Chapter 15 Ear and Hearing Flashcards
sound
a mental experience or a variation in air pressure generated by an action
physical and perceptual properties
mental experience of sound believed to be generated by processes of the nervous system elicited by the physical stimulus of rhythmic air pressure variation
frequency
the higher the frequency, the shorter the wavelength and the lower the frequency, the longer the wavelength; associated with pitch (higher frequency is a higher pitch)
amplitude
the height of a wave; associated with volume
tone
higher frequency is higher tone; lower frequency is lower tone
loudness
associated with the amplitude or magnitude of the pressure variation, with high amplitude variations experienced as louder than low amplitude variations
human hearing range (frequency)
20 Hz - 20,000 Hz
speed of sound
1,100 ft/second, 335 m/s, 750 mph
timbre
a quality used to describe sound experience, related to the complexity of the sound waveform (i.e. musical instruments)
Joseph Fourier (1768-1830)
French mathematician who studied the mathematical property of vibration using sine waves
Fourier analysis
representing any complex waveform describing a vibration as a sum of sine waves having various frequencies and amplitudes
cochlea
a wave propagates through the interior of the cochlea (located in the inner ear), which sets the fluid into vibration
basilar membrane
varies in thickness, being thickest at the end nearest the oval window and thinnest at the other end, this causes different regions of the basilar membrane to be set into vibration by different frequencies (resonance) - thicker end vibrates resonantly with higher frequencies and the thinner end vibrates with lower frequencies; Fourier analysis of sound in the basilar membrane: creates a spatial representation of the component frequencies of sound entering the ear
hair cells
little cells along the length of the basilar membrane; characterized by a bundle of hairs or cilia attached to one end; extremely sensitive; only about 3500 inner hair cells; vibrate as the basilar membrane vibrates causing cilia to move through the surrounding fluid; bending of the hairs initiates a signal from the hair cell to the nerves carrying signal information to the brain (hairs are interconnected by tiny molecular cables which are couple to positive ion channels, so when hairs bend, cables tug on channels and cause them to open, so K+ ions flow in the hairs, causing depolarization, so voltage-gated Ca++ channels open releasing Ca++ ions into the cell resulting in neurotransmitter molecules being released into the synaptic cleft); at the opposite end of the cell from the bundle of cilia, hair cells form chemical synapses with fibers of an auditory nerve called cranial nerve
perception of one’s own voice
air pressure variations enter one’s own external ear canal; much of the vibrational energy sensed when we hear ourselves speak enters the auditory system via internal vibration of the skull (different than the same voice heard by another listener - rhythm and temp are the same but Fourier frequency composition is different)
auditory nerve
bundle of nerve fibers that carry hearing information between the cochlea and the brain
auditory neural pathways into the brain
neurotransmitter is released from the hair cell, and a signal is generated in the postsynaptic dendrite of cranial nerve 8 (cell bodies for these nerves are located nearby in a cluster called the spiral ganglion, one cluster for each ear), then bipolar neurons (with a single myelinated dendrite receiving the signal from the hair cell and a myleinated axon) carry the signal into the brainstem, in the brainstem’s medulla
axons of auditory nerve synapse with cells in a region called the cochlear nucleus, neurons of the cochlear nucleus send axons to cells in regions of the pons called the superior olive and lateral lemniscus
various brainstem auditory centers all send axons into the inferior colliculus in the midbrain, inferior colliculus projects to the nearby medical geniculate nucleus (MGN) of the thalamus, then MGN sends axons into the primary auditory cortex
primary auditory cortex (A1)
a region in the temporal lobe of the cerebral cortex where axons are sent to by the MGN
hearing loss due to infection
infections of the inner ear cause irreversible damage to hair cells
genetic hearing loss
genetic anomalies result in malfunctions of the cochlea (i.e. a mutation in the gene coding for a particular channel in the cochlea, connexin 26, produces abnormal ion balances within the cochlea which means hair cells cannot function); individuals may be born with impaired hearing or even complete deafness
noise-induced hearing loss
acoustic trauma ( brief/chronic exposure to loud sounds or chronic exposure to sounds that are moderately loud) can result in permanent hearing loss; intense overstimulation of hair cells permanently damage the hair cell, which cannot be repaired or replaced
vestibular system
the sensory system that provides the leading contribution about the sense of balance and spatial orientation for the purpose of coordinating movement with balance; functioning of our vestibular system is out of our conscious awareness except when something disrupts it
vertigo
a condition in which one feels dizzy or in motion even while sitting or standing still, usually associated with something unusual happening in the vestibular system
semicircular canals
three orthogonal canals that gather complete information as to how the head is oriented and accelerating in the three dimensions of space
utricle, saccule
the two otolith organs located in the vertebrate inner ear; contain receptor cells that detect the movement of fluid in the attached semicircular canals
otolith
ear stones that are suspended in the fluid above the hair cells; inertia of these little stones as the body accelerates contributes to bending the hairs of the sensory cells (which generates and amplifies the sensory signals that allow us to maintain balance as we move through the world)
