve (CN IX)
The ninth cranial nerve is responsible for the following functions.
- Sends sensory information from your sinuses, back of the throat, parts of the inner ear, and the back portion of your tongue
- Provides the sensation of taste to the back (posterior) part of your tongue
- Stimulates voluntary movements of a muscle present in the back of the throat known as the stylopharyngeus
The glossopharyngeal nerve originates from the brainstem and exits the skull through the jugular foramen. The fibers commence from the four nuclei listed below.
- Inferior salivatory nucleus
- Nucleus ambiguous
- Nuclei of the solitary tract
- Spinal nucleus of the trigeminal nerve
This nerve enables swallowing, salivation, taste sensation, and blood gas levels regulation.
Its motor fibers innervate the stylopharyngeus and pharyngeal constrictors. Some fibers also supply the parotid gland. Sensory information is processed via fibers from the posterior one-third of the tongue, middle ear, pharynx, epiglottis, carotid body, carotid sinus.
Vagus Nerve (CN X)
The Vagus nerve is also a mixed cranial nerve that contains somatic and visceral fibers supplied to various parts of the body. It starts from multiple nuclei present in the brainstem that leave the skull through the jugular foramen.
It has the following nuclei: nucleus ambiguus, the posterior nucleus of the vagus nerve, nuclei of the solitary tract (dorsal motor nucleus), and spinal nucleus of the trigeminal nerve.
The Vagus nerve has a parasympathetic supply to the visceral organs in the thoracic and abdominal cavity. It is the only cranial nerve that exits the head and neck region. The tenth cranial nerve is responsible for the following functions.
Its somatic (motor) fibers supply the thoracic and abdominal visceral organs. They also supply the laryngeal and pharyngeal muscles as special fibers.
Sensory fibers from the vagus nerve supply the epiglottis, external acoustic meatus, the skin around the ear, and posterior (back) part of meninges which are linings covering the brain.