Download Chapter 28: Nervous

BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 28
Nervous Systems
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Can an Injured Spinal Cord Be Fixed?
• The spinal cord is the
central communication
conduit between the
brain and the body
– It consists of a bundle
of nerves
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• Spinal cord injury disrupts communication
between the central nervous system and the rest
of the body
– Paraplegia is paralysis of
the lower half of the body
– Quadriplegia is paralysis
from the neck down
– Research on nerve cells is
leading to new therapies
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NERVOUS SYSTEM STRUCTURE AND
FUNCTION
28.1 Nervous systems receive sensory input,
interpret it, and send out appropriate
commands
• The nervous system has three interconnected
functions
– Sensory input
– Integration
– Motor output
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SENSORY INPUT
INTEGRATION
Sensory receptor
MOTOR OUTPUT
Brain and spinal cord
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Figure 28.1A
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• The nervous system can be divided into two
main divisions
– The central nervous system (CNS) consists of the
brain and, in vertebrates, the spinal cord
– The peripheral nervous system (PNS) is made up
of nerves and ganglia that carry signals into and
out of the CNS
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• Three types of neurons correspond to the
nervous system’s three main functions
– Sensory neurons convey signals from sensory
receptors into the CNS
– Interneurons integrate data and relay signals
– Motor neurons convey signals to effectors
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1 Sensory
2 Sensory neuron
receptor
Brain
Ganglion
3
Motor
neuron
4
Quadriceps
muscles
Spinal
cord
Interneuron
CNS
Nerve
Flexor
muscles
PNS
Figure 28.1B
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28.2 Neurons are the functional units of nervous
systems
• Neurons are cells specialized to transmit
nervous impulses
• They consist of
– a cell body
– dendrites (highly branched fibers)
– an axon (long fiber)
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• Supporting cells protect, insulate, and reinforce
neurons
• The myelin sheath is the insulating material in
vertebrates
– It is composed of a chain of Schwann cells linked
by nodes of Ranvier
– It speeds up signal transmission
– Multiple sclerosis (MS) involves the destruction
of myelin sheaths by the immune system
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Signal direction
Dendrites
Cell body
Cell
body
Node of Ranvier
Myelin sheath
Axon
Signal
pathway
Schwann cell
Nucleus
Nucleus
Nodes of
Ranvier
Myelin sheath
Schwann cell
Synaptic knobs
Figure 28.2
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NERVE SIGNALS AND THEIR TRANSMISSION
28.3 A neuron maintains a membrane potential
across its membrane
• The resting potential of a neuron’s plasma
membrane is caused by the cell membrane’s
ability to maintain
Voltmeter
– a positive charge
on its outer surface
– a negative charge
on its inner
(cytoplasmic) surface
Plasma
membrane
Microelectrode
outside cell
–70 mV
Microelectrode
inside cell
Axon
Neuron
Figure 28.3A
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• Resting potential is generated and maintained
with help from sodium-potassium pumps
– These pump K+ into the cell and Na+ out of the
cell
OUTSIDE OF CELL
Na+
K+
Na+
K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
channel
Na+
K+
Plasma
membrane
Na+
Na+ - K+
pump
K+
channel
K+
K+
Protein
K+
K+
K+
K+
K+
INSIDE OF CELL
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K+
K+
K+
Figure 28.3B
28.4 A nerve signal begins as a change in the
membrane potential
• A stimulus alters the permeability of a portion
of the plasma membrane
– Ions pass through the plasma membrane,
changing the membrane’s voltage
– It causes a nerve signal to be generated
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• An action potential is a nerve signal
– It is an electrical change in the plasma
membrane voltage from the resting potential to a
maximum level and back to the resting potential
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Na+
K+
Na+
K+
3 Additional Na+ channels open,
K+ channels are closed; interior of
cell becomes more positive.
4 Na+ channels close and
inactivate. K+ channels
open, and K+ rushes
out; interior of cell more
negative than outside.
Na+
Action
potential
3
Na+
2 A stimulus opens some Na+
channels; if threshold is reached,
action potential is triggered.
Threshold
potential
1
2
4
5 The K+ channels close
5
relatively slowly, causing
a brief undershoot.
1
Resting potential
Neuron
interior
Neuron
interior
1 Resting state: voltage gated Na+
and K+ channels closed; resting
potential is maintained.
1 Return to resting state.
Figure 28.4
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28.5 The action potential propagates itself along
the neuron
Axon
Action potential
1
Axon
segment
Na+
K+
2
Action potential
Na+
K+
K+
3
Na+
K+
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Action potential
Figure 28.5
• An action potential is an all-or-none event
– Its size is not affected by the stimulus strength
– However, the frequency changes with the
strength of the stimulus
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28.6 Neurons communicate at synapses
• The synapse is a key element of nervous systems
– It is a junction or relay point between two
neurons or between a neuron and an effector cell
• Synapses are either electrical or chemical
– Action potentials pass between cells at electrical
synapses
– At chemical synapses, neurotransmitters cross
the synaptic cleft to bind to receptors on the
surface of the receiving cell
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1
SENDING
NEURON
Axon of
sending
neuron
Action
potential
arrives
Vesicles
Synaptic
knob
SYNAPSE
2
Vesicle fuses with
plasma membrane
Receiving
neuron
3
Neurotransmitter
is released into
synaptic cleft
SYNAPTIC
CLEFT
4
RECEIVING
NEURON
Neurotransmitter
Ion channels molecules
Neurotransmitter
Receptor
Neurotransmitter
binds to
receptor
Neurotransmitter broken
down and released
Ions
5 Ion channel opens
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6 Ion channel closes
Figure 28.6
28.7 Chemical synapses make complex information
processing possible
• Excitatory neurotransmitters trigger action
potentials in the receiving cell
• Inhibitory neurotransmitters decrease the cell’s
ability to develop action potentials
• The summation of excitation and inhibition
determines whether or not the cell will transmit
a nerve signal
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• A neuron
may receive
input from
hundreds of
other
neurons via
thousands of
synaptic
knobs
Dendrites
Synaptic knobs
Myelin
sheath
Receiving
cell body
Axon
Synaptic
knobs
Figure 28.7
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28.8 A variety of small molecules function as
neurotransmitters
• Most neurotransmitters are small, nitrogencontaining organic molecules
– Acetylcholine
– Biogenic amines (epinephrine, norepinephrine,
serotonin, dopamine)
– Amino acids (aspartate, glutamate, glycine,
GABA)
– Peptides (substance P and endorphins)
– Dissolved gases (nitric oxide)
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28.9 Connection: Many drugs act at chemical
synapses
• Drugs act at synapses and may increase or
decrease the normal effect of neurotransmitters
– Caffeine
– Nicotine
– Alcohol
– Prescription
and illegal drugs
Figure 28.9
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NERVOUS SYSTEMS
28.10 Nervous system organization usually
correlates with body symmetry
• Radially symmetrical
animals have a nervous
system arranged in a
nerve net
– Example: Hydras
Nerve
net
Neuron
A. Hydra (cnidarian)
Figure 28.10A
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• Most bilaterally symmetrical animals exhibit
– cephalization, the concentration of the nervous
system in the head end
– centralization, the presence of a central nervous
system
Eye
Brain
Brain
Brain
Nerve
cord
Transverse
nerve
B. Planarian (flatworm)
Ventral
nerve
cord
Ventral
nerve
cord
Brain
Ganglia
Giant
axon
Segmental
ganglion
C. Leech (annelid)
D. Insect (arthropod)
E. Squid (mollusk)
Figure 28.10B-E
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28.11 Vertebrate nervous systems are highly
centralized and cephalized
CENTRAL NERVOUS
SYSTEM (CNS)
Brain
Spinal cord
PERIPHERAL
NERVOUS
SYSTEM (PNS)
Cranial
nerve
Ganglia
outside
CNS
Spinal
nerves
Figure 28.11A
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• The brain and spinal cord contain fluid-filled
spaces
Meninges
BRAIN
Dorsal root
ganglion
(part of PNS)
Gray matter
White matter
Central canal
Spinal nerve
(part of PNS)
Ventricles
Central canal
of spinal cord
SPINAL CORD
(cross section)
Spinal cord
Figure 28.11B
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28.12 The peripheral nervous system of vertebrates
is a functional hierarchy
Peripheral
nervous system
Sensory
division
Sensing
external
environment
Motor
division
Sensing
internal
environment
Autonomic
nervous system
(involuntary)
Sympathetic
division
Somatic
nervous system
(voluntary)
Parasympathetic
division
Figure 28.12A
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• Referred pain is when we feel pain from an
internal organ on the body surface
– This happens
because neurons
carrying
information from
the skin and those
carrying
information from
the internal organs
synapse with the
same neurons in
the CNS
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Liver
Gallbladder
Liver
Heart
Lungs and
diaphragm
Heart
Stomach
Pancreas
Small intestine
Appendix
Colon
Ovaries
Kidney
Urinary
bladder
Ureters
Figure 28.12B
• The motor division of the PNS
– The autonomic nervous system exerts
involuntary control over the internal organs
– The somatic nervous system exerts voluntary
control over skeletal muscles
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28.13 Opposing actions of sympathetic and
parasympathetic neurons regulate the
internal environment
• The autonomic nervous system consists of two
sets of neurons that function antagonistically on
most body organs
– The parasympathetic division primes the body
for activities that gain and conserve energy
– The sympathetic division prepares the body for
intense, energy-consuming activities
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PARASYMPATHETIC DIVISION
SYMPATHETIC DIVISION
Eye
Brain
Constricts
pupil
Dilates
pupil
Salivary
glands
Stimulates
saliva
production
Inhibits
saliva
production
Lung
Relaxes
bronchi
Constricts
bronchi
Slows
heart
Adrenal
gland
Heart
Stimulates
epinephrine
and norepinephrine release
Liver
Spinal
cord
Stomach
Stimulates
stomach,
pancreas,
and intestines
Pancreas
Intestines
Bladder
Stimulates
urination
Promotes
erection of
genitals
Accelerates
heart
Stimulates
glucose
release
Inhibits
stomach,
pancreas,
and intestines
Inhibits
urination
Genitals
Promotes ejaculation and vaginal
contractions
Figure 28.13
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THE HUMAN BRAIN
28.14 The vertebrate brain develops from three
anterior bulges of the neural tube
• The vertebrate brain evolved by the
enlargement and subdivision of three anterior
bulges of the neural tube
– Forebrain
– Midbrain
– Hindbrain
• Cerebrum size and complexity in birds and
mammals correlates with sophisticated
behavior
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Embryonic
Brain Regions
Brain Structures
Present in Adult
Cerebrum (cerebral hemispheres; includes
cerebral cortex, white matter, basal ganglia)
Forebrain
Diencephalon (thalamus, hypothalamus,
posterior pituitary, pineal gland)
Midbrain
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Hindbrain
Medulla oblongata (part of brainstem)
Diencephalon
Cerebral
hemisphere
Midbrain
Midbrain
Pons
Cerebellum
Hindbrain
Medulla
oblongata
Spinal cord
Forebrain
Embryo one month old
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Fetus three months old
Figure 28.14
28.15 The structure of a living supercomputer:
The human brain
Table 28.15
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Cerebrum
Forebrain
Thalamus
Cerebral
cortex
Hypothalamus
Pituitary gland
Midbrain
Pons
Hindbrain
Medulla
oblongata
Spinal cord
Cerebellum
Figure 28.15A
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• Most of the cerebrum’s integrative power
resides in the cerebral cortex of the two cerebral
hemispheres
Left cerebral
hemisphere
Corpus
callosum
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Right cerebral
hemisphere
Basal
ganglia
Figure 28.15B
28.16 The cerebral cortex is a mosaic of
specialized, interactive regions
• The motor cortex sends commands to skeletal
muscles
• The somatosensory cortex receives information
about pain, pressure, and temperature
• Several regions receive and process sensory
information (vision, hearing, taste, smell)
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• The association areas are the sites of higher
mental activities (thinking)
– Frontal association area (judgment, planning)
– Auditory association area
– Somatosensory association area (reading,
speech)
– Visual association area
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FRONTAL LOBE
PARIETAL LOBE
Speech
Frontal
association
area
Taste
Somatosensory
association
area
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
TEMPORAL LOBE
OCCIPITAL LOBE
Figure 28.16
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• In lateralization, areas in the two hemispheres
become specialized for different functions
– “Right-brained” vs. “left-brained”
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28.17 Connection: Injuries and brain operations
have provided insight into brain function
• Much knowledge about
the brain has come from
individuals whose
brains were altered
through injury, illness,
or surgery
– The rod that pierced
Phineas Gage’s skull
left his intellect intact
but altered his
personality and
behavior
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Figure 28.17A
• A radical surgery called
hemispherectomy
removes almost half of
the brain
– It demonstrates the
brain’s remarkable
plasticity
Figure 28.17B
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28.18 Several parts of the brain regulate sleep and
arousal
• Sleep and arousal
are controlled by
– the hypothalamus
– the medulla
oblongata
– the pons
– neurons of
reticular
formation
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Eye
Reticular formation
Input from touch,
pain, and temperature
receptors
Input from
ears
Motor
output to
spinal cord
Figure 28.18A
• An electroencephalogram (EEG) measures
brain waves during sleep and arousal
• Two types of deep sleep alternate
– Slow-wave (delta waves) and REM sleep
Awake but quiet (alpha waves)
Awake during intense mental activity (beta waves)
Delta waves
Asleep
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REM sleep
Delta waves
Figure 28.18B, C
28.19 The limbic system is involved in emotions,
memory, and learning
• The limbic system is a functional group of
integrating centers in the cerebral cortex,
thalamus, and hypothalamus
• It is involved in emotions, memory (short-term
and long-term), and learning
– The amygdala is central to the formation of
emotional memories
– The hippocampus is involved in the formation of
memories and their recall
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Thalamus
CEREBRUM
Hypothalamus
Prefrontal
cortex
Smell
Olfactory
bulb
Amygdala
Hippocampus
Figure 28.19
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28.20 The cellular changes underlying memory and
learning probably occur at synapses
• Memory and learning involve structural and
chemical changes at synapses
– Long-term depression (LTD)
– Long-term potentiation (LTP)
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1 Repeated
Sending
neuron
action
potentials
Sending
neuron
Synaptic
cleft
2
2
4
3 Ca2+
Receiving neuron
Cascade of
chemical changes
Ca2+
3
LTP
Figure 28.20
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