2-Vertebrate Structure and Development (Part II)
DEVELOPMENT OF CHORDATE CHARACTERS IN VERTEBRATES
NEURAL CREST
SCALING
Weekly Quizzes
• Posted Wednesday by 17:00
• First Quiz Next Friday
• Due Friday before 17:00
2
zygote
morula
blastula
Gastrulation: one layer to three
Q: What is the fate of the blastopore?
http://
worms.zoology.wisc.edu/
frogs/gastxen/wholegas.html
Fate maps of the blastula
Major derivatives of each germ layer
Q: what is the relationship of the “3 chordate characters” to the 3 germ
(tissue) layers?
http://www.gastrulation.org/Movie13_1.mov
Differentiation of
the ectoderm to
form the dorsal
tubular nerve cord
Differentiation of the mesoderm to form somites (paraxial mesoderm),
intermediate mesoderm, and lateral plate mesoderm and their many
derivatives…..including the notochord.
Differentiation of the anterior gut (endoderm) to form the perforated
pharynx
QQ: what is the ancestral function of the perforated pharynx?
CHORDATE BODY PLAN
“tube within a tube” organization
Amphioxus, a NONvertebrate chordate
Branchiostoma (Amphioxus)
Q: Predict organ systems that must have been elaborated in early,
predaceous vertebrates
ELABORATION OF CHORDATE CHARACTERS IN
VERTEBRATES
Ectoderm
neural tube differentiation
ectodermal placodes associated with the “special senses”
olfactory
placode
lens placode
otic placode
Mesoderm
Cranial mesoderm –
braincase
Postcranial mesoderm
notochord
paraxial mesoderm or somites
vertebrae and axial skeleton
more
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
Endoderm
each perforation of the pharynx is
associated with a skeletal support (= gill
bar), blood vessels and a gill.
The heart is VENTRAL
Q: what is the function of the perforated pharynx in vertebrates?
Summary of chordate and vertebrate structure
vertebrate chordate
mouth
perforated pharynx
gut
anus notochord
dorsal tubular
nerve cord
non-vertebrate chordate
Q: in what ways do vertebrate chordates differ from non-vertebrate
chordates?
NEURAL CREST
The essential vertebrate tissue: =
the 4th germ layer?
Neural crest formation
Neural crest cells, labeled
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
Scaling and allometry: importance of size
Scaling basics:
-allometric equation
-geometric similarity
Groovy and childish examples
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….
Predicting LSD dosage for a large animal……
0.5-1.0 mg/kg is
the minimum to
cause a
“transient rage”
6.5 mg/kg is
lethal.
0.1 - 0.2 mg
causes mental
disturbance
0.02 mg/kg
causes psychotic
symptoms
297 mg (= 0.10 mg/kg) was administered to “Tusko”,
a male Indian elephant (West et al. 1962).
Q: Was Tusko overly “sensitive” to LSD?
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.
Harwood, P. 1963. Therapeutic dosage in small and large mammals . Science 139: 684-685.
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