instrumentation 2/22/00. magnetic resonance imaging magnetic field through tissue pass radio waves...
TRANSCRIPT
Instrumentation
2/22/00
Magnetic Resonance Imaging
• Magnetic field through tissue
• Pass radio waves through tissue
– Protons absorb some energy & change direction
– They then move back to the original position when the
charge is shut off
• Release absorbed energy to create an image
• Tissues have different densities (absorb different amounts of
protons)
MRI
• Purpose:
• Acquiring images inside body- no radiation
• Detailed information about anatomical structures
• Speech:
– Precise measurements of the entire vocal tract without
radiation effects
– Well defined pharyngeal cavity- measurements
– Central control and the actual speech events that result
Electromyography (EMG)
• Purpose: Record the action potential of muscles
during contraction
• Investigation in pathology of muscles
• Speech:
– Provide information about speech control mechanisms
& speech gestures in natural units
– Central nervous system control of muscles
Auditory System
Hearing: Mechanoreceptors
• Hearing = sensitivity to mechanical vibrations transmitted through air.
• Mechanoreceptors= mechanical sensitivity; monitor mechanical stimuli such as pressure, position & movement.
– Hair cell= sensory receptor for audition & balance– Site of mechanoelectric transduction
Ear: Three Parts
• Outer Ear– Visible externally– Captures vibrations in the air & funnels them into the
ear canal (External Auditory Meatus)
• Middle Ear– Starts at the ear drum (Tympanic Membrane)– Contains ossicles (Stapes, Incus, Malleus)
• Inner Ear– Sensory end organ of hearing (Cochlea)– Fluid filled
Outer ear
Pinna
Outer Ear Middle Ear
Eustachian Tube
External Auditory Meatus
Inner Ear
Auditory Nerve
Ear Anatomy
Electrical Events
• Bending hair cells are responsible for the generation of neural impulses– Transmits signal to brain
– Signals can be recorded
• Otoacoustic Emission– Faint sounds produced by the cochlea as it
responds to acoustic stimuli
– Emissions recorded in the human ear
– Miniature probe placed in EAM
Otoacoustic Emission
• Two types of emission:– 1. Spontaneous otoacoustic emission-
• weak tonal signals that occur naturally, without acoustic stimuli
– 2. Evoked otoacoustic emission-• occur in almost everyone; elicited with low to
moderate level test sounds
• Clinical application
Otoacoustic Emission
• Reflect the biomechanical activity of the outer hair cells– outer hair cells are susceptible to: 1) Disease, 2)
Damage due to loud sounds,
• Provides a means to test hearing in infants & subjects who cannot complete behavioral tests of auditory function
• Otoacoustic emissions are absent in some disorders of the cochlea
Energy & Information Flow in the Auditory System
• Both energy & information have two paths of travel
• Acoustic stimulation in the environment = flow of energy from the outer ear to inner ear
• Reverse flow= otoacoustic emission– Allows the brainstem to influence actions in the inner
ear
Inner Hair cells
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AuditoryCortex
Middle ear
Nerve Fibers
Brain Stem Center
Outer ear
Inner Ear
Flow of Information & Energy in the Auditory System
Auditory Function: Comparative
• Frequency range– Humans: 20-20,000 Hz
• Greatest sensitivity at 1000 Hz
– Dogs: 20-60,000 Hz
– Elephants: better low frequency range• as low as 12 Hz
• Auditory frequencies most important to humans– 100 Hz-5000Hz (Speech frequencies)
Life Course Considerations
• Auditory system development:– 5 1/2 months after conception– Cochlea is the last structure to reach maturity – Auditory function in the fetus (Heper & Shahidullah,
1994):• Fetuses: 19-35 weeks gestation
• Pure tones (100, 250, 500, 1000, 5000) presented with speaker
• Fetal response: ultrasound of movement
• 19 weeks- Response to 500 Hz
• With maturation: response spread to low frequencies (27 weeks) than high (33-35 weeks)
Audition: Age
• Hearing high frequencies: Decline after the age of 20 years
• 30 Years: Hearing in men declines 2x as rapidly as women’s
• Hearing low frequencies: Declines in the 7th decade
• Older women have more sensitive hearing than older men
Risk factors: Hearing Loss
• Industrial noise
• Aging
• Combination of aging and noise exposure
• Diet
• Medications (ototoxic drugs)– Aspirin– Some antibiotics (Streptomyocin)– Alcohol
• Cardiovascular disease