Chapter 10 Notes:

Sense of Hearing and Equilibrium

Sense of Hearing

  • Ability to hear and maintain equilibrium.

Major Structures

External Ear

  • Auricle or pinna: Outer ear.

  • External auditory meatus: Canal leading into the temporary bone.


  • Collect sound waves.

Middle Ear:

Three Parts:

  1. Tympanic Cavity

  • Air filled space in the temporal bone.

  1. Tympanic Membrane (Eardrum)

  • The outside of the membrane is skin and the inside is a mucus membrane.

  • Cone shaped.

  • Sound waves change the pressure on the eardrum causing it to move.

  1. Auditory Ossicles

  • Ear Bones: Mallelus, incus and stapes.

  • Bridges the eardrum to the inner ear.

  • Path of A Sound Wave: Eardrum → Mallelus→ Incus→ Stapes→ Oval Window

  • Vibration of the oval window moves fluid within the ear stimulating hearing receptors.

  • Also functions to amplify the sounds.

Auditory Tubes (Eustachian Tubes)

  • Connects middle ear to the throat.

  • Conducts air between tympanic cavity and the outside of the body.

  • Maintains air pressure on both sides, which is necessary for normal breathing.

  • Altitude changes (going from high to low) causes pushing in on the eardrum.

  • Air movement in the auditory tube equalize air pressure on both sides causes a popping sound during a change in altitude.

  • Make up the semicircular canals and cochlea.

  • Two types: Osseous (bone) and membranous.

  • Osseous is located in the temporal bone. Filled with fluid called perilymph.

  • Membranous is located within the osseous. Filled with fluid called endolymph.


  • Function: Hearing.

  • Fluid-filled tubes that pick up sound vibrations from the oval window that are brought to the Organ of Corti.

Organ of Corti

  • Contains a basilar and tectorial membrane.

  • Hair cells (receptor cells) are found anchored in the basilar membrane.

  • Sound vibrations cause hair cells to rub against tectorial membrane.

  • Different sound frequencies cause their hair cells to bend.

  • Bent hair receptor signals neurotransmitter to be released and send an impulse along the vestibucochlear nerve to the temporal lobe.

Sense of Equilibrium

Two Senses

  1. Static Equilibrium

  • Organ: Vestibule, between semicircular canals and cochlea.

  • Hair cells (receptor cells) are located in the vestibule.

  • Function: Senses the position of the head and maintains correct posture when the head and body are still.

  1. Dynamic Equilibrium

  • Organ: Semicircular Canals

  • Hair cells are located in a structure called the crista ampulloris within the semicircular canals.

  • Function: Detects motion of the head and body during sudden movement.

  • Cerebrum and cerebellum work closely together to aid in balancing the body.


Two Types

  • Conductive: Caused by interferences with vibrations to the inner ear.

  • Sensorineural: Caused by damage to the cochlea nerve fiber or nerve pathway in brain.