1. The Special Senses
Chapter 7 (Pages )

2. The 6 special senses
Sight
Hearing
Equilibrium
Touch
Smell
Taste

3. 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 types of receptors
Chemical
Light
Mechanical

4. 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

5. Basic external anatomy of the eye

6. Extrinsic muscles Attach to the outer surface of the eye and are responsible for moving the eye within the orbital socket

7. Basic internal Anatomy of the eye

8. 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 to the optic nerve
The optic nerve transmits sensory signals to the occipital lobe of the brain

9. 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

10. 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

11. 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

12. Presbyopia (age related farsightedness) the lens ages and stiffens, images are formed behind the retina causing blurry close up vision

13. Astigmatism irregular curvature of the cornea or lens results in blurred vision

14. 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

16. Stare at this flag for 30 seconds without moving your eyes

18. 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 experience retinal fatigue - when the image disappears, we see the complimentary color.
Or in other words, your cones get tired!

19. Mechanical senses HEARING, TOUCH & EQUILIBRIUM
Type of receptor: Mechanoreceptors
Receptors that detect sound waves and pressure on the skin and in the inner ear

20. 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

21. 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

22. 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

23. How do you hear?
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)

24. How do you balance?
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

25. 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 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

26. 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

27. Anatomy of the olfactory region

28. How do you smell?
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

29. Smelly facts
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

30. rhinitis
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

31. anosmia 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

32. 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

33. Basic tongue & taste bud anatomy

34. 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

35. How do you taste?
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

36. 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