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Sensory physiology Instructor: DU Jing Department of Physiology

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1 Sensory physiology Instructor: DU Jing Department of Physiology
Jining medical college Office: 0850 physiological sciences

2 Section A General Physiological Properties of Receptors
Sensory Receptors & Sensory Organs General physiological properties of receptors Section B Special Sensory systems Vision Hearing Vestibular system Somatic sensation

3 Introduction Sensation 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 A Receptors & Sensory Organs ⅠDefinition: 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 organs Sensory organ is the special organ that is composed of sensory receptor and its 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 A ⅡClassification of receptors Interoceptors Exteroceptors By location mechanoreceptors thermoreceptors noticeptors (pain receptors) electromagnetic receptors chemoreceptors By types of stimuli

7 General physiological properties of receptors
1. Adequate stimulus of receptor 2.Transducer function of receptor 3. Encoding of receptor 4. Adaptation of receptor

8 General physiological properties of receptors
Section A General physiological properties of receptors 1. 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 of wavelength to the photoreceptor cells in the retina; mechanical vibration at a specific rang of frequency to 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 A General physiological properties of receptors 2. Transducer function of receptor The 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 potential During 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 reflected by the magnitude, duration and direction of receptor potential.

14 Steps of sensation stimulus receptors (receptor potential →AP)
electrical information cerebral cortex Transducer function along afferent nerves (receptor potential →AP) sensation or perception

15 Mechanism of transducer function
Stimulus Receptor Through Second Messenger Ion channel (+) Change in ion fluxes across receptor membrane Receptor potential (a separate cell) (ending of afferent neuron) alters the release of neurotransmitter AP on afferent nerves EPSP/IPSP CNS

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 → AP Transducing of energy form Transformation of information

17 General physiological properties of receptors
Section A General physiological properties of receptors 3. 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 distinguished both by the frequency of AP generated on the afferent N and by the number of the fibers transporting the messages.

19

20 General physiological properties of receptors
Section A General physiological properties of receptors 4. Adaptation of receptor: Receptors have the ability to reduce the frequency of AP generated on the afferent neuron in spite of a sustained stimulus strength.

21 Classification according to adaptation:
Rapidly adapting receptor --important for the body to detect new stimuli eg. Touch and pressure receptors in the skin Slowly adapting receptor --important for monitoring the continuous functions of the body eg. Stretch receptors in muscles participating in maintaining posture

22 Section B Special Sensory systems Vision

23 Refractive system (optical portion) Cornea Aqueous humor Lens
Vitreous humor Structures in the eye involved in vision Retina (photoreceptive system) Photoreceptor cells (rods, cones) Bipolar cells Ganglion cells

24 Adequate stimulus: nm electromagnetic waves (visible wavelengths of light) Processes of vision: Formation of the image on the retina --refractive system Phototransduction by the photoreceptors --rods and cones Electrical signals is sent along the optic never to the visual cortex in the brain

25 Ⅰ Refractive function of the eye and accommodation
Vision Ⅰ Refractive function of the eye and accommodation

26 Ⅰ Refractive function of the eye and accommodation
Vision Ⅰ Refractive function of the eye and accommodation As in a camera, image is up-side down and inverted. The brain interprets this correctly.

27 Refractive structures of the eye
Cornea Aqueous humor Lens Vitreous humor (Outside to inside)

28 Refractive structures of the eye
fovea centralis optic nerve ← Viewed through an ophthalmoscope

29 Reduced eye Vision If 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 include shape changes of the lens diameter changes of the pupil convergence of two eyes Ability of lens accommodation: Near point of vision is the nearest distance distinguished by the eye.

32 Shape changes of the lens
Controlled by the zonular fibers and the ciliary muscle . Ciliary muscle Zonular fibers The periphery of the lens is joined to the ciliary muscle (circular like a sphincter) by the zonular fibers.

33 Shape changes of the lens

34 Shape changes of the lens
Near object Ciliary muscle contracts Lessens tension on zonular fibers Lens becomes more spherical Far object Ciliary muscle relaxes Increases tension on zonular fibers Lens 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 wear corrective glasses for close work.

37

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).

41 Concave lens Convex lens Cylindrical lens

42 Ⅱ Phototransduction of the retina
fovea centralis optic nerve

43 ⅡPhototransduction of the retina
Structure of the retina – four layers Pigment cells Photoreceptor cells Bipolar cells Ganglion cells outside →inside Back → front

44 ganglion cell

45 Structure of the photoreceptor cell
retinal opsin photopigment mitochondria nucleus Synaptic terminal Inner segment Stacked layers of membrane--discs lipid bilayer with proteins mosaiced in it

46 Comparison of rods and cones
more sensitive less sensitive highest density--6mm from the fovea centralis highest density--center of the fovea centralis, only cones more convergent connections to neurons more single connections to neurons one type (no color vision) three types (color vision)

47 a photopigment Photochemistry of vision
Chemical composition of photopigment an opsin (membrane protein binding to retinal) chromophore (retinal, derivative of Vit A) a photopigment four 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 retinal AP A unique character: hyperpolarized receptor potential

51 1. Hyperpolarized receptor potential
Inhibits release of neurotransmitter (glutamte) is depolarized Hyperpolarized receptor potential

52

53 (a) In light (b) In darkness

54 2. Information modification of the retina
Local potential on bipolar cells

55 Summarization

56 Visual pathways Optic nerve carries information to thalamus
Some processing edits information Visual cortex interprets information Creates visual image

57 phototransduction by the cones and color vision
Trichromatic theory (different)

58 Trichromatic theory

59

60 Color blindness It’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.

61 Ⅲ Some vision phenomena

62 2) Landolt arc Snellen map

63 3

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 fields Monocular 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.

66 Section B Special Sensory systems Hearing

67 Hearing 0.0002~1000 dyn/cm2 most sensitive: 1000~3000Hz

68 Hearing threshold and hearing range

69

70 Structure of the ear Middle ear cavity separated from external ear by eardrum and from internal ear by oval & round window Auditory tube leads to nasopharynx--helps to equalize pressure on both sides of eardrum Membranous labyrinth contains cochlea (organs of hearing) and vestibular apparatus (equilibrium)

71 Hearing Sound waves are conducted through the auditory canal and cause vibration of the eardrum Sound waves are conducted and amplified by moving of the ossicular chain in the middle ear Vibration 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 canal Functions: Collect sound waves Conduct sound waves Sound localization Resonant phenomenon

73 ⅠFunctions of the external ear
Resonant phenomenon By 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 tube Functions: Conduct sound waves Amplify the sound pressure Protect auditory apparatus in the inner ear Equilibrate the pressure

75 Conduct sound waves ⅡFunctions of the middle ear
The eardrum vibrates as the same frequency as the sound waves conducted from the the auditory canal. With the vibration of the eardrum, the ossicular chain moves forward and backward.

76 Amplify the sound pressure
ⅡFunctions of the middle ear Amplify the sound pressure Ossicular 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 ear Amplify the sound pressure The sound force of per unit is increased when conducted from the eardrum to the oval window. The area of eardrum is 17 times larger than that of oval window and the long arm of the ossicles is 1.3 times longer than the short arm. Thus total amplification is about 22 times. Oval window

78 Protect the apparatus in the inner ear
ⅡFunctions of the middle ear Protect the apparatus in the inner ear The 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 receptor apparatus in the inner ear is protected from continuous intense sound stimuli.

79 Equalize the pressure on both sides of the eardrum
ⅡFunctions of the middle ear Equalize the pressure on both sides of the eardrum The 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
canal Middle ear cavity The round window Air 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 hearing vestibular apparatus for equilibrium Transducer function Sound 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 membrane Traveling 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 P Vibration of basilar membrane Bending of the stereocilia of the hair cells (receptors) K+ channel (mechanically gated ion channel) is opened Influx of K+ depolarizes the hair cells Receptor P (Bending in the other direction hyperpolarizes the hair cells)

92 Transducer function of the cochlea
3. Receptor P of the hair cells to AP Receptor 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 neurons Auditory cortex in the temporal lobe Auditory nerve AP

93 Special Sensory systems
Section B Special Sensory systems Vestibular system Somatic sensation Please study by yourself.

94 Objectives You need to know the following content: Types of receptor
The refractive system of the eye The structure characters of retina Information transforming in retina Color blindness Binocular vision and stereoscopic vision Function of outer ear

95 Objectives You need to know well the following content: Color vision
Light adaptation and dark adaptation Visual field Visual acuity Functions of the middle ear

96 Objectives You need to hold the following content:
The general properties of receptors: adequate stimulus, transducer function, encoding, and adaptation visual accommodation Phototransduction of rods Air conduction and bone conduction. Transducer function of the cochlea

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103 optic nerve fovea centralis

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106 Diameter changes of the pupil

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109 Air conduction


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