The document summarizes the physiology of hearing. It discusses how sound is transmitted through the ear as a transducer, converting sound energy to mechanical and then electrical energy. It describes the external, middle, and inner ear. The external ear collects and concentrates sound. The middle ear acts as an impedance matcher, increasing the intensity of vibrations through a lever system before transmitting to the inner ear. The inner ear converts vibrations to electrical signals via hair cells and sends signals through the auditory nerve and central pathways to the brain for processing.
This presentation explains the working of the ear... It is best for medical students.. It includes all the key points necessary for an exam too... So this presentation can also be used as a notes for your exams...
Physiology of Hearing by Dr. Sudin Kayastha Sudin Kayastha
Contains: fundamentals of sound, role of external ear in hearing, role of middle ear in hearing, role of inner ear in hearing, central auditory pathway
the ppt includes the anatomy of larynx, the physiology of sound production and pathology of vocal cords explaining the myoelastic aerodynamic theory and bernoulli effect in phonation
This presentation explains the working of the ear... It is best for medical students.. It includes all the key points necessary for an exam too... So this presentation can also be used as a notes for your exams...
Physiology of Hearing by Dr. Sudin Kayastha Sudin Kayastha
Contains: fundamentals of sound, role of external ear in hearing, role of middle ear in hearing, role of inner ear in hearing, central auditory pathway
the ppt includes the anatomy of larynx, the physiology of sound production and pathology of vocal cords explaining the myoelastic aerodynamic theory and bernoulli effect in phonation
Physiology of ear.
Basic definition related to sound -hearing,sound,sound wave.
mechanism of hearing
mechanical conduction of sound
transfer action of middle ear
impedence
areal ratio/ hydraulic lever
lever ratio of ossicles
catenary lever
transduction of mechanical energy
travelling wave theory of Bekesy
sound propagation in cochlea
electrical conduction of sound
central auditory pathway
acoustic reflex
INTRODUCTION:
The relationship between ontogeny and phylogeny is a recurring theme in developmental, systematic, and evolutionary biology (e.g., Gould, 1977; Alberch et al., 1979; Fink, 1982; Humphries, 1988)
All growth is the result of cell division of pre- existing cells, through a process known as mitosis. The cell and nucleus then subdivided into 2 identical daughter cells. one of the earliest organizational developments in the embryo is the differentiation of cells into 3 super- imposed, cellular plates called germ layers. These germ layers are known as ectoderm, mesoderm and endoderm. Ectoderm is generally responsible for development of the outer skin layers but also gives rise to the nervous system and the sense organs.
The outer and inner portions of the ear develop from ectodermal tissue, while the M.E ossicles and the bone surrounding the inner ear originate from mesodermal tissue. The ear begins its development during the early life of the embryo. The embryonic disk is split by a primitive streak at about 25 hours, which leads the way for development of the ectodermal lined primitive groove
and primitive fold. The primitive groove deepens into a primitive pit, which in turn becomes the neural groove and neural fold. The ectodermal lined neural folds come together to close off the neural groove, which is now known as the neural tube. It is during the stage of the neural tube that the earliest beginning of the ear is seen.
The ear is contained within the temporal bone. The cochlea as well as the middle and external ear, vestibular apparatus, and seventh and eighth cranial nerves are all housed in the temporal bone. Temporal bone is a hard bone that has myriad cavities, channels, and canals that subserve the organs of hearing and balance. Temporal bone is paired: RIGHT TEMPORAL BONE & LEFT TEMPORAL BONE. The ear is the organ that detects sounds. It not only acts as a receiver for sound, but also plays a major role in the sense of balance and body position. The ear is the part of auditory system.
The word ear may be used correctly to describe the entire organ or just the visible portion. In most animals the visible ear is a flap of tissue that is also called the pinna and is the first of many steps in hearing. In people the pinna is often called the auricle. Vertebrates have a pair of ears placed symmetrically on opposite side of the face. This arrangement aids in the ability to localize sound source.
We humans hear the way we do because of at least three major forces. The first is phylogeny, the evolutionary changes in the auditory system since its beginnings. Another is embryology, the development of the system in each individual before birth. Finally, there is the biologically determined auditory mechanism we are born with and our interaction with the environment in early postnatal life.
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
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2. Outline
Introduction to sound
Ear
Function as a transducer
Parts and how it functions
External ear
Middle ear
Internal ear
Electrical potential
Auditory path way
2
3. SOUND
A form of energy
propagates in the form of waves
The speed of sound depend on the medium
through which the wave pass
air - 343m/s
water - 1482m/sec
Audible frequencies t for humans 20 to 20,000
cycles per second (cps, Hz).
It can detect the difference between two sounds
occurring 10micro seconds apart in time
3
4. EAR AS A TRANSDUCER
SOUNDENERGY
MECHANICAL
ENERGY
ELECTRICAL
ENERGY
4
5. Technical jargons
• Strength of the sound
• Loudness denotes the appreciation of sound
intensity
• Expressed in decibel (dB)
Amplitude/loudness
• Number of cycles per second
• Pitch /Tone denotes the appreciation of
frequency
• Expressed in Hertz(Hz)
Frequency/Pitch/Tone
• Resistance offered by a medium to sound
waves Impedence
5
6. • Resonance is the tendency of a system
to oscillate with larger amplitude at
some frequencies than at others
RESONANCE
• Attenuation is a general term that refers
to any reduction in the strength of a
signal
ATTENUATION
6
7. Values of hearing:
15-25dB —Whisper
35dB —Background noise
40-60dB —Background noise ( home )
65—70dB –- normal speaking voice
130dB —painful noise
140-180dB —jet air craft engine noise
10. Functions of EXTERNAL EAR
Sound collection
Increasing pressure on the tympanic
membrane in a frequency sensitive way
Sound localization
10
11. Sound collection
Pinna- concha system catches sound over
large area and concentrate it to smaller area
of ext. auditory meatus.
This increases the total energy available to
the tympanic membrane
11
12. Pressure increase by EAC
If a tube which is closed at one end and open
at other is placed in a sound field then
pressure is low at open end and high at closed
end.
12
13. Sound localization
Because of its shape, the pinna shield the
sound from rear end,change timbre,and helps
to localize sound from infront or back
Cues for sound localization from right/left
Sound wave reaches the ear closer to sound source before it arise
in farthest ear
Sound is less intense as it reaches the farthest ear because head
act as barrier
Auditory cortex integrates these cues to
determine location.
13
16. Impedence mismatch
IF THERE WAS NO MIDDLE EAR SYSTEM
,99% OF SOUND WAVES WOULD HAVE
REFLECTED BACK FROM OVAL WINDOW
MIDDLE EAR BY ITS IMPEDENCE
MATCHING PROPERTY ALLOWS 60% OF
SOUND ENERGY TO DISSIPATE IN
INNER EAR
16
17. “Impedance Matching” by the
middle ear System
(a) Area of tympanic membrane relative to oval window
(b)The lever action of middle ear ossicles
(c)The shape of tympanic membrane
17
18. (a) HYDRAULIC ACTION OFTYMPANIC MEMBRANE
Total effective area of tympanic membrane
45mm2
Area of stapes footplate is 3.2mm2
Effective areal ratio is 14:1
Thus by focusing sound pressure from
large area of tympanic membrane to small
area of oval window the effectiveness of
energy transfer between air to fluid of
cochlea is increased
18
19. (b) Lever action of ossicles
Handle of malleus is 1.3 times
longer than long process of
incus
Overall this produces a lever
action that converts low
pressure with along lever
action at malleus handle to
high pressure with a short lever
action at tip of long process of
incus
19
20. (c) Action of tympanic membrane
Eustachian tube equilibrates the air
pressure in middle ear with that of
atmospheric pressure, thus
permitting tympanic membrane to
stay in its most neutral position.
A buckling motion of tympanic
membrane result in an increased
force and decreased velocity to
produce a fourfold increase in
effectiveness of energy transfer
20
21. Total gain
Total transformer ratio=14x1.3x4=73:1
21
22. Attenuation reflex
When loud sounds are transmitted through the
ossicular system and from there into the central
nervous system, a reflex occurs after a latent period
of only 40 to 80 ms to cause contraction of the
stapedius muscle and the tensor tympani muscle
The tensor tympani muscle pulls the handle of the
malleus inward while the stapedius muscle pulls the
stapes outward. These two forces oppose each other
and thereby cause the entire ossicular system to
develop increased rigidity, thus greatly reducing the
ossicular conduction of low frequency sound
22
23. Function of attenuation
reflex
To protect the cochlea from damaging
vibrations caused by excessively loud sound.
To mask low-frequency sounds in loud
environments. This usually removes a major
share of the background noise
To decrease a person’s hearing sensitivity to
his or her own speech
23
24. PHASE DIFFERENTIAL EFFECT
Sound waves striking the tympanic membrane
do not reach the oval and round window
simultaneously.
There is preferential pathway to oval window
due to ossicular chain.
This acoustic separation of windows is achieved
by intact tympanic membrane and a cushion of
air around round window
This contributes 4dB when tympanic membrane
is intact
24
26. COCHLEA ---TWO FUNCTIONS….
A TRANSDUCER that translates sound energy
into a form suitable for stimulating the
dendrites of auditory nerve.
AN ENCODER that programs the features of
an acoustic stimulus so that the brain can
process the information contained
instimulating sound.
26
28. Endocochlear potential
An electrical potential of
about +80 millivolts exists all
the time between endolymph
and perilymph, with positivity
inside the scala media and
negativity outside.
This is called the endocochlear
potential, and it is generated
by continual secretion of
positive potassium ions into
the scala media by the stria
vascularis
28
29. Cochlear microphonic
When basilar membrane move in response to
sound stimulus electrical resistance at the tip
of hair cells change allowing flow of K+
through hair cells and produce voltage
fluctuations called cochlear micro phonic.
This is AC potential
29
30. Summating potential
Produced by hair cells
DC potential superimposed on VIII nerve
action potential
30
32. Central auditory pathway
• nerve fibers from the spiral
ganglion of Corti enter the dorsal
and ventral cochlear nuclei
• second-order neurons pass
mainly to the opposite side of
the brain stem to terminate in
the superior olivary nucleus
• the superior olivary
nucleus,the auditory pathway
passes upward through the
lateral lemniscus.
32
33. Some of the fibers terminate in the
nucleus of the lateral lemniscus, but many
bypass this nucleus and travel on to the
inferior colliculus, where all or almost all
the auditory fibers synapse
From there, the pathway passes to the
medial geniculate nucleus, where all the
fibers do synapse
Finally, the pathway proceeds by way
of the auditory radiation to the
auditory cortex, located mainly in the
superior gyrus of the temporal lobe.
33
34. Pecularities of auditory
pathway
First,signals from both ears are
transmitted through the pathways of both
sides of the brain, with a preponderance
of transmission in the contralateral
pathway
Second, many collateral fibers from the
auditory tracts pass directly into the
reticular activating system of the brain
stem
Third, a high degree of spatial orientation
is maintained in the fiber tracts from the
cochlea all the way to the cortex
34
35. Function of auditory cortex
Perception of sound
Judging the intensity of the sound
Analysis of different property of sound
35