Sensory systems: Hearing Flashcards
What can the auditory pathway be overall divided into?
Outer ear, middle ear, inner ear
What is the outer ear and what is it made up of?
The outer ear is the most outer part of the auditory pathway. It consists of the pinna (ear lobe), the auditory canal, and the tympanic membrane.
What is the middle ear made up of and what is its role?
The middle ear is a cavity that contains 3 little bones: malleus, incus, and stapes. These bones connect the tympanic membrane to the inner ear.
What is the middle ear connected to and via what?
The middle ear has a connection to the nasal cavity via the eustachian tube.
What is the inner ear made up of and what are its roles?
The inner ear includes the cochlea, which is responsible for hearing, and the semi-lunar canal, which relates to vestibular functions (balance).
What is the role of the little bones in the ear?
They work as a lever system to transmit sound waves from the tympanic membrane to the oval window of the inner ear and amplify sound (about 20x) for low intensity sounds.
What is the mechanism to reduce amplification in the ear?
The mechanism is provided by two muscles of the middle ear: the stapedius muscle and the tensor tympani muscle. They contract in reflex to very high intensity sounds, stopping the amplification of sound by the three bones.
What is the structure of the cochlea?
The cochlea looks like a snail and is coiled up. Uncoiled, it has three tubes: the Scala vestibuli, the Scala media, and the Scala tympani.
What connects and divides the Scala tympani and vestibuli?
They are connected at the apex of the coil via a hole called the Helicotrema. The division is provided by the basilar membrane.
What does the Scala media contain?
The Scala media contains the organ of Corti, which is the sensory organ of hearing.
What is the mechanism of hearing?
When the sound wave hits the little bones, they move and the stapes pushes onto the membrane on the oval window, pushing the liquid in the cochlea and causing it to move.
What is the liquid in the cochlea called?
The liquid in the cochlea is called endolymph.
What does the movement of the endolymph cause?
The back-and-forth movement of the endolymph leads to deflections of the basilar membrane inside the inner ear.
Describe the structure of the basilar membrane.
The basilar membrane’s width and rigidity change along its length. It is narrow and stiff at the base, and wider and floppier at the apex.
What is the organ of Corti?
The Organ of Corti is the sensory organ of hearing found on the basilar membrane.
What cells are found in the organ of Corti and how does sound affect them?
The important sensory cells are the hair cells (outer and inner). Movement of the organ of Corti causes the tectorial membrane to move, which bends the stereocilia of the hair cells, leading to depolarization.
What are the action potentials (APs) elicited in hair cells linked to?
The APs in hair cells are linked directly to the movement of the stereocilia.
What allows for depolarization of hair cells?
Depolarization occurs due to mechanically gated K+ ion channels. Movement of stereocilia opens these channels, allowing K+ influx, leading to membrane depolarization.
What are auditory nerve fibers made up of?
Most of the auditory nerve is made up of fibers from spiral ganglion cells that innervate the inner hair cells.
What allows outer hair cells to contract or relax?
Outer hair cells have motor proteins associated with their wall that can contract or relax.
What happens when the motor proteins in outer hair cells contract?
When these motor proteins contract, they pull the stereocilia in a different direction, tugging the tectorial membrane and amplifying sound perceived by the inner hair cells.
What two phenomena allow us to identify sounds with different frequencies?
Tonotopy and characteristic frequency allow us to distinguish sounds of different frequencies.
What is tonotopy?
Tonotopy is the topographical organization of the auditory system.
