Presentation on theme: "Sensory physiology Instructor: DU Jing Department of Physiology"— Presentation transcript:
1 Sensory physiology Instructor: DU Jing Department of Physiology Jining medical collegeOffice: 0850 physiological sciences
2 Section A General Physiological Properties of Receptors Sensory Receptors & Sensory OrgansGeneral physiological properties of receptorsSection B Special Sensory systemsVisionHearingVestibular systemSomatic sensation
3 IntroductionSensation and perception are reflection of the objective world in the subjective consciousness.Stimulus energy is transduced by Sensory Receptors/Sensory Organs into nerve impulse which travels along specific neuron pathways to specific areas in the cerebral cortex of the brain.
4 Receptors & Sensory Organs Section AReceptors & Sensory OrgansⅠDefinition:1) Receptors (Sensory receptors, not proteins)Sensory receptors is referred to the cells or structures located on the surface of the body or within tissues, the function of which is to detect changes in internal or external environment and transduce these changes to electrical response.2) Sensory organsSensory organ is the special organthat is composed of sensory receptor andits subsidiary structures.
5 For example: Receptors -- Rods and cones in the retina; the endings of sensory nerves;Sensory Organs – Eyes, ears, the vestibular apparatus in the inner ear, the taste buds on the tongue, the olfactory epithelium of the nasal cavity
6 ⅡClassification of receptors Section AⅡClassification of receptorsInteroceptorsExteroceptorsBy locationmechanoreceptorsthermoreceptorsnoticeptors (pain receptors)electromagnetic receptors chemoreceptorsBy types of stimuli
7 General physiological properties of receptors 1. Adequate stimulus of receptor2.Transducer function of receptor3. Encoding of receptor4. Adaptation of receptor
8 General physiological properties of receptors Section AGeneral physiological properties of receptors1. Adequate stimulus of receptor:Each kind of receptors is very highly sensitive to one type of stimulus for which it is designed. This special stimulus is called adequate stimulus of the receptor.eg. electromagnetic waves with specific rangs ofwavelength to the photoreceptor cells in the retina;mechanical vibration at a specific rang of frequencyto the hair cells in the cochlea
9 Receptors can also respond to inadequate stimuli; Each receptor has its own sensory threshold.
10 Perceptions of the world are created by the brain from action potentials (APs) sent from sensory receptors.Receptors can transduce (change) different forms of stimulus energy to electrical signals that are conducted along the specific afferent nerve pathways to CNS.
11 General physiological properties of receptors Section AGeneral physiological properties of receptors2. Transducer function of receptorThe process in which a stimulus energy is transduced into the electrical response is known as transducer function of receptor.stimulus→ electrical response → brain
12 Receptor potentialDuring the process of transducing, the receptor firstly changes the stimulus energy into a graded local electrical response across the receptor membrane or the sensory nerve ending, this transitional potential that can later initiate the action potential is known as a receptor potential.
13 Characters of receptor potential • Slow, local potential, can summate• Extends by electrotonic propagation, decreases with distance• Stimulus information is reflectedby the magnitude, duration anddirection of receptor potential.
14 Steps of sensation stimulus receptors (receptor potential →AP) electrical informationcerebral cortexTransducer functionalong afferent nerves(receptor potential →AP)sensation or perception
15 Mechanism of transducer function StimulusReceptorThrough Second MessengerIon channel (+)Change in ion fluxes across receptor membraneReceptor potential(a separate cell)(ending of afferent neuron)alters the release of neurotransmitterAP on afferent nervesEPSP/IPSPCNS
16 During the process in which stimulus is changed to AP by a receptor, not only the form of stimulus energy is transduced, but also the information brought by stimulus is transformed into the sequence of AP.Stimulus → APTransducing of energy formTransformation of information
17 General physiological properties of receptors Section AGeneral physiological properties of receptors3. Encoding of receptor:Receptor could transfer the messages of environmental changes brought by stimuli into the information conveyed in the action potential sequence on the afferent neuron. This function of information transformation is termed as encoding of receptor.
18 Encoding of stimulus characteristics: Special receptor, special neuron pathway,Special CNS location .Encoding of stimulus intensity:Stimulus intensity is distinguishedboth by the frequency of AP generatedon the afferent N and by the numberof the fibers transporting the messages.
20 General physiological properties of receptors Section AGeneral physiological properties of receptors4. Adaptation of receptor:Receptors have the ability to reduce the frequency of AP generated on the afferent neuron in spite of a sustained stimulusstrength.
21 Classification according to adaptation: Rapidly adapting receptor--important for the body to detect new stimulieg. Touch and pressure receptors in the skinSlowly adapting receptor--important for monitoring the continuous functions of the bodyeg. Stretch receptors in muscles participating in maintaining posture
23 Refractive system (optical portion) Cornea Aqueous humor Lens Vitreous humorStructures in the eye involved in visionRetina (photoreceptive system)Photoreceptor cells (rods, cones)Bipolar cellsGanglion cells
24 Adequate stimulus:nm electromagnetic waves(visible wavelengths of light)Processes of vision:Formation of the image on the retina--refractive systemPhototransduction by the photoreceptors--rods and conesElectrical signals is sent along the optic never to the visual cortex in the brain
25 Ⅰ Refractive function of the eye and accommodation VisionⅠ Refractive function of the eyeand accommodation
26 Ⅰ Refractive function of the eye and accommodation VisionⅠ Refractive function of the eyeand accommodationAs in a camera, image is up-side down and inverted. The brain interprets this correctly.
27 Refractive structures of the eye CorneaAqueous humorLensVitreous humor(Outside to inside)
28 Refractive structures of the eye fovea centralisoptic nerve← Viewed through an ophthalmoscope
29 Reduced eyeVisionIf all the refractive surfaces are algebraically added together and considered to be a single lens with its center placed 15cm in front of the eye, the normal eye may be schematically regarded as ‘reduced eye’ .It’s an imaginative artificial model which has the same refractive effect as the eye.
30 Under the condition of non-accommodation, the focal point of normal human eye is on the retina. Lights from an object at infinite distance (>6m) can form a image on the retina.
31 Visual accommodation Vision When focusing at objects at different distance from the eye, some adjustments are made, especially when focusing at near objects (<6m) --visual accommodation.Accommodation includeshape changes of the lensdiameter changes of the pupilconvergence of two eyesAbility of lens accommodation:Near point of vision is the nearest distancedistinguished by the eye.
32 Shape changes of the lens Controlled by the zonular fibers and the ciliary muscle .Ciliary muscleZonular fibersThe periphery of the lens is joined to the ciliary muscle (circular like a sphincter) by the zonular fibers.
34 Shape changes of the lens Near objectCiliary muscle contractsLessens tension on zonular fibersLens becomes more sphericalFar objectCiliary muscle relaxesIncreases tension on zonular fibersLens becomes more flattened
35 Light rays from close objects diverge and require more accommodation for focusing.
36 Since the lens must be elastic to assume a more spherical shape during accommodation for near objects, the increasing stiffness of the lens that occurs with aging makes accommodation for near vision increasingly difficult --- presbyopia, a normal part of the aging process in people around 45 years old.Old people often wearcorrective glasses for close work.
38 Diameter changes of the pupil -- The amount of light entering the eye is controlled by the diameter of the pupil, the hole in the center of the iris through which light enters the eye.-- a reflexive process (light-sensitive reflex)-- protect the retina from damage induced by too bright light-- also one of the symbols of deep anesthesia or death
39 Convergence of two eyes Focusing on an object moving from the distance to the near, the two eye balls convergent towards the nasal sides, so that the images could be focused on corresponding points of the two retinas.
40 Errors of refraction Vision The normal condition, in which the eyes has the full adjustment range that allows the maximum capacity for accommodation to keep objects in focus as they get nearer and nearer, is termed as emmetropia.The eyes of many individuals don’t achieve this ideal. Errors of refraction include myopia, hyperopia, astigmatism and cataract (opacity of the lens with aging).
45 Structure of the photoreceptor cell retinalopsinphotopigmentmitochondrianucleusSynaptic terminalInner segmentStacked layers of membrane--discslipid bilayer with proteins mosaiced in it
46 Comparison of rods and cones more sensitiveless sensitivehighest density--6mm from the fovea centralishighest density--center of the fovea centralis, only conesmore convergent connections to neuronsmore single connections to neuronsone type (no color vision)three types (color vision)
47 a photopigment Photochemistry of vision Chemical composition of photopigmentan opsin (membrane protein binding to retinal)chromophore (retinal, derivative of Vit A)a photopigmentfour types--one called rhodopsin in the rods and one in each of three different cones
48 Photochemistry of vision -- a reversible chemical reaction
49 In bright light, decomposing of rhodopsin excels composing; in the dark ,composing excels decomposing.Vitamin A can derive 11-cis retinal which can bind to opsin to produce rhodopsin.The amount of retinal lost during the process of decomposing and composing of rhodopsin is replaced by Vit A from foods.Serious Vit A deficiency leads to nyctalopia, (night blindness, impaired vision in dim light and in the dark .)
50 Phototransduction of the retina Light stimlus(by photoreceptors)Electrical response, all-trans retinalAPA unique character:hyperpolarized receptor potential
60 Color blindnessIt’s a condition in which certain colors cannot be distinguished, and is most commonly due to an inherited condition. It is caused by missing of one or more of the cones, or by poor function of the cones. Red/Green color blindness is the most common form, about 99%, and causes problems in distinguishing reds and greens.
64 4) Binocular Vision and Stereopsis Binocular vision: The ability to maintain visual focus on an object with both eyes, creating a single visual image. Lack of binocular vision is normal in infants. Adults without binocular vision experience distortions in depth perception and visual measurement of distance.Binocular Vision –with overlapped optic fieldsMonocular Vision--with no overlapped optic fields
65 4) Binocular Vision and Stereopsis Stereopsis is one of the processes of the human visual system that extracts depth information from a viewed scene and builds a three dimensional understanding of that scene. It makes use of the slight difference in perspective of one eye relative to the other.
70 Structure of the earMiddle ear cavity separated from external ear by eardrum and from internal ear by oval & round windowAuditory tube leads to nasopharynx--helps to equalize pressure on both sides of eardrumMembranous labyrinth contains cochlea (organs of hearing) and vestibular apparatus (equilibrium)
71 HearingSound waves are conducted through the auditory canal and cause vibration of the eardrumSound waves are conducted and amplified by moving of the ossicular chain in the middle earVibration of sound waves is converted into receptor potential by hair cells in the organ of Corti of the cochlea. Receptor P triggers release of neurotransmitter and then cause AP which travels along the afferent nerves to the auditory cortex of the brain.
72 ⅠFunctions of the external ear pinna, external auditory canalFunctions:Collect sound wavesConduct sound wavesSound localizationResonant phenomenon
73 ⅠFunctions of the external ear Resonant phenomenonBy revibrating the sides and the end of the external auditory canal, sound is amplified. When sound waves arrive the eardrum, the intensity is increased almost 10 desibel (dB).
74 ⅡFunctions of the middle ear eardrum , ossicular chain, auditory tubeFunctions:Conduct sound wavesAmplify the sound pressureProtect auditory apparatus in the inner earEquilibrate the pressure
75 Conduct sound waves ⅡFunctions of the middle ear The eardrum vibrates as the same frequency as the sound waves conducted from thethe auditory canal.With the vibration of the eardrum, the ossicular chain moves forward and backward.
76 Amplify the sound pressure ⅡFunctions of the middle earAmplify the sound pressureOssicular chain--Three flexibly linked ossicles include malleus (hammer), incus (anvil) and stapes (stirrup) .The ossicles form a ‘lever’ which can conduct sound waves with high effectiveness when moving with vibration of the eardrum.
77 Amplify the sound pressure ⅡFunctions of the middle earAmplify the sound pressureThe sound force of per unit is increased when conducted from the eardrum to the oval window.The area of eardrum is17 times larger than thatof oval window and thelong arm of the ossiclesis 1.3 times longer thanthe short arm.Thus total amplificationis about 22 times.Oval window
78 Protect the apparatus in the inner ear ⅡFunctions of the middle earProtect the apparatus in the inner earThe amount of the energy transmitted to the inner ear is lessened reflexively by the contraction of two small skeletal muscles in the middle ear. This alter the intension of the eardrum and the position of the stapes in the oval window.The delicate receptorapparatus in the innerear is protected fromcontinuous intensesound stimuli.
79 Equalize the pressure on both sides of the eardrum ⅡFunctions of the middle earEqualize the pressure on both sides of the eardrumThe auditory tube which connects the middle ear to the nasopharynx helps to equalize the pressure on both sides of the eardrum.
80 Sound conduction to the inner ear canalMiddle ear cavityThe round windowAir conduction -- normally, main way of sound conduction.
81 Sound conduction to the inner ear Less sensitive than air conduction.Bone conduction plays very minor role in normal hearing.
82 Identify the causes of hearing loss: Conductive Hearing Loss is caused by pathologies in the eardrum or middle ear -- the sensitivity of air conduction is obviously lessened. While the bone conduction is still normal and eventually more sensitive than air conduction.Sensorineural Hearing Loss is caused by pathologies in the cochlea or the auditory nerve – the sensitivity of air conduction and bone conduction are both lessened.
83 Ⅲ Functions of the inner ear The inner ear is also called labyrinth ----a system of coiled, membranous tubes filled with fluid.cochlea for hearingvestibular apparatusfor equilibriumTransducer functionSound conduction
84 Structure of the cochlea Three coiled tubes side by side which are separated by two layers of membranes ----Scala vestibuli (filled with perilymph, connected with oval window )Scala media (filled with endolymph)Scala tympani (filled with perilymph, connected with round window)
85 The cross section of the cochlea (Reinssner’s membrane)
86 Transducer function of the cochlea 1. Vibration of basilar membrane
87 Waves in the fluid of the cochlea caused by movement of the stapes produce distortions of the basilar membrane.
88 Transducer function of the cochlea 1. Vibration of basilar membraneTraveling wave theory of sound
89 The region nearest to the middle ear vibrates most easily in response to high-frequency tones (undergoes the greatest movement).Progressively more distant regions of the basilar membrane vibrate maximally in response to progressively lower tones.
90 Transducer function of the cochlea 2. Excitation of hair cells and receptor P
91 Transducer function of the cochlea 2. Excitation of hair cells and receptor PVibration of basilar membraneBending of the stereocilia of the hair cells (receptors)K+ channel (mechanically gated ion channel) is openedInflux of K+ depolarizes the hair cellsReceptor P(Bending in the other direction hyperpolarizes the hair cells)
92 Transducer function of the cochlea 3. Receptor P of the hair cells to APReceptor P opens Ca2+ channel (voltage-gated, on the flank membrane of hair cells)Ca2+ influx triggers release of neurotransmitter (Glutamate)Glutamate binds to and activates protein binding sites on the terminals of the afferent neuronsAuditory cortex in the temporal lobeAuditory nerveAP
93 Special Sensory systems Section BSpecial Sensory systemsVestibular systemSomatic sensationPlease study by yourself.
94 Objectives You need to know the following content: Types of receptor The refractive system of the eyeThe structure characters of retinaInformation transforming in retinaColor blindnessBinocular vision and stereoscopic visionFunction of outer ear
95 Objectives You need to know well the following content: Color vision Light adaptation and dark adaptationVisual fieldVisual acuityFunctions of the middle ear
96 Objectives You need to hold the following content: The general properties of receptors: adequate stimulus, transducer function, encoding, and adaptationvisual accommodationPhototransduction of rodsAir conduction and bone conduction.Transducer function of the cochlea