Download PowerLecture: Chapter 13

PowerLecture:
Chapter 13
The Nervous System
Learning Objectives



Describe the visible structure of neurons,
neuroglia, nerves, and ganglia, both
separately and together as a system.
Describe the distribution of the invisible
array of proteins, ions, and other molecules
in a neuron, both at rest and as a neuron
experiences a change in potential.
Understand how a nerve impulse is
received by a neuron, conducted along a
neuron, and transmitted across a synapse
to a neighboring neuron, muscle, or gland.
Learning Objectives (cont’d)




Outline some of the ways by which
information flow is regulated and integrated
in the human body.
Describe the organization of peripheral
versus central nervous systems.
Summarize the major parts of the human
brain and the principal functions of each.
Characterize the major groups of drugs,
emphasizing their effects on the nervous
system.
Impacts/Issues
In Pursuit of Ecstasy
In Pursuit of Ecstasy
Ecstasy is a drug that can make you feel
really good, at least for a time.



The active ingredient is MDMA, an
amphetamine-like drug that interferes with the
function of serotonin in the brain.
Excess serotonin can relieve anxiety, sharpen
the senses, and make you feel socially
accepted; it can also kill.
In Pursuit of Ecstasy
 How
we function as
individuals depends
on whether we nurture
or abuse our nervous
system.
How Would You Vote?
To conduct an instant in-class survey using a classroom response
system, access “JoinIn Clicker Content” from the PowerLecture main
menu.
 Would
you support legislation that forces
nonviolent drug offenders to enter drug rehab
programs as an alternative to jail?


a. Yes, treatment is more effective than jail at
reducing drug use, and it is more cost effective
too.
b. No, easing penalties will lead to more drug
use.
Section 1
Neurons—The
Communication
Specialists
Neurons
The role of the nervous system is to detect
and integrate information about external
and internal conditions and carry out
responses.


Neurons form the basis of the system’s
communication network.
Figure 13.2
Neurons

There are three types of neurons:
•
•
•
Sensory neurons are receptors for specific sensory
stimuli (signals).
Interneurons in the brain and spinal cord integrate
input and output signals.
Motor neurons send information from integrator to
muscle or gland cells (effectors).
Neurons
Neurons have several functional zones.


Neurons form extended cells with several
zones:
•
•
•
•
The cell body contains the nucleus and organelles.
The cell body has slender extensions called
dendrites; the cell body and the dendrites form the
input zone for receiving information.
Next comes the trigger zone, called the axon
hillock in motor neurons and interneurons; the
trigger zone leads to the axon, which is the neuron’s
conducting zone.
The axon’s endings are output zones where
messages are sent to other cells.
dendrites
input zone
cell body
trigger zone
conducting zone
axon
axon endings
output zone
Fig. 13.1, p. 226
Neurons


Only 10% of the nervous system consists of
neurons; the rest of the 90% is composed of
support cells called neuroglia, or glia.
Neurons function well in communication
because they are excitable (produce electrical
signals in response to stimuli).
Neurons
Properties of a neuron’s plasma membrane
allow it to carry signals.


The plasma membrane prevents charged
substances (K+ and Na+ ions) from moving
freely across, but both ions can move through
channels.
•
•
•
Some channel proteins are always open, others are
gated.
In a resting neuron, gated sodium channels are
closed; sodium does not pass through the
membrane, but potassium does.
According to the gradients that form, sodium diffuses
into the cell, potassium diffuses out of the cell.
fluid outside cell
cytoplasm
Passive transporters
with open channels let
ions steadily leak
across the membrane.
Na+/K+ pump
Other passive
transporters have
voltage-sensitive
gated channels that
open and shut. They
assist diffusion of Na+
and K+ across the
membrane as the ions
follow concentration
gradients.
lipid bilayer
Active
transporters of neuron
pump Na+ and membrane
K+ across the
membrane,
against their
concentration
gradients.
They counter
ion leaks and
restore resting
membrane
conditions.
Fig. 13.3b, p. 227
Neurons

The difference across the membrane that forms
because of the K+ and Na+ gradients results in
a resting membrane potential of ‒70 millivolts
(cytoplasmic side of the membrane is negative).
K+
Na+
outside
Plasma
membrane
K+
Na+
inside
Fig. 13.3a, p. 227
Section 2
Action Potentials =
Nerve Impulses
Action Potentials = Nerve Impulses
Sufficient signals at the input zone of a
resting neuron can trigger reversal of the
voltage difference across the membrane.



The signal opens gated sodium channels,
allowing Na+ to rush into the neuron.
The internal charge near the membrane
becomes less negative, stimulating more
channels to open (positive feedback).
Action Potentials = Nerve Impulses

When the voltage difference crosses a key
threshold level of stimulation, an action
potential (nerve impulse) occurs.
•
•
Thresholds can only be reached in areas of the
neuron where there are voltage-sensitive sodium
channels.
Stimuli must be strong enough to trigger the
potential.
fluid outside
neuron
gated sodium
channel
In a membrane at rest, the inside of the neuron is negative relative to
the outside. An electrical disturbance (yellow arrow) spreads from an
input zone to an adjacent trigger zone of the membrane, which has a
large number of gated sodium channels.
Fig. 13.4a, p. 228
Na+
Na+
Na+
voltage
reversed
©2007 Thomson Higher Education
A strong disturbance initiates an action potential. Sodium gates open.
Sodium flows in, reducing the negativity inside the neuron. The
change causes more gates to open, and so on until threshold is
reached and the voltage difference across the membrane reverses.
Fig. 13.4b, p. 228
Action Potentials = Nerve Impulses
Action potentials spread by themselves.



The action potential is self-propagating and
moves away from the stimulation site.
Potentials can self-propagate because the
changes to the membrane potential don’t lose
strength.
K+
K+
K+
Na+
Na+
Na+
©2007 Thomson Higher Education
At the next patch of membrane, another group of gated sodium channels
open. In the previous patch, some K+ moves out through other gated
channels. That region becomes negative again.
Fig. 13.4c, p. 229
Na+/K+ pump
K+
K+ K+
Na+
Na+
Na+
K+
propagating
action potential
©2007 Thomson Higher Education
After each action potential, the sodium and potassium concentration
gradients in a patch of membrane are not yet fully restored. Active
transport at sodium–potassium pumps restores them.
Fig. 13.4d, p. 229
Action Potentials = Nerve Impulses
A neuron can’t “fire” again until ion pumps
restore its resting potential.



By diffusion, some potassium ions will always
leak out of the cell and some sodium will
always leak in.
The sodium-potassium pump uses ATP to
actively pump potassium ions in and sodium
ions out of the neuron to keep the concentration
of sodium ions higher outside, ready for another
action potential to form.
Action Potentials = Nerve Impulses
Action potentials are “all-or-nothing.”


Action potentials are all-or-nothing events.
•
•
Once a positive-feedback cycle starts, nothing stops
the full “spiking” of a potential.
If threshold is not reached, however, the membrane
disturbance will subside when the stimulus is
removed.
action potential
threshold
level
resting
level
1
2
3
4
Time (milliseconds)
5
6
Fig. 13.6, p. 229
Action Potentials = Nerve Impulses

When the action potential is terminated, the
sodium gates close, potassium gates open, and
the sodium-potassium membrane pumps
become operational to fully restore the resting
potential.
Na+
pumped out
K+
leaks out
fluid
outside
plasma
membrane
neuron’s
plasma
membrane
cytoplasm
next to the
membrane
Na+
leaks in
K+
pumped in
Fig. 13.5, p. 229
Section 3
Chemical Synapses:
Communication Junctions
Chemical Synapses:
Communication Junctions
Action potentials can stimulate the release
of neurotransmitters.


Neurotransmitters diffuse across a chemical
synapse, the junction between a neuron and
an adjacent cell (between neurons and other
neurons, or between neurons and muscle or
gland cells).
Chemical Synapses:
Communication Junctions

The neuron that releases the transmitter is
called the presynaptic cell.
•
•

In response to an action potential, gated calcium
channels open and allow calcium ions to enter the
neuron from the synapse.
Calcium causes the synaptic vesicles to fuse
with the membrane and release the transmitter
substance into the synapse.
The transmitter binds to receptors on the
membrane of the postsynaptic cell.
plasma membrane
of an axon ending
of a presynaptic
cell
vesicle
containing
neurotransmitter
membrane receptor
for neurotransmitter
synapse
plasma
membrane of a
postsynaptic cell
Fig. 13.7a, p. 230
molecule of neurotransmitter in
synapse
ions (black) that
now can diffuse
through channel
receptor for the neurotransmitter on gated channel
protein in plasma membrane of postsynaptic cell
Fig. 13.7b, p. 230
Chemical Synapses:
Communication Junctions
Neurotransmitters can excite or inhibit a
receiving cell.


How a postsynaptic cell responds to a
transmitter depends on the type and amount of
transmitter, the receptors it has, and the types
of channels in its input zone.
•
•
Excitatory signals drive the membrane toward an
action potential.
Inhibitory signals prevent an action potential.
Chemical Synapses:
Communication Junctions

Examples of neurotransmitters:
•
•
•
Acetylcholine (ACh) can excite or inhibit target cells
in the brain, spinal cord, glands, and muscles.
Serotonin acts on brain cells to govern sleeping,
sensory perception, temperature regulation, and
emotional states.
Some neurons secrete nitric oxide (NO), a gas that
controls blood vessel dilation, as in penis erection.
muscle fiber
axon endings
Fig. 13.8a, p. 231
Motor end plate
(troughs in muscle cell membrane)
axon ending
©2007 Thomson Higher Education
gap
muscle cell membrane
Fig. 13.8b, p. 231
Chemical Synapses:
Communication Junctions

Neuromodulators can magnify or reduce the
effects of a neurotransmitter.
•
•
•
One example includes the natural painkillers called
endorphins.
Release of endorphins prevents sensations of pain
from being recognized.
Endorphins may also play a role in memory, learning,
and sexual behavior.
Chemical Synapses:
Communication Junctions
Competing signals are “summed up.”


Excitatory and inhibitory signals compete at the
input zone.
•
•
An excitatory postsynaptic potential (EPSP)
depolarizes the membrane to bring it closer to
threshold.
An inhibitory postsynaptic potential (IPSP) either
drives the membrane away from threshold by a
hyperpolarizing effect or maintains the membrane
potential at the resting level.
Chemical Synapses:
Communication Junctions

In synaptic integration, competing signals that
reach the input zone of a neuron at the same
time are summed; summation of signals
determines whether a signal is suppressed,
reinforced, or sent onward to other body cells.
Chemical Synapses:
Communication Junctions
Neurotransmitter molecules must be
removed from the synapse.



Neurotransmitters must be removed from the
synaptic cleft to discontinue stimulation.
There are three methods of removal:
•
•
•
Some neurotransmitter molecules simply diffuse out
of the cleft.
Enzymes, such as acetylcholinesterase, break down
the transmitters.
Membrane transport proteins actively pump
neurotransmitter molecules back into the presynaptic
cells.
Section 4
Information Pathways
Information Pathways
Nerves are long-distance lines.


Signals between the brain or spinal cord and
body regions travel via nerves.
•
•
Axons of sensory neurons, motor neurons, or both,
are bundled together in a nerve.
Within the brain and spinal cord, bundles of
interneuron axons are called nerve tracts.
Information Pathways

Axons are covered by a myelin sheath derived
from Schwann cells.
•
•
•
Each section of the sheath is separated from
adjacent ones by a region where the axon
membrane, along with gated sodium channels, is
exposed.
Action potentials jump from node to node (saltatory
conduction); such jumps are fast and efficient.
There are no Schwann cells in the central nervous
system; here processes from oligodendrocytes
form the sheaths of myelinated axons.
blood vessels
many neurons bundled together
inside a connective tissue sheath
axon of one neuron
outer
connective
tissue of
one nerve
myelin sheath formed
by Schwann cells
unsheathed
node containing
gated Na+
channels
axon
Fig. 13.9, p. 232
Table 13.1, p. 232
Information Pathways
Reflex arcs are the simplest nerve
pathways.




A reflex is a simple, stereotyped movement in
response to a stimulus.
In the simplest reflex arcs, sensory neurons
synapse directly with motor neurons; an
example is the stretch reflex, which contracts
a muscle after that muscle has been stretched.
In most reflex pathways, the sensory neurons
also interact with several interneurons, which
excite or inhibit motor neurons as needed for a
coordinated response.
a Fruit being loaded into a bowl
puts weight on an arm muscle and
stretches it.
STIMULUS
Biceps stretches.
b Stretching stimulates sensory
receptor endings in this muscle
spindle.
d The stimulation is strong
enough to generate action
potentials
e Axon endings of the motor
neuron synapse with muscle
cells in the stretched muscle.
c Axon endings of the
sensory neuron
release a neurotransmitter
RESPONSE
Biceps contracts.
f ACh released from the motor
neuron’s axon endings
stimulates muscle cells.
g Stimulation makes the
stretched muscle contract.
muscle neuromuscular
spindle
junction
Fig. 13.10, p. 233
extensor muscle of knee
(quadriceps femoris)
muscle
spindle
patellar tendon
reflex arc
motor neuron
Fig. 13.27, p. 248
Information Pathways
In the brain and spinal cord, neurons
interact in circuits.


The overall direction of flow in the nervous
system: sensory neurons >>> spinal cord and
brain >>> interneurons >>> motor neurons.
receptor
endings
axon
cell
body
axon
ending
cell
body
cell
body
axon
axon
axon
axon
endings
dendrites
dendrites
sensory neuron
interneuron
motor neuron
In-text Fig., p. 233
Information Pathways

Interneurons in the spinal cord and brain are
grouped into blocks, which in turn form circuits;
blocks receive signals, integrate them, and then
generate new ones.
•
•
•
Divergent circuits fan out from one block into
another.
Other circuits funnel down to just a few neurons.
In reverberating circuits, neurons repeat signals
among themselves.
Section 5
Overview of the Nervous
System
Overview of the Nervous System
The central nervous system (CNS) is
composed of the brain and spinal cord; all
of the interneurons are contained in this
system.



Nerves that carry sensory input to the CNS are
called the afferent nerves.
Efferent nerves carry signals away from the
CNS.
Overview of the Nervous System
The peripheral nervous system (PNS)
includes all the nerves that carry signals to
and from the brain and spinal cord to the
rest of the body.




The PNS is further divided into the somatic
and autonomic subdivisions.
The PNS consists of 31 pairs of spinal nerves
and 12 pairs of cranial nerves.
At some sites, cell bodies from several neurons
cluster together in ganglia.
brain
cranial nerves
cervical nerves
(eight pairs)
spinal cord
thoracic nerves
(twelve pairs)
ulnar nerve
sciatic nerve
lumbar nerves
(five pairs)
sacral nerves (five pairs)
coccygeal nerves
(one pair)
Fig. 13.11, p. 234
CENTRAL
NERVOUS
SYSTEM
brain
spinal
cord
sensory
nerves
axons of
motor nerves
somatic
subdivision
(motor functions)
autonomic
subdivision
(visceral
functions)
parasympathetic sympathetic
nerves
nerves
peripheral nervous system
Fig. 13.12, p. 235
I Olfactory nerve
II Optic nerve (from the retina)
III To eye muscles
IV To eye muscles
V To jaw muscles; from mouth
VI To eye muscles
VII To facial muscles, glands;
from the taste buds
VIII From inner ear
IX To/from pharynx
X To tongue muscles
XI To/from internal organs
XII To neck and back muscles
© 2007 Thomson Higher Education
Fig. 13.13, p. 235
Section 6
Major Expressways:
Peripheral Nerves and
the Spinal Cord
Major Expressways: Peripheral Nerves
and the Spinal Cord
The peripheral nervous system consists of
somatic and autonomic nerves.


Somatic nerves carry signals related to
movement of the head, trunk, and limbs;
signals move to and from skeletal muscles for
voluntary control.
Major Expressways: Peripheral Nerves
and the Spinal Cord

Autonomic nerves carry signals between
internal organs and other structures; signals
move to and from smooth muscles, cardiac
muscle, and glands (involuntary control).
•
•
The cell bodies of preganglionic neurons lie within
the CNS and extend their axons to ganglia outside
the CNS.
Postganglionic neurons receive the messages
from the axons of the preganglionic cells and pass
the impulses on to the effectors.
Major Expressways: Peripheral Nerves
and the Spinal Cord
Autonomic nerves are divided into
parasympathetic and sympathetic groups.


They normally work antagonistically towards
each other.
•
•

Parasympathetic nerves slow down body activity
when the body is not under stress.
Sympathetic nerves increase overall body activity
during times of stress, excitement, or danger; they
also call on the hormone norepinephrine to increase
the fight-flight response.
When sympathetic activity drops,
parasympathetic activity may rise in a rebound
effect.
optic nerve
eyes
salivary glands
heart
larynx
bronchi
lungs
Vagus
nerve
midbrain
medulla oblongata
cervical nerves
(8 pairs)
stomach
liver
spleen
pancreas
thoracic nerves
(12 pairs)
kidneys
adrenal glands
© 2007
5 Thomson Higher Education
sympathetic
(most
ganglia
near
spinal
cord)
small intestine
upper colon
lower colon
rectum
(all
ganglia
in walls of
organs)
lumbar nerves
(5 pairs)
bladder
uterus
genitals
pelvic
nerve
sacral nerves
(5 pairs)
parasympathetic
Fig. 13.14, p. 236
Major Expressways: Peripheral Nerves
and the Spinal Cord
The spinal cord is the pathway between the
PNS and the brain.



The spinal cord lies within a closed channel
formed by the bones of the vertebral column.
Signals move up and down the spinal cord in
nerve tracts.
•
•
The myelin sheaths of these tracts are white; thus,
they are called white matter.
The central, butterfly-shaped area (in cross-section)
consists of dendrites, cell bodies, interneurons, and
neuroglia cells; it is called gray matter.
Major Expressways: Peripheral Nerves
and the Spinal Cord


The spinal cord and brain are covered with
three tough membranes—the meninges.
The spinal cord is a pathway for signal travel
between the peripheral nervous system and the
brain; it also is the center for controlling some
reflex actions.
•
•
Spinal reflexes result from neural connections made
within the spinal cord and do not require input from
the brain, even though the event is recorded there.
Autonomic reflexes, such as bladder emptying, are
also the responsibility of the spinal cord.
spinal cord
ganglion
spinal nerve
vertebra
white
matter
meninges
(protective
coverings)
central canal
grey matter
intervertebral
disk
© 2007 Thomson Higher Education
Fig. 13.15, p. 237
Section 7
The Brain—Command
Central
The Brain – Command Central
The spinal cord merges with the body’s
master control center, the brain.


The brain is protected by bone and meninges.
•
•

The tough outer membrane is the dura mater; it is
folded double around the brain and divides the brain
into its right and left halves.
The thinner middle layer is the arachnoid; the
delicate pia mater wraps the brain and spinal cord
as the innermost layer.
The meninges also enclose fluid-filled spaces
that cushion and nourish the brain.
Fig. 13.16, p. 238
ventricles
cerebrospinal
fluid
arachnoid mater
dura mater
three meninges
pia mater
spinal chord
cerebrospinal
fluid in spinal
canal
Fig. 13.16a, p. 238
scalp
skull bone
cerebrospinal
fluid
© 2007 Thomson Higher Education
pia mater
dura
mater
arachnoid
mater Fig. 13.16b, p. 238
The Brain – Command Central
The brain is divided into a hindbrain,
midbrain, and forebrain.



The hindbrain and midbrain form the brain
stem, responsible for many simple reflexes.
Hindbrain.
•
•
•
The medulla oblongata has influence over
respiration, heart rate, swallowing, coughing, and
sleep/wake responses.
The cerebellum acts as a reflex center for
maintaining posture and coordinating limbs.
The pons (“bridge”) possesses nerve tracts that
pass between brain centers.
The Brain – Command Central

The midbrain coordinates reflex responses to
sight and sound.
•

It has a roof of gray matter, the tectum, where visual
and sensory input converges before being sent to
higher brain centers.
The forebrain is the most developed portion of
the brain in humans.
•
The cerebrum integrates sensory input and selected
motor responses; olfactory bulbs deal with the
sense of smell.
The Brain – Command Central
•
•
The thalamus relays and coordinates sensory
signals through clusters of neuron cell bodies called
nuclei; Parkinson’s disease occurs when the
function of basal nuclei in the thalamus is disrupted.
The hypothalamus monitors internal organs and
influences responses to thirst, hunger, and sex, thus
controlling homeostasis.
Cerebrospinal fluid fills cavities and canals
in the brain.


The brain and spinal cord are surrounded by
the cerebrospinal fluid (CSF), which fills
cavities (ventricles) and canals within the brain.
The Brain – Command Central

A mechanism called the blood-brain barrier
controls which substances will pass to the fluid
and subsequently to the neurons.
•
•
The capillaries of the brain are much less permeable
than other capillaries, forcing materials to pass
through the cells, not around them.
Lipid-soluble substances, such as alcohol, nicotine,
and drugs, diffuse quickly through the lipid bilayer of
the plasma membrane.
Section 8
A Closer Look at the
Cerebrum
A Closer Look at the Cerebrum
There are two cerebral hemispheres.


The human cerebrum is divided into left and
right cerebral hemispheres, which
communicate with each other by means of the
corpus callosum.
•
•
Each hemisphere can function separately; the left
hemisphere responds to signals from the right side of
the body, and vice versa.
The left hemisphere deals
mainly with speech, analytical
skills, and mathematics;
nonverbal skills such as music
and other creative activities reside in the right.
Figure 13.18
A Closer Look at the Cerebrum


The thin surface (cerebral cortex) is gray
matter, divided into lobes by folds and fissures;
white matter and basal nuclei (gray matter in
the thalamus) underlie the surface.
Each hemisphere is divided into frontal,
occipital, temporal, and parietal lobes.
A Closer Look at the Cerebrum
The cerebral cortex controls thought and
other conscious behavior.


Motor areas are found in the frontal lobe of
each hemisphere.
•
•
•
•
The motor cortex controls the coordinated
movements of the skeletal muscles.
The premotor cortex is associated with learned
pattern or motor skills.
Broca’s area is involved in speech.
The frontal eye field controls voluntary eye
movements.
primary
motor
cortex
frontal lobe
(planning
movements;
some aspects
of memory;
inhibition of
inappropriate
behavior)
temporal lobe
(hearing; advanced
visual processing)
primary
somatosensory
cortex
parietal
lobe (body
sensations)
occipital lobe
(vision)
Fig. 13.19a, p. 241
Motor cortex activity
when speaking
Prefrontal cortex activity
when generating words
Visual cortex activity
when observing words
Fig. 13.19b, p. 241
Fig. 13.20, p. 241
A Closer Look at the Cerebrum

Several sensory areas are found in the parietal
lobe:
•
•
•
The primary somatosensory cortex is the main
receiving center for sensory input from the skin and
joints, while the primary cortical area deals with
taste.
The primary visual cortex, which receives sensory
input from the eyes, is found in the occipital lobe.
Sound and odor perception arises in primary
cortical areas in each temporal lobe.
A Closer Look at the Cerebrum

Association areas occupy all parts of the
cortex except the primary motor and sensory
regions:
•
•
Each area integrates, analyzes, and responds to
many inputs.
Neural activity is the most complex in the prefrontal
cortex, the area of the brain that allows for complex
learning, intellect, and personality.
A Closer Look at the Cerebrum
The limbic system: Emotions and more.



Our emotions and parts of our memory are
governed by the limbic system, which consists
of several brain regions.
Parts of the thalamus, hypothalamus,
amygdala, and the hippocampus form the
limbic system and contribute to producing our
“gut” reactions.
(olfactory tract)
cingulate gyrus
thalamus
hypothalamus
amygdala
hippocampus
Fig. 13.21, p. 241
Section 9
Memory and
Consciousness
A Closer Look at the Cerebrum
Memory is how the brain stores and
retrieves information.


Learning and adaptive modifications to
behavior are possible because of memory, the
storage information.
•
•
Short-term memory lasts from seconds to hours
and is limited to a few bits of information.
Long-term memory is more permanent and seems
to be limitless.
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
© 2007 Thomson Higher Education
Fig. 13.22, p. 242
A Closer Look at the Cerebrum

Facts are processed separately from skills
using separate memory circuits.
•
•
Facts, such as names or faces, are forgotten or
stored in long term memory where they can be
recalled through association.
Skills, such as playing the piano, can only be
recalled by doing them.
Figure 13.23b
touch
thalamus and
hypothalamus
hearing
basal nuclei
vision
smell
prefrontal cortex
amygdala
hippocampus
Fig. 13.23a, p. 242
A Closer Look at the Cerebrum

Amnesia is a loss of fact memory; the severity
of loss depends on the extent of damage to the
brain, but amnesia does not prevent a person
from learning new skills.
A Closer Look at the Cerebrum
States of consciousness include alertness
and sleeping.


Consciousness ranges from being wide
awake and alert to drowsiness, sleep, and
coma.
•
•
The constant electrical
activity of the brain can
be measured by an
electroencephalogram (EEG).
PET scans can show
the precise location of brain activity.
Figure 13.24
A Closer Look at the Cerebrum

Neurons of the reticular formation control the
changing levels of consciousness by releasing
serotonin from sleep centers in the neural
network.
•
•
High serotonin levels trigger drowsiness and sleep.
Sleep has two major stages: slow-wave, “normal”
sleep and REM (rapid eye movement) sleep.
Fig. 13.24a, p. 243
Fig. 13.24b, p. 243
The Central
Nervous
System
Section 10
Disorders of the Nervous
System
Disorders of the Nervous System
Some diseases attack and damage
neurons.


Alzheimer’s disease involves the progressive
degeneration of brain neurons, while at the
same time there is an abnormal buildup of
amyloid protein, leading to the loss of memory.
Disorders of the Nervous System

Parkinson’s disease (PD) is characterized by
the death of neurons in the thalamus that
normally make dopamine and norepinephrine
needed for normal muscle function.
Figure 13.25a
Disorders of the Nervous System



Meningitis is an often fatal inflammatory
disease caused by a virus or bacterial infection
of the meninges covering the brain and/or
spinal cord.
Encephalitis is very dangerous inflammation of
the brain, often caused by a virus.
Multiple sclerosis (MS) is an autoimmune
disease that results in the destruction of the
myelin sheath of neurons in the CNS.
Disorders of the Nervous System
The CNS can also be damaged by injury or
seizure.



A concussion can result from
a severe blow to the head,
resulting in blurred vision and
brief loss of consciousness.
Damage to the spinal cord can
result in lost sensation, muscle
weakness, or paralysis below
the site of the injury.
Figure 13.25b
Disorders of the Nervous System


Epilepsy is a seizure disorder, often inherited
but also caused by brain injury, birth trauma, or
other assaults on the brain.
Headaches occur when the brain registers
tension in muscles or blood vessels of the face,
neck, and scalp as pain; migraine headaches
are extremely painful and can be triggered by
hormonal changes, fluorescent lights, and
certain foods, particularly in women.
Section 11
The Brain on Drugs
Disorders of the Nervous System
Drugs can alter mind and body functions.



Psychoactive drugs exert their influence on
brain regions that govern states of
consciousness and behavior.
There are four categories of psychoactive
drugs:
•
Stimulants (caffeine, cocaine, nicotine,
amphetamines) increase alertness or activity for a
time, and then depress you.
Fig. 13.26, p. 245
Disorders of the Nervous System
•
•
•
Depressants (alcohol) depress brain activity, limit
judgment, and interfere with coordinated movement;
blood alcohol concentration (BAC) measures alcohol
in the blood to determine the level of intoxication.
Analgesics (pain relievers) include morphine and
OxyContin, a synthetic derivative; analgesics block
pain signals and some may produce euphoria.
Hallucinogens, such as marijuana, act like
depressants at low levels, but may also skew
perception and performance of complex tasks.
Disorders of the Nervous System
Drug use can lead to addiction.




As the body develops tolerance to a drug,
larger and more frequent doses are needed to
produce the same effect; this reflects physical
drug dependence.
Psychological drug dependence, or
habituation, develops when a user begins to
crave the feelings associated with using a
particular drug and cannot function without it.
Habituation and tolerance are evidence of
addiction.
Table 13.2, p. 245