Hearing and balance Flashcards
What other regions of the brain, broadly, are associated with hearing?
The amygdala and hippocampus, involved in memory and emotion.
The visual system. Important for communcicaton.
Somatosensory system and vestibular system for sound localisation.
What are the common hearing problems experienced by infants?
Moderate to profound deafnes. Could be genetic cause, caused by cytomegalovirus.
Otitis media with effusion
Infections (meningitis)
Trauma
What are the most common hearing issues in adults?
Age related Noise exposure Genetic Trauma Tumours Drugs (aminoglycoside antibiotics, cisplatins (cytotoxic drugs)
What is the function of the outer ear?
Collect sound
Protection of middle ear
Pinna important for sound localisation.
How does the inner ear act as a transformer to overcome the resistance of the inner ear/ how does it amplify the sound?
Goes from a large area of the tympanic membrane to the small oval window.
The malleus is longer than the incus, larger movements of the malleus are transferred into more forceful movements of the smaller incus
97% of the energy is transferred withthe midle ear. It would be 0.3% without it.
What are the names of the channels in the cochlear, heir ion concentrations and the name of the cells that maintain those levels.
The scala vestibuli (superior) and the scala tympani (inferior) contain perilymph, wich has 150 mM concentration of Na and a 5 mM concentration of K.
Scala media is in the middle and contains endolymph, which contains Na 5 mM and K 150 mM.
The cells that mainain this balance are called the stria vascularis and they are in the scala media.
Describe the organ of corti.
It s the scala media and contains in the inner and outer hair cells. There are 5000 inner and 15000 outer hair cells.
They sit on a basilar membrane and the movement of this transmits energy to the sensory hairs.
How do the hair cells activate?
When the stapes pushes on the ova window it causes a travelling wave along the organ of corti/basilar membrane. This causes the steriocillia to brush against the tectoral membrane and the tip links between them cause the opening of the mechanical ion channels in the steriocillia.
What part of the ear does excessive sound damage?
The tip links of the steriocillia.
What happens once a hair cell is activated?
The opening of these channels allows the high conc of K+ in the endolymph to enter causing depolarisation. This allows the Ca2+ channels to open and then the synaptic vesicles to be released and the neuron to fire.
Because the scala tympani is very low in K+ the K+ from the hair cells is just reabsorbed, thus negating the need for high energy potassium pumps ant therfore less O2 and blood is required in this area.
The potissum goes from the scala tympani back to the stria vascularis via a chain of fibroblasts.
What is the main cause of congenital deafness?
Disruptions in the gap junctions between the fibroblasts that recycle the potassium.
What do the outer hair cells do?
Important for hearing different frequencies and boosts the low intensity sounds.
They are motor cells. They constrict to increase the firing of the inner hair cells. Propagate the movement on the inner hair cells.
What type of nerve fiberes innervate the hair cells?
The type I fibres for the inner hair cells, which make up 95% of the nerve fibers.
The type 2 nerve fibres innervate the outer hair cells and make up 5%.
The nerve bodies are very close to the coclear and are called spiral ganglion cells.
There are a lot of descending nerve fibres to innervate the motor control of the outer hair cells.
What in the organ of corti causes the tonotopic organisation?
The stiffness and mass of the basilar membrane. At the base it is thin and stiff and at the apex it is wide and floppy, the hair cells are also larger at the apex.
When a wave passes through the basilar membrane it will find a point of resonance dependingon the properties of the basilar membrane and the frequency.
High frequency at the base, low at the apex.
What principles determine the frequency and intensity of sound heard?
The place principle: tonotopic organisation
The volley principle: fibres can fire together but out of phase to increase the frequency
Intensity principle: more fibres and firing morefrequently
What is binaural hearing important for?
Identifying where sound is coming from and to hear in background noise.
What is the neuronal auditory pathway?
Cochlea > cochlea nucleus > superior olivary complex > inferior colliculus > median geniculate body > primary auditory complex
