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Sensory PhysiologySensory Physiology

Dr. ZHANG Xiong

Dept. of Physiology

ZJU School of Medicine

Http:// /10.202.77.12

What is a sense?

Part 1. Summary of sense

What is a sense?A sense of warmth, hunger, pain, light, etc.

A part of reflex arc which carry on the basal function of

nervous system

How to produce a sense?Invoked by a kind of stimulation and produced by brain

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Definition of ReceptorsSpecialized cells or group of nerve

Receptors and Sense Organs

Specialized cells or group of nerve endings that respond to stimuli

TypesMechanoreceptorChemoreceptorEl t ti tElectromagnetic receptorThermoreceptorNociceptor

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Definition of Sense OrgansA i li d t t h t llA specialized organ or structure where receptor cells are concentrated and supported by affiliated cells

TypesEye--VisionEar--HearingInner Ear--EquilibriumNose--SmellTongue--Taste

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Physiological Properties of Receptors

Ad t ti lAdequate stimulusParticular form of energy to which a receptor is most sensitive- Mechanoreceptor- Chemoreceptor

Electromagneticreceptor (photoreceptor)- Electromagneticreceptor (photoreceptor)- Thermoreceptor- Voltage receptor- etc.

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Sensory transductionSensory transduction

Receptor potential

An intermediate step between stimulus

and nerve impulse

Graded according to stimulus intensity

Generator potential

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Stimulus features are electrically

encoded

Frequency code

Population code

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AdaptationWhen a maintained stimulus of constant strength is applied to a receptor, the frequency of the action potentials in its sensory nerve declines over a period of time

Rapidly adapting receptorRapidly adapting receptor

Slowly adapting receptor

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Part 2. Visual Sense

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Visual Sense Organ- Eye

Eye -photoreceptor

Structure of the Eye

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Function of the Eye

Refracti e s stemRefractive system

Receptor system-

Retina

Refractive system

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Refraction of Light in the Eye

Function of refractive System

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Reduced eye model

It will help to make a clear images in retina for the

Accommodation of Refractive Function

It will help to make a clear images in retina for the

objects in the different distance.

Accommodation of lens

Accommodation of PupilsAccommodation of Pupils

Convergence of Eyeballs

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Accommodation of Lens

Accommodation of Lens

Controlled by theControlled by the parasympathetic nerves

Parasympathetic nerves(+)→ciliary

l imuscle contraction →lens ligament relaxation → lens becomes thicker → refractive power↑

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Far point of visionFar point of vision

The farthest point at which an object can be

seen distinctly by the eye

Near point of vision

The nearest point at which an object can be

seen distinctly by the eye

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Accommodation of Pupils

Near reflex of the pupilNear reflex of the pupil

The pupil constricts when an individual

looks at a near object

Pupillary light reflex

Consensual light reflex

Convergence of Eyeballs

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Abnormalities of Refractive Function

Myopia

(Nearsightedness)

Hyperopia

(Farsightedness)

Astigmatism

Presbyopia

Myopia

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Hyperopia

Astigmatism

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Presbyopia

Receptor system-Retina

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Photoreceptive Function of Retina

PhotoreceptorRod

Rhodopsin

Coneh d i lik iRhodopsin-like pigments

red-sensitive pigmentgreen-sensetiveblue-sensitive

Rod cell -- Scotopic Vision SystemNot color sensitiveMore sensitive to light (more rhodopsin)g ( p )Mainly peripheral distribution

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Cone cell -- Photopic Vision System

Color sensitive (3 types of rhodopsin-like pigments)Less sensitive to lightLess sensitive to light Mainly distributed in fovea

Mechanism of photoreceptor

Photochemistry of rhodopsin

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R l f i i A i hRole of vitamin A in the

formation of rhodopsin

Nyctalopia (Night

blindness)

Generation of a

hyperpolarized

receptor potentialp p

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Color vision by the conesTrichromacy theory

Blue green or red-sensitive pigmentBlue, green or red sensitive pigment

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Color Blindness

Red-green color blindnessRed-green color blindness

Blue weakness

Inheritance of red-green color blindness

A typical pedigree of inheritance of red-green color blindness shows the pattern of transmission.

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Information Process in Retina

Depolarizing andDepolarizing and

hyperpolarizing cells

Bipolar cell

Ganglion cell

Action potential

60 rods and 2 cones

converge on 1 cell

Action potential conduction

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Some Phenomena Related with Vision

Visual acuity

The visual ability to

resolve fine detail

Some Phenomena Related with Vision

Dark adaptation

Light adaptation

MechanismsChanges in concentrations of 11-cis-retinalChange in pupillary sizeNeural adaptation

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Some Phenomena Related with Vision

Visual field

not circular

White＞yellow＞

d＞red＞green

Blind spot

Some Phenomena Related with Vision

Binocular vision and stereopsis

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Video Review

General Questions

Terms:

Receptor potential

Visual acuity

Dark adaptation

Describe the mechanism of accommodation of the eyeDescribe the mechanism of accommodation of the eye.

What are the differences between scotopic vision system

and photopic vision system?