The ear Flashcards
Label the ear
Describe outer ear anatomy
Pinna (mobile elastic cartilage) & external acoustic meatus (L shaped tube ending in ear drum) collect sound wave vibrations & direct them towards eardrum
Tympanic membrane (ear drum) detects pressure waves as they cause it to vibrate
Describe middle ear anatomy
Air filled cavity in temporal bone containing ossicles transferring tympanic membrane vibrations to inner ear
Ossicles act as series of levers to transmit sound wave vibrations
What is the eustachian tube
AKA auditory tube
Connects middle ear with pharynx
Purpose is to equalise air pressure on both sides of tympanic membrane
What is the cochlear
3 fluid filled canals
Upper & lower filled with perilymph (joined together)
Middle filled with endolymph (higher in K+ & positive electric potential)
Sensory cells sit on basilar membrane
Pressure waves in fluid cause vibrations of basilar membrane –> movement of sensory hairs –> transmit mechanical energy to electrical energy which goes to brain
Explain frequency discrimination
The higher the frequency the less distance traveled
Different frequencies picked up at different places along cochlear
Explain directional hearing
Brain determines direction of sound based on differences in arrival time between both ears
Mobile external ears help with location of sound from behind/in front
What is brainstem auditory evoked response
Objective measuring method recording electric activity within auditory pathways of brain
Each ear stimulated separately by click stimuli
Accumulated action potential from cochlea can be measured as auditory evoked potential
Sedation required
Describe vestibular connection to brain
Otolith organs & semi-circular canals synapse with vestibular nerves
Vestibular nerves connect to vestibular nuclei in brainstem, cerebellum & cerebral cortex
They interpret info and cause response
What is the role of semicircular canals & otolith organs
Semicircular canals - dynamic information - movement
Otolith organs - static information - where head is in space
Label the diagram
Describe central vs peripheral vestibular syndrome
Peripheral (outside brain):
- Head tilt
- Nystagmus (fast & slow phase, slow towards lesion)
- Asymmetric ataxia
- Circling
Central (in brain):
- Anything else
What are semicircular canals
Endolymph filled tubes involved in dynamic reaction
3 canals on each side, oriented at right angles to each other
Cupula found at base of membranes - fluid movement deviates cupula which gives information
