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Immagini e concetti della biologia Sylvia S. Mader Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

C3 - Sensory organs Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Sensory receptors Sensory receptors are divided into five categories: Chemoreceptors Pain receptors Electromagnetic receptors Thermoreceptors Mechanoreceptors Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Sensory receptors Sensory receptors in the PNS communicate with the CNS. Sensory adaptation Sensation Perception Sensory adaptation is an integration by which response to a stimulus gradually decreases. Sensation occurs when the impulse reaches the cerebral cortex, here the brain interprets it into perception. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Chemoreceptors Taste receptors are located in the taste buds which lie on the papillae of the tongue. The four primary types of taste are sweet, sour, salt and bitter. A fifth taste is umami (a savory taste). Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Chemoreceptors Olfactory receptors are modified neurons located high in the nasal cavity and are well developed in mammals. The sense of smell depends on 10-20 million olfactory cells in the olfactory epithelium. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Photoreceptors Photoreceptors are receptors sensitive to light. The camera-type eye is composed of three layers working as a single lens: the sclera, the choroid and the retina. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Structure of the eye The sclera (or white of the eye), is a protective layer that forms the cornea in the front of the eye. sclera cornea Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Structure of the eye The choroid is a vascular layer forming the iris (muscle tissue) which opens and closes the pupil. The lens is a transparent structure that helps to focus. choroid iris pupil lens Focus of a distant object Focus of a nearby object Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Structure of the eye The retina contains photoreceptors, mostly concentrated in the fovea. The blind spot is the area containing no receptors, where the optic nerve exits the retina. retina fovea optic nerve Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Structure of the eye The retina sends information to the visual cortex and is composed of three layers. The first layer contains the photoreceptors: cones (for bright light and colors) and rods (for night vision). The other layers contain bipolar cells and ganglion cells. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Eye’s diseases Frequent causes of blindness are retina disorders, glaucoma (damage of the optic nerve) and cataracts (clouding of the lens). Macular degeneration and cataracts can be caused by long term exposure to UV-rays and heavy cigarette smoking. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The inability to form clear images Nearsightedness The incoming light does not focus on the retina but in front of it. Hence distant images are out of focus. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The inability to form clear images Farsightedness The eyeball is too short, causing difficulties on focusing on near objects. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The inability to form clear images Astigmatism Inability of the eye to focus an object owing to the uneven curvature of the cornea. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Mechanoreceptors Hearing: The mammalian ear has three main regions: outer (collects and directs sounds) , middle (amplifies the signals) and inner ear (hearing and balance functions). Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Ear Hair cells with stereo cilia, in the organ of Corti inside the cochlea, detect vibrations previously transformed in the middle ear. hair cells stereo cilia In response to vibrations, hair cells send impulse to the cerebral cortex where they are interpreted as sound. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Protect ears from loud noises Middle ear is subjected to infections (otitis) that can lead to hearing impairments. Noise above 80 decibels (db) could result in damages to hair cells. Undamaged (left) and damaged (right) hair cells in the organ of Corti Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The sense of balance Some mechanoreceptors of the inner ear are involved in the sense of balance. Balance mechanoreceptors pick up changing in positions (gravitational balance) and in the head rotation velocity (rotational balance). Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The sense of balance Mechanoreceptors in semicircular canals detect rotational and/or angular movements of the head. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The sense of balance Mechanoreceptors in utricle and saccule detect head movements in the vertical or horizontal plane. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Other mechanoreception systems The lateral line system in fish, guides movements and locate other fish and obstacles. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Other mechanoreception systems Statocysts in some arthropods indicate information about head position. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018