Special Senses pt 2

middle ear

middle ear

• also called tympanic cavity is a small air-filled space inside a region of the temporal bone.

• contains three of the smallest bones in the body called the auditory ossicles which include the malleus, incus and stapes.

• these bones transmit the vibrations of the eardrum across the cavity to the fluid of the inner ear

pharyngotympanic tube

• (formerly called the auditory or eustachian tube) links the middle ear to the pharynx.

• normally flattened and closed tube can be opened briefly by swallowing or yawning so that the air pressure in the middle ear equalizes with the outside air pressure (something that must be done during takeoff and landing of an airplane).

tensor tympani and stapedius

two tiny skeletal muscles of the middle ear responsible for protecting the ear from loud sounds by contracting reflexively to limit the vibration of the ossicles.

internal ear

also called the labyrinth and consists of two main regions: bony labyrinth and membranous labyrinth. 

membranous labyrinth

• a continuous series of membrane-walled sacs and ducts that have three main parts:

  1. semicircular ducts (inside of semicircular canal)

  2. utricle/saccule (in vestibule) 

  3. cochlear ducts (in cochlea).

• walls of membranous labyrinth contain parts of epithelium that are thickened and contain sensory receptors for equilibrium and hearing.

• coiled portion within the bony cochlea is called the cochlear duct which contains a basilar membrane that supports the spiral organ of Corti (containing a strip of sensory epithelium made of hair cells)

• The hair cells contain sensory receptors for hearing.

bony labyrinth

is a cavity consisting of a system of twisting channels that have three parts: semicircular canals, vestibule and cochlea

utricle and saccule housed in the bony vestibule contain sensory epithelium called macula

macula

contain the sensory receptors for equilibrium

Auditory (Hearing) Nerve Pathway

Auditory information >>> sensory receptors in spiral organ of Corti >>> vestibulocochlear nerve >>> medulla >>> midbrain >>> primary auditory cortex in the temporal lobe of the cerebral cortex.

Equilibrium (Balance) Nerve Pathway

Equilibrium information >>> sensory receptors in macula epithelium (utricle and saccule) >>> vestibulocochlear nerve >>> 1.) medulla or 2.) cerebellum or  continue up to the 3.) thalamus >>> posterior insula of the cerebrum.