Hearing And Balance Flashcards
(44 cards)
1
Q
How many parts of the ear is there?
A
- # three
- outer ear
- middle ear
- inner ear
2
Q
The outer ear, what is it?
A
- extends from the outer skin and cartilaginous part, the auricle / pinna
- to the auditory canal
- to the tympanic membrane (eardrum)
3
Q
The middle ear, what is it?
A
- begins with the tympanic membrane
- behind this there are three small bones
= malleus, incus, stapes - they are loosely connected
- they are collectively known as = auditory ossicles
- the stapes sits inside a gap in the wall of the cochlea = the oval window
- this marks the end of the middle ear
4
Q
The inner ear, what is it?
A
- cochlea of the inner ear = converts the kinetic energy from sound waves to action potentials
- allowing a signal to be sent to the appropriate area of the brain
- to generate a conscious sensation of sound
- this is known as = signal transduction
5
Q
What are the semi-circular canals involved with?
A
BALANCE
6
Q
A
7
Q
What is sound?
A
Any audible vibration of molecules and it travels in wave form
8
Q
How many ways can waves be described?
A
- 2 ways
- pitch
- the frequency, how many there are per second
- measured in hertz
- one hertz = one wave per second
- amplitude
- the greater the height of the sound wave, the louder the sound
- measured in decibels
- normal human speech ranges = 100-8000Hz, 60 decibels
- threshold of pain = 120db
- prolonged exposure to greater than 90db = permanent hearing loss can happen
9
Q
What are the two pathways in which sound can reach the cochlea?
A
- the ossicular conduction pathway
- the bone conduction pathway
10
Q
What is the ossicular pathway?
A
- sound waves are directed down the auditory canal toward the tympanic membrane
- sound strikes the tympanic membrane causing it to vibrate
- attached to the membrane is the handle of the malleus, the vibrations are passed onto the malleus
- the malleus is bound to the incus, when the malleus moves so does the incus - the vibrations are passed on
- the opposite end of the incus joins with the stapes, which is in the oval window of the cochlea - it then receives these vibrations
11
Q
Summary of the ossicular conduction pathway:
A
- sound waves cause the eardrum to vibrate
- these vibrations are passed from the eardrum to the malleus
- then to the incus
- then the stapes
- the stapes vibrates within the oval, in turn the membranes and the fluid inside the cochlea are vibrated
12
Q
The bone pathway:
A
- occurs when the fluid and membranes within the cochlea are vibrated
- with this method the vibrations are passed to the cochlea via the bony labyrinth that surrounds it
- bypassing the structures of the outer and middle ear
= the eardrum & auditory ossicles
13
Q
Why is ossicular conduction better than bone conduction?
A
- the ossicular pathway involves the auditory ossicles = malleus, incus, stapes
14
Q
What do the tympanic membrane and ossicular system provide?
A
- impedance matching between the sound waves in the air and sound waves in the cochlear fluid
15
Q
How many times does the ossicular system increase the force of movement in the stapes?
A
1.3 times out of
16
Q
What allows the kinetic energy of the stapes to be concentrated over a smaller area?
A
- the oval window is 18 times smaller than the tympanic membrane
17
Q
What is the attenuation reflex?
A
- when loud sounds are transmitted through the ossicular system from there to the CNS a reflex occurs almost immediately = 40-80milliseconds
- to protect the cochlea from damaging vibrations caused by excessively loud noise and to mask low frequency background noise
- the stapedius muscle pulls the stapes outward and the tensor tympanic muscle pulls the handle of the malleus inward
- these two forces oppose one another and cause the ossicular system to develop rigidity
- reducing the ossicular conduction of sound
18
Q
What is another function of the attenuation reflex?
A
- decrease a persons hearing sensitivity to their own voice
19
Q
What is the cochlea?
A
- a system of coiled tubes that when cross sectioned can be divided into three chambers by two membranes
20
Q
What does the reissners membrane do?
A
- separates the scala vestibuli from the scala media
- which is separated from the scala tympani by the basilar membrane
21
Q
What is the auditory receptor?
A
- the organ of corti, which houses hair cells = receptor cells for hearing
22
Q
Where are the hair cells?
A
- the bases of the hair cells are embedded in the basilar membrane and the tips are embedded in the tectorial membrane
23
Q
What does sound induced vibration of the basilar membrane produce?
A
- shearing movements between the hairs and the tectorial membrane
- this sets up receptor potentials as mechanically sensitive channels in the hair cells open up
- allowing K+ to depolarize the cells
- endolymph = the fluid which fills the scala media & bathes the tips of the hair cells in a very high K+ conc)
24
Q
What does the depolarisation cause?
A
- the release of neurotransmitter so that an action potential can be passed on to the auditory nerve fibres
- at the base of the hair cells
- these fibres come together as the cochlear nerve, which carries the auditory information to the appropriate area of the brain
- low frequency sound stimulates hair cells in the basilar membrane near the apex of the cochlea and ..
- high frequency sounds activate the basilar membrane at the base of the cochlea
25
What do the oval window end and intermediate frequencies activate?
- the membrane somewhere between the two extremes
26
What is the major method used by the nervous system to detect different sound frequencies?
- to determine the positions along the basilar membranes that are most stimulated
27
What are the two main types of deafness?
- conduction deafness
- nerve deafness
28
What is conduction deafness?
- occurs when passage of sound waves from outside the ear to the cochlea is reduced
- most common cause = earwax blocking the canal
29
What is nerve deafness?
- occurs when there is a problem with initiating or relaying electrical impulses from the cochlea to the CNS
- most common cause = prolonged exposure to noise over 90dB
30
What do the cochlear nerves form a part of for the auditory pathways?
- the cochlear nerves form part of the VIII cranial nerve
- travel to the cochlear nuclei in the medulla oblongata
- where the signal crosses over to the opposite side of the
31
The signal then goes as follows:
1. Superior olivary nucleus = compares the sound coming from the two ears to determine its direction
2. Inferior colliiculus = processes fluctuations in pitch to help the understanding of speech
3. Thalamus = acts like a switchboard and relays the signal to
4. Primary auditory cortex = this is housed in the temporal lobe of the cerebrum and is the site of the conscious perception of sound
32
What is the second major function of the inner ear?
- to provide information about the positions along and acceleration of the head
33
Why is the second function of the inner ear extremely important?
- important in the maintenance and balance and control of movement
- depends on the vestibular apparatus
- which is located in the bony labyrinth
34
What is the vestibular apparatus?
- the sensory organ for detecting sensations of equilibrium - static & dynamic
35
What are the 5 functional components of the inner membranous labyrinth of the vestibular apparatus?
- 3 semicircular canals that detect head rotation
- 3 otolothic organs
- the utricle
- the saccule
- which detect gravity = head position
36
What does the mediation of static and dynamic equilibrium depend on?
- the deflection or movement of hair cells which synapse with the vestibular nerve & are relayed to the cerebellum via the vestibulocochlear nerve
37
What are the otolothic organs?
- pair of large organs near the centre of the labyrinth
- they have a small sensory patch of hair cells & supporting cells called the macula
38
What does the macula of the uricle do?
- important role in determining orientation of the body when the head is upright
- whilst the macula of the saccule signals head orientation when the person is lying down
39
In the maculae of both structures, what happens?
- thousands of hair cells project cilia up into a gelatinous membrane known as the otolithic membrane
- as it contains tiny crystals of calcium carbonate
- hair cells are stimulated when the gelatinous material surrounding them shifts their position
40
What way are the three semicircular canals orientated?
- at right angles to one another
- detects any rotation in its own plane
41
What is the sensory organ within the semicircular canal?
- tiny swelling = crista ampullaris
- which contain hair cells, which project stereocilia into the gelatinous cupula
42
What happens when the head starts to rotate in the plane of the canal?
- the canal moves too
- the fluid initially remains stationary but will move, causing deflection in the cupula in the opposite direction to the rotation
- which causes the stereocilia of the hair cells to bend
- activating the hair cellls, signals will be sent via the vestibulococholear nerve
- to the cerebellum
43
Where is information from the vestibular apparatus carried in?
- the vestibular portion of the vestibulocochlear nerve
- to the vestibular nuclei in the brainstem
44
What do these connect with?
- areas of the cerebellum & spinal cord involved in control of motor activity
- the occulomotor centre which helps control eye movements
- the thalamus, relays to the post central gyrus in the temporal lobe
- which allows us to be aware of position, acceleration & to voluntarily control balance
