Sensation; Module 5 EYE: VISION • Structure and function – eyes perform two separate processes 1. first: gather and focus light into precise area in the back of eye 2. second: area absorbs and transforms light waves into electrical impulses – process called transduction EYE: VISION • Structure and function – Vision: 7 Concepts To Know • Cornea • Iris/Pupil • Lens • Retina/Macula/Fovea • Optic Nerve • Function of Light Waves • Image Reversed EYE: VISION Retina • located at the very back of the eyeball, is a thin film that contains cells that are extremely sensitive to light • light sensitive cells, called photoreceptors, begin the process of transduction by absorbing light waves p96 RETINA Color Vision • There are three types of specialized cones in our retinas that allow us to see light. 1. Red equals long light rays; 500-700nm 2. Green equals medium light rays; 450-630 nm 3. Blue equals short light rays; 400-500nm Color Vision • When a person is born without one of these cone types they are then color-blind to those specific colors. 1. Monochromat = Total color blindness 2. Dichromat = Missing one cone type. Usually trouble telling reds from greens. • Very common in men; very seldom seen in women EYE: VISION • Visual pathways: eye to brain – Optic nerve 1. nerve impulses flow through the optic nerve as it exits from the back of the eye • the exit point is the “blind spot” 2. the optic nerves partially cross and pass through the thalamus 3. the thalamus relays impulses to the back of the occipital lobe in the right and left hemisphere EYE: VISION • Visual pathways: eye to brain 4. Primary visual cortex • the backs of the occipitals lobes is where primary visual cortex transforms nerve impulses into simple visual sensations 5. Visual association areas • the primary visual cortex sends simple visual sensations to neighboring association areas Structures of the ear are categorized into (3) areas: 1.Outer Ear 2.Middle Ear 3. Inner Ear EAR: AUDITION • We Hear: – Sound waves • stimuli for hearing (audition) • ripples of different sizes • Sound waves travel through space with varying heights and frequency. – Height • distance from the bottom to the top of a sound wave • called amplitude Amplitude = How loud something is to us Small amplitude= whisper Large amplitude= yell Frequency/How close sound waves are to one another Wavelength/How Big or Small Speed/How fast they travel What Is Sound? Any sound that you hear as a tone is made of regular, evenly spaced waves of air molecules. The most noticeable difference between various tonal sounds is that some sound higher or lower than others. These differences in the pitch of the sound are caused by different spacing in the waves; the closer together the waves are, the higher the tone sounds. The spacing of the waves - the distance from the high point of one wave to the next one - is the wavelength. All sound waves are travelling at about the same speed the speed of sound. So waves with a longer wavelength don't arrive (at your ear, for example) as often (frequently) as the shorter waves. This aspect of a sound - how often a wave peak goes by, is called frequency by scientists and engineers. They measure it in hertz, which is how many wave peaks go by in one second. People can hear sounds that range from about 20 to about 17,000 hertz. What Is Sound? Wavelength, Frequency, and Pitch Figure 1: Since the sounds are travelling at about the same speed, the one with the shorter wavelength will go by more frequently; it has a higher frequency, or pitch. In other words, it sounds higher. EAR: AUDITION • Measuring sound waves –decibel: unit to measure loudness –threshold for hearing: • 0 decibels (no sound) • 140 decibels (pain and permanent hearing loss p101 DECIBEL CHART p102 EAR DIAGRAM EAR: AUDITION • Outer, middle, and inner ear – Middle ear • bony cavity sealed at each end by membranes -the membranes are connected by three tiny bones called ossicles 1.)hammer 2.)anvil 3.)stirrup –hammer is attached to the back of the tympanic membrane –anvil receives vibrations from the hammer –stirrup makes the connection to the oval window (end membrane) EAR: AUDITION • Outer, middle, and inner ear – Inner ear contains two structures sealed by bone – cochlea: involved in hearing – vestibular system: involved in balanceCochlea – bony coiled exterior that resembles a snail’s shell – contains receptors for hearing – function is transduction which (once again!) is the: transformation of vibrations into nerve impulses that are sent to the brain for processing into auditory information EAR: AUDITION • Auditory brain areas: – there is a two step process occurs after the nerve impulses reach the brain 1. primary auditory cortex which is at top edge of temporal lobe: – transforms nerve impulses into basic auditory sensations 2. auditory association area: – combines meaningless auditory sensations into perceptions, which are meaningful melodies, songs, words, or sentences VESTIBULAR SENSE: BALANCE • Position and balance – vestibular system is located above the cochlea in the inner ear in which are the semicircular canals – each semicircular canal is filled with fluid that moves in response to movements of your head – These (3) canals have hair cells that respond to the fluid movement – function of vestibular system include sensing the position of the head, keeping the head upright, and maintaining balance Smell Taste CHEMICAL SENSES • Taste – is a chemical sense because the stimuli are various chemicals • organ: tongue – surface of the tongue contains: • taste buds CHEMICAL SENSES (CONT.) • Tongue – Six basic tastes 1. sweet 2. salty 3. sour 4. bitter 5. umami: meaty-cheesy taste 6. fat ________________________________ 7. Menthol? CHEMICAL SENSES (CONT.) • Surface of the tongue 1. chemicals, which are the stimuli for taste, break down into molecules 2. molecules mix with saliva an run into narrow trenches on the surface of the tongue 3. molecules then stimulate the taste buds http://www.ajinomoto.com/features/aji-no-moto/en/umami/index.html CHEMICAL SENSES (CONT.) • Taste buds shaped like miniature onions are the receptors for taste here the chemicals dissolved in saliva activate taste buds….. … which then produces nerve impulses that reach areas of the brain’s parietal lobe… … then the brain transforms impulses into sensations of taste CHEMICAL SENSES (CONT.) • Smell, or olfaction – Olfaction • called a chemical sense because its stimuli are various chemicals that are carried by the air • Our smelling function is carried out by two small odor-detecting patches – made up of about five or six million yellowish cells – high up in the nasal passages. •The human nose can detect (approx.) 10,000 smells. •The human nose (not as sensitive as a hound dog) can detect a smell that is 1 part chemical per billion parts of air molecules CHEMICAL SENSES (CONT.) • Smell / Olfaction – Stimulus • we smell volatile substances… …these volatile substances are released molecules in the the air at room temperature example: – a skunk’s spray, warm brownies; perfumes/colognes of lovers, gasoline, dog poo, I think you get it! CHEMICAL SENSES (FYI’s) – Sensations and memories • nerve impulses travel to the olfactory bulb… …where we can identify as many as 10,000 different odors • Why do we stop smelling our own deodorants or perfumes? Because of decreased responding! …It’s called Adaptation CHEMICAL SENSES (CONT.) • Functions of olfaction 1. one function: to intensify the taste of food 2. second function: to warn of potentially dangerous foods 3. third function: elicit strong memories; emotional feelings TOUCH • Our sense of touch is controlled by a huge network of nerve endings and touch receptors in the skin known as the somatosensory system. • This system is responsible for all the sensations we feel - cold, hot, smooth, rough, pressure, tickle, itch, pain, vibrations, and more. Within the somatosensory system, there are four main types of receptors: mechanoreceptors, thermoreceptors, pain receptors, and proprioceptors. TOUCH • Receptors in the skin 1. Mechanoreceptors 2. Thermoreceptors 3. Pain receptors 4. Proprioceptors 5. Hair follicles TOUCH • Skin – the outermost layer… …is a thin film of dead cells containing no receptors just below, are the first receptors which look like groups of threadlike extensions next: the middle and fatty layer …encompass a variety of receptors with different shapes and functions TOUCH • 1. Mechanoreceptors: These receptors perceive sensations such as pressure, vibrations, and texture. There are four known types of mechanoreceptors whose only function is to perceive indentions and vibrations of the skin: Merkel's disks, Meissner's corpuscles, Ruffini's corpuscles, and Pacinian corpuscles. are in the fatty layer of skin – are the largest touch sensor are also highly sensitive vibration • 2. Thermoreceptors: As their name suggests, these receptors perceive sensations related to the temperature of objects the skin feels. They are found in the dermis layer of the skin. There are two basic categories of thermoreceptors: hot and cold receptors. – Hot receptors start to perceive hot sensations when the surface of the skin rises above 86 º F and are most stimulated at 113 º F. But beyond 113 º F, pain receptors take over to avoid damage being done to the skin and underlying tissues. – Cold receptors start to perceive cold sensations when the surface of the skin drops below 95 º F. They are most stimulated when the surface of the skin is at 77 º F and are no longer stimulated when the surface of the skin drops below 41 º F. This is why your feet or hands start to go numb when they are submerged in icy water for a long period of time. TOUCH • 3. Pain receptors: These receptors detect pain or stimuli that can or does cause damage to the skin and other tissues of the body. There are over three million pain receptors throughout the body, found in skin, muscles, bones, blood vessels, and some organs. They can detect pain that is caused by mechanical stimuli (cut or scrape), thermal stimuli (burn), or chemical stimuli (poison from an insect sting). 4. Proprioceptors: these receptors sense the position of the different parts of the body in relation to each other and the surrounding environment. Proprioceptors are found in tendons, muscles, and joint capsules. This location in the body allows these special cells to detect changes in muscle length and muscle tension. Without proprioceptors, we would not be able to do fundamental things such as feeding or clothing ourselves. TOUCH • 5. Hair receptors • free nerve endings wrapped around the base of each hair follicle – these hair follicles fire with a burst of activity when first bent and give a sense of light touch. • If the hair remains bent for a period of time, the receptors will cease firing. ….. Sensory adaptation. example: wearing a watch, wearing a shirt with a collar etc. TOUCH • Brain areas (that translate nerve firings into sensation) somatosensory cortex located in the parietal lobe: transforms nerve impulses into sensations of touch temperature, and pain PAIN What causes pain? pain is the complex mixture of sensation and perception that is in part mediated by emotion; it may result from physical damage, one’s thoughts, or environmental stressors …therefore pain results from many different stimuli, most of which are subjective in nature Gate-Control Theory When we are occupied with other physical/mental activities we often feel less or no pain at all. -such as when you stub a toe, then you rub it or……. -when you nearly sever a finger with a power tool and pound your fist into a wall only to sense that your finger doesn’t feel so bad anymore Gate-Control Theory ….On a serious note… nearly five years ago now…. • For example: A NYC cop was shot through the heart he didn’t realize until the situation was over b/c he was physically/mentally absorbed in something. PAIN • Perhaps your thinking: How does the mind stop pain? (according to the Gate Theory) well…… non-painful nerve impulses compete with pain impulses in trying to reach the brain …they create a bottleneck or neutral gate so…shifting attention or rubbing an injured area decreases the passage of painful impulses result: Pain is dulled! PAIN (Biologically) • What does the body do to help us cope? Endorphins neurotransmitters secreted in response to injury or severe physical or psychological stress the…… …pain reducing properties of endorphins are similar to those of morphine so our….. …brain produces endorphins in situations that evoke great fear, anxiety, stress or bodily injury as well as intense aerobic activity.