Structure• Free nerve ending: a form of peripheral ending of sensory nerve fibers in which the terminal filaments end freely in the tissue. Synonyms: terminationes nervorum liberae (40)• Root Hair Plexuses: free nerve endings associated with hair follicle - very sensitive to touch which moves the hair (41)• Merkel Disks: Merkels disks are located in the epidermis, where they are precisely aligned with the papillae that lie beneath the dermal ridges. They account for about 25% of the mechanoreceptors of the hand and are particularly dense in the fingertips, lips, and external genitalia. (42)• Meissner Corpuscle: enclosed in connective tissue capsule, just below epidermis in hairless areas of skin such as lips, finger tips, nipples, external genitalia, palms of hands and soles of feet - fine touch and pressure (41)• Pacinian Corpuscles: enclosed in multilayered connective tissue capsule, in deeper skin and tendons, sensitive to deep pressure and high pressure vibrations (41)• Muscle Spindles: small sensory organs that are enclosed within a capsule. They are found throughout the body of a muscle, in parallel with typical muscle fibers. There are several small, specialized muscle fibers known as intrafusal fibers. (43)• Golgi tendon Organs: are in series with muscle fibers, located in the tendons that attach muscle to bone. The sensory dendrites of the Golgi tendon organ afferent are interwoven with collagen fibrils in the tendon. (43)
SMELLSmell (give diagram of nose indicating receptors)Describe each(1) smell, also called Olfaction, the detection and identification by sensory organs ofairborne chemicals. The concept of smell, as it applies to humans, becomes less distinctwhen invertebrates and lower vertebrates (fish and amphibians) are considered, becausemany lower animals detect chemicals in the environment by means of receptors invarious locations on the body, and no invertebrate possesses a chemoreceptive structureresembling the vertebrate nasal cavity. For this reason, many authorities prefer to regardsmell as distance chemoreception and taste as contact chemoreception.Left Rightreceptor receptorbulb bulb (20)
Olfactory receptorsolfactory receptor, also calledsmell receptor, of binding odourmolecules that plays a central rolein the sense of smell (olfaction). Interrestrial vertebrates, includinghumans, the receptors are locatedon olfactory receptor cells, whichare present in very large numbers(millions) and are clustered withina small area in the back of thenasal cavity, forming an olfactoryepithelium. (2) (20) OLFACTORY RECEPTOR BULB
Olfactory pathways Olfactory OLFACTORY straie RECEPTOR (yellow) BULB (blue) (20) The sense of smell can create a powerful and long lasting memories. These memories couples with unique sensory inputs especially ordor, often persist from early child hood to death. New car, baby, kitchen and people odors are all olfactory triggers that often bring back memories of events that have occurred from the past. There is a huge relationship between the olfactory and gustatory pathways because our sense of smell and taste are closely related. (8)
Com paring human and canine olfaction(5)Taste bud organ located on the tongue in terrestrial vertebrates thatfunctions in the perception of taste. In fish, taste buds occur on the lips, theflanks, and the caudal (tail) fins of some species and on the barbells ofcatfish. In most animals, including humans, taste buds are most prevalent onsmall pegs of epithelium on the tongue called papillae The taste receptorcells of other animals can often be characterized in ways similar to those ofhumans, because all animals have the same basic needs in selecting food.(4)
Neural pathwayThe gustatory sensations or taste are closely associated with olfaction. Tastereceptors are located inside structures called taste buds that line the surfaceof the tongue, and are found on the soft palate, pharynx, and larynx.Nervous impulses generated in the anterior two thirds of the tongue travelover the facial nerve where they are generated from the posterior one thirdare conducted by fibers of the glossopharynegal.(10) (9)
Taste (20) Taste buds: bitter, sweet, papillaeh sour, saltyThe taste buds are embedded in the epithelium of the tongue and makecontact with the outside environment through a taste pore.Taste Buds are small organs located on the tongue interrestrial vertebrates that functions in the perception of tasteTaste buds are composed of groups of between 50 and 150 columnar taste receptorcells bundled together like a cluster of bananas. The taste receptor cells within a budare arranged such that their tips form a small taste pore, and through this poreextend microvilli from the taste cells. The microvilli of the taste cells bear tastereceptors.
The Mechanism of Hearing When one hears a sound or someone speaking, then an image comes to mind that is called the cartilaginous tissue, or the pinna. The pinna directs the sound energy into the ear canal. The eternal meatus is about one inch in length and is closed at the inner end near the ear drum; it forms a passage way in which sound energy may be transmitted into the inner reaches of the ear. (30) (45)
Neuronal pathway of Hearing Cochlear N. to the brain stem interneurons to multi-neuron pathway to the thalamus then to the auditory cortex The Organ of Corti with its sound-sensitive hair cells and basilar membrane are important parts of the sound transducing system for hearing. Mechanical vibrations of the basilar membrane generate membrane potentials in the hair cells which produce impulse patterns in the cochlear portion of the vestibulocochlear nerve (cranial nerve VIII). (53)
Vestibule and semicircular canals The vestibule has a round open space that accesses various passageways, it is the central structure within the inner ear. The outer wall of the vestibule contains the oval and round windows (which are the connection sites between the middle and inner ear). Internally, the vestibule contains two membranous sacs, the utricle and the saccule, which are lined with tiny hair cells. (47) The semicircular canals have three bony tubes that form loops. Each tube ends in a bulge, or ampulla, containing sensors that detect the movement of fluid in the loop—which depends on your body’s movement. Similar receptors called maculae detect how upright you are. Your brain uses these signals to correct your balance. (48) The vestibular system serves the bodily functions of balance and equilibrium. It accomplishes this by assessing head and body movement and position in space, generating a neural code representing this information, and distributing this code to appropriate sites located throughout the central nervous system. Vestibular function is largely reflex and unconscious in nature. (46)
Having a sense of balance is… The semicircular canals are three pretzel-like curved tubes arranged at angles roughly perpendicular to each other, with the two vestibular sacs located at their base. Both the canals and sacs contain fluid and tiny hair cells, which act as receptors. When a persons head moves, the fluid disturbs the hair cells, which stimulate a branch of the auditory nerve, signaling the brain to make adjustments in the eyes and body. A movement at any given angle will have its primary effect on one of the three canals. Overstimulation from extreme movements will produce dizziness and nausea. (32)
Dynamic Equilibrium… The special sense which interprets balance when one is moving, or at least the head is moving; the semicircular canals contain the receptors for dynamic equilibrium; within each semicircular canal is a complex mechanoreceptor called a crista ampullaris which contains the mechanoreceptors (Hair cells) for dynamic equilibrium; when the perilymph in one of the semicircular canals moves, the hair cells in the crista ampullaris are stimulated to send nerve impulses to the brain; this advises the brain of whether or not a person has their balance during body movements or if their body is in motion, such as moving their head side-to-side.(50)
Cavities and humors of the eye• Humors- is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous body or simply "the vitreous".• Cavities of the eye- the anterior cavity is actually divided into two subcategories.• the anterior chamber ( from iris to cornea)• the posterior chamber ( from iris to lens)
Muscles of the eyeSince only the fovea provides sharp distinct vision, the eye must move tofollow a target. It must be precise and fast. This is seen in scenarios likereading, wherein the reader must shift gaze constantly, or following a smallobject like a golf ball, in which the extraocular muscles must lead the eye tofollow the head movements. Although under voluntary control, mostmovement is done without thinking, such as those based on head or otherbody movement, or movement of objects in the area. Researchers still havesome work in order to find the parallel nature of the environment-based(involuntary) and voluntary control
accessory structuresThe site of accessory structures ofthe eye are as follows: eyebrows,eyelashes, eyelids, conjunctiva,and lacrimal apparatus.
PhotopigmentsThe photopigments that absorb light all have asimilar structure, which consists of a proteincalled an opsin and a small attached moleculeknown as the chromophore. The chromophoreabsorbs photons of light, using a mechanism thatinvolves a change in its configuration. Invertebrate rods the chromophore is retinal, thealdehyde of vitamin A1
Retinal imageformation of focused images on thephotoreceptors of the retina depends on therefraction (bending) of light by the cornea and thelens . The corna is responsible for most of thenecessary refraction, a contribution easilyappreciated by considering the hazy out-of-focusimages experienced when swimming underwater.Water, unlike air, has a refractive index close tothat of the cornea; as a result, immersion in watervirtually eliminates the refraction that normallyoccurs at the air/cornea interface.
Rods & conesRods are responsible for vision at low light levels (scotopic vision). They donot mediate color vision, and have a low spatial acuity.Cones are active at higher light levels (photopic vision), are capable of colorvision and are responsible for high spatial acuity. The central fovea ispopulated exclusively by cones. There are 3 types of cones which we willrefer to as the short-wavelength sensitive cones, the middle-wavelengthsensitive cones and the long-wavelength sensitive cones or S-cone, M-cones, and L-cones for short
QuestionsWhy dont deer see Hunters who wear Bright orange?Deer have no red-sensitive cone cells in their eyes, so they cant tell red ororange from green and brown.What is the difference between "nearsighted" and "farsighted"? How areeach of these corrected?There are several differences between being nearsighted and beingfarsighted, as these are two different vision problems. Nearsightedness iscalled myopia, and farsightedness is known as hyperopia. The mainbiological difference in the two is that in myopia, the images seen arefocused in front of the retina, rather than directly on the retina. Inhyperopia, the images are focused behind the retina, rather than on top ofit. You can fix these problems by simply getting eye glasses
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