Exam 2 Flashcards
Describe the structure of the external ear
Auricle made of of elastic cartilage with many regions (helix, antihelix, tragus, antitragus, concha, and lobule
There are also sebaceous glands associated with hairs on the external ear
What do ceruminous glands secrete? What is the function?
Cerumen - makes up ear wax along with sebaceous secretions and desquamated meatal cells - protects ear canal against pysical damage and microbial invasion
Which nerves provide sensory innervation to the external ear?
Greater auricular Lesser occipital Auriculotemporal (V3) Facial Vagus
What nerve innervates the middle ear?
Glossopharyngeal
What structures are found in the middle ear?
Tympanic cavity, containing ossicles and their muscles
What are the ossicles? What is their function?
Malleus is vibrated by tympanic membrane
Incus transmits vibration from malleus to stapes
Stapes transmits vibrations through oval window into cochlea
*The tympanic membrane collects energy through vibration in a large area and transmits through ossicles to the smallest area of the stapes, ultimately transmitting that energy in the fluid of the inner ear to sense sound
What are the functions of the Tensor tympani and the stapedius muscles?`
They dampen ossicle movement to protect against loud noises - innverated by V3 and VII respectively
What is the chorda tympani?
Branch from fascial nerve (VII) in the tympanic cavity that joins V3, containing both sensory and autonomic neurons
Sensory neurons innervate anterior 2/3 of tongue
Parasympathetic neurons innervate submandibular and sublingual salivary glands
*Susceptible to infection (otitis media)
What is the umbo?
Central depression in the tympanic membrane created by tension of the malleus
What is otitis media?
Infection/inflammation of the middle ear - can spread to cause meningitis or brain abscess
What is cholesteatoma?
Skin cysts that migrate through ear canal and perforate tympanic membrane to damage middle ear
Describe the organization of the cochlea.
Helical bony canal, divided into 3 spaces - cochlear duct (scala media), scala vestibuli, and scala tympani
What is endolymph? Where is it found? What about Perilymph?
Endolymph is fluid (high K+) secreted by stria vascularis into the cochlear duct
Perilymph is fluid (high Na+) found is the surrounding scala vestibuli and scala tympani, separated by vestibular and basilar membranes
What is the oval window? What about the round window?
The oval window is at the base of the stapes and triggers fluid vibration of perilymph through scala vestibuli.
The round window absorbs fluid vibrations that are transmitted through the scala vestibuli and continuous scala tympani
What is the organ of corti?
Refers to the the inner and outer layers of non-neural receptor ‘hair cells’ covered by the tectorial membrane within the cochlear duct that activate sensory neurons of the cochlear nerve
How do hair cells of the organ of corti ultimately trigger sensory nerves?
Distortion of stereocilia due to movement of endolymph causes physically gated K channels to open leading to deplarization and release of transmitters that trigger sensory neurons (cochlear nerve)
How are different pitches perceived?
Frequency of incoming sound waves travels along length of basilar membrane, producing a maximal amplitude at the place on the membrane where vibratory resonance occurs (membrane stiffness + hair cell length)
How do inner hair cells differ from outer hair cells?
Inner hair cells respond to specific frequencies of sound and transmit information to the brain - fewer, but the primary cell innervated by cochlear nerve axons
Outer hair cells serve as mechanical amplifiers
What is a major mechanism for age-related hearing loss? Why is it primarily high frequency hearing that is lost?
Destruction of outer hair cells from loud noises - lack of amplification and sharpening of sound
Hair cells at the base of cochlea resonate with higher frequencies, and these are the cells that are first lost
Differentiate between the dorsal and ventral auditory path to the brain.
DORSAL registers the quality of sound (What is it?)
Dorsal cochlear nucleus of medulla –> lateral leminscus –> inferior colliculus –> medial geniculate –> primary auditory cortex (temporal lobe)
VENTRAL localizes the sound (Where is it?)
Ventral cochlear nucleus (medulla) –> superior olivary complex (medulla) –> lateral leminscus –> inferior colliculus –> medial geniculate –> primary auditory cortex (temporal lobe)
What is the main function of the inferior colliculus?
Receives auditory and somatosensory input so that the head/body can be oriented for sound localization
What is the difference between the ventral and dorsal stream for auditory association?
Ventral stream is for comprehension, through Wernicke’s area to integrate aspects of language
Dorsal stream is involved with sensory-motor integration for vocal articulation, through Broca’s area
What is auditory selective attention?
Efferent olivocochlear neurons from superior olive terminate on outer and inner hair cells to regulate their sensitivity to sound - gets rid of background noice
What are the two types of deafness?
Conductive deafness - due to mechanical damage
Sensorineural deafness - due to nerve/cochlea damage
What is subjective tinnitus?
Phantom auditory perception - abnormal neural activity, often as a result of hearing loss with an attempt to compensate through conditioning the dorsal cochlear nucleus
What is somatic tinnitus?
Form of subjective tinnitus, usually triggered by somatosensory stressors via trigeminal/dorsal ganglia
What are the structural components of the vestibular system?
Semicircular ducts within the semicircular canals + the saccule and utricle within the vestibule
Where does endolymph drain? What about perilymph?
Endolymph, secreted by cochlear ducts drains into the dural sinuses via endolymphatic duct
Perilymph, secreted by the periosteum and drains into CSF via the perilymphatic duct
What is Meniere’s disease?
Transient vertigo/dizziness due to excess endolymph/pressure affecting receptor functions
Describe the orientation of the 3 semicircular ducts.
Anterior, horizontal, and posterior - oriented to detect movement in 3 planes of space
What is the crista (ampullaris)?
A receptor in the ampulla (base) of each semicircular canal containing epithelium of receptor cells (hair cells) that contain sterocilia which project into the surrounding cupula
How does the macula detect movement information?
Macule of saccule and utricle are oriented in vertical and horizontal planes respectively, containing hair cells that optimally respond to acceleration in direction of alignment