Transcript Chapter 11 Notes

Human Biology Concepts and Current Issues
Seventh Edition
Michael D. Johnson
11
The Nervous
System:
Integration and
Control
© 2014 Pearson Education, Inc.
Lecture Presentations by
Robert J. Sullivan
Marist College
Nervous System Overview
 Characteristics of the nervous system
1. Receives information from many sources
simultaneously
2. Integrates information (processes, compiles, makes
sense of this information)
3. Extremely fast—can receive, integrate, and respond
in tenths of a second
4. Can initiate specific responses such as muscle
contraction, glandular secretion, conscious control
over movement
© 2014 Pearson Education, Inc.
Nervous System Has Two Principal Parts
 Central nervous system (CNS)
– Components: brain and spinal cord
– Functions: receives, processes, and transfers
information
 Peripheral nervous system (PNS)
– Components: nerves outside CNS
– Sensory division: carries information toward the CNS
– Motor division: carries information away from CNS
– Somatic and autonomic divisions
© 2014 Pearson Education, Inc.
Figure 11.1
CNS
Brain
Sensory (input)
Spinal
cord
Signals
Signals
Signals
from internal
from external from skin,
environment tendons, and organs
muscles
PNS
Motor (output)
Somatic division
Autonomic division
(control of
skeletal muscle)
(autonomic control of
smooth muscle, cardiac
muscle, and glands)
Parasympathetic
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Sympathetic
Neurons Are the Communication Cells of the Nervous
System
 Neurons are specialized cells for communication
– Generate and conduct electrical impulses
 Types of neurons
– Sensory neurons: neurons found in the PNS that
receive stimuli and transmit information to the CNS
– Interneurons: transmit information between
components of the CNS
– Motor neurons: neurons found in the PNS that
transmit information away from the CNS
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Neurons Are the Communication Cells of the Nervous
System
 Three parts of the neuron
– Cell body: main part of the cell, has the nucleus and
most of the cytoplasm and organelles
– Dendrites: small slender extensions of the cell body,
receive incoming information
– Axon: long slender extension, specialized to conduct
electrical impulses away from the cell body
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Figure 11.2
Skin
Receptor
Dendrite
Axon
Muscle
Axon
bulb
Sensory
neuron Axon
terminals
Cell body
Axon
Impulse direction
Motor
neuron
Axon hillock
Dendrites
Interneuron
Cell
body
Dendrites
Cell body
Axon
Brain and spinal cord
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Neurons Initiate Action Potentials
 Neurons generate and transmit action potentials
 An action potential is basically an electrical impulse
 Action potentials are the primary means of
communication throughout the nervous system
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Sodium-Potassium Pump Maintains Resting Potential
 Functions of Na/K pump
– Maintains cell volume
– Establishes and maintains resting potential by
ongoing active transport of three Na out of the cell
and two K into the cell
 Resting potential: measurable difference in voltage
across the cell membrane in a resting cell
– 70 mV
– Interior of cell negative relative to the exterior
© 2014 Pearson Education, Inc.
Figure 11.3
Interstitial fluid
Na
Sodium(3) Na
potassium
pump
K
Resting
potential:
70 mV
(inside
negative)
Membrane
(2) K
Axon cytoplasm
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Na
K
Graded Potentials Alter the Resting Potential
 Graded potential
– Transient local changes in the resting potential
– May depolarize or hyperpolarize the membrane
 Summation
– Graded potentials can add up in space or time
– This additive effect may reach a “trigger point” or
threshold, which initiates an action potential
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An Action Potential Is a Sudden Reversal of
Membrane Voltage
 Initiated when graded potentials reach a certain
threshold (triggering point)
 Depolarization: Voltage-sensitive Na channels
open, Na moves into the axon (this reverses the
voltage across the membrane, interior becomes )
 Repolarization: Na channels close, K channels
open, K moves out of the axon (this restores the
initial polarity, actually becomes temporarily
hyperpolarized)
 Reestablishment of the resting potential: K
channels close, the normal activity of the sodiumpotassium pump restores resting potential
© 2014 Pearson Education, Inc.
Membrane potential
in millivolts (mV)
Figure 11.4
30
20
A depolarizing
10
graded potential
0
10 Resting
A hyperpolarizing
20 membrane
graded potential
30 potential
40
Summation
50
60
70
80
0
20
40
60
80
Time (milliseconds)
© 2014 Pearson Education, Inc.
Action
potential
Threshold
100
120
140
Figure 11.5
Interstitial fluid
Axon cytoplasm
1
Interstitial fluid
Na
Na
K
Na
K
Na
Axon cytoplasm
2
DEPOLARIZATION
K
K
REPOLARIZATION
• Sodium channels close
• Potassium channels open
• Potassium diffuses out
• Membrane repolarizes
• Sodium channels open
• Sodium diffuses in
• Membrane depolarizes
Membrane potential (mV)
30
0
PNa
Threshold
PK
70
0
1
2
4
3
5
6
Time (milliseconds)
3
RESTING POTENTIAL
• Potassium channels close
Interstitial fluid
Interstitial fluid
Axon cytoplasm
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REESTABLISHMENT OF RESTING
POTENTIAL
• Sodium and potassium channels closed
• Na-K pump matches rate of leakage
Na
Na
K
K
Axon cytoplasm
Na
Na
K
K
Action Potentials Are All-or-None and SelfPropagating
 All-or-none
– Individual neuron threshold sets extent of stimulus
needed
– If threshold is achieved, it triggers
– Once triggered, an action potential is always the
same in speed and voltage
 Self-propagating
– Continues to propagate itself in the next region of the
axon
– Moves like a wave down the axon, with constant
speed and amplitude
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Action Potentials Are All-or-None and SelfPropagating
 The number of action potentials/unit time encodes
the strength of the stimulus
– Stronger stimuli generate more action potentials/unit
time
 Speed of action potential
– Always the same for a particular neuron
– Can be different in different neurons
– In larger diameter axons, action potentials travel at
greater speed
© 2014 Pearson Education, Inc.
Neuroglial Cells Support and Protect Neurons
 Neuroglial cells make up 80% of nervous system
cells
– Function
– Support
– Protection
– Glial cells do NOT transmit action potentials
– Two types
– Schwann cells
– Oligodendrocytes
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Neuroglial Cells Support and Protect Neurons
 Schwann cells: form myelin sheaths in PNS
– Role of myelin sheath:
– Save the neuron energy
– Speed up the transmission of impulses
– Saltatory conduction: leaping pattern of action potential
conduction
– Help damaged or severed axons regenerate
 Oligodendrocytes
– Form myelin sheaths in CNS
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Figure 11.7
In saltatory conduction,
the nerve impulse jumps
from node to node.
A myelinated
motor neuron
of the peripheral
nervous system
Myelin
sheath
Neuron
axon
TEM cross section
of part of an axon
(yellow) and its
surrounding
myelin sheath
(beige).
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Node of Ranvier
Schwann cell
Disorders Associated with Degeneration of Myelin
Sheaths
 Multiple sclerosis (MS)
– Progressive damage to myelin sheaths in brain and
spinal cord
– Weakness, visual impairment, incontinence
 Amyotrophic lateral sclerosis (ALS)
– Progressive damage to myelin sheaths in motor area
of spinal cord
– Progressive weakening and wasting of skeletal
muscle
© 2014 Pearson Education, Inc.
Information Is Transferred from a Neuron to Its
Target
 Targets: another neuron, muscle cell, or gland
 Synapse: special junction between axon terminus
and target cell
 Synaptic transmission
– Process of transmission of impulse from sending
(presynaptic neuron) across synaptic cleft to receiving
(postsynaptic) target
– Involves release and diffusion of chemical
neurotransmitter
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Neurotransmitter Is Released
 Events that occur during synaptic transmission
 Action potential arrives at axon terminus, causing
Ca2 to diffuse into axon bulb
 Ca2 causes release of neurotransmitter from
vesicles
 Neurotransmitter diffuses across synaptic cleft
 Neurotransmitter binds to receptors on target
(postsynaptic) membrane and opens gated channels
 Graded potential results from Na movement
through opened channels
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Figure 11.8
Axon bulbs form synapses
with a postsynaptic neuron
1
An action potential
arrives, causing
Ca2 to diffuse
into the axon bulb.
Action potential
2
Ca2 causes
vesicles containing
neurotransmitter
to fuse with the
cell membrane
releasing
neurotransmitter.
Axon of
presynaptic
neuron
Ca2
Synaptic cleft
Mitochondrion
Vesicles containing
neurotransmitter
Neurotransmitter
Axon
bulb
Na
Presynaptic
neuron
Synaptic cleft
Dendrite or cell body
of postsynaptic neuron
Close-up of a synapse
Cytoplasm of postsynaptic cell
Presynaptic membrane
Postsynaptic membrane
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Na
3
4
Neurotransmitter binds to
receptors on chemically gated
sodium channels, causing the
channels to open.
Diffusion of sodium produces
a graded potential in the
local region of the synapse.
Neurotransmitters Exert Excitatory or Inhibitory
Effects
 Response of postsynaptic target cell depends on
– Type of neurotransmitter (50 types)
– Type of receptors
– Type of gated ion channels
 Excitatory neurotransmitters
– Depolarize the postsynaptic cell, approaching or
exceeding threshold
 Inhibitory neurotransmitters
– Hyperpolarize the postsynaptic cell
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Table 11.1
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Postsynaptic Neurons Integrate and Process
Information
 Response in postsynaptic cell depends on
– How many neurons are forming synapses
with it
– Whether the neurons forming synapses with
it are excitatory or inhibitory
 Convergence: occurs when one neuron receives
input from many others
 Divergence: occurs when one neuron sends action
potentials to multiple other neurons
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Figure 11.9
Convergence
Divergence
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Peripheral Nervous System Relays Information
Between Tissues and CNS
 Nerve
– contains axons of many neurons wrapped together in
a protective sheath
– Carries information to and from the CNS
 Cranial nerves
– 12 pairs
– Connect directly to brain
 Spinal nerves
– 31 pairs
– Connect to spinal cord
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Sensory Neurons Provide Information to the CNS
 Provide information for both the somatic and
autonomic motor divisions of the PNS
 Incoming information arrives at the CNS as action
potentials from sensory neurons located throughout
the body
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The Somatic Division Controls Skeletal Muscles
 Functions
– Voluntary
– Conscious control of skeletal muscles
– Involuntary (reflexes)
– Spinal reflexes: Involuntary responses mediated
primarily by spinal cord and spinal nerves, with little
brain involvement
– Flexor (withdrawal) reflex
– Crossed extensor reflex
– Stretch reflex: important in maintaining upright posture,
movement
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Figure 11.10
3
To brain
Interneurons (gray) stimulate
specific motor neurons on
both sides of the body and
send signals to the brain.
Dorsal root (sensory)
Cell body of
sensory neuron
Ventral
root
(motor)
2
Sensory
neurons carry
the signal to the
spinal cord.
Spinal cord
Motor neuron
Motor neuron
4a
Flexor reflex:
withdraws the
right leg.
1
A painful stimulus is
applied to the right foot.
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Effector
muscles
(thigh)
4b
Crossed extensor
reflex: extends
the left leg.
The Autonomic Division Controls Automatic Body
Functions
 Part of the motor output of the PNS
 Controls automatic body functions of many internal
organs
 Consists of two divisions
1. Sympathetic division
2. Parasympathetic division
 Both sympathetic motor neurons and
parasympathetic neurons enervate each organ
 Targets: smooth muscle, cardiac muscle, internal
organs
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The Sympathetic and Parasympathetic Divisions
Oppose Each Other
 Sympathetic division
– Prepares the body for emergencies
– Norepinephrine is the key neurotransmitter
– Produces fight-or-flight response
– Increases heart rate and respiration
– Raises blood pressure
– Dilates pupils
– Slows digestion and urine production
– Generally produces a unified response in all organs at
once
– Opposes parasympathetic division
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The Sympathetic and Parasympathetic Divisions
Oppose Each Other
 Parasympathetic division
–
–
–
–
Relaxes the body
Opposes sympathetic division
Acetylcholine is the key neurotransmitter
Actions: lowers heart rate and respiration, increases
digestion, permits defecation and urination
 Sympathetic and parasympathetic divisions work
antagonistically to maintain homeostasis
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Figure 11.12
SYMPATHETIC DIVISION
PARASYMPATHETIC DIVISION
Constricts
pupil
Dilates
pupil
Decreases
salivation
Increases
salivation
Cranial
nerves
Decreases
respiration
rate
Increases
respiration
rate
Increases
heart rate
Thoracic
nerves
Decreases
heart rate
Constricts
blood
vessels
Dilates
blood
vessels
Inhibits
digestive
processes
Stimulates
digestive
processes
Lumbar
nerves
Inhibits
digestive
processes
Sacral
nerves
Relaxes
bladder
muscles
Inhibits
defecation
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Stimulates
digestive
processes
Stimulates
secretion of
epinephrine and
norepinephrine
Ganglion
Causes salt and
water retention
Synapse
between neurons
Contracts
bladder
muscles
Stimulates
defecation
Table 11.2
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The Brain and Spinal Cord Constitute the CNS
 CNS protection
– Bone: skull and vertebrae
– Meninges: protective membranes
– Dura mater, arachnoid, and pia mater
– Cerebrospinal fluid: bathes the brain, spinal cord
– Shock absorber
– Produced within the ventricles of the brain
– Blood-brain barrier: prevents entry of certain
chemicals and pathogens
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Figure 11.13
Right ventricle
Skull
Left
ventricle
Hair
Scalp
Skull
Dura mater
Arachnoid
Meninges
Pia mater
Brain tissue
Third ventricle
Cerebrospinal
fluid
Meninges
Spinal canal
Spinal cord
Fourth ventricle
Right
ventricle
Left
ventricle
Third
ventricle
Cerebral
aqueduct
Fourth
ventricle
Anterior view.
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Sagittal view.
Cerebrospinal
fluid
The Spinal Cord Relays Information
 Spinal cord is a superhighway for action potentials
between the brain and the rest of the body
 White matter
– Outer portion of spinal cord
– Consists of myelinated ascending (sensory) and
descending (motor) nerve tracts
 Gray matter
– Center portion of spinal cord
– Contains cell bodies, dendrites
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Figure 11.14
Spinal cord
Gray matter
Central canal
White matter
Ganglion
Nerve
Intervertebral
disc
Pia mater
Arachnoid
A transverse slice of the cord,
showing white and gray matter.
Meninges
Dura mater
Spinal cord
Vertebra
The spinal cord lies
within the vertebral
column.
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A closer look at the spinal cord
and its relationship with a
vertebra.
Superior view of vertebra.
The Brain Processes and Acts on Information
 Brain: command center of the body
 Three major anatomical/functional divisions
– Hindbrain: coordinates basic, automatic, and vital
tasks
– Midbrain: coordinates muscle groups and responses
to sight and sound
– Forebrain: receives, integrates sensory input,
determines complex behavior
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Figure 11.15
FOREBRAIN
Cerebrum
• Coordinates language
• Controls decision
making
• Produces conscious
thought
MIDBRAIN
• Relays visual
and auditory
inputs
• Coordinates
movement
Corpus callosum
• Bridges the,
two cerebral
hemispheres
Thalamus
• Receives, processes,
and transfers
information
HINDBRAIN
Pons
• Connects cerebellum, spinal cord
with higher brain centers
• Aids medulla in regulating
respiration
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Medulla oblongata
• Controls automatic
functions of
internal organs
Cerebellum
• Controls basic
and skilled
movements
Hindbrain: Movement and Automatic Functions
 Oldest, most primitive part of brain, from an
evolutionary perspective
 Three basic parts
– Medulla oblongata
– Cerebellum
– Pons
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Hindbrain: Movement and Automatic Functions
 Medulla oblongata
– Connects to spinal cord
– Controls vital automatic functions of internal organs
– Cardiovascular center: regulates heart rate and blood
pressure
– Respiratory center: adjusts respiration in response to
CO2 and O2 levels
– Motor nerves cross over in medulla oblongata
– Right forebrain controls left side of body
– Left forebrain controls right side of body
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Hindbrain: Movement and Automatic Functions
 Cerebellum
– Coordinates basic body movements
– Stores and replicates sequences of skilled
movements
– Examples
– Tying a shoe
– Swinging a bat
– Using a keyboard
– Excessive alcohol consumption disrupts normal
cerebellum function
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Hindbrain: Movement and Automatic Functions
 Pons
– Connects higher brain centers and the spinal cord
– Coordinates the flow of information between the
cerebellum and higher brain centers
– Aids medulla oblongata in regulating respiration
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Midbrain: Vision and Hearing
 Coordinates movements of the head related to vision
and hearing
 Controls movement of eyes and size of pupils
 Reticular formation: group of neurons that extend
through medulla oblongata, pons, and midbrain
– Works with cerebellum to control skeletal muscle
activity related to posture/balance
– Maintains wakefulness
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Forebrain: Emotions and Conscious Thought
 Receives and integrates information concerning
emotions and conscious thought
 Hypothalamus
– Helps regulate homeostasis
 Thalamus
– Receiving, processing, and transfer center
 Limbic system
– Pathways involved in emotions and memory
 Cerebrum
– Language, decision making, conscious thought
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Forebrain: Emotions and Conscious Thought
 Cerebrum
– Structure
– Right and left hemispheres
– Hemispheres connected by corpus callosum
– Nerve tracts in corpus callosum allow two hemispheres to
share information
– Cerebral cortex: gray matter, the outer layer of the
cerebrum
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A Closer Look at the Cerebral Cortex
 Functions: memory storage, abstract thought,
conscious awareness, conscious control of skeletal
muscle
 Divided into four lobes
– Occipital lobe: processes visual information
– Temporal lobe: interprets auditory information,
comprehends spoken/written language
– Parietal lobe: receives and interprets sensory
information from the skin
– Frontal lobe: initiates motor activity, responsible for
speech, conscious thought
 All four lobes: memory storage
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Figure 11.16
Parietal lobe
Right cerebral
hemisphere
Surface fold
• Interprets sensory
information from
skin
Occipital lobe
• Processes visual
information
Posterior
Corpus
callosum
Anterior
Cerebral
white
matter
Cerebral cortex
(gray matter)
Temporal lobe
Left
cerebral
hemisphere
The cerebral cortex (gray matter; outer
layer, shown in four colors) consists of
interneurons that integrate and process
information. White matter (inner core)
consists of ascending and descending nerve
tracts. The two separate hemispheres are
joined by the corpus callosum.
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Frontal lobe
• Initiates motor activity
• Responsible for speech
• Conscious thought
• Interprets auditory
information
• Comprehends language
• Perceptual judgment
The functions of the four lobes of the
cerebral cortex are location-specific.
Figure 11.17
Leg
Trunk
Hip Trunk
Hip
Arm
Neck
Elbow
Arm
Wrist
Elbow
Fingers Hand
Forearm
Thumb
Fingers
Neck
Thumb
Toes
Brow
Genitals
Eye
Eye
Face
Primary
somatosensory
area
Primary
motor
area
Lips
Nose
Face
Lips
Jaw
Teeth
Tongue
Thumb
Gums
Frontal
lobe
Swallowing
Tongue
Pharynx
Right
hemisphere
Left
hemisphere
Parietal lobe
Posterior
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Brain Activity Continues During Sleep
 Reticular activating system (RAS)
– Group of neurons within the reticular formation
– Controls levels of sleep and wakefulness
– Sleep center in RAS
– Releases the neurotransmitter serotonin
– Induces sleep by inhibiting arousal
– To return to wakefulness, norepinephrine (secreted by
another area in the brain) inhibits the serotonin
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Brain Activity Continues During Sleep
 Sleep stages
– Based on electroencephalograms (EEGs)
– Stage 1: transitional, random small waves on EEG
– Stage 2: skeletal muscles relax, little eye or body
movement, EEG shows sleep spindles
– Stage 3: heart and respiration slower, EEG shows slow
wave sleep
– Stage 4: difficult to awaken, heart and respiration
slowest, body temperature decreased
– REM (rapid eye movement) sleep: dreaming, EEG
same as awake
– Typical night’s sleep: cycle through stages
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Figure 11.18
Awake
Stage
(Sleep spindles)
Stage
Stage
Awake
Stage
0
10 seconds
EEG recordings in an awake person and during
Stages 1-4 and REM sleep. Note the similarity
between REM sleep and wakefulness.
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1
2
3
4
5
6
7
Hours
Patterns of sleep during a typical night.
8
The Limbic System Is the Site of Emotions and Basic
Behaviors
 Includes all neuronal structures that together control
emotional behavior and motivational drives
 Hypothalamus serves as a gateway to and from
limbic system
 Emotions
– Fear, anger, sorrow, love, etc.
 Basic behavior
– Seeking food, satisfying thirst
– Sexual gratification
 Behaviors modified by cerebrum
 Short-term memory
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Figure 11.19
Cerebrum
Limbic system
Thalamus
Corpus
callosum
Hypothalamus
Cerebellum
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Memory Involves Storing and Retrieving Information
 Short-term
– Working memory
– Information from previous few hours
– Stored in the limbic system
 Long-term
– Information from previous days to years
– Involves permanent changes in neurons and
synapses in the cerebral cortex
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Psychoactive Drugs Affect Higher Brain Functions
 Psychoactive drugs
– Affect states of consciousness, emotions, or behavior
 Action
– Able to cross blood-brain barrier
– Influence concentrations or actions of
neurotransmitters
– Affect higher brain functions
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Psychoactive Drugs Affect Higher Brain Functions
 Psychological dependence
– User craves the feeling associated with the drug
 Tolerance
– Requires more of the substance to achieve the same
effect
 Addiction
– The need to continue obtaining and using a
substance
– No free choice
 Withdrawal
– Physical symptoms that occur upon stopping the drug
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Disorders of the Nervous System
 Trauma
– Physical injury to brain or spinal cord
– Concussion
– Blow to the head may lead to unconsciousness
– Disruption of electrical activity in the brain
– Risk of subdural hematoma
– Spinal cord injuries
– Impairment of sensation and function below site of injury
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Disorders of the Nervous System
 Infections: Caused by viruses or bacteria that
manage to pass through the blood-brain barrier
– Encephalitis
– Inflammation of the brain caused by viral infection
– Meningitis
– Inflammation of the meninges caused by viral or
bacterial infection
– Rabies
– Infectious viral disease
– Spread by bite or saliva of infected animal
– Virus spreads from bite to brain via sensory neurons
 Brain tumors: abnormal growth in or on the brain
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Disorders of the Nervous System
 Disorders of neural and synaptic transmission
– Epilepsy
– Recurring episodes of abnormal electrical activity
(seizures)
– Alzheimer’s disease
– Most common cause of dementia
– Accumulation of abnormal protein, beta amyloid
– Progressive memory lapses and dementia
– Parkinson’s disease
– Loss of dopamine-releasing neurons
– Progressive degenerative disorder affecting motor
activity
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Figure 11.21
A PET scan of a healthy brain.
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A PET scan of a patient with Alzheimer’s
disease, showing decreased activity and
an irregular pattern.