Neural Control
Chapter 33 Part 1
Impacts, Issues
In Pursuit of Ecstasy
 Neural controls maintain life; drugs like Ecstasy
flood the brain with signaling molecules and
saturate receptors, disrupting these controls
Fig. 33-1a, p. 552
Fig. 33-1b, p. 552
Fig. 33-1c, p. 552
33.1 Evolution of Nervous Systems
 Interacting neurons allow animals to respond to
stimuli in the environment and inside their body
 Neuron
• A cell that can relay electrical signals along its
plasma membrane and can communicate with
other cells by specific chemical messages
 Neuroglia
• Support neurons functionally and structurally
Three Types of Neurons
 Sensory neurons detect stimuli and signal
interneurons or motor neurons
 Interneurons process information from sensory
neurons and send signals to motor neurons
 Motor neurons control muscles and glands
The Cnidarian Nerve Net
 Cnidarians are the simplest animals that have
neurons, which are arranged as a nerve net
 Nerve net
• A mesh of interconnecting neurons with no
centralized controlling organ
Bilateral, Cephalized Nervous System
 Flatworms are the simplest animals with a
bilateral, cephalized nervous system
 Cephalization
• The concentration of neurons that detect and
process information at the body’s head end
 Ganglion
• A cluster of neuron cell bodies that functions as
an integrating center
Nerve Cords
 Annelids and arthropods have paired ventral
nerve cords that connect to a simple brain
• Pair of ganglia in each segment for local control
 Chordates have a single, dorsal nerve cord;
vertebrates have a brain at the anterior region of
the nerve cord
Simple Nervous Systems
a nerve net
(highlighted
in purple)
controls the
contractile
cells in the
epithelium
Hydra, a cnidarian
Fig. 33-2a, p. 554
pair of
ganglia
pair of nerve
cords crossconnected
by lateral
nerves
Planarian, a flatworm
Fig. 33-2b, p. 554
rudimentary
brain
ventral
nerve cord
ganglion
c Earthworm, an annelid
Fig. 33-2c, p. 554
brain
brain
optic lobe
(one pair, for
visual stimuli)
branching
nerves
paired ventral
nerve cords
ganglion
Crayfish, a crustacean
(a type of arthropod)
Grasshopper, an insect
(a type of arthropod)
Fig. 33-2 (d-e), p. 554
The Vertebrate Nervous System
 Central nervous system (CNS)
• Brain and spinal cord (mostly interneurons)
 Peripheral nervous system (PNS)
• Nerves from the CNS to the rest of the body
(efferent) and from the body to CNS (afferent)
• Autonomic nerves and somatic nerves control
different organs of the body
Functional
Divisions
of the
Vertebrate
Nervous
System
Central Nervous System
Brain
Spinal Cord
Peripheral Nervous System
(cranial and spinal nerves)
Autonomic Nerves
Somatic Nerves
Nerves that carry signals
to and from smooth muscle,
cardiac muscle, and glands
Nerves that carry signals
to and from skeletal muscle,
tendons, and the skin
Sympathetic Parasympathetic
Division
Division
Two sets of nerves that often
signal the same effectors and
have opposing effects
Stepped A
Major
Nerves
of the
Human
Nervous
System
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)
Fig. 33-4, p. 555
33.1 Key Concepts
How Animal Nervous Tissue is Organized
 In radially symmetrical animals, excitable
neurons interconnect as a nerve net
 Most animals are bilaterally symmetrical with a
nervous system that has a concentration of
neurons at the anterior end and one or more
nerve cords running the length of the body
33.2 Neurons—The Great Communicators
 Neurons have special cytoplasmic extensions for
receiving and sending messages
• Dendrites receive information from other cells
• Axons send chemical signals to other cells
 Sensory neurons have an axon with one end
that responds to stimuli; the other sends signals
 Interneurons and motor neurons have many
dendrites and one axon
A Motor Neuron
dendrites
input zone
cell body
trigger zone
conducting zone
axon
output zone
axon terminals
Fig. 33-5, p. 556
Direction of Information Flow
STIMULI
RESPONSE
receptor peripheral cell axon axon
endings
axon
body
terminal
cell
body
axon
dendrites
a sensory neuron
b interneuron
cell axon
body
axon
terminals
dendrites
c motor neuron
Stepped Art
Fig. 33-6, p. 556
33.3 Membrane Potentials
 Resting membrane potential
• The interior of a resting neuron is more negative than
the fluid outside the cell (-70 mV)
• Negatively charged proteins and active transport of Na+
and K+ ions maintain the resting potential
150 Na+
interstitial
fluid
5 K+
plasma
membrane
15 Na+
150 K+
65
neuron’s
cytoplasm
p. 557
Action Potentials
 Action potential
• An abrupt reversal in the electric gradient across
the plasma membrane
• When properly stimulated, voltage-gated
channels open, ions flow through, and the
membrane potential briefly reverses
Membrane Proteins: Pumps,
Transporters, and Gated Channels
interstitial fluid
neuron cytoplasm
A Sodium–potassium
pumps actively transport
3 Na+ out of a neuron for
every 2 K+ they pump in.
B Passive transporters
allow K+ ions to leak
across the plasma
membrane, down their
concentration gradient.
C In a resting neuron,
gates of voltage-sensitive
channels are shut (left).
During action potentials,
the gates open (right),
allowing Na+ or K+ to flow
through them.
Fig. 33-7, p. 557
33.4 A Closer Look at Action Potentials
 An action potential begins
• Stimulation of a neuron’s input zone causes a
local, graded potential
• When stimulus in the neuron’s trigger zone
reaches threshold potential, gated sodium
channels open
• Voltage difference decreases and starts the
action potential
An All-or-Nothing Spike
 Once threshold level is reached, membrane
potential always rises to the same level as an
action potential peak (all-or-nothing response)
An All-or-Nothing Spike
action potential
threshold
level
resting
level
Fig. 33-10, p. 559
Direction of Propagation
 An action potential is self-propagating
• Sodium ions diffuse to adjoining region of axon,
triggering sodium gates one after another
 An action potential can only move one way,
toward axon terminals
• Brief refractory period after sodium gates close
Propagation of an Action Potential
interstitial fluid
with high Na+,
low K+
Na+–K+
pump
voltage-gated
ion channels
cytoplasm with
low Na+, high K+
A Close-up of the trigger zone of a neuron. One sodium–potassium pump and some of
the voltage-gated ion channels are shown. At this point, the membrane is at rest and
the voltage-gated channels are closed. The cytoplasm’s charge is negative relative to
interstitial fluid.
Fig. 33-8a, p. 558
Propagation of an Action Potential
Na+
Na+
Na+
Na+
Na+
Na+
B Arrival of a sufficiently large signal in the trigger zone raises the
membrane potential to threshold level. Gated sodium channels open and
sodium (Na+) flows down its concentration gradient into the cytoplasm.
Sodium inflow reverses the voltage across the membrane.
Fig. 33-8b, p. 558
Propagation of an Action Potential
K+
K+
K+
Na+
Na+
Na+
C The charge reversal makes gated Na+ channels shut and gated K+
channels open. The K+ outflow restores the voltage difference across
the membrane. The action potential is propagated along the axon as
positive charges spreading from one region push the next region to
threshold.
Fig. 33-8c, p. 559
Propagation of an Action Potential
Na+–K+
pump
K+
K+ K+
Na+
Na+
Na+
K+
D After an action potential, gated Na+ channels are briefly inactivated, so the
action potential moves one way only, toward axon terminals. Na+ and K+
gradients disrupted by action potentials are restored by diffusion of ions that
were put into place by activity of sodium–potassium pumps.
Fig. 33-8d, p. 559
electrode
inside
electrode
outside
++++ ++++++++
––––––––––––
unstimulated axon
Fig. 33-9, p. 559
33.5 How Neurons
Send Messages to Other Cells
 An action potential travels along a neuron’s axon
to a terminal at the tip
 Terminal sends chemical signals to a neuron,
muscle fiber, or gland cell across a synapse
Chemical Synapses
 Synapse
• The region where an axon terminal (presynaptic
cell) send chemical signals to a neuron, muscle
fiber or gland cell (postsynaptic cell)
 Action potentials trigger release of signaling
molecules (neurotransmitters) from vesicles in
the presynaptic terminal into the synaptic cleft
Neurotransmitter Action
 Release of neurotransmitters from presynaptic
vesicles requires an influx of calcium ions, Ca++
 Postsynaptic membrane receptors bind the
neurotransmitter and initiate the response
 Example: A neuromuscular junction and the
neurotransmitter acetylcholine (ACh)
A Neuromuscular Junction
Neuromuscular junctions
A An action potential B The action potential
propagates along a
reaches axon terminals that
motor neuron.
lie close to muscle fibers.
muscle
fiber
axon of
a motor
neuron
axon
terminal
muscle
fiber
Fig. 33-11 (a-b), p. 560
Close-up of a neuromuscular junction (a type of synapse)
C Arrival of the action
potential causes
calcium ions (Ca++) to
enter an axon terminal.
one axon terminal
of the presynaptic
cell (motor neuron)
plasma membrane
of the postsynaptic
cell (muscle cell)
Ca++
D
causes
vesicles with
signaling molecule
(neurotransmitter) to
move to the plasma
membrane and
release their
contents by
exocytosis.
synaptic
vesicle
receptor protein
in membrane of
post-synaptic cell
synaptic cleft (gap
between pre- and
postsynaptic cells)
Fig. 33-11 (c-d), p. 560
Close-up of neurotransmitter receptor proteins in the plasma
membrane of the postsynaptic cell
binding site for
neurotransmitter
is vacant
channel through
interior is closed
E When neurotransmitter is not
present, the channel through the
receptor protein is shut, and ions
cannot flow through it.
neurotransmitter
in binding site
ion crossing
plasma membrane
through the nowopen channel
F Neurotransmitter diffuses across
the synaptic cleft and binds to the
receptor protein. The ion channel
opens, and ions flow passively into
the postsynaptic cell.
Fig. 33-11 (e-f), p. 560
Receiving the Signal
 A neurotransmitter may have excitatory or
inhibitory effects on a postsynaptic cell
 Synaptic integration
• Summation of all excitatory and inhibitory signals
arriving at a postsynaptic cell at the same time
 The neurotransmitter must be cleared from the
synapse after the signal is transmitted
Synaptic Integration
what action
potential spiking
would look like
threshold
excitatory
signal
inhibitory
signal
integrated
potential
resting
membrane
potential
Fig. 33-12, p. 561
Neural Control
Chapter 33 Part 2
33.6 A Smorgasbord of Signals
 Different types of neurons release different
neurotransmitters; Parkinson’s disease involves
dopamine-secreting neurons and motor control
Battling Parkinson’s disease.
(a) This neurological disorder
affects former heavyweight
champion Muhammad Ali, actor
Michael J. Fox, and about half
a million other people in the
United States. (b) A normal
PET scan and (c) one from an
affected person. Red and
yellow indicate high metabolic
activity in dopamine-secreting
neurons. Section 2.2 explains
PET scans.
Major Neurotransmitters
and Their Effects
The Neuropeptides
 Neuromodulators
• Neuropeptides made by some neurons that
influence the effects of neurotransmitters
• Substance P enhances pain
• Enkephalins and endorphins are pain killers
33.7 Drugs Disrupts Signaling
 Psychoactive drugs exert their effects by interfering
with the action of neurotransmitters
• Stimulants (nicotine, caffeine, cocaine,
amphetamines)
• Depressants (alcohol, barbiturates)
• Analgesics (narcotics, ketamine, PCP)
• Hallucinogens (LSD, THC)
PET Scan: Effects of Cocaine
Signs of Drug Addiction
33.2-33.7 Key Concepts
How Neurons Work
 Messages flow along a neuron’s plasma
membrane, from input to output zones
 Chemicals released at a neuron’s output zone
may stimulate or inhibit activity in an adjacent
cell
 Psychoactive drugs interfere with the information
flow between cells
33.8 The Peripheral Nervous System
 Peripheral nerves carry information to and from
the central nervous system
 Nerves are bundled axons of many neurons
 Each axon is wrapped in a myelin sheath that
increases transmission speed
myelin
sheath
axon
blood vessels
nerve fascicle (a number
of axons bundled inside
connective tissue)
the nerve’s outer wrapping
Nerve Structure and Function
Fig. 33-15a, p. 564
(b–d) In axons with a myelin sheath, ions flow across the neural membrane at nodes, or small
gaps between the cells that make up the sheath. Many gated channels for sodium ions are
exposed to extracellular fluid at the nodes. When excitation caused by an action potential
reaches a node, the gates open and sodium rushes in, starting a new action potential.
Excitation spreads rapidly to the next node, where it triggers a new action potential, and so on
down the axon to the output zone.
unsheathed node
axon
b “Jellyrolled” Schwann
cells of an axon’s myelin
sheath
Nerve Structure and Function
Fig. 33-15b, p. 564
(b–d) In axons with a myelin sheath, ions flow across the neural membrane at nodes, or small
gaps between the cells that make up the sheath. Many gated channels for sodium ions are
exposed to extracellular fluid at the nodes. When excitation caused by an action potential
reaches a node, the gates open and sodium rushes in, starting a new action potential.
Excitation spreads rapidly to the next node, where it triggers a new action potential, and so on
down the axon to the output zone.
Na+
action potential
resting potential
Nerve Structure and Function
resting potential
Fig. 33-15c, p. 564
(b–d) In axons with a myelin sheath, ions flow across the neural membrane at nodes, or small
gaps between the cells that make up the sheath. Many gated channels for sodium ions are
exposed to extracellular fluid at the nodes. When excitation caused by an action potential
reaches a node, the gates open and sodium rushes in, starting a new action potential.
Excitation spreads rapidly to the next node, where it triggers a new action potential, and so on
down the axon to the output zone.
K+
resting potential restored
Na+
action potential
Nerve Structure and Function
resting potential
Fig. 33-15d, p. 564
Divisions of
the Peripheral Nervous System
 Somatic nervous system
• Conducts information about the environment to
the central nervous system (involuntary)
• Controls skeletal muscles (voluntary)
 Autonomic nervous system
• Conducts signals to and from internal organs and
glands
Divisions of
the Autonomic Nervous System
 The two divisions of the autonomic nervous
system have opposing effects on effectors
 Sympathetic neurons are most active in times
of stress or danger (fight-flight response)
 Parasympathetic neurons are most active in
times of relaxation
Divisions of the Autonomic Nervous System
eyes
optic nerve
salivary glands
heart
vagus
nerve
larynx
bronchi
lungs
midbrain
medulla
oblongata
cervical
nerves (8
pairs)
stomach
liver
spleen
pancreas
thoracic
nerves
(12 pairs)
kidneys
adrenal glands
small intestine
upper colon
lower colon
rectum
(most ganglia
near spinal
cord)
(all ganglia
in walls of
organs)
bladder
uterus
pelvic
nerve
lumbar
nerves (5
pairs)
sacral
nerves (5
pairs)
genitals
Fig. 33-16, p. 565
33.9 The Spinal Cord
 Spinal cord
• Runs through the vertebral column and connects
peripheral nerves with the brain
• Serves as a reflex center
 Central nervous system (CNS)
• The brain and spinal cord
Protective Features
 Meninges
• Three membranes that cover and protect the
CNS
 Cerebrospinal fluid
• Fills central canal and spaces between meninges
• Cushions blows
White Matter and Gray Matter
 White matter
• Bundles of myelin-sheathed axons (tracts)
• Outermost portion of spinal cord
 Gray matter
• Nonmyelinated structures (cell bodies, dendrites,
neuroglial cells)
Reflex Pathways
 Reflex
• An automatic response to a stimulus
• Stretch reflex, knee-jerk reflex, withdrawal reflex
 Spinal reflexes do not involve the brain
• Signals from sensory neurons enter the cord
through the dorsal root of spinal nerves
• Commands for responses go out on the ventral
root of spinal nerves
Fruit being loaded into a bowl puts
Stretch Reflex Aweight
on an arm muscle and stretches it.
STIMULUS
Biceps stretches.
Will the bowl drop? NO! Muscle spindles
in the muscle’s sheath also are stretched.
B Stretching stimulates sensory
receptor endings in this muscle
spindle. Action potentials are
propagated toward spinal cord.
E Axon terminals of the
motor neuron synapse
with muscle fibers in
the stretched muscle.
F ACh released from the
motor neuron’s axon
terminals stimulates
muscle fibers.
muscle neuromuscular
spindle
junction
D The stimulation
is strong enough
to generate action
potentials that selfpropagate along the
motor neuron’s axon.
C In the spinal cord,
axon terminals of the
sensory neuron release
a neurotransmitter that
diffuses across a
synaptic cleft and
stimulates a motor
neuron.
RESPONSE
Biceps contracts.
G Stimulation makes the
stretched muscle contract.
Ongoing stimulations
and contractions hold the
bowl steady.
Fig. 33-18, p. 567
33.8-33.9 Key Concepts
Vertebrate Nervous System
 The central nervous system consists of the brain
and spinal cord
 The peripheral nervous system includes many
pairs of nerves that connect the brain and spinal
cord to the rest of the body
 The spinal cord and peripheral nerves interact in
spinal reflexes
33.10 The Vertebrate Brain
 The brain is the body’s main information
integrating organ, part of the CNS
 During development, the brain is organized as
three functional regions: forebrain, midbrain and
hindbrain
Hindbrain and Midbrain
 The hindbrain includes the medulla oblongata,
the pons, and the cerebellum
 The midbrain in mammals is reduced
 The brain stem (pons, medulla, and midbrain) is
involved in reflex behaviors
The Forebrain
 Cerebrum
• Main processing center in humans
• Evolved as an expansion of the olfactory lobe
 Thalamus and hypothalamus
• Important in thirst, temperature regulation, and
other responses related to homeostasis
Development of the Human Brain
forebrain
midbrain
hindbrain
Fig. 33-19 (a-c), p. 568
Protection at the Blood-Brain Barrier
 Blood-brain barrier
• Protects the CNS from harmful substances
• Tight junctions form a seal between adjoining
cells of capillary walls
• Some toxins (nicotine, alcohol, caffeine, mercury)
are not blocked
The Human Brain
 Cerebellum
• Has more interneurons than other brain regions
• Involved in balance, motor skills and language
 Cerebrum
• Divided into two hemispheres, coordinated by
signals across the corpus callosum
• Each hemisphere deals with the opposite side of
the body
Major Brain Regions of Vertebrates
olfactory
lobe
forebrain
midbrain
hindbrain
FISH
shark
AMPHIBIAN
frog
REPTILE
alligator
BIRD
goose
(a) Major brain regions of five vertebrates, dorsal
views. The sketches are not to the same scale.
Fig. 33-20a, p. 569
corpus
callosum
part of
optic
nerve
hypothalamus
thalamus
pineal
gland
location
midbrain
cerebellum
pons
medulla oblongata
(b) Right half of a human brain in sagittal section, showing the locations of the major
structures and regions. Meninges around the brain were removed for this photograph.
Fig. 33-20b, p. 569
33.11 The Human Cerebrum
 Each cerebral hemisphere is divided into frontal,
temporal, occipital and parietal lobes
 Cerebral cortex
• Outermost gray matter of the cerebrum
• Controls voluntary activity, sensory perception,
abstract thought, language and speech
• Distinct areas receive and process signals
Lobes of the Brain
frontal lobe
(planning of
movements,
aspects of
memory,
inhibition of
unsuitable
behaviors)
primary
motor
cortex
primary
somatosen
sory cortex
parietal
lobe
(visceral
sensations)
Wernicke’s
area
Broca’s area
temporal lobe (hearing,
advanced visual processing)
occipital lobe
(vision)
Fig. 33-21, p. 570
Functions of the Cerebral Cortex
 Specific areas of the cerebral cortex correspond
to specific body parts or functions
 Examples:
• The body is spatially mapped out in the primary
motor cortex of each frontal lobe
• Association areas are scattered throughout the
cortex, but not in motor or sensory areas
The Primary Motor Cortex
Association Areas Integrate Inputs
Motor cortex activity
when speaking
Prefrontal cortex activity
when generating words
Visual cortex activity when
seeing written words
Three PET scans that identify which brain areas were
active when a person performed three kinds of tasks.
Yellow and orange indicate high activity.
Fig. 33-23, p. 570
Connections With the Limbic System
 The cerebral cortex oversees the limbic system
 Limbic system
• Governs emotions, assists in memory, correlates
emotional-visceral responses
• Includes the hypothalamus, hippocampus,
amygdala, and cingulate gyrus
Limbic System Components
(olfactory
tract)
cingulate gyrus
thalamus
hypothalamus
amygdala
hippocampus
Fig. 33-24, p. 571
Making Memories
 The cerebral cortex receives information and
processes some of it into memories
 Memory forms in stages
•
•
•
•
Short-term memory lasts seconds to hours
Long-term memory is stored permanently
Skill memory involves the cerebellum
Declarative memory stores facts and impressions
Stages in
Memory
Processing
Sensory stimuli, as from
the nose, eyes, and ears
Temporary storage in
the cerebral cortex
Input forgotten
SHORT-TERM MEMORY
Recall of
stored
input
Emotional state, having time
to repeat (or rehearse) input,
and associating the input with
stored categories of memory
influence transfer to long-term
storage
LONG-TERM MEMORY
Input irretrievable
Stepped Art
Fig. 33-25, p. 571
33.12 The Split Brain
 Investigations by Roger Sperry into the
importance of information flow between the
cerebral hemispheres showed that the two
halves of the brains have a division of labor
 Typically, math and language skills reside in the
left hemisphere; the right hemisphere interprets
music, spatial relationships, and visual inputs
Visual Information and the Brain
Left Half of
Visual Field
Right Half of
Visual Field
COW BOY
COWBOY
pupil
optic
nerves
retina
optic
chiasm
corpus
callosum
left
visual
cortex
right
visual
cortex
Fig. 33-26, p. 572
Split-Brain Studies
33.13 Neuroglia—
The Neurons’ Support Staff
 Neuroglial cells make up the bulk of the brain
 The adult brain has four types of neuroglial cells
• Oligodendrocytes make myelin
• Microglia have immune system functions
• Astrocytes secrete various substances, take up
neurotransmitters, assist in immune defenses,
and stimulate formation of the blood-brain barrier
• Ependymal cells line brain cavities
Astrocytes
About Brain Tumors
 Unlike neurons, neuroglia continue to divide in
adults, and can be a source of primary brain
tumors (gliomas)
 Exposure to ionizing radiation such as x-rays, or
to chemical carcinogens, increases risk
33.10-33.13 Key Concepts
About the Brain
 The brain develops from the anterior part of the
embryonic nerve cord
 A human brain includes evolutionarily ancient
tissues and newer regions that provide the
capacity for analytical thought and language
 Neuroglia make up the bulk of the brain
Animation: Neuron structure and
function
Animation: Ion concentrations
Animation: Measuring membrane
potential
Animation: Action potential propagation
Animation: Chemical synapse
Animation: Bilateral nervous systems
Animation: Comparison of nervous
systems
Animation: Nerve net
Animation: Vertebrate nervous system
divisions
Animation: Nerve structure
Animation: Ion flow in myelinated axons
Animation: Autonomic nerves
Animation: Stretch reflex
Animation: Sagittal view of a human
brain
Animation: Receiving and integrating
areas
Animation: Path to visual cortex
Animation: Action potential
Animation: Human brain development
Animation: Organization of the spinal
cord
Animation: Primary motor cortex
Animation: Regions of the vertebrate
brain
Animation: Structures involved in
memory
Animation: Synapse function
Animation: Synaptic integration
ABC video: New Nerves
Video: In pursuit of ecstasy
Video: Brain stem
Video: Limbic system dissection