Transcript peripheral nervous system

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 49
Nervous Systems
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: Command and Control Center
• The human brain contains about 100 billion
neurons, organized into circuits more complex
than the most powerful supercomputers
• A recent advance in brain exploration involves a
method for expressing combinations of colored
proteins in brain cells, a technique called
“brainbow”
• This may allow researchers to develop detailed
maps of information transfer between regions of
the brain
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Figure 49.1
Concept 49.1: Nervous systems consist of
circuits of neurons and supporting cells
• Each single-celled organism can respond to
stimuli in its environment
• Animals are multicellular and most groups
respond to stimuli using systems of neurons
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• The simplest animals with nervous systems, the
cnidarians, have neurons arranged in nerve nets
• A nerve net is a series of interconnected nerve
cells
• More complex animals have nerves
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• Nerves are bundles that consist of the axons of
multiple nerve cells
• Sea stars have a nerve net in each arm
connected by radial nerves to a central nerve
ring
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• In vertebrates
– The CNS is composed of the brain and spinal
cord
– The peripheral nervous system (PNS) is
composed of nerves and ganglia
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Organization of the Vertebrate Nervous
System
• The spinal cord conveys information from and
to the brain
• The spinal cord also produces reflexes
independently of the brain
• A reflex is the body’s automatic response to a
stimulus
– For example, a doctor uses a mallet to trigger
a knee-jerk reflex
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Figure 49.3
Quadriceps
muscle
Cell body of
sensory neuron in
dorsal root
ganglion
Gray
matter
White
matter
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron
• Invertebrates usually have a ventral nerve cord
while vertebrates have a dorsal spinal cord
• The spinal cord and brain develop from the
embryonic nerve cord
• The nerve cord gives rise to the central canal
and ventricles of the brain
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Figure 49.4
Central nervous
system (CNS)
Brain
Peripheral nervous
system (PNS)
Cranial nerves
Spinal cord
Ganglia outside
CNS
Spinal nerves
Figure 49.5
Gray matter
White
matter
Ventricles
• The central canal of the spinal cord and the
ventricles of the brain are hollow and filled with
cerebrospinal fluid
• The cerebrospinal fluid is filtered from blood and
functions to cushion the brain and spinal cord as
well as to provide nutrients and remove wastes
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• The brain and spinal cord contain
– Gray matter, which consists of neuron cell
bodies, dendrites, and unmyelinated axons
– White matter, which consists of bundles of
myelinated axons
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Glia
• Glia have numerous functions to nourish,
support, and regulate neurons
– Embryonic radial glia form tracks along which
newly formed neurons migrate
– Astrocytes induce cells lining capilaries in the
CNS to form tight junctions, resulting in a
blood-brain barrier and restricting the entry of
most substances into the brain
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Figure 49.6
CNS
PNS
Neuron
VENTRICLE
Cilia
Astrocyte
Oligodendrocyte
Schwann cell
Microglial cell
Ependymal cell
50 m
Capillary
LM
The Peripheral Nervous System
• The PNS transmits information to and from the
CNS and regulates movement and the internal
environment
• In the PNS, afferent neurons transmit information
to the CNS and efferent neurons transmit
information away from the CNS
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• The PNS has two efferent components: the
motor system and the autonomic nervous system
• The motor system carries signals to skeletal
muscles and is voluntary
• The autonomic nervous system regulates
smooth and cardiac muscles and is generally
involuntary
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Figure 49.7
Central Nervous
System
(information processing)
Peripheral Nervous
System
Efferent neurons
Afferent neurons
Sensory
receptors
Autonomic
nervous system
Motor
system
Control of
skeletal muscle
Internal
and external
stimuli
Sympathetic Parasympathetic Enteric
division
division
division
Control of smooth muscles,
cardiac muscles, glands
• The autonomic nervous system has
sympathetic, parasympathetic, and enteric
divisions
• The sympathetic regulates arousal and energy
generation (“fight-or-flight” response)
• The parasympathetic system has antagonistic
effects on target organs and promotes calming
and a return to “rest and digest” functions
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• The enteric division controls activity of the
digestive tract, pancreas, and gallbladder
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Figure 49.8
Sympathetic division
Parasympathetic division
Action on target organs:
Action on target organs:
Constricts pupil
of eye
Dilates pupil of eye
Stimulates salivary
gland secretion
Inhibits salivary
gland secretion
Constricts
bronchi in lungs
Cervical
Sympathetic
ganglia
Relaxes bronchi
in lungs
Slows heart
Accelerates heart
Stimulates activity
of stomach and
intestines
Inhibits activity of
stomach and intestines
Thoracic
Stimulates activity
of pancreas
Inhibits activity
of pancreas
Stimulates
gallbladder
Stimulates glucose
release from liver;
inhibits gallbladder
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Promotes erection
of genitalia
Inhibits emptying
of bladder
Sacral
Synapse
Promotes ejaculation
and vaginal contractions
Concept 49.2: The vertebrate brain is
regionally specialized
• Specific brain structures are particularly
specialized for diverse functions
• These structures arise during embryonic
development
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Figure 49.9a
Figure 49.9b
Brain structures in child and adult
Embryonic brain regions
Telencephalon
Cerebrum (includes cerebral cortex, white
matter, basal nuclei)
Diencephalon
Diencephalon (thalamus, hypothalamus,
epithalamus)
Forebrain
Midbrain
Mesencephalon
Midbrain (part of brainstem)
Metencephalon
Pons (part of brainstem), cerebellum
Myelencephalon
Medulla oblongata (part of brainstem)
Hindbrain
Cerebrum
Mesencephalon
Midbrain
Hindbrain
Metencephalon
Diencephalon
Diencephalon
Midbrain
Myelencephalon
Pons
Medulla
oblongata
Spinal
cord
Forebrain
Telencephalon
Embryo at 1 month
Embryo at 5 weeks
Cerebellum
Spinal cord
Child
Figure 49.9ba
Mesencephalon
Metencephalon
Midbrain
Hindbrain
Diencephalon
Myelencephalon
Spinal
cord
Forebrain
Telencephalon
Embryo at 1 month
Embryo at 5 weeks
Figure 49.9bb
Cerebrum
Diencephalon
Midbrain
Pons
Medulla
oblongata
Cerebellum
Spinal cord
Child
Figure 49.9c
Left cerebral
hemisphere
Right cerebral
hemisphere
Cerebral cortex
Corpus callosum
Cerebrum
Basal nuclei
Cerebellum
Adult brain viewed from the rear
Figure 49.9d
Diencephalon
Thalamus
Pineal gland
Hypothalamus
Brainstem
Midbrain
Pituitary gland
Pons
Medulla
oblongata
Spinal cord
Arousal and Sleep
• The brainstem and cerebrum control arousal
and sleep
• The core of the brainstem has a diffuse network
of neurons called the reticular formation
• This regulates the amount and type of
information that reaches the cerebral cortex
and affects alertness
• The hormone melatonin is released by the
pineal gland and plays a role in bird and
mammal sleep cycles
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Figure 49.10
Eye
Reticular formation
Input from touch,
pain, and temperature
receptors
Input from nerves
of ears
• Sleep is essential and may play a role in the
consolidation of learning and memory
• Dolphins sleep with one brain hemisphere at a
time and are therefore able to swim while
“asleep”
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Figure 49.11
Key
Low-frequency waves characteristic of sleep
High-frequency waves characteristic of wakefulness
Location
Left
hemisphere
Right
hemisphere
Time: 0 hours
Time: 1 hour
Biological Clock Regulation
• Cycles of sleep and wakefulness are examples
of circardian rhythms, daily cycles of biological
activity
• Mammalian circadian rhythms rely on a
biological clock, molecular mechanism that
directs periodic gene expression
• Biological clocks are typically synchronized to
light and dark cycles
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• In mammals, circadian rhythms are coordinated
by a group of neurons in the hypothalamus
called the suprachiasmatic nucleus (SCN)
• The SCN acts as a pacemaker, synchronizing
the biological clock
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RESULTS
Wild-type hamster
Wild-type hamster with
SCN from  hamster
Circadian cycle period (hours)
Figure 49.12
 hamster
 hamster with SCN
from wild-type hamster
24
23
22
21
20
19
Before
procedures
After surgery
and transplant
Emotions
• Generation and experience of emotions involves
many brain structures including the amygdala,
hippocampus, and parts of the thalamus
• These structures are grouped as the limbic
system
• The limbic system also functions in motivation,
olfaction, behavior, and memory
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Figure 49.13
Thalamus
Hypothalamus
Olfactory
bulb
Amygdala
Hippocampus
• Generation and experience of emotion also
require interaction between the limbic system
and sensory areas of the cerebrum
• The structure most important to the storage of
emotion in the memory is the amygdala, a mass
of nuclei near the base of the cerebrum
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Figure 49.14
Nucleus accumbens
Happy music
Amygdala
Sad music
Concept 49.3: The cerebral cortex controls
voluntary movement and cognitive functions
• The cerebrum, the largest structure in the
human brain, is essential for awareness,
language, cognition, memory, and
consciousness
• Four regions, or lobes (frontal, temporal,
occipital, and parietal) are landmarks for
particular functions
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Figure 49.15
Frontal lobe
Motor cortex
(control of
skeletal muscles)
Somatosensory cortex
(sense of touch)
Parietal lobe
Prefrontal cortex
(decision making,
planning)
Sensory association
cortex (integration of
sensory information)
Visual association
cortex (combining
images and object
recognition)
Broca’s area
(forming speech)
Temporal lobe
Occipital lobe
Auditory cortex (hearing)
Wernicke’s area
(comprehending language)
Cerebellum
Visual cortex
(processing visual
stimuli and pattern
recognition)
Language and Speech
• Studies of brain activity have mapped areas
responsible for language and speech
• Broca’s area in the frontal lobe is active when
speech is generated
• Wernicke’s area in the temporal lobe is active
when speech is heard
• These areas belong to a larger network of
regions involved in language
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Figure 49.16
Max
Hearing
words
Seeing
words
Min
Speaking
words
Generating
words
Lateralization of Cortical Function
• The two hemispheres make distinct contributions
to brain function
• The left hemisphere is more adept at language,
math, logic, and processing of serial sequences
• The right hemisphere is stronger at pattern
recognition, nonverbal thinking, and emotional
processing
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• The differences in hemisphere function are
called lateralization
• Lateralization is partly linked to handedness
• The two hemispheres work together by
communicating through the fibers of the corpus
callosum
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Information Processing
• The cerebral cortex receives input from sensory
organs and somatosensory receptors
• Somatosensory receptors provide information
about touch, pain, pressure, temperature, and
the position of muscles and limbs
• The thalamus directs different types of input to
distinct locations
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• Adjacent areas process features in the sensory
input and integrate information from different
sensory areas
• Integrated sensory information passes to the
prefrontal cortex, which helps plan actions and
movements
• In the somatosensory cortex and motor cortex,
neurons are arranged according to the part of
the body that generates input or receives
commands
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Figure 49.17
Frontal lobe
Parietal lobe
Jaw
Tongue
Leg
Hip
Trunk
Neck
Head
Knee
Hip
Genitalia
Toes
Tongue
Pharynx
Primary
motor cortex
Abdominal
organs
Primary
somatosensory
cortex
Frontal Lobe Function
• Frontal lobe damage may impair decision
making and emotional responses but leave
intellect and memory intact
• The frontal lobes have a substantial effect on
“executive functions”
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Figure 49.UN01
Evolution of Cognition in Vertebrates
• Previous ideas that a highly convoluted
neocortex is required for advanced cognition
may be incorrect
• The anatomical basis for sophisticated
information processing in birds (without a highly
convoluted neocortex) appears to be the
clustering of nuclei in the top or outer portion of
the brain (pallium)
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Figure 49.18
Human brain
Cerebrum (including
cerebral cortex)
Thalamus
Midbrain
Hindbrain
Cerebellum
Avian brain
to scale
Cerebrum
(including pallium)
Avian brain
Cerebellum
Hindbrain
Thalamus
Midbrain
Concept 49.4 Changes in synaptic
connections underlie memory and learning
• Two processes dominate embryonic
development of the nervous system
– Neurons compete for growth-supporting factors
in order to survive
– Only half the synapses that form during embryo
development survive into adulthood
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Neural Plasticity
• Neural plasticity describes the ability of the
nervous system to be modified after birth
• Changes can strengthen or weaken signaling at
a synapse
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Figure 49.19
N1
N1
N2
N2
(a) Synapses are strengthened or weakened in response to
activity.
(b) If two synapses are often active at the same time, the
strength of the postsynaptic response may increase at
both synapses.
Memory and Learning
• The formation of memories is an example of
neural plasticity
• Short-term memory is accessed via the
hippocampus
• The hippocampus also plays a role in forming
long-term memory, which is stored in the
cerebral cortex
• Some consolidation of memory is thought to
occur during sleep
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Long-Term Potentiation
• In the vertebrate brain, a form of learning called
long-term potentiation (LTP) involves an
increase in the strength of synaptic transmission
• LTP involves glutamate receptors
• If the presynaptic and postsynaptic neurons are
stimulated at the same time, the set of receptors
present on the postsynaptic membranes
changes
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Figure 49.20
Ca2
PRESYNAPTIC
NEURON
Na
Mg2
Glutamate
NMDA receptor (open)
NMDA
receptor
(closed)
Stored
AMPA
receptor
POSTSYNAPTIC
NEURON
(a) Synapse prior to long-term potentiation (LTP)
1
2
3
(b) Establishing LTP
3
1
2
Depolarization
(c) Synapse exhibiting LTP
4
Action
potential
Stem Cells in the Brain
• The adult human brain contains neural stem
cells
• In mice, stem cells in the brain can give rise to
neurons that mature and become incorporated
into the adult nervous system
• Such neurons play an essential role in learning
and memory
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Figure 49.21
Concept 49.5: Nervous system disorders can
be explained in molecular terms
• Disorders of the nervous system include
schizophrenia, depression, drug addiction,
Alzheimer’s disease, and Parkinson’s disease
• Genetic and environmental factors contribute to
diseases of the nervous system
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Figure 49.22
Genes shared with relatives of
person with schizophrenia
12.5% (3rd-degree relative)
25% (2nd-degree relative)
50% (1st-degree relative)
100%
40
30
20
Child
Fraternal
twin
Identical
twin
Full sibling
Parent
Half sibling
0
Uncle/aunt
Nephew/
niece
Grandchild
10
Individual,
general
population
First cousin
Risk of developing schizophrenia (%)
50
Relationship to person with schizophrenia
Schizophrenia
• About 1% of the world’s population suffers from
schizophrenia
• Schizophrenia is characterized by hallucinations,
delusions, and other symptoms
• Available treatments focus on brain pathways
that use dopamine as a neurotransmitter
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Depression
• Two broad forms of depressive illness are
known: major depressive disorder and bipolar
disorder
• In major depressive disorder, patients have a
persistent lack of interest or pleasure in most
activities
• Bipolar disorder is characterized by manic
(high-mood) and depressive (low-mood) phases
• Treatments for these types of depression include
drugs such as Prozac
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Drug Addiction and the Brain’s Reward
System
• The brain’s reward system rewards motivation
with pleasure
• Some drugs are addictive because they
increase activity of the brain’s reward system
• These drugs include cocaine, amphetamine,
heroin, alcohol, and tobacco
• Drug addiction is characterized by compulsive
consumption and an inability to control intake
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• Addictive drugs enhance the activity of the
dopamine pathway
• Drug addiction leads to long-lasting changes in
the reward circuitry that cause craving for the
drug
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Figure 49.23
Nicotine
stimulates
dopaminereleasing
VTA neuron.
Inhibitory neuron
Dopaminereleasing
VTA neuron
Opium and heroin
decrease activity
of inhibitory
neuron.
Cocaine and
amphetamines
block removal
of dopamine
from synaptic
cleft.
Cerebral
neuron of
reward
pathway
Reward
system
response
Alzheimer’s Disease
• Alzheimer’s disease is a mental deterioration
characterized by confusion and memory loss
• Alzheimer’s disease is caused by the formation
of neurofibrillary tangles and amyloid plaques in
the brain
• There is no cure for this disease though some
drugs are effective at relieving symptoms
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Figure 49.24
Amyloid plaque
Neurofibrillary tangle
20 m
Parkinson’s Disease
• Parkinson’s disease is a motor disorder
caused by death of dopamine-secreting
neurons in the midbrain
• It is characterized by muscle tremors, flexed
posture, and a shuffling gait
• There is no cure, although drugs and various
other approaches are used to manage
symptoms
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