Exam 2 Flashcards
• What are the three parts of the ear?
o External, middle, and inner ear
What is the function of the external ear?
o Air waves generate vibrations in tympanic membrane
• What is the function of the middle ear?
o Ossicles (malleus, incus, stapes) transmit sound to inner ear
• What is the function of the inner ear?
o Vibration conducted through fluid into cochlea
• What are the regions of the external ear?
o Auricle, helix and antihelix, tragus and antitragus, concha and lobule
• What structures are found in the auricle?
o Elastic cartilage covered with skin; sebaceous glands associated with hairs
• What are ceruminous glands?
o Modified apocrine glands that secrete cerumen; protects ear canal against physical damage and microbial invasion
• What is ear wax?
o Mixture of cerumen, sebaceous gland secretion and desquamated meatal cells; found in outer 1/3 of ear canal
• What part of the outer ear is easily traumatized?
o Inner 2/3, due to thin skin over osseous canal
• What is the sensory innervation of the external ear and external acoustic meatus? Middle ear?
o Greater auricular; lesser occipital; auriculotemporal, V3; facial; vagus o Glossopharyngeal (IX)
• What does the tympanic cavity contain?
o The ossciles and their muscles
• What does the auditory (Eustachian) tube do?
o Connects tympanic cavity to nasopharynx
o Tubal cartilage: opened by levator/tensor palate. Salpingopharyngeus
• What do the ossicles do?
o Amplify vibration from wide tympanic membrane through narrow base of stapes
• What are the ossicles and their roles?
o Malleus: vibrated by tympanic membrane
o Incus: transmits from malleus to stapes
o Stapes: transmits vibrations through oval window to cochlea
• What are the muscles that dampen ossicle mov’t? Innervation?
o Tensor tympani: dampens extreme low frequency vibrations; innervated by V3
o Stapedius: dampens extreme vibrations of stapes; innervated by VII
• What is the physical route of the chorda tympani?
o Passes b/w tympanic membrane and malleus (possibly impacted by otitis media)
o Branches from facial nerve in tympanic cavity, exits and joins V3 as it approaches the oral cavity
• What type of neurons in the chorda tympani?
o Contains both sensory and autonomic neuronal axons
o Sensory neurons mediate taste from anterior 2/3 of tongue
o Parasympathetics to submandibular and sublingual salivary glands
• Where do the post-and preganglionic axons of chorda tympani come from?
o Pre: from superior salivary nucleus
o Post: from submandibular ganglion
• What is the central feature of the tympanic membrane?
o Umbo: central depression created by tension of the malleus
• What are the visible landmarks in an auriscopic view?
o Malleus (lateral process, handle, umbo); incus; stapes; cone of light; flaccid and tense parts of TM
• What is otitis media?
o Infection/inflammation of the middle ear; fluid buildup blocks middle ear, air is absorbed, negative pressure pulls TM inward (or viral/bacterial-laden fluid upward from pharynx into tympanic cavity)
• How can otitis media be treated? What can happen if untreated?
o Fluid drained by tube inserted in TM
o Infection can get through TM or spread through tegmen tympani; meningitis or brain abscess
• What is cholesteatoma?
o Skin cyst; skin from ear canal fills with cysts and migrates through a hole in TM; grows out of control, damages middle ear and mastoid
• What is the cochlea?
o Part of inner ear; fluid-filled spirally formed bony canal; contains the membranous cochlear duct that contains the hearing receptors
• What does the term cochlea technically refer to?
o The helical bony canal (as distinguished from cochlear duct)
• What are the parts of the cochlea?
o Cochlear duct (scala media); separated from other spaces by the vestibular and basilar membranes; contains endolymph (secreted by stria vascularis)
o Scala vestibule
o Scala tympani (both scala are continuous, meet at the apex (helicotrema) and contain perilymph)
• What are the parts of the cochlear duct?
o Membranous tube that encloses organ of corti; contains endolymph, surrounded by perilymph; oval window; round window
• What are the electrolyte concentrations in perilymph and endolymph?
o Perilymph: high Na+
o Endolymph: high K+
• What happens at the oval window?
o Base of stapes triggers fluid vibrations in perilymph
• What happens at the round window?
o Absorbs outward displacements of fluid vibrations
• What are the sound transductions of the external, middle, and inner ears?
o External: air waves
o Middle: ossicle vibrations
o Inner: fluid vibrations in cochlea
• What is the organ of corti?
o covered in hair cells (I and O) with many nerve receptors; covered by the tectorial membrane
• What type of cells are in the organ of corti?
o Inner and outer layers of non-neural receptor cells (“hair cells”) embedded among support cells on the basilar membrane
o Cells have stereocilia (actually, microvilli) that contact the overlying tectorial membrane
• What do hair cells do?
o Activate sensory neurons of the cochlear (auditory) nerve
• What do sound waves do as they travel through the cochlea?
o Produce vertical oscillations in the basilar membrane against the tectorial membrane, whose shear forces bend the receptor stereocilia
• What happens when stereocilia are bent?
o Distortions trigger depolarization (K+ influx) followed by release of transmitter onto sensory neurons
• What happens in the cochlear nerve when hair cells are bent?
o Sensory neurons respond and form the cochlear portion of CN VIII; spiral ganglion contains cells bodies of sensory neurons
• What is tonotopic representation of sound?
o Frequency (pitch) of incoming sound is initially coded by difference in basilar membrane stiffness and width from base to apex
• Even though the sound wave travels along the full length of the basilar membrane, what happens?
o There are only certain locations where a complex sound wave has a maximal amplitude; where the membrane has the physical properties to resonate with the vibration of the certain pitch
• What is resonance frequency?
o A specific frequency of sound produces an envelope of pressure waves in the basilar membrane, with a maximum amplitude at a unique point
• What cells does the organ of corti use to transduce vibrations into neural auditory information?
o Inner and outer hair cells
• What are inner hair cells?
o Primary sensory cells transmitting sound info to the brain; respond to basilar membrane mov’ts at specific frequencies
• What innervated the inner hair cells?
o 95% of sensory neuron axons in cochlear nerve (other 5% for outer hair cells)
o Cochlear nerve projects inner cell activity to cochlear nuclei in the medulla
• What is the main purpose of outer hair cells?
o Mostly don’t activate sensory neurons; act as mechanical amplifiers that enhance weak auditory signals transduced by the IHCs
• What happens in OHCs when cilia are bent?
o Produces electromotile response in which the cell contracts and then elongates to its original length with each deflection of the basilar membrane
• What happens as OHCs elongate against the tectorial membrane?
o The recoil force pushes in the basilar membrane amplifying its oscillation; outer cells responses are frequency specific
• How does OHC response produce a positive feedback?
o Enhances the amplitude of basilar membrane oscillation and IHC responses (like pushing someone on a swing at the right frequency)
• What can happen with overstimulation of the OHCs?
o Produce a vibration that returns through the oval window and ossicles and projects out through the tympanic membrane as sound (oto-acoustic emissions, OAEs, like a loudspeaker)
• What is the result of too much loud noise?
o Destroys mostly outer hair cells leading to hearing loss (dead zones in the cochlea)
• What is the form of the sound wave without the action of OHCs?
o Dull and rounded peak, passively stimulating many adjacent frequencies simultaneously
• What is accomplished in the form of the sound only with OHCs?
o Sharpening of the peak; increases the ability to distinguish b/w frequencies that are close together
• What 2 auditory pathways arise from the medullary cochlear nuclei?
o dorsal and ventral (goes to superior olive)cochlear nuclei; both project up lateral lemniscus -> IC -> medial geniculate -> primary auditory cortex in temporal lobe
• What is the dorsal cochlear nucleus?
o Quality of sound: analyzes tiny frequency differences among “bet,” “bat,” and “debt”
• What is the ventral cochlear nucleus?
o Localization: disparity in time and intensity b/w R and L sounds localizes object in space
• What happens when sound approaches from an angle?
o Reaches each ear at different time and intensite/amplitude/loudenss;
• How are high and low frequencies localized when sound comes at an angle?
o Time difference localizes low frequencies; intensity differences localize high frequencies
• How does the IC get auditory and somatosensory input?
o Auditory: from cochlear nuclei and superior olive
o Somatosensory: orient:ation of head and other body regions for sound localization
• What does the medial geniculate body of thalamus do?
o Projects sound to cortex tonotopically
• Where is the primary auditory cortex and what does it do?
o Superior temporal lobe; tonotopic organization of frequencies is synthesized into sound forms
• What is the ventral stream of the auditory association cortex?
o For speech comprehension (voice, language, or any symbolic system), flows to temporal lobe; largely bilateral
o Includes Wernicke’s area, angular gyrus and other association cortices
• What is Wernicke’s area?
o Integrates auditory, visual and somatosensory aspects of language; for understanding speech, writing, or any symbolic system
• What is Wernicke’s are connected to?
o Speech motor area in premotor cortex of frontal lobe (Broca’s area) via the arcuate fasciculus (Ex: can still read jumbled words if first are last letter are correct)
• What is the dorsal stream of the auditory association cortex?
o Sensory-motor integration of vocal articulation that projects to the parietal-temporal junction of frontal lobe, esp Broca’s area; left dominant
o Localization of sound in body schema
• What is the old view how music is processed?
o Lateralization of auditory functions on the right and left sides of cortex; rhythm on left, melody on right
• What is new view of how music is processed?
o Temporal, parietal and motor cortices all involved bilaterally in higher levels of auditory activity
• What sides of brain associated with speech, rhythm and melody?
o Uses both sides, but asymmetrically
• What sides of brain for speaking and singing?
o Both sides, but singing is more pronounced in right auditory region of temporal lobe; motor areas related to vocal production
• How does music affect emotions?
o Music activity in auditory cortex can modulate activity in limbic regions of emotions, like amygdala, cingulate cortex, orbitofrontal cortex; other areas affected include hippocampus and insula
• What is auditory selective attention?
o Efferent olivocochlear neurons from the superior olive terminate on IHC/OHCs to regulate their sensitivity and electromotility responses to sounds
• How do olivocochlear efferents indirectly inhibit inner cell responses?
o Inhibit outer cell responses to basilar membrane waves; especially to low level sounds
• What happens in a quiet situation?
o Efferent activity inhibits outer cell responses to low level sound detection
• What happens when there is background noise?
o Efferent activity improves signal detection and discrimination by suppressing the low level background noise responses -> inhibition “unmasks” the louder, primary sound to be heard (convo in noisy restaurant)
• What is efferent control stimulated by?
o Sensory input from cochlear nuclei; auditory cortex; reticular formation (locus ceruleus- NE), to focus attention on specific stimuli
• What are the 2 types of deafness?
o Conductive: due to damage of tympanic membrane, ossicles, etc (eg otitis media)
o Sensorineural: damage of cochlea or cochlear portion of CN VIII (eg Meniere’s dx, toxins, acoustic neuroma, diabetic neuropathy)
• What are the 2 types of tinnitus?
o Subjective and somatic
• What is subjective tinnitus?
o Sensation of sound w/o external stimulation- a phantom auditory perception, eg cicadas, winds, grinding steel, escaping steam
• What is the mechanism of subjective tinnitus?
o Abnormal neural activity in brain stem auditory pathways; DCN is a possible site of conditioning and plasticity that can produce long term increases in spontaneous activity and changes in sensitivity to sound
• How can subjective tinnitus be treated?
o Deconditioning via methods such as white noise
• How is the phantom sound created in subjective tinnitus?
o Changes in primary auditory cortex
• What are possible causes of subjective tinnitus?
o Disease processes (TMJ, noise-induced OHC damage)
o Neurological: whiplash, VIII tumors, MS
o Infections: otitis media, meningitis
o Side effects of drugs (aspirin)
• What is somatic tinnitus?
o A form of subjective tinnitus, usually triggered by synergistic effects of 2 or more causes, including somatosensory stressors
• What is the mechanism of somatic tinnitus?
o Trigeminal and dorsal root ganglia relay afferent somatosensory info from periphery to secondary sensory neurons in brainstem, specifically spinal trigeminal nucleus and dorsal column nuclei, respectively. Each structure sends excitatory projections to cochlear nucleus and can thus enhance tinnitus (hence cnxn of tinnitus w/ whiplash and TMJ)
• Where does cochlear nucleus project to and bias sensation?
o Somatic efferent systems (hearing a high pitched sound alters sense of texture)
• Where is the vestibular system located?
o Within the petrous portion of the temporal bone
• What is the vestibular system?
o Bony labyrinth, complex system of canals, subdivided into vestibule and semicircular canals
• What is the membranous labyrinth?
o membranous tube with receptors for head mov’t/position; divided into semicircular ducts (in semicircular canals) and Saccule & Utricle (in vestibule)
• What is endolymph?
o Secreted by cochlear duct; drains into dural sinuses via endolymphatic duct
• What is perilymph?
o Secreted by periosteum; drains into CSF via perilymphatic duct
• What is Meniere’s disease?
o Transient vertigo and dizziness, nausea, vomiting and abnormal saccadic eye mov’ts (nystagmus)
o Excess endolymph secretion and fluid pressure affect receptor function
• What are the semicircular ducts/canals?
o Anterior (superior), horizontal and posterior ducts; mutually perpendicular; rotation of ducts with head mov’t causes flow of endolymph
• What is the crista (ampullaris)
o Receptor in the ampulla of each semicircular canal; covered in hair cells, supporting cells, gelatinous mass (cupola), sense angular acceleration
• What are the features of the hair cells of the crista?
o Have a single kinocilium and several stereocilia which project into the gelatinous mass (cupola)
• What distorts the hair cells of the crista?
o Relative motion of endolymph during head rotation; most sensitive to angular acceleration (0.1 degree/sec)
