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Lecture PowerPoint to accompany Inquiry into Life Twelfth Edition Sylvia S. Mader Chapter 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18.1 Sensory Receptors and Sensations • Sensory Receptors – Specialized to detect specific stimuli – Interoreceptors - detect stimuli inside body • Includes receptors for blood pressure, blood volume, and pH of the blood. • Directly involved in homeostasis, regulated by negative feedback – Exteroreceptors - detect stimuli outside body • Includes receptors for taste, smell, vision, hearing, and equilibrium. • They function to inform the CNS about environmental conditions 18.1 Sensory Receptors and Sensations • Types of Sensory Receptors – Chemoreceptors • Taste, smell, blood pH – Photoreceptors • Vision (light) – Mechanoreceptors • Hearing, gravity, motion, body position – Thermoreceptors • Temperature – Located in the hypothalamus and skin 18.1 Sensory Receptors and Sensations Detection Sensation 18.1 Sensory Receptors and Sensations • 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 part of the brain receiving the nerve impulses 18.1 Sensory Receptors and Sensations • How Sensation Occurs – Integration: the summing up of environmental signals by sensory receptors – Sensory Adaptation: a decrease in response to a stimulus (not being consciously aware of a stimulus) 18.2 Somatic Senses • Three Types of Somatic Sensory Receptors – Proprioceptors – Cutaneous Receptors – Pain Receptors 18.2 Somatic Senses • Three Types of Somatic Sensory Receptors – Proprioceptors • Mechanoreceptors involved in reflex action – Help maintain muscle tone – Muscle spindles increase the degree of muscle contraction – Golgi tendon organs decrease the degree of muscle contraction – The result is proper muscle length and tension (tone) Muscle Spindle 18.2 Somatic Senses • Three Types of Somatic Sensory Receptors – Cutaneous Receptors – In the dermis of the skin – 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 – Pressure receptors • Pacinian corpuscles - onion-shaped, deep in dermis • Ruffini endings - encapsulated receptors with complex nerve networks – Temperature receptors - free nerve endings Cutaneous Receptors in the Human Skin 18.2 Somatic Senses • Three Types of Somatic Sensory Receptors – Pain Receptors • Free nerve endings • Damaged tissues release chemicals that stimulate pain receptors • 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- impulses from internal pain receptors also synapse in cord with neurons receiving pain impulses from skin – Ex: pain originating in heart is also referred to left arm and shoulder 18.3 Senses of Taste and Smell • Sense of Taste – Taste buds contain chemoreceptors and are located in the tongue, hard palate, pharynx, epiglottis – There are different receptors for salty, sour, bitter, and sweet tastes – Taste bud structure • Each has a pore surrounded by supporting cells and taste cells • Taste cells have microvilli with receptors – How the brain receives taste information • Chemicals bind to receptors on microvilli-impulses generated • Gustatory (taste) cortex surveys incoming pattern of impulses • “Weighted average” is the perceived taste Taste Buds in Humans 18.3 Senses of Taste and Smell • Sense of Smell – 80-90% of what we perceive as taste is actually smell – Olfactory Cells • Chemoreceptors (modified neurons) located high in nasal cavity • Olfactory cells have a tuft of olfactory cilia with receptors for odor molecules – How the Brain Receives Odor Information • Nerve fibers lead to olfactory bulb, an extension of the brain, • A single odor is composed of many different molecules which activates a characteristic combination of receptor proteins • Odor’s “signature” is interpreted by brain Olfactory Cell Location and Anatomy 18.4 Sense of Vision Anatomy of the Human Eye Anatomy and Physiology of the Eye 18.4 Sense of Vision • Anatomy and Physiology of the Eye – Function of the Lens • Focuses light rays onto the retina – Image is inverted and upside down on the retina – If eyeball is too long or too short corrective lenses are needed to bring image into focus on the retina • Visual accommodation – For viewing close objects » Lens rounds up to bring the image into focus on the lens » Lens shape is controlled by the ciliary muscle » Elasticity of the lens may decrease with age Focusing the Human Eye 18.4 Sense of Vision 18.4 Sense of Vision • Visual Pathway to the Brain – Function of Photoreceptors (Rods and Cones) • Rods – Very sensitive to light, important for night vision – Visual pigment is rhodopsin – Also provide us with peripheral vision and the perception of motion • Cones – Activated by bright light – Allow for color perception Photoreceptors in the Eye 18.4 Sense of Vision • Visual Pathway to the Brain – Function of the Retina • Three Layers of Cells – Layer closest to choroid contains rods and cones – Middle layer composed of bipolar cells – Inner layer composed of ganglion cells » Sensory fibers become the optic nerve • Rod and cone cells synapse with bipolar cells which synapse with ganglion cells • Integration occurs as signals pass to bipolar and ganglion cells • Considerable processing occurs in the retina before ganglion cells generate impulses • Impulses from the ganglion cells travel in the optic nerve to the visual cortex where further integration occurs Structure and Function of the Retina 18.4 Sense of Vision • 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 • 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 Optic Chiasma 18.5 Sense of Hearing • The Ear Has Two Sensory Functions – Hearing and Balance • Mechanoreceptors (hair cells) located in the inner ear associated with both functions Anatomy of the Human Ear 18.5 Sense of Hearing • Auditory Pathway to the Brain – – – – – Sound waves enter the auditory canal Tympanic membrane (ear drum) begins to vibrate Vibrations are amplified across the middle ear bones The stapes is attached to the oval window Oval window vibrates and transmits vibrations to fluid inside the cochlea Mechanoreceptors for Hearing 18.5 Sense of Hearing • Auditory Pathway to the Brain Continued . . . – Stapes causes the oval window to vibrate – Vibrations move from the vestibular canal to the tympanic canal across the basilar membrane – Basilar membrane moves up and down and the stereocilia of the hair cells bend – This generates nerve impulses in the cochlear nerve – The nerve impulses travel to the brain – The auditory cortex interprets them as sound 18.6 Sense of Equilibrium • Rotational Equilibrium Pathway – Three semicircular canals arranged so that one is in each plane of motion – 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, the stereocilia are bent and this changes the pattern of impulses carried in the vestibular nerve to cerebellum and cerebrum • Brain uses this information to make postural corrections 18.6 Sense of Equilibrium • 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 Mechanoreceptors for Equilibrium 18.7 Disorders that Affect the Senses • Disorders of Taste and Smell – Sense of smell begins to decline after age 60 – Some people are born without a sense of smell – Other factors that contribute to a decrease in the ability to taste and/or smell include: • Upper respiratory infections • Allergies • Exposure to certain drugs or chemicals (including tobacco smoke) • Brain trauma 18.7 Disorders that Affect the Senses • Disorders of the Eye – Color Blindness • Complete colorblindness is rare • Most common types involve deficiency in one type of cone • Red-green colorblindness – Most common type – X-linked recessive trait – 5-8% of the male population Testing for Colorblindness 18.7 Disorders that Affect the Senses – Distance Vision • Nearsighted – Can see close objects better than distant ones – Eyeball 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 • Farsighted – Can see distant objects better than close ones – Eyeball 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 Corrective Abnormalities of the Eye and Possible Corrective Lenses 18.7 Disorders that Affect the Senses • Common Causes of Blindness – Retinal Disorders • Capillaries to the retina may become damaged • Macular Degeneration – Cones are destroyed • Detached retina – Glaucoma • Fluid builds up in the eye destroying nerve fibers associated with peripheral vision – Cataracts • Cloudy spots on the lens • Exposure to UV light, diabetes, heavy alcohol consumption,and smoking are all risk factors 18.7 Disorders that Affect the Senses • Disorders of Hearing and Equilibrium – Hearing Loss • Mobility of the middle ear bones decreases with age • The ability to hear high-pitched sounds is affected first. – 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 and/or environmental causes (pathogens) 18.7 Disorders that Affect the Senses • Disorders of Hearing and Equilibrium – Vertigo (dizziness) • Can be caused by problems in the brain or inner ear – Meniere’s Disease • Caused by an increased fluid volume in the inner ear • Hearing loss and vertigo are both characteristics of this condition