L.+SENSORY+ORGANS

SENSORY ORGANS http://www.fotosearch.com/CSP127/k1274262/ __OVERVIEW __

Although this chapter is not larger than any other chapter, Sensory Physiology covers a lot of information. In this chapter we learned about the characteristics of sensory receptors and the types of cutaneous sensations. We learned about the special sense organs that allow you to taste, smell, see, hear and keep your equilibrium. Along with all of this, we learned about the neural pathways that all of the senses take when sending and receiving information. One day our group discussed which sense you could go without, I think I said touch. In learning about the senses though, I don’t think I would want to choose. It would have to be chosen for me. The way we perceive information from our sensory nerves is created by the brain from electrochemical nerve impulses which are delivered from sensory receptors. Our sensory receptors transduce different forms of energy from the external environment into nerve impulses that are sent into the CNS by sensory neurons. The brain then interprets the impulses as steak and potatoes, Eternity, a beautiful picture or as classical concerti. Different modalities of sensation are sensed by different types of sensory receptors, neural pathways and synaptic connections.

**The functional categories of sensory receptors: ** **Chemoreceptors ** sense chemical stimuli from the environment-Taste buds and olfactory epithelium. **Photoreceptors ** are for vision-Rods and Cones of the retina. **Thermoreceptors **respond to heat and cold. **Mechanoreceptors ** are stimulated by deformation of the cell membrane-Touch, pressure and hair cells in the inner ear. **Nociceptors ** are the receptors for pain. **Proprioceptors **<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> provide a sense of body position and help with fine motor control of the skeleton-Muscle spindles, Golgi tendon organs and joint receptors. **<span style="color: #431cc9; font-family: 'Times New Roman',Times,serif; font-size: 110%;">Cutaneous receptors **<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> include receptors to touch and pressure (mechanoreceptors), heat and cold (thermoreceptors) and pain receptors (nociceptors)



<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Receptors can be tonic or phasic. This just means that they either adapt quickly to constant stimulus or that they maintain their response the entire time a stimulus is applied. Phasic receptors adapt quickly to constant stimulus. An example of this would be when you walk into a room and smell a perfume, it is strong at first, but the odor fades the longer you are around the perfume. Tonic receptors do not adapt quickly as with a migraine that just won’t go away. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Another characteristic of sensation is that the sensory neurons need adequate stimulation to produce impulses. Each nerve fiber only produces one sensation (touch or cold or pain, etc.), this is because the synaptic pathways are different for each of the different type of sensory neurons. Sensation of each sensory neuron is what is produced by its normal or adequate stimulus. This is the law of specific nerve energies. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Cutaneous sensations are the sensations we feel through our skin. These include touch, pressure, heat, cold and pain. There are different sensory neurons for the different sensations that we feel. Heat, cold and pain receptors are naked endings of sensory neurons. We can feel touch by the Ruffini endings and Merkels’s discs. Other receptors for touch and pressure are encapsulated dendrites call Meissner’s and pacinian corpuscles. The receptors for cold are located in the upper region of the dermis where the receptors for warm are somewhat deeper. The receptors for pain are also free sensory nerve endings and can be myelinated or unmyelinated. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">The neural pathways for proprioceptors and pressure receptors are carried by myelinated nerve fibers that ascend to the dorsal columns of the spinal cord to synapse with the medulla oblongata. From there they are sent to the thalamus and then on to the postcentral gyrus. Sensations for heat, cold and pain are carried by either myelinated or unmyelinated nerve fibers to synapse in the spinal cord. From there the impulses are carried to the thalamus and then to then also to the postcentral gyrus.



<span style="color: #431cc9; font-family: 'Times New Roman',Times,serif; font-size: 110%;">Taste
<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Taste is also termed gustation. On the tongue, we have taste buds which are made up of taste cells. Each taste cell can recognize five different categories of taste: salty, sour, sweet, bitter and umami which is related to the flavor of meat and means savory. The receptors for salty and sour use ion channels, where the sweet, bitter and umami use a second messenger to stimulate their sensory neurons. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">We get a salty taste because of the presence of sodium ions. The sodium passes through ion channels in the plasma membrane of the taste cell. This depolarizes the cell causing it to release its neurotransmitter to stimulate the sensory neuron. In this way we are able to taste sour except that the ion present is hydrogen. Sweet, bitter and umami use membrane receptors that are coupled with G-proteins. The G-proteins within the cell activate a second messenger which leads to depolarization and the release of the neurotransmitter to the sensory neuron. The taste sensations use the facial nerve(VII) and the glossopharyngeal nerve (IX) to send the impulses to the medulla oblongata and from there they are passed to the thalamus. After the thalamus they are sent to the postcentral gyrus as well as to the prefrontal cortex.



<span style="color: #431cc9; font-family: 'Times New Roman',Times,serif; font-size: 110%;">Smell
<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">The olfactory epithelium at the top of the nose is where the receptors for olfaction (smell) are located. The olfactory apparatus has receptor cells which have cilia that project into the nasal cavity. The plasma membrane of the cilia has the receptor proteins that bind with odorant molecules. This process also uses G-proteins that dissociate when the odorant binds with a receptor. When the G-proteins dissociate, the process of transforming ATP into cAMP begins. The cAMP is the second messenger which opens ion channels to allow the influx of sodium and calcium which then produces graded depolarization and in turn the action potential. The action potential is then carried to the brain. The pathway for smell is different from taste because the path does not include the medulla oblongata or the thalamus. Olfaction sensory is transmitted from the olfactory neuron to the olfactory bulb and then straight to the prefrontal cortex.



<span style="color: #431cc9; font-family: 'Times New Roman',Times,serif; font-size: 110%;">Equilibrium
<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Our equilibrium is provided by the vestibular apparatus which with the cochlea form the inner ear. The semicircular canals and otolith organs make up the vestibular apparatus. The otolith organs which are the saccule and utricle send information about our linear acceleration and the semicircular canal sends information about our angular or rotational acceleration. Hair cells in the saccule, utricle and semicircular canals are the receptors for equilibrium. These hair cells are called stereocilia. When the stereocilia bend toward a larger structure called a kinocilium it depresses the plasma membrane and causes it to depolarize. The hair cell then releases its neurotransmitter which stimulates the vestibulocochlear (VIII) cranial nerve. These impulses then transmit to the cerebellum and vestibular nuclei which sends the information to the occulomotor center of the brainstem and spinal cord. This stimulates eye movements along with movements of the head, neck and limbs which serve to maintain balance.



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<span style="color: #431cc9; font-family: 'Times New Roman',Times,serif; font-size: 110%;">Hearing
<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">The cochlea is the organ that allows us to hear. Sound waves are funneled by the pinna to the external auditory canal and channeled to the tympanic membrane. The vibrations on the tympanic membrane are conducted to the inner ear by the ossicles in the middle ear. These ossicles called the malleus, incus and the stapes conduct the vibrations to an oval window in the cochlea. Vibrations at the oval window induce pressure waves in the perilymph of the cochlear duct which cause the basilar membrane to vibrate. The basilar membrane is connected to the organ of corti which contains hair cells. These hair cells are the receptor cells that are stimulated by the vibrations of the basilar membrane. When the hairs are bent, ion channels in the hairs open causing a diffusion of cations into the hair. This causes depolarization and release of the neurotransmitter which stimulates the vestibulocochlear (VII) nerve. The impulse is sent to the medulla oblongata and on to the inferior colliculus of the midbrain. From here it is projected to the thalamus and then to the auditory cortex of the temporal lobe.



<span style="color: #431cc9; font-family: 'Times New Roman',Times,serif; font-size: 110%;">Vision
<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Light passes through a structure in the front of the eye called the cornea. From there it passes through the pupil which is surrounded by the iris. Next the light passes the lens of the eye to the neural layer in the back of the eye which contains the photoreceptors called the rods and cones. The neural layer is called the retina. The light that passes through the retina stimulates the photoreceptors which stimulate the neurons that gather at the optic disc. The optic disc is where the neurons exit the retina as the optic nerve. The neural pathway from the retina can be confusing if you aren’t paying attention-here goes. The image that comes through the cornea and lens is upside down and backwards, so the information has to get straightened out so we aren’t actually seeing images that way. The right side of the visual field is focused on the left half of the retina as the left side of the visual field is focused on the right half of the retina of each eye. Axons from neurons in the left half of the left retina pass to the left lateral geniculate nucleus of the thalamus and axons from neurons in the left half of the right retina cross over at the optic chiasma to synapse in the left lateral geniculate nucleus. So for the other eye, axons from the right half of the right retina pass to the right lateral geniculate nucleus and the axons from the right half of the left retina cross over at the optic chiasma to synapse in the right lateral geniculate. Did I get it right?? Therefore both left and right lateral geniculate bodies receive information from both of the eyes. Axons from the retina pass to the lateral geniculate bodies and to the striate cortex. The geniculostriate system is involved with perception and answers the question, “What is it?”. Some of the axons from the retina also pass to the superior colliculus of the midbrain which is also called the optic tectrum. The axons that leave the superior colliculus activate eye and body movements. The tectal system answers the question “Where is it?”.



<span style="font-family: 'Times New Roman','serif';">Fox, Stuart Ira. (2009). //Human Physiology//. New York, NY: McGraw-Hill.

LJ

__<span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif;">ESSENTIAL QUESTIONS __ **Use a flow chart to describe how sound waves in the air within the external auditory meatus are transduced into the movements of the basilar membrane.**



JD **Describe how light is transmitted through the structures of the eye, refracted, and photoreceptors are stimulated to sent the CNS to be interpreted. Trace the path of light and the neural impulses sent to the brain.** The eyes can turn color and light into nerve impulses. Visible light is when the wavelengths are from 400 nanometers to 700 nanometers. The eye is protected by the sclera which is a tough layer of connective tissue. Behind the sclera is the cornea. After light passes through the cornea it continues into the anterior chamber. After light leaves the anterior chamber it enters the pupil. The pupil is surrounded by the iris, which controls the size of the pupil, it can dilate it or contract it. The iris is also the colored part of the eye which comes from epithelial cells in the posterior region. The lens of the eye is held in place by the suspensory ligament. The anterior chamber separates the iris and the cornea. The posterior chamber separates the iris, the ciliary body, and the lens. The anterior chamber contains a solution called aqueous humor. The posterior chamber contains a solution called vitreous humor. The light will go through the vitreous humor and into the vitreous body and then into the neural layer also known as the retina, where the photoreceptors can be found. After the light goes through the retina it will be absorbed by the choroid layer. Some of the photoreceptors will be stimulated as the light goes through the retina. Stimulation of the photoreceptors will also cause stimulation of other neurons. These neurons in the retina are known as the optic disc which lacks photoreceptors. These neurons will then send impulses to the brain. **Describe how light is transmitted through the structures of the eye, refracted, and photoreceptors are stimulated to sent the CNS to be interpreted. Trace the path of light and the neural impulses sent to the brain.**Light that is reflected off of something enters the eye through the cornea, then the light rays pass through an opening in the iris called the pupil. The iris controls the amount of light entering the eye by dilating or contriscting the pupil. For example, in dim light, the pupil enlarges (dilates) to allow more light to enter the eye and in bright light, the pupil shrinks (constricts) to prevent too much light from entering. The light then reaches the crystalline lens where is focuses light rays onto the retina by bending (refracting) the rays. The cornea does most of the refraction and the crystalline lens fine-tunes the focus. In a healthy eye, the lens can accommodate to provide clear vision at various distances. If an object is close, the ciliary muscles contract and the lens becomes more round. If an object is at a distance, the ciliary muscles relax and the lens flattens. Behind the lens and in front of the retina is a chamber called the vitreous body, which contains clear, gelatinous fluid called vitreous humor. Light rays pass through the vitreous before reaching the retina. The retina lines the back 2/3 of the eye is responsible for the wide field of vision that mosxt people experience. For clear vision, light rays must focus directly on the retina. When light focuses in front of or behind the retina, blurry vision occurs. The retina contains millions of specialized photoreceptor cells called rods and cones that convert light rays into electrical signlas that transmitted to the brain through the optic nerve. Rods and cones provide the ability to see in dim light and to see in color. The macula, located in the center of the retina, is where most of the cone cells are located. The fovea, which is a small depression in the center of the macula, has the highest concentration of cone cells. The macula is responsible for central vision, seeing color, and distinguishin fine detail. The outer portion is the primary location of rod cells and allows for night vision and seeing movement and objects to the side aka peripheral vision. The optic nerve which is located behind the retina transmits signals from the photoreceptor cells to the brain. Each eye transmits signals of a slightly different image and the images are inverted. Once they reach the brain, they are corrected and combined into one image. AR



__<span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif;">SUMMARY __ Your bodies senses are an amazing thing. You have sensory receptors all over your body that help you to touch, taste, smell, hear, and see. My favorite sense would have to be taste, due to my love affair with food. Then sense of taste is called gustation. Gustation happens by way of taste buds that are little barrel-shaped receptors located mainly on the dorsal side of your tongue. Each taste bud, as small as they are, have an amazing 50-100 epithelial cells that come out of a pore in the taste bud and are then exposed to the outside environment. The epithelial cells, all known as taste cells, in the taste receptors act like a neuron even though they are nor. There are two sections of taste buds. The ones regulated by the facial nerve (VII) are located in the front 2/3 of the tongue. These are responsible for touch and temperature. The taste buds located in the rear 1/3 of the tongue are regulated by the glossopharyngeal nerve (IX). These taste buds are responsible for taste association and flavor itself. The synapse from the taste buds through the glossopharyngeal nerve (IX) have a long path to follow. they travel from the taste buds to the medulla oblongata. From the medulla oblongata a second-order neuron carries them to the thalamus. From the thalamus a third-order neuron takes them to the postcentral gyrus of the the cerebral cortex and the prefrontal cortex. The taste cells have always been thought to be responsible for four different tastes: sour, sweet, salty, and bitter. Amazingly scientists have come up with a fifth taste, umami or savory. Scientists also believe now that all the areas of the tongue can taste all five tastes, whereas before they thought that each area of the tongue could only taste one taste. Now even though the entire tongue can taste every taste, each tastebud can still only taste one taste. Taste is also dependent on smell, texture, and temperature of food. Salty taste comes from the activation of salty taste receptors by mostly Na+ ions. The cells are depolarized by Na+ passing though channels located in the apical membrane. This depolarization causes the cells to release a transmitter. The sour taste is produced by the H+ ion. Because of the H+ ion presence, acidic foods cause the pH in the taste buds to decrease creating a sour taste. Sweet, bitter, and umami are all created by taste molecules combined with G-proteins called gustducins.

__<span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif;">APPLICATION __

Most of us live day by day not even realizing how lucky we are to have all our senses. We have touch, taste, smell, sight, sound, and hearing. We may not even notice how lucky we are until we have an issue, such as a cold that blocks our sense of taste and smell, or problems seeing the blackboard at school, or even noticing that we can't hear those speaking to us as well as we us to. Many of us as nurses realize how hard it is to get the elderly to eat their daily amount of calories, how it is necessary to speak a person with hearing deficiency at a steady pace and facing them so they can see our lips, and how necessary it is to function in every day cares via eyeglasses to see images. It is vital that we as nurses remember that every individual is unique, and we must remind ourselves that even though we live day by day with all our senses, we must be attuned to those that have deficits and how to best meet their needs. What is truly amazing about our bodies is that if one of our senses is gone or decreased, our body will compensate for it. I have a son who was born with very limited vision (20/600 OS and 20/200 OD with correction lenses), he currently goes to school with the "normal" children, but, does have the School of the Blind come 4 times a year for assistance. The School of the Blind has assisted my son with magnifying glasses, larger print on his computer, larger print text books, and even his own special black desk (all the others are white). What is truly amazing about my little boy is that even though numerous doctors have told me he probably would not succeed like other students his age, he manages to stay active with them in sports (he does have issues with balls flying at his face, but, is an awesome runner), managed to get on the honor roll this semester in school, and has adapted well to his environment and the everyday person who sees him may not recognize the fact that he is legally blind. The doctors have told me that there is no surgery or anything at this time that they can do to make my son see better, but, he has surpassed all of their expectations so far, and with love and that gentle tap to persevere and never give up, he has come along way.