2-Vertebrate Structure and Development (Part II)

DEVELOPMENT OF CHORDATE CHARACTERS IN VERTEBRATES

NEURAL CREST

SCALING

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Articles• Meant to be read as exam prep • PK prep/background

zygote morula blastula

Q: What is the fate of the blastopore?

Gastrulation: one layer to three

http://worms.zoology.wisc.edu/frogs/gastxen/wholegas.html

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So, why do we care . . .

Evolution shaped chordates into vertebrates (us!)

From this …… ….. to this

Devonian “Age of Fishes” ~ 400 MYA

“tube within a tube” organization

Amphioxus, a NON-vertebrate chordate

Q: Predict organ systems that must have been elaborated in early, predaceous vertebrates

Branchiostoma (Amphioxus)

CHORDATE BODY PLAN

Quick Quiz!

neural tube differentiation

ectodermal placodes associated with the “special senses”

Ectoderm

ELABORATION OF CHORDATE CHARACTERS IN VERTEBRATES

olfactory placode

lens placode

otic placode

Cranial mesoderm –

braincase

Postcranial mesoderm

notochord

paraxial mesoderm or somites

vertebrae and axial skeleton

more

Mesoderm

paraxial mesoderm or somites, cont’d.

segmental muscles (myomeres)

migratory muscle cells

(somitic derivatives are segmental)

intermediate mesoderm

kidneys

lateral plate mesoderm

appendicular skeleton

heart

The heart is VENTRAL

each perforation of the pharynx is associated with a skeletal support (= gill arch), blood vessels and a gill.

Endoderm

Q: what is the function of the perforated pharynx in vertebrates?

non-vertebrate chordate

vertebrate chordate

Q: in what ways do vertebrate chordates differ from non-vertebrate chordates?

Summary of chordate and vertebrate structure

mouth perforated pharynx gut anus notochord dorsal tubular nerve cord

Neural crest cells, labeledNeural crest formation

The essential vertebrate tissue: = the 4th germ layer?

NEURAL CREST

Neural crest cells contribute to many distinctively vertebrate structures: Pharyngeal arches, jaws, teeth, cranial nerves, heart, melanocytes, teeth, adrenal glands, autonomic nervous system, dermal bone

Scaling and allometry: importance of size

Scaling basics:

-allometric equation

-geometric similarity

Groovy and childish examples

SCALING

SCALING

Q: How much bigger is the larger “animal” than the smaller?

Scaling basics: geometric similarity (large organisms could be (but are not necessarily) just geometrically scaled-up versions of small organisms)

Metabolism, as well as structure, is scaled….

Harwood, P. 1963. Therapeutic dosage in small and large mammals . Science 139: 684-685.

West, L. J., C. M. Pierce and W. D. Thomas. 1962. Lysergic acid diethylamide: its effects on a male Asiatic elephant. Science 138:1100-1103.

0.5-1.0 mg/kg is the minimum to cause a “transient rage”

6.5 mg/kg is lethal.

297 mg (= 0.10 mg/kg) was administered to “Tusko”, a male Indian elephant (West et al. 1962).

0.1 - 0.2 mg causes mental disturbance

0.02 mg/kg causes psychotic symptoms

Predicting LSD dosage for a large animal……

Q: Was Tusko overly “sensitive” to LSD?

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