Types of Sensory Receptors 8/30/2013. Chapter Sensory Receptors and Sensations. Lecture Outline. Sensory Receptors

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1 Chapter 18 Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes Sensory Receptors and Sensations Sensory Receptors Specialized cells to detect specific stimuli Interoceptors - detect stimuli inside body Include receptors for blood pressure, blood volume, and blood ph Directly involved in homeostasis, regulated by negative feedback Exteroceptors - detect stimuli outside body Include receptors for taste, smell, vision, hearing, and equilibrium Function to inform CNS about environmental state 2 Types of Sensory Receptors Chemoreceptors respond to chemicals. Taste, smell, blood ph Photoreceptors respond to light energy. Vision (light) Mechanoreceptors are stimulated by mechanical forces. Hearing, gravity, motion, body position Thermoreceptors are stimulated by changes in temperature. Located in the hypothalamus and skin 3 1

2 4 How Sensation Occurs Detection occurs when environmental changes, such as pressure to the fingertips or light to the eye, stimulate sensory receptors. Sensation occurs when nerve impulses arrive at the cerebral cortex of the brain. Perception occurs when the brain interprets the meaning of stimuli. 5 Peripheral Nervous System stimulus sensory receptor nerve impulses along sensory fiber spinal cord brain Figure 18.1 Central Nervous System 6 2

3 How Sensation Occurs We are aware of a reflex action when sensory information reaches the brain. The brain integrates this information with other information received from other sensory receptors. Some receptors are free nerve endings. Others are specialized cells associated with neurons. The plasma membrane of a sensory receptor contains proteins that react to the stimulus. 7 How Sensation Occurs Sensory Transduction Energy from a chemical or physical stimulus is converted into an electrical signal (nerve impulse). The stronger the stimulus, the more frequent the action potentials. The sensation that results depends on the part of the brain receiving the nerve impulse. 8 How Sensation Occurs Integration occurs before sensory receptors initiate nerve impulses. Summing up of environmental signals by sensory receptors Sensory Adaptation Decrease in response to a stimulus (not being consciously aware of a stimulus) Two possible explanations Sensory receptors have stopped sending impulses. The thalamus has filtered out the ongoing stimulus. 9 3

4 18.2 Somatic Senses Somatic senses are those whose receptors are associated with the skin, muscles, joints and viscera. Three types of somatic sensory receptors Proprioceptors Cutaneous receptors Pain receptors 10 Proprioceptors Proprioceptors are mechanoreceptors involved in reflex actions. Help maintain muscle tone Muscle spindles increase the degree of muscle contraction Golgi tendon organs decrease the degree of muscle contraction Result is proper muscle length and tension (tone) 11 Muscle Spindle 1 2 muscle spindle 2 muscle fiber 1 quadriceps muscle 3 sensory neuron to spinal cord Golgi tendon organ bundle of muscle fibers tendon Figure

5 Cutaneous Receptors Both layers of the skin contain cutaneous receptors. Fine touch receptors Meissner corpuscles and Krause end bulbs - fingertips, lips, palms, penis, clitoris Merkel disks - junction of epidermis and dermis Root hair plexus - free nerve endings at base of follicles Allows sensation when hair is touched 13 Cutaneous Receptors Pressure receptors Pacinian corpuscles - onion-shaped, deep in dermis Ruffini endings - encapsulated receptors with complex nerve networks Temperature receptors - free nerve endings Some respond to cold; more numerous Some respond to warmth 14 Cutaneous Receptors in the Human Skin epidermis Figure 18.3 dermis 15 5

6 Cutaneous Receptors in the Human Skin free nerve endings (pain, heat, cold) epidermis Meissner corpuscles (touch) Merkel disks (touch) Pacinian corpuscles (pressure) Krause end bulbs (touch) Ruffini endings (pressure) root hair plexus (touch) Figure 18.3 dermis 16 Pain Receptors Pain receptors (or free nerve endings nociceptors) Stimulated by chemicals released by damaged tissue Alert us to possible danger Referred pain In some areas stimulation of internal pain receptors is also perceived as pain from the skin. Most likely explanation is that impulses from internal pain receptors also synapse in cord with neurons receiving pain impulses from the skin. Ex: pain originating in heart is also referred to left arm and shoulder Senses of Taste and Smell Taste and smell are called chemical senses because their receptors are sensitive to molecules in the food we eat and in the air we breathe. Taste cells and olfactory cells are classified as chemoreceptors. 18 6

7 Sense of Taste Taste buds contain chemoreceptors and are located primarily in the tongue. Many lie along the walls of the papillae. Isolated taste buds are also found in the hard palate, pharynx, epiglottis. Different receptors exist for salty, sour, bitter, sweet tastes and umami. Umami receptors detect the amino acid glutamate Present in the flavor enhancer monsodium glutamate (MSG) 19 How the Brain Receives Taste Information Taste buds open at a taste pore. The taste pore is surrounded by supporting cells and taste cells. Taste cells have microvilli with receptors. The gustatory cortex interprets as particular tastes. The brain appears to survey the overall pattern of incoming impulses and takes a weighted average is the perceived taste. 20 Taste Buds in Humans tonsils epiglottis Figure 18.4a Tongue 21 7

8 Taste Buds in Humans papillae 10µm Figure 18.4b Papillae Omikron/SPL/Photo Researchers, Inc. 22 Taste Buds in Humans Figure 18.4c taste bud Taste buds Omikron/SPL/Photo Researchers, Inc. 23 Taste Buds in Humans sensory nerve fiber supporting cell taste pore Figure 18.4d connective tissue One taste bud taste cell microvilli 24 8

9 tonsils epiglottis Taste Buds in Humans sensory nerve fiber supporting cell taste pore papillae 10µm taste bud connective tissue taste cell microvilli a. Tongue b. Papillae c. Taste buds d. One taste bud Omikron/SPL/Photo Researchers, Inc. Figure Sense of Smell Sense of smell 80-90% of what we perceive as taste is due actually to smell. Olfactory cells Chemoreceptors (modified neurons) are located high in the nasal cavity. Olfactory cells have a tuft of olfactory cilia with receptors for odor molecules. 26 How the Brain Receives Odor Information Each olfactory cell has only one out of about 1,000 different types of receptor proteins. Nerve fibers lead to the olfactory bulb, an extension of the brain. A single odor is composed of many different molecules which activate a characteristic combination of receptor proteins. An odor s signature is interpreted by the brain. 27 9

10 Olfactory Cell Location and Anatomy frontal lobe of cerebral hemisphere olfactory bulb olfactory epithelium nasal cavity odor molecules Figure 18.5a 28 Olfactory Cell Location and Anatomy olfactory bulb neuron olfactory tract sensory nerve fibers olfactory epithelium Figure 18.5b supporting olfactory cell cell olfactory cilia of olfactory cell odor molecules 29 Olfactory Cell Location and Anatomy frontal lobe of cerebral hemisphere olfactory bulb neuron olfactory tract olfactory bulb olfactory epithelium nasal cavity odor molecules sensory nerve fibers olfactory epithelium a. Figure 18.5 supporting olfactory cell cell b. olfactory cilia of olfactory cell odor molecules 30 10

11 18.4 Sense of Vision Vision requires the work of the eyes and the brain. It is believed that at least a third of the cerebral cortex takes part in processing visual information. 31 Anatomy and Physiology of the Eye The eye is an elongated sphere about 2.5 cm in diameter made of three layers. Sclera outer layer, white and fibrous The cornea is made of transparent collagen fibers. The conjuctiva is a membrane that covers the sclera. Choroid middle layer, darkly pigmented and vascular Toward the front, the choroid becomes a donut-shaped iris. The iris contains smooth muscle to control the size of the pupil. 32 Anatomy and Physiology of the Eye Choroid (continued) Behind the iris, the choroid thickens into the ciliary body. The ciliary body contains the ciliary muscle, which controls the lens shape for near and far vision. The lens divides the eye into two compartments. The anterior compartment is in front of the lens and is filled with aqueous humor, a clear watery fluid. The posterior compartment is behind the lens

12 Anatomy and Physiology of the Eye Retina the third layer, located in the posterior compartment Filled with a clear, gelatinous material, vitrous humor Contains photoreceptor cells, rods and cones Has a special region called the fovea centralis, where cone cells are densely packed Optic nerve, which takes impulses to the visual cortex, is formed from sensory nerve fibers from the retina. 34 Function of the Lens Lens focuses images on the retina Starts with the cornea and continues as the rays pass through the lens and humors Visual accommodation For viewing close objects Lens rounds up to bring the image into focus on retina Lens shape is controlled by the ciliary muscle Ciliary muscle contracts and lens rounds up to elasticity Elasticity of the lens may decrease with age 35 Anatomy of the Human Eye sclera choroid retina retinal blood vessels ciliary body lens iris optic nerve pupil fovea centralis cornea posterior compartment filled with vitreous humor anterior compartment filled with aqueous humor retina choroid suspensory ligament sclera Figure

13 Functions of the Parts of the Eye 37 Focusing the Human Eye ciliary muscle relaxed lens flattened light rays Focusing on distant object suspensory ligament taut Figure 18.7a 38 Focusing the Human Eye ciliary body ciliary muscle contracted lens rounded Focusing on near object suspensory ligament relaxed Figure 18.7b 39 13

14 Focusing the Human Eye ciliary muscle relaxed lens flattened light rays a. Focusing on distant object ciliary body suspensory ligament taut ciliary muscle contracted lens rounded Figure 18.7 b. Focusing on near object suspensory ligament relaxed 40 Visual Pathway to the Brain Vision begins once light has been focused on photoreceptors in the retina. Some integration occurs in the retina, where nerve impulses begin. Then the optic nerve transmits the integrated impulses to the brain. 41 Visual Pathway to the Brain Function of photoreceptors Rod cells Visual pigment is rhodopsin Very sensitive to light, important for night vision Provide peripheral vision and the perception of motion 42 14

15 Visual Pathway to the Brain Cone cells Located primarily in fovea centralis Activated by bright light Permits fine detail and color perception Three different kinds of cones Blue, green and red Different combinations of stimulation produce different colors 43 Photoreceptors in the Eye membrane of disk rod cell cone cell outer segment ion channels in plasma membrane inner segment cell body 20 µm nucleus synaptic vesicles Lennart Nilsson, from "The Incredible Machine" synaptic endings Figure Photoreceptors in the Eye light rays ion channels close retinal opsin Figure 18.8 membrane of disk Rhodopsin molecule (opsin + retinal) 45 15

16 membrane of disk ion channels close rod cell cone cell outer segment ion channels in plasma membrane light rays retinal inner segment cell body opsin nucleus 20 µm synaptic vesicles synaptic endings membrane of disk Rhodopsin molecule (opsin + retinal) Lennart Nilsson, from "The Incredible Machine" Figure Visual Pathway to the Brain Function of the retina Three layers of neurons Layer closest to choroid contains rods and cones. Middle layer is composed of bipolar cells. Inner layer is composed of ganglion cells. Sensory fibers become the optic nerve 47 Structure and Function of the Retina optic nerve retina blind spot Figure 18.9a Location of retina 48 16

17 Structure and Function of the Retina choroid rod cell and cone cell layer bipolar cell layer ganglion cell layer axons of ganglion cells Figure 18.9a to optic nerve light rays 49 Structure and Function of the Retina sclera choroid rod cell and cone cell layer bipolar cell layer ganglion cell layer Figure 18.9b Micrograph of retina Biophoto Associates/Photo Researchers, Inc. 50 Structure and Function of the Retina optic nerve retina sclera choroid rod cell and cone cell layer blind spot bipolar cell layer ganglion cell layer a. Location of retina axons of ganglion cells to optic nerve b: Biophoto Associates/Photo Researchers, Inc. light rays b. Micrograph of retina Figure

18 Visual Pathway to the Brain Function of the retina Rod and cone cells synapse with bipolar cells which synapse with ganglion cells. Axons become the optic nerve. Sensitivity of cones versus rods is due in part to how directly they connect to ganglion cells. As many as 150 rods may synapse on the same ganglion cell. Some cone cells in the fovea centralis activate only one ganglion cell. 52 Visual Pathway to the Brain Blind spot No rods and cones where the optic nerve exits the retina No vision is possible in this area optic nerve retina blind spot Figure 18.9a Location of retina 53 Visual Pathway to the Brain From the retina to the visual cortex Optic nerves from each eye travel to the optic chiasma. Some of the axons cross over at the optic chiasma. Fibers from the right half of each retina join together to form the right optic tract. Fibers from the left half of each retina join together to form the left optic tract

19 Visual Pathway to the Brain From the retina to the visual cortex Optic tracts travel around the hypothalamus and most fibers synapse with nuclei in the thalamus. Axons from the thalamic nuclei form optic radiations that carry impulses to the visual area. Right and left visual areas must communicate for us to see entire visual field. 55 Optic Chiasma primary visual area of occipital lobe thalamic nucleus optic tract optic chiasma optic nerve Right visual field Left visual field Figure Sense of Hearing The ear has two sensory functions - hearing and balance (equilibrium) Sensory receptors for both of these are located in the inner ear. Each consists of hair cells with stereocilia (long microvilli) that are sensitive to mechanical stimulation. Mechanoreceptors 57 19

20 Anatomy of the Ear The ear has three divisions Outer ear consists of the pinna Pinna collects and funnels sounds to the auditory canal. The opening of the canal is lined with fine hairs and sweat glands. Modified sweat glands secrete earwax. 58 Anatomy of the Ear Middle ear begins at the tympanic membrane and ends at a bony wall with openings called oval window and round window Between the tympanic membrane and oval window are three bones, the ossicles. Malleus, incus and stapes An auditory tube extends from the middle ear to the nasopharynx, permitting equalization of air pressure. 59 Anatomy of the Ear Inner ear the only part that is fluid-filled Three areas Semicircular canals role in equilibrium Vestibule role in equilibrium Cochlea role in hearing 60 20

21 Anatomy of the Human Ear Outer ear Middle ear Inner ear stapes incus malleus semicircular canals pinna vestibular nerve cochlear nerve tympanic membrane auditory canal cochlea earlobe round window auditory tube Figure Auditory Pathway to the Brain Through the auditory canal and middle ear Process begins when sound waves enter the auditory canal Tympanic membrane (ear drum) begins to vibrate Vibrations are amplified across the middle ear bones Stapes touches the oval window Oval window vibrates and transmits vibrations to fluid inside the cochlea 62 Auditory Pathway to the Brain From the cochlea to the auditory cortex Cochlea has three fluid-filled canals Vestibular canal - fluid is perilymph Cochlear canal fluid is endolymph Sense organ for hearing is called organ of Corti Hair cells sit on basilar membrane with stereocilia embedded in tectorial membrane Tympanic canal - fluid is perilymph 63 21

22 Auditory Pathway to the Brain From the cochlea to the auditory cortex When the stapes strikes the oval window membrane, pressure waves move from the vestibular canal to tympanic canal across basilar membrane. Basilar membrane moves up and down, and the stereocilia in the tectorial membrane bend. Then nerve impulses begin in the cochlear nerve and travel to the brain. When they reach the auditory cortex in the temporal lobe, they are interpreted as a sound. 64 Auditory Pathway to the Brain Each part of the organ of Corti is sensitive to different wave frequencies, or pitch. Near the tip, it responds to low pitches. Near the base, it responds to higher pitches. The pitch sensation depends upon which region of the basilar membrane vibrates and which area of the auditory complex is stimulated. 65 Auditory Pathway to the Brain Volume is a function of the amplitude of sound waves. Loud noises cause fluid in the vestibular canal to exert more pressure and the basilar membrane to vibrate more. The brain interprets the increased stimulation as volume

23 Mechanoreceptors for Hearing semicircular canals oval window stapes cochlea round window Figure Mechanoreceptors for Hearing vestibular canal cochlear canal tympanic canal cochlear nerve Figure Cochlea cross section 68 Mechanoreceptors for Hearing tectorial membrane stereocilia basilar membrane hair cell Spiral organ Figure cochlear nerve tympanic canal 69 23

24 Mechanoreceptors for Hearing Stereocilia P. Motta/SPL/Photo Researchers, Inc. 2 µm Figure Mechanoreceptors for Hearing semicircular canals cochlea oval window stapes round window vestibular canal cochlear canal tympanic canal cochlear nerve Cochlea cross section tectorial membrane stereocilia basilar membrane hair cell tympanic cochlear nerve canal Spiral organ Figure Stereocilia P. Motta/SPL/Photo Researchers, Inc. 2 µm 71 Rotational Equilibrium Pathway Three semicircular canals are arranged so that one is in each dimension of space. Each semicircular canal has an enlarged base called an ampulla. Each ampulla contains hair cells with stereocilia embedded in a cupula. As fluid within a canal flows and bends a cupula, stereocilia are bent; this changes the pattern of impulses carried in vestibular nerve to cerebellum and cerebrum. Brain uses this information to make postural corrections 72 24

25 8/30/2013 Gravitational Equilibrium Pathway Depends on utricle and saccule Utricle is sensitive to horizontal movements of the head. Saccule is sensitive to vertical movements of the head. Both contain hair cells with stereocilia embedded in an otolithic membrane. Large central cilium called the kinetocilium Calcium carbonate granules (otoliths) rest on otolithic membrane When head or body moves in horizontal or vertical plane, the otoliths are displaced and the otolithic membrane sags, bending stereocilia. 73 Mechanoreceptors for Equilibrium semicircular canals ampullae receptorin ampulla vestibular nerve cochlea liquid cupula stereocilia hair cell supporting cell vestibular nerve flow of liquid Figure 18.13a Rotational equilibrium: receptorsin ampullae of semicircular canal 74 Mechanoreceptors for Equilibrium liquid utricle saccule otoliths otolithic membrane hair cell supporting cell vestibular nerve flow of otolithic membrane kinocilium stereocilia Figure 18.13b Gravitational equilibrium: receptorsin utricle and saccule of vestibule 75 25

26 8/30/2013 Mechanoreceptors for Equilibrium semicircular canals ampullae receptorin ampulla vestibular nerve liquid cochlea utricle saccule liquid cupula stereocilia hair cell otoliths otolithic membrane hair cell supporting cell vestibular nerve supporting cell vestibular nerve flow of liquid flow of otolithic membrane kinocilium stereocilia Figure a. Rotational equilibrium: receptorsin ampullae of semicircular canal b. Gravitational equilibrium: receptorsin utricle and saccule of vestibule Disorders that Affect the Senses Disorders of Taste and Smell Sense of smell begins to decline after age 60. Some people born without sense of smell (anosmia). Other factors can contribute to a decrease in ability to taste and/or smell. Upper respiratory infections Allergies Exposure to certain drugs or chemicals (including tobacco smoke) Brain trauma 77 Disorders of the Eye Color blindness and problems with visual focus are two common abnormalities of the eye. More serious disorders can result in blindness

27 Color Blindness Complete colorblindness is rare. In most instances a particular cone is lacking or deficient in number. Red-green colorblindness is the most common type. X-linked recessive trait 5-8% of males 0.5% of females 79 Testing for Color Blindness Figure Visual Focus Nearsightedness Can see close objects better than distant ones Eye is elongated so image is brought to point focus in front of the retina Corrected by concave lenses which diverge light rays so point focus is farther back 81 27

28 Visual Focus Farsightedness Can see distant objects better than close ones Eye is shortened so image is brought to point focus behind the lens Corrected by convex lenses to increase bending of light rays so point focus is farther forward 82 Astigmatism Visual Focus The cornea or lens is uneven, producing a fuzzy image. The light rays are not evenly focused on the retina. This can be corrected by wearing an unevenly ground lens to compensate for the uneven cornea. 83 Corrective Abnormalities of the Eye and Possible Corrective Lenses normal eyeball Long eyeball; rays focus in front of retina when viewing distant objects. Concave lens allows subject to see distant objects. Nearsightedness Figure 18.15a 84 28

29 8/30/2013 Corrective Abnormalities of the Eye and Possible Corrective Lenses normal eyeball Short eyeball; rays focus behind retina when viewing close objects. Convex lens allows subject to see close objects. Farsightedness Figure 18.15b 85 Corrective Abnormalities of the Eye and Possible Corrective Lenses Uneven cornea; Rays do not focus evenly. Uneven lens allows subject to see objects clearly. Astigmatism Figure 18.15c 86 Corrective Abnormalities of the Eye and Possible Corrective Lenses normal eyeball Long eyeball; rays focus in front of retina when viewing distant objects. Concave lens allows subject to see distant objects. a. Nearsightedness normal eyeball Short eyeball; rays focus behind retina when viewing close objects. Convex lens allows subject to see close objects. b.farsightedness Figure Uneven cornea; Rays do not focus evenly. c. Astigmatism Uneven lens allows subject to see objects clearly

30 Common Causes of Blindness Retinal Disorders Diabetic retinopathy - capillaries to the retina may become damaged Hemorrhages and blocked vessels can occur Macular degeneration - cones are destroyed because thickened choroid vessels no longer function Retinal detachment - following trauma, the retina is torn or separated from the choroid 88 Common Causes of Blindness Glaucoma Fluid builds up in the eye because the drainage system fails Causes an increase in pressure Nerve fibers associated with peripheral vision are destroyed due to pressure Cataracts Cloudy spots on lens, eventually cover whole lens Risk factors - exposure to UV light, diabetes, heavy alcohol consumption, smoking 89 Cataract in a Human Eye Figure

31 Disorders of Hearing and Equilibrium Hearing loss can develop gradually or suddenly and has many potential causes. One in three people over age 60 have hearing loss. The middle ear is subject to infections that can lead to impairment if not properly treated. The first signs are problems understanding conversation with background noise. Hearing problems may begin around age 20. Mobility of ossicles decreases with age. 91 Disorders of Hearing and Equilibrium Sudden Deafness Usually occurs in only one ear Causes include infections, trauma, and side effects of some drugs Sometimes resolves itself Deafness at Birth Genetic disorders German measles or mumps virus infecting mother during pregnancy 92 Disorders of Hearing and Equilibrium Disorders of equilibrium Vertigo Feeling that a person or the environment is moving when no motion is occurring Can be caused by problems in the brain or inner ear Benign positional vertigo (BPV) due to particles in semicircular canals 93 31

32 Disorders of Hearing and Equilibrium Meniere s Disease Caused by an increased fluid volume in the inner ear Characterized by vertigo, a feeling of fullness in affected ear(s), tinnitus (ringing in the ears), and hearing loss 94 32