1. Comparative Anatomy Sensory Organs
Kardong
Chapter 17
Part 16

2. Sense Organs Monitor external and internal environment
Somatic or visceral receptors
Specific or general

3. Special Somatic Receptors Neuromasts
In skin of fish and amphibians
Monitors mechanical, electrical, and chemical stimuli
Ampullae of Lorenzini in shark snout
Figure Ampullae of Lorenzini in shark.

4. Special Somatic Receptors (cont.’d) Neuromasts
Pit organs along shark gill region
Lateral line canal
Linear series
Derived from ectodermal placodes
Figure External openings of neuromast organs in Squalus.
Figure Neuromast organ and lateral line canal in a fish.

5. Special Somatic Receptors Membranous Labyrinth
Vertebrates have pair of fluid filled membranous labyrinths
Filled with endolymph
Surrounded by perilymph
Figure Membranous labyrinths of human.
Figure Left membranous labyrinth of craniates; semicircular canals (1, 2, & 3), sacculus (s) and utriculus (u).

6. Fig. 16.6. Membranous labyrinths of vertebrates (book figure 17.34).

7. Special Somatic Receptors (cont
Special Somatic Receptors (cont.’d) Membranous Labyrinth The vestibular apparatus
Semicircular canals, utriculus, and sacculus
Inside canals:
Otoliths
Sensory hairs - perceive motion (modified neuromast)
Angular acceleration detected by the cristae of semicircular canals
Linear motion and gravity detected by maculae of utriculus and sacculus.
Figure Vestibular apparatus.

8. Figure 16.8. Human anatomy of the ear.
Figure Anlagen of amniote inner ear (otocyst). Embryonic head (a) and cross section of head (b).

9. Special Somatic Receptors (cont.’d) Membranous Labyrinth
Lagena
Out pocketing of sacculus wall
Gives rise to cochlea in mammals
Organ of Corti
Figure Cochlea and organ of Corti in mammal.

10. Special Somatic Receptors (cont.’d) Membranous Labyrinth
Weberian ossicles
Fish transmit sound waves
Modified transverse process
Sinus impar (some fish)
Assists in transport of sound
(a)
Figure (a) Weberian ossicles (b) Weberian apparatus for transmitting swim bladder vibrations to ear.
(b)

11. Special Somatic Receptors (cont.’d) Membranous Labyrinth
Middle Ear of Tetrapods
Canal from evagination of 1st pharyngeal pouch
Eustachian tube
Communication between pharynx and middle ear
Figure Position of Eustachian tube.

12. Outer, Middle, and Inner Ear of a Bat
Figure Bat ear
(book figure 17.44).

13. Special Somatic Receptors (cont.’d) Membranous Labyrinth
Middle Ear of Tetrapods
Bones:
Malleus, incus, and stapes
Derived from 1st and 2nd visceral arches
Stapes is columella in reptiles and birds
Figure Middle ear bones.

14. Special Somatic Receptors (cont.’d) Membranous Labyrinth
Sensory receptors: Cristae (in semicircular canals)and maculae (within sacculus
and utriculus of inner ear (book figure 17.45).

15. Special Somatic Receptors (cont.’d) Membranous Labyrinth
Middle Ear of Tetrapods
Figure Development of the middle ear bones.

16. Special Somatic Receptors (cont.’d)
Outer Ear of Tetrapods
Pinnae
Ear drum set back into skull
Crocs, birds, and mammals
Tympanic membrane on outside
Frogs
External auditory meatus
Canal leading to tympanic membrane

17. Special Somatic Receptors Infrared Receptors
Pits that open to surface
Between epidermal scales
Loreal pits
Pit vipers
Between nostril and eye
thermosensitive
Labial pits
Pythons
Other thermosensitive pits
Appear similar to neuromasts
Infrared receptors in snakes
(book figure 17.30).

18. Special Somatic Receptors Light Receptors
Pineal Complex
Depending upon the species,
the epithalamus may evaginate to
produce up to four discrete organs.
Paraphysis (most anterior)
Dorsal sac
Parietal organ – no retinal image
Epiphysis
(two or more present = Pineal complex)
Fig Pineal complex (a). Generalized
parietal eye (b) (book figure 17.28)

19. Special Somatic Receptors Light Receptors (cont.’d)
Figure Pineal complex in lower vertebrates (book figure 17.29).

20. Pineal Complex (cont.’d)
Figure Parietal eye of iguana (book figure 17.19).

21. Special Somatic Receptors (cont.’d) Light Receptors
Median eye (3rd or pineal eye) (con’t)
Part of epiphyseal (pineal) complex
Anterior parapineal is often photosensitive
Lamprey- both epiphysis and parietal organ
Both photosensitive
Lizard- parietal becomes 3rd eye
Frontal organs
3rd eye in larval frogs
Photosensitive
Figure Epiphyseal (pineal) complex of lamprey and embryonic and adult lizard.

22. Special Somatic Receptors Light Receptors
Photoreceptors
Lateral eyes
A reflective surface, the
tapetum lucidum,
is found in the choroid
layer in some nocturnal
mammals and produces the
“eye-shine” in car headlights
Figure Lateral eyes
(book figure 17.18).

23. Special Chemoreceptors Olfactory Organs
Ectodermal placodes
Sink into head
Internal naris- opening inside
Lungfish and tetrapods
External naris- opening outside
Fish
Higher vertebrates possess both types
Figure Internal and external naris shown and vomeronasal organ.

24. Special Chemoreceptors (cont’d.) Olfactory Organs
Vomeronasal organ (Jacobson’s Organ)
Olfactory mechanisms isolated form nasal
Snakes and lizards
Insert forked tongue into organ
(a)
(b)
Figure Snake collecting scent molecules (a) that are then delivered to the vomeronasal organ by the tongue (b).

25. Snake Vomeronasal Organ (cont.’d)
Figure Tongue flicking (book figure 17.14).

26. Special Chemoreceptors Organs of Taste
Taste buds
Similar to neuromasts
In oral cavity and pharynx
Figure Anatomy of the taste bud.

27. Special Chemoreceptors Organs of Taste (cont.’d)
Figure Distribution of taste buds on the human tongue (book figure 17.15).