Lecture 20

Question 1

Types of Sense Organs:

Answer 1

• Chemoreceptors - smell, taste
• Photoreceptors - vision, light
• Mechanoreceptors - touch, hearing, lateral line, balance/position

Question 2

Chemoreception – Olfactory Organs:

Answer 2

• Ectodermal origin
• Olfactory epithelium located in the nasal pit or respiratory
• Olfactory hairs (dendrites) of olfactory receptor cells increase surface area and contain olfactory receptors that bind odorants/smells
• Activation of receptors sends electric signals to brain via olfactory nerve
• Olfaction is used for discrimination of chemicals (like odorants and pheramones) in the environment

Question 3

Chemoreception – Olfactory Organs (In Animals):

Answer 3

• Fishes: variable sense of smell but well-developed in some species; nasal pits with olfactory epithelium; barbels also smell
• Air-breathing Vertebrates: add mucous cells to dissolve the odorants and wash away old samples
• Tetrapods: size and complexity of nasal chamber increased
• Mammals: complex turbinate (scrolls of bone) increase surface area of olfactory epithelium; distinguish many scents

Question 4

Photoreception - General:

Answer 4

• Involve cells capable of phototransduction (ex. generate electrical signals with photon absorption
• Photoreceptor neurons are organized into the complex epithelium of the retina in the eyes
• Photoreceptor cells (rods and cones) detect light
• Converted to electrical signal and relayed to brain via optic nerve
• Brain translates the electrical signals into an image

Question 5

Eye Adaptation to Dim Light:

Answer 5

• Large eyes: large pupil, large lens close to retina
• Retina with few cone cells or none, slender rod cells closely packed together
• Tapetum lucidum, a reflective layers behind the retina, can be present

Question 6

Mechanoreception – the Lateral Line System in Aquatic Animals

Answer 6

• Present in all fish and larval (some adult) amphibians
• Consists of thousands of neuromasts dispersed on body surface or inside later line canal
• Neuromast contain hair cell mechanoreceptors
• Hair cells detect water movement by converting mechanical stimuli neural information

Question 7

Mechanoreception – the Inner Ear in Tetrapods
A) The Vestibular Organs and Equilibrium (4)

Answer 7

1. The vestibular organs, ex. the semucircular canals and two chambers (saccule and utricle), detect position and motion of head and are important for balance
2. Liquid movement in the semicircular canals causes deflection of hair cells mechanorecptors in ampullae
3. Integration of signals from all ampullae permits precise determination of head movement in 3 dimensions
4. Similar structure and function to lateral line system

Question 8

Mechanoreception – the Inner Ear in Tetrapods
B) The Cochlea and Hearing

Answer 8

• Tympanum (eardrum) receives airbone sound waves/vibrations
• Middle ear bones mechanically transmit the vibration to the oval window
• Motion of waves in cochlea fluid translates into shearing force over the hair cells mechanoreceptors
• Hearing sensitivity and selectivity depend on amplification in middle ear and differential responsiveness to sound frequencies along the length of tectorial membrane in inner ear

Question 9

Modifications of the Ear (fish, amphibians, reptiles, mammals)

Answer 9

• Fishes: inner ear only and no cochlea; saccule is primarily responsible for sound
• Amphibian: middle and inner ear; sound arrives to inner ear via two routes: tympanum-stapes (sound waves) and scapula-operculum (ground vibrations)
• Reptiles: some snakes have no middle ear; stapes joins the mandible or quadrate for reception of vibration from the substrate
• Mammals: complex middle ear, very long cochlea, external ear