The ear is situated bilaterally on the human cranium, at the same level as the nose, bordering the face and the head. It is the motherboard for somatic balance and hearing and consists of the outer, middle and inner ear. It is innervated by the vestibulocochlear nerve, number eight of the twelve cranial nerves, as well as smaller branches from other nerves, This mixture of bones, nerves, vessels, membranes, skin and muscles which collectively form the ear is essential for the everyday function of one of the five human senses - hearing
The outer ear consists of the auricle, which is a cartilaginous structure that is covered with skin and which is lightly vascularized. It consists of the following convexities, concavities and folds (in a clockwise direction):
- Intertragic Notch
- Auricular Lobule
- Auricular Concha
- Auricular Tubercle
- Antihelical Crura
- Scaphoid Fossa
- Triangular Fossa
- Helical Crux
Within these structures lies the orifice known as the external acoustic meatus, which is the entrance to the middle and inner ear.
The tympanic membrane is the border between the external acoustic meatus of the outer ear and the middle ear. Just behind it sit the three auricular bones known as the:
They articulate upon each other and the malleus balances upon the tympanic membrane, transmitting sound vibration from the outer to the inner ear. The membrane is thin and when looking at it directly the malleus and the articulating incus can be seen. The incus connects the malleus and the stapes, which articulates directly with the fossa ovale or the vestibular window as it is known. This is the doorway to the inner ear.
In the most inner cavity of the ear, runs the facial nerve and vestibulocochlear nerves, cranial nerves VII and VIII respectively. Just below these nervous structures lies the auricular vestibule made up of the semicircular canals and the cochlea, which consists of:
- the scala tympani
- the cochlear duct
- the scala vestibuli
It is here that the fibers of the vestibulocochlear nerve separate, to innervate both the auricular vestibule and the cochlear one individually.
Within the cochlea are tiny hollow canals which are split into three parts, as mentioned above. Within the cochlear duct is an arrangement of hair cells, that vibrate in correlation to sound and transmit the information to the following tract:
- Hair cells of the cochlear duct in the cochlea of the inner ear
- Nerve terminals of the cochlear part of the vestibulocochlear nerve (CN VIII)
- Spiral ganglia
- Ventral and dorsal cochlear nuclei in the spinal cord
- Lateral lemniscus
- Nucleus of the lateral lemniscus
- Inferior colliculus
- Medial geniculate body
- Auditory radiations in the temporal lobe
- Acoustic area of the cortex - auditory cortex
The ear is situated bilaterally on the human cranium and consists of three parts: the outer, middle and inner ear portions.
The outer ear consists of the auricle, which is a lightly vascularized, cartilaginous structure covered with skin. It consists of a large collection of convexities, concavities and folds that can be easily seen with the naked eye.
The middle ear starts from the tympanic membrane onwards and contains three important auricular bones: the incus, malleus, and stapes. They articular upon each other, transmitting the vibrations of the tympanic membrane all the way to the inner ear, via the fossa ovale (vestibular window).
The inner ear contains the facial and vestibulocochlear nerves, with the auricular vestibule being situated below those cranial nerves. This vestibule consists of the semicircular canals and the cochlea.