11 - NS Ear and Audition Flashcards
What are the sensory nerves involved in hearing
CN VIII (vestibulocochlear): hearing and balance
CN X (vagus): sensory to auditory canal
What are the motor nerves involved in hearing
CN V (trigeminal): tensor tympani muscle of middle ear
CN VII (facial): stapedius muscle of middle ear
From where are the components of the ear carved from
the petrous portion of the temporal bone
What are the three principle regions of the ear
external, middle, inner
External Ear - glands
ceruminous glands secrete wax that traps foreign bodies and repels insects
describe how the skin of the external auditory canal is attached
2/3 = cartilage (contains fat)
1/3 = bone
- firmly attached to the periosteum of the bone
What are the parts of the middle ear
ossicles (in middle ear interior)
tympanic membrane cone (eardrum)
connective tissue covered by skin externally, mucosa internally
What is the function of the ossicles
mechanically relay vibrations from the tympanic membrane to the oval window of the inner ear
where are the ossicles found
suspended by ligaments and connected by synovial joints
what are the parts of the ossicles
malleus (hammer)
incus (anvil)
stapes (saddle)
which muscles help to dampen sounds
tensor tympani (dampens ossicle movement when chewing - CN V)
stapedius (dampens ossicle movement during loud sounds - CN VII)
muscles tense (constrict) so tympanic membrane can’t vibrate as much
What ensures that the tympanic membrane vibrates effectively
pressure equilibration
Tympanic membrane should be able to move back and forth
What would happen if there was high pressure in the middle ear
tympanic membrane would be bulging out
can’t vibrate as effectively as sounds come in
deaf
What tubes in the middle ear connect to the great outdoors
external auditory canal
auditory tube (from pharanx)
Auditory tube
runs through pharanx
surrounded by skeletal muscle
changes shape when you swallow
- swallowing allows pressure to be equilibrated
What is the mastoid process
bored out bone at the back of the ear
sponge-like covered by mucous membrane
any part of skull that is not needing absolute strength is hollowed out and put air spaces in
air spaces communicate to great outdoors so head doesn’t explode on the plane
makes skull lighter
How do middle ear infections occur
respiratory tract infections ascend that auditory tube to the middle ear
What could happen as a result of infections in the middle ear
- rupture of tympanic membrane and drainage of fluid through external ear (collagen build up)
- infection spread into mastoid air cells leading to mastoiditis (increase pressure in bone)
- erosion of temporal bone above middle ear leading to meningitis
What is the inner ear made of
series of channels carved out of the temporal bone
- cochlea
- semicircular canals
How is hearing transmitted to the inner ear
stapes acts on the oval (vestibular) window to transmit vibrations to the organ of hearing (spial organ) contained within the cochlea which resembles a snail shell
How are sound waves transmitted
- sounds waves collected by the auricle and external auditory meatus and directed to the eardrum
- sound waves vibrate the tympanic membrane
- transmission of vibrations across middle ear by the ossicles
- stapes transfers vibrations to the oval (vestibular) window
- vibrations transferred to perilymph of scala vestibuli
- vibrations transfer to scala tympani and eventually cochlear (round) window
- pressure waves in scala vestibuli and tympani set up waves in the endolymph of the cochlear duct
- pressure waves in the endolymph cause the basilar membrane to vibrate, moving hair cells (receptors) of the spiral organ -> nerve impulses generated in the cochlear nerve (CN VIII)
What does the spinal organ do
Converts vibrations into nerve impulses
What does the spinal organ consist of
hair cells (stereo cilia)
supporting cells
How are the first order neurons stimulated
stimulation of stereo cilia on hair cells causes NT release, stimulating first order neurons of the cochlear nerve (CN VIII)
How does frequency detection work
The length of the basilar membrane fibres acts to tune the different parts of the cochlea to different frequencies
Describe the auditory pathway to the brain
- auditory info travels bilaterally after entering the brainstem
- Cochlear nuclei (CN VIII): info decussates beyond this point - medulla oblongata
- Superior olivary nuclei: stereo sound (localization) - pons
- Lateral lemniscus: white matter tract (part of RAS)
- Inferior colliculus: acoustic startle reflex - dorsal midbrain
- Thalamus: selective attention, filters out self-generated sounds (voice, heart, chewing) - medial geniculate nucleus
- Primary auditory cortex: conscious perception of sound - temporal lobe
What are the types of hearing loss
conduction deafness
sensory deafness
Conduction deafness (where, what, causes)
- middle and outer ear
- reduction in sound amplitude
- hear sound of blood rushing in carotid arteries
- Causes: ear wax, rupture of tympanic membrane, damage to ossicles (arthritis)
Sensory Deafness (where, what, causes)
- inner ear, CN VIII
- high tones affected (rumbling)
- tinnitus (continuous hiss)
- Causes: infarct, trauma, prolonged noise, drug toxicity, tumours, Meniere’s disease - high endolymph pressure)
What are the parts of the vestibular apparatus
Consists of receptor organs for equilibrium
- utricle (bag)
- saccule (small sac)
- semicircular ducts (x3)
What are the utricle and saccule
otolithic organs that contain an inner region called the macula
What is the semi-circular duct
in a linear plane
- the anterior and posterior ducts are on the vertical plane
- the lateral duct is on the horizontal plane
- all three ducts lie at right angles to one another
What is the maculae
Contains hair cells and supporting cells and is part of the utricle and saccule
- detects linear acceleration/deceleration
What is a hair bundle
hair cells/sensory receptors contain a hair bundle
What do the supporting cells do
surround the hair cells and produce the otolithic membrane and otoliths (calcium carbonate crystals)
How are the utricle and saccule positioned
perpendicular to each other within the inner aspect of the vestibular apparatus
What position does the utricle have when head is upright
what do the hair cells respond to
horizantal
linear acceleration and deceleration and when the head tilts forward or backward
What position does the saccule have when the head is upright
what do the hair cells respond to
vertical
linear acceleration and deceleration in the vertical direction
What is an ampulla
dilated region of the ducts that contain a crista (folds), each consisting of hair cells and supporting cells
What is the crista
covered in gelatinous substance (the capula) that moves and bends the hair cells when the surrounding endolymph moves as the head rotates
What does bending hair bundles do
in one direction, depolarizes hair cells
in opposite direction, hyperpolarizes
How does vestibular information travel
from the cortex and is integrated in the brainstem
hair bundles –> vestibulocochlear nerve (CN VIII) –> vestibular nuclei (medula/pons) –> thalamus –> sensory cortex (verstibular area in the parietal lobe)
How is vestibular information integrated into the brainstem
- cranial nerves for eye movement (CN III, IV, VI) - scanning motions
- Accessory nerve (XI) for head/neck control - sternocleidomastoid + trapezius
- Vestibulospinal tract for skeletal muscle control - indirect motor pathway, posture and balance
- Cerebellum for limb and axial positional control - dedicated pipeline to coordinate movements
