1. Essentials of Human Anatomy
Special Senses

2. Special Senses
sensory receptors are within large, complex sensory organs in the head
smell in olfactory organs
taste in taste buds
hearing and equilibrium in ears
sight in eyes

3. Sense of Smell Olfactory Receptors chemoreceptors
respond to chemicals dissolved in liquids
Olfactory Organs
contain olfactory receptors and supporting epithelial cells
cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

4. Olfactory Receptors

5. Olfactory Nerve Pathways
Once olfactory receptors are stimulated, nerve impulses travel through
olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions) and olfactory cortex (for interpretation)

6. Olfactory Stimulation
olfactory organs located high in the nasal cavity above the usual pathway of inhaled air
olfactory receptors undergo sensory adaptation rapidly
sense of smell drops by 50% within a second after stimulation

7. Sense of Taste Taste Buds organs of taste
located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx
Taste Receptors
chemoreceptors
taste cells – modified epithelial cells that function as receptors
taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells

8. Taste Receptors

9. Taste Sensations Four Primary Taste Sensations
sweet – stimulated by carbohydrates
salty – stimulated by salts
sour – stimulated by acids
bitter – stimulated by many organic compounds
Spicy foods activate pain receptors

10. Taste Nerve Pathways
Sensory impulses from taste receptors travel along
cranial nerves to
medulla oblongata to
thalamus to
gustatory cortex (for interpretation)

11. Hearing
Ear – organ of hearing
Three Sections
External
Middle
Inner

12. External Ear auricle external auditory meatus tympanic membrane
collects sounds waves
external auditory meatus
lined with ceruminous glands
carries sound to tympanic membrane
terminates with tympanic membrane
tympanic membrane
vibrates in response to sound waves

13. Middle Ear tympanic cavity air-filled space in temporal bone
auditory ossicles
vibrate in response to tympanic membrane
malleus, incus, and stapes
oval window
opening in wall of tympanic cavity
stapes vibrates against it to move fluids in inner ear

14. Auditory Tube eustachian tube connects middle ear to throat
helps maintain equal pressure on both sides of tympanic membrane
usually closed by valve-like flaps in throat

15. Inner Ear complex system of labyrinths osseous labyrinth
bony canal in temporal bone
filled with perilymph
membranous labyrinth
tube within osseous labyrinth
filled with endolymph

16. Inner Ear Three Parts of Labyrinths cochlea semicircular canals
functions in hearing
semicircular canals
functions in equilibrium
vestibule

17. Cochlea Scala vestibuli upper compartment
leads from oval window to apex of spiral part of bony labyrinth
Scala tympani
lower compartment
extends from apex of the cochlea to round window
part of bony labyrinth

18. Cochlea Cochlear duct portion of membranous labyrinth in cochlea
Vestibular membrane
separates cochlear duct from scala vestibuli
Basilar membrane
separates cochlear duct from scala tympani

19. Organ of Corti group of hearing receptor cells (hair cells)
on upper surface of basilar membrane
different frequencies of vibration move different parts of basilar membrane
particular sound frequencies cause hairs of receptor cells to bend
nerve impulse generated

20. Auditory Pathway Cochlear branch of CN VIII
To cochlear nucleus of medulla
To inferior colliculus of opposite side of midbrain
To thalamus
To auditory cortex

21. The Sense of Vision
Visual receptors (photoreceptors) in the eyes to detect light, color, and movement.
Accessory structures of the eye.
provide a superficial covering over its anterior exposed surface (conjunctiva)
prevent foreign objects from coming into contact with the eye (eyebrows, eyelashes, and eyelids)
keep the exposed surface moist, clean, and lubricated (lacrimal glands)

23. Lacrimal Apparatus lacrimal gland lateral to eye secretes tears
canaliculi
collect tears
lacrimal sac
collects from canaliculi
nasolacrimal duct
collects from lacrimal sac
empties tears into nasal cavity

24. Structure of the Eye hollow spherical wall has 3 layers
outer fibrous tunic
middle vascular tunic
inner nervous tunic

25. Cavities and Chambers of the Eye
The internal space of the eye is subdivided by the lens into two separate cavities.
anterior cavity
posterior cavity

26. Cavities and Chambers of the Eye
The anterior cavity is
the space anterior to the lens and posterior to the cornea
The iris of the eye subdivides the anterior cavity further into two chambers.
anterior chamber is between the iris and cornea
posterior chamber is between the lens and the iris

27. Vitreous Humor
Posterior cavity is posterior to the lens and anterior to the retina.
Transparent, gelatinous vitreous body which completely fills the space between the lens and the retina.

28. Optic Disc Optic disc lacks photoreceptors.
Called the blind spot because no image forms there.
Just lateral to the optic disc is a rounded, yellowish region of the retina called the macula lutea containing a pit called the fovea centralis (the area of sharpest vision).
contains the highest proportion of cones and almost no rods

29. Visual Pathways Each optic nerve conducts visual stimulus information.
At the optic chiasm, some axons from the optic nerve decussate.
The optic tract on each side then contains axons from both eyes.
Visual stimulus information is processed by the thalamus and then interpreted by visual association areas in the cerebrum.

30. Extrinsic Eye Muscles Superior rectus rotates eye up and medially
Lateral rectus
rotates eye laterally
Medial rectus
rotates eye medially
Inferior rectus
rotates eye down and medially
Superior oblique
rotates eye down and laterally
Inferior oblique
rotates eye up and laterally

31. THE END