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Muscle and Development
Diverse body movements require
variation in muscle activity
• An individual muscle cell either contracts
completely or not all.(muscle fiber)
• Individual muscles, composed of many individual
muscle fibers, that can contract to varying
degrees.
– One way variation is
accomplished is by
varying the frequency
of action potentials
reaching the muscle
from a single motor neuron.
– Graded muscle
contraction can
also be
controlled by
regulating the
number of
motor units
involved in the
contraction.
Fig. 49.38
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– Recruitment of motor neurons increases the
number of muscle cells involved in a
contraction.
– Some muscles, such as those involved in
posture, are always at least partially contracted.
• Fatigue is avoided by rotating among motor units.
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• Fast and Slow Muscle Fibers.
– Fast muscle fibers are adapted for rapid,
powerful contractions.
• Fatigue relatively quickly.
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– Slow muscle fibers are adapted for sustained
contraction.
• Relative to fast fibers, slow fibers have.
– Less SR  Ca2+ remains in the cytosol longer.
– More mitochondria, a better blood supply, and
myoglobin.
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• Other Types of Muscle.
– In addition to skeletal muscle, vertebrates have
cardiac and smooth muscle.
– Cardiac muscle: similar to skeletal muscle.
• Intercalated discs facilitate the coordinated
contraction of cardiac muscle cells.
• Can generate there own action potentials (even
single cells in cell culture).
• Action potentials of long duration.
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Fig. 40.4
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– Smooth muscle: lacks the striations seen in
both skeletal and cardiac muscle.
• Contracts with less tension, but over a greater range
of lengths, than skeletal muscle.
• No T tubules and no SR.
• Ca2+ enters the cytosol from via the plasma membrane.
• Slow contractions, with more control over
contraction strength than with skeletal muscle.
• Found lining the walls of hollow organs.
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• Invertebrate muscle cells are similar to vertebrate
skeletal and smooth muscle cells.
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Relevant pages in Campbell
for reproduction and
development
• 975-980
• 998-1010
CHAPTER 46
ANIMAL REPRODUCTION
Overview of Animal Reproduction
1. Both asexual and sexual reproduction occur in the animal kingdom
2. Diverse mechanisms of asexual reproduction enable animals to produce
identical offspring rapidly
3. Reproductive cycles and patterns vary extensively among mammals
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Both asexual and sexual
reproduction occur in the animal
kingdom
 Asexual reproduction involves the formation of
individuals whose genes all come from one parent.
 There is no fusion of sperm and egg.
 Sexual reproduction is the formation of offspring by the
fusion of haploid gametes.
 Ovum: female gamete - usually large and nonmotile.
 Spermatozooan: male gamete - usually small and motile.
(the Echinoderm, an urchin)
 Sexual reproduction increases genetic variation among
offspring (allows for possible survival if environment
changes).
2. Diverse mechanisms of asexual
reproduction enable animals to
produce identical offspring rapidly
 Invertebrates:
 Fission: asexual reproduction in which a parent
separates into two or more approximately equal sized
individuals.
 Budding: asexual reproduction in which new
individuals split off from existing ones (phylum
Cindaria (hydrozoans, hydra, budding of new polyps
from colonial polyps).
 Gemmules of sponges are an example of a type of
asexual reproduction that involves the release of
specialized cells that can grow into new individuals.
 Fragmentation: the breaking of the body into
several pieces, some or all of which develop into
complete adults.
 Requires regeneration of lost body parts (associated with
lower phyla, not possible in higher vertebrates.
 Advantages of asexual reproduction:
 Can reproduce without needing to find a mate
 Can have numerous offspring in a short period of
time
 In stable environments, allows for the perpetuation
of successful genotypes.
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3. Reproductive cycles and patterns
vary extensively among animals
 Reproductive cycles are controlled by both
environmental and hormonal cues.
 Animals may be solely asexual or sexual. Or
they may alternate between the two modes
depending on environmental conditions.
Daphnia (an Arthropod crustacean) reproduce by
parthenogenesis under favorable conditions
abundant food, absence of predators and sexually
during times of environmental stress.
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 Parthenogenesis is the process by which an
unfertilized egg develops into (often) a haploid
adult.
 Parthenogenesis plays a role in the social
organization of species of bees, wasps, and ants.
 Male honeybees are haploid and female honeybees are
diploid.
 Several genera of fishes, amphibians, and lizards
produce by a form of parthenogenesis that produces
diploid zygotes.
 Some lizards require the simulation of intercourse
without fertilization to activate their eggs. Other
member can be a female.
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Mechanisms of Sexual Reproduction
1. Internal and external fertilization both depend on mechanisms
ensuring that mature sperm encounter fertile eggs of the same species
2. Species with internal fertilization usually produce fewer zygotes but
provide more parental protection than species with external
fertilization
3. Complex reproductive systems have evolved in many animal phyla
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1. Internal and external
fertilization both depend on
mechanisms ensuring that mature
sperm encounter fertile eggs of the
same species
 Internal fertilization requires cooperative behavior that
leads to copulation.
 Example of delayed implantation in seals and mustelids
(weasels). Females congregate in a colony to have pups
so are accessible to males at that time. Other times they
are ranging far and wide for food.
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 External fertilization requires a moist habitat that will
protect a developing egg from desiccation and heat stress
Example: amphibians,annelids molluscs and fishes.
– Specific mating behaviors assure that sperm and egg will
be in the same place at the same time (Frogs calling in the
spring).
Fig. 46.4
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 Pheromones: chemical signals released by one
organism that influence the behavior of other
individuals of the same species. In mammals
signals the female is ready to mate and is
ovulating a egg that can be fertilized.
 Many act as male attractants.
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2. Species with internal fertilization
usually produce fewer zygotes but
provide more parental protection
than species with external
fertilization
 Internal fertilization usually results in the production of
fewer zygotes than does internal fertilization.
 However, the survival rate is lower for external fertilization
than it is for internal fertilization. Fishes as an example. Less
than 1% survive to establish a new cohort for that year. If
conditions are very favorable more than 1% survive and when
mature there is a bountiful harvest. Especially important for
the fishing industry to understand reproductive strategies. Cod
fisheries collapsed.
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 The externally fertilized eggs of fishes and
amphibians are surrounded by a gelatinous coat.
 The internally fertilized amniote eggs of birds,
reptiles, and monotremes are protected by calcium
and protein shells and have large yolks as sources of
building blocks (amino acid, lipids nucleic acids)
and energy resources.
 In mammals the embryo is retained within the females
reproductive tract and nourished there.
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– Parental care of
offspring may occur
regardless of
whether
fertilization is
external
or internal.
Example in this
picture is a male
water bug with
fertilized eggs on its
back. Fish, birds,
some reptiles and
mammals.
Fig. 46.5
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3. Complex reproductive systems
have evolved in many animal phyla
• Insects storing sperm and getting rid of it
sometimes.
• Delayed implantation.
• Sequential hermaphrodites female first mal
2nd or vice versa. Large female can produce more
eggs or large male can guard a harem.
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 Most insects have separate sexes with complex
reproductive systems.
 In many species the female reproductive system
includes a spermatheca, a sac in which sperm may
be stored for a year or more.
Fig. 46.7
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 The basic plan of all vertebrate reproductive
systems are very similar.
 However, there are variations.
 In many non-mammalian vertebrates the digestive,
excretory, and reproductive systems share a common
opening to the outside, the cloaca (birds,reptiles and
monotremes egg laying mammals).
 Mammals have separate opening for the digestive and
reproductive systems.
 Female mammals also have separate openings for the excretory
and reproductive system.s.
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CHAPTER 47
ANIMAL DEVELOPMENT
The Stages of Early
Embryonic Development
1.
From egg to organism, an animal’s form develops gradually: the concept of
epigenesis
2. Fertilization activates the egg and bring together the nuclei of sperm and egg
3. Cleavage partitions the zygote into many smaller cells
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1. From egg to organism, an
animal’s form develops gradually:
the concept of epigenesis
• Preformation: the egg or sperm contains an
embryo that is a preformed miniature adult.
• Epigenesis: the form of an animal emerges from
a relatively formless egg. Aristotle proposed that
2000 years ago, but preformation hypothesis only
died a couple hundred years ago.
• An organism’s development is primarily
determined by the genome of the zygote and the
organization of the egg cytoplasm.
Figure 47.1 A “homunculus” inside the head of a human sperm
2. Fertilization activates the egg
and bring together the nuclei of
sperm and egg
• Sea urchins are models for the study of the early
development of deuterostomes(Echinoderms and
Chordates).
– Sea urchin eggs are fertilized externally.
– Sea urchin eggs are surrounded by a jelly coat.
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Inject with 0.5M KCl to
Induce spawning
Acrosomal tip binds
vitellin membrane receptor
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• The Acrosomal Reaction.
– Acrosomal reaction: when exposed to the jelly coat
the sperm’s acrosome discharges it contents by
exocytosis.
• Hydrolytic enzymes enable the acrosomal process to
penetrate the egg’s jelly coat.
• The tip of the acrosomal process adheres
to the vitelline layer just external to the
egg’s plasma membrane. Binds to a
receptor on the vitelline layer.
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– The sperm and egg plasma membranes fuse and a
single sperm nucleus enter the egg’s cytoplasm.
• Na+ channels in the egg’s plasma membrane opens.
– Na+ flows into the egg and the membrane depolarizes: fast block
to polyspermy.
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• The Cortical Reaction.
– Fusion of egg and sperm plasma membranes also
triggers a signal-transduction pathway.
• Ca2+ from the eggs ER is released into the cytosol and
propagates as a wave across the fertilized egg
 inositol triphosphate (IP3) and diacylglycerol (DAG)
are produced.
– IP3 opens ligand-gated channels in the ER and the Ca2+ released
stimulates the opening of other channels.
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– High concentrations of Ca2+ cause cortical
granules to fuse with the plasma membrane and
release their contents into the perivitelline space.
• The vitelline layer separates from the plasma membrane.
• An osmotic gradient draws water into the perivitelline
space, swelling it and pushing it away from the plasma
membrane.
• The vitelline layer hardens into the fertilization
envelope: a component of the slow block to polyspermy.
• The plasma membrane returns to normal and the fast
block to polyspermy no longer functions.
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• Activation of the Egg,
– High concentrations of Ca2+ in the egg stimulates an
increase in the rates of cellular respiration and
proteins synthesis.
– In sea urchins, DAG activates a protein that
transports H+ out of the egg.
• The reduced pH may be indirectly responsible for the
egg’s metabolic responses to fertilization.
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– In the meantime, back at the sperm nucleus...
• The sperm nucleus swells and merges with the egg
nucleus  diploid nucleus of the zygote.
– DNA synthesis begins and the first cell division occurs.
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• Fertilization in Mammals (early steps same as
urchin).
• Capacitation, a function of the female reproductive
system, enhances sperm function.
– A capacitated
sperm migrates
through a layer
of follicle cells
before it reaches
the zona pellucida.
– Binding of
the sperm cell
induces an
acrosomal
reaction similar
to that seen in the
sea urchin.
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Fig. 47.5
• Enzymes from the acrosome enable the sperm cell to
penetrate the zona pellucida and fuse with the egg’s
plasma membrane.
– The entire sperm enters the egg.
– The egg membrane depolarizes: functions as a fast block to
polyspermy.
– A cortical reaction occurs.
• Enzymes from cortical granules catalyze
alterations to the zona pellucida:
functions as a slow block to polyspermy
like in the urchin vitelline membrane.
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– The envelopes of both the egg and sperm nuclei
disperse.
• The chromosomes from the two gametes share a common
spindle apparatus during the first mitotic division of the
zygote.
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3. Cleavage partitions the zygote
into many smaller cells
• Cleavage follows fertilization. (sea urchin)
– The zygote is partitioned into blastomeres.
• Each blastomere contains different regions of the undivided
cytoplasm and thus different cytoplasmic determinants.
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Fig. 47.6
– Except for mammals, most animals have both eggs
and zygotes with a definite polarity.
• Thus, the planes of division follow a specific pattern
relative to the poles of the zygote.
• Polarity is defined by the heterogeneous distribution of
substances such as mRNA, proteins, and yolk.
– Yolk is most concentrated at the vegetal pole and least
concentrated at the animal pole.
• In some animals, the animal pole defines
the anterior end of the animal.
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• A blastocoel forms within the morula 
blastula
Frog
Fig. 47.8d
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• In birds the yolk is so plentiful that it restricts
cleavage to the animal pole: meroblastic
cleavage.
• In animals with less yolk there is complete
division of the egg: holoblastic cleavage.
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Figure 47.6x Sea urchin development, from single cell to larva
Pluteus
Sea urchin
gastrulation
Gastrulation rearranges
the embryonic blastula
into a triploblastic
gastrula with three
embryonic germ layers
that are the ectoderm
endoderm and mesoderm
Fig. 47.9
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• Sea urchin gastrulation.
– Begins at the vegetal pole where individual cells
enter the blastocoel as mesenchyme cells.
• The remaining cells flatten and buckle inwards:
invagination.
– Cells rearrange to form the archenteron.
• The open end, the blastopore, will
become the anus.
• An opening at the other end of the
archenteron will form the mouth of the
digestive tube.
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5. In organogenesis, the organs of
the animal body form from the
three embryonic germ layers
• The derivatives of the ectoderm germ layer are:
–
–
–
–
Epidermis of skin, and its derivatives
Epithelial lining of the mouth and rectum.
Cornea and lens of the eyes.
The nervous system; adrenal medulla; tooth enamel;
epithelium of the pineal and pituitary glands.
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• The endoderm germ layer contributes to:
– The epithelial lining of the digestive tract (except
the mouth and rectum).
– The epithelial lining of the respiratory system.
– The pancreas; thyroid; parathyroids; thymus; the
lining of the urethra, urinary bladder, and
reproductive systems.
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• Derivatives of the mesoderm germ layer are:
–
–
–
–
–
–
The notochord.
The skeletal and muscular systems.
The circulatory and lymphatic systems.
The excretory system.
The reproductive system (except germ cells).
And the dermis of skin; lining of the body cavity;
and adrenal cortex.
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Neural crest found only
in vertebrates
Dorsal
Hollow nerve tube
Fig. 47.11
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6. Amniote embryos develop in a
fluid-filled sac within a shell or
uterus
• The amniote embryo is the solution to
reproduction in a dry environment.
– Shelled eggs of reptiles and birds.
– Uterus of placental mammals.
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• Avian Development.
• Cleavage is meroblastic, or incomplete.
• Cell division is restricted to a small cap of cytoplasm
at the animal pole.
• Produces a blastodisc, which becomes arranged into
the epiblast and
hypoblast that
bound the
blastocoel, the
avian version
of a blastula.
Fig, 47.12 (1)
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• During gastrulation some cells of the epiblast migrate
(arrows) towards the interior of the embryo through
the primitive streak.
• Some of these cells move laterally to form the
mesoderm, while others move downward to form the
endoderm.
Fig, 47.12 (2)
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• In early organogenesis the archentreron is formed as
lateral folds pinch the embryo away from the yolk.
• The yolk stalk (formed mostly by hypoblast cells) will
keep the embryo attached to the yolk.
• The notochord, neural tube, and somites form as they
do in frogs.
• The three germ
layers and hypoblast
cells contribute to
the extraembyonic
membrane system.
Fig, 47.12 (3)
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• The four extraembryonic membranes are the yolk
sac, amnion, chorion, and allantois.
– Cells of the yolk sac digest yolk providing nutrients
to the embryo.
– The amnion encloses the embryo in a fluid-filled
amniotic sac which protects the embryo from drying
out.
– The chorion cushions the embryo against
mechanical shocks.
– The allantois functions as a disposal sac for uric
acid.
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Fig. 47.14
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