The Special Senses Chapter 7 (Pages 237-265).
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Transcript of The Special Senses Chapter 7 (Pages 237-265).
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