The Ear Flashcards
Divisions of external ear
Pinna (auricle), external auditory canal, tympanic membrane
Pinna (auricle)
- Outer ear made up of cartilage
- Collects and transmits sound waves to middle ear
-Causes tympanic membrane to vibrate
External Auditory Canal
-Short curved tube in temporal bone
-Filled with ceruminous (wax) gland
-includes hairs & earwax for protection from particles
Tympanic membrane (eardrum)
- Thin connective tissue membrane, separates out & middle ear
-Vibrates in response to sound
-Transfers sound energy to middle ear ossicles
Divisions of the Middle Ear
-Ear ossicles (malleus, stapes, incus)
-Pharyngotympanic/Eustachian tube
-Mastoid Cavity of temporal bone
-Oval & round windows
Difference between Oval & Round window
Oval - phase of compression
Round - phase of rarefaction
Pharyngotympanic/Eusrachian Tube
- Equalizes pressures on both sides of tympanic membrane by preventing rupturing
How does the middle ear provide protection from large sounds of low frequency
Contracting malleus (tensor tympani) & stapes (stapedius) to reduce motion of ossicles
Smallest skeletal muscle in the body
strapdius
Why does the middle ear only provide protection for prolonged loud noises and not sudden loud noises?
Because the malleus (tensor tympani) and stapes (stapedius) need time for contract
Ear ossicles
- Transits vibrations of eardrum (tympanic membrane) to fluid in cochlea via oval window
- Loud sound protection (malleus & stapes contracting)
Divisions of Inner Ear
Bondy Labyrinth - Vestibule, semicircular canals, cochlea
Membranous Labyrinth - Semicircular ducts, cochlear duct
Perilymph
- Fluid found in bony labyrinth (inner ear)
- Transmits vibrations to cochlea
- Similar to Cerebrospinal fluid (CSF)
Endolymph
- Found in membranous labyrinth
- Stimulates hair cells for hearing, helps detect head movement in semicircular canals
-Potassium rich fluid
- Similar to intracellular fluid
-Helps facilitate movement of hair cells in cochlea
What is the cochlea and what does it contain
- Spiral, bondy chamber in inner ear
- Contains cochlear duct & organic of corti l (hearing receptor)
Basilar membrane
- Composes bottom of cochlear duct
- Supports the organ of Corti
What are the three chambers of the Cochlea
Scala Vestibule & Scala Tympani - filled with perilymph, continues with tympanic via helicotrema
Scala Tympani terminates at round window
Scala Media - filled with endolymph
Semicircular canals
Monitors head movement and regulates dynamic equilibrium
Vestibule Apparatus
- Maintains orientation & balance
Organ of Corti
Hearing receptor
Nerve VIII
- Transmits sound & balance from ear to brain
- Runs from organ of Corti to the brain
-Organic of court detect vibrations converts into nerve impulses
What happens in the cochlea when sound waves cause the fluid inside it to move?
Fluid (perilymph) movement bends the hair cells in the cochlea, generating neural signals that are sent to the brain
Hair cells in sound detection
- Fluid bends hairs cells cilia, ion channels open causing depolarization
- releases of neurotransmitters glutamate sendings signals to brain
Basilar membrane Base vs middle vs apex
Base (near oval window) - short stiff fibres that detect high frequency
Middle - detect medium frequency
Apex - long fibres that detect low frequency
Organ of Corti
- Includes stereocilia (hairs) in endolymph & touch tectorial membrane
- Afferent fibers of cochlear nerve attach to base of hair cells
What neurotransmitter is released during depolarization by the stimulation of cilia
Glutamate, stimulates cochlear nerve which sends impulses to the brain
How do sound signals travel through auditory pathway
- Cochlear bench of vestibulocochlear nerve (CN VIII)
-Medulla -> thalamus -> primary auditory cortex (temporal lobe)
What are the two types of balance
Static - head is stationary or moving in a straight line, detects head position
Dynamic - head is rotating, detects body position
The Vestibule
- Includes two sacs in perilymph (utricle - superior & saccule - inferior)
-Houses equilibrium receptors in maculae
-responds to gravity & position changes
Maculae
- Static balance receptor
- in walls of utricle & saccule
- stereocilia embedded in otolithic membrane
Otolithic membrane
- Jelly-like mass studded with CaCO3 (otoliths) which add weight and sensitivity to movement
- sits over hairs in maculae
- causes stereocilia to bend when head tilts of moves linearly
- detects gravity-related movement
Utricular & saccular hair cells
utricular - detect horizontal movement
saccular - detect vertical movement
Mechanism of static balance when head tilts forward
- otolithic membrane slides forward, bending sterocilia
-K channels open, hair cells depolarize, neurotransmitter released
-increased action potential frequency
Mechanism of static balance when head tilts backwards
- K channels close, reducing neurotransmitter release
- fewer action potentials
Crista Ampullaris
- receptor for dynamic balance
- located in ampulla of each semicircular duct
- dendrites of vestibular nerve fibres surround hair cells
Summarize mechanism of dynamic balance
head moves -> semicircular ducts & hairs move with it
endolymph lags behind causing cupula to bend
bending of stereociliar
-opens or closes K channels
-neurotransmitter release which alters action potential frequency
- brain interprets frequency changes from all three canals and determines rotation movement
Equilibrium pathway to the brain
- Impulse Transmission
- Processing centres
- Integration
- no conscious perception
Receptor for dynamic balance
Crista Ampullaris
Action potential decreases, K+ channels close
Head tilts backward
Action potential increases, K+ channels open
Head tilts forward
Detects horizontal movement
Utricular hair cells
Detects vertical movement
Saccule hair cells
How does the brain determine rotational movement?
Head moves - semicircular ducts & hair cells move - endolymph lags behind, cupula bends, bending of stereocilia causing K+ channels to open or close & action potential to increase or decrease from release of neurotransmitter , brain interprets frequency change from all three canals & determines rotational movement
Where is the maculae located?
Walls of utricle & saccule
Responds to gravity & head position changes
vestibule
Detects position of head movement when stationary or moving in a straight line
Static balance
Detects body position when head if rotation
Dynamic balance
