Senses- Ch. 12. Pain receptors- respond to tissue damage in all tissues except in the brain

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1 Senses- Ch general types of sensory neurons or receptors are known. These specialized neurons detect stimuli from the eyes, ears, nose, mouth, and skin. The stimuli are changed into electrical signals (nerve impulses) that the brain can interpret. They include: Thermoreceptors- respond to temperature changes in the skin Pain receptors- respond to tissue damage in all tissues except in the brain Mechanoreceptors- respond to movement/pressure on/in skin, muscles, blood vessels Photoreceptors- respond to light changes only in the eyes Chemoreceptors- respond to changes in chemical concentration (like O2, H + and glucose) in the nose, mouth, and in internal organs

2 Smell the process of smelling is called olfaction the nerves associated with olfaction pass through the olfactory foramina olfactory nerves are the only cranial nerves that go directly to the cerebrum and do not have to be relayed by the thalamus these nerves are identified as cranial nerve I

3 Taste the process of tasting is called gustation the cells involved are gustatory cells the cells are clustered inside taste buds taste buds line the papillae, which are the little bumps on the tongueʼs surface dissolved food particles stimulate the gustatory cells and a signal is sent via the facial nerve (cranial nerve VII) to the brain for interpretation 5 primary taste sensations include: sweet, sour, salty, bitter and umami (meaty--msg)

4 Tongue " As food enters the mouth and is partially dissolved, the dissolved food stimulates the gustatory cells of the taste buds. These cells send a signal - via the facial nerve- to the brain for the interpretation of taste. p.466 Fig. 12.8

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7 Vision light enters the pupil of the eye and stimulates special cells that make up the retina of the eye once these cells are stimulated, they send an impulse along the optic nerve and then the impulse is relayed to the occipital lobe of the brain the special cells of the retina are called rods and cones rods function during dim light conditions, they donʼt sense color cones function only during bright light conditions, they sense color

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9 Wake up! Botfly

10 Pathway of Light into the Eyes " " (pg. 481/482 fig /12.25 & pg. 484 fig ) Light rays pass through the pupil and ultimately to the cells of the retina at the back of the eye. The retina cells send signals to the brain- via the optic nerve- for the interpretation of vision. 1. Light passes through the cornea of the eye 2. Light passes through the pupil 3. Light passes through the lens 4. The lens will focus the light on the retina of the eye 5. For the light to reach the retina, it must pass through the vitreous chamber of the eye 6. The light will activate the rods and cones of the retina, which will send a nerve signal- via the optic nerve- to the occipital lobe of the brain

11 " " Pathway of Light into the Eyes The retina consists of a combination of rods and cones. The fovea centralis is the area of the retina that consists of 100% cones. Therefore, the best vision is during the day when you are looking straight at an object. During the daylight, only cones are operating. The rest of the retina has a combination of rods and cones, therefore there arenʼt as many cones as there are in the fovea centralis region. This is why peripheral vision is not as clear as looking straight at an object. The optic disc region is the area where the blood vessels and the optic nerve exit the eye. In this location, there arenʼt any rods or cones. If an image is focused directly on the optic disc, vision will not be interpreted. Because the optic nerve exits the eye a little bit medial to center, it is not in the same location for both eyes. So, if an object is focused on the optic disc in the right eye, that same object will be focused elsewhere on the retina of the left eye. So basically, whatever the right eye canʼt see, the left eye can. When we look at objects, rarely are our eyes stationary. Therefore, if a person has only one eye, objects wonʼt be focused on the optic disc unless the eye is kept very still. Because of the lack of vision in the optic disc region, this area is also known as the blind spot. The lens can change shape in order to properly focus an image on the retina. The lens changes its shape due to the contraction of the ciliary muscles attached to the suspensor ligaments. There are 6 muscles that control the movement of the eye.

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14 Hearing sound waves create vibrations in the cochlear region of the ear these vibrations stimulate special cells that send an impulse via the cochlear nerve ( of the vestibulocochlear nerve--cranial nerve VIII ) to the brain for interpretation

15 Balance the movement of the body causes movement of fluid within the semicircular canals of the internal ear this fluid movement stimulates special cells that send an impulse via the vestibular nerve ( of the vestibulocochlear nerve--cranial nerve VIII ) to the brain for interpretation

16 Inner Ear and Balance: the ear is also important in maintaining balance. When a person moves his head, the fluid inside the canals begin to move, thus sending signals to the brain for the interpretation of balance. Middle Ear and Pressure: If you are in an airplane, as it ascends or descends, you may experience ear pain. This is due to the fact that at high altitudes, air pressure is less than compared to ground level. This means that the pressure in the middle ear area is groundlevel pressure and the pressure in the ear canal is less-than-ground- level pressure. This causes the tympanic membrane to bulge outward and this bulging causes pain. To equalize the pressure, many people chew gum. The action of chewing gum causes movement of the pharyngotympanic tube, which in turn, helps to move air out of the middle ear area, thus equalizing pressure.

17 Pathway of Sound Waves into the Ears The inner " ear " consists of the hearing apparatus and the balance apparatus. The hearing apparatus is the cochlea, which is a snail-shaped organ. Sound waves vibrate the ossicles, which, in turn, causes the movement of fluid inside the cochlea. This fluid movement stimulates a special organ inside the cochlea called the organ of Corti. The organ of Corti stimulates cranial nerve VIII, which transmits a signal to the brain for the interpretation of hearing. Refer to your text or the following diagram to trace the pathway of sound waves into the ear. 1. Sound waves are trapped by the pinna/auricle (outer rim of ear) 2. Sound waves travel through the ear canal (auditory canal) 3. The sound waves cause the tympanic membrane to vibrate 4. This vibration causes the 1st ossicle (malleus) to vibrate 5. The vibrating malleus causes the 2nd ossicle (incus) to also vibrate

18 Pathway of Sound Waves into the Ears 6. The vibrating incus will cause the 3rd ossicle (stapes) to vibrate " " 7. The vibrating stapes will cause fluid inside the cochlea to begin moving. The stapes covers an area called the oval window of the cochlea 8. The movement of the fluid stimulates the cells within the cochlea, which in turn stimulates the cochlear nerve ( a portion of the vestibulocochlear nerve--cranial nerve VIII ) 9. A signal is sent to the brain for the interpretation of hearing 10. Mr Luera is beautiful!!!!! (a beautiful jerk) outer ear----external ear structure of skin and cartilage middle ear---composed of the tympanic membrane, the ossicle (bones) and the pharyngotympanic tube or auditory tube (formerly known as the Eustachian tube) inner ear---composed of the cochlea and vestibular apparatus

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20 Incus = anvil Malleus = hammer Stapes = stirrup