Organs - The Ear (Inner) Flashcards
What are the functions of the inner ear?
1) To convert mechanical signals from the middle ear into electrical signals, which can transfer information to the auditory pathway in the brain.
2) To maintain balance by detecting postion and motion.
Where is the inner ear located?
It is located within the petrous part of the temporal bone. It lies between the middle ear and the internal acoustic meatus, which lies laterally and medially respectively.
What are the contents of the inner ear?
1) Bony labyrinth - consists of a series of bony cavities within the petrous part of the temporal bone. It is composed of the cochlea, vestibule, and three-semi circular canals. All these structures are lined internally with periosteum and contain a fluid called perilymph.
2) Membranous labyrinth - lies within the bony labyrinth. It consists of the cochlear duct, semi-circular ducts, utricle and the saccule. The membranous labyrinth is filled with a liquid called endolymph.
What are the openings into the middle ear?
These opening are covered by membranes.
1) Oval window - between the middle ear and the vestibule.
2) Round window - separates the middle ear from the scala tympani (part of the cochlear duct).
What is the bony labyrinth composed of?
Consists of three parts:
1) Vestibule
2) Cochlea
3) Semi-circular canals
Where is the vestibule located? What is its function?
What two parts of the membronous labyrinth is located within the vesitbule.
This is the central part of the bony labyrinth. It is separated from the middle ear by the oval window, and communicates anteriorly with the cochlea and posteriorly with the semi-circular canals.
Two parts of the membranous labyrinth are located in the vestibule:
1) Saccule
2) Utricle
What are the features of the cochlea?
How is it oriented?
What are the relevant nerves involved?
The cochlea houses the cochlea duct of the membranous labyrinth - the auditory part of the inner ear. It twists upon itself around a central portion of bone called the modiolus, producing a cone shape with point in the anterolateral direction. Branches from the cochlear portion of the vestibulocochlear nerve (CN VIII) are found at the base of the modiolus.
Extending outwards from the modiolus is a ledge of bone known as the spiral lamina, which attaches to the cochlear duct, holding it in position. The presence of the cochlear duct creates two perilymph-filled chambers above and below:
1) Scala vestibuli - located superiorly to the cochlear duct. As it name suggests, it is continuous with the vestibule.
2) Scala tympani - located inferiorly to the cochlear duct. It terminates at the the round window.
What are the semi-circular canals?
There are three semi-circular canals:
1) Anterior semi-circular canal
2) Lateral semi-circular canal
3) Posterior semi-circular canal
These are responsible for balance (along with the utricle and saccule).
The canals are situated superoposterior to the vestibule. at right angles to each other. They have a swelling at one end known as the ampulla.
What is the membranous labyrinth composed of?
This a continuous system of ducts filled with endolymph.
It lies within the bony labyrinth, surrounded by perilymph. It is compposed of the cochlear duct, three semi-circular ducts, saccule and utricle.
What are the features of the cochlear duct?
The cochlear duct is located within the bony scaffoldin of the cochlea. It is held in place by the spiral lamina. The presence of the duct creates two canals above and below it - the scale vestibuli and scale tympani respectively. The cochlear duct can be described as having a triangular shape.
What are the borders of the cochlear duct?
Lateral wall - Formed by a thickened periosteum, known as the spiral ligament.
Roof - formed by a membrane which separates the cochlear duct from the scala vesitible, known as the Reissner’s membrane.
Floor - formed by a membrane which separates the cochlear duct from the scala tympani, known as the basilar membrane.
The basilar membrane houses epithelial cells of hearing - the Organ of Corti. A more detailed description of the Organ of Corti is beyond the scope of this deck.
Where is the saccule and utricle located?
These are two membranous sacs located within the vestibule. They are organs of balance which detect movement or acceleration of the head in the vertivle and horizontal planes, respectively.
Utricle - the larger of the two, receiving the three semi-circular ducts.
Saccule - globular in shape and receives the cochlear duct.
Where does the endolymph drain into?
The endolymph drains from the saccule and utricle into the endolymphatic duct. The duct travels through the vestibular aqueduct to the posterior aspect of the petrous part of the temporal bone. Here, the duct expands to a sac where endolymph can be secreted and absorbed.
Where are the semi-circular ducts located?
The semi-circular ducts are located within the semi-circular canals, and share their orientation.
Upon movement of the head, the flow of endolymph within the ducts changes speed and/ or direction. Sensory receptors in the ampullae of the semi-circular canals detect this change, and send signals to the brain, allowing for the processing of balance.
What is the vasculature of the bony labyrinth?
1) Anterior tympanic branch (from maxillary artery)
2) Petrosal branch (from middle meningeal artery)
3) Stylomastoid branch (from posterior auricular artery)
