Lesson 7: Hearing Flashcards
What is the difference between motor activity and motor control?
Motor activity: presence of movement - via corticospinal & corticobulbar tract
Motor control: quality of motor activity - via cerebellum & basal nuclei
How is intensity of sound measured? What can the human ear detect, and where is most language?
In decibels. 0dB-140dB, 60dB
How many decibels is painful? How many causes damage with time?
140dB is painful, and 90 causes damage with time
How is frequency of sound measured (pitch)?
Hertz
What are the two structures of the outer ear?
The pinna and the external auditory meatus
What is the purpose of the Eustachian tube? Where does it attach to?
From the middle ear to the nasopharynx. It equalizes middle-ear pressure with atmospheric pressure
What are the 3 ossicles?
Malleus, incus and stapes
What two muscles control the ossicles? What is their role?
The tensor tympani and stapedius. They protect the auditory mechanism from damage through the attenuation reflex
What is the bony labyrinth composed of?
Cochlea, vestibule and the semicircular canals.
What is the membranous labyrinth composed of?
The cochlear duct, the semicircular ducts, the saccule and the utricle - which are in the vestibule
How does the ear compensate for the discrepancy in size and consistency between the tympanic membrane (fluid) and the oval window (aid). What is the production of this restriction?
The stiffness of the ossicles. It results in restricted motion speed, and thus species can only hear frequencies within the ossicular motion limitations
What apparatus are responsible for equilibrium detection ?
The saccule, utricle, and the semicircular ducts
What is the primary receptor of hearing? Where is it located?
The organ of Corti, which is 3 rows of outer hairs and one row of inner hair cells, with stereocilia at their tips.
In the scala media, along the basilar membrane (bottom)
What is the difference in projection of outer hair cells vs inner hair cells?
IHCs: innervate the cochlear nerve
OHCs: project to the olivocochlear bundle
What is the structure of the cochlea? What are these parts filled with?
Scala vestibuli, cochlear duct (scala media), and scala tympani.
Vestibuli and tympani join in the back via the helicotrema, and are both filled with perilymph. The scala media is filled with endolymph
What is the primary receptor of equilibrium, and where are these located? What gel is it in?
The maculae (in the saccule and utricle), in the otolithic membrane The cristae ampullaris (in the tips of the semicircular ducts), in the cupula among endolymph
What is the site of maximum amplitude of high frequencies vs low frequencies?
Lower frequencies: near the helicotrema
Higher frequencies: near the oval window
How do sound waves in the tectorial membrane result in activation of the nerve?
The movement bends the ends of the cilia, which increases the cilia’s permeability to potassium ions - this depolarization results in the release of neurotransmitters to the cochlear nerve
What is the role of the spinal ganglia? Where are they located, and what are the types?
In the modiolus of the cochlea, they receive input from hair cells, and thus form the acoustic branch of the vestibulocochlear nerve. Type I responds to a select range of hair cells, whereas Type II synapses with 10+ hair cells
What cranial nerve is responsible for hearing? What number is it?
The vestibulocochlear nerve - CN VIII
How does the tympanic membrane work?
Vibration of the tympanic membrane, as received from the external auditory meatus, is converted to mechanical energy to the ossicles
How do the ossicles work?
They receive the mechanical energy from the tympanic membrane, which then is sent to the cochlea, where it becomes hydraulic energy
Where does hearing secondly synapse?
In the cochlear nuclear complex in the pons
What is the nature of the cochlear nuclear complex? Both in structure and in function
Dorsal and ventral cochlear nuclei
Low frequencies = surface of the cochlear nucleus
High frequencies = deeper in the nucleus
How does hearing ascend from the cochlear nuclear complex?
Trapezoid body - either crosses here or doesn’t
Then, either goes to superior olivary nucleus, or directly to lateral lemniscus
Then to the inf colliculus
What are the features of the superior olivary nucleus?
In the pons
Has binaural cells (lateral and medial superior olive)
This allows it to calculate differences in time and intensity