1A. What you will draw
The ear handles two senses: hearing (cochlea) and equilibrium (vestibular system). Today you'll draw the three regions of the ear, then the organ of Corti inside the cochlea.
BIO 304 . WEEK 5 . THURSDAY . LAB WORKBOOK
Hearing and Equilibrium
From sound waves at the eardrum to hair cells in the cochlea; and how we sense head position and motion.
Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.
Part 1 of 2
Anatomy Lab
Box A. Outer, middle, and inner ear
Directions
- Draw an ear in cross-section from outside to inside. Divide into three regions with vertical lines.
- Outer ear (left): pinna (the visible external ear) and external auditory canal leading to the tympanic membrane (eardrum). Label.
- Middle ear (center): air-filled space behind the eardrum, containing three tiny bones (the ossicles): malleus, incus, stapes. Label each. Show the stapes contacting the oval window of the cochlea.
- Inner ear (right): draw the cochlea as a snail-shell spiral (fluid-filled, handles hearing). Above it, draw the three semicircular canals (orthogonal loops) and the vestibule (linear motion). Label all four structures.
- Add the Eustachian tube connecting the middle ear to the throat (pressure equalization).
Draw here. Sketch by hand.
Box B. Organ of Corti close-up
Directions
- Draw a cross-section of the cochlear duct showing the organ of Corti sitting on the basilar membrane.
- Label the basilar membrane (under the hair cells, vibrates at different frequencies along its length).
- Draw hair cells: a single row of inner hair cells (the main sensory cells) and three rows of outer hair cells (amplifiers). Label.
- Show stereocilia (hair-like projections) on top of each hair cell, contacting the tectorial membrane above. Label both.
- Show the cochlear nerve fibers leaving the base of the hair cells.
- Note the principle: when the basilar membrane vibrates, the stereocilia bend against the tectorial membrane, opening ion channels in the hair cell, leading to neurotransmitter release.
Draw here. Sketch by hand.
1C. Structures to label (17)
After you finish each drawing, label every structure below directly on your sketch.
- Pinna
- External auditory canal
- Tympanic membrane
- Malleus
- Incus
- Stapes
- Oval window
- Cochlea
- Vestibule
- Semicircular canals
- Eustachian tube
- Basilar membrane
- Tectorial membrane
- Inner hair cell
- Outer hair cell
- Stereocilia
- Cochlear nerve
Part 2 of 2
Physiology Lab
2A. Trace: sound wave to action potential
List the 8 steps that occur from a sound wave in air to an action potential in the cochlear nerve. Identify each structure the signal passes through and what changes.
2B. Synthesis questions
Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.
1. A patient has conductive hearing loss (e.g., a fluid-filled middle ear from an infection). Explain mechanistically why sound transmission fails, and contrast with sensorineural hearing loss (damaged hair cells or cochlear nerve).
2. A passenger gets out of a spinning teacup ride and feels dizzy. Explain what is happening in their semicircular canals during and just after the spin, and why the world appears to keep moving even after they've stopped.
3. High-frequency sounds are detected near the BASE of the cochlea, while low-frequency sounds are detected near the APEX. Explain how the basilar membrane's structural properties produce this 'tonotopic' map.
3. What to submit
Complete both the Anatomy Lab (your own drawings, hand-labeled, plus the structures list) and the Physiology Lab (activity and synthesis questions). Photograph or scan every page and upload to Canvas before the deadline listed on the schedule. Hand-drawn, hand-labeled work is the integrity mechanism for this course. Typed or AI-generated diagrams are not accepted.