Special Senses Flashcards
What is sound?
A pressure wave that spreads out from a source, using a medium whose particles vibrate.
What is frequency?
Pitch
The number of vibrations per second in Hertz
What is a typical range of hearing for a young human?
20-20,000Hz
What is loudness?
Intensity
Strength of the vibrations
What is the loudest sound we can hear?
100 trillion times the energy of the quietest sound we can hear.
Use log scale called decibels
What would differ in a 10dB increase in terms of perception and energy?
Perceived as twice as loud
Has 10 times the amount of energy
Why do we have two ears?
So we can localize sounds on a horizontal plane.
Time difference is cue
What is the pinna
External portion of ear
Amplifies, shapes, and filters sound to give directionality
Filters out high frequency sound from behind
Helps distinguish front from back, and up from down (due to shape)
What is the ear canal?
A tube
Sounds at central frequencies are amplified (by about 10dB) in here because of resonance.
What structures make up the outer ear?
Pinna and ear canal
What structures make up the middle ear?
Tympanic membrane Ossicles (malleus, incus, stapes) Eustachian tube Stapedius Muscle Tensor Tympani
What structures make up the inner ear?
Cochlea
Vestibule
Semi-circular canals
Oval window
What amplifies sound?
- The area ratio of tympanic membrane and the oval window causing a 25dB increase in loudness
- The lever action of the ossicles
What embryological structures give rise to the ossicles?
First branchial arch turns into mandible and gives rise to malleus and incus
Second branchial arch gives rise to stapes
What structures are found within the middle ear that help protect from load noises?
Stapedius Reflex- connects to stapes and contracts when ear is exposed to loud sound to protect the cochlea
Tensor Tympani- Large muscle running up eustachian tube joining onto back of malleus. Stop you from blowing out tympanic membrane when coughing and sneezing. Protects from loud sound
What is the eustachian tube?
Cartilage and bone lined in mucosa moving from nasopharynx to middle ear.
Allow air into middle ear to equalize pressure, allowing tympanic membrane to vibrate appropriately
What are conductive hearing loss problems?
Inner ear works fine, but sound is appropriately conducted to the cochlea
Can correct by vibrating the skull
What are some causes of hearing loss in the outer and middle ear?
Ear canal- wax, foreign body, congenital atresia
Tympanic Membrane Perforation
Ossicles- congenital fusion, damage from infection
Middle ear space- fluid instead of air
What structures sit on either end of the ossicles?
Tympanic membrane sits by malleus, and oval window (fenestra ovalis) sits beside the stapes and is much smaller
What is the vestibular apparatus for and what structures are apart of it?
For balance
Utricle & Saccule - linear acceleration
Semi-circular canal- rotatory motion in 3 planes
Contain sensory epithelial
What is the Cochlea and what is it used for?
Forms part of the inner ear, used for converting physical vibrations into electrical impulses
Joined to utricles/saccule, and semi-circular canal
How does sound move from the oval window through the inner ear?
Vibrations passed to oval window -> vestibule -> scala vestibuli -> helicotrema -> back through scala tympani (lower cochlear duct) -> waves terminate at round window
What is found within the Scala Media?
Contains the Organ of Corti (sensory epithelium containing auditory hair cells) Stria Vascularis (regulates electrolyte composition within endolymph so it optimal for hair cell function)
What is contained within the organ of corti?
Tectorial membrane superior
Spiral ganglion
Auditory nerve fibers
Basilar membrane
How do we pick up frequency within the cochlea?
As the sound moves through the scala vestibuli/tympani, certain frequencies are optimally picked up by certain portions of the basilar membrane.
Base- high frequency
Apex- low frequency (hairs at helicotrema are more stiff)
What are the different hairs within the inner ear?
Outer hairs- efferent, help amplify sound. We have more of these
Inner Hairs- afferent, carry sound stimuli to brain using vestibulocochlear nerve
What does the tectorial membrane touch?
Hairs rub against it
What do the nasal concha do?
Increase turbulence to help circulate air so we can smell it all.
What nerves supply the tongue?
Anterior 2/3 is supplied by the facial (taste) and the lingual nerve, a sub-branch of the trigeminal nerve (general sensation)
Posterior 1/3- glossopharyngeal nerve
Hypoglossal nerve supplies the tongue muscle
What is the tallest stereocilia called and why is it relevant to membrane potential?
Kinocilium- pushing of hairs towards kinocilium causes depolarization (K influx), where as movement of the kinocilium towards the other shorter hair causes hyperpolarization
Does increased frequency cause hyperpolarization or depolarization?
Depolarization
What is the function of the inner hair cell?
Transducer
It works as a receptor that picks up basilar membrane vibrations and changes that form of energy into another
Afferent
What are the roles of outer hair cells?
Cochlear Amplification - contract in response to sound actively, which feeds energy into basilar membrane (reverse transduction) helping it to move more
Make frequency response more selective by reducing vibration besides them on the basilar membrane, helping with localization of sound
How could you test to see if an infant has hearing problems?
Otoacoustic emissions test.
Placed over babies ears, and can pick up on the sound of the movement of outer hair cells
What happens with hair loss within the cochlea?
Inner- complete hearing loss
Outer- loss of sound (50db) and loss of sound discrimination
How does reception of high vs low pitch in terms of frequency change?
You can hear low pitches moving at a high frequencies more than high pitches at high frequencies because refractory period isn’t as long for low pitches
How does sound move through the central pathways?
First order neuron axons project through cochlear nerve (CN8) in internal acoustic meatus -> cerebello-pontine angle -> synapse in cochlear nuclei (medulla-pons junction) and may move contralaterally now -> Move through olive and trapezoid body in pons to midbrain (inferior colliculus) -> thalamus (medial geniculate body) -> cortex (superior temporal gyrus)
How long is pitch maintained when moving from the cochlea to the brain?
All the way to the temporal lobe
What is the Occipital Somite?
What most of the tongue muscles develop from- somites are from the paraxial mesoderm
Describe the embryology of the tongue and corresponding nerves.
1st Brachial Arch Endoderm- Forms mucosal surface of anterior 2/3 of tongue. Trigeminal nerve 5 for touch and pain, and facial nerve 7 for taste
3rd Brachial Arch Endoderm- forms epithelial lining of posterior 3rd of tongue. Glossopharyngeal nerve 9
Mesoderm of upper neck- intrinsic/extrinsic muscles. Hypoglossal nerve 12
What bones is the tongue suspended by?
Mandible, hyoid, and styloid process