Download Human Biology I - Control and Development

Hewitt/Lyons/Suchocki/Yeh
Conceptual Integrated
Science
Chapter 19
HUMAN BIOLOGY I—
CONTROL AND DEVELOPMENT
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This lecture will help you
understand:
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Organization of the Human Body
Homeostasis
The Brain
The Nervous System
How Neurons Work
How Fast Can Action Potentials Travel?
Endorphins
The Senses—Vision, Hearing, Smell and Taste, Touch
Hormones
Reproduction and Development
The Skeleton and Muscles
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Organization of the Human Body
The many processes that occur in our body require
coordination.
Cells achieve this coordination by working together in
structures with varying levels of complexity: tissues,
organs, and organ systems.
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Organization of the Human Body
There are 10 major organ systems in the
human body:
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Nervous
Endocrine
Reproductive
Sensory
Muscular and
skeletal
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Circulatory
Respiratory
Digestive
Immune
Excretory
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Homeostasis
Homeostasis is maintenance of a stable internal
environment.
Examples:
• Temperature control
• Oxygen level of blood
• Amount of water in the body
• Concentration of ions inside and outside cells
• Blood pH
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The Brain
Certain functions are associated with certain
parts of the brain
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The Brain
The brain stem controls involuntary
activities such as heartbeat, respiration,
and digestion.
The cerebellum controls balance, posture,
coordination, and fine motor control.
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The Brain
The cerebrum:
• Largest part of the brain
• Takes in information from the senses
• Controls all conscious, voluntary activities
• Left hemisphere controls the right side of
the body and vice versa
• Performs information processing in the
cerebral cortex (the thin, wrinkled layer
covering the cerebrum)
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The Brain
The cerebrum’s four lobes:
• Frontal lobes—reasoning, control of
voluntary movement, speech
• Parietal lobes—temperature, touch, taste,
and pain
• Occipital lobes—visual information
• Temporal lobes—sound, language
comprehension
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The Brain
The control of certain cognitive functions is
dominated by either the right or left
cerebral hemisphere:
Left hemisphere: math, reasoning,
language, detail-oriented activities
Right hemisphere: spatial relations,
emotional processing, music
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The Brain
Thalamus: receives information from many parts
of the brain, sorts it, and passes important data
on to the cerebral cortex
Hypothalamus controls:
• Emotions, such as pleasure and rage
• Bodily drives, such as hunger, thirst, sex drive
• Body temperature and blood pressure
• Internal clock
• Release of hormones
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The Brain
CHECK YOUR NEIGHBOR
What part of your brain allows you to consciously
hold your breath? What part makes you finally
take a breath?
Explain your answer to your neighbor.
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The Brain
CHECK YOUR ANSWER
Your cerebrum allows you to decide to hold
your breath.
Your brainstem protects you by making you
take a breath eventually.
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The Nervous System
The nervous system consists of two parts:
• Central nervous system—brain and spinal cord
• Peripheral nervous system—all of the other nerves in
the body
And two cell types:
• Neurons—receive and transmit electrical impulses
• Glial cells—support, protect, and insulate neurons
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The Nervous System
A typical neuron consists of extensions called
dendrites, a cell body, and an axon. The
dendrites receive information from other neurons
or cells. The axon transmits information.
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The Nervous System
Depending on the origin and destination of their
messages, neurons are divided into three
categories:
• Sensory neurons carry messages from the
senses to the central nervous system.
• Interneurons, found only in the central nervous
system, connect neurons to each other.
• Motor neurons carry messages from the central
nervous system to the rest of the body.
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The Nervous System
There are two types of motor neurons:
• Somatic nervous system: controls
voluntary actions
• Autonomic nervous system: controls
involuntary muscles and other internal
organs
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The Nervous System
Within the autonomic nervous system are two divisions:
• Sympathetic:
fight-or-flight response
• Parasympathetic:
operates in times of
relaxation
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How Neurons Work
Neurons use electrical signals in the form of
changes in voltage, or electric potential, across
the cell membrane. The electric potential across
the membrane is called the membrane potential.
The inside of a neuron is normally negatively
charged and the outside is normally positively
charged. The resting potential is about -70 mV.
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How Neurons Work
A neuron must be stimulated in order to fire.
A neuron is stimulated when its membrane
potential is increased.
If the membrane potential reaches a certain
threshold value, sodium channels open,
sodium ions rush into the cell, and the
membrane potential spikes, creating an
action potential.
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How Neurons Work
Once the spike occurs, the
sodium channels close and
potassium channels open,
and the membrane potential
returns to resting value.
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How Neurons Work
Action potentials are all-or-nothing events. A
neuron either fires or it doesn’t.
A neuron cannot fire “harder” in response to
a stronger stimulus. But it can fire more
frequently.
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How Neurons Work
Action potentials travel down
the axon to signal to a
target cell. How is the
action potential propagated
down the axon?
Once an action potential has
occurred in one part of the
axon membrane, there’s a
brief period when the area
cannot be stimulated again.
This prevents the action
potential from moving
backwards.
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How Neurons Work
Myelin sheaths speed the movement of a signal by
insulating the axon.
The disease multiple sclerosis causes the body to
destroy myelin.
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How Neurons Work
At the end of its axon, the neuron connects
with a target cell—either another neuron or
a cell that does something (such as a
muscle cell).
The connections between neurons and their
target cells are called synapses.
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How Neurons Work
In electrical synapses, ions flow directly from
a neuron to a target cell through channels
called gap junctions.
Electrical synapses transmit action
potentials rapidly and are found in places
like heart muscle.
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How Neurons Work
Most synapses are chemical synapses.
Chemical synapses allow for a finer degree of control.
When the action potential reaches the end of the axon, the
neuron releases a chemical messenger called a
neurotransmitter into the space between the neuron and the
target cell.
Neurotransmitters diffuse to the target cell and bind to receptors
on the target cell. This opens ion channels in the target cell,
changing its membrane potential.
The effect of the neurotransmitter may be to make the target cell
more likely to fire. Or, the effect may be to make the target cell
less likely to fire.
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How Neurons Work
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How Fast Can Action Potentials
Travel?
An action potential’s speed depends on how quickly
successive parts of the axon’s cell membrane can be
induced to increase to threshold.
This is determined by how quickly sodium ions travel
downstream. This depends on Ohm’s law:
Current = voltage/resistance
Thicker axons have lower resistance. Myelinated axons
have lower resistance. In myelinated axons, the ability of
the action potential to jump from one gap in the myelin
sheath to the next makes it faster still.
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Endorphins
Endorphins bind to opiate receptors on
neurons. Like opiates, endorphins
decrease sensitivity to pain and induce
euphoria.
Endorphin release is associated with many
activities, including “runner’s high,” eating
chocolate, and meditation.
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The Senses—Vision
Vision depends on light entering the eye through
the cornea and the pupil. The light then passes
through the lens, which focuses it on the retina.
The retina holds the actual
light-sensitive cells of the eye—
rods and cones. When light hits
these cells, action potentials
occur that transmit information
to the brain via the optic nerve.
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The Senses—Vision
Rods are very sensitive to light and are responsible for
vision in dim light. Rods cannot discriminate colors, so at
night we see shades of gray.
Cones detect color by responding to red, green, and blue
light. Cones also provide us with our ability to see fine
details.
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The Senses—Hearing
The ear consists of three parts: the
outer, middle, and inner ear.
Sound waves vibrate the eardrum.
The movement of the eardrum, in
turn, moves three middle ear
bones—hammer, anvil, and stirrup—
in sequence, amplifying the sound.
In the cochlea, vibrations bend tiny
sensory “hairs,” starting action
potentials.
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The Senses—Smell and Taste
Smell and taste rely on chemoreception—a
process in which chemicals bind to receptors on
the surface of special chemosensory cells. The
binding opens ion channels and begins action
potentials.
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The Senses—Touch
The sense of touch includes several different senses,
including pressure, temperature, and pain.
Separate sensory cells detect light
touch and heavy pressure.
Unlike other touch receptors, pain
receptors become more sensitive
with continued stimulation.
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Hormones
Hormones are chemical messengers that
give instructions to the body. Hormones
are:
• Produced in one place in the body
• Released into the bloodstream
• Received by target cells elsewhere
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Hormones
Protein hormones bind to receptors on the
cell membranes of their target cells.
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Hormones
Steroid hormones cross the cell membrane and
bind to receptors in either the cytoplasm or
nucleus of the target cell. The hormone and
receptor then bind to DNA in the nucleus and
directly affect gene transcription.
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Hormones
Endocrine organs include:
• Hypothalamus
• Anterior and posterior pituitary glands
• Thyroid
• Parathyroid
• Adrenal glands
• Pancreas
• Ovaries
• Testes
• Pineal gland
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Hormones
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Reproduction and Development
Eggs and sperm are gametes—haploid cells
produced through meiosis.
Eggs are large, because they are the result
of unequal meiosis—during cell division,
the future egg gets almost all of the
cytoplasm and the other cells receive very
little. These other cells quickly degenerate.
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Reproduction and Development
The ovaries are made up of follicles, developing eggs
surrounded by support cells.
After ovulation, the egg moves down the oviduct, where
fertilization can take place. If the egg becomes fertilized,
it completes meiosis.
After fertilization, the egg continues to the uterus, where it
implants and continues development.
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Reproduction and Development
Sperm are made in the testes, which is located in the
scrotum. From the testes, sperm move to the epididymis,
where they complete development and become mobile.
Each mature sperm has a head that contains DNA,
mitochondria, enzymes for penetrating the egg, and a
tail.
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Reproduction and Development
The egg is surrounded by the zona
pellucida. Once a sperm has reached the
egg’s cell membrane, the two membranes
fuse. The zona pellucida changes to
become impenetrable to additional sperm.
This ensures that the fertilized egg does
not end up with too many chromosomes.
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Reproduction and Development
CHECK YOUR NEIGHBOR
What organ provides oxygen and nutrients
to the developing embryo and carries
away wastes?
Explain your answer to your neighbor.
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Reproduction and Development
CHECK YOUR ANSWER
The placenta delivers oxygen and nutrients
to the developing embryo and carries
away wastes.
The placenta also produces the sex
hormones estrogen and progesterone
throughout pregnancy to prevent further
ovulation and maintain the uterus in
nurturing condition.
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The Skeleton and Muscles
The skeleton:
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Consists of bones and cartilage
Includes 206 bones
Protects the body
Supports and moves the body
Produces red and white blood cells in the bone
marrow
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The Skeleton and Muscles
Muscles:
• Contract, or shorten
• Are connected to our bones via tendons
• Pull on our bones, moving us
• Can only pull, not push, so
we often have pairs of muscles
that work in opposition
(biceps, triceps)
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The Skeleton and Muscles
How do muscles contract?
• A muscle receives a signal from a motor neuron
— Motor neurons connect to muscles through a
chemical synapse that uses the
neurotransmitter acetylcholine
• Acetycholine starts an action potential in the
muscle cells
• The muscle cells contract
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The Skeleton and Muscles
A muscle consists of a bundle of elongated muscle
fibers. Each fiber is actually a single cell with
multiple nuclei.
Each muscle fiber contains myofibrils, which are
made of contractile units called sarcomeres.
The sarcomeres are made up of actin and myosin,
which work together to shorten and contract the
muscle.
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The Skeleton and Muscles
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