1. Chapter 8 Special Senses
Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 8 Special Senses
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

2. The Senses General senses of touch Special senses
Temperature- thermoreceptors
Pressure/Pain- mechanoreceptors
Special senses
Smell/taste- chemoreceptors
Sight- photoreceptors
Hearing/equilibrium- mechanoreceptors

3. The Eye and Vision 70 percent of all sensory receptors are in the eyes
Protection for the eye
skull bones (orbit)
fat
eyelids/eyebrows
lacrimal apparatus (gland, duct, tears)
conjunctiva

4. Extrinsic Eye Muscles Muscles attach to the outer surface of the eye
Produce eye movements

5. When Extrinsic Eye Muscles Contract
Superior oblique- eyes counterclockwise
Superior rectus- eyes looks up
Lateral rectus- eyes look outward
Medial rectus- eyes look inward
Inferior rectus- eyes looks down
Inferior oblique- eyes clockwise

6. Structure of the Eye The wall is composed of three tunics
Fibrous tunic (sclera) – outside layer
Choroid – middle layer
Sensory tunic (retina) – inside layer

7. The Fibrous Tunic Sclera
white of the eye/tough connective tissue
Cornea
Transparent
Allows for light to pass through - refracts light
Repairs itself easily
The only human tissue that can be transplanted without fear of rejection

9. Choroid Layer Blood-rich nutritive tunic
Pigment (melanin) prevents light from scattering
Cilliary body – smooth muscle; changes shape of lens
distant object - muscle relaxes, lens flattens
near object - muscle contracts, lens rounded
Iris- pigmented layer that gives eye color; regulates size of pupil

10. Lens
Biconvex structure
Refracts light greatly

11. Lens Accommodation
Light must be focused to a point on the retina for optimal vision
The lens must change shape to focus for closer objects

12. Internal Eye Chamber Fluids
Refracts light slightly
Aqueous humor
Watery fluid found in chamber between the lens and cornea
Helps maintain intraocular pressure
Provides nutrients for the lens and cornea

13. Internal Eye Chamber Fluids
Vitreous humor
Gel-like substance behind the lens
Keeps the eye from collapsing
Lasts a lifetime and is not replaced
Refracts light slightly
Holds lens and retina in place

14. Sensory Tunic (Retina)
Contains receptor cells (photoreceptors)
Rods
Cones
Signals leave the retina toward the brain through the optic nerve

15. Neurons of the Retina and Vision
Rods
Most are found towards the edges of the retina
Allow dim light vision and peripheral vision (more sensitive to light, do not respond in bright light)
Perception is all in gray tones

16. Neurons of the Retina and Vision
Cones
Allow for detailed color vision (red, green, blue)
Densest in the center of the retina
Fovea centralis and Optic Disk

17. COLORBLINDNESS TEST PLATES

18. COLORBLINDNESS
Comes from a lack of one or more types of color receptors.
Most are green or red or both and that is due to a lack of red receptors.
Another possibility is to have the color receptors missing entirely, which would result in black and white vision.
An inherited trait that is transferred on the sex chromosomes (23rd pair)- sex-linked trait
Occurs more often in males
Can not be cured or corrected

19. The Ear Houses two senses Receptors are mechanoreceptors Hearing
Equilibrium (balance)
Receptors are mechanoreceptors

20. Anatomy of the Ear The ear is divided into three areas
Outer (external) ear
Middle ear
Inner ear

21. The External Ear Involved in hearing only Structures:
Pinna (auricle)- collects sound
External auditory canal- channels sound inward

22. The External Auditory Canal
Narrow chamber in the temporal bone- through the external auditory meatus
Lined with skin
Ceruminous (wax) glands are present
Ends at the tympanic membrane (eardrum)

23. The Middle Ear or Tympanic Cavity
The opening from the auditory canal is covered by the tympanic membrane (eardrum)
The auditory tube connecting the middle ear with the throat (also know as the eustacian tube)

24. Bones of the Tympanic Cavity
Three bones span the cavity
Malleus (hammer)
Incus (anvil)
Stapes (stirrip)

26. Inner Ear or Bony Labyrinth
Includes sense organs for hearing and balance
Filled with perilymph

27. Inner Ear or Bony Labryinth
A maze of bony chambers within the temporal bone
Cochlea
Vestibule
Semicircular canals

28. Organ of Corti
Located within the cochlea
Receptors = hair cells on the basilar membrane
Endolymph flows through and bends hair cells
Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

29. Organs of Equilibrium Receptor cells are in two structures Vestibule
Semicircular canals

30. Organs of Equilibrium Equilibrium has two functional parts
Static equilibrium- in the vestibule
Dynamic equilibrium- in the semicircular canals