Chapter 7 (Pages 237-265)
 Sight
 Hearing
 Equilibrium
 Touch
 Smell
 Taste
 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 types
of receptors
 Chemical
 Light
 Mechanical
 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
 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 to
the optic nerve
 The optic nerve transmits sensory signals to the occipital lobe of the
brain
 The image of an object
travels as sensory
information through the
optic nerves
 The optic nerves cross at
the optic chiasma
 The optic tracts then carry
the visual stimuli to the
occipital lobe of the brain
 Images seen on the left side
of the body are interpreted
in the right visual cortex
 Images seen on the right
side of the body are
interpreted in the left visual
cortex
 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
 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 experience
retinal fatigue - when the image disappears, we see the
complimentary color.
 Or in other words, your cones get tired!
 HEARING, TOUCH &
EQUILIBRIUM
 Type of receptor: Mechanoreceptors
 Receptors that detect sound
waves and pressure on the skin
and in the inner 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
 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
 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
 Sound waves enter the outer ear
(auricle/pinna) and move through the
auditory canal towards the tympanic
membrane
 The sound waves vibrate the tympanic
membrane which transfers to the
ossicles (hammer, anvil, stirrup)
 The vibrations are then amplified by the
ossicles and transferred to the cochlea
 The cochlea is attached to nerve fibers
which join to form the cochlear nerve
 The vibrations are translated into action
potentials which are sent via the
cochlear nerve to the brain where they
are interpreted as sound in the auditory
cortex (in the temporal lobe)
 The vestibule of the inner ear contains three
semicircular canals filled with fluid and
hair cells
 Each semicircular canal is on a different axis
 As your head moves, the fluid moves
accordingly, stimulating the hair cells
 The hair cells send action potentials to the
vestibular nerve which communicates with
the cerebellum
 Your cerebellum then interprets these
signals about the orientation of the body and
motion of the head
 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 you’re 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
 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
 When you smell something, odor
molecules dissolve in the mucous
layer surrounding the olfactory
hairs
 Olfactory receptor cells send action
potentials through to the olfactory
nerve
 The olfactory nerve sends the
impulses through the ethmoid bone
to the olfactory bulb which then
sends impulses to the olfactory
cortex in the temporal lobe
 Humans have about 40 million olfactory receptors that
allow us to identify about 10,000 different smells
 Dogs have a better sense of smell because they have 20
times 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 action
potential, which is why people can become used to smells
easily
 Example: Someone who wears the same perfume everyday
tends to not smell it on themselves
 The nerve pathway between the nose and the brain
travels through the limbic system (responsible for
emotions)
 This is why smells can trigger positive or negative emotions
 Rhinitis: an inflammation of the mucous
membranes 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 = odor
molecules can’t reach olfactory hairs
 Why you can’t smell well when you’re sick
 Treated with antihistimines
 Loss of functioning olfaction or inability to smell
 Unfortunate because smell is responsible for
80% of taste!
 Can be temporary or permanent
 Possible causes:
 Nasal polyps
 Cocaine abuse
 Head trauma
 Toxic chemical exposure
 Radiation (cancer treatment)
 Certain medications
 Deviated 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
 Can be surgically repaired
 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
 When you eat
something, chemical
molecules from the food
called tastants are
dissolved in saliva
 Tastants diffuse through
the taste pore, hitting
the gustatory hairs
 This activates the
gustatory cells which
triggers action
potentials through three
cranial nerves to the
gustatory cortex of the
brain
 Sweet
 Salty
 Sour
 Bitter
 Umami
 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 50-100
gustatory cells per taste bud
 In other words, each taste bud can sense all 5 tastes