09/06/2015
Biology
Concepts and Applications | 9e
Starr | Evers | Starr
Chapter 29
Neural Control
© Cengage Learning 2015
© Cengage Learning 2015
What Are the Functions of the Cerebral
Cortex? (cont’d.)
toes
lips
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Chapter Objectives
• Understand main types of nervous
systems
• Describe structure of vertebrate nervous
system
• How does neuron structure relate to
function?
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29.1 What Are the Types of Nervous
Systems?
• Cell-to-cell communication is important for
an animal body to function as an
integrated whole
• Neurons make up the communication lines
of nervous systems
– Neurons transmit electrical signals and send
chemical messages to other cells
– Neuroglial cells support the neurons
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Nerve Net
• Animals with radial symmetry have a mesh
of interconnected neurons, a nerve net
– Information flows in all directions among cells
– Sea anemones and other cnidarians are
simple animals with nerve net
– Echinoderms have nerve net + nerves
• Nerve: bundle of neuron fibers (cytoplasmic
extensions) wrapped in connective tissue
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Getting a Head
• Cephalization: evolutionary trend whereby
neurons became concentrated at the
“head” of bilateral animals
• Planarian flatworms have a simple
nervous system
– A pair of ganglia (cluster of neurons) in the
head serves as an integrating center
– The ganglia connect to a pair of nerve cords
(may nerve fibers)
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Getting a Head (cont’d.)
• Annelids and arthropods have paired
nerve cords that connect to a simple brain
– Brain: central control organ of nervous system
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ANIMATION: Comparisons of animal
nervous systems
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The Vertebrate Nervous System
• A dorsal nerve cord is one of the defining
features of chordate embryos
• Central nervous system (CNS): brain
and spinal cord (evolved from dorsal cord)
• Peripheral nervous system (PNS):
nerves that carry signals between the
central nervous system and the rest of the
body
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ANIMATION: Vertebrate nervous system
divisions
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The Vertebrate Nervous System (cont’d.)
Brain
cranial nerves
(twelve pairs)
cervical nerves
(eight pairs)
Spinal Cord
thoracic nerves
(twelve pairs)
ulnar nerve
(one in
each arm)
sciatic nerve
(one in each leg)
lumbar nerves
(five pairs)
sacral nerves
(five pairs)
coccygeal nerves
(one pair)
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29.2 How Does Neuron Structure Relate to
Function?
• Information typically flows from sensory
neurons, to interneurons, to motor neurons
– Sensory neurons: become activated when
receptor endings detect a specific stimulus
– Interneurons: both receives signals and
sends signals to other neurons
– Motor neurons: controls muscles or glands
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Flow of Information
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How Does Neuron Structure Relate to
Function? (cont’d.)
receptor
endings
peripheral cell
axon axon
axon
body
terminals
cell
body
axon
cell
body
axon
axon
terminals
dendrites
dendrites
A
B
C
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How Does Neuron Structure Relate to
Function? (cont’d.)
• Structure of a neuron:
– Cell body: contains nucleus and other
organelles
– Axon: transmits electrical signals and
releases chemical signals at its terminal
– Dendrites: receive chemical signals from
other neurons
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What type of nerve cell?
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What type of nerve cell?
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What type of nerve cell?
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What type of nerve cell?
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What type of nerve cell?
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© Cengage Learning 2015
What type of nerve cell?
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Movement of Information In Nerve Cells
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Movement of Information In Nerve Cells
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ANIMATION: Neuron structure and
function
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29.3 What Is Membrane Potential?
• Membrane potential: voltage difference
across a cell membrane
– Arises from differences in charge on opposite
sides of the membrane
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What Is Membrane Potential? (cont’d.)
electrode
outside
electrode
inside
unstimulated axon
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Membrane Potential
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29.3 What Is Resting Potential?
• Resting potential: membrane potential of
a neuron at rest
– At rest, the inside of the neuron is more
negative than the outside (-70 mV)
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Resting Potential
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Action Potential
• Neurons and muscle cells are said to be
“excitable” because they can undergo an
action potential
– Abrupt reversal in the electric gradient across
the plasma membrane
– Charge reversal occurs when sodium and
potassium ions follow their concentration
gradients through voltage-gated ion channels
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Action Potential (cont’d.)
3 Na+
2 K+
B
interstitial fluid
plasma membrane
cytoplasm
ADP + Pi
A
B
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Resting and Action Potential
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29.4 What Happens During an Action
Potential?
• An action potential begins in a neuron’s
trigger zone
• A signal from another neuron shifts the
membrane potential in the trigger zone
• If stimulus is large enough, the membrane
potential reaches threshold potential
– At threshold potential, gated sodium channels
in trigger zone open, initiating the action
potential
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A Positive Feedback Mechanism
• When gated sodium channels open in a
trigger zone, Na+ flows into the cytoplasm
– Cytoplasm becomes more positive
– This causes nearby gated sodium channels to
open, creating a positive feedback
mechanism
• A biological response that continuously intensifies
– Action potentials are an all-or-nothing event
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ANIMATION: Action potential propagation
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A Maximum Value
• All action potentials are +30 mV
• When the membrane potential reaches
+30 mV, gated sodium channels close and
gated potassium channels open
– K+ diffuses out of the cell and the axon once
again has a negative membrane potential
– Gated potassium channels shut
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A Maximum Value (cont’d.)
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Conduction Along an Axon
• An action potential is self-propagating and
does not weaken with distance
• Sodium channels open in one region of
axonal membrane after another
• Action potential moves only in the forward
direction (from trigger zone to terminal)
– After a voltage-gated sodium channel closes,
it cannot open for a brief period – preventing
the action potential from moving backwards
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Conduction Along an Axon (cont’d.)
• Neuroglial cells increase the rate of
conduction by making myelin: a fatty
material that wraps around the axon
– Action potentials only occur at unmyelinated
regions of the axon, called nodes
– By jumping from node to node in a myelinated
axon, an action potential can move as fast as
120 meters per second
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Conduction Along an Axon (cont’d.)
axon
myelin sheath
around axon
node (unsheathed region
of the axon)
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29.5 What Happens at a Synapse?
• Action potentials cannot pass directly from
a neuron to another cell
• Signaling molecules (neurotransmitters)
relay signals between a neuron and
another cell
– Synapse: region where axon terminals
transmit neurotransmitters to another cell
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What Happens at a Synapse? (cont’d.)
• Steps of signal transmission at a
neuromuscular junction (synapse between
a neuron and a muscle):
– Action potentials travel along the neuron’s
axon to the axon terminals
– Arrival of the action potential at an axon
terminal triggers the release of
neurotransmitters into the synaptic cleft
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What Happens at a Synapse? (cont’d.)
• Steps of signal transmission at a
neuromuscular junction (cont’d.):
– Motor neurons release the neurotransmitter
acetylcholine (ACh)
– ACh binds to receptors on skeletal muscles,
allowing Na+ to pass into these cells
– Subsequent action potentials stimulate
muscle contraction
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3D ANIMATION:
Neurons: Synaptic Transmissions
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Signal and Receptor Variety
• Acetylcholine: muscle contraction
• Norepinephrine and epinephrine: stress
response or excitement
• Dopamine: reward-based learning; fine
motor control
• Serotonin: mood and memory
• Glutamate: excitatory signal
• Endorphins: pain reliever
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Synaptic Integration
• Synaptic integration: summation of
excitatory and inhibitory signals by a
postsynaptic neuron
• When excitatory signals outweigh
inhibitory ones, an action potential occurs
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Synaptic Integration (cont’d.)
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29.6 How Do Drugs Act at Synapses?
• Psychoactive drugs alter brain function:
– Mimic a neurotransmitter’s effect on a
postsynaptic cell (e.g., morphine and heroin)
– Stop neurotransmitter action (e.g., caffeine)
– Inhibit neurotransmitter release (e.g., alcohol)
– Block reuptake of neurotransmitter (e.g.,
cocaine)
– Slow reuptake of neurotransmitter (e.g.,
antidepressants)
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How Do Drugs Act at Synpases? (cont’d.)
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29.7 What Is the Peripheral Nervous
System?
• Peripheral nervous system: all nerves
outside the brain or spinal cord
• Each nerve has outer layer of connective
tissue surrounding bundles of axons
• Two major functional divisions of the
peripheral system:
– Somatic nervous system
– Autonomic nervous system
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ANIMATION: Nerve structure
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What Is the Peripheral Nervous System?
(cont’d.)
• Somatic nervous system: controls skeletal
muscles; relays sensory signals about
movements and external conditions
• Autonomic nervous system: relays signals
to and from internal organs and glands
– Parasympathetic neurons: encourage
digestion and other “housekeeping” tasks
– Sympathetic neurons: activated during stress
and danger
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What Is the Peripheral Nervous System?
(cont’d.)
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ANIMATION: Autonomic nerves
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29.8 What Are the Organs of the Central
Nervous System?
• Central nervous system: brain and spinal
cord
– Meninges: membranes that enclose the brain
and spinal cord
– Cerebrospinal fluid: surrounds the brain and
spinal cord; fills ventricles
– Blood–brain barrier: prevents unwanted
substances from entering cerebrospinal fluid
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What Are the Organs of the Central
Nervous System? (cont’d.)
brain
ventricle
spinal cord
canal in spinal cord
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What Are the Organs of the Central
Nervous System? (cont’d.)
– White matter: myelinated axons
• Tract: bundle of axons in the central nervous
system
– Gray matter: axon terminals, cell bodies,
dendrites, and neuroglial cells
– Spinal cord: connects peripheral nerves with
the brain
• Reflex: automatic response; occurs without
conscious thought or learning
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ANIMATION: Organization of the spinal
cord
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ANIMATION: Stretch reflex
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29.9 What Are the Features of a Vertebrate
Brain?
• Embryonic neural tube develops into a
spinal cord and a brain
• Three functional regions of the brain:
– Forebrain (cerebrum, thalamus,
hypothalamus)
– Midbrain
– Hindbrain (pons, cerebellum, medulla
oblongata)
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What Are the Features of a Vertebrate
Brain? (cont’d.)
forebrain
midbrain
hindbrain
7 weeks
At birth
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ANIMATION: Sagittal view of a human
brain
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29.10 What Are the Functions of the
Cerebral Cortex?
• Cerebral cortex: outer gray matter layer of
the cerebrum
– Responsible for most complex behavior
• Making reasoned choices, concentrating on tasks,
planning for the future, behaving appropriately in
social situations
– Primary motor cortex: controls voluntary
movement
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What Are the Functions of the Cerebral
Cortex? (cont’d.)
primary
motor
cortex
primary
somatosensory
cortex
parietal
lobe
frontal lobe
Broca’s area
occipital lobe
temporal lobe
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What Are the Functions of the Cerebral
Cortex? (cont’d.)
toes
lips
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29.11 What Brain Regions Govern Emotion
and Memory?
• Limbic system: group of structures deep in
the brain that function in expression of
emotion
• Hippocampus: brain region essential to
formation of declarative memories
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What Brain Regions Govern Emotion and
Memory? (cont’d.)
hypothalamus
thalamus
cingulate
gyrus
amygdala
hippocampus
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29.12 How Do Scientists Study Human
Brains?
• Electroencephalograph (EEG): graph of
electrical activity of the brain
• Positronemission tomography (PET):
tracks the uptake of radioactively labeled
glucose to reveal areas of metabolic
activity in the brain
• Functional magnetic resonance imaging
(fMRI): reveals details of brain activity by
detecting changes in blood flow
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How Do Scientists Study Human Brains?
(cont’d.)
normal
with Parkinson’s disease
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How Do Scientists Study Human Brains?
(cont’d.)
without virtual reality goggles
with virtual reality goggles
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