Cranial Nerves Overview

The trigeminal nerve (CN V) is responsible for sensory innervation to the face and motor control of the muscles of mastication (chewing).

The ophthalmic division (V1) of the trigeminal nerve provides sensory innervation to the forehead, scalp, and upper eyelid. It exits the skull through the superior orbital fissure.

The maxillary division (V2) of the trigeminal nerve provides sensory innervation to the cheek, nose, upper teeth, and palate. It exits the skull through the foramen rotundum.

The mandibular division (V3) of the trigeminal nerve provides sensory innervation to the lower jaw, lower teeth, and tongue. It also controls the muscles of mastication (chewing). This branch exits the skull through the foramen ovale.

Dural venous sinuses are spaces within the dura mater membrane of the brain that drain venous blood from the brain.

The superior sagittal sinus is a large sinus that runs along the midline of the superior surface of the brain.

The inferior sagittal sinus is a smaller sinus that runs along the underside of the falx cerebri.

The confluence of sinuses is a point where several sinuses meet, including the superior sagittal sinus, straight sinus, and transverse sinus.

The maxillary artery, a branch of the external carotid artery, supplies the buccal area of the face.

The superficial temporal artery, originating from the external carotid artery, supplies the upper forehead area.

The carotid sheath encases the internal jugular vein, common carotid artery, and vagus nerve in the neck.

The temporalis muscle, located superiorly, and the masseter muscle, positioned inferiorly, both contribute to closing the jaw.

The lateral pterygoid muscle opens the jaw and moves the chin to the opposite side, while the medial pterygoid muscle helps close the jaw.

The mandibular division (V3) of the trigeminal nerve supplies sensory innervation to the lower jaw, teeth, and tongue, and motor innervation to the muscles of mastication.

The chorda tympani nerve, a branch of cranial nerve VII, joins the lingual nerve to provide taste sensation from the anterior tongue and parasympathetic fibers to salivary glands.

The glossopharyngeal nerve (CN IX) provides parasympathetic innervation to the parotid gland through the auriculotemporal nerve.

The ophthalmic division of the trigeminal nerve (CN V1) splits into three branches: frontal, lacrimal, and nasociliary.

The frontal nerve divides into two branches: supratrochlear and supraorbital.

The facial vein drains into the ophthalmic veins, which ultimately drain into the cavernous sinus.

The cavernous sinus is a critical structure located near the brain; infections from the face can spread through the ophthalmic veins and reach the sinus, potentially causing serious complications.

Pupillary constriction is controlled by the parasympathetic nervous system, while pupillary dilation is controlled by the sympathetic nervous system.

The sympathetic nervous system arises from T1 to L2 segments of the spinal cord.

Preganglionic sympathetic neurons are located within the thoracic and lumbar segments of the spinal cord, and their axons synapse with postganglionic neurons in the sympathetic trunk.

The white ramus communicans is a bundle of preganglionic sympathetic fibers connecting the spinal nerve to the sympathetic trunk.

The oculomotor nerve (CN III) controls four of the six extraocular muscles: medial rectus, superior rectus, inferior rectus, and inferior oblique. These muscles are responsible for eye movements such as adduction, elevation, depression, and intorsion/extorsion.

The trochlear nerve (CN IV) controls the superior oblique muscle, responsible for intorsion, depression, and abduction of the eye.

The abducens nerve (CN VI) controls the lateral rectus muscle, responsible for abducting the eye, moving it outwards.

Sound waves enter the external auditory meatus, cause the tympanic membrane to vibrate, and set off the ossicular chain (malleus, incus, stapes). The stapes presses on the oval window, generating pressure in the fluid of the cochlea. This pressure stimulates receptor hair cells, which send impulses via the vestibulocochlear nerve (CN VIII) to the brain for interpretation as sound.

The tensor tympani muscle, innervated by the trigeminal nerve (CN V), and the stapedius muscle, innervated by the facial nerve (CN VII), help control sound transmission. A dysfunction in these muscles can lead to hyperacusis, a condition where sounds are perceived as louder than normal.

Conduction deafness occurs when sound transmission is impaired in the external or middle ear, often due to obstructions or dysfunction of the ossicular chain. Sensorineural deafness arises from damage to the inner ear (receptor organ) or the vestibulocochlear nerve (CN VIII).

Middle ear infections (otitis media) are common in children due to the shorter and more horizontal position of the auditory tube. Chronic ear infections can occur if the lateral or medial walls of the middle ear cavity are breached.

Middle ear infections can spread to neighboring structures, including the mastoid air cells (mastoiditis), the middle cranial fossa, and the temporal lobe. This can lead to serious complications.

The superior laryngeal nerve has two branches: the internal branch, which provides sensory innervation to the supraglottic region, and the external branch, which supplies motor innervation to the cricothyroid muscle.

The cricothyroid muscle is the only muscle of the larynx innervated by the external branch of the superior laryngeal nerve. All the other muscles receive innervation from the recurrent laryngeal nerve.

The aditus is the opening into the larynx.

The rima glottidis is the space within the larynx between the vocal folds.

The glottis is the area of the larynx formed by the vocal folds and the rima glottidis.

The laryngeal vestibule is the part of the larynx above the vocal folds.

The space between the thyroid cartilage and the cricoid cartilage is called the cricothyroid ligament.

The space between the hyoid bone and the thyroid cartilage is called the thyrohyoid ligament.

The maxillary division (V2) of the trigeminal nerve provides sensory innervation to the cheek, nose, upper teeth, and palate. It also contributes to innervating the maxillary sinus.

The pterygopalatine ganglion receives preganglionic parasympathetic fibers from the facial nerve (greater petrosal branch) via the nerve of the pterygoid canal. These fibers then synapse with postganglionic neurons that innervate glands in the nasal cavity and palate.

The lingual nerve is a branch of the mandibular division (V3) of the trigeminal nerve. It joins with the facial nerve to provide sensory innervation to the anterior two-thirds of the tongue, including taste.

The olfactory system is highly sensitive and responsible for our sense of smell. The olfactory pathway starts with olfactory receptor neurons in the olfactory epithelium of the superior concha.

The optic disk is a circular area on the retina where the optic nerve exits the eye. It is located medially and lacks photoreceptor cells, resulting in a 'blind spot'.

The eye is innervated by several cranial nerves: CN II (optic) for sensory input, CN III (oculomotor), CN IV (trochlear), and CN VI (abducens) for motor control, and the autonomic nervous system for pupil control.

The three layers of the eyeball are: the fibrous tunic (outermost), composed of the cornea and sclera; the vascular tunic (middle layer), containing the iris; and the neural tunic (innermost), containing the retina.

Fovea is a small pit in the retina responsible for sharp central vision, located laterally. The optic disk is a blind spot on the retina, located medially where the optic nerve exits the eye.