Chapter 9 Function of the Sense Organs

1. Chapter 9 Function of the Sense Organs Song Jun & Wang Guoqing Department of Physiology, Medical School, Soochow University, Suzhou 215123, China E-mail:wangguoqing@suda.edu.cn Tel:0512-62096158; 13506212030

2. What will we discuss in this chapter?(Outline) Ⅰ. Receptor 1. concepts and classification 2. general properties of receptors Ⅱ. Visual Sense Organ 1. dioptric system 2. light perception and signal processing in the retina 3. vision related terminology Ⅲ. Hearing 1. external ear and middle ear 2. inner ear (cochlea) 3. AP in auditory nerve Ⅳ.Vestibular apparatus 1. receptor 2. adequate stimulus 3. vestibular reaction Ⅴ. Other receptors (sense of smell and sense of taste)

3. Introduction • Human life would be very different without the ability to sense and perceive external stimulus. • Imagine your world without the ability to see, hear, smell, touch, and feel……

4. Ⅰ. Receptor Which receptor?

5. ⒈ Concepts and Classification(1) Concepts • 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. • In a word: • A state of awareness of a stimulus. • A part of neuron or a specialized cell.

6. (2) Classification（A） • Location 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.

7. (2) Classification（B） • Modalities 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.

8. (2) Classification（C） • Complexity 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.

9. 2. General properties of receptors • Adequate stimulus of sensory receptors 感受器的适宜刺激 • Transducer function of sensory receptors 感受器的换能作用 • Encoding of sensory receptor 感受器的编码作用 • Adaptation of sensory receptor 感受器的适应现象

10. Summary • 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.

11. Ⅱ.Visual Sense Organ

12. 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.

13. ⒈ Dioptric system(1) Structure of the Eyeball

14. A slightly irregular hollow sphere with anterior and posterior poles; • The wall is composed of three tunics – fibrous, vascular, and sensory; • The internal cavity is filled with fluids called humors; • The lens separates the internal cavity into anterior and posterior segments. • Dioptric system:cornea, humors, lens, vitreous chamber.

15. (2) Reduced eye * • Reduced eye is an artificial model. • Calculation of image: Optical Parameter: anteroposterior diameter: 20 mm refractive index : 1.333 radius of curvature : 5 mm AB ab ＝ Bn nb

16. (3) Accommodation of eye * • Accommodation of lens • near point: 人眼作最大调节能看清物体的最近距离 • far point: 人眼不作任何调节时所能看清的物体的最远距离 • Pupillary reflex • Decrease size of pupils (parasympathetic) prevents divergent light rays from entering • near reflex of the pupil(瞳孔近反射) • pupillary light reflex(瞳孔对光反射) • 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.

17. (4) Error of refraction * • Error of refraction :Caused by shape of eye and/or power of lens • Myopia • Hyperopia • Astigmatism • Presbyopia (老视) • Definition:The crystalline lens tends to harden and the capsule itself becomes less elastic with age • Treatment ：convex lens

18. Emmetropia Myopia Hyperopia Astigmatism Ametropia and Correction

19. ⒉ Light perception and signal processing in the retina（ 1） Structure of Retina From outside to inside: Pigment cell Photosensory cell Bipolar cell Ganglion cell rods cones

20. (2) Photosensory cell (A) • The photoreceptor cells are two types, rod cells (rods) and cone cells (cones)

21. (2) Photosensory cell (B) • The outer segment of a rod cell has a rod-like appearance, whereas that of a cone cell has a cone-shaped appearance. • The outer segments of the photoreceptor cell contain stacks of membranous discs. • The visual pigments appear to be built into the disc membranes.

22. (2) Photosensory cell (C) • Distribution of the cones and rods on the retina.

23. (2) Photosensory cell (D) • Characteristics • Cones see detail but require bright light • Rods see in low light but lack detail

24. Comparison rods cones • located mainly in fovea; • work best in bright light; • enable us to see fine detail; • responsible for color vision; • each cone has its own bipolar and ganglion cell; • this allows us to see detail but bright light is needed. • located mainly in periphery of retina; • responsible for night vision; • detail not detected; • see black, white, and gray (no color); • several rods share 1 bipolar and 1 ganglion cell; • rod vision lacks detail, but, by combining their efforts, groups of rods allow us to see in low light.

25. cones multicolor rods Black and white

26. (3) Two types of retinal transduction systems • Other evidence that two photoreceptor system of retina exit. • The nocturnal animals have a preponderance of rods, whereas the diurnal animals have a preponderance of cones in their retina. • 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.

27. (4) General transduction mechanism of rods • Photopigments are located in the membrane of the outer segment of rods and cones; • Each pigment consists of an opsin (a protein) and retinal (a lipid); • In the dark, membrane Na+ channels are open -> glutamate is released which depolarizes the membrane • Light splits the opsin and retinal apart-> • Activates transduction (G protein)-> • Activates phosphodiesterase-> • Reduces cGMP -> closes Na+ channels • The net effect of light is to hyperpolarize the retinal receptor and reduce the release of glutamate.

29. Rhodopsin Cycle

30. Rod Cell Hyperpolarization

32. (5) Color Vision

33. Trichromatic Theory of Color Vision（三原色学说） Light of a single wavelength

34. Visible spectrum: 380-760 nm(nm is a billionth of a meter)

35. 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 color； • For Visual System:set of interest is “Red Green and Blue”. Young Helmholtz

36. Color Sensitivity of Different Cones

37. Color Blindness • Sex-linked conditions: genes on X chromosome, so more common in men. • Protanopia (红色盲), missing red photopigment; • Deuteranopia (绿色盲), missing green photopigment; • Non-sex-linked condition: • Tritanopia (蓝色盲), missing blue photopigment or blue cones • Monochromats (全色盲): people who are totally colorblind, more severe.

38. Color Vision Systems Tritanopia deuteranopia protanopia

39. Blind point (盲点) :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.

40. 3. Vision related terminology • Visual acuity （视敏度） • Visual field （视 野） • Dark adaptation （暗适应） • Light adaptation （明适应） • After image （视后像） • Fusion phenomenon （融合现象） • Stereopsis （立体视觉）

41. Visual Acuity • Visual acuityis 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 : 两点光源入眼，通过节点交叉后，直接到达视网膜，在节点交叉所成的角。 • Visual chart

42. Dark Adaptation and Light Adaptation • Dark adaptation (暗适应) • 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. • Mechanism：与感光色素在暗处再合成有关 • 第一阶段：视锥细胞的感光色素合成量增加 • 第二阶段：视杆细胞中视紫红质的合成增加 • Light adaptation (明适应) • 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 seconds. • Mechanism：暗处合成的大量视紫红质在进入亮处迅速分解。

43. 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:鼻侧与上侧，wide:颞侧与下侧 • After image • 持续时间与光刺激的强度有关。 • Fusion phenomenon • 是由于闪光的间歇时间比视后像的时间更短所产生的。 • Binocular vision • 可弥补单眼视野中的盲区缺损，扩大视野，并产生立体视觉。 • Stereopsis • 同一物体在左右视网膜上成的像并不完全相同。

44. O Ⅲ、Hearing

45. Hearing Threshold(听阈) • Hearing thresholdis the lowest intensity that the faintest sound could be heard. • Maximum hearing threshold(最大可听阈) • 当强度增加到某一限度，它引起的将不单是听觉，同时还会引起鼓膜的疼痛，这个限度称为最大可听阈。 • Audible area(听域) • 听阈与最大可听阈所包含的面积。

46. 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.

47. pitch frequency （Hz） loudness amplitude（dB）

48. Loudness of Sound • 0 dB = hearing threshold • 50 dB = normal conversation • 90 dB = danger zone • 120 dB = rock concert • 130 dB = pain threshold

49. ⒈ External ear and middle ear

50. External ear