Transcript （一）Functional Anatomy of the Retina

CHAPTER 9
THE SENSORY ORGANS
王俊 副教授
博雅楼 402室
[email protected]
Section 1
General Principles of
Sensory Organs
一、Definitions and Classifications
Receptors: structures that monitor both external
and internal environmental conditions and
conduct information about those stimuli to the
central nervous system.
环层小体
触觉小体
肌梭
Pacinian copuscle
Messner’s corpuscles
Muscle spindle
Receptor Classification by Location
Exteroreceptors
Respond to stimuli arising outside the body; Include
touch, pressure, pain, and temperature receptors in
the skin and most receptors of the special senses
(vision, hearing equilibrium, smell, taste)
Interoceptors
Visceroceptors: Found in internal viscera and blood
vessels
Proprioceptors: Found in skeletal muscles, tendons,
joints, ligaments
Receptor Classification by Stimulus Type
Mechanoreceptors – respond to touch, pressure,
vibration, stretch, and itch
Thermoreceptors – sensitive to changes in temperature
Photoreceptors – respond to light energy (e.g., retina)
Chemoreceptors – respond to chemicals (e.g., smell,
taste, changes in blood chemistry)
Nociceptors – sensitive to pain-causing stimuli
二、General Characteristics of
Sensory Receptors
1. Adequate Stimulus
2. Transduction
3. Coding
4. Adaption
Adequate stimulus
Specific sensory R are more sensitive to certain
types of stimuli (photo R in eye). The types of
stimulus to which the R is most sensitive (has the
lowest threshold) is called adequate stimulus.
Transduction
Receptor detects a stimulus and convert the energy
(light, pressure) of stimulus into electrical signals
(action potentials) in afferent nerve.
During the transduction, receptor respond to a
stimulus by generating a series of graded
potentials in their associated afferent fiber, not
action potentials directly.
The response of the pacinian corpuscle to an
adequate stimulus is called a generator potential. It
is able to "generate" action potentials in the region
of the receptor cell that has voltage-sensitive
channels.
However, not all receptors have voltage-sensitive
channels. In receptor cells incapable of generating
action potentials (typically specialized receptors such
as the cones and rods of the retina), the change in
membrane potential in response to an adequate
stimulus is referred to as a receptor potential.
The membrane of the receptor region is, however, electrically inexcitable; it contains no voltage-gated ionic channels and
does not generate spikes. If the receptor region generated action potentials, the graded nature of the generator potential
would be destroyed because as soon as the generator potential exceeded the critical firing level an action potential would
be initiated, reversing the membrane polarization no matter how large or small the stimulus, i.e., the membrane potential
would no longer encode the stimulus intensity.
Coding
The speed of conduction and other characteristics
of sensory nerve fibers vary, but action potentials
are similar in all nerves. This raises the question of
why stimulation of a touch receptor causes a
sensation of touch and not of warmth. It also raises
the question of how it is possible to tell whether the
touch is light or heavy.
Adaption
When a maintained stimulus of constant strength is
applied to a receptor, the frequency of the action
potentials in its sensory nerve declines over time.
This phenomenon is known as adaption.
快适应感受器
慢适应感受器
举例 皮肤触觉感受器
肌梭、颈动脉窦、关节囊感
受器
特点 仅在刺激开始后的短时间内有
传入冲动发放，以后虽然刺激
仍在作用，但其传入冲动的频
率却很快降低到零
刺激持续作用时，一般仅在
刺激开始后不久出现冲动频
率的轻微降低，以后可以较
长时间维持在这一水平。
意义 对刺激变化十分灵敏，适于传
递快速变化的信息，有利于机
体探索新异的物体或障碍物，
有利于感受器和中枢再接受新
的刺激
有利于机体对某些功能状态
进行长时间持续的检测，并
根据其变化随时调整机体的
功能。
Section 2
Visual Function of the Eye
760
一、The light-Refracting System of the Eye
（一）Optical Property of the Light-Refracting
System of the Eye
（二）Refraction of Light in the Eye and Reduced Eye
AB
Bn
=
ab
nb
（三）Accommodation
Far point of vision : farthest point to the eye at which an
object can be brought into clear focus without accomodation
Near point of vision :nearest point to the eye at which an
object can be brought into clear focus by accomodation
1. Accommodation of the Lenses
2. Accommodation of the Pupils (1.5~8mm)
Pupillary accommodation reflex/Near reflex of pupil:
is the reduction of pupil size in response to an object
coming close to the eye.
强光－－视网膜－－中脑顶盖
前区－－动眼神经缩瞳核－－
动眼神经副交感神经－－瞳孔
括约肌收缩－－瞳孔缩小
Pupillary light reflex： is the reduction of pupil size in
response to light.
consensual light reflex: each pupil constricts with light
shone into one eye.
3. Convergence
Convergence reflex:
is the simultaneous inward movement of both eyes
toward each other, usually in an effort to maintain single
binocular vision when viewing an object far to near.
（四）Defects in Accommodation and Light Reflex
emmetropia
ametropia
myopia
hyperopia
astigmatism
myopia
hyperopia
astigmatism
（五）Aqueous humor
Aqueous humor circulation
non-pigmented epithelium of the
ciliary body—posterior chamber—
anterior chamber— trabecular
meshwork—Schlemm's canal—vein
Function
Maintains the intraocular pressure
and inflates the globe of the eye.
Provides nutrition for the avascular
ocular tissues; posterior cornea,
trabecular meshwork, lens, and
anterior vitreous.
二、Functional Anatomy of the Retina
and Two Photoreceptor System
（一）Functional Anatomy of the Retina
Pigment epithelia cells
Photoreceptor cell layer
bipolar cells
ganglion cells
1 色素上皮层
Pigment epithelia cells
2 光感受器细胞层
Photoreceptor cell layer
Rod cell 视杆细胞
Cone cell 视锥细胞
Synaptic
terminal
3 双极细胞和神经节细胞
bipolar cells and ganglion cells
Physiological blind spot is the place in the visual field that
corresponds to the lack of light-detecting photoreceptor cells on
the optic disc of the retina where the optic nerve passes
through it. Since there are no cells to detect light on the optic
disc, a part of the field of vision is not perceived.
（二）Retinal Photoreceptor System
Rods system, Scotopic vision system
Scotopic vision not color sensitive, more sensitive to
light and mainly peripheral (rods)
Cones system, Photopic vision system
Photopic vision color sensitive, less sensitive to light
and mainly central (cones)
Rods
Cones
1.2x108
6x106
Vision in shades of gray
Color vision
High sensitivity
Low sensitivity
Low acuity
High acuity
Night vision
Day vision
Much convergence in retinal
pathways
Little convergence in retinal
pathways
More numerous in periphery
Concentrated in fovea
（三）Mechanism of Photoreception of
the Rod
1、Photochemistry of Rhodopsin
Rhodopsin(500nm)
opsin
retinal
VitA
Rhodopsin
light
opsin + retinal
2、Generation of Receptor Potential
Dark current is the
depolarizing current,
carried by Na+ ions,
that flows into a
photoreceptor cell
when unstimulated.
GP:-30～-40mv
超极化－感受器电位
GC
Ca2+
Ca2+
（四）The Cone System and Color Vision
Rhodopin
opsin
retinal
视锥细胞的特点是它具有辨别颜色的能力。波长只要
有3－5nm的增减，就可被视觉系统分辨为不同的颜色
760
Trichromatic Theory
三 、Information Process in the Retina
四、Visual Pathway
五、Other Visual Phenomena
（一）Visual Acuity
Visual acuity refers to the clarity or clearness of
one’s vision, a measure of how well a person
sees. This may be thought of as the ability of the
eye to see fine detail.
Visual acuity test：Landolt C
Snellen eye chart
Landolt 环
Landolt C
Snellen eye chart
（二）Dark and Light Adaptation
Dark Adaptation
It occurs when going from a well light area to a dark area.
Initially blackness is seen because our cones cease functioning
in low intensity light. Also, all the rod pigments have been
bleached out due to the bright light and the rods are initially
nonfunctional.
Light Adaptation
This occurs when we move from the dark into bright light. The
bright light momentarily dazzles us and all we see is white light
because the sensitivity of the receptors is set to dim light. Rods
and cones are both stimulated and large amounts of the
photopigment are broken down instantaneously, producing a
flood of signals resulting in the glare.
（三）Visual Field
The visual field is
the total area in
which objects can
be seen in the
peripheral vision
while the eye is
focused on a
central point.
（四）After Image and Fusion Phenomenon
An image continuing to appear in one‘s vision after
the exposure to the original image has ceased.
One of the most common afterimages is the bright
glow that seems to float before one’s eyes after
staring at a light bulb or a headlight for a few
seconds.
The phenomenon of afterimages may be closely
related to persistence of vision, which allows a
rapid series of pictures to portray motion, which is
the basis of animation and cinema.
（五）Binocular Vision and Stereopsis
Function of Binocular Vision
Expand visual field
Function of Binocular Vision
Stereopsis
Section 3
Function of the Auditory
System
一、Auditory Threshold and Auditory
Sensation Area
F: 20—20000Hz, P: 0.0002—1000dyne/cm2
Fs: 1000--3000Hz, Language: 300—3000Hz
二、Functions of the External Ear
 Pinna (ear lobe):
collects sound waves
helps to distinguish the direction of sound
 Exteral auditory canal:
sound waves conduction
air pressure increase
一端封闭的管道对于波长为其长度4倍的声波能产生
最大的共振作用。
L=2.5cm λ=4L=0.1m
λ = ν /ƒ=340/3000=0.1m
三、Functions of the Middle ear
1.Supercharging：
2.Protection：
四、Air and Ossicular Conduction
Bone conduction
Air conduction
Sound waves
Sound waves
Vibration of
temporal bone
Exteral auditory canal
Tympanic membrane
Middle ear bones
Air in the drum
Oval window
Round window
cochlea
cochlea
Vibration of
endolymph in
cochlea
五、Functions of Cochlea
（一）Anatomy of Cochlea
helicotrema
Scala vestibuli
Reissner’s membrane
Scala media
basilar membrane
Scala tympani
Cochlea
• A light microscopic image of a
hair cell isolated from tissues
normally surrounding it.
• This hair cell is about 30 m
long; the hair bundle is about 5
m wide.
• Hair cells convert mechanical
energy into an electrical
energy through ion channels
which open and close in sync
with sound vibrations.
•This slide from (A.J. Hudspeth, Science, 230:745-752, 1985)
（二）Vibration of Basilar Membrane
and Traveling Wave Theory
Cochlear Representation of Sound
basilar membrane
• Frequency Theory
Membrane vibrates at frequency
of Sound source
• Place Theory
High Frequency sounds cause
vibration near oval window
Low frequency sounds cause
vibration near helicotrema
Place
Theory
Different parts of the basilar membrane respond most to different
frequencies: high frequency at base; low frequency at apex.
Cochlear Mechanics
Actual Response to high frequency
Passive Response
Passive response caused by mechanical properties of
membranes (e.g. width)
Active Response is caused by outer hair cells, which
inject energy back into vibration of cochlear membranes
• Outer hair cells move (tilt slightly and change length) in response to
sound (frequency specific).
• The movement pushes on the basilar membrane which amplifies and
sharpens its response a given location along the membrane.
（三）Transduction Function of Hair cells
基底膜振动
？
毛细胞
DISPLACEMENT OF THE BASILAR MEMBRANE
TOWARD THE SCALA VESTIBULI (UPPER) RESULTS I
DEPOLARIZATION OF THE OHC - ASSOCIATED WITH
DECREASE OF OHC LENGTH
DISPLACEMENT IN THE OPPOSITE DIRECTION
PRODUCES HYPERPOLARIZATION AND AN INCREAS
IN OHC LENGTH
Inner hair cell
Outer hair cell
Cell number
3500
20000
Nerve innerved
90—95%
5—10%
（四）Electrophysiology of the Cochlea
1. Endocochlear or endolymphatic potential
+80mv
-80mv
0mv
2. Cochler microphonic potential, CM
六、Action Potential in Auditory Nerves
七、Hearing Pathway
Section 4
The Vestibular Sensation Of
Equilibrium
一、Vestibular Apparatus and
Adequate Stimulus
-80mv
-60mv
-120mv
半规管壶腹脊的适宜刺激是正负角加速度
椭圆囊和球囊的适宜刺激是直线加速度运动
utricle
saccule
二、Vestibular Reactions and
Nystagmus
（一） vestibular postural reflex
（二）vestibular autonomic reactions
（三）nystagmus
三、Equilibrium Pathway