SandP: Hearing and Vestibular (balance) Sense

Question 1

• Pinna (auricle)

- External Auditory Canal

Answer 1

• It is the outer ear, its job is to funnel sound waves into the ear.
• Where the sound waves are funneled, it leads down to the Tympanic Membrane (eardrum)

Question 2

-Tympanic Membrane

Answer 2

• The eardrum, divides the outer eat and the middle the ear.
• When sound hits hear it vibrates the ear drum, the Higher the frequencies the faster it vibrates, the lower the frequency the slower it vibrates.
• Louder Sounds have greater Intensity, which corresponds to an increased amplitude of the vibration.

Question 3

• The Middle Ear houses?
• What are They?
• Name them

Answer 3

• Ossicles
• Help transmit and amplify the vibrations of the eardrum to the inner ear
• Malleus (Hammer), Incus (anvil), and Stapes (Stirrup)

Question 4

• Malleus (Hammer), Incus (Anvil), Stapes (Stirrup)

- Stapes connects to what

Answer 4

• Affixed to the Tympanic Membrane (eardrum), Which acts on Incus, which acts on Stapes.
• The baseplate of the stapes connects to the Oval (round) window of the Cochlea, which is the entrance to the inner ear.

Question 5

-Eustachian Tube (auditory tube)

Answer 5

-Connects the middle ear to the nasal cavity, which helps equalize pressure between the middle ear and the environment.

Question 6

• Bony Labyrinth
• It houses?
• Membranous Labyrinth (Perilymph)
• Endolymph

Answer 6

-Where the inner ear sits
It houses the Cochlea, the Vestibule, and Semicircular Canals.These structures are continuous and are mostly filled by the Membranous Labyrinth
- Suspended within the Bony Labyrinth by a thin layer of fluid called Perilymph. This fluid simultaneously transmits vibrations from the outside world and cushions the inner ear structures.
- What the Membranous Labyrinth is bathed with, its a potassium-rich fluid.

Question 7

• Cochlea has three parts called?
• What does the middle one house?
• What do the other do?

Answer 7

• Scalae, which run the length of the cochlea
• Houses the Organ of Corti (Hearing Apparatus), which rests on a thin, flexible membrane called the Basilar Membrane.
• Surround the hearing apparatus and are filled with Perilymph. They are continues with round and oval windows of the Cochlea. Thus, sound entering the Cochlea, through the window causes vibration in Perilymph which are transmitted to Basilar membrane.

Question 8

• Organ of Corti
• Hair Cells
• Where are the signals carried?

Answer 8

• Composed of thousands of hair cells, which are bathed in endolymph.
• Convert the physical stimulus into an electrical signal
• to the CNS, via the auditory (Vestibulocochlear) nerve.

Question 9

• Vestibule contain what
• What do theses structures do?
• Modified Hair Cells?

Answer 9

• Refers to the portion of the bony labyrinth that contains the Utricle and Saccule.
• These structures are sensitive to linear acceleration, so are used as pat of the balancing apparatus and to determine one’s orientation in three dimensional space.
• Contain Modified hair cells covered with Otoliths. As the body accelerates, Otoliths, resist motion. This bends and stimulates the underlying hair cells, which send a signal to the brain.

Question 10

• How many Semicircular Canals?
• How different from structures of Vestibule?
• How arranged? End with what? What is on the ends?
• How does the Semicircular Canal work?

Answer 10

• Three Semicircular canals
• While the Vestibule is sensitive to linear acceleration the Semicircular canals are sensitive to rotational acceleration.
• They are arranged perpendicular to each other and each ends in a swelling called the Ampulla.
• When a person’s head rotates, endolymph in the Semicircular canals resists this motion, bending the underlying hair cells, which send signal to the brain

Question 11

• Main Auditory Pathway

- Where else does sound go

Answer 11

• Most Sound (not all) information passes through Vestibulocochlear Nerve (Auditory Nerve) –> to the Medial Geniculate Nucleus (MGN) of the thalamus (brainstem)–> From there it projects to the auditory cortex in the temporal lobe for sound processing
• Some information sent to the Superior Olive (localizes sound) and some is sent to the Inferior Colliculus which is involved in the startle reflex and helps keep the eyes fixed on a point as the head turns (vestibulo-ocular reflex)

Question 12

MGN VS LGN Mnemonic

Answer 12

-MGN is for Music LGN is for Light

Question 13

• Hair cells made of?
• How do they work?
• Tonotopically Organized?

Answer 13

• Names for the long tufts called Sterocilia
• When vibrations reach the basilar membrane underlying the organ of corti the Sterocilia begin to sway. The swaying causes the opening of ion channels, which cause a receptor potential.
• Which hair cells vibrate tell the brain about the pitch of the sound. The thickness of the Basilar membrane changes (Highest frequencies give vibrations close to Oval window, Lowest frequencies give vibrations close to Apex)