Overview
This lecture reviews a past exam question about the human ear, focusing on labeling structures, functions, and application questions relevant to hearing and balance.
Diagram Labeling & Structure Identification
- Always label the ear diagram before answering to build familiarity.
- A: Ossicles (middle ear bones)
- B: Auditory nerve (can include vestibular nerve)
- C: Cochlea (spiral-shaped organ for hearing)
- D: Round window (exit point in cochlea for excess sound waves)
- E: Tympanic membrane (eardrum)
- Semicircular canals are shown for balance.
Function of Brain Regions
- Impulses from the cochlea (C) are sent to the cerebrum for processing sound.
- For most exams, you do not need to know the specific lobe of the cerebrum.
Role of Semicircular Canals in Balance
- Stimulus (head movement) causes endolymph (fluid) in semicircular canals to move.
- Movement stimulates cristae (receptors) in the canals.
- Receptors generate nerve impulses sent via auditory nerve to the cerebellum.
- Cerebellum sends impulses to muscles (effectors) to maintain balance.
- Always mention receptor, stimulus, nerve pathway, and muscle response in your answer.
Effects of Mucus on Tympanic Membrane (Eardrum)
- Mucus buildup may block the eustachian tube, preventing air pressure equalization in the middle ear.
- Pressure imbalance can press against and burst the tympanic membrane.
- Alternatively, mucus may drain into the middle ear via the eustachian tube, directly increasing pressure on the eardrum.
Effect of Ossicle Fusion on Hearing
- Ossicles (A) need to vibrate to transmit sound.
- Fusion (sticking together) of ossicles stops movement.
- Immobilized ossicles cannot transmit vibrations to the cochlea, resulting in hearing loss.
Key Terms & Definitions
- Ossicles — Three small bones in the middle ear that transmit sound vibrations.
- Auditory nerve — Carries hearing signals from the cochlea to the brain.
- Cochlea — Spiral-shaped organ that converts sound waves into nerve impulses.
- Round window — Membrane that releases excess pressure from the cochlea.
- Tympanic membrane (eardrum) — Membrane that vibrates in response to sound.
- Semicircular canals — Structures in the inner ear that help maintain balance.
- Cristae — Receptors in the semicircular canals detecting head movement.
- Eustachian tube — Tube connecting the middle ear to the throat, equalizes ear pressure.
Action Items / Next Steps
- Review and memorize the functions of each labeled ear structure.
- Practice the balance explanation (semicircular canal question) for exams.
- Study the role of the eustachian tube in pressure balance.
- Go over application questions on the tympanic membrane and ossicles.