Human Body, The: Sense Organs (1965)

[Music] we're beginning this picture about the sense organs with a familiar situation one that brings all the senses into play memories of a big date will very likely be sensory ones the way your date looks a visual [Music] memory the touch of her hand a tacal sensation the sound of her voice an auditory stimulus good night and the scent of her perfume an all Factory [Music] sensation and uh oh yes the taste of her lipstick a gustatory sensation all these stimuli and that includes some of the nicer ones are perceived by the brain Central organ of the nervous system nerve impulses received by the brain originate in the various sense organs each of the sense organs is in the simplest terms a structure containing specialized nerve endings or receptors adapted to be most sensitive to one kind of stimulus these receptors convert the physical or chemical stimulus into nerve impulses these impulses Move Along various nerves to particular areas of the cerebral cortex or other structures of the brain where perception takes [Music] place now let's repeat our demonstration purely for the sake of science this time keep in mind that our objective is to see how nerve endings or receptors of the sensory systems react to certain stimuli in the environment The receptors within the eye react to the stimulus of light you probably know the anatomy of the eye already but simply as a review light enters the eye through the transparent cornea and passes through the anterior chamber containing a liquid substance the aquous humor passing through the pupil the light r rays coming from an object to meet at a point called the principal Focus the biconvex lens of the eye does the same thing in addition the curvature of the human lens is adjustable through the action of attached muscles and ligaments in this way the lens is so corrected that light rays reflected from objects at various distances converge on the area of principal Focus the retina from a Latin word meaning net this is a good descriptive term because the retina is actually a net made up of two kinds of Highly specialized nerve cells The receptors of light on most of the surface of the retina are receptors called rods concentrated around the center of the retina are groupings of receptors called cones the theory is that the cones enable us to see color as well as giving us AC cute daylight Vision the cones seen here under the microscope are stimulated by relatively bright illumination It is believed that the physical stimulus is possibly converted within the cones into nerve impulses by the breakdown of iodopsin or some similar compound may be responsible for this one theory of color vision states that there are three sets of cones each set seems to be sensitive to a band of wavelengths corresponding to one primary color full color vision occurs when combinations of cones are stimulated in color blindness one or more sets of cones are not stimulated in dim illumination the cones are not stimulated either but the rods are the theory about rods and this is how they look under the microscope is that they are stimulated by less intense light the chemical compound ropson converts the physical stimulus of less intense light into nerve impulses because the rods are most dense at the periphery of the retina we have support for the old saying about seeing better out of the corner of the eye at night or in a darkened room the fibers of the rod and Cone cells combined to form the optic nerve nerve impulses pass along the optic nerve and then along a pathway of nerves up to this area of the cerebral cortex of the brain here the impulses are perceived and among the other things that occur the inverted image is wred psychologically and that's the process by which the eye receives and transmits physical stimuli the process which enables you to see your date it's pretty complicated but worth it right now from sight to touch the quite Pleasant sensation you get from the touch of her hand begins with the physical stimulus of touch affecting specialized nerve cells or free ner if for example our boy's date squeezes his hand the Pilan cor pusle which reacts to heavy pressure will be stimulated if her hand is warm the corosal of rufini will respond to this stimulus if her hand is cold K's end bulb will probably respond to this stimulus if she scratches him a free nerve ending will respond to the painful stimulus all nerve impulses conveying these different Sensations from the skin receptors eventually reach the cerebral cortex in much the same way that impulses travel from mner cor pusle you may want to keep this specialized receptor mner cor pusle and similar receptors in mind the next time you're holding hands remembering that you experienced this sensation through quite a complex process now then where were we oh yes that special good night good night to the scientist those words are merely sound stimuli affecting the ear you probably know the three parts of the ear the external ear which has a tube leading to the tanic membrane the middle ear containing three small bones the auditory OES and another membrane and finally the inner ear named the ccka for its shape ccka is Latin for snail the ccka contains the actual sense organs of hearing Shifting the position of the ccka gives a better idea of its structure this view shows a central pillar of bone around which a bony tube spirals slicing the cocka in half reveals a membranous tube within the Bony tube called the membranous Cleo let's take a closer look at this tube which is divided into three compartments called Scala these are filled with fluid the very important Basel membrane forms the base of the middle compartment if we could unroll the ccka and its Bassel membrane we'd see that the Bassel membrane is narrow at the base of the ccka and broadens at the Apex or top lying on the Bassel membrane is a series of fibers shortest near the base and progressively longer toward the Apex an arrangement like the strings of a harp one theory is that waves in the Cocker fluid cause these fibers to vibrate sympathetically to the frequency of a given sound wave the shorter fibers respond to short highfrequency waves longer fibers respond to medium frequency waves and the longest fibers respond to low frequency waves up to this point the stimulus of sound is a physical one changing the physical stimulus involves a structure embedded within the Bassel membrane the organ of C this organ found at thousands of points along the Bassel membrane is actually a specialized grouping of nerve cells with tiny hairlike projections the organ of CTI seen in this specially stained tissue section is the actual receptor of sound converting the movements of the fibers of the Bassel membrane into nerve impulses oh one more thing about the organ of Cy each of the hairlike structures has a connection with nerve cells that eventually combine to form the auditory nerve which carries nerve impulses along to the brain now that we've finished with with the Cram Course on the ear remember that all this goes into action when your girl says good night skipping the details sound waves enter the external ear and set the tanic membrane to vibrating this in turn causes vibrations of the auditory oses these vibrations set another membrane the oval window in motion this vibrating membrane in turn sets up waves in the fluid that fill the chambers of the cocko these waves then cause the fibers of the Bassel membrane to vibrate this vibration stimulates the organ of CTI which transforms the physical stimulus into nerve impulses which then move into the auditory nerve from the auditory nerve certain nerve Pathways carry these impulses up into the brain stem and finally to this area of the cerebral cortex where the sounds are perceived and that's the process through which the ear receives and transmits sound in other words it's the process through which you hear that special good night so far we've been talking about senses that involve physical stimuli but when you smell perfume chemical stimuli are involved the specialized nerve cells reacting to these stimuli are located in the upper portions of the nasal cavities along the inner lining call the AL Factory epithelium within the olfactory epithelium we find a grouping of cells and Associated organs the organs Bowman's glands are filled with a liquid secretion the cells olfactory receptors are the actual receptors of smell under the microscope a stained section of the olfactory epithelium shows both glands and receptors the fibers of the olfactory receptors are called the olfactory nerves these nerves end in a small structure named after its shape the olfactory bulb from the olfactory bulb other nerve cells are grouped to form the olfactory tract which extends back to the brain so much for the anatomy now what happens when you smell perfume again simplifying the details this molecules of the perfume are fused into the air and form a vapor drawn up into the nasal cavities the molecules pass over the olfactory epithelium and go into solution in the secretion of Bowman's glands the molecules in solution stimulate the olfactory receptors which convert the chemical stimuli into nerve impulses these nerve impulses move along the olfactory nerves to the olfactory bulb and then along the olfactory tract to the cortex of the brain where the the odor is perceived why certain odors produce certain reactions is part of the study of psychology our subject is physiology this brings us to another of our chemical senses the sense of taste The receptors which react to taste stimuli are found throughout what physiologists call the oral cavity or more simply the mouth and throat these tiny organs taste buds are most concentrated on the surface of the tongue where they are embedded in tiny projections called pil all pil in this area of the tongue contain taste Birds receptive to Sweet and salt tastes in this area the pil contain tastes buds receptive to sour tastes and back in this area the pil contain taste buds receptive to Bitter tastes among the key structures in any taste bud are a Poe opening to the surface gustatory cells which are the actual taste receptors and nerves formed by the fibers of these cells here's a pillar and taste BU as they appear under the microscope the nerves of the individual taste bud extend back depending on the location of the bud into one of three larger nerves the facial nerve the glossop fenial nerve or the vagus nerve so when you take taste lipstick this is more or less what happens molecules of lipstick represented by dots go into solution in saliva the solution enters the pores of the taste buds being sweet it stimulates the gustatory cells in this region the gustatory cells convert the chemical stimuli into nerve impulses which in this case enter the facial nerve through the facial and Associated nerves these impulses are carried up to the cortex where the sweet taste is perceived with a sense of taste often associated with a sense of smell we've completed our survey of the sense organs structures which contain specialized nerve endings or receptors each kind of receptor we saw responds to a particular stimulus it'll take just a couple of seconds to review the various stimuli and receptors in the skin specialized nerve endings respond to touch temperature pressure and pain in the oral cavity taste stimuli affect the taste buds in the nasal cavity odors stimulate the olfactory receptors in the eye light waves affect the rods and cones and in the ear sound waves affect the organ of Cy from the specialized nerve endings in the sense organs nerve impulses travel to the cerebral cortex and other structures of the brain where the stimuli are perceived so through the functions of the sense organs we are able to react to our environment and respond to the world around [Music] us