1. Somatic and Special Senses

2. Receptors and Sensations
Types of Receptors
Chemoreceptors – stimulated by changes in chemical concentrations of substances
Pain receptors – stimulated by tissue damage
Thermoreceptors – stimulated by changes in temperature
Mechanoreceptors – stimulated by changes in pressure or movement
Photoreceptors – stimulated by light energy

3. Receptors and Sensations
Sensation = feeling that occurs when a brain interprets a sensory impulse
Sensory adaptation = sensory receptors stop sending signals when they are repeatedly stimulated
Walking into a room that has an intense scent, it eventually is less noticeable as olfactory receptors adapt

4. Somatic Senses Touch and Pressure Senses
Sensory Nerve Fibers – associated with touch and pressure
Meissner’s Corpuscles – abundant in hairless portions of the skin, respond to the motion of objects that barely contact the skin
Pacinian Corpuscles – common in deeper subcutaneous tissues, muscle tendons and joint ligaments; respond to heavy pressure

5. Somatic Senses Temperature Senses
Heat receptors – sensitive to temps above 25°C and are unresponsive above 45°C
Cold receptors – sensitive to temps between 10°C and 20°C

6. Sense of Pain Visceral Pain – occurs in visceral tissue
Referred Pain – pain that feels as though it is coming from some other part of the body
Acute Pain – originates from skin, usually stops when stimulus stops (pricking finger with a pin)
Chronic Pain – dull aching sensation

7. Regulation of Pain Pain Inhibitors
Enkephalins – suppress acute and chronic pain impulses and can relieve severe pain (morphine)
Serotonin – stimulate neurons to release enkephalins
Endorphins – found in the pituitary gland and hypothalamus and are released in response to extreme pain

8. Special Senses Eyes - Sight Olfactory – Smell Taste buds – Taste
Ears – Hearing, equilibrium

9. Sense of Sight Visual Accessory Organs Eyelid
Conjunctive – lines the inner surfaces of the eyelids
Lacrimal gland – secretes tears, lubricates the eye and contains enzymes to kill bacteria
Extrinsic muscles – move the eye in various directions

10. Structure of the eye Outer Tunic Middle Tunic
Cornea: helps focus entering light
Sclera: protection
Optic Nerve
Middle Tunic
Choroid coat: contains blood vessels and melanocytes (absorb light)
Transparent lens: focusing
Iris: colored portion
Aqueous humor: watery fluid
Pupil: opening in the center of the iris.

11. Structure of the eye Inner Tunic Retina: visual receptors
Fovea centralis: yellowish spot where the retina produces the sharpest vision
Optic disk: nerve fibers from the retina leave the eye and join the optic nerve; creates blind spot
Vitreous humor: transparent jelly-like fluid

12. Retina
Photoreceptors
Rods: black and white
Cones: color vision

14. For each picture, describe what you see. Quietly.

15. For each picture, describe what you see. Quietly.

16. For each picture, describe what you see. Quietly.

17. For each picture, describe what you see. Quietly.

18. Illusions
How do we see different when looking at the same pattern of black and white print?
The test for the duck and rabbit were to determine how fast participants could change their perception of the image.
Depending on the time of year and people’s experiences would depend on the original responses.

19. What do you see?

20. Do the two women look approximately the same size or different?

21. Illusions
These examples illustrate some of the many complex processes your brain uses to interpret visual stimuli. You know that the eyes play a crucial role in vision, but these examples illustrate that the brain is also crucial for vision.

22. Which is the real Mona Lisa?

23. We have difficulty seeing images upside down.

24. How does vision work?
Light signals are converted into images in the brain.
Light passes through the lens, where it is focused, to the retina where photoreceptors called rods and cones convert the information to electrical impulses that can be interpreted by the brain.

25. Eye Problems Cataracts: clouding of the lens
Treatment: remove lens and replace it

26. Eye Problems
The function is to constrict or dilate the pupil (opening) to allow light in.
Therefore, it regulates the amount of light passing to the visual receptors of the eye.
ANIRIDIA = a condition where a person is born without an iris

27. Why are all babies born with blue eyes?
Melanin is a brownish pigment that adds color to your hair, eyes, and skin.
At the time babies are born, melanin hasn't yet been "deposited" in the eyes' iris. Hence, they appear blue. 
After about six months, eyes change color depending on the amount of melanin.
If you have a lot of it, your eyes will turn dark brown.  If you have little, they'll stay blue. And if you have no melanin, your eyes may appear pink (albino).

28. Colorblindness

29. ASTIGMATISM is when the cornea has an irregular shape
ASTIGMATISM is when the cornea has an irregular shape. Part of the field of view is out of focus.
They eyeball changes shape until age 24.

30. Scratched cornea – painful, causes tearing, and may obstruct vision.
Treatment: may heal on its own, may require antibiotics.

31. Glaucoma – increased pressure of the aqueous humor
Causes blind spots
May damage the optic nerve.

32. Sense of Smell
Olfactory organs – cover the upper parts of the nasal cavity.
Olfactory receptors – stimulants enter the nasal cavity as gases, but they dissolve at least partially to watery fluids before they are detected.
Olfactory bulbs – impulses are analyzed.
Olfactory tracts – impulses travel.

33. Sense of Taste
Taste Sensations:
Sweet
Sour
Salty
Bitter
Umami

34. Sense of Hearing Auricle – outer ear
External Auditory Meatus – external auditory canal.
Middle Ear – Tympanic Cavity
Eardrum (tympanum)
Auditory Ossicles - malleus, incus, stapes - transmit vibrations and amplify the signal
Auditory Tube (eustachian tube) - connects the middle ear to the throat - helps maintain air pressure

35. Sense of Hearing Inner Ear Semicircular Canals - sense of equilibrium
Cochlea - sense or hearing
Organ of Corti - contains hearing receptors, hair cells detect vibrations

36. Sense of Hearing Inner Ear: Cochlea
Inside the cochlea are special neurons called HAIR CELLS
The stapes is attached to the OVAL WINDOW, and vibrations cause the perilymph to vibrate; the hair cells here transmit this vibration.
Therefore the HAIR CELLS in this region are receptors for HEARING.

37. Sense of Equilibrium
Static Equilibrium - sense the position of the head, maintain stability and posture
Dynamic Equilibrium (semicircular canals) - balance the head during sudden movement
Cerebellum - interprets impulses from the semicircular canals and maintains overall balance and stability