Download 28. Nervous Systems

Chapter 28
Nervous Systems
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 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 rest of the
body
• Injuries to the spinal cord can produce
paraplegia or quadriplegia
• The spinal cord cannot repair itself
• Researchers are working on ways to
regenerate or replace damaged nerve cells
– Growth factor proteins
– Embryonic stem cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
NERVOUS SYSTEM STRUCTURE AND FUNCTION
28.1 Nervous systems receive sensory input,
interpret it, and send out appropriate commands
• The nervous system obtains and processes
sensory information and sends commands to
effector cells
– Central nervous system (CNS): brain and
spinal cord
– Peripheral nervous system (PNS): nerves
that carry signals to and from CNS
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Nervous tissue
– Neuron: nerve cell specialized for carrying
signals from one location in the body to
another
– Nerve: bundle of neuron extensions
wrapped in connective tissue
– Ganglia: clusters of neuron cell bodies;
found in PNS
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A nervous system has three interconnected
functions
– Sensory input: Sensory neurons conduct
signals from sensory receptors to
integration centers
– Integration: Interneurons interpret signals
and formulate responses
– Motor output: Motor neurons conduct
signals from integration centers to effector
cells
• A reflex is an automatic response to stimuli
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-1a
Sensory input
Integration
Sensory receptor
Motor output
Brain and spinal cord
Effector cells
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
LE 28-1b
Sensory
receptor
Sensory neuron
Brain
Ganglion
Motor
neuron
Spinal
cord
Quadriceps
muscles
Interneuron
Nerve
Flexor
muscles
PNS
CNS
28.2 Neurons are the functional units of nervous
systems
• Neurons are cells specialized for carrying
signals
– Cell body: contains most organelles
– Dendrites: highly branched extensions that
carry signals from other neurons toward the
cell body
– Axon: long extension that transmits signals
to other cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Many axons are enclosed by an insulating
myelin sheath
– Chain of Schwann cells
– Nodes of Ranvier: points where signals can
be transmitted
– Speeds up signal transmission
• Supporting cells (glia) are essential for
structural integrity and normal functioning of
the nervous system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The axon ends in a cluster of branches
– Each branch ends in a synaptic terminal
– A synapse is a site of communication
between a synaptic terminal and another
cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-2
Signal direction Dendrites
Cell Body
Cell body
Node of Ranvier
Layers of myelin
in sheath
Axon
Schwann cell
Nucleus
Signal
pathway
Nucleus
Nodes of
Ranvier
Myelin sheath
Synaptic terminals
Schwann cell
NERVE SIGNALS AND THEIR TRANSMISSION
28.3 A neuron maintains a membrane potential
across its membrane
• A resting neuron has potential energy
– Membrane potential: electrical charge
difference across the neuron's plasma
membrane
– Resting potential: voltage across the
plasma membrane of a resting neuron
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•
The resting potential depends on differences in ionic
composition inside and outside the cell
– More K+ than Na+ diffuses inward through
membrane channels
– Sodium-potassium pumps actively transport Na+
out of cell and K+ in
– The ionic gradient produces a voltage across the
membrane
•
The basis of nervous system signals
Animation: Resting Potential
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Animation: Sodium Potassium Pump
LE 28-3a
Voltmeter
Plasma
membrane
–70 mV
Microelectrode
outside cell
Microelectrode
inside cell
Axon
Neuron
LE 28-3b
Outside of cell
Na+
Na+
K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
channel
K+
Plasma
membrane
Na+
Protein
Na+
Na+
Na+
Na+-K+
pump
K+ channel
K+
K+
K+
K+
K+
K+
Inside of cell
Na+
K+
Na+
K+
K+
28.4 A nerve signal begins as a change in the
membrane potential
• Electrical changes make up an action
potential, a nerve signal that carries
information along an axon
– Stimulus raises voltage from resting
potential to threshold
– Action potential is triggered; membrane
polarity reverses abruptly
– Membrane repolarizes; voltage drops
– Voltage undershoots and then returns to
resting potential
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cause of electrical changes of an action
potential
– Movement of K+ and Na+ across the
membrane
– Controlled by the opening and closing of
voltage-gated channels
Animation: Action Potential
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-4-5
Na+
K+
Na+
K+
Additional Na+ channels open,
K+ channels are closed; interior of
cell becomes more positive.
Na+
Na+
A stimulus opens some Na+
channels; if threshold is reached,
action potential is triggered.
Membrane potential
(mV)
+50
Na+ channels close and
inactivate. K+ channels
open, and K+ rushes
out; interior of cell more
negative than outside.
Action
potential
0
The K+ channels close
relatively slowly, causing
a brief undershoot.
50 Threshold
100
Resting potential
Time (msec)
Neuron
interior
Resting state: voltage-gated Na+
and K+ channels closed; resting
potential is maintained.
Neuron
interior
Return to resting state.
28.5 The action potential propagates itself along
the neuron
•
An action potential transmits a signal in a
domino effect
1. Na+ channels open, Na+ rushes inward
2. K+ channels open, K+ diffuses outward;
Na+ channels are closed and inactivated
3. Membrane returns to resting potential
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• Action potentials are propagated only from cell
body to synaptic cleft
– Cannot be generated where K+ is leaving
axon and Na+ channels are inactivated
• Action potentials are all-or-none events
– Same events occur no matter how strong or
weak the stimulus
– Intensity of stimulus determines frequency
of action potentials
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-5
Axon
Action potential
Axon
segment
Na+
K+
Action potential
Na+
K+
K+
Action potential
Na+
K+
28.6 Neurons communicate at synapses
• The transmission of signals occurs at
synapses
– Junction between synaptic terminal and
another cell
• Electrical synapse
– Electrical current passes directly from one
neuron to the next
– Receiving neuron stimulated quickly and at
same frequency as sending neuron
– Found in human heart and digestive tract
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•
Chemical synapse
1. Action potential arrives in sending neuron
2. Vesicle containing neurotransmitter fuses
with plasma membrane
3. Neurotransmitter is released into synaptic
cleft
4. Neurotransmitter binds to receptor on
receiving neuron
– Following events vary with different types
of chemical synapses
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-6
Sending neuron
Vesicles
Axon of
sending
neuron
Action
potential
arrives
Synaptic
terminal
Synapse
Vesicle fuses
with plasma
membrane
Neurotransmitter
is released into
synaptic cleft
Synaptic
cleft
Receiving
neuron
Receiving
neuron
Neurotransmitter
Ion channels molecules
Neurotransmitter
Receptor
Neurotransmitter binds
to receptor
Neurotransmitter broken
down and releases
Ions
Ion channel opens
Ion channel closes
Animation: Synapse
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
28.7 Chemical synapses make complex information
processing possible
•
A neuron may receive information from hundreds of
other neurons via thousands of synaptic terminals
•
Some neurotransmitters excite the receiving cell
•
Other neurotransmitters inhibit the receiving cell's
activity by decreasing its ability to develop action
potentials
•
If excitatory signals are strong enough to initiate an
action potential, a neuron will transmit a signal
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-7
Synaptic terminals
Dendrites
Inhibitory Excitatory
Myelin
sheath
Receiving
cell body
Axon
SEM 5,500
Synaptic
terminals
28.8 A variety of small molecules function as
neurotransmitters
• Many small, nitrogen-containing molecules
serve as neurotransmitters
– Acetylcholine
• Important in brain and at synapses between
motor neurons and muscles
– Biogenic amines
• Important in central nervous system
• Seratonin, dopamine
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Amino acids
– Important in central nervous system
• Peptides
– Substance P, endorphins influence
perception of pain
• Dissolved gases
– NO functions during sexual arousal
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CONNECTION
28.9 Many drugs act at chemical synapses
•
Many psychoactive drugs act at synapses and affect
neurotransmitter action
– Caffeine
– Nicotine
– Alcohol
– Psychoactive prescription drugs
– Stimulants
– THC (marijuana)
– Opiates
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
AN OVERVIEW OF ANIMAL NERVOUS SYSTEMS
28.10 Nervous system organization usually
correlates with body symmetry
• Sponges have no nervous system
• Radially symmetrical animals
– Nervous system arranged in a weblike
system of neurons called a nerve net
– Though uncentralized, not simple
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Most bilaterally symmetrical animals
– Tendency to move through environment
headfirst
– Cephalization, concentration of the nervous
system in the head region
– Centralization, presence of a central
nervous system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-10a
Nerve
net
Neuron
Hydra (cnidarian)
LE 28-10b
Eyespot
Brain
Nerve
cord
Transverse
nerve
Flatworm (planarian)
LE 28-10c
Brain
Ventral
nerve
cord
Segmental
ganglion
Leech (annelid)
LE 28-10d
Brain
Ventral
nerve
cord
Ganglia
Insect (arthropod)
LE 28-10e
Brain
Giant
axon
Squid (mollusc)
28.11 Vertebrate nervous systems are highly
centralized and cephalized
• Peripheral nervous system (PNS) includes
cranial and spinal nerves and ganglia
• Central nervous system (CNS) made up of
spinal cord and brain
– Spinal cord
• Inside vertebral column
• Conveys information from brain
• Integrates simple responses
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– Brain, the master control center
• Homeostatic centers keep body
functioning smoothly
• Sensory centers integrate data from
sense organs
• Can include centers of emotion and
intellect
• Sends motor commands to muscles
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-11a
Central nervous
system (CNS)
Brain
Peripheral
nervous
system (PNS)
Cranial
nerves
Spinal cord
Ganglia
outside
CNS
Spinal
nerves
•
Vast network of blood vessels services the CNS
•
Blood-brain barrier maintains a stable chemical
environment for the brain
•
Ventricles in brain are continuous with central canal of
spinal cord
– Filled with cerebrospinal fluid
– Protected by meninges (layers of connective
tissue)
•
Two distinct areas in CNS
– White matter: axons
– Gray matter: nerve cell bodies and dendrites
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-11b
Cerebrospinal fluid
Brain
Meninges
Gray matter
White matter
Central canal
Ventricles
Central canal
of spinal cord
Spinal cord
Spinal cord
(cross section)
Dorsal root
ganglion
(part of PNS)
Spinal nerve
(part of PNS)
28.12 The peripheral nervous system of
vertebrates is a functional hierarchy
• The PNS has two functional components
– Somatic nervous system
• Carries signals to and from skeletal muscles
• Responds mainly to external stimuli
– Autonomic nervous system
• Regulates internal environment
• Controls smooth and cardiac muscle,
various organs; involuntary
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-12
Peripheral
nervous system
Autonomic
nervous
system
Somatic
nervous
system
Sympathetic
division
Parasympathetic
division
Enteric
division
28.13 Opposing actions of sympathetic and
parasympathetic neurons regulate the internal
environment
• The autonomic nervous system has two sets of
neurons with opposing effects
– Parasympathetic division
• Primes the body for activities that gain and
conserve energy for the body
– Sympathetic division
• Prepares the body for intense, energyconsuming activities
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The enteric division is regulated by the
sympathetic and parasympathetic divisions
– Controls the digestive process
• Sympathetic and parasympathetic neurons
emerge from different regions of the CNS
– Use different neurotransmitters
• Somatic and autonomic components of PNS
cooperate to maintain homeostasis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-13
Parasympathetic division
Sympathetic division
Brain
Eye
Constricts
pupil
Dilates
pupil
Salivary
glands
Stimulates
saliva
production
Inhibits
saliva
production
Lung
Dilates
bronchi
Constricts
bronchi
Slows
heart
Spinal
cord
Accelerates
heart
Heart
Adrenal
gland
Stimulates
epinephrine
and norepinephrine release
Liver
Stomach
Stimulates
stomach,
pancreas,
and intestines
Pancreas
Intestines
Bladder
Stimulates
urination
Promotes
erection of
genitals
Stimulates
glucose release
Inhibits
stomach,
pancreas,
and intestines
Inhibits
urination
Genitalia
Promotes ejaculation and vaginal
contractions
28.14 The vertebrate brain develops from three
anterior bulges of the neural tube
• Early embryonic divisions of the vertebrate
brain develop into different adult structures
– Forebrain, midbrain, hindbrain
• Evolution of complex behavior paralleled
increases in forebrain integrative power
• During embryonic development, most profound
changes occur in the forebrain
• The cerebrum, an outgrowth of the forebrain,
controls homeostasis and integration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-14
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)
Cerebral
hemisphere
Midbrain
Hindbrain
Diencephalon
Midbrain
Pons
Cerebellum
Medulla
oblongata
Forebrain
Embryo (one month old)
Spinal cord
Fetus (three months old)
THE HUMAN BRAIN
28.15 The structure of a living supercomputer:
The human brain
• The human brain is composed of around 100
billion neurons and more supporting cells
• Hindbrain
– Pons and medulla oblongata
• Conduct information to and from other brain
areas
• Control involuntary activities
• Help coordinate whole-body movement
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– Cerebellum
• Coordinates movement of limbs
• Is responsible for learned motor
responses
• Midbrain
– Integrates auditory information
– Coordinates visual reflexes
– Relays sensory data to higher brain centers
• Midbrain and hindbrain make up the brain
stem
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• Forebrain
– Thalamus
• Relays information to and from cerebral
cortex
– Hypothalamus
• Regulates homeostasis
• Controls hormonal output of pituitary gland
• Serves as biological clock, regulating
circadian rhythms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Cerebrum
• Two cerebral hemispheres connected by
corpus callosum
• Performs sophisticated integration
• Plays major role in memory, learning,
speech, emotions
• Formulates complex behavioral responses
– Basal ganglia important in motor
coordination
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-15a
Cerebral
cortex
Cerebrum
Forebrain
Thalamus
Hypothalamus
Pituitary gland
Midbrain
Hindbrain
Pons
Medulla
oblongata
Cerebellum
Spinal
cord
LE 28-15b
Left cerebral
hemisphere
Corpus
callosum
Right cerebral
hemisphere
Basal
ganglia
28.16 The cerebral cortex is a mosaic of specialized,
interactive regions
•
The cerebral cortex occupies more than 80% of total
brain mass
•
The most distinctively human traits are produced in the
cerebral cortex
•
Right and left hemispheres are connected through the
corpus callosum
– Lateralization specializes the two sides for different
functions
– Each side has four lobes with different functional
areas
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-16
Parietal lobe
Frontal lobe
Frontal
association
area
Speech
Taste
Somatosensory
association
area
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Temporal lobe
Occipital lobe
CONNECTION
28.17 Injuries and brain operations provide
insight into brain function
• Injuries have revealed how healthy brains
operate
– Example: Phineas Gage
• PET scans, MRIs, and neurosurgery have
enhanced understanding of brain function
– Example: hemispherectomy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
28.18 Several parts of the brain regulate sleep
and arousal
• Hypothalamus, medulla oblongata, and pons
help regulate our sleep/wake cycles
• Sensory information sent from reticular
formation to cortex makes us alert and aware
• EEG measures electrical activity in the brain
during arousal and sleep
– In REM sleep, brain waves are similar to the
awake state; most dreams occur
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-18a
Data to cerebral
cortex
Eye
Reticular formation
Input from touch, pain,
and temperature receptors
Input from
ears
LE 28-18c
Awake but quiet (alpha waves)
Awake during intense mental activity (beta waves)
Delta waves
Asleep
REM sleep
Delta waves
28.19 The limbic system is involved in emotions,
memory, and learning
• The limbic system is a group of integrating
centers in the cerebral cortex, thalamus, and
hypothalamus
– Amygdala
• Lays down emotional memories
• Acts as a memory filter
– Hippocampus
• Involved in formation and recall of
memories
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LE 28-19
Thalamus
Cerebrum
Hypothalamus
Prefrontal
cortex
Smell
Olfactory
bulb
Amygdala
Hippocampus
• Memory is the ability to store and retrieve
information derived from experience
– Short-term memory: lasts only a few
minutes
– Long-term memory: lasts weeks or longer
– Information can be transferred from shortterm to long-term memory
– Factual memories are different from skill
memories
• Information processing by the brain involves
complex interplay of integrating centers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
28.20 Changes in brain physiology can produce
neurological disorders
• Schizophrenia is a severe mental disturbance
– Characterized by psychotic episodes in
which patients lose the ability to distinguish
reality
– Causes unknown, but research is looking
for gene for predisposition
– Treated by drugs that affect the
neurotransmitter dopamine
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Two broad forms of depressive illness have
been identified
– Major depression leaves a person unable to
live a normal life
– Bipolar disorder is characterized by extreme
mood swings
– Most common treatment is selective
serotonin reuptake inhibitors (SSRIs)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-20a
140
Prescriptions (millions)
120
100
80
60
40
20
0
1995
1996
1997
1998
1999
Year
2000
2001
2002
2003
• Alzheimer's disease (AD) is a form of mental
deterioration
– Characterized by confusion, memory loss,
and many other symptoms
– Progressive; usually age related
– Neurofibrillary tangles and senile plaques
destroy neurons in brain
– Currently no cure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 28-20b
Senile plaque
Neurofibrillary tangle
• Parkinson's disease is a motor disorder
– Characterized by difficulty in initiating
movements, slowness of movement, and
rigidity
– Progressive; increases with age
– Symptoms result from death of neurons in
midbrain
– Results from combination of environmental
and genetic factors
– At present, no cure available
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings