Hearing & balance Flashcards
(46 cards)
1
Q
- The external ear consists of the ___ or ___ which is composed of elastic cartilage.
- Function: to direct sound waves into the external acoustic meatus.
A
auricle or pinna
2
Q
The rim of the pinna or auricle is called
A
helix
3
Q
the fleshy dangling part of the pinna or auricle
A
lobule; aka earlobe
4
Q
- a short tube that extends from the auricle to the eardrum.
- is lined with skin that has short hairs which screen out large debris, sebaceous glands and modified apocrine sweat glands called ceruminous glands.
A
The auditory canal
5
Q
- apocrine sweat glands called __ __
- These glands secrete ear wax or cerumen which provides a means of entrapping foreign objects and repelling insects.
A
ceruminous glands
6
Q
- Sound waves entering the external acoustic meatus eventually hit the __ __ or __.
- is the boundary between the outer and middle ears.
- Sound waves striking this make it vibrate, and the vibration is transferred to the middle ear bones or ossicles making them vibrate. T
A
tympanic membrane or eardrum
7
Q
- the middle ear
- is lined with mucous membrane and filled with air. The posterior part communicates with the mastoid air cells in temporal bone (tympanic antrum). The mastoid process is a good place to check for conduction block in hearing deficits.
A
tympanic cavity
8
Q
- ___, our auditory tube (formerly known as the Eustachian tube) connects the middle ear cavity to the nasopharynx so we can equalize pressure between the middle ear cavity and external air pressure.
- When you fly in a jet, or drive up a mountain, you can feel increasing pressure on the eardrum and it is more difficult to hear. When you swallow or yawn, the auditory tube opens up temporarily so that the middle ear cavity can equalize pressure with the external environment. This permits the tympanic membrane to once again vibrate freely, and hearing is restored. The auditory tube is also a route by which infections can spread from the throat to the ear and even reach the brain. Ear infections are common in kids because their auditory tubes are short and run more horizontally, whereas the auditory tubes in adults are longer and at an oblique angle.
A
pharyngotympanic
9
Q
Inflammation of the middle ear is called __ __.
A
otitis media
10
Q
Extending from the inner aspect of the tympanic membrane to the inner ear are the three smallest bones in the body, collectively referred to as the ___ __.
A
auditory ossicles
11
Q
The inner ear is also called the ____ because of its complex shape. It lies deep in the temporal bone and consists of the cochlea which is involved with hearing, and the vestibule and semicircular canals which are the sense organs of balance.
A
labyrinth
12
Q
The middle ear chamber contains the three ear bones which are named for their shapes, the malleus (hammer), incus (anvil) and stapes (stirrup). The handle of the malleus is attached to the eardrum, and the base of the stapes fits into the oval window. Tiny ligaments suspend the ossicles, and mini synovial joints link them together into a chain that spans the middle ear cavity. The ossicles transmit the vibration of the tympanic membrane to the oval window, which in turn sets the fluids of the cochlea into motion which ultimately excites the receptors for hearing. There are two muscles that insert on two of the ear bones: the tensor tympani arises from the wall of the auditory tube and inserts on the malleus, and the stapedius runs from the posterior was of the middle ear cavity to the stapes.
A
…
13
Q
- has the distinction of being the smallest skeletal muscle in the body.
- innervated by the facial nerve.
- When the ears are exposed to loud noises, the muscle contract reflexively to prevent damage to the hearing receptors which are first order neurons. Once killed, the receptors cannot be replaced.
A
The stapedius
14
Q
- When bombarded with loud noise, the __ __ tenses the ear drum by pulling it medially and the stapedius impedes the vibration of the whole ossicle chain and limits the movement of the stapes in the oval window.
- innervated by the mandibular division of cranial nerve N (Trigeminal). Its contraction limits the movement of the eardrum which protects against prolonged loud noises.
A
tensor tympani
15
Q
is a condition that results if the stapedius is paralyzed. This makes noises seem excessively loud to the point of being painful.
A
Hyperacousia
16
Q
- is where the organs of hearing and balance are found.
- is like a series of channels that are bored out of the temporal bone, filled with fluid, and contain a fluid-filled tube floating inside.
- Because the channels are similar to a maze, the they are referred to as a labyrinth.
A
The inner ear
17
Q
- consists of cavities running through the temporal bone.
- filled with a fluid called perilymph which is similar in composition to CSF.
A
The bony labyrinth
18
Q
- are the tubes that float inside the bony labyrinth.
- is also filled with fluid called endolymph which is similar to intracellular fluid, but the electrolyte composition is different. These two fluids conduct the sound vibrations involved in hearing and respond to the mechanical forces occurring during changes in body position and acceleration.
A
The membranous labyrinth
19
Q
- is the central egg-shaped cavity of the bony labyrinth.
A
The vestibule
20
Q
- Suspended in its perilymph and united by a small duct are two membranous sacs called the __ & ___
- They house receptors called the maculae that respond to the pull of gravity and changes in the position of the head.
A
utricle and saccule
21
Q
project from the posterior aspect of the vestibule, project in three directions anterior, posterior, and lateral, and contain the membranous semicircular duct which communicates with the utricle anteriorly.
A
The semicircular canals
22
Q
Each __ __ has a swelling at one end called an ampulla which houses an equilibrium receptor called the crista ampullaris.
A
semicircular duct
23
Q
respond to angular or rotational movements of the head.
A
The cristae ampullares
24
Q
- is where the organ of hearing is located.
- extends from the anterior part of the vestibule and coils around a bony pillar called the modiolus.
A
The cochlea
25
* which ends blindly at the cochlear apex.
* contains the spiral organ of Corti which is the receptor organ for hearing.
cochlear duct
26
* The cavity of the bony cochlea is divided into three separate chambers or scalae (scala means ladder).
* is the upper chamber that ends at the oval window;
the scala vestibuli
27
* is the lower chamber that ends at the round window. Both chambers contain perilymph.
* They are separated from each other except at the apex of the cochlea called the helicotrema.
the scala tympani
28
Running between the scala vestibuli and scala tympani is the cochlear duct which is filled with endolympth. It is separated from the scala vestibuli by the vestibular membrane and from the scala tympani by the basilar membrane.
..
29
* In the outer wall of the cochlear duct is a structure called the __ \_\_
* As the name indicates, it is composed of a highly vascularized mucous membrane that secretes endolymph into the duct.
he stria vascularis
30
* The spiral organ of Corti which rests on top of the basilar membrane is composed of supporting cells and hearing receptor cells called __ \_\_\_ .
* have numerous sterocilia which are actually modified microvilli that protrude into the potassium-rich endolymph. The longest of the hairs project into the tectorial membrane.
hair cells
31
Sound is channeled into the external auditory meatus and strikes the eardrum making it vibrate.
This causes the malleus to vibrate and the vibration is further passed on (and amplified) to the incus and stapes.
The stapes vibrates and moves the membrane of the oval window in and out.
Waves in the perilymph of the scala vestibuli displaces the vestibular and basilar membranes. This produces waves in the endolymph in the cochlear duct.
These waves jiggle the basilar membrane upon which the organ of Corti sits.
The movement bends the hairs (microvilli) of the hair cells that are embedded in the tectorial membrane and the hair cells send an electrical impulse back to the brain via cranial nerve VIII
...
32
Different sound frequencies cross the basilar membrane at different locations along the cochlea.
have a short wavelength that displaces proximal end of the basilar membrane
High frequency sounds
33
displace the basilar membrane near the middle of the cochlea
medium-frequency sounds
34
displace the basilar membrane at its distal end near the apex.
35
Nerve impulses are sent out the cochlear division of cranial nerve VIII.
From CN VIII, the impulses travel to the auditory or cochlear nuclei in the medulla oblongata.
Most of the fibers decussate in the medulla oblongata before heading up to the thalamus.
From the thalamus, impulses are relayed to the auditory area of the temporal lobe (#41 & 42). Notice that different regions of the auditory cortex are tuned to different frequencies of sound wave corresponding to the cochlea.
Some fibers don’t reach the thalamus by end in the inferior colliculi. These fibers are involved with the orientation of the eyes, head and neck in response to auditory stimuli.
..
36
* The sense organ for static equilibrium and dynamic linear acceleration and deceleration is the
* Each utricle and saccule contains a this
* monitor the position of the head in space, and in so doing, they play an important role in controlling posture.
* Notice that \_\_\_ are oriented at right angles to each other; one being parallel to the base of the skull and the other perpendicular to it. This allows us to detect linear acceleration and deceleration in both the horizontal and vertical planes. For example, imagine sitting in your car at a stop light. When the signal changes to green and you step on the accelerator the __ in the utricles respond to the change in horizontal position. Similarly, when riding in an elevator, the __ in the saccules respond to the up and down movement.
macula
37
* Each macula is a flat patch of epithelium that contains hair cells. The hair cells have stereocilia plus one kinocilium that project into a gelatinous mass call the __ \_\_
otolithic membrane.
38
* Embedded in the mass (otolithic membrane) are small calcium carbonate crystals called
* increase the membrane’s weight and its inertia (resistance to change in motion). The hair cells synapse with fibers of the vestibular division of Cranial nerve VIII.
otoliths
39
* resistence to change in motion
* When your head starts or stops moving in a linear direction, __ causes the otolithic membrane to slide backward or forward over the hair cells, bending the hairs. For example, when you flex your head, the otolithic membranes lag behind, bending the hairs backward. When you extend or hy
inertia
40
The receptor for dynamic rotational equilibrium is a minute elevation called the __ \_\_ found in the ampulla of each semicircular canal. Recall that each of the three semicircular canals is oriented in one of planes; anterior, posterior, and lateral. The anterior and posterior canals are oriented at right angles to each other in the vertical plane, whereas the lateral canal lies horizontally. There is a membranous semicircular duct filled with endolymph in each semicircular canal. Each duct has an enlarged swelling at one end called an ampulla which contains the __ \_\_ . Each crista is composed of support cells and hair cells. The hair cells have stereocilia and one kinocilium that projected into a gelatinous mass called the cupula.
crista ampullaris
41
respond to changes in the velocity of rotational movements of the head.
The cristae
42
Because of its inertia, the endolymph in the semicircular ducts moves briefly in the direction opposite the body's’ rotation. The flow of endolymp bends the cupula and excites the hair cells which depolarize and send impulses to the brain at a faster rate. Bending the cilia in the opposite direction causes hyperpolarization and reduces generation of impulses. When the body is rotating at a constant rate, the endolymph eventually comes to rest—it moves along at the same speed as the body and stimulation of the hairs cells ends. If we are blindfolded, we cannot tell whether we are moving at a constant speed or not moving at all after the first few seconds of rotation. However, when we suddenly stop moving, the endolymph keeps on going which in effect is like reversing direction. The sudden reversal in the direction of hair bending results in changes in membrane voltage in the receptor cells and modifies the rate of impulse transmission, which tells the brain that we have slowed or stopped. Impulses transmitted from the semicircular canals are particular important to reflex movements of the eyes. As you rotate, your eyes slowly drift in the opposite direction. This is because of the backflow of endolymph in the semicircular canals. Then, because of CNS compensating mechanisms, the eye jump rapidly toward the direction of rotation to establish a new fixation point. These alternating eye movements are called **vestibular nystagmus**, continue until the endolymph comes to rest. When you stop rotating, at first your eyes continyue to move in the direction of the previous spin, and then they jerk rapidly in the opposite direction. This sudden change is caused by the change in the direction in which the cristae are bent after you stop. Nystagmus is frequently accompanied by vertigo or dizziness and inability to walk in a straight line.
43
Information from the equilibrium receptors goes directly to reflex centers in the brain stem, rather than to the cerebral cortex. Impulses travel initially to one of two destinations: the vestibular nuclear complex in the brain stem or the cerebellum. T**he vestibular nuclei,** the major integrative center for balance, also receive inputs from the visual and somatic receptors, particularly from proprioceptors in neck muscles that report on the position of the head. They integrate this information and then send commands to the brain stem motor centers that control the extrinsic eye muscles (cranial nerves III, IV, and IV) and reflex movements of the neck, limb and trunk muscles (via the vestibulospinal tracts). The reflex movements of the eyes and body allow us to remain focused on the visual field and to quickly adjust our body position to maintain or regain balance. **The cerebellum** also integrates inputs from the eyes and somatic receptors. It coordinates skeletal muscle activity and regulates muscle tone so that head position, posture and balance are maintained, often in the face of rapidly changing inputs.
..
44
From the vestibular branch of CN VII, most of the fibers relay in the vestibular nuclei of the pons. Some fibers enter the cerebellum (via the inferior cerebellar peduncle). Fibers and their impulses are routed to the nuclei of cranial nerves III, IV and IV that control eye movements, and to the accessory nerve (XI) that control head and neck movements.
...
45
is involved with keeping the head positioned with respect to the force of gravity
static equilibrium
46
is for keeping the head positioned when it is subjected to movements. There are two types of dynamic equilibrium, linear and rotational.
dynamic equilibrium
