Special Senses 2

Question 1

Hearing - Detection of Sound Waves

Answer 1

• Sound is the result of vibration, or waves, traveling through a medium
• Auditory stimuli travel farther and more quickly than chemical ones
• Auditory receptors provide better directional information than chemoreceptors

Question 2

Anatomy of the ear

Answer 2

-Air vibrations are channeled through the auditory canal of the
External Ear
-Vibrations reach the Tympanic Membrane
-Movement of bones in the Middle Ear
-Malleus (hammer),
-Incus (anvil)
-Stapes (stirrup)

-Vibration of Oval Window

Cochlea

• A bony structure containing part of the cochlear duct
• The Vestibular Canal lies above this duct, while the Tympanic Canal lies below it
• All three chambers are filled with fluid
• Pressure waves travel down the tympanic canal to the Round Window
• Transmits pressure back to middle ear

Question 3

Hearing Structures

Answer 3

Organ of Corti transduces sound in the cochlea

• Basilar membrane: Bottom of cochlear duct
• Hair cells: With associated sensory neurons
• Tectorial membrane: Overhanging, gelatinous membrane
• Stereocilia of hair cells bend in response to vibrations of the basilar membrane
• Nerve impulses travel to the auditory cortex of the temporal lobe

Question 4

Hearing process

Answer 4

1. sound waves arrive at trympanic membrane
2. movement of the tympanic membrane causes displacement of the auditory ossicles
3. movement of the stapes at the oval window establishes pressure waves in the perilymph of the scala vestibuli
4. the pressure waves distort the basilar membrane on their way to the round window of the scala tympani
5. vibration of the basilar membrane causes vibration of hair cells against the tecctorial membrane
6. information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve Vlll

Question 5

Hearing pathway

Answer 5

1. stimulation of hair cells at a specific location along the basilar membrane activates sensory neurons
2. sensory neurons carry the sound information in the cochlear branch of the vestibulocochlear nerve (Vlll) to the cochlear nucleus on that side
3. information ascends from each cochlear nucleus to the inferior colliculi of the midbrain
4. the inferior colliculi direct a variety of unconscious motor responses to sounds
5. ascending acoustic goes to the medial geniculate nucleus
6. projection fivers then deliver the information to specific locations within the auditory cortex of the temporal lobe