1) Communication in the nervous system
a. Nervous tissue: the basic hardware: The cells in the nervous
system fall into two major categories: glia and neurons
i. Neurons are individual cells in the nervous system that receive,
integrate, and transmit information. Majority communicates only
with other neurons. Small minority receives signals from outside
the nervous system or carry message from the nervous system to
the muscles that move the body.
1. Soma, or cell body, contains the cell nucleus and much of
the chemical machinery common to most cells.
2. Dendrites: are the parts of a neuron that are specialized to
3. Axon: a long, thin fibre that transmits signals away from the
soma to other neurons or to muscles or glands.
a. Many axons are wrapped in cells with a high
concentration of a white, fatty substance called
b. Myelin sheath is insulating material, derived from
glial cells, that encases some axons. It can speed up
the transmission of signals that move along axons.
Example: multiple sclerosis.
4. Terminal buttons: small knobs that secrete chemicals called
neurotransmitters. These chemicals serve as messengers
that may activate neighboring neurons.
5. Synapses: a junction where information is transmitted from
one neuron to another.
6. Summary: information is received at the dendrites, is
passed through the soma and along the axon, and is
transmitted to the dendrites of other cells at meeting point
called synapse. But many exemptions.
ii. Glia is cells found throughout the nervous system that provides
various types of support for neurons.
1. Much smaller than neurons, outnumber neurons by about
10 to 1.
2. Over 50% of the brain’s volume.
3. Glial cells supply nourishment to neurons, help remove
neurons’ waste products, and provide insulation around
many axons. The myelin sheaths that encase some axons
are derived from special types of glial cells.
4. Orchestrating the development of the nervous system in the
5. Glia may also send and receive chemical signals; they may
be implicated in diseases such as amyotrophic lateral
sclerosis and Parkinson’s disease.
6. Memory formation: Alzheimer’s disease
b. The neural impulse: using energy to send information
i. The neuron at rest: a tiny battery 1. Neural impulse: a complex electrochemical reaction. The
electrical discharge that travels along a nerve fiber; "they
demonstrated the transmission of impulses from the cortex
to the hypothalamus"
2. Ions: electrically charged atoms and molecules.
3. The cell membrane is semipermeable, permitting
movement of some ions. Positively charged sodium and
potassium ions and negatively charged chloride ions flow
back and forth across the cell membrane, but they do not
cross at the same rate. This difference in flow rates leads to
a slightly higher concentration of negatively charged ions
inside the cell. The resulting voltage means that the neuron
at rest is a tiny battery, a store of potential energy.
4. The resting potential of a neuron is its stable, negative
charge when the cell is inactive.
ii. The action potential
1. Constant voltage of a neuron leads to the cell is quiet and no
messages are being sent.
2. When the neuron is stimulated, channels in its cell
membrane open, briefly allowing positively charged sodium
ions to rush in.
3. Action potential: a very brief shift in a neuron’s electrical
charge that travels along an axon.
4. Absolute refractory period: the minimum length of time
after an action potential during which another action
potential cannot begin.
5. Followed by a brief relative refractory period: the neuron
can fire, but its threshold for firing is elevated, so more
intense stimulation is required to initiate an action
iii. The all-or-none law
1. The neural impulse is an all-or-none proposition.
2. Neuron’s action potentials are all the same size. Weaker
stimuli do not produce smaller action potentials.
3. Neurons can convey information about the strength of a
stimulus. They do so by varying the rate at which they fire
action potentials. Stronger stimulus will cause a cell to fire a
more rapid volley of neural impulses than a weaker
4. Various neurons transmit neural impulses at different
speeds. Thicker axons transmit more rapidly than thinner
c. The synapse: where neurons meet (depend on chemical
i. Sending signals: chemicals as couriers.
1. Two neurons don’t actually touch. They are separated by
the synaptic cleft: a microscopic gap between the terminal
button of one neuron and the cell membrane of another neuron. Signals have to cross this gap to permit neurons to
2. Presynaptic neuron: neuron that sends a signal across the
3. Postsynaptic neuron: neuron that receives the signals.
4. The arrival of an action potential at an axon’s terminal
buttons triggers the release of Neurotransmitters:
chemicals that transmit information from one neuron to
5. Synaptic vesicles: store neurotransmitters chemicals in the
6. The neurotransmitters are released when a vesicle fuses
with the membrane of the presynaptic cell and its contents
spill into the synaptic cleft. After their release,
neurotransmitters diffuse across the synaptic cleft to the
membrane of the receiving cell. There they may bind with
special molecules in the postsynaptic cell membrane at
various receptor sites: specifically tuned to recognize and
respond to some neurotransmitters but not to others.
ii. Receiving signals: postsynaptic potentials
1. When a neurotransmitter and a receptor molecule combine,
cause Postsynaptic potential (PSP): a voltage change at a
receptor site on a postsynaptic cell membrane. It does not
follow the all-or-none law as action potentials do. They are
graded. They vary in size and they increase or decrease the
probability of a neural impulse in the receiving cell in
proportion to the amount of voltage change.
2. Two types of messages can be sent from cell to cell:
excitatory and inhibitory. Excitatory PSP is a positive
voltage shift that increases the likelihood that the
postsynaptic neuron will fire action potentials. Inhibitory
PSP is a negative voltage shift that decreases the likelihood
that the postsynaptic neuron will fire action potentials.
They depend on which receptor sites are activated in the
3. The excitatory or inhibitory effects produced at a synapse
last only a fraction of a second. Then neurotransmitters
drift away from receptor sites or are inactivated by
enzymes that metabolize (convert) them into inactive forms.
Most are reabsorbed into the presynaptic neuron through
reuptake: a process in which neurotransmitters are
sponged up from the synaptic cleft by the presynaptic
a. Synthesis and storage of neurotransmitter molecules
in synaptic vesicles
b. Release of neurotransmitter molecules into synaptic
cleft. c. Binding of neurotransmitters at receptor sites on
d. Inactivation by enzymes or removal drifting away of
e. Reuptake of neurotransmitters sponged up by the
iii. Integrating signals: neural networks
1. A neuron must integrate signals arriving at many synapses
before it “decides” whether to fire a neural impulse. Enough
excitatory PSPs, action potential fires.
2. Our perceptions, thoughts and actions depend on patterns
of neural activity in elaborative neural networks. These
networks consist of interconnected neurons that frequently
fire together or sequentially to perform certain functions.
3. Elimination of old synapses appears to play a larger role in
the sculpting of neural networks than the creation of new
synapses. The nervous system normally forms more
synapses than needed and then gradually eliminates the
less active synapses.
4. Synaptic pruning is a key process in the formation of the
neural networks that are crucial to communication in the
5. Donald Hebb: the organization of behavior. Cell assemblies.
Hebbian learning rule. One neuron stimulating another
neuron repeatedly produces changes in the synapse.
d. Neurotransmitters and behavior
1. ACh has been found throughout the nervous system. It is
the only transmitter between motor neurons and voluntary
muscles. (Activates motor neurons controlling skeletal
2. Contribute to attention, arousal, and memory.
3. Some Ach receptors stimulated by nicotine. When smoke,
some of your Ach synapses will be stimulated by the
nicotine that arrives in your brain. At these synapses, the
nicotine acts like Ach itself. It binds to receptor sites for
ACh, causing postsynaptic potentials. Nicotine is an ACh
agonist: a chemical that mimics the action of a
4. Antagonist: a chemical that opposes the action of a
neurotransmitter. Like curare. It temporarily blocks the
action of the natural transmitter by occupying its captor
sites, rendering them unusable. As a result, muscles are
unable to move.
a. Include three neurotransmitters: dopamine,
norepinephrine, and serotonin. b. Abnormal levels of monoamines in the brain have
been related to the development of certain
c. Temporary alterations at monoamine synapses also
appear to account for the powerful effects of
amphetamines and cocaine.
2. Dopamine (DA): (L-dopa: treat Parkinson)
a. Contributes to control of voluntary movement,
b. Decreased levels associated with Parkinson’s disease.
The reduction in dopamine synthesis occurs because
of the deterioration of a structure located in the
c. Over activity at DA synapses associated with
d. Cocaine and amphetamines elevate activity at DA
e. Dopamine hypothesis asserts that abnormalities in
activity at dopamine synapses play a crucial role in
the development of schizophrenia.
3. Norepinephrine (NE):
a. Contributes to modulation of mood and arousal
b. Cocaine and amphetamines elevate activity at NE
a. Involved in regulation of sleep and wakefulness,
b. Abnormal levels may contribute to depression and
c. Prozac and similar antidepressant drugs affect
d. Dysregulation in serotonin circuits has also been
implicated as a factor in eating disorders, such as
anorexia and bulimia and in obsessive-compulsive
iii. GABA (gamma-aminobutyric acid) and Glutamate:
1. Serves as widely distributed inhibitory transmitter.
2. Valium and similar antianxiety drugs work at GABA
3. GABA (consist of amino acid) receptors are widely
distributed in the brain and may be present at 40% of all
synapses. GABA appears to be responsible for much of the
inhibition in the central nervous system. (Only has
inhibitory effect) It also contributes to the regulation of
anxiety in humans and that it plays a central role in the
expression of seizures.
4. Glutamate is another amino acid neurotransmitter that is
widely distributed in the brain. It has both inhibitory and exhibitory effects. It is best known for its contribution to
learning and memory.
5. Long-term potentiation (LTP): durable increases in
excitability at synapses along a specific neural pathway.
One of the basic building blocks of memory formation.
1. Morphine exerts its effects by binding to specialized
receptors in the brain.
2. Endorphins: internally produced chemicals that resemble
opiates in structure and effects.
3. Endogenous opioids also contribute to the modulation of
eating behaviour and the body’s response to stress.
4. Contribute to pain relief and perhaps to some pleasurable
2) Looking inside the brain: research methods
a. Electrical recordings
i. The electroencephalograph (EEG): a device that monitors the
electrical activity of the brain over time by means of recording
electrodes attached to the surface of the scalp.
ii. An EEG electrode sums and amplifies electric potentials occurring
in many thousands of brain cells.
iii. The resulting EEG recordings are translated into line tracings,
commonly called brain waves.
iv. The EEG is often used in the clinical diagnosis of brain damage and
v. In research applications, EEG can be used to identify patterns of
brain activity that occur when participants engage in specific
behaviors or experience specific emotions.
vi. EEG is invaluable to researchers exploring the physiology of sleep.
i. Case study method. Most conduct with animal.
ii. Limitations: subjects are not plentiful, and neuroscientists can’t
control the location or severity of their subjects’ brain damage.
Variations in the participant’s histories create a host of extraneous
variable that make it difficult to isolate cause-and-effect
relationships between rain damage and behaviour.
iii. Lesioning involves destroying a piece of the brain. It is typically
done by inserting an electrode into a brain structure and passing a
high-frequency electric current through it to burn the tissue and
disable the structure.
c. Electrical stimulation of the brain
i. Electrical stimulation of the brain (ESB) involves sending a weak
electric current into a brain structure to stimulate (activate) it.
ii. Most on animal, sometime on human who has brain surgery.
iii. Wilder Penfield: Montreal neurological institute and hospital.
Treatment of epilepsy.
iv. Both techniques depend on the use of stereotaxic instruments that
permit researchers to implant electrodes at precise locations in
animals’ brains. d. Transcranial magnetic stimulation
i. Transcranial magnetic stimulation (TMS) is a new technique that
permits scientists to temporarily enhance or depress activity in a
specific area of the brain.
ii. In essence, this technology allows scientists to create “virtual
lesions” in human subjects for short periods of time, using a
painless, noninvasive method.
iii. Moreover, this approach circumvents the host of uncontrolled
variables that plague the study of natural lesions in humans who
have experienced brain damage.
iv. Limitation: it cannot be used to study areas deep within the brain.
e. Brain-imaging procedures
i. Computerized tomography (CT) scan: a computer-enhanced x-ray
of brain structure. CT is the least expensive, and it has been widely
used in research. It can portray only brain structure.
ii. Position emission tomography (PET) scanning is proving
especially valuable. It can examine brain function, mapping actual
activity in the brain over time. It can provide a color-coded map
indicating which areas of he brain become active when subjects
clench their fist, sing, or contemplate the mysteries of the universe.
Because PET scans monitor chemical processes, they can also be
used to study the activity of specific neurotransmitters.
iii. Magnetic resonance imaging (MRI) scan: uses magnetic fields,
radio waves, and computerized enhancement to map out brain
structure. Better images of brain structure than CT scans. 3-D of
the brain, high resolution.
iv. Functional magnetic resonance imaging (fMRI): new variation on
MRI technology that monitors blood flow and oxygen consumption
in the brain to identify areas of high activity. Like PET scans, it can
map actual activity in the brain over time, but with vastly greater
3) Organization of the nervous system
a. The peripheral nervous system: The first and most important
division separates the central nervous system (The brain and spinal cord)
from the peripheral nervous system. Peripheral nervous system: made up
of all those nerves that lie outside the brain and spinal cord. Nerves:
bundles of neuron fibers (axons) that are routed together in the
peripheral nervous system.
i. The somatic nervous system
1. Somatic nervous system: made up of nerves that connect to
voluntary skeletal muscles and to sensory receptors.
2. These functions require two kinds of nerve fibers:
a. Afferent nerve fibers: axons that carry information
inward to the central nervous system from the
periphery of the body.
b. Efferent nerve fibers are axons that carry
information outward from the central nervous
system to the periphery of the body.
ii. The autonomic nervous system 1. Autonomic nervous system (ANS): made up of nerves that
connect to the heart, blood vessels, smooth muscles, and
glands. It controls automatic, involuntary, visceral functions
that people don’t normally think about, like heart rate,
digestion, and perspiration.
2. The autonomic nervous system can be subdivided into two
a. Sympathetic division: the branch of the autonomic
nervous system that mobilizes the body’s resources
for emergencies. It creates the fight-or-flight
response. Activation of the sympathetic division
slows digestive processes and drains blood from the
periphery, lessening bleeding in the case of an injury.
Key sympathetic nerves send signals to the adrenal
glands, triggering the release of hormones that ready
the body for exertion.
b. Parasympathetic division: the branch of the
autonomic nervous system that generally conserves
bodily resources. It activates processes that allow
the body to save and store energy. Slow heart rate,
reduce blood pressure, and promote digestion.
b. The central nervous system: consists of the brain and the spinal
cord. Protected by enclosing sheaths called the meninges. The
cerebrospinal fluid (CSF) nourishes the brain and provides a protective
cushion for it. Ventricle: the how cavities in the brain that are filled with
i. The spinal cord
1. The spinal cord connects the brain to the rest of the body
through the peripheral nervous system. It is an extension of
2. It houses bundles of axons that carry the brains commands
to peripheral nerves and that relay sensations from the
periphery of the body to the brain.
3. Many forms of paralysis result from spinal cord damage, a
fact that underscores the critical role the spinal cord plays
in transmitting signals from the brain to the motor neurons
that move the body’s muscles.
ii. The brain
1. The hindbrain: include the cerebellum and two structures
found in the lower part of the brainstem: the medulla and
a. Cerebellum: relatively large and deeply folded
structure located adjacent to the back surface of the
brainstem. It is critical to the coordination of
movement and to the sense of equilibrium, or
physical balance. It plays a key role in organizing the
sensory information that guides these movements. It
is one of the structures first depressed by alcohol.
Damage to the cerebellum disrupts fine motor skills. b. Medulla: which attaches to the spinal cord, is in
charge of largely unconscious but vital functions,
including circulating blood, breathing, maintain
muscle tone, and regulating reflexes such as
sneezing, coughing, and salivating.
c. Pons: includes a bridge of fibers that connects the
brainstem with the cerebellum. The pons also
contains several clusters of cell bodies involved with
sleep and arousal.
2. The midbrain: the segment of the brainstem that lies
between the hindbrain and the forebrain.
a. It contains an area that is concerned with integrating
sensory processes, such as vision and hearing.
b. An important system of dopamine-releasing neurons
that projects into various higher brain centers
originates in the midbrain.
c. Reticular formation: running through both the
hindbrain and the midbrain.
d. It is best known for its role in the regulation of sleep
3. The forebrain: the largest and most complex region of the
brain, encompassing a variety of structures, including the
thalamus, hypothalamus, limbic system and cerebrum.
a. Cerebrum: the seat of complex thought. Responsible
for sensing, thinking, learning, emotion,
consciousness, and voluntary movement. It is
divided into two halves called hemispheres.
i. This fissure descends to a thick band