How Animals Sense their Environment: Senses, Receptors, and Perception

1. Figure 38-3 A myelinated axon An action potential jumpsfrom node to node, greatlyspeeding up conductiondown the axon myelin-producingglial cell node myelin myelinsheath axon axon

2. 【跳跃式传导】有髓神经的轴突外包裹有多层高度绝缘的髓鞘，且并非连续而是分段的，所以造成其膜电阻的不均匀。在郎飞氏结之间的结间区电阻极高，而结区电阻极低，加之轴突膜仅仅在结区可接触细胞外液，局部电流必须在郎飞氏结处穿出膜在髓鞘处形成回路，进行跳跃式传导，这就是所谓的跳跃传导学说。【跳跃式传导】有髓神经的轴突外包裹有多层高度绝缘的髓鞘，且并非连续而是分段的，所以造成其膜电阻的不均匀。在郎飞氏结之间的结间区电阻极高，而结区电阻极低，加之轴突膜仅仅在结区可接触细胞外液，局部电流必须在郎飞氏结处穿出膜在髓鞘处形成回路，进行跳跃式传导，这就是所谓的跳跃传导学说。

3. 39 The Senses 0

4. Chapter 39 At a Glance • 39.1 How Do Animals Sense Their Environment? • 39.2 How Are Mechanical Stimuli Detected? • 39.3 How Is Sound Detected? • 39.4 How Are Gravity and Movement Detected? • 39.5 How Is Light Perceived 感觉? • 39.6 How Are Chemicals Sensed? • 39.7 How Is Pain Perceived?

5. 39.1 How Do Animals Sense Their Environment? • All sensory perception 知觉 begins with a receptor感受器 ; a molecule, cell, or multicellular structure that produces a response when it is acted on by a stimulus • Every cell has many types of receptor molecules that bind hormones and trigger responses in the cell

6. 39.1 How Do Animals Sense Their Environment? • A sensory receptor 感觉感受器 is a specialized cell that produces an electrical signal in response to specific stimuli • The sensory receptor translates environmental stimuli into the language of the nervous system • Sensory receptors are grouped into categories according to the stimulus to which they respond

7. Table 39-1 Principal Categories of Vertebrate Sensory Receptors 游离神经末梢 温度感受器 毛细胞 机械刺激感受器 光感受器 视网膜 化学感应器 嗅觉感受器

8. 39.1 How Do Animals Sense Their Environment? • The senses inform the brain about the nature and intensity of environmental stimuli • Determining the nature of stimulus light, sound, odor, or touch begins with sensory receptor cells, each of which contains receptor molecules that respond to certain stimuli and not others • Each type of sensory receptor is linked to a specific set of axons that connect to particular places in the brain or spinal cord

9. 39.1 How Do Animals Sense Their Environment? • The senses inform the brain about the nature and intensity of environmental stimuli (continued) • Electrical activity in specific regions of the brain is then interpreted as a specific form of sensory perception 感官知觉 • In mammals, neurons that detect odors send axons to a part of the brain called the olfactory bulb 嗅球 • The activity of specific sets of neurons in the olfactory bulb results in the perception of specific odors, such as coffee or roses

10. 39.1 How Do Animals Sense Their Environment? • The senses inform the brain about the nature and intensity of environmental stimuli (continued) • Determining the intensity of a stimulus—loud versus soft sound, for instance—begins with sensory receptor cells • When a sensory receptor is stimulated, it produces an electrical signal called a receptor potential感受器电位 • The receptor potential may bring the neuron above threshold and trigger action potentials • The axons of these sensory receptor neurons often connect directly with the central nervous system (CNS)

11. Figure 39-1 Converting an environmental stimulus to action potentials 80 actionpotentials 40 Stimulus on Stimulus off 0 potential(millivolts) threshold restingpotential 40 receptorpotential 80 time

12. 39.1 How Do Animals Sense Their Environment? • The senses inform the brain about the nature and intensity of environmental stimuli (continued) • Unlike action potentials that are always the same size, receptor potentials vary in size with the intensity of a stimulus: The stronger the stimulus, the larger the receptor potential • A small receptor potential may barely reach threshold and will produce only one or two action potentials, but a large receptor potential will go far above threshold, causing a high frequency of action potentials

13. Figure 39-2 Stimulus intensity is encoded by the frequency of action potentials 80 40 A weak stimulusproduces a smallreceptor potentialthat reaches justabove thresholdand triggersonly a few actionpotentials 0 potential (millivolts) 40 threshold 80 time Weak stimulus 80 A strong stimulusproduces a largereceptor potentialthat reaches farabove thresholdand triggersmany actionpotentials 40 potential (millivolts) 40 threshold 80 time Strong stimulus

14. 39.1 How Do Animals Sense Their Environment? • The senses inform the brain about the nature and intensity of environmental stimuli (continued) • Some sensory receptors, such as those in the inner ear, do not have axons, but instead, form synapses with neurons whose axons connect with the CNS • Receptor potentials in this type of sensory receptor cause neurotransmitters to be released onto a neuron, ultimately stimulating action potentials that can move down the neuron’s axon to the CNS

15. 39.2 How Are Mechanical Stimuli Detected? • Mechanoreceptors机械感受器 are found throughout the human body and include • Receptors in the skin that respond to touch, vibration, or pressure • Stretch 伸展 receptors in many internal organs 内脏, including the intestines 肠, stomach, urinary bladder 膀胱 , and muscles • Receptors in the inner ear that respond to sound, gravity, or movement

16. 39.2 How Are Mechanical Stimuli Detected? • Embedded in the human skin are the endings of several types of mechanoreceptor neurons, which produce receptor potentials when their membranes are stretched or dimpled • The free nerve endings of some touch receptors produce sensations 感觉 of touch, itching瘙痒, or tickling • The endings of other receptors are enclosed in accessory structures • For example, Pacinian corpuscles 环层小体, which respond to changes in pressure such as a sharp poke

17. 39.2 How Are Mechanical Stimuli Detected? • The endings of other receptors are enclosed in accessory structures (continued) • Meissner’s corpuscles 梅斯纳氏小体 respond to light touch or slow vibrations • Ruffini corpuscles 鲁菲尼小体 respond to steady pressure • The density of mechanoreceptors in the skin varies tremendously over the surface of the body • Each square inch of fingertip 指尖, for example, has hundreds of touch receptors, but on the back, there may be less than one per square inch

18. 39.2 How Are Mechanical Stimuli Detected? • Mechanoreceptors in many hollow 空的 organs, such as the stomach and urinary bladder, signal fullness by responding to stretch • Mechanoreceptors in the joints, also responding to stretch, let us know whether the joints are straight or bent, and by how much • Stretch receptors in muscles tell the brain if the muscle is contracted or stretched, and by how much

19. 39.2 How Are Mechanical Stimuli Detected? • Joint and muscle receptors combine to inform the brain of the position, angle, and force of movement of arms, legs, hands, and feet • Mechanoreceptors are important to all animals • Spiders, for example, use mechanoreceptors in their legs to detect vibrations of their webs • Fish have mechanoreceptors in organs called lateral lines 体侧线, which detect movement and vibration of water around them

20. 39.3 How Is Sound Detected? • The mammalian ear performs two very different functions 1. Perceiving 察觉 sounds and determining direction of gravity 重力的方向 2. The orientation 方向 and movement of the head, information that is used to control balance and body posture 身体姿式

21. 39.3 How Is Sound Detected? • The ear converts sound waves into electrical signals • Sound is produced by vibrating objects—drums, vocal cords 声带, or the speakers 扬声器 in your cell phone • Our ears convert the resulting sound waves into electrical signals that our brains interpret as the direction, pitch 音高, and loudness of a sound • The ears of humans and other mammals consist of three parts: the outer, middle, and inner ear

22. 39.3 How Is Sound Detected? • The ear converts sound waves into electrical signals (continued) • The outer ear consists of the pinna and the auditory canal • The pinna耳廓 is a flap of skin-covered cartilage 软骨结构 attached to the surface of the head; it collects sound waves • The auditory canal耳道 conducts the sound waves from the pinna to the middle ear

23. 39.3 How Is Sound Detected? • The ear converts sound waves into electrical signals (continued) • The middle ear consists of the tympanic membrane 鼓膜, or eardrum; three tiny bones called the hammer锤骨(malleus), anvil砧骨(incus) , and stirrup镫骨(stapes); and the auditory tube 耳咽管(Eustacian tube) • The auditory tube connects the middle ear to the pharynx 咽 and equalizes the air pressure between the middle ear and the atmosphere

24. 39.3 How Is Sound Detected? • The ear converts sound waves into electrical signals (continued) • Sound waves traveling down the auditory canal vibrate the tympanic membrane, which in turn moves the hammer, the anvil, and the stirrup • These small bones transmit vibrations to the inner ear

25. 39.3 How Is Sound Detected? • The ear converts sound waves into electrical signals (continued) • The fluid-filled hollow bones of the inner ear form a spiral-shaped 螺旋形 tube called the cochlea 耳蜗 • The stirrup bone transmits sound waves to the fluid within the cochlea by vibrating the oval window 卵圆窗, a flexible membrane covering the opening at the beginning of the cochlea • A second membrane, the round window 圆窗, covers an opening at the far end of the cochlea

26. 39.3 How Is Sound Detected? • The ear converts sound waves into electrical signals (continued) • Sound waves cause the oval window and round window to move in opposite directions • When the crest of the sound wave pushes the oval window inward, the fluid in the cochlea causes the round window to bulge outward 向外膨胀 • When the trough of the sound wave pulls the oval window outward, the round window flexes inward

27. 39.3 How Is Sound Detected? • Vibrations are converted into electrical signals in the cochlea • The cochlea consists of three fluid-filled compartments 分隔 • The central compartment houses the receptors and the supporting structures that activate them in response to sound vibrations • The floor of this central chamber is the basilar membrane 基底膜, on top of which sit mechanoreceptors 机械感受器 called hair cells

28. 39.3 How Is Sound Detected? • Vibrations are converted into electrical signals in the cochlea (continued) • Hair cells have cell bodies topped by hairlike projections that resemble stiff cilia 纤毛 • Some of these hairs are embedded 埋入 in a gelatinous 胶状的 structure called the tectorial membrane 耳蜗,覆膜 • As the fluid in the cochlea moves back and forth in synchrony with 同步 incoming sound waves, it moves the basilar membrane relative to the tectorial membrane • Movement of the membranes bends the hairs

29. 39.3 How Is Sound Detected? • Vibrations are converted into electrical signals in the cochlea (continued) • This movement bends the hairs of the hair cells, producing receptor potentials that induce the hair cells to release neurotransmitters onto neurons whose axons form the auditory nerve听觉神经 • The auditory nerve axons produce action potentials that travel to the auditory centers of the brain

30. 39.3 How Is Sound Detected? • Vibrations are converted into electrical signals in the cochlea (continued) • How do the structures of the inner ear allow us to perceive loudness and pitch? • Soft sounds cause small vibrations of the tympanic membrane, the bones of the middle ear, the oval window, and the basilar membrane, bending the hairs on hair cells only a little, producing a small receptor potential

31. 39.3 How Is Sound Detected? • Vibrations are converted into electrical signals in the cochlea (continued) • The small receptor potential causes the release of a tiny bit of neurotransmitter and results in a low frequency of action potentials in axons of the auditory nerve • Loud sounds cause large vibrations, which cause greater bending of the hairs and a larger receptor potential, producing a high rate of action potentials in the auditory nerve • Very loud sounds can damage the hair cells, resulting in hearing loss

32. 39.3 How Is Sound Detected? • Vibrations are converted into electrical signals in the cochlea (continued) • The perception of pitch is a little more complex • The basilar membrane is narrow and stiff 坚硬的at the end near the oval window, wider and more flexible near the tip 末梢 of the cochlea

33. 39.3 How Is Sound Detected? • Vibrations are converted into electrical signals in the cochlea (continued) • The perception of pitch is a little more complex (continued) • This progressive change in width and stiffness causes each portion of the membrane to vibrate most strongly when stimulated by a particular frequency of sound • High notes near the oval window • Low notes near the tip of the cochlea

34. 39.3 How Is Sound Detected? • Vibrations are converted into electrical signals in the cochlea (continued) • The brain interprets signals originating in hair cells near the oval window as high-pitched sound, whereas signals from hair cells located progressively closer to the tip of the cochlea are interpreted as increasingly lower in pitch • Young people with undamaged cochleas can hear sounds from a very low bass 低音 to a very, very high treble 高音

35. Animation: The Human Ear

36. 39.4 How Are Gravity and Movement Detected? • The inner ear contains structures, collectively called the vestibular apparatus 前庭器官, that detect gravity and the orientation and movement of the head • The vestibular apparatus is a fluid-filled tube embedded in the bones of the skull, consisting of the vestibule 前庭 and the semicircular canals 半规管 • The vestibule contains the utricle 椭圆囊 and saccule 球囊 , which detect the direction of gravity and the orientation of the head

37. 39.4 How Are Gravity and Movement Detected? • The hairs in the utricle are vertical 垂直的, whereas those in the saccule are horizontal 水平的 • Gravity pulls tiny stones of calcium carbonate 碳酸钙embedded on the hairs downward, causing the hairs to bend in various directions, depending on the tilt 倾斜 of the head • People can detect about a half-degree tilt

38. 39.4 How Are Gravity and Movement Detected? • Beyond the vestibule are three semicircular canals that detect head movement • Each semicircular canal consists of a fluid-filled tube with a bulge 凸出 at one end called an ampulla壶腹 • Hair cells sit inside each ampulla, with their hairs embedded in a gelatinous capsule 壶腹帽 • Acceleration of the head pushes the fluid against the capsule, bending the hairs

39. 39.4 How Are Gravity and Movement Detected? • The three semicircular canals are arranged perpendicular 垂直的 to each other, allowing you to detect head movement in any direction • Axons from the auditory nerve innervate the hair cells of the vestibular apparatus • When the hairs bend, the hair cells release neurotransmitter onto the endings of these axons, triggering action potentials in the axons that travel to balance and equilibrium centers in the brain

40. 39.5 How Is Light Perceived? • The vast majority of animals can detect light • Some, such as flatworms and jellyfish水母, can distinguish light from dark, but their eyespots 眼点 cannot form an image • In all animals, regardless of the sophistication of their eyes, vision begins with cells called photoreceptors光受体 • These cells contain photopigments 光色素 , receptor molecules that change shape when they absorb light

41. 39.5 How Is Light Perceived? • The compound eyes of arthropods 节肢动物 produce a mosaic image • Many arthropods, including insects and crustaceans甲壳纲动物, have compound eyes 复眼, which consist of a mosaic of many individual light-sensitive subunits called ommatidia 小眼 • Each ommatidium functions as an individual light detector, like the pixels 像素 in a digital camera • The best arthropod eyes—in dragonflies, for example—contain only about 30,000 ommatidia

42. 39.5 How Is Light Perceived? • The compound eyes of arthropods produce a mosaic image (continued) • A human eye, in contrast, contains more than 100 million photoreceptors • By human standards, the image formed by a compound eye is very pixilated 看不清, like an extremely low-resolution digital image that has been enlarged too much • Compound eyes are excellent at detecting movement, as light and shadow flicker 闪烁 across adjacent ommatidia

43. Figure 39-8 An insect’s view of the world A tropical orchid The same orchid as seen by abee

44. 39.5 How Is Light Perceived? • The mammalian eye collects and focuses light and converts light into electrical signals • A mammalian eye is built something like a camera and consists of two major modules 1. Accessory structures that hold the eye in a fairly fixed shape, control the amount of light that enters, and focus the light rays 2. The retina 视网膜, which contains the photoreceptors that respond to the incoming light

45. 39.5 How Is Light Perceived? • The mammalian eye collects and focuses light and converts light into electrical signals (continued) • The eyeball is surrounded by the sclera 巩膜, a tough connective tissue layer visible as the white of the eye and continuous with the transparent cornea眼角膜 at the front • Light enters the eye through the cornea • The light then travels through a chamber filled with a watery fluid called aqueous humor 眼房水, which provides nourishment for the cells of both the lens 水晶体 and cornea

46. 39.5 How Is Light Perceived? • The mammalian eye collects and focuses light and converts light into electrical signals (continued) • The light continues through the pupil 瞳孔, a circular opening in the center of the colored iris 虹膜 • Contraction and relaxation of the muscles of the iris regulate the size of the pupil and the amount of light entering the rest of the eye • Light next encounters the lens 水晶体, a structure composed of transparent proteins and shaped like a flattened sphere

47. 39.5 How Is Light Perceived? • The mammalian eye collects and focuses light and converts light into electrical signals (continued) • Behind the lens is a large chamber filled with vitreous humor 玻璃状液, a clear jelly-like substance that helps maintain the shape of the eyeball • After passing through the vitreous humor, light hits the retina 视网膜 • Here light is converted into action potentials that are conducted to the brain

48. 39.5 How Is Light Perceived? • The mammalian eye collects and focuses light and converts light into electrical signals (continued) • Behind the retina is the choroid 脉络膜 • The choroid’s rich blood supply helps nourish the cells of the retina • In people, the choroid is darkly pigmented • It absorbs stray light 杂散光, preventing the light from bouncing around inside the eyeball and interfering with sharp vision

49. 39.5 How Is Light Perceived? • The mammalian eye collects and focuses light and converts light into electrical signals (continued) • The lens focuses light on the retina • Light coming from an object is focused most sharply on a small area of the retina called the fovea视网膜的中央凹 • If your eyeball is too long or your cornea is too rounded, you will be nearsighted—light from distant objects will focus in front of the retina, so you will not see them clearly

50. 39.5 How Is Light Perceived? • The mammalian eye collects and focuses light and converts light into electrical signals (continued) • The lens focuses light on the retina (continued) • Farsighted people have eyeballs that are too short or corneas that are too flat and focus light behind the retina • Both of these conditions can be corrected by either contact lenses or glasses of the appropriate shape • Both of these conditions can also be corrected with laser surgery that reshapes the cornea