The Ear Flashcards
Hearing
The pinna traps and directs sound waves into the auditory canal towards the tympanic membrane.
The tympanic membrane vibrates as the sound waves strike against it.
The vibrating tympanic membrane causes the ossicles to vibrate (causing vibrations).
The malleus (hammer), incus (anvil) and stapes (stirrup) amplify and transmit the vibrations to the oval window.
The oval window is smaller than the tympanic membrane. As a result, the pressure increases, causing the sound to be amplified.
The vibrating oval window causes pressure waves to travel through the endolymph in the cochlea.
The organ of Corti in the middle chamber of the cochlea is stimulated.
The stimulus is converted into a nerve impulse which is transmitted to the auditory nerve.
The auditory nerve transmits the impulse to the cerebrum for interpretation.
The pressure waves in the cochlea are absorbed into the middle ear through the round window and exit the body via the Eustachian tube.
HOW WE BALANCE
The maculae in the utriculus and sacculus are stimulated by changes in the position of the head.
The cristae in the semi-circular canals are stimulated by changes in the direction and speed of movement.
When stimulated, the cristae and maculae convert the stimuli into nerve impulses
The nerve impulses are transmitted through the auditory nerve to the cerebellum where they are interpreted
The cerebellum then sends impulses via the motor neurons to the skeletal muscles to restore balance
The function of the sacculae and utriculae:
The Sacculus and utriculus contain special receptors called maculae that are stimulated.
When the position of the head changes, the pull of gravity stimulates sensory hair cells in the macula to generate impulses.
The impulses generated from the maculae are sent to the cerebellum.
The cerebellum sends impulses to the skeletal muscles to restore the balance.
The function of the ampullae:
The ampullae are situated at the end of semi-circular canals and contain cristae.
The three semi-circular canals are positioned in three different planes and therefore, any sudden changes in the direction and speed of body movement, cause the endolymph to move in at least one of the semi-circular canals.
The movement of endolymph stimulates the cristae to generate impulses which are sent to the cerebellum.
The cerebellum sends impulses to the skeletal muscles to restore the balance.
Middle ear infection
Eustachian tube cannot function properly. Air cannot be replaced in the middle ear, resulting in the air pressure in the middle ear being lower than the atmospheric pressure in the external auditory canal. A pressure builds up in the middle ear leading to tympanic membrane to rupture
Describe the role of the semi-circular canals in maintaining
balance.
- The cristae in the semi-circular canals
- are stimulated by changes in speed and direction
- when the endolymph moves
- The cristae convert the stimuli to nerve impulses
- The nerve impulses are transported along the auditory nerve
- to the cerebellumto be interpreted
- Impulses sent to muscles to restore balance
