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Chapter 28
The Nervous system
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
1 Nervous systems receive sensory input, interpret
it, and send out appropriate commands

Nervous systems are the most intricately organized data processing systems

Brain contains--100 billion neurons,

Nerve cells that transmit signals from one location in the body to another.

A neuron consists of a cell body, containing the nucleus and other cell organelles, and long,
thin extensions that convey signals.

Each neuron may communicate with thousands of others, forming networks that enable us to
learn remember, perceive our surroundings, and move.

Nervous systems have two main anatomical divisions.

1. central nervous system (CNS), consists of the brain and, in vertebrates, the spinal cord.

2. peripheral nervous system (PNS),is made up mostly of nerves that carry signals into and out
of the CNS.

A nerve is a communication line consisting of a bundle of neurons tightly wrapped in connective
tissue.

In addition to nerves, the PNS also has ganglia (singular, ganglion), clusters of neuron cell bodies.
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 A nervous system has three interconnected
functions
1. Sensory input is the conduction of signals
from sensory receptors, such as lightdetecting cells of the eye, to the CNS.
2. Integration is the analysis and
interpretation of the sensory signals and the
formulation of appropriate responses.
3. Motor output is the conduction of signals
from the integration centers to effector
cells, such as muscle cells or gland cells,
which perform the body’s responses.
 The integration of sensory input and motor
output is not usually rigid and linear, but
involves the continuous background activity
symbolized by the circular arrow
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Three functional types of neurons
correspond to a nervous system’s three
main functions:
1. Sensory neurons convey signals from
sensory receptors into the CNS.
2. Interneurons are located entirely
within the CNS. They integrate data and
then relay appropriate signals to other
interneurons or to motor neurons.
3. Motor neurons convey signals from
the CNS to effector cells.
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2 Neurons are the functional units of nervous
systems

Most of a neuron’s organelles, including its nucleus, are located in the in the cell body. Arising from the cell
body are two types of extensions: numerous dendrites and a single axon.
1.
Dendrites (from the Greek dendron, tree) are highly branched extensions that receive signals from other
neurons and convey this information toward the cell body. Dendrites are often short.
2.
The axon is typically a much longer extension that transmits signals to other cells, which may be other
neurons or effector cells. Some axons, such as the ones that reach from your spinal cord to muscle ells in your
feet, can be over a meter long.
3. The axon ends in a cluster of branches. A typical axon has hundreds
or thousands of these branches, each with a synaptic terminal at the
very end.
4. The junction between a synaptic terminal and another cell is called a
synapse.
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 To function normally, neurons of all vertebrates and most invertebrates require
supporting cells called glia.
 Depending on the type, glia may nourish neurons, insulate the axons of neurons,
or help maintain homeostasis of the extracellular fluid surrounding neurons.
 In the mammalian brain, glia outnumber neurons by as many as 50 to 1.
 The glial cell is called a Schwann cell, which is found in the PNS. (Analogous cells
are found in the CNS.)
 In many vertebrates, axons that convey signals rapidly are enclosed along most of
their length by a thick insulating material, analogous to the plastic insulation that
covers electrical wires.
 This insulating material, called the myelin sheath, resembles a chain of oblong
beads. Each bead is actually a Schwann cell, and the myelin sheath is essentially
a chain of Schwann cells, each wrapped many times around the axon.
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 The gaps between Schwann cells are called nodes of Ranvier,and they are the
only points along the axon that require nerve signals to be regenerated, which is a
time-consuming process.
 The myelin sheath insulates the axon, preserving the signal and allowing it to
propagate quickly. Thus, a nerve signal travels along a myelinated axon will be
much faster
 In the human nervous system, signals can travel along a myelinated axon about
150 m/sec (over 330 miles per hour), which means that a command from your
brain can make your fingers move in just a few milliseconds. Without myelin
sheaths, the signals would be over 10 times slower.
 The debilitating autoimmune disease multiple sclerosis (MS) demonstrates the importance of
myelin. MS leads to a gradual destruction of myelin sheaths by the individual’s own immune
system. The result is a progressive loss of signal conduction, muscle control, and brain
function.
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28.11 Vertebrate nervous systems are highly
centralized
 Vertebrate nervous systems are
diverse in structure and level of
sophistication.
 The nervous system of dolphins and
humans are much more complex
structurally than those of frogs or
fishes --- more powerful integrators.
 All vertebrate nervous systems have
fundamental similarities-- distinct
central and peripheral elements and
are highly centralized.
 The brain and spinal cord make up
the CNS, while the PNS comprises
the rest of the nervous system
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 The spinal cord, a jellylike
bundle of nerve fibers that
runs lengthwise inside the
spine---conveys information to
and from the brain and
integrates simple responses to
certain stimuli
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The master control center of the
nervous system, the brain, includes
1. homeostatic centers that keep the
body functioning smoothly;
2. sensory centers that integrate data
from the sense organs; and (in
humans, at least)
3. centers of emotion,
4. intellect
5. Sends motor commands to
muscles
blood-brain barrier
 A vast network of blood vessels services the CNS. Brain capillaries are
more selective than those elsewhere in the body
 They allow essential nutrients and oxygen to pass freely into the brain,
but keep out many chemicals, such as metabolic wastes
 This selective mechanism, called the blood-brain barrier, maintains a
stable chemical environment for the brain.
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 Fluid-filled spaces in the brain are called ventricles and are continuous with the
narrow central canal of the spinal cord
 These cavities are filled with cerebrospinal fluid, which is formed within the brain
by the filtration of blood.
 Circulating slowly through the central canal and ventricles (and then draining back
into veins), the cerebrospinal fluid cushions the CNS and assists in supplying
nutrients and hormones and removing wastes.
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Meninges
 Protecting the brain and spinal
cord are layers of connective
tissue, called meninges.
 If the cerebrospinal fluid
becomes infected by bacteria or
viruses, the meninges may
become inflamed, a condition
called meningitis.
 In mammals, cerebrospinal fluid
circulates between layers of the
meninges, providing an
additional protective cushion for
the CNS.
CNS has white matter and gray matter.
White matter is composed mainly of
axons (with their whitish myelin sheaths);
gray matter consists
mainly of nerve cell bodies and dendrites.
The ganglia and nerves of the vertebrate
PNS are a vast communication network.
Cranial nerves originate in the brain
and usually end in structures of the head
and upper body (eyes, nose, and ears, for
instance).
Spinal nerves originate in the spinal cord
and extend to parts of the body below the
head.
All spinal nerves and most cranial nerves
contain sensory and motor neurons.
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28.12 The peripheral nervous system of
vertebrates is a functional hierarchy
 The PNS can be divided into two functional components:
1. The Motor Nervous System
 The motor system carries signals to and from skeletal muscles, mainly in
response to external stimulli.
 The control of skeletal muscles can be voluntary, as when you raise your
hand to ask a question, or involuntary, as in a knee-jerk reflex controlled by
the spinal cord.
2. The Autonomic Nervous System.
 The autonomic nervous system regulates the internal environment by
controlling smooth and cardiac muscles and the organs and glands of the
digestive, cardiovascular, excretory, and endocrine systems.
 This control is generally involuntary.
 The autonomic nervous system is composed of three divisions:
parasympathetic, sympathetic, and enteric.
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1. The neurons of parasympathetic division primes
the body for activities that gain and conserve
energy for the body (“rest and digest”)
 These include stimulating the digestive
organs, such as the salivary glands,
stomach, and pancreas; decreasing the
heart rate; and increasing glycogen
production.
2. Neurons of the sympathetic division tend to have
the opposite effect, preparing the body for
intense, energy-consuming activities, such as
fighting, fleeing, or competing in a strenuous
game (the “fight-or-flight” response).
 The digestive organs are inhibited, the
bronchi dilate so that more air can pass,
The heart rate increases, the liver releases
the energy compound glucose into the
blood, and the adrenal glands secrete the
hormones epinephrine and norepinephrine.
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Fight-or-flight and relaxation are
opposite extremes, but body usually
operates at intermediate levels,
 Most of
sympathetic
signals. The
an organ’s
level.
organs receiving both
and parasympathetic
opposing signals adjust
activity to a suitable
In regulating some body functions,
the two divisions complement rather
than antagonize each other.
For
example,
in
regulating
reproduction, erection is promoted
by the parasympathetic division
while ejaculation is promoted by the
sympathetic division.
Sympathetic and parasympathetic neurons emerge from
different regions of the CNS
 Neurons of the parasympathetic
system emerge from the brain
and lower part of the spinal cord.
 Most parasympathetic neurons
produce their effects by releasing
the neurotransmitter
acetylcholine at synapses within
target organs.
Neurons of the sympathetic
system emerge from the middle
regions of the spinal cord.
 Most sympathetic neurons
release the neurotransmitter
norepinephrine at target organs.
It is convenient to divide the PNS into motor and autonomic components, it is
important to realize that these two divisions cooperate to maintain homeostasis.
In response to a drop in body temperature, for example, the brain signals the
autonomic nervous system to constrict surface blood vessels, which reduces heat
loss.
At the same time, the brain also signals the motor nervous system to cause
shivering, which increases heat production.
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Enteric division of the autonomic nervous system
 The enteric division of the autonomic nervous system consists of networks of
neurons in the digestive tract, pancreas, and gallbladder.
 Within these organs, neurons of the enteric division control secretion as well as
activity of the smooth muscles that produce peristalsis.
 Enteric division can function independently, it is normally regulated by the
sympathetic and parasympathetic divisions.
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28.13 The vertebrate brain develops from three anterior
bulges of the neural tube
 One of the four distinguishing features of chordates is the embryonic development of the
vertebrate nervous system from the dorsal hollow nerve cord
 During early embryonic development, three bilaterally symmetric bulges—the forebrain,
midbrain, and hindbrain—appear at the anterior end of the neural tube
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
During course of vertebrate evolution, the forebrain and hindbrain
gradually became subdivided—both structurally and functionally—
into regions that assume specific responsibilities.

Another trend in brain evolution was the increasing integrative
power of the forebrain. Evolution of the most complex vertebrate
behavior paralleled the evolution of the cerebrum– the most
sophisticated center of homeostatic control and integration.

During the embryonic development of the human brain, the most
profound changes occur in the region of the forebrain.

Rapid, expansive growth of during the second and third
months creates the cerebrum, which extends over and
around much of the rest of the brain

By the sixth month of development, foldings increase the
surface area of the cerebrum. This extensively convoluted
outer region is called the cerebral cortex.

The cerebrum develops into two halves, called the left and
right cerebral hemispheres.
–
The brains of humans and other primates are strongly
oriented toward visual perceptions. Humans have the
largest brain surface area, relative to body size, of all
animals.
28.14 The structure of a living supercomputer: The
human brain
 Composed of up to 100 billion intricately organized
neurons, with a much larger number of supporting
cells, the human brain is more powerful than the
most sophisticated computer
Hind brain
 Two sections of the hindbrain, the medulla
oblongata and pons, and the midbrain make up a
functional unit called the brainstem.
 Consisting of a stalk with cap-like swellings at the
anterior end of the spinal cord, the brainstem is,
evolutionarily one of the older parts of the
vertebrate brain.
 The brainstem coordinates and filters the
conduction of information from sensory and motor
neurons to the higher brain regions.
 It also regulates sleep and arousal and helps
coordinate body movements, such as walking.
 Another part of the hindbrain, the cerebellum, is a
planning center for body movements.
 It also plays a role in learning, decision making, and
remembering motor responses.
 The cerebellum receives sensory information about
the position of joints and the length of muscles, as
well as information from the auditory and visual
systems.
 It also receives input concerning motor commands
issued by the cerebrum.The cerebellum uses this
information to coordinate movement and balance
 Hand eye coordination
Fore brain
 The thalamus, the hypothalamus, and the
cerebrum.
 The thalamus
 The thalamus contains most of the cell
bodies of neurons that relay information to
the cerebral cortex.
 The thalamus first sorts data into categories
(all of the touch signals from a hand). It also
suppresses some signals and enhances
others.
 The thalamus then sends information on to
the appropriate higher brain centers for
further interpretation and integration.
 The hypothalamus
 Regulates body temperature, blood
pressure, hunger, thirst, sex drive, and
fight-or-flight responses, and it helps us
experience emotions such as rage and
pleasure.
 A“pleasure center” in the hypothalamus
could also be called an addiction center,
for it is strongly affected by certain
addictive drugs, such as amphetamines
and cocaine.
 These drugs increase the effects of
norepinephrine and dopamine at
synapses in the pleasure center,
producing a short-term high, often
followed by depression.
 Cocaine addiction may involve chemical
changes in the pleasure center and
elsewhere in the hypothalamus.
A pair of hypothalmic structures called the
suprachiasmatic nuclei function as an
internal timekeeper, our biological clock.
Receiving visual input from the eyes
(light/dark cycles), the clock maintains our
circadian rhythms—daily cycles of
biological activity such as the sleep/wake
cycle.
 The cerebrum
 It is the largest and most complex part of our
brain, consists of right and left cerebral
hemispheres. each responsible for the
opposite side of the body.
 A thick band of nerve fibers called the corpus
callosum facilitates communication between
the hemispheres, enabling them to process
information together.
 Under the corpus callosum, groups of neurons
called the basal nuclei are important in motor
coordination.
 If they are damaged, a person may be
immobilized. Degeneration of the basal nuclei
occurs in Parkinson’s disease
28.3 Nerve function depends on charge differences across
neuron membranes
 Membrane Potential
 Like all cells, a resting neuron has potential
energy, can be put to work sending signals from
one part of the body to another.
 It exists as an electrical charge difference across
the neuron’s plasma membrane:
 The inside of the cell is negatively charged relative
to the outside as a result of unequal distribution of
positively and negatively charged ions.
 The opposite charges tend to move toward each
other, a membrane stores energy by holding
opposite charges apart, like a battery.
 The strength (voltage) of a neuron’s stored energy
can be measured with microelectrodes connected
to a voltmeter.
 The voltage across the plasma membrane of a
resting neuron is called the resting potential. A
neuron’s resting potential is about –70 millivolts
(mV)
28.3 Nerve function depends on charge differences across
neuron membranes
 The resting potential exists because of differences in
ionic composition of the fluids inside and outside the
neuron
 The plasma membrane surrounding the neuron has
protein channels and pumps that regulate the passage
of inorganic ions
 A resting membrane has many open potassium (K)
channels but only a few open sodium (Na) channels,
allowing much more potassium than sodium to diffuse
across the membrane--Na more concentrated outside
the neuron than inside

But K, which is more concentrated inside, can flow out
through the many open K channels. As the positively
charged potassium ions diffuse out, the inside of the
neuron becomes less positive—that is, more
negative—relative to outside

Also helping maintain the resting potential are membrane
proteins called sodium-potassium (Na-K) pumps. Using
energy from ATP, these pumps actively transport Na out of the
neuron and K in, thereby helping keep the concentration of Na
low in the neuron and K high.
28.3 Nerve function depends on charge differences across
neuron membranes
 The resting potential exists because of differences in
ionic composition of the fluids inside and outside the
neuron
 The plasma membrane surrounding the neuron has
protein channels and pumps that regulate the passage
of inorganic ions
 A resting membrane has many open potassium (K)
channels but only a few open sodium (Na) channels,
allowing much more potassium than sodium to diffuse
across the membrane--Na more concentrated outside
the neuron than inside

But K, which is more concentrated inside, can flow out
through the many open K channels. As the positively
charged potassium ions diffuse out, the inside of the
neuron becomes less positive—that is, more
negative—relative to outside

Also helping maintain the resting potential are membrane
proteins called sodium-potassium (Na-K) pumps. Using
energy from ATP, these pumps actively transport Na of the
neuron and K in, thereby helping keep the concentration of Na
low in the neuron and K high.
28.4 A nerve signal begins as a change in the membrane
potential
 Stimulating a neuron’s plasma membrane can trigger the use of the membrane’s
potential energy to generate a nerve signal.
 A stimulus is any factor that causes a nerve signal to be generated. Examples
include light, sound, a tap on the knee, or a chemical signal from another
neuron.
 The discovery of giant axons in squids (up to 1 mm in diameter) gave
researchers their first chance to study how stimuli trigger signals in a living
neuron.
 From microelectrode studies with squid neurons, British biologists A. L. Hodgkin
and A. F. Huxley worked out the details of nerve signal transmission in the
1940s, earning a Nobel Prize for their findings.
 The graph in the middle of the figure traces the electrical changes that make up
an action potential, a change in membrane voltage that transmits a nerve
signal along an axon.
 The graph records electrical events over time (in milliseconds) at a particular
place on the membrane where a stimulus is applied.
The stimulus is applied. If it is strong enough,
the voltage rises to what is called the threshold
(–50 mV, in this case). The difference between
the threshold and the resting potential is the
minimum change in the membrane’s voltage
that must occur to generate the action
potential(+20 mV, in this case).
Once the threshold is reached, the action
potential is triggered. The membrane
polarity reverses abruptly, with the
interior of the cell becoming positive with
respect to the outside.
The membrane then rapidly
repolarizes as the voltage
drops back down
undershoots the
resting potential,
Finally returns to it
In a typical mammalian neuron, this entire process takes just a few milliseconds,
meaning that a neuron can produce hundreds of nerve signals per second.
28.5 The action potential propagates itself along the axon
 An action potential is a localized electrical
event—a rapid change from the resting
potential at a specific place along the neuron.
 A nerve signal starts out as an action
potential generated in the axon, typically
where the axon meets the cell body.
 To function as a long-distance signal, this
local event must be passed along the axon
from the cell body to the synaptic terminals. It
does so by regenerating itself along the axon
1. When this region of the axon (blue) has its
Na channels open, Na rushes inward, and
an action potential is generated--corresponds to the upswing of the curve
(step 2)
2. Soon, the K channels in that same region
open, allowing K to diffuse out of the axon;
at this time, its Na channels are closed and
inactivated at that point on the axon---the
downswing of the action potential
3. A short time later, we would see no signs of
an action potential at this (far-left) spot
because the axon membrane here has
restored itself and returned to its resting
potential.
 In step 1 of the figure, the blue arrows pointing
sideways within the axon indicate local
spreading of the electrical changes caused by
the inflowing Na associated with the first
action potential.
 These changes are large enough to reach
threshold in the neighboring regions triggering
the opening of Na channels.
 As a result, a second action potential is
generated, as indicated by the blue region in
step 2.

In the same way, a third action potential is
generated in step 3, and each action potential
generates another all the way down the axon.
 The net result is the movement of a nerve
impulse from the cell body to the synaptic
terminals.
 As the blue arrows indicate, local electrical
changes do spread in both directions in the
axon. However, these changes cannot open
Na channels and generate an action potential
when the Na channels are inactivated
 Thus, an action potential cannot be
generated in the regions where K is leaving
the axon (green in the figure) and Na
channels are still inactivated.
 Consequently, the inward flow of Na that
depolarizes the axon membrane ahead of the
action potential cannot produce another
action potential behind it.
 Once an action potential starts where the cell
body and axon meet, it moves along the
axon in only one direction: toward the
synaptic terminals.
 How, do action potentials relay different intensities of information (such as a
loud sound versus a soft sound) to your central nervous system?
 It is the frequency of action potentials that changes with the intensity of stimuli.
For example, in the neurons connecting the ear to the brain, loud sounds
generate more action potentials per second than quiet sounds.
28.6 Neurons communicate at synapses
 If an action potential travels in one direction along an axon, what happens when the signal
arrives at the end of the neuron?
 To continue conveying information, the signal must be passed to another cell.
 This occurs at a synapse, or relay point, between a synaptic terminal of a sending
neuron and a receiving cell.
 The receiving cell can be another neuron or an effecter cell such as a muscle cell or
endocrine cells
 Synapses come in two varieties:
 Electrical synapses --- In an electrical synapse, electrical current flows directly from a
neuron to a receiving cell. The receiving cell is stimulated quickly and at the same
frequency of action potentials as the sending neuron.
 Lobsters and many fishes can flip their tails with lightning speed because the neurons that
carry signals for these movements communicate by fast electrical synapses.

In the human body, electrical synapses are found in the heart and digestive tract, where
nerve signals maintain steady, rhythmic muscle contractions.
 Chemical synapses-- when an action potential reaches a chemical synapse, it stops
there at a narrow gap, called the synaptic cleft, separating a synaptic terminal of the
sending (presynaptic) cell from the receiving (postsynaptic) cell.
 The cleft is very narrow—only about 50 nm, about 1/1,000th the width of a human hair—
but it prevents the action potential from spreading directly to the receiving cell.
 The action potential (an electrical signal) is first converted to a chemical signal
consisting of molecules of neurotransmitter.
 The chemical signal may then generate an action potential in the receiving cell.
Molecules of the neurotransmitter
are in membrane-enclosed sacs
called synaptic vesicles in the
sending neuron’s synaptic
terminals.
An action potential arrives at the
synaptic terminal.
The action potential causes some
synaptic vesicles to fuse with the
plasma membrane of the sending
cell
The fused vesicles release their
neurotransmitter molecules by
exocytosis into the synaptic cleft,
and the neurotransmitter rapidly
diffuses across the cleft.
The released neurotransmitter binds to
complementary receptors on ion
channel proteins in the receiving cell’s
plasma membrane.
The neurotransmitter is broken down by an
enzyme or is transported back into the
signaling cell, and the ion channels close.
28.7 Chemical synapses enable complex information to be
processed
•
A neuron may interact with many others-----a neuron may receive information via
neurotransmitters from hundreds of other neurons connecting at thousands of synaptic
terminals (red and green in the drawing).
 The inputs can be highly varied because each sending neuron may secrete a different
quantity or kind of neurotransmitter.
 The binding of a neurotransmitter to a receptor may open ion channels in the receiving
cell’s plasma membrane or trigger a signal transduction pathway that does so.
A.
The effect of the neurotransmitter depends on the kind of membrane channel it opens.
Neurotransmitters that open Na channels, for instance, may trigger action potentials in the
receiving cell. Such effects are referred to as excitatory (green in the drawing).
B. Many neurotransmitters open membrane channels for ions that decrease the tendency to
develop action potentials in the receiving cell—such as channels that admit Cl–or release
K. These effects are called inhibitory (red).
 The effects of both excitatory and inhibitory signals can vary in magnitude. In general,
the more neurotransmitter molecules that bind to receptors on the receiving cell and the
closer the synapse is to the base of the receiving cell’s axon, the stronger the effect.

The receiving neuron’s plasma
membrane may receive signals—both
excitatory and inhibitory—from many
different sending neurons.
 If the excitatory signals are collectively
strong enough to raise the membrane
potential to threshold, an action
potential will be generated in the
receiving cell.
28.8 A variety of small molecules function as
neurotransmitters
The propagation (transfer) of nerve signals across chemical synapses depends
on neurotransmitters.
 A variety of small molecules serve as neurotransmitters.
 Many neurotransmitters are small, nitrogen-containing organic molecules.
1. Acetylcholine, is important in the brain and at synapses between motor neurons and
muscle cells. Depending on the kind of receptors on receiving cells, acetylcholine may be
excitatory or inhibitory.
 Acetylcholine makes our skeletal muscles contract but slows the rate of contraction of
cardiac muscles.
 Botulinum toxin (sold as Botox), made by the bacteria that cause botulism food poisoning,
inhibits the release of acetylcholine. Botox injections disable the synapses that control
certain facial muscles, eliminating wrinkles around the eyes or mouth.
2. Four other neurotransmitters—aspartate, glutamate, glycine, and GABA (gamma
aminobutyric acid)—are amino acids.
 All are important in the central nervous system.
 Aspartate and glutamate act primarily at excitatory synapses, while glycine and GABA
act at inhibitory synapses.
3. Biogenic amines are neurotransmitters derived from amino acids.
 It includes epinephrine, norepinephrine, serotonin, and dopamine.

Biogenic amines are important neurotransmitters in the central nervous system.
 Serotonin and dopamine affect sleep, mood, attention, and learning.
 Imbalances of biogenic amines are associated with various disorders. For example, the
degenerative illness Parkinson’s disease is associated with a lack of dopamine in the
brain.
 Reduced levels of norepinephrine and serotonin seem to be linked with some types of
depression. Some psychoactive drugs, including LSD and mescaline, apparently produce
their hallucinatory effects by binding to serotonin and dopamine receptors in the brain.
4. Many neuropeptides, relatively short chains of amino acids, also serve as
neurotransmitters.
 The endorphins are peptides that function as both neurotransmitters and hormones,
decreasing our perception of pain during times of physical or emotional stress.
 Endorphins may be released in response to a wide variety of stimuli, including traumatic
injury, muscle fatigue, and even eating very spicy foods.
5. Neurons also use some dissolved gases, notably nitric oxide (NO), as chemical
signals. During sexual arousal in human males, certain neurons release NO into blood
vessels in the erectile tissue of the penis, and the NO triggers an erection.
 Neurons produce NO molecules on demand, rather than storing them in synaptic vesicles.
The dissolved gas diffuses into neighboring cells, produces a change, and is broken
down—all within a few seconds.
Chapter 30
How Animals Move
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
30.4 Bones are complex living organs
 Bones are actually complex organs consisting of
several kinds of moist, living tissues.
 The bone itself contains living cells that secrete a
surrounding material, or matrix. Bone matrix
consists of flexible fibers of the protein collagen
with crystals of a mineral made of calcium and
phosphate bonded to them. The collagen keeps
the bone flexible and nonbrittle, while the hard
mineral matrix resists compression.
 A sheet of fibrous connective tissue, covers most
of the outside surface, helps to form new bone in
the event of a fracture.
 A thin sheet of cartilage forms a cushion-like
surface for movable joints, protecting the ends of
bones as they glide against one another.
 The shaft of this long bone is made of compact
bone, or dense structure.
30.4 Bones are complex living organs
 Bones are actually complex organs consisting of
several kinds of moist, living tissues.
 The bone itself contains living cells that secrete a
surrounding material, or matrix. Bone matrix
consists of flexible fibers of the protein collagen
with crystals of a mineral made of calcium and
phosphate bonded to them. The collagen keeps
the bone flexible and nonbrittle, while the hard
mineral matrix resists compression.
 A sheet of fibrous connective tissue, covers most
of the outside surface, helps to form new bone in
the event of a fracture.
 A thin sheet of cartilage forms a cushion-like
surface for movable joints, protecting the ends of
bones as they glide against one another.
 The shaft of this long bone is made of compact
bone, or dense structure.
30.4 Bones are complex living organs
 Bones are actually complex organs consisting of
several kinds of moist, living tissues.
 The bone itself contains living cells that secrete a
surrounding material, or matrix. Bone matrix
consists of flexible fibers of the protein collagen
with crystals of a mineral made of calcium and
phosphate bonded to them. The collagen keeps
the bone flexible and nonbrittle, while the hard
mineral matrix resists compression.
 A sheet of fibrous connective tissue, covers most
of the outside surface, helps to form new bone in
the event of a fracture.
 A thin sheet of cartilage forms a cushion-like
surface for movable joints, protecting the ends of
bones as they glide against one another.
 The shaft of this long bone is made of compact
bone, or dense structure.
30.4 Bones are complex living organs
 Bones are actually complex organs consisting of
several kinds of moist, living tissues.
 The bone itself contains living cells that secrete a
surrounding material, or matrix. Bone matrix
consists of flexible fibers of the protein collagen
with crystals of a mineral made of calcium and
phosphate bonded to them. The collagen keeps
the bone flexible and nonbrittle, while the hard
mineral matrix resists compression.
 A sheet of fibrous connective tissue, covers most
of the outside surface, helps to form new bone in
the event of a fracture.
 A thin sheet of cartilage forms a cushion-like
surface for movable joints, protecting the ends of
bones as they glide against one another.
 The shaft of this long bone is made of compact
bone, or dense structure.
 The compact bone surrounds a central cavity,
contains yellow bone marrow, which is mostly
stored fat brought into the bone by the blood.
 The ends, or heads, of the bone have an outer
layer of compact bone and an inner layer of
spongy bone. The cavities contain red bone
marrow--specialized tissue that produces blood
cells
 Like all living tissues, bone cells carry out
metabolism. Blood vessels that extend through
channels in the bone transport nutrients and
regulatory hormones to its cells and remove
waste materials.
 Nerves running parallel to the blood vessels help
regulate the traffic of materials between the bone
and the blood.
30.6 Joints permit different types of movement
 Much of the versatility of the vertebrate skeleton
comes from its joints.
 Bands of strong fibrous connective tissue called
ligaments hold together the bones of movable
joints.
1. Ball-and-socket joints, such as are found where
the humerus joins the pectoral girdle, enable us
to rotate our arms and legs and move them in
several planes.
 A ball-and-socket joint also joins the femur to the
pelvic girdle.
2. Hinge joints permit movement in a single
plane, Our elbows and knees are hinge joints.
 Hinge joints are especially vulnerable to injury
in sports like volleyball, basketball, and tennis
that demand quickturns, which can twist the
joint sideways.
3. A pivot joint enables us to rotate the forearm
at the elbow.
 A pivot joint between the first and second
cervical vertebrae allows movement of the
head from side to side.
30.7 The skeleton and muscles interact in movement
 Muscles are connected to bones by
tendons.
 For example, the upper ends of the biceps
and triceps muscles are anchored
(attached) to bones in the shoulder.
 The lower ends of these muscles are
attached to bones in the forearm.
 The action of a muscle is always to
contract, or shorten. A muscle pulls the
bone to which it is attached—it can only
move the bone in one direction. A different
muscle is needed to reverse the action.
 Thus, back-and-forth movement of body
parts involves antagonists, a pair of
muscles that can pull the same bone in
opposite directions. While one antagonist
contracts, the other relaxes.
Examples, the biceps and triceps muscles and
the quadriceps and hamstring muscles
All animals—very small ones like ants and
giant ones like elephants—have antagonistic
pairs of muscles that apply opposite forces to
move parts of their skeleton.
30.8 Each muscle cell has its own contractile apparatus
 The skeletal muscle system is a beautiful illustration of the relationship between
structure and function.
 Each muscle in the body is made up of a hierarchy of smaller and smaller parallel
strands, from the muscle itself down to the contractile protein molecules that produce
body movements.
 Figure 30.8 shows the levels of organization of skeletal muscle.
A muscle consists of many bundles of
muscle fibers—roughly 250,000 in a
typical human biceps muscle—oriented
parallel to each other.
Each muscle fiber is a single long,
cylindrical cell that has many nuclei.
Most of its volume is occupied by
hundreds or thousands of myofibrils,
discrete bundles of proteins that
include the contractile proteins actin
and myosin.
A sarcomere is the region between two
dark, narrow lines, called Z lines, in the
myofibril.
Each myofibril consists of a long series
of sarcomeres.
Functionally, the sarcomere is the
contractile apparatus in a myofibril—
the muscle fiber’s fundamental unit of
action.
The pattern of horizontal stripes is the
result of the alternating bands of thin
filaments, composed primarily of actin
molecules, and thick filaments, which
are made up of myosin molecules.
The Z lines consist of proteins that
connect adjacent thin filaments.
The light band surrounding each Z line
contains only thin filaments.
30.9 A muscle contracts when thin filaments slide along
thick filaments
 According to the sliding-filament model of
muscle contraction, a sarcomere contracts
(shortens) when its thin filaments slide along
its thick filaments.
 In the contracting sarcomere, the Z lines and
the thin filaments have moved closer together.
 In the fully contracted sacromere, the thin
filaments overlap in the middle.
 Contraction shortens the sarcomere without
changing the lengths of the thick and thin
filaments, muscle can shorten about 35% of
its resting length.
30.9 A muscle contracts when thin filaments slide along
thick filaments
 According to the sliding-filament model of
muscle contraction, a sarcomere contracts
(shortens) when its thin filaments slide along
its thick filaments.
 In the contracting sarcomere, the Z lines and
the thin filaments have moved closer together.
 In the fully contracted sacromere, the thin
filaments overlap in the middle.
 Contraction shortens the sarcomere without
changing the lengths of the thick and thin
filaments, muscle can shorten about 35% of
its resting length.
30.9 A muscle contracts when thin filaments slide along
thick filaments
 According to the sliding-filament model of
muscle contraction, a sarcomere contracts
(shortens) when its thin filaments slide along
its thick filaments.
 In the contracting sarcomere, the Z lines and
the thin filaments have moved closer together.
 In the fully contracted sacromere, the thin
filaments overlap in the middle.
 Contraction shortens the sarcomere without
changing the lengths of the thick and thin
filaments, muscle can shorten about 35% of
its resting length.
 Myosin acts as the engine of movement.
 Each myosin molecule has a long “tail” region
and a globular “head” region.
 The tails of the myosin molecules in a thick
filament lie parallel to each other, with their
heads sticking out to the side.
 Each head has two binding sites. One of the
bindingsites matches a binding site on the actin
molecules (subunits) of the thin filament
 ATP binds at the other site, which is also
capable of hydrolyzing the ATP to release its
energy—the energy that powers muscle
contraction.
 Each myosin head pivots back and forth in a
limited arc as it changes shape from a lowenergy configuration to high energy
configuration and back again.
During these changes, the myosin head
swings toward the thin filament, binds
with an actin molecule, and drags the thin
filament through the remainder of its arc.
The myosin head then releases the
actin molecule and returns to its
starting position to repeat the same
motion with a different actin molecule.
key events of this process of
sacromere contraction
1. The myosin head binds a molecule of ATP, at
low-energy position.
1. Myosin hydrolyzes the ATP to ADP and
phosphate (P), releasing energy that extends
the myosin head toward the thin filament.

The myosin head extends further, and its other
binding site latches on to the binding site of an
actin. The result is a connection between the
two filaments—a cross-bridge.
4. ADP and Phosphate are released,
and the myosin head pivots back to its
low-energy configuration.
This action, called the power stroke,
pulls the thin filament toward the
center of the sarcomere.
5. The cross-bridge remains intact until
another ATP molecule binds to the myosin
head, and the whole process repeats.
On the next power stroke, the myosin
head attaches to an actin molecule ahead of
the previous one on the thin filament ,
This sequence—detach, extend, attach,
pull, detach—occurs again and again in a
contracting muscle.
a typical thick filament has about 350
heads, each of which can bind and unbind to
a thin filament about five times per second.
The combined action of hundreds of myosin heads
on each thick filament ratchets the thin filament
toward the center of the sarcomere, as long as
sufficient ATP is present, the process continues
until the muscle is fully contracted or until the
signal to contract stops.
30.10 Motor neurons stimulate muscle contraction
 What prevents muscles from contracting
whenever ATP is present?
 Signals from the central nervous system,
conveyed (transfer) by motor neurons are required
to initiate and sustain muscle contraction.
 A motor neuron sends out an action potential, its
synaptic terminals release the neurotransmitter
acetylcholine, which diffuses across the synapse
to the plasma membrane of the muscle fiber
 the plasma membrane of a muscle fiber is
electrically excitable—it can propagate action
potentials----- and the plasma membrane extends
deep into the interior of the muscle fiber via (by)
infoldings called transverse (T) tubules.
 The T tubules are in close contact with the
endoplasmic reticulum
 The action potential causes channels in the ER to
open, releasing calcium ions into the cytoplasmic
fluid
 How does the endoplasmic reticulum help
regulate muscle contraction?
 In a resting muscle fiber (not transferring signals),
the regulatory proteins tropomyosin and troponin
block the myosin binding sites on the actin
molecules.
 The muscle fiber cannot contract while these
sites are blocked.
 When Ca binds to troponin, the tropomyosin
moves away from the myosin binding sites,
allowing contraction
 When motor neurons stop sending action
potentials to the muscle fibers, the ER pumps Ca
back out of the cytoplasmic fluid, and binding
sites on the actin molecules are again blocked,
thus the sarcomeres stop contracting, and the
muscle relaxes.
Motor unit
 A large muscle such as the calf muscle is composed
of roughly a million muscle fibers.
 About 500 motor neurons run to the calf muscle.
 Each motor neuron has axons that branch out to
synapse with many muscle fibers distributed
throughout the muscle.
 An action potential from a single motor neuron in the
calf causes the simultaneous contraction of roughly
2,000 muscle fibers.
 A motor neuron and all the muscle fibers it
controls is called a motor unit.
 The organization of individual neurons and muscle cells into
motor units is the key to the action of whole muscles.
 The amount of force can be increased several times in biceps
and triceps, when additional motor units are activated ---resulting in more signals for forceful contraction from CNS

In muscles requiring precise control, such as those controlling
eye movements, a motor neuron may control only a single
muscle fiber.