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Functions of the sense organs

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Function of the Sense Organs
What will we discuss in this chapter?
в… . Receptor
1. concepts and classification
2. general properties of receptors
в…Ў. Visual Sense Organ
1. dioptric system
2. light perception and signal processing in the retina
3. vision related terminology
в…ў. Hearing
1. external ear and middle ear
2. inner ear (cochlea)
3. AP in auditory nerve
в…Ј. Vestibular apparatus
1. receptor
2. adequate stimulus
3. vestibular reaction
в…¤. Other receptors (sense of smell and sense of taste )
п‚•Human life would be very different without the
ability to sense and perceive external stimulus.
п‚•Imagine your world without the ability to see,
hear, smell, touch, and feel……
в… . Receptor
Which receptor?
в’€ Concepts and Classification
(1) Concepts
п‚•Receptor is referred to the organ or structure located on the
body surface or within tissues, the function of which is to
detect the changes in internal or external environments and
to convert stimulus into electrical signals.
п‚•In a word:
• A state of awareness of a stimulus.
• A part of neuron or a specialized cell.
(2) Classificationпј€Aпј‰
1) Exteroceptors
Located on the body surface or specialized to detect external stimuli
Pressure, pain, temp, touch, etc.
2) Visceral receptors
Located within internal organs, detect internal stimuli,
Blood pressure, pain, fullness.
3) Proprioceptors
Found in the joints and muscles,
Also in the vestibular structures and the semicircular canals of the
inner ear. Limb and body position and movement.
(2) Classificationпј€Bпј‰
1) Mechanoreceptor
Detects stimuli which mechanically deform the receptor;
pressure, vibration, touch, sound.
2) Thermoreceptor
Detects changes in temperature, hot/cold;
3) Nociceptor (pain)
Detects damage to the structures;
4) Photoreceptor
Detect light, vision, retina of the eye;
5) Chemoreceptor
Detect chemical stimuli; CO2 and O2 in the blood, glucose, small, taste.
(2) Classificationпј€Cпј‰
1) Simple receptors
Usually a single modified dendrite
General sense;
Touch, pressure, pain, vibration, temperature;
2) Complex receptors
High modified dendrites, organized into complex structures; ear, eye.
Special senses:
Vision, hearing, smell, taste.
2. General properties of receptors
п‚•Adequate stimulus of sensory receptors
п‚•Transducer function of sensory receptors
п‚•Encoding of sensory receptor
п‚•Adaptation of sensory receptor
• The external & internal environments are monitored by
sensory receptors.
• Each type of receptor is excited most effectively by only one
modality of stimulus known as the adequate stimulus.
• The stimulus is converted into an electrical potential.
• Stimuli are detected as either static or dynamic events.
• The intensity & duration of the stimulus is frequency coded
as bursts of action potentials in the primary afferent nerve.
в…Ў.Visual Sense Organ
Functions of the Complete Eye
• Eye functions like a camera
• Iris allows light into eye
• Cornea, Lens & humors focus light onto retina
• Light striking retina is converted into action
potentials relayed to brain.
в’€ Dioptric system
(1) Structure of the Eyeball
п‚•A slightly irregular hollow sphere with anterior and
posterior poles;
The wall is composed of three tunics – fibrous, vascular,
and sensory;
п‚•The internal cavity is filled with fluids called humors;
п‚•The lens separates the internal cavity into anterior and
posterior segments.
п‚•Dioptric system: cornea, humors, lens, vitreous chamber.
(2) Reduced eye *
п‚•Reduced eye is an artificial model.
Optical Parameter:
anteroposterior diameter: 20 mm
refractive index :
radius of curvature :
п‚•Calculation of image:
5 mm
(3) Accommodation of eye *
п‚•Accommodation of lens
• near point:
• far point:
п‚•Pupillary reflex
• Decrease size of pupils (parasympathetic) prevents divergent light rays from
• near reflex of the pupil
• pupillary light reflex
п‚•Convergence of eyeballs
• Viewing near object causes reflexly both eyes to move inward to focus on a
near object, this process is called convergence reflex.
(4) Error of refraction *
п‚•Error of refraction :Caused by shape of eye
and/or power of lens
• Myopia
• Hyperopia
• Astigmatism
• Definition: The crystalline lens tends to harden and the capsule
itself becomes less elastic with age
• Treatment :convex lens
Ametropia and Correction
в’‰ Light perception and signal processing in
the retina
пј€ 1пј‰ Structure of Retina
From outside to inside:
Pigment cell
Photosensory cell
Bipolar cell
Ganglion cell
(2) Photosensory cell (A)
п‚•The photoreceptor cells are two types, rod cells
(rods) and cone cells (cones)
(2) Photosensory cell (B)
п‚•The outer segment of a rod cell has a rod-like
appearance, whereas that of a cone cell has a cone-
shaped appearance.
п‚•The outer segments of the photoreceptor cell contain stacks
of membranous discs.
п‚•The visual pigments appear to be built into the disc
(2) Photosensory cell (C)
п‚•Distribution of the cones and rods on the retina.
(2) Photosensory cell (D)
• Cones see detail but require bright light
• Rods see in low light but lack detail
п‚•located mainly in periphery of
п‚•located mainly in fovea;
п‚•responsible for night vision;
п‚•detail not detected;
п‚•work best in bright light;
п‚•enable us to see fine detail;
п‚•see black, white, and gray (no
п‚•responsible for color
п‚•several rods share 1 bipolar
and 1 ganglion cell;
п‚•each cone has its own
п‚•rod vision lacks detail, but, by
combining their efforts,
groups of rods allow us to see
in low light.
bipolar and ganglion cell;
п‚•this allows us to see detail
but bright light is needed.
(3) Two types of retinal
transduction systems
п‚• Other evidence that two photoreceptor system of retina exit.
п‚• The nocturnal animals have a preponderance of rods, whereas the
diurnal animals have a preponderance of cones in their retina.
п‚• The visual pigment in the rods is only rhodopsin. There are three
classes of cones in the retina, each containing different pigment
sensitive to particular region of visible spectrum.
(4) General transduction mechanism
of rods
п‚•Photopigments are located in the membrane of the outer
segment of rods and cones;
п‚•Each pigment consists of an opsin (a protein) and retinal (a
• In the dark, membrane Na+ channels are open -> glutamate is released
which depolarizes the membrane
• Light splits the opsin and retinal apart->
п‚•Activates transduction (G protein)->
п‚•Activates phosphodiesterase->
п‚•Reduces cGMP -> closes Na+ channels
п‚•The net effect of light is to hyperpolarize the retinal receptor
and reduce the release of glutamate.
Rhodopsin Cycle
Rod Cell Hyperpolarization
(5) Color Vision
Trichromatic Theory of Color Vision
Light of a single wavelength
Visible spectrum: 380-760 nm (nm is a billionth of a meter)
Theories of Color Vision
• Trichromatic theory
– Occurs at the receptor level ;
– Each cone is coated by one of 3 photopigments:
• Short-wave (blue)
• Medium-wave (green)
• Long-wave (red)
– Ratio of activated cones = color differentiation;
– Primary Colors: sets of 3 colors that can be mixed to produce any
other colorпј›
– For Visual System: set of interest is “Red Green and Blue”.
Color Sensitivity of Different Cones
Color Blindness
• Sex-linked conditions: genes on X
chromosome, so more common in men.
– Protanopia, missing red photopigment;
– Deuteranopia : missing green photopigment;
• Non-sex-linked condition:
– Tritanopia , missing blue photopigment or
blue cones
– Monochromats : people who are
totally colorblind, more severe.
Color Vision Systems
Blind point (з›Із‚№) : In
the visual field of each eye,
there is a physiological
scotoma, the blind point,
which coincides with the
place where the optic
nerve passes out of the
eye through the sclera and
there is no retina.
3. Vision related terminology
п‚•Visual acuity
п‚•Visual field
п‚•Dark adaptation
п‚•Light adaptation
п‚•After image
п‚•Fusion phenomenon
п‚•Visual Acuity
• Visual acuity is defined as the ratio of the distance
of the individual from the chart to the distance at
which the details of the correctly read line subtend
1'of arc.
• Visual angle :
• Visual chart
п‚•Dark Adaptation and Light Adaptation
• Dark adaptation
п‚•Definition: On going from a light environment into a darker one,
there is a gradual increase in sensitivity allowing dimmer lights to be
seen, a mechanism known as dark adaptation.
• Light adaptation
п‚•Definition: When one passes suddenly from a dim to a brightly
lighted environment, the light seems intensely and even
uncomfortably bright until the eyes adapt to the increased illumination
and the visual threshold rise. This adaptation occurs over a period of
п‚•Visual field
• The field of the view that can be seen without moving the head
is known as the visual field.
• white > blue > red> green
• narrow: wide:
п‚•After image
п‚•Fusion phenomenon
п‚•Binocular vision
п‚•Hearing Threshold
• Hearing threshold is the lowest intensity that the faintest
sound could be heard.
п‚•Maximum hearing threshold
п‚•Audible area
Properties of Sound
Sound travels in waves as does light
• 1. Pitch: determined by “frequency,” the number of cycles
per second of a sound wave, measured in hertz (Hz).
• 2. Loudness: determined by “amplitude” (height) of the
sound wave, measured in decibels (dB) .
• 3. Timbre: determined by “complexity and shape” of the
sound wave, gives each sound its unique quality.
frequency пј€Hzпј‰
Loudness of Sound
0 dB = hearing threshold
50 dB = normal conversation
90 dB = danger zone
• 120 dB = rock concert
• 130 dB = pain threshold
в’€ External ear and middle ear
External ear
Outer Ear:
– Pinna (auricle): directs sound waves into the auditory
– Auditory Canal: conducts
sound to the eardrum
– Tympanic membrane
(Eardrum): thin membrane
that vibrates in response to
sound, and transfers sound
energy to bones of the
middle ear
Middle Ear
• Three tiny bones “amplify sound” and transfer sound
energy to the inner ear
п‚•B: Incus
п‚•C: Stapes
– Ossicles are smallest
bones in the body
– Act as a lever system
– Footplate of stapes
enters oval window of the
2. Inner Ear
Place where sound energy is transduced
– Cochlea: snail shaped fluid-filled structure;
– Oval window: thin membrane, transfers vibrations from
stapes to fluid of cochlea.
–Basilar membrane: runs the length of the cochlea
–Organ of Corti: rests on basilar membrane, contains
“receptor” cells
–Round window: absorbs energy and equalizes pressure
in the cochlea
Pathway Transmitting Sound Wave from External
Environment to Inner Ear *
Air Conduction
Sound wave
Auditory Canal
Sound wave
Auditory Canal
Air in tympanic cavity
Tympanic membrane
Ossicular chain
Round window
Bone Conduction
Sound wave
Oval window
Inner ear
Vibration of skull
Function of Cochlea
п‚•Cochlea - Snail-shaped organ with a series of fluid-filled
п‚•Converts mechanical energy into electrical energy
п‚•The scala vestibuli a
is separated from the scala media by
vestibular membrane.
scala media is in turn separated from the scala
tympani by the basilar membrane.
Fluids in the cochlea: perilymph-fills the scala
vestibuli and scala tympani.
п‚• Endolymph fills the scala media.
п‚•At the end of thea
cochlea, the helicotrema joins the
scala vestibuli and the scala tympani.
Hearing Summary, So Far!!
Sound Waves Г movement of tympanic
membrane Г movement of Malleus Г movement
of Incus Г movement of Stapes Г movement
oval window Г movement of fluid inside the
cochlea Г Movement of round window
Organ of Corti
A structure rests atop the basilar membrane along its
п‚• Contains approx. 16,000 cochlear hair cells.
How to discriminate the frequency of the sound ? ---
Traveling Wave Theory
п‚•Sound wave entering at the oval window is to cause
the basilar membrane at the base of the cochlea to
п‚•different frequencies cause vibrations at different
locations (places) along basilar membrane;
п‚•higher frequencies at base, lower frequencies at top.
3. Electrical Potentials of cochlea
п‚•Perilymph-similar in composition to extracellular fluid. High
in Na+ and low in K+.
п‚•Endolymph-found in the scala media. Similar to intracellular
fluid. High in K+ and low in Na+
п‚•Endocochlear Potential (EP); Microphonic potential (CM)
• Békésy discovered EP by putting the electrode in the scala media and
discovered a +80 mV potential with respect to a neutral point on the
• Tasaki discovered EP was due to the Stria Vascularis.
п‚•Intracellular Potential (IP) or organ of corti potential (resting
• Recorded -80 mV inside cells of organ of corti.
Homeostatic imbalances of hearing
• Deafness.
– Conduction deafness • possible causes include: perforated eardrum,
inflammation, otosclerosis (иЂізЎ¬еЊ–).
– Sensineural deafness - nerve damage.
• Tinnitus
• Ringing in the ear
• Meniere's syndrome
• attacks of dizziness, nausea, caused by excess
endolymph in the media canal.
How Sound Travels through the Ear?
п‚•Acoustic energy, in the form of sound waves, is channeled into the ear
canal by the pinna.
п‚•Sound waves strike the tympanic membrane, causing it to vibrate like
a drum, and changing it into mechanical energy.
п‚•The malleus, which is attached to the tympanic membrane, starts the
ossicles into motion.
п‚•The middle ear components mechanically amplify sound.
п‚•The stapes moves in and out of the oval window of the cochlea
creating a fluid motion.
п‚•The fluid movement within the cochlea causes membranes in the
Organ of Corti to shear against the hair cells.
п‚•This creates an electrical signal which is sent via the auditory nerve to
the brain, where sound is interpreted!
в…Ј.Vestibular apparatus
Structure of Vestibular Apparatus
semicircular canal
Vestibular apparatus
1. Receptor of Vestibular Apparatus
• Hair Cell
п‚•Kinocilium: only one, the longest.
п‚•Stereocilium: more, ladder-like arrangement
• Bioelectricity of Hair Cell
п‚•Resting potential пјљпјЌ80 mv
п‚•Change of membrane potential
• -60 mv
• -120 mv
Vestibular apparatus
2. Adequate Stimulus of Vestibular Apparatus
• Semicircular canal
п‚•Adequate Stimulus
• angular acceleration
• Utricle and saccule
п‚•Adequate Stimulus
• line variable velocity
п‚• Mechanism
3. Vistibular Reaction
п‚•Vestibular postural reflex
• maintain posture, keep balance.
п‚•Vestibular autonomic reaction
• exciation of vagus
• giddy
• Conception:
• Classification:
п‚•Slow component
п‚•Quick component
V. Other receptors
1. Sense of smell
• Receptor:
п‚•olfactory cell
• Adequate Stimulus:
п‚• chemicals in the air
• Basic odor:
п‚•Camphor , muskiness , flower, mint , aether , pungency , rancidness ,
• Characteristic:
п‚•Sensitivity of the big differences between species
п‚•Adapting quickly
2. Sense of taste
• Receptor:
п‚•gustatory cell
• Basic gustation
• effect factor :
Temperature, the maximum sensitivity in 20℃—30℃;
п‚•Chemical component in blood;
Consideration after class
1. How do the eyes make regulation when watching
near- distance objectпјџ
2. How can we correct ametropia or refraction error?
3. Please describe the dualistic theory of vision.
4. Please describe main content of the travelling
wave theory.
5. How do ears hear voice?
sense organ Physiology
Thank You for Your Attention
п‚•Each type of receptor is highly sensitive to one type of
stimulus for which it is designed and yet is almost
nonresponsive to normal intensities of other type of
п‚•The stimulus to which a given receptor has the lowest
threshold is termed the adequate stimulus of the sensory
п‚•For instance, the roes and cones are highly responsive to
light but almost completely nonresponsive to heat and
п‚•Transducer function: The process by which an
environmental stimulus becomes encoded as a sequence
of nerve impulses in an afferent nerve fiber is called
sensory transduction.
• Sense orgrans transduce sensory energy into neural
(bioelectrical) energy.
• Converting one type of energy into another type is the
process of transduction.
• Your brain only deals with bioelectrical impulses so
transduction must occur; what cannot be transduced cannot
be a stimulus.
• The quality of the stimulus is encoded in the frequency
of the action potentials transmitted down the afferent
fibre and the number of sensory receptors activated.
Stretch Receptors:
Weak stretch causes
low impulse
frequency on neuron
leaving receptor.
Strong stretch causes
high impulse
frequency on neuron
leaving receptor.
Frequency Code
Sensory Adaptation is one form of Integration
Phasic receptors quickly
adapt. The frequency of
action potentials diminishes
or stops if the stimulus is
Tonic receptors adapt
slowly or not at all.
Most exteroreceptors
(receptors that monitor the
external environment) are
phasic receptors.
Accommodation of Lens. The solid lines represent the
shape of the lens, iris, and ciliary body at rest, and the
dotted lines represent the shape during accommodation.
Lens less
Focus far
Lens more
Focus near
ciliary muscle
ciliary zonule
Pupillary reflex
Error of refraction(A)
• Definition: The axis of the eye is too long, and even with full relaxation,
images of objects at infinity are focused in front of the retina. This
abnormality is called myopia.
• Treatment :(concave lens)
Error of refraction(B)
• Definition: In some individuals, the eyeball is shorter than normal and
the parallel rays of light are brought to focus behind the retina. This
abnormality is called hyperopia or far sightedness.
• Treatment (convex lens)
• Reason:abnormal curvature of the cornea.
• Treatment :(uneven lens)
y of
Frequency of sound
Fig The range of hearing of human
Fig Vibration of the tympanic membrane
and ossicular chain,
Fig Sound conduction
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