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Chapter 26
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26-1
Coordination in Multicellular
Animals

Maintaining a constant internal environment is
crucial for large multicellular organisms.
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26-2

Accomplished by monitoring and modifying the functioning
of various systems
Called homeostasis
Homeostasis maintains oxygen levels, blood
pressure, heart rate, body temperature, fluid levels,
pH, etc.
Homeostasis is maintained by the nervous,
endocrine and immune systems.
Example: Running up a hill
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Negative Feedback Control

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26-3
A common homeostatic
mechanism
Occurs when an
increase in the stimulus
results in a decrease in
response
Functions to maintain a
set point
Example: Thermostat
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Positive Feedback Regulation


When an increase in
stimulus results in an
increase in response
Does not result in
homeostasis, but plays
an important role in
homeostasis
–
26-4
Childbirth
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Nervous System Function


26-5
Important in making adjustments over a short
time period
Transmission of information is very fast in the
nervous system.
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The Structure of the Nervous
System


Consists of a network of cells that carry
information from one part of the body to
another
Made up of specialized cells called neurons
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26-6
Cell body or soma-contains the nucleus
Dendrites-receive information and carry it to the
cell body
Axons-carry information away from the cell body
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The Anatomy of a Neuron
26-7
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Central Nervous System

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26-8
Brain and spinal cord
Protected by skull and vertebrae
Receives input from sensory organs
Interprets and integrates information
Generates responses
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Peripheral Nervous System


Located outside the skull and vertebral
column
Consists of bundles of axons and dendrites
called nerves
–
Somatic nervous system

–
Autonomic nervous system

26-9
Nerves that control the skeletal muscles
Nerves that control the involuntary muscles, the heart
and glands
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Types of Neurons

Motor neurons
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
Sensory neurons
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26-10
Carry messages from the central nervous system
to muscles and glands
Usually have one long axon that runs from the
spinal cord to the muscle or gland
Carry input from sense organs to the central
nervous system
Have long dendrites that carry input from the
sense organ to the brain or spinal cord
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Organization of the Nervous
System
26-11
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The Nature of Nerve Impulses

Information is transmitted through neurons in
the form of nerve impulses.
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26-12
Also known as action potentials
Involve a sequence of chemical events at the cell
membrane of the neuron
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Neurons have an Unequal Distribution
of Ions Inside and Outside of the Cell

Active transport pumps sodium out and
potassium in
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–
More sodium is pumped out than potassium
pumped in
As a result

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26-13
Sodium is concentrated outside the cell.
Potassium is concentrated inside the cell.
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Neurons have an Unequal Distribution
of Ions Inside and Outside of the Cell

This unequal distribution of charge generates a
voltage across the neuronal cell membrane.
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26-14
Voltage is a measure of the electrical charge difference that
exists between two points.
The inside of the cell is more negative than the outside.
At rest, the membrane voltage of a neuron is about -70mV.
The voltage across the membrane makes it
polarized.
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The Polarization of Cell
Membranes
26-15
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Generation of a Nerve Impulse

When a neuron is stimulated by an input …
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26-16
The cell membrane becomes more permeable to
sodium.
Sodium ions enter the cell down their
concentration gradient.
The inside of the cell becomes more positive.
The cell is depolarized.
The depolarization spreads down the axon.
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Generation of a Nerve Impulse

Depolarization of any one segment of
membrane is brief.
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Repolarization is followed by the pumping of
sodium out of and potassium into the cell.
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26-17
Membrane becomes repolarized when potassium
flows out of the cell
This re-establishes the original concentration
gradients.
This brings the cell back to its resting membrane
potential.
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The Nerve Impulse
26-18
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Activities at the Synapse



The synapse is the small space between the axon of
one neuron and the dendrite of another neuron.
Neurons communicate with one another through the
activities at the synapse.
When the nerve impulse in one neuron reaches the
synapse, chemicals are released from the end of the
axon.
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26-19
Called neurotransmitters
Diffuse across the synapse and bind to receptor sites on the
dendrite of the other neuron
This can cause depolarization and generate a nerve
impulse in the second neuron.
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Events at the Synapse
26-20
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Neurotransmitters

Made in the cell body and transported to the end of
the axon to be stored until released.
–


Bind to receptors and stimulate them as long as they
are bound
Enzymes in the synapse destroy neurotransmitters,
allowing the second cell to return to resting state.
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26-21
Acetylcholine was the first neurotransmitter identified.
Acetylcholinesterase is the enzyme that breaks down
acetylcholine.
Many drugs interfere with neurotransmission at the
synapse.
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Direction of Information Flow

Information in the nervous system only
travels in one direction…
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26-22
From the axon of one cell to the dendrite of
another in a synapse
From the dendrites to the cell body of one neuron
From the cell body through the axon to the
synapse
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The Organization of the Central
Nervous System


The brain consists of several different
regions that have specific functions.
The functions of the brain can be divided into
three major levels.
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26-23
Automatic activities
Basic decision making and emotions
Thinking and reasoning
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The Organization of the Central
Nervous System

Spinal cord
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
Collection of neurons and nerve fibers surrounded by the
vertebrae
Conveys information to and from the brain
Medulla oblongata
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The base of the brain where the spinal cord enters the brain
Controls fundamental life support activities such as

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Fibers from the spinal cord cross sides in the medulla
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26-24
Blood pressure
Breathing
Heart rate
Right side of body is controlled by left side of brain and vice
versa
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The Organization of the Central
Nervous System

Cerebellum
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–
Large bulge at the base of the brain
Connected to the medulla oblongata
Receives information from sensory organs that
involve balance

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26-25
Inner ear, eyes, pressure sensors in muscles and
tendons
Regulates muscle activity to establish balance
and coordination
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The Organization of the Central
Nervous System

Pons
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The region of the brain that is anterior to the medulla
oblongata
Controls many sensory and motor functions of the head and
face
Thalamus
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Located between the pons and the cerebrum
Relays information between the cerebrum and the lower
centers of the brain

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26-26
Spinal cord, medulla, pons
Important in awareness
Involved in sleep and arousal
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The Organization of the Central
Nervous System

Hypothalamus
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Involved in sleep and arousal
Important in emotions

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Regulates body temperature, blood pressure and
blood volume
Connected to and controls the pituitary gland
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26-27
Fear, anger, pleasure, hunger, sexual responses, pain
Controls the release of hormones
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The Functions of More Primitive
Brain Regions
26-28
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The Organization of the Central
Nervous System

Cerebrum
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26-29
The thinking part of the brain.
Comprised of two hemispheres
Controls memory, language, movement
Responsible for the integration of sensory input
The major site of association and cognition.
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Specialized Areas
of the Cerebrum
26-30
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Endocrine System

The Endocrine system
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
Hormones
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
A collection of glands that communicate with one another and with
body tissues through the release of hormones.
Chemical signals released by one organ that are transported to
another organ where it triggers a change in activity
Glands
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Organs that make and release specific chemicals
Endocrine glands
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Exocrine glands
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26-31
Lack ducts
Secrete hormones in to the circulatory system

Have ducts
Release their products into the digestive tract or onto the skin
Digestive glands, sweat glands
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Endocrine Glands
26-32
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Endocrine System Function

Hormones released by endocrine glands
travel throughout the entire body.
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
Target cells respond by
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26-33
However, they only bind to and affect target cells
that have receptors.
Releasing products that have been previously
made
Making new molecules or increasing metabolic
activity
Dividing and growing
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Some Examples of Hormone
Action

Epinephrine and norepinephrine
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–
Released by the adrenal medulla during emergency
situations
Acts quickly
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Antidiuretic hormone
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Released from posterior pituitary in response to dehydration
Acts more slowly
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26-34
Increases heart rate, blood pressure and breathing rate
Shunts blood to muscles
Targets kidney cells
Increases the re-absorption of water
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Some Examples of Hormone
Action

Insulin
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Works rapidly
Produced and released from the pancreas
Stimulates cells to take in glucose
Is released in response to high glucose levels in the blood
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Diabetes is a lack of insulin
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Cells don’t take in glucose
Growth-stimulating hormone
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26-35
Would occur after a high carbohydrate meal
Works over a period of several years during childhood
Produced by the anterior pituitary
Stimulates growth
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Integration of Nervous System
and Endocrine System Function

The pituitary gland links the endocrine system to the
nervous system.
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–
Located at the base of the brain
Divided into two parts

Anterior pituitary
–
An endocrine gland
– Produces hormones that trigger other glands to release their
hormones
– Receives commands from the chemicals released from the
hypothalamus

Posterior pituitary
–
Part of the brain
– Holds the axons from cells in the hypothalamus
– Releases specific hormones into the bloodstream
26-36
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Hormones of the Pituitary
26-37
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Integration of Nervous System
and Endocrine System Function

Example: In songbirds, the length of day causes
hormonal changes that prepare the animals for
reproduction.
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26-38
Length of day is sensed by the pineal body in the brain.
The pineal gland controls the release of chemicals from the
hypothalamus.
The chemicals released by the hypothalamus trigger the
pituitary to release hormones into the bloodstream.
These pituitary hormones stimulate the reproductive organs
to secrete reproductive hormones.
These reproductive hormones trigger courtship and mating
rituals in birds.
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Interaction Between the
Endocrine and Nervous Systems
26-39
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Sensory Input

The nervous and endocrine systems respond
to sensory input.
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This input comes from sense organs.
Some sense organs detect external stimuli.

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Other sense organs detect internal stimuli.
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26-40
Vision, hearing, touch
Pain and pressure
The sense organs detect changes; the brain
is responsible for perception.
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Chemical Detection

All neurons have chemical receptors on their
surface.
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Other types of cells have chemical receptors
as well.
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26-41
When chemicals bind to these receptors, the
activity of the cell changes.
Usually results in depolarization and the
generation of a nerve impulse.
The aorta can sense and respond to changes in
hydrogen ions, carbon dioxide and oxygen in the
blood.
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Taste



Taste buds are sensory cells located on the
tongue.
They have chemical receptors that respond
to classes of molecules.
These classes correspond with the five kinds
of taste we experience.
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26-42
Sweet, sour, salt, bitter and umami (meaty)
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Taste

Sour and salty sensation results from ions entering
taste buds and causing a depolarization.
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Sweet, bitter and umami sensations result from
molecules binding to receptors on taste buds.
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26-43
Sour sensing taste buds respond to hydrogen ions.
Salty sensing taste buds respond to sodium chloride.
Sweet receptors are stimulated by sugars, artificial
sweeteners, etc.
Umami receptors are stimulated by glutamate.
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Smell

The sensory receptors in the nose are more
versatile than taste buds.
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26-44
They can sense thousands of different molecules
at low concentrations.
Found in the olfactory epithelium
Very sensitive
Fatigue quickly
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Vision


The sensory cells in the eyes respond to changes in
the flow of light energy.
Light-sensing cells are found in the retina.
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Light-sensing cells are called rods and cones.
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26-45
At the back of the eye
The other parts of the eye are designed to focus light
onto the retina
–
Rods are very sensitive and can detect dim light but
not color.
Cones are less sensitive, but can detect different
wavelengths of light (color).
This is why we cannot see color at night.
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The Structure of the Eye
26-46
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Vision

The fovea centralis is a region in the retina with
many cones and no rods.
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Rods and cones sense light because they contain
pigment molecules.
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26-47
This area gives us the most focused and detailed vision.
Rhodopsin is the pigment in rods.
When light hits rhodopsin, it changes shape and causes the
rod to depolarize.
This generates a nerve impulse that is sent to the brain.
Different types of cones have different pigments that
respond to specific wavelengths of light.
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Light Reception by Cones
26-48
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Hearing and Balance

One set of sensory cells in the ear responds to
changes in sound waves.
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These sensory cells are found in the cochlea.
Sound is produced by the vibration of molecules.
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The other set of sensory cells in the ear responds to
movements of the head.
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These cells are found in the fluid-filled semi-circular canals.
They sense the position of the head with respect to the
force of gravity.

26-49
Volume is a measure of the intensity of the vibration.
Pitch is determined by the frequency of the vibration.
Helps maintain balance
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The Anatomy of the Ear
26-50
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Hearing

The ear is designed to funnel sound and transmit the
vibrations to the sensory cells.
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26-51
External ear funnels sound to the eardrum.
The eardrum (tympanic membrane) vibrates in response to
sound.
The vibration is passed to small bones (malleus, incus and
stapes) in the middle ear.
The bones, in turn, vibrate another membrane covering the
oval window.
The oval window is an opening into the cochlea.
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Hearing

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26-52
The cochlea is a tube filled with fluid under pressure.
When the oval window vibrates, the fluid in the
cochlea vibrates.
This vibration causes the basilar membrane to
vibrate.
Sensory cells on the basilar membrane are
depolarized when it vibrates.
The depolarization generates a nerve impulse that is
transmitted to the brain.
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Touch

Sensory receptors in the skin and internal organs
respond to changes in pressure and temperature.
–
Found all over the body, but more concentrated in certain
areas
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Pain receptors in the skin and internal organs
respond to cell damage and extreme pressure and
temperature.
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26-53
Tips of fingers, genitalia, lips, etc.
That is why these areas are the most sensitive to touch.
Allows our brain to monitor our internal activities
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Output Coordination

After sensing changes in the external or
internal environments,
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Responses may involve
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26-54
The nervous and endocrine systems work
together to cause a change in response.
Muscle contraction
Hormone secretion by glands
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Muscles
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Muscle contraction facilitates movement.
Muscles pull by contracting.
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Muscles exist in antagonistic sets.
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26-55
But, they do not push by lengthening.
Relaxation is merely passive.
The biceps cause the arm to bend.
The triceps cause the arm to extend.
Biceps and triceps are antagonistic muscles.
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Antagonistic Muscles
26-56
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Muscular Contraction



A muscle is made up of many muscle cells.
Muscle cells are made up of many myofibrils.
Myofibrils are bundles of fibers made up of
myofilaments.
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26-57
When these fibers move past one another, the
muscle contracts.
This movement requires the energy from ATP.
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Myofilaments and Contraction

Myofilaments are either thick or thin.
–
Thick filaments are made of myosin.


–
Shaped like a golf club
The head of the ‘golf club’ is positioned to bind to the
thin filaments.
Thin filaments are made of actin, tropomyosin and
troponin.


Actin filaments are shaped like two pearl necklaces
intertwined.
Tropomyosin and troponin are shaped like a gold thread
that is laid on the pearl necklace.
–
26-58
These molecules block actin and prevent the interaction
between actin and myosin.
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The Events of Muscle Contraction
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26-59
The nerve impulse arrives at the muscle cell.
The muscle cell depolarizes.
Calcium ions are released onto the myofibrils.
The calcium ions bind to troponin, causing the
troponin-tropomyosin complex to move.
This exposes actin, allowing myosin and actin to
interact.
Myosin heads bind to actin, the heads flex, pulling
actin.
This causes the muscle cell to shorten (contract).
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Interaction Between Actin
and Myosin
26-60
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Types of Muscles

There are three types of muscles:
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Skeletal

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Smooth

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Mediate involuntary movement
Digestive tract, reproductive tract
Cardiac

26-61
Mediate voluntary movement
Arms, legs, neck, back, abdomen, lungs
Heart muscle
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Skeletal Muscles


Voluntary muscle
Controlled by the brain
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26-62
Brain sends the command to the spinal cord
Spinal cord sends the command to the muscles
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Skeletal Muscles

Many neurons from the spinal cord end in
each muscle.
–
Each neuron stimulates a specific set of muscle
cells called a motor unit.

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26-63
A motor unit is one neuron and all of the muscle cells it
stimulates to contract.
Each muscle has many motor units.
This allows for different intensities of contraction
in one muscle.
The intensity of contraction is dependent on how
many motor units are stimulated at once.
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Skeletal Muscles

Skeletal muscle cells contract quickly, but
fatigue quickly.
–
26-64
Different motor units must be recruited to keep a
muscle contracted for a long time.
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Motor Units
26-65
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Smooth Muscles


Found in the muscular walls surrounding internal
organs
Contract in response to being stretched
–
Digestive system
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Involuntary
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Do not need direct messages from nervous system
Some respond to hormones
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26-66
Is constantly stretched as food passes through
The responsive contractions result in rhythmic movements that
move food through
Uterine contractions in response to oxytocin
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Cardiac Muscle



Makes up the heart
Can contract rapidly without direct nervous
system stimulation
The rate of contraction can be controlled by
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Cannot stay contracted for a long time
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26-67
The nervous system
Hormones (epinephrine and norepinephrine)
Must relax between contractions
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Characteristics of Different
Kinds of Muscles
26-68
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Activities of Glands

There are two types of glands.
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Endocrine glands
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Exocrine glands
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26-69
Secrete hormones into the bloodstream
Pituitary, thyroid, ovary, testes, etc.
Secrete substances to the surface of the body or into the
tubular organs (gut, reproductive tract)
Salivary glands, intestinal mucus glands, sweat glands, etc.
Some are controlled by the nervous system (salivary).
Some are controlled by hormones (digestive).
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Growth Responses

Hormones regulate growth.
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Growth-stimulating hormone is produced throughout
childhood to increase the size of the body.
Testosterone released during puberty in males stimulates

Bone and muscle growth
–
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–
Growth of the penis, larynx and hair on face and body
Estrogen released during puberty in females stimulates
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26-70
This is why men are generally taller and more muscular than
women.
Growth of reproductive organs
Development of breast tissue
Start of the menstrual cycle
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The Body’s Defense Mechanisms

Immunity is the ability to maintain homeostasis by
resisting or defending against potentially harmful
agents.
–

The immune system is made up of specialized cells
and molecules that fight infection and disease.
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26-71
Microbes, toxins, tumor cells, etc.
Generates nonspecific and specific defenses
Nonspecific defenses protect the body from a lot of things.
Specific defenses recognize specific threats and attack
them in specialized ways.
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Nonspecific Defenses


26-72
General ways that the body prevents disease
and infection
No previous contact with the danger is
required.
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Nonspecific Defenses
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Defensive barriers
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Chemicals
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Skin and mucous membranes
Block the entry of pathogens
Lysozyme, found in skin, destroys bacterial cells.
Mucus traps pathogens so that they can be eliminated.
Complement proteins circulate in the blood and help
immune cells attack and kill pathogens.
Interferons are proteins that prevent viruses from attaching
to and entering cells.
Certain types of cells
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Cells and chemicals interact to mediate inflammation.
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A series of events that clears a damaged area of harmful
agents and damaged tissue
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Inflammation
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Specific Defenses
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These mechanisms must be turned on by a primary
exposure to the harmful agent.
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The harmful agent that causes a response is called an
antigen.
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Usually a large protein
Stimulates the production of a specific defense mechanism
Becomes neutralized or destroyed by that mechanism
Can be toxins or parts of viruses or bacterial cells
T-lymphocytes and B-lymphocytes respond to antigens.
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Therefore, it is called “acquired immunity”.
Each type of lymphocyte works a little bit differently.
Each are needed for specific immunity to work correctly.
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B-cell and Antibody Mediated
Immunity
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B-lymphocytes (B-cells) are made in bone marrow.
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When a B-cell contacts an antigen
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Found mostly in lymph nodes and spleen
Information is sent to the nucleus and genes are activated.
This results in an antibody being made that is specific to
that antigen.
The antibody will be released by the B-cell and will bind to
the antigen, making it a target for destruction.
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Classes of Antibodies
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B-cell and Antibody Mediated
Immunity
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After antigen binding, that B-cell will only make
that specific antibody.
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It has been activated.
All of their descendants will only produce that antibody.
Some descendants will be plasma cells that make and
release antibodies.
Some descendants will be memory cells.
During the infection/danger, plasma cells
outnumber memory cells.
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B-cell and Antibody Mediated
Immunity
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After the infection/danger, plasma cell
number drops; but memory cells remain.
When the same antigen appears again
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The memory B-cells produce more plasma cells
very rapidly.
The plasma cells make and release antibody that
leads to the elimination of the threat.
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Immunization
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A technique to induce an acquired immune
response
Utilizes vaccines to expose the body to an
antigen without causing an infection
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Usually contains pieces of the bacteria or virus
Some are synthetic, with molecules that mimic the
real antigen.
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Immunization
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When the vaccine is given, the B-cells react
as described.
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When the real antigen is encountered again
(during infection)
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This is called a primary immune response.
Generates memory B cells
The memory B cells generate a swift, massive
response.
Eliminates the infection before illness sets in
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Active Immunity
due to Immunization
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T-cell and Cell-mediated
Immunity
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T-lymphocytes (T-cells) are made in bone
marrow.
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Mature in thymus
Found in blood, lymph and lymph tissue
Regulate B-cell activity
Rupture pathogens, virus-infected cells and
cancer cells
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Becoming a Specialized T cell
26-84
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Activating T-cells
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T-cells only become active if the pathogen is
“presented” to it by other cells.
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Called antigen presenting cells (APCs)
These are macrophages that have ingested the
pathogen.
They break the pathogen into pieces and send
the pieces to their cell surface.
The APCs then present the antigen to the T-cells.
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Activating T-cells
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When the T-cell detects the antigen, a signal
is sent to the nucleus, DNA is altered and the
cell becomes differentiated into one of three
forms.
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T-regulator cells
Cytotoxic T-cells
T-memory cells
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Types of T-cells
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T-regulator cells
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Communicate with B-cells and help them control
the amount of antibody produced
Two types of T-regulator cells
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T-helper cells encourage B-cells to make antibodies.
T-suppressor cells inhibit B-cells from making
antibodies.
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Types of T-cells
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Cytotoxic T-cells
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T-memory cells
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Move toward the pathogen and make holes in it
Target bacteria, cancer cells, transplanted cells,
parasites
Release cytokines, chemicals that attract WBCs
to the site of infection
Remember specific antigens so that a faster
response can be initiated upon repeated
exposure
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Allergic Reactions

An allergy is an abnormal immune reaction to
an antigen.
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If the antigen comes from outside the body, it is
called an allergen.
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Food, pollen, drugs
Involves an interaction between the antigen and a
B-cell antibody
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Allergic Reactions
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Type I hypersensitivity
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Associated with an antibody called IgE
Upon first exposure, the allergen stimulates a
B-cell to make IgE.
Upon second exposure to the allergen, the B-cells
make a lot of IgE.
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IgE stimulates the release of histamine, leukotrienes and
prostaglandins.
These chemicals cause skin rashes, hives, asthma,
eczema, headaches, etc.
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Allergic Reactions

Anaphylactic shock
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The most severe allergic reaction
Starts with reddening of the skin and progresses
through a severe drop in blood pressure and can
lead to death.
Epinephrine will block the progression of
anaphylactic shock.
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How an IgE Allergy Works
26-92
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Autoimmune and
Immunodeficiency Diseases

Autoimmune diseases result from the immune
system turning against normal cells or molecules in
one’s body.
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Immunodeficiency disease results when one or more
components of the immune system do not work
properly.
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The immune system attacks and kills normal, healthy cells.
Rheumatoid arthritis - normal cartilage is attacked.
Type I diabetes - cells that make insulin are attacked.
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Makes people more susceptible to infections and cancers.
SCIDS - a genetic immunodeficiency disease
AIDS - a viral-induced immunodeficiency disease
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