Anatomy and function of hearing, smell and taste Flashcards
What dictates the pitch of a sound?
The frequency: the higher the frequency, the higher the pitch
What dictates the intensity of sound?
The amplitude
Overview of hearing
- First transduction: sound wave strikes the tympanic membrane and becomes vibrations
- The sound wave’s energy is transferred to the 3 bones of the middle war which vibrate (malleus -> incus -> stapes)
- Second transduction: the stapes is attached to the membrane of the oval window, vibrations of the oval window create fluid waves within the cochlea
- Third transduction: fluid waves push on the flexible membranes of the cochlear duct. Hair cells bend and release the neurotransmitter
- Fourth transduction: neurotransmitter release onto sensory neurones creates action potentials that travel through the cochlear nerve to the brain
- Energy from the waves transfers across the cochlear duct into the tympanic duct and is dissipated back into the middle ear at the round window
What makes up the external ear?
- Pinna (auricle)
* External auditory (acoustic) meatus
What is the pinna?
- Also called auricle
- Single piece of cartilage
- Ear lobe, tragus, helix etc.
Describe the external auditory (acoustic) meatus
- Cartilaginous and bone parts: not in the same direction
- Ceruminous glands secrete earwax making it waterproof preventing the maceration of skin and preventing entry of foreign objects
How can you test to see if pain is referred or coming from the ear?
Palpate the tragus
What is the supply of the external auditory meatus?
- Auricular branch of the vagus
* Auriculotemporal branch of the trigeminal
Describe the tympanic membrane
- Concave
- 4 quadrants divided by the (shadow of the) handle of malleus
- Triangular reflection (Pulitzers triangle) in the anterior inferior quadrant
Which quadrant is chorda tympani found in?
Postero- superior quadrant
Which of the quadrants of the tympanic membrane is the safest?
• Antero-inferior quadrant
What is the middle ear?
- An air filled cavity with ossicles (malleus, incus and stapes- attached to walls by ligaments), muscles/tendons (tensor tympani and stapedius) and nerves (chorda tympani)
- it has 4 walls (lat. wall is the tympanic membrane), a roof (bone between the middle ear cavity and the middle cranial fossa) and a floor
What are the ossicles of the ear?
- Malleus
- stapes
- Incus
What muscles are found in the middle ear?
- Tensor tympani
* Stapedius
What is the auditory tube? What is the nerve supply?
- Also called pharyngotympanic/ Eustachian tube
- Mucous membrane continuous with the pharynx
- Supplied by glossopharyngeus
What happens if there is a fracture to the roof of the middle ear cavity?
• CSF will leak through, if the tympanic membrane is ruptured, CSF will leak out of the ear
What is the opening in the posterior aspect of the middle ear cavity?
- Adits as antrum
* Connects to the mastoid antrum and the mastoid air cells
What is chorda tympani a branch of?
The facial nerve
What is the role of tensor tympani?
- Pulls the tympanic membrane medially
* Increases the tension in response to loud noises which reduces the vibration of the tympanic membrane
What is the innervation of tensor tympani?
• Mandibular nerve (branch of the trigeminal)
What is the role of stapedius?
- Pulls the base of the stapes away from the oval window
* Protects the inner ear from injury from a loud noise
What is the innervation of stapedius?
• Facial nerve
What happens if there is injury to the muscles of the inner ear?
Hyperacusis
Describe the pharyngotympanic tube
- The walls are normally closed
- Actively opened by the simultaneous contraction of tensor veli palatini and salpingopharyngeus muscle
- This forces air into the cavity and equalises pressure
Describe the pharyngotympanic tube in children
- Straight and short
* pharyngeal infections can easily spread to the middle ear
What makes up the inner ear?
- bony labyrinth: vestibule (utricle and saccule), semicircular canals, cochlea
- Membranous labyrinth
- Perilymph (between the two labyrinths)