Download Lecture 9 - Fredonia.edu

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
Ear Anatomy
Inner Ear
External Auditory Meatus
Pinna
Auditory
Nerve
Outer Ear Middle Ear
Eustachian Tube
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
AuditoryCortex
Flow of Information & Energy
in the Auditory System
Inner
Hair cells
Inner Ear
Middle ear
Outer ear
Acoustic Reflex
Nerve Fibers
Efferent System
Brain Stem Center
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