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Review of Chapter 11

Review of Chapter 11

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Review of Chapter 11

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  1. Review of Chapter 11

  2. Chapter 12: Sensory Reception Section 12.1 Sensory Receptors and Sensation

  3. Your senses of sight, hearing, taste, smell, and touch keep you informed about the external environment so that you can respond to it. • The senses transmit sensory information, in the form of electrochemical nerve impulses, to the brain. • The nerve endings and cells that detect sensory information are called sensory receptors. • Sensation occurs when the neural impulses arrive at the cerebral cortex and are processed. • Each person processes theses impulses differently leading to each person’s unique perception.

  4. A. Sensory Adaptation • A massive amount of sensory information is brought to your brain every second. Your brain filters out redundant information and this is called sensory adaptation. • In order to process all of the incoming information quickly, the brain parallels or splits up the input to various parts of the brain to process. • Sometimes the sensory information is misinterpreted or not integrated precisely and we perceive differently than we actually had sensed. Ex. Optical Illusions


  6. B. Sensory Receptors • Sensory receptors are specialized cells or neuron endings that detect specific stimuli. • Humans have four categories of sensory receptors:

  7. Photoreceptors • Light energy stimulates the photoreceptors in our eyes called rods and cones. These allow us to sense different levels of light and shades of colour.

  8. Chemoreceptors • Certain chemicals stimulate chemoreceptors in the tongue (taste buds), in the nose (olfactory cells that detect odours), and in other places in the body to detect things like blood pH.

  9. Mechanoreceptors • Mechanoreceptors respond to a physical form of pressure. Hair cells in the inner ear are activated when sound waves cause them to vibrate allowing you to hear. Other hair cells are stimulated when they bend giving you information needed for balance. Mechanoreceptors in your skin allow the body to detect touch, pressure, and pain.

  10. Thermoreceptors • Thermoreceptors in the skin detect heat and cold. • Damage to sensory receptors lead to loss of the associated sense even if the rest of the sense organ and nervous system are fully functional.

  11. Chapter 12: Sensory Reception Section 12.2 Photoreception

  12. A. The Human Eye In people that can see, vision supplies 80 to 90 percent of the important sensory information reaching the brain. The human eye is a fluid-filled ball measuring 2.5 cm in diameter that focusses incoming light energy on the photoreceptors of the retina. The eye has three layers that have different tissues and functions:

  13. 1. External • The external layer of the eye is white, tough, and fibrous and it protects the eye. • It is called the sclera. • Light enters the eye through the cornea which is the transparent part of the sclera at the front of the eye.

  14. 2. Intermediate • The intermediate layer of the eye is called the choroid. • The choroid absorbs stray light rays that are not detected by the photoreceptors. It also contains blood vessels that nourish the eye. • At the front of the choroid is a doughnut-shaped muscle called the iris which allows light to enter the inner eye by adjusting the size of the opening of the eye. This adjustment process is called adaptation. • The dark opening within the iris is called the pupil and it is where the light enters the inner eye. • Behind the iris is the ciliary muscle which is attached to the lens, which focuses images on the retina.

  15. 3. Internal • The internal layer of the eye is the retina, which is a thin layer that contains the photoreceptors. • The photoreceptors are called the rods and the cones. • The rods are sensitive to light intensity or brightness • The cones are sensitive to different colours. They are packed most densely at the back of the eye in an area called the fovea centralis which allows for acute vision. • The rods and cones convert the light energy into nerve impulses that are sent to the brain via the optic nerve.

  16. The Humours • There is also fluid within the eye to help it maintain its shape. The lens and the attached ciliary muscles divide the eye into two chambers: • The anterior chamber is in front of the lens. It is filled with a clear, watery fluid called the aqueous humour. • The aqueous humour provides oxygen and nutrients for the lens and cornea. A small amount is produced every day and drained. If the drainage ducts become plugged pressure can build up and the blood vessels could rupture causing the eye cells to deteriorate because of lack of oxygen and nutrients leading to glaucoma which could cause blindness. • The posterior chamber, behind the lens and surrounded by the retina, contains the vitreous humour which helps maintain the shape of the eyeball.

  17. B. Focussing • Light rays bend as they pass through the lens in order to focus the light in a particular direction. • After light rays are bent by the rigid cornea, flexible lens, and fluid humours, the resultant image on the retina is smaller, upside down, and reversed from left to right.

  18. Because the lens is flexible it can account for seeing things at short and far distances. The ability of the lens to change shape in order to focus images clearly on the retina is called accommodation. • If an object is far away, the ciliary muscles relax so that the suspensory ligaments become tight so that the lens flattens. • If the object is nearby, the ciliary muscles contract so the suspensory ligaments relax and the lens is more rounded

  19. C. Conditions Affecting the Cornea and Lens • As the lens ages, proteins within it begin to degenerate and it becomes opaque, preventing light to pass through it. This leads to grey-white spots or cataracts in someone’s vision which can be corrected by replacing the lens in a cataract surgery.

  20. Astigmatism occurs naturally in many people if there is an uneven curvature of part of the cornea. This prevents the cornea from being able to bend light rays so that they meet at the correct focal point causing blurry vision.

  21. Some people have an elongated eyeball so that the focussed light falls in front of the retina. This condition is called myopia or nearsightedness since they can see close objects but not far objects. This condition can be corrected by wearing concave lenses that diverge incoming light rays.

  22. Some people have short eyeballs that cause the light rays to not focus before they reach the retina so they can see farther distances but not up close. This condition is called hyperopia or farsightedness. This can be corrected using convex lenses that converge light rays. • Summary of Conditions

  23. D. The Photoreceptors: The Rods and Cones • The human retina contains about 125 million rods and 6 million cones. • The rods are very sensitive to light and are stimulated by a single photon of light. They distinguish degrees of black and white but not colour. • Rods detect motion and are responsible for our peripheral vision. • They are spread out throughout the retina but are more concentrated in the outside edges.

  24. The cones are colour-detecting sensors. • They are most concentrated at the fovea centralis at the back and centre of the retina. • Cones require intense light to stimulate them so the structure of the eye focusses light onto the fovea centralis in order to produce a sharp image. • In addition to allowing us to see in colour, the cones allow for high-acuity tasks such as reading.

  25. There are three types of cones that can detect red, blue, and green wavelengths of light. The combination of these cones being activated allows us to see the range of colours. • Colour blindness is caused by a lack of or a deficiency in particular cones, usually red and green cones. This causes difficulty for a person to distinguish between these colours.

  26. The rods contain a light-absorbing pigment called rhodopsin, which is composed of retinal (from Vitamin A) and the protein opsin. In the dark, rods emit an inhibitory neurotransmitter that inhibits nearby nerve cells. When the rod absorbs light, the rhodopsin splits into retinal and opsin which triggers a reaction that stops the release of the inhibitory neurotransmitter, thus allowing a neural impulse to the optic nerve. • A similar process happens in the cones except the pigment is photopsin, which reacts only to certain wavelengths of light. • Once the rods and cones have stopped releasing the inhibitory neurotransmitter, the bipolar cells then transfer a neural impulse to the ganglion cells. • The axons of the ganglion cells form the optic nerve. Optic nerve fibres transmit visual images to the occipital lobe of the brain.

  27. E. Visual Interpretation • Where the ganglion cells merge to form the optic nerve is called the blind spot since it does not contain any photoreceptors so it cannot detect light. Our other eye usually compensates for the visual information that the blind spot misses so we do not notice it. • The visual information travels from the optic nerve to the thalamus and then to the occipital lobe of the cerebral cortex for interpretation. • The left optic tract carries information about the right portion of the visual field, and the right optic tract carries information about the left visual field. • In the cerebrum, the various pieces of visual information are processed and integrated so we can perceive the upright image.

  28. Humans have forward-facing eyes, called binocular vision, which allows us to perceive depth and three-dimensional images. • Movement, colour, depth, and shape all are handled simultaneously in different areas of the occipital lobe to speed up processing.

  29. F. Preventing Vision Loss • Two of the most frequent causes of vision loss are glaucoma and cataracts. • The leading cause is retinal disorders including: • Diabetic retinopathy causes capillaries to the retina to burst so that blood enters the vitreous fluid. Careful regulation of blood glucose levels can guard against this.

  30. Changes in the consistency of the vitreous fluid can cause retinal detachment where the retina is pulled away from the choroid vessels that supply it with nutrients and oxygen. This is caused by an inflammatory disorder, advanced diabetes, or trauma to the eye.

  31. Macular degeneration occurs when the cones are destroyed due to thickened choroid vessels. This causes blurred vision or a blind spot in central vision. Age is the principal factor in developing this but other factors include cigarette smoking, obesity and exposure to sunlight. Exercise, not smoking, and a diet rich in green leafy vegetables and fish can help prevent this.

  32. Chapter 12: Sensory Reception Section 12.3 Mechanoreceptors and Chemoreceptors

  33. A. Hearing and Balance • Capturing Sound • Sound causes particles around the source to vibrate and move. The auditory system (sense of hearing) detects this movement as small fluctuations in air pressure, called sound waves. • Mechanoreceptors in the inner ear convert the energy of sound waves into the electrochemical energy that the brain perceives as sound.

  34. The ear can be divided into three main divisions which each collect and direct auditory information to the hearing receptors: • The outer ear: • The pinna is the outside flap of the ear, made of skin and cartilage that is shaped in a way that enhances sound vibrations and focusses them into the ear. • The auditory canal is a 2.5 cm long tube that leads to the eardrum and middle ear. It amplifies sound waves, making sounds louder. Hair and earwax prevent foreign material from getting deeper into the ear and causing damage.

  35. The middle ear: • It is an air filled space bordered on one side by the tympanum (eardrum or tympanic membrane). The tympanum vibrates in response to sound waves. • These vibrations are passed on and amplified by the neighbouring ossicles: three tiny, interconnected bones. Each bone acts as a lever for the next so the movement is amplified as they pass from the malleus (hammer) to the incus (anvil) to the stapes (stirrup). The stapes concentrates vibrations into the membrane-covered opening in the wall of the inner ear – the oval window. • The middle ear is connected to the throat by the Eustachian tube. This tube allows air pressure to equalize when there is a difference in air pressure within and outside ear.

  36. The inner ear consists of three interconnecting structures: • The semicircular canals and vestibule contain sensors for balance. • The cochlea (Latin for “snail”) contains the structures that convert sound energy into electrochemical impulses that are transmitted to the brain.

  37. The middle chamber of the cochlea contains the organ of Corti which is the organ of hearing. • Along the base of the organ of Corti is the basilar membrane which the sensory mechanoreceptors known as hair cells are attached. • The hair cells have thin projections called stereocilia which stick out at the top of the cells. The far ends are embedded within the tectorial membrane.

  38. The stapes strike the oval window, which vibrates the window and creates pressure waves in the fluid of the cochlea. The pressure waves make the basilar membrane move up and down, which causes the stereocilia of the hair cells to bend against the tectorial membrane. The hair cells sense this bending and relay the message to the nerves which carry an impulse to the brain.

  39. B. Frequencies of Sound • The hair cells of the organ of Corti are able to distinguish both the frequency (pitch) and the amplitude (intensity) of sound waves. • Humans can hear sounds that are between 20 and 20000 Hz • Different areas of the organ of Corti are sensitive to different frequencies. High frequencies strongly stimulate the hair cells closest to the oval window and low frequencies strongly stimulate the hair cells farthest from the oval window.

  40. C. Hearing Loss • Hearing loss generally results from nerve damage (damage to the hair cells) or damage to the sound-conduction system of the outer or middle ear. • The louder the noise is, the more pressure that the fluid in the cochlea puts on the hair cells of the basilar membrane. • The stereocilia of the hair cells are delicate and repeated or sustained exposure to loud noise destroys the stereocilia, resulting in permanent hearing loss. • Any noise over 80 dB can damage hair cells. • Nerve deafness is more difficult to treat but some devices are available to be implanted to directly relay signals to the auditory nerve or to regenerate damaged or lost hair cells.

  41. D. The Perception of Sound • Sensory neurons in the ear send information through the auditory nerve to the thalamus and then to the temporal lobes of the cerebrum for processing.

  42. E. Balance and Coordination • Three major structures in the inner ear help us stand upright and move without losing our balance. • The semicircular canals: • They contain mechanoreceptors that detect head and body rotation (rotational equilibrium). • They are three fluid-filled loops arranged in three planes for each dimension of space (left-right, up-down, forward-backward). • When the head rotates, the stereocilia of the hair cells are bent by the pressure that the fluid provides sending rotational information to the brain.

  43. The utricle and saccule: • The balance required while moving the head forward and backward is called gravitational equilibrium. This depends on the utricle and saccule, which together make up the fluid-filled vestibule of the inner ear. • These structures contain calcium carbonate granules, called otoliths. These otoliths lay in a cupula (little sac) above a layer of hair cells. • When the head dips forward or back, gravity pulls on the otoliths which put pressure on some of the hair cells, which prompt them to send a neural impulse to the brain.

  44. Proprioceptors are another type of mechanoreceptors involved in coordination. They are found in muscles, tendons, and joints throughout the body and provide information about body position to the brain.

  45. F. Taste • The tongue contains chemoreceptors that allow us to taste substances. The tongue recognizes four basic tastes: sour, sweet, salty, and bitter. • When we eat saliva dissolves some of our food. Specific molecules dissolved in the saliva are detected by the taste buds. • Specific taste cells within the taste buds detect molecules from one of these four basic tastes. The taste cells depolarize in response to particular tastes, causing an action potential that is sent to the gustatory centre of the parietal lobe where taste is perceived. • The combination of taste information and information from sensory neurons in the nose allow us to perceive flavours. • The salivary glands are connected to the brain stem and are stimulated whenever we taste, smell, or think about something delicious.

  46. G. Smell • Scientists estimate that our sense of smell can distinguish over 10000 different odours. • These odours are resultant from different particles that fit into specific chemoreceptors called olfactory cells that line the upper nasal cavity. • When the particles bind to the olfactory cells, ion channels in the cell membrane open which generate an action potential that is sent to the olfactory bulb of the brain. • From the olfactory bulb of the brain, the impulse is sent to the emotional centres of the brain and the frontal lobe, where the perception of odour occurs. • Taste and Smell are closely linked – in fact 80-90% of what we perceive as taste is actually due to our sense of smell. • Many animals release substances called pheromones that aid in the recognition and attraction of a mate. These chemicals are detected in the nose by a structure called the vomeronasal organ.

  47. H. Touch • The skin contains more than four million sensory receptors but they are not evenly distributed. • Most are concentrated in the fingers, tongue, lips and genitals. • Different receptors are sensitive to different stimuli, such as light touch, pressure, pain, and high and low temperatures. . • If tissue is damaged nerve cells called nociceptors release chemicals that trigger pain receptors to send impulses to the brain. Painkillers such as ibuprofen and Aspirin block the release of these chemicals. • How we experience pain and the effects of different painkillers is very subjective.

  48. Conclusion: • Sensation and Homeostasis • The senses relay information to the nervous system that allows the body to maintain homeostasis