Sense organs

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Sense organs

Sense organs -

functional classification

i

(a) Mechanoreceptors

(b) Radioreceptors

–Radiation: narrow high-frequency band

of heat and light.

–Light: wavelengths to which human visual

system is sensitive (380-780 nm).

(c) Chemoreceptors


Heat

Light


Examples of radioreceptors

• Cutaneous receptors

•Pit organs

• Electromagnetic receptors

•Eyes

– Medial eyes

– Lateral eyes


Examples of radioreceptors

• Cutaneous receptors

•Pit organs

– Detect infrared radiation

• Electromagnetic receptors

•Eyes

– Medial eyes

– Lateral eyes


Facial pit of a pit viper

Yellow eyelash viper

Western diamondback


Image of rat recorded on infrared film:

Infrared

frequencies

proportional to

temperature:


Examples of radioreceptors

• Cutaneous receptors

•Pit organs

• Electromagnetic receptors

•Eyes

– Medial eyes

– Lateral eyes


Evolution of electroreception


Ampullae of Lorenzini


Electrical receptors

Facial nerve

Hammerhead shark


Buried live fish

Shark finds fish

Detection

of buried

prey by

sharks

Buried live fish

isolated in agar

Shark chooses fish

over odors

Buried fish parts

Shark finds odors

Buried fish

insulated and isolated

Shark ignores fish

Buried electrodes

Shark finds electrodes

Buried electrodes

Visible fish parts

Shark finds electrodes


Examples of radioreceptors

• Cutaneous receptors

•Pit organs

• Electromagnetic receptors

•Eyes

– Medial eyes

– Lateral eyes

– Both outgrowths of the

diencephalon region of the brain


Eyes

•Dorsal medialeyes:

– Outgrowths from roof of brain.

– Induce overlying epidermal tissue.

–Two “bodies”:

•Anterior parietal body.

• Posterior pineal body.

– Only one active in any species.


Pineal eyes of

lampreys and

ostracoderms

Parietal eyes

of lizards

Anterior

Posterior


Anterior

Generalized

parietal eye

Posterior


Eyes

• Dorsal medial eyes

• Lateral paired eyes:

– Outgrowths from sides of brain.

– Induce overlying epidermal tissue.

– Common vertebrate plan, many structural

variations.

– Analogs, but not homologs, in other phyla.


• Outer tunic:

Structure of the vertebrate eye

– Sclera: fibrous wall.

– Cornea: transparent external layer.

• Middle uvea:

– Pigmented choroid layer, against sclera.

– Ciliary body.

• Secretions.

• Origin of intrinsic eye muscles to lens.

– Pigmented iris diaphragm, separated from

cornea by chamber.

• Inner retina:

– Light-insensitive region, against ciliary body

and iris.

– Light-sensitive region, against choroid and

sclera.


Light-sensitive region of retina

• Sensory (nervous) layer, with tertiary

photoreceptors:

p

– Rods: dim-light (scotopic) vision.

– Cones: bright-light (photopic) and color vision.

• Primates: 3 types (S, M, L) that detect short,

medium, and long wavelengths.

• Other mammals: 2 types (R-G colorblind).

• Fishes, amphibians, reptiles, birds: 2-5.

– Ultraviolet (UV) receptors in some vertebrates.

• Optic stalk: afferent and efferent neurons.

• Layer of neurons preprocesses visual signals

before passing them on to retina and brain.


Light


Variation i in the

vertebrate eye


Nictitating membranes

• Protective fold over eye in

many vertebrates:

–Chondrichthyans

h h

– Some amphibians

– Most reptiles, crocodilians, birds

– Some mammals

• Transparent / translucent

eye-lid:

– Moistens, tn, cleans and prtct protects eye

without losing sight completely.

– Protects against sun blindness in

many desert and arctic

vertebrates.

Shark

Frog

Bird

Mammal


Extrinsic skeletal

muscles of the eyeball

• Three sets of muscles:

– Innervated by 3 (of 12)

sets of cranial nerves.

• Constant “fixational eye

movements”:

– Counteracts neural

adaptation to light input.

– Without movements,

image would fade.


Development of

sensory placodes


Induction of lens and cornea

by the optic vesicle


• Spherical lenses are

better adapted to vision

in water.

• Elliptical lenses are

better adapted to vision

in air.

Astigmatism: poor focus


Spherical lenses allow many fishes to

focus simultaneously at different

distances:


Archer fish (Toxotes)


Fish eyes


Anableps

anableps


• Lens:

Trends in the eye

– Fishes, amphibians, reptiles: spherical lenses.

• Focus by movement of lens.

– Birds, mammals: elliptical lenses.

• Focus by changing shape of lens.

• Tetrapods have:

– Eyelids for protection.

–Irisdiaphragm for light control.

–Tear glandsand ducts.


Sense organs -

functional n classification

(a) Mechanoreceptors

(b) Radioreceptors

(c) Chemoreceptors

– Chemical substances:

•Fat-soluble (smelled).

• Water-soluble (tasted).

•Pheromones (vomeronasal organ).

“We are all more influenced by smell than we know.” (Hercule Poirot)

Agatha Christie

Murder in Retrospect


Vertebrate olfactory epithelium


Development of

sensory placodes


Olfactory organs of fishes


Teleost

Lungfish

Amphibian

Reptile

Mammal


• Humans; ~400 kinds of odor receptors.

– Produce graded responses.

– Detection of 10 4 -10

6 different odors.

• Other mammals: up to 600 kinds of odor

receptors.


Sense organs

(1) Morphological classification

cat (2) Functional classification

(3) Developmental classification

–Somaticreceptors:

• Provide information about the external

environment and body orientation.

– Visceral receptors:

• Provide information about the internal

environment.


Sense organs


developmental classification

•Somaticreceptors:

– Derived primarily from ectoderm and

mesoderm.

– Receptors of the skin, brain, muscles.

– Provide information about external

environment and body orientation.

– Organism makes appropriate skeletalmuscle

response.


Examples of somatic receptors

• Cutaneous receptors

• Lateral-line organs

•Labyrinth organs

• Radioreceptors

• Proprioceptors


Sense organs

developmental l classification

• Somatic receptors

• Visceral receptors:

– Derived primarily from endoderm and

mesoderm.

– Receptors of the gut, respiratory, circulatory

systems.

– Provide information about the internal

environment.

– Organism makes appropriate smooth-muscle or

glandular l

response.


Examples of visceral receptors

• General visceral receptors

• Vascular monitors

• Olfactory organs

•Taste buds

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