10+Sense+Organs

 Sensory Organs Chapter 10 //The sensory physiology chapter covers a plethora of information about the parts of the body that are considered the sensory organs. Throughout this chapter the organs are highlighted and then a little detail is provided about each one in great enough detail to understand how they function. This chapter highlights the characteristics of sensory receptors, cutaneous sensations, taste and smell, the vestibular apparatus and equilibrium, the ears and hearing, the eyes and vision, retina, neural processing of visual information and interactions. The three topics that I found to be the most interesting were the characteristics of the sensory receptors, the vestibular apparatus and equilibrium, and the eyes and vision. //
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//There are three specific ways in which sensory receptors can be categorized, their structure, the stimulus energy they transduce, or the nature of their response. Receptors may be a number of different structures. The most common are the dendritic nerve endings, specialized neurons, or specialized epithelial cells associated with sensory nerve endings. Along with those there are the chemoreceptors, photoreceptors, thermoreceptors, mechanoreceptors, or nociceptors. Of course all receptors react differently to their stimuli, and the intensity of that stimulus. The law of specific nerve energies states that each sensory receptor responds with the lowest threshold to only one modality of sensation. That specific stimulus is known as the adequate stimulus. Any form of stimulation to a sensory nerve is perceived by the brain as the adequate modality of that receptor. Another interesting topic to me was the generator potentials. Generator potentials are usually depolarization in the membrane potential of the dendritic endings of sensory nerves. The strength of the stimulus is directly reflected in the magnitude of the potential change of the generator potential. Once the threshold is reached, there is a direct reaction that causes there to be a higher frequency of action potential production in the sensory neuron itself. // Source(Physiology Book)

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//The next topic that I chose from this chapter was the vestibular apparatus and equilibrium. The equilibrium fascinates me because prior to knowing anything about this, I assumed that it was found in the brain, and not in the ear. The membranous labyrinth is where the structures for equilibrium and hearing are located within the ear. Equilibrium is derived from three main structures. These three structures are the utricle, saccule, and the semicircular canals. The utricle and the saccule are also known as the otolith organs. The otolith organs provide one piece of information needed to form equilibrium which is the linear acceleration. The other needed information is collected from the semicircular canals, which provides the angular acceleration. The sensory receptors for equilibrium are hair cells. These hair cells are made up of many stereocilia, and just one single kinocilium. The direction in which these stereocilia are bent in relation to the kinocilium is what causes the cell membrane to either become depolarized or hyperpolarized. When the stereocilia are bent toward the kinocilium the cell membrane becomes depolarized, and when they are bent away from the kinocilium the opposite happens and the cell membrane is then hyperpolarized. //

//The eyes and vision was the next section of the chapter that I found to be very interesting. When the light enters the eye it travels through the opening in the pupil known as the iris, after this it is projected onto the retina in the back of the eye. The light rays are bent or refracted onto the retina by the cornea and the lens. When the light reaches the retina it is upside down and the right is really the left. Everything is opposite because it is essentially a mirror image of what you are actually seeing. Accommodation is the ability of your eye to maintain a quality image on the retina while the object is changing distance from the eye. This is achieved by the slight changing in the refractive power of the lens. The sharpness of the image refers to the visual acuity of the eye. When the object is seen as a sharp image, it is because the eye has no trouble bringing it to resolution on the retina the way it is supposed to be done. // Source (Physiology Book)



//This special classification of sensory organs is vital to us as human beings to be able to survive. Eye sight is probably one of the largest keys to this, and for many of us is need every moment of every day. The role that these senses play has a great deal of influence on the way in which we live each and every day. The most interesting of all of the special senses to me is the sense of equilibrium. The ability of tiny little hairs to be able to tell your entire body if you are right side up or upside down is incredible. The intricacy of each of these processes is enough to baffle just about anyone who is hearing about it for the first time. The endless processes that each special sensory organ goes through in order to achieve the correct response to the rest of the body is incredibly diverse and unique. //
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//A thick layer known as the sclera, which protects the eye, covers the outside of the eye. The sclera is one continuous shell in the middle of which is a transparent lens known as the cornea. Light travels through only the cornea, which it then passes through to reach the anterior chamber of the eye. It then passes through this chamber to reach the pupil, which is surrounded by a muscle, which is known as the iris. The iris regulates the diameter of the pupil, and helps decide how much light is to be let into the eye. Once the light moves through the pupil it reaches the lens. The lens is supported in the eye by the suspensory ligament, and is also located in the posterior chamber. Both the interior and posterior chambers are filled with aqueous humor. The area directly behind the lens is filled with a substance known as vitreous humor. Light that passes through the lens and into the vitreous humor then has reached the neural layer, which is where the photoreceptors are located. This neural layer is also known as the retina. When the light reaches the retina some of the light stimulates photoreceptors as it passes by, and it ultimately is absorbed in the darkly pigmented area known as the choroid layer. When these photoreceptors are activated they send signals to activate other neurons. The light then gathers in an area known as the optic disc. Since the light passes from on medium to another in the process, the air into the eye, refraction then takes place. Most refraction occurs at the air to cornea interface. The rods and cones of the retina are really a neural extension from the brain. The rods and cones send signals to the optic nerve, and the ganglion cells that originate there receive them. The exact order from eye to the brain looks something like this- Outside, Cornea, Aqueous humor of anterior cavity, pupil, lens, vitreous humor of posterior cavity, photoreceptors, bipolar cell layer, retinal ganglion cells, retinal ganglion cell axons, optic disc, optic head, optic nerve, optic chiasma, optic tract, superior colliculus, lateral geniculate nucleus of the thalamus, primary visual cortex of the occipital lobe of the brain.//