(Labyrinth)
It is located within the petrous part of the temporal bone between the middle ear and the internal auditory canal. Its length is 20 mm and consists of a membranous labyrinth surrounded by a bony labyrinth:
The bony labyrinth is a hollow bony capsule, which is a part of the petrous portion of the temporal bone. The membranous labyrinth is a group of delicate ducts and sacs. The membranous labyrinth is filled with a fluid called endolymph and is surrounded by a fluid called perilymph, the membranous labyrinth contains the labyrinthine sensory end organs.

THE MIDDLE EAR CAVITY (TYMPANIC CAVITY):
It is located in the temporal bone between the external ear and the inner ear. It is a six-walled cavity about 15 mm in height, 15 mm antro-posteriorly and 2-6 mm from side to side. All the walls are bony, except the lateral wall (tympanic membrane) and are lined with mucous membrane, which is ciliated columnar epithelium except its postero-superior part that has flattened squamous epithelium.
It is divided into three regions: 1- Meso-tympanum (middle ear cavity proper): lies opposite to the tympanic membrane.

PARTS: 1- The auricle.
2- The external auditory canal.
3- The tympanic membrane. THE AURICLE (Ear pinna):
It is the comma shaped structure attached to the side of the head by ligaments and muscles. It is composed of a sheet of fibro-elastic cartilage. The covering skin is closely adherent to the perichondrium on the lateral surface.
The auricle is devoid of cartilage in two places:

CRANIAL FOSSA: The cranium is divided into three regions (fossae), according to the cranial lobes that each region houses. 1 Anterior Cranial Fossa: Houses frontal lobes.
o Includes all of Frontal and Ethmoid bones, and the Lesser Wing of the Sphenoid.
2 Middle Cranial Fossa: Houses temporal lobes.
o Includes the Greater Wing of the Sphenoid, Sella Turcica, and the majority of Temporal Bones.

SCALP: Cutaneous cranium superficial to the skull. Its layers fit the acronym SCALP SkinConnective tissue -- highly vascularAponeurosis -- Galea Aponeurotica = dense connective tissue § This is continuous with the Epicranius muscle from all sides, consisting of Frontalis and Occipitalis muscles.
Loose connective tissue, upon which the aponeurosis glidesPeriosteum -- adherent to bony skull
SCALP LESION: The outermost connective tissue is highly vascular, and the loose connective tissue tends to hold cuts open, resulting in profuse bleeding of scalp. It is easily fixed with stitches

OPTIC CHIASM: The convergence of the two optic nerves. It occurs at the sella turcica, on the body of the sphenoid bone, right at the Pituitary Gland.Fibers from the medial side of each eye cross at the Optic Chiasm, to join the Optic Tract on the opposite side. i. So medial fibers from the Left Eye will go to the right side of the brain, and medial fibers from the right eye will go to the left side of the brain.

SUPERIOR DIVISION: Somatic innervation to the superior rectus and levator palpebrae muscles. INFERIOR DIVISION: Somatic innervation to the medial and inferior rectus muscles.
The inferior division also carries Parasympathetic Fibers, via the Short Ciliary Nerve, to the Sphincter Pupillae and Ciliary Muscles (constrict eye and accommodate for near vision). UNILATERAL LESION OF OCULOMOTOR NERVE: Damage would be as follows.
1. "Lateral Strabismus" = the eyeball will point downward and outward.

PATHWAY IN BRAIN:
It is the only cranial nerve that originates from the opposite of the brain.It is the only cranial nerve that exits from the dorsal side of the cranium, so it has a very long path.It is the only cranial nerve associated with the eye, that doesn't enter the orbit through a tendinous ring. CAVERNOUS SINUS: It runs in the cavernous sinus. If there is ever brain hemorrhage, pressure from excess CSF can damage the Abducens nerve.

TRIGEMINAL GANGLION: It contains the sensory cell bodies for the Trigeminal Nerve. It contains no synapses. The Motor cell bodies are in the Masticator Nucleus within the pons.
V1 -- OPHTHALMIC NERVE -- Purely Sensory Nerve.
It runs through the lateral wall of the Cavernous Sinus. It exits through Superior Orbital Fissure to enter the orbit.Associated Ganglion: CILIARY GANGLION. It carries parasympathetic motor fibers from the Oculomotor Nerve (CN III), which go on to innervate extrinsic eye muscles. V2 -- MAXILLARY NERVE -- Purely Sensory Nerve.

CAVERNOUS SINUS: It runs in the cavernous sinus. If there is ever brain hemorrhage, pressure from excess CSF can damage the Abducens nerve. STRABISMUS: The inability to direct both eyes toward the same object.
INJURY TO ABDUCENS: The eye on the affected side rotates inward (adducts), due to the unopposed action of the medial rectus muscle.
Tags: nerve, strabismus, eye

Motor Innervation: The cell bodies for the motor fibers of all cranial nerves are located in the respective brainstem nuclei (lower motor neurons).
Sensory Innervation: The cell bodies for the sensory fibers of all cranial nerves are located in the parasympathetic ganglia (see below) or special sensory organs.
Sympathetic Innervation: The sympathetic fibers mostly run along the internal and external carotid arteries to get to their target organs.
Superior Cervical Ganglion: The highest sympathetic chain ganglia, which contains synapses for all the major sympathetic fibers for the head and neck region.External Carotid Artery: Post-Ganglionic sympathetics run along the external carotid to supply the salivary glands and lower face.Internal Carotid Artery: Larger portion of sympathetics run along internal carotid, forming the internal carotid plexus.INTERNAL CAROTID PLEXUS: In cavernous sinus (probably).

Three Main Functions:
Innervate the Muscles of Facial ExpressionSupply special sense of taste to anterior 2/3 of tongue, via Chorda Tympani Nerve.To innervate all facial glands (salivary, nasal, lacrimal), EXCEPT the Parotid.There is also a small area of somatic sensation carried by the facial nerve, around the ear canal ear drum.The GENICULATE GANGLION houses the cell bodies for all fibers of the Facial Nerve. It has no synapses. PATHWAYS OF THE FACIAL NERVE:

VESTIBULAR NERVE:
Innervates the semicircular canals, utricle, and saccule, and is responsible for dynamic and static balance. COCHLEAR NERVE:
Innervates the cochlea and is responsible for hearing. INTERNAL ACOUSTIC MEATUS: Cranial Nerve VIII exits out the internal acoustic meatus, along with the Facial Nerve.
ACOUSTIC NEUROMAS: A neuroma from a Schwann Cell in the Vestibulocochlear may impinge upon the Vestibular and Cochlear nerves in the Internal Acoustic Meatus. If it is large enough, it may impinge on the Facial Nerve, too.

Five Functions of Glossopharyngeal Nerve:
Innervates Stylopharyngeus Muscle.Special sense of taste to posterior 1/3 of tongueGeneral sensation to posterior 1/3 of tongue, lateral oropharyngeal wall, part of soft palateParasympathetic secretomotor to Parotid GlandVisceral Sensation from the Baroreceptors ("blood-pressure" receptors) at the Carotid Body (Sinus), at the bifurcation of the Carotids. These guys carry special chemoreceptors and stretch receptors. They provide feedback to the heart to control heart rate and modulate blood pressure.

Type of Innervation:
BRANCHIAL MOTOR (SVE): All muscles of the larynx, pharynx, and palate, EXCEPT the Stylopharyngeus (IX) and Tensor Palati (V3). In this role, the Vagus is "stealing" some of the innervation from the Spinal Accessory (XI). Hence in this case the Vagus is actually innervating striated rather than smooth muscle. VISCERAL MOTOR (GVE): Parasympathetics to the Thoracic and Abdominal viscera. The Vagus serves no Parasympathetic function in the head and neck region -- only the thorax and abdomen. VISCERAL SENSORY (GVA): Sensory info from tongue, pharynx and larynx, heart and lungs, CAROTID SINUS (along with CN IX), stomach and intestine.GENERAL SENSORY (GSA): General sensory from larynx, pharynx, and a small portion of the outer ear and tympanic membrane. General Sensory innervation may include the eardrum itself. These individuals may elicit a gag reflex when cleaning their ears -- due to sensory response from the Vagus! SPECIAL SENSORY (SVA): Maybe a few taste buds carry taste information via the Vagus.

Two Roots:
Spinal Root: Gives SVE (Branchial) innervation to Sternocleidomastoid and Trapezius muscles.Cervical Root: Quickly joins up with Vagus (and could be considered part of Vagus) to form the Recurrent Laryngeal Nerve.
NERVE GRAFTS: The function of Spinal Accessory is somewhat redundant.
It can be used to replace innervation lost by other muscles. The nerve can be redirected to the muscles of facial expression, e.g., and patients can learn to use the new pathway with physical therapy.