Three of the Tiniest Bones in Your Body Carry Sound Deep Into Your Head
Learn the parts of the external, middle and inner ear, follow a sound from the pinna to the auditory nerve, and see how the semicircular canals and vestibule keep your body balanced.
How does the ear let you hear and keep your balance at the same time?
The ear does two quite different jobs. It turns vibrations in the air into nerve impulses the brain hears as sound, and it senses the position and movement of your head so you do not topple over.
This part covers the three regions of the ear, the path of sound to the auditory nerve, and the organs of balance in the inner ear.
This part covers the three regions of the ear, the path of sound to the auditory nerve, and the organs of balance in the inner ear.
What are the parts of the external, middle and inner ear, and what does each do?
The external ear collects sound, the middle ear passes vibrations across three tiny bones, and the inner ear contains the cochlea for hearing and the vestibule and semicircular canals for balance.
1. External ear
- Pinna — the visible flap; collects and directs sound waves inwards
- Auditory canal — tube whose hairs and wax trap dust and germs
- Tympanum (eardrum) — thin membrane that vibrates when sound strikes it
2. Middle ear — an air-filled cavity
- Ear ossicles — malleus (hammer), incus (anvil) and stapes (stirrup), joined in a chain that passes on and amplifies vibrations; the stapes is the smallest bone in the body
- Oval window — membrane where the stapes meets the inner ear
- Eustachian tube — connects the middle ear to the throat and keeps air pressure equal on both sides of the eardrum
3. Inner ear — a fluid-filled system of canals
- Cochlea — coiled like a snail shell; contains sensory hair cells for hearing
- Vestibule — two small sacs; senses the position of the head
- Semicircular canals — three curved canals; sense movement of the head
- Auditory nerve — carries impulses to the brain
An everyday example. Your ears pop on a steep ghat road or in an aeroplane; swallowing opens the Eustachian tube and evens out the pressure.
The boundary case. Only the cochlea is concerned with hearing — the vestibule and canals serve balance, even though they share the inner ear.
1. External ear
- Pinna — the visible flap; collects and directs sound waves inwards
- Auditory canal — tube whose hairs and wax trap dust and germs
- Tympanum (eardrum) — thin membrane that vibrates when sound strikes it
2. Middle ear — an air-filled cavity
- Ear ossicles — malleus (hammer), incus (anvil) and stapes (stirrup), joined in a chain that passes on and amplifies vibrations; the stapes is the smallest bone in the body
- Oval window — membrane where the stapes meets the inner ear
- Eustachian tube — connects the middle ear to the throat and keeps air pressure equal on both sides of the eardrum
3. Inner ear — a fluid-filled system of canals
- Cochlea — coiled like a snail shell; contains sensory hair cells for hearing
- Vestibule — two small sacs; senses the position of the head
- Semicircular canals — three curved canals; sense movement of the head
- Auditory nerve — carries impulses to the brain
An everyday example. Your ears pop on a steep ghat road or in an aeroplane; swallowing opens the Eustachian tube and evens out the pressure.
The boundary case. Only the cochlea is concerned with hearing — the vestibule and canals serve balance, even though they share the inner ear.
What path does sound take from the pinna to the auditory nerve?
Sound waves are collected by the pinna, make the eardrum vibrate, are passed and amplified by the ossicles to the oval window, set the fluid in the cochlea moving, stimulate hair cells, and travel as impulses along the auditory nerve to the brain.
- Pinna and canal — funnel the sound inwards
- Eardrum — vibrates with the sound
- Ossicles — act as levers, passing vibrations on with greater force
- Oval window — much smaller than the eardrum, so the force is concentrated and pressure rises
- Cochlea — moving fluid bends the hair cells, which fire impulses
- Auditory nerve — carries impulses to the hearing centre of the cerebrum, where sound is actually perceived
An everyday example. Listening through earphones at full volume for hours can damage the delicate hair cells, and lost hair cells do not grow back.
The substance. The ear does not hear — the brain does. The ear converts vibrations into impulses; damage to the auditory nerve or hearing centre causes deafness even with a healthy ear.
- Pinna and canal — funnel the sound inwards
- Eardrum — vibrates with the sound
- Ossicles — act as levers, passing vibrations on with greater force
- Oval window — much smaller than the eardrum, so the force is concentrated and pressure rises
- Cochlea — moving fluid bends the hair cells, which fire impulses
- Auditory nerve — carries impulses to the hearing centre of the cerebrum, where sound is actually perceived
An everyday example. Listening through earphones at full volume for hours can damage the delicate hair cells, and lost hair cells do not grow back.
The substance. The ear does not hear — the brain does. The ear converts vibrations into impulses; damage to the auditory nerve or hearing centre causes deafness even with a healthy ear.
How do the semicircular canals and vestibule keep the body balanced?
The semicircular canals detect turning movements of the head through moving fluid, and the vestibule detects the head's position relative to gravity; both send impulses to the cerebellum, which adjusts the muscles to keep balance.
1. Semicircular canals — balance during movement
- Three canals lie at right angles to one another, one for each direction of movement
- Each has a swelling, the ampulla, containing sensory hair cells
- When the head turns, the fluid inside lags behind and bends the hairs
- Impulses tell the brain the direction and speed of turning
2. Vestibule — balance at rest
- Contains hair cells topped with tiny chalky particles
- When the head tilts, gravity pulls these particles and bends the hairs
- Impulses tell the brain which way the head is tilted
3. The response. Impulses travel to the cerebellum, which signals muscles in the neck, trunk and legs to correct posture.
An everyday example. Spin round and round in a game of phugdi and then stop — the fluid in the canals keeps swirling, so the brain thinks you are still turning and you feel dizzy.
The link. Motion sickness on a winding bus ride happens when the inner ear senses movement that the eyes, fixed on a phone screen, do not see.
1. Semicircular canals — balance during movement
- Three canals lie at right angles to one another, one for each direction of movement
- Each has a swelling, the ampulla, containing sensory hair cells
- When the head turns, the fluid inside lags behind and bends the hairs
- Impulses tell the brain the direction and speed of turning
2. Vestibule — balance at rest
- Contains hair cells topped with tiny chalky particles
- When the head tilts, gravity pulls these particles and bends the hairs
- Impulses tell the brain which way the head is tilted
3. The response. Impulses travel to the cerebellum, which signals muscles in the neck, trunk and legs to correct posture.
An everyday example. Spin round and round in a game of phugdi and then stop — the fluid in the canals keeps swirling, so the brain thinks you are still turning and you feel dizzy.
The link. Motion sickness on a winding bus ride happens when the inner ear senses movement that the eyes, fixed on a phone screen, do not see.
Exam tip
What earns full marks on the structure and working of the ear?
Label all three regions, write the path of sound as an ordered chain, and separate hearing organs from balance organs.
- Label: pinna, auditory canal, eardrum, malleus, incus, stapes, oval window, Eustachian tube, cochlea, vestibule, semicircular canals, auditory nerve
- Write the sound path with arrows, in order
- State the Eustachian tube's role in equalising pressure
- Semicircular canals: dynamic balance; vestibule: static balance
- Name the cerebellum as the brain part that receives balance impulses
The trap. Writing that the semicircular canals help in hearing. They sense movement for balance; hearing is the cochlea's job.
- Label: pinna, auditory canal, eardrum, malleus, incus, stapes, oval window, Eustachian tube, cochlea, vestibule, semicircular canals, auditory nerve
- Write the sound path with arrows, in order
- State the Eustachian tube's role in equalising pressure
- Semicircular canals: dynamic balance; vestibule: static balance
- Name the cerebellum as the brain part that receives balance impulses
The trap. Writing that the semicircular canals help in hearing. They sense movement for balance; hearing is the cochlea's job.
Did you know
Why does your own voice sound strange in a recording?
Most people dislike hearing a recording of their own voice — it sounds thinner and higher than they expect.
When you speak, sound reaches your inner ear by two routes: through the air into your ear canal, and as vibrations through the bones of your skull. Bone carries the deeper sounds well, so your voice seems fuller to you.
A recording captures only the sound travelling through air — which is exactly how everyone else hears you.
When you speak, sound reaches your inner ear by two routes: through the air into your ear canal, and as vibrations through the bones of your skull. Bone carries the deeper sounds well, so your voice seems fuller to you.
A recording captures only the sound travelling through air — which is exactly how everyone else hears you.
Exam relevance
How does the ear lead into NEET and JEE preparation?
This is foundation work linking Biology and Physics.
Physics. Sound as a vibration carried through a medium returns in Class 11 Waves, part of JEE Main and NEET Physics, where frequency, wavelength and speed of sound appear as numericals.
Biology. Class 11 Neural Control and Coordination in NEET Biology covers how impulses travel and are processed; check the current NEET syllabus for the ear and sense organs, since recent textbook editions have trimmed this material. Where it is included, the organ of Corti and the fluids of the inner ear are the details added.
The trap that costs marks. Mixing up the order of the ossicles. Malleus touches the eardrum, stapes touches the oval window, with incus between.
Physics. Sound as a vibration carried through a medium returns in Class 11 Waves, part of JEE Main and NEET Physics, where frequency, wavelength and speed of sound appear as numericals.
Biology. Class 11 Neural Control and Coordination in NEET Biology covers how impulses travel and are processed; check the current NEET syllabus for the ear and sense organs, since recent textbook editions have trimmed this material. Where it is included, the organ of Corti and the fluids of the inner ear are the details added.
The trap that costs marks. Mixing up the order of the ossicles. Malleus touches the eardrum, stapes touches the oval window, with incus between.
Key takeaways
What must you be able to do from this part?
- External ear: pinna collects, canal traps dust, eardrum vibrates
- Middle ear: malleus, incus, stapes amplify; Eustachian tube equalises pressure
- Inner ear: cochlea for hearing; vestibule and semicircular canals for balance
- Sound path: pinna, canal, eardrum, ossicles, oval window, cochlear fluid, hair cells, auditory nerve, cerebrum
- Semicircular canals: fluid lags during turning, bends hairs — dynamic balance
- Vestibule: gravity pulls particles on hair cells — static balance
- Cerebellum uses these impulses to adjust posture
Cover the labels on an ear diagram and see whether you can trace a single clap from the air outside all the way to your brain.
- Middle ear: malleus, incus, stapes amplify; Eustachian tube equalises pressure
- Inner ear: cochlea for hearing; vestibule and semicircular canals for balance
- Sound path: pinna, canal, eardrum, ossicles, oval window, cochlear fluid, hair cells, auditory nerve, cerebrum
- Semicircular canals: fluid lags during turning, bends hairs — dynamic balance
- Vestibule: gravity pulls particles on hair cells — static balance
- Cerebellum uses these impulses to adjust posture
Cover the labels on an ear diagram and see whether you can trace a single clap from the air outside all the way to your brain.