The Special Senses Chapter 7 (Pages ) The 6 special senses Sight Hearing Equilibrium Touch Smell Taste How do we sense? TRANSDUCTION
Sensory cells translate chemical, electromagnetic, and mechanical stimuli into action potentials that our nervous system can make sense of There are three basic categories of senses, depending on the typesof receptors Chemical Light Mechanical Light senses SIGHT Type of receptor: Photoreceptors
Receptors that detect light waves Rods: Only register black white (Grayscale) and general shapes Rods rule your peripheral vision Cones: Color (red, green, blue) and fine details Cones only work in bright conditions Basic external anatomy of the eye Extrinsic muscles Attach to the outer surface of the eye and are responsible for moving the eye within the orbital socket Basic internal Anatomy of the eye How do you see? Light is reflected from an object that you see
The light passes through the cornea pupil lens retina The rods and cones in the retina are stimulated to send impulses tothe optic nerve The optic nerve transmits sensory signals to the occipital lobe of thebrain The image of an objecttravels as sensoryinformation through theoptic nerves
The optic nerves cross atthe optic chiasma The optic tracts then carrythe visual stimuli to theoccipital lobe of the brain Images seen on the left sideof the body are interpretedin the right visual cortex Images seen on the rightside of the body areinterpreted in the left visualcortex Myopia (Nearsightedness) the lens focuses objects in front of the retina due to an elongated eye shape, nearby objects are seen clearly, but distant objects appear blurry Hyperopia (farsightedness) The distance from the lens to the retina is shortened because the eye is flatter, objects at a distance can be seen clearly, but objects close up appear blurry Presbyopia (age related farsightedness) the lens ages and stiffens, images are formed behind the retina causing blurry close up vision Astigmatism irregular curvature of the cornea or lens results in blurred vision Color blindness the cone cells on the retina are affected and certain colors cannot be distinguished
Remember cones sense Red, Green, and Blue light Color blindness is an inherited disorder (recessive) Much more common in males Son only needs to inherit it from his mother Daughter needs to inherit it from both mother and father A common form of color blindness is red-green color blindness Inability to distinguish red from green Stare at this flag for 30 seconds without moving your eyes What did you see on the white screen?
You should have seen a full American flag (Red, White, and Blue) This is a common optical illusion called an after image When we stare at a bright object for some time, we can experienceretinal fatigue - when the image disappears, we see thecomplimentary color. Or in other words, your cones get tired! Mechanical senses HEARING, TOUCH & EQUILIBRIUM
Type of receptor: Mechanoreceptors Receptors that detect sound waves and pressure on the skin and in the inner ear anatomy of the outer ear
Auricle (Pinna) Channels sound waves into the ear Auditory Canal Tube that carries sound waves to the middle ear Tympanic Membrane the eardrum Sound waves cause this to vibrate Anatomy of the middle ear
Ossicles: 3 smallest bones in the body,they transmit and amplify sound waves Hammer (malleus) Anvil (Incus) Stirrup (stapes) Oval Window The stapes attaches to the oval window and transmits sound waves into the inner ear Eustachian Tube Connects the middle ear to the pharynx to equalize pressure on each side of the tympanic membrane Anatomy of the inner ear
Cochlea Snail shaped structure, enables one to hear Vestibule Chamber that connects the three semicircular canals Semicircular Canals Channels containing receptor hair cells that play an important role in balance How do you hear? Sound waves enter the outer ear(auricle/pinna) and move through theauditory canal towards the tympanicmembrane The sound waves vibrate the tympanicmembrane which transfers to theossicles (hammer, anvil, stirrup) The vibrations are then amplified by theossicles and transferred to the cochlea The cochlea is attached to nerve fiberswhich join to form the cochlear nerve The vibrations are translated into actionpotentials which are sent via thecochlear nerve to the brain where theyare interpreted as sound in the auditorycortex (in the temporal lobe) How do you balance? The vestibule of the inner ear contains threesemicircular canals filled with fluid andhair cells Each semicircular canal is on a different axis As your head moves, the fluid movesaccordingly, stimulating the hair cells The hair cells send action potentials to thevestibular nerve which communicates withthe cerebellum Your cerebellum then interprets thesesignals about the orientation of the body andmotion of the head Motion sickness Usually a result of contradictory messages being sent to the brain from receptors Example: You spin quickly in a chair The hair cells in your semicircular canals are being stimulated due to rotation You suddenly stop spinning and sit still The fluid in your semicircular canals is still moving (aka the hair cells are telling your brain youre still spinning) But your eyes and the receptors in your spine tell your brain that you are sitting still (NOT spinning) These contradictory messages confuse the brain and can cause motion sickness Chemical Senses SMELL & TASTE Type of receptor: Chemoreceptors
Receptors that only respond to chemicals, detect molecules from the environment Excited by chemicals dissolved in saliva and airborne chemicals dissolved in nasal membranes Anatomy of the olfactory region How do you smell? When you smell something, odormolecules dissolve in the mucouslayer surrounding the olfactoryhairs Olfactory receptor cells send actionpotentials through to the olfactorynerve The olfactory nerve sends theimpulses through the ethmoid boneto the olfactory bulb which thensends impulses to the olfactorycortex in the temporal lobe Smelly facts Humans have about 40 million olfactory receptors thatallow us to identify about 10,000 different smells Dogs have a better sense of smell because they have 20times more olfactory receptor cells than humans Their olfactory cortex is 40 times larger than ours It only takes a few odor molecules to trigger an actionpotential, which is why people can become used to smellseasily Example: Someone who wears the same perfume everyday tends to not smell it on themselves The nerve pathway between the nose and the braintravels through the limbic system (responsible foremotions) This is why smells can trigger positive or negative emotions rhinitis Rhinitis: an inflammation of the mucousmembranes that line the nasal passage Usually caused by the common cold (the rhinovirus) Causes the release of histamines Molecules that trigger a reaction causing nasal congestion and drainage Congestion = thicker mucous layer = odormolecules cant reach olfactory hairs Why you cant smell well when youre sick Treated with antihistimines anosmia Loss of functioning olfaction or inability to smell
Unfortunate because smell is responsible for80% of taste! Can be temporary or permanent Possible causes: Nasal polyps Cocaine abuse Head trauma Toxic chemical exposure Radiation (cancer treatment) Certain medications Septum problems Deviated Septum Perforated Septum
A large shift of the septum away from the center Usually caused by injury Can be surgically repaired Perforated Septum Development of one or more holes in the septum Can be caused by injury, ulcer, long-term exposure to toxic fumes, or illegal drug abuse Basic tongue & taste bud anatomy Specific gustatory cells
Basal epithelial cells Stem cells that replace gustatory cells every week or so Why burned tongues heal so quickly Gustatory epithelial cells (gustatory receptor cells in picture) Do the actual tasting using gustatory hairs How do you taste? When you eatsomething, chemicalmolecules from the foodcalled tastants aredissolved in saliva Tastants diffuse throughthe taste pore, hittingthe gustatory hairs This activates thegustatory cells whichtriggers actionpotentials through threecranial nerves to thegustatory cortex of thebrain 5 basic tastes Sweet Salty Sour Bitter Umami Taste maps are WRONG!
The savory taste of beef or MSG Taste maps are WRONG! Each gustatory cell can only respond to one type of taste, BUT there are gustatory cells per taste bud In other words, each taste bud can sense all 5 tastes