Comparative Anatomy Sensory Organs

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Comparative AnatomySensory Organs

• Kardong
• Chapters 15

Part 16
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Sense Organs

• Monitor external and internal environment
• Somatic or visceral receptors
• Specific or general

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Special Somatic ReceptorsNeuromasts

• In skin of fish and amphibians
• Monitors mechanical, electrical, and chemical
  stimuli
• Ampullae of Lorenzini in shark snout

Figure 16.1. Ampullae of Lorenzini in shark.
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Special Somatic Receptors (cont.)Neuromasts

• Pit organs along shark gill region
• Lateral line canal
• Linear series
• Derived from ectodermal placodes

Figure 16.2. External openings of neuromast
organs in Squalus.
Figure 16.3. Neuromast organ and lateral line
canal in a fish.
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Special Somatic ReceptorsMembranous Labyrinth

• Vertebrates have pair of fluid filled membranous
  labyrinths
• Filled with endolymph
• Surrounded by perilymph

Figure 16.5. Membranous labyrinths of human.
Figure 16.4. Left membranous labyrinth of
craniates semicircular canals (1, 2, 3),
sacculus (s) and utriculus (u) (see book Fig.
17.34).
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Special Somatic Receptors (cont.)Membranous
Labyrinth

• Semicircular canals, utriculus, and sacculus
• Inside canals
• Otoliths
• Sensory hairs- perceive motion
• Angular motion detected by semicircular canals
• Linear motion detected by utriculus and sacculus

Figure 16.6. Vestibular apparatus.
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Figure 16.7. Human anatomy of the ear.
Figure 16.8. Anlagen of amniote inner ear
(otocyst). Embryonic head (a) and cross section
of head (b).
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Special Somatic Receptors (cont.)Membranous
Labyrinth

• Lagena
• Out pocketing of sacculus wall
• Gives rise to cochlea in mammals
• Organ of Corti

Figure 16.9. Cochlea and organ of Corti in
mammal.
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Special Somatic Receptors (cont.)Membranous
Labyrinth

• Weberian ossicles
• Fish transmit sound waves
• Modified transverse process
• Sinus impar (some fish)
• Assists in transport of sound

(a)
Figure 16.10. (a) Weberian ossicles (b) Weberian
apparatus for transmitting swim bladder
vibrations to ear.
(b)
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Special Somatic Receptors (cont.)Membranous
Labyrinth

• Middle Ear of Tetrapods
• Canal from evagination of 1st pharyngeal pouch
• Eustachian tube
• Communication between pharynx and middle ear

Figure 16.11 Position of Eustachian tube.
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Middle and Inner Ear of a Bat
16.12. Bat ear.
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Special Somatic Receptors (cont.)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 16.13 Middle ear bones.
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Special Somatic Receptors (cont.)Membranous
Labyrinth
16.14. Crista and macula of inner ear.
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Special Somatic Receptors (cont.)Membranous
Labyrinth

• Middle Ear of Tetrapods

Figure 16.15. Development of the middle ear
bones.
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Special Somatic Receptors (cont.)

• 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

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Special Somatic ReceptorsInfrared 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

16.16. Infrared receptors in snakes (book figure
17.30).
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• Special Somatic ReceptorsLight 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. 16.17. Pineal complex (a).
Generalized parietal eye (b) (book figure 17.28)
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Pineal Complex (cont.)
Figure 16.18. Parietal eye of iguana (book
figure 17.19).
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Special Somatic Receptors Light Receptors

• Photoreceptors
• Lateral eyes

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Special Somatic Receptors (cont.) Light
Receptors

• Median eye (3rd or pineal eye) (cont)
• 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 16.16. Epiphyseal (pineal) complex of
lamprey and embryonic and adult lizard.
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Special ChemoreceptorsOlfactory Organs

• Ectodermal placodes
• Sink into head
• Internal naris- opening inside
• Lungfish and tetrapods
• External naris- opening outside
• Fish
• Higher vertebrates possess both types

Figure 16.17. Internal and external naris shown
and vomeronasal organ.
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Special Chemoreceptors (cont.)Olfactory Organs

• Vomeronasal organ (Jacobsons Organ)
• Olfactory mechanisms isolated form nasal
• Snakes and lizards
• Insert forked tongue into organ

(a)
(b)
Figure 16.18 Snake collecting scent molecules
(a) that are then delivered to the vomeronasal
organ by the tongue (b).
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Snake Vomeronasal Organ
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Special ChemoreceptorsOrgans of Taste

• Taste buds
• Similar to neuromasts
• In oral cavity and pharynx

Figure 16.19. Anatomy of the taste bud.