UNIT 2
THE NEURAL
IMPULSE

I am a brain, Watson. The rest of me is a
mere appendix.
 Sherlock
Holmes
BIOLOGICAL PSYCHOLOGY


A branch of psychology concerned with the
links between biology and behavior
Behavioral neuroscientists,
neuropsychologists, behavior geneticists,
physiological psychologists, or
biopsychologists
KEY PRINCIPLES OF THE NERVOUS SYSTEM




Complex
 An extensive assembly of nerve cells combine to carry
out every task
Integration
 Is able to pull all sensory information in while running all
vital biological processes.
Adaptable
 Plasticity allows the brain’s special physical capacity to
change.
Electrochemical
 Communication occurs through electrical impulses and
chemical messengers
NEURONS



Nerve cells specialized
for communication
100 billion neurons in
the brain
160 trillion connections
in the human brain
100,000,000,000 neurons!!
160,000,000,000,000 connections!!
(A LOT!)
NERVES (TYPES OF NEURONS)

Afferent Nerves (Sensory Nerves) carry information about the external
environment and internal conditions

Tells your brain your hungry.
Carries Information TO the Brain

Efferent Nerves (Motor Nerves) carry information from the brain to the rest
of the body

Tells your muscles to move.
Carries Information OUT of the Brain
NEURONS: THE MESSENGERS

Neurons have many of the
same features as other
cells




Nucleus
Cytoplasm
Cell membrane
What makes neurons
unique is their shape and
their function
THE STRUCTURE OF NEURONS




Cell Body (Soma)
 Contains nucleus
Dendrites
 Carry information to the cell body
from other neurons
Axon
 Carries information to the next cell
Myelin Sheath
 Insulates the axon and speeds up
the neural impulse
NEURON STRUCTURE
Cell Body
- builds new cell components
Nucleus
Dendrites
Axon Terminals
(Buttons)
Axon – message sender
NEURON STRUCTURE


Axon: portion of neuron that sends signals
Dendrite: portion of neuron that receives
signals
Dendrite
Axon
GLIAL CELLS – THE OTHER CELL


Cells in nervous system
that play role in the
formation of myelin and
the blood-brain barrier
Respond to injury, remove
debris, and enhance
learning and memory
MYELIN SHEATH
With Myelin Sheath
Without Myelin Sheath
SYNAPSE

Synapse: space between two connecting neurons through
which messages are transmitted chemically
Synaptic cleft: gap into which neurotransmitters are released

Involves release of molecules called neurotransmitters

THE NEURAL IMPULSE

Polarization
 When
the inside of the Neuron is negatively
charged relative to the outside (resting potential)

Depolarization
 When
the electrical charge of a cell moves toward
zero (action potential)
ELECTROCHEMICAL POTENTIAL

Molecules with a positive charge are attracted to those
with a negative charge
+
–
RESTING POTENTIALS


When the balance of +
and – particles is normal
Resting Potential – Nothing
is happening


The gates are closed and the
positive ions are on the outside
with the negative ions on the
inside of the cell.
higher negative charge
INSIDE the neuron
Resting Potential
+
+
+
+
-
-
+
+
-
-
+
+
+
+
+
•Semi-permeable membrane
•Channels
+
 Positive ions want to get into the axon to
be with negative cells
+
+
+
+
-
-
+
+
-
-
+
+
+
+
+
+
ACTION POTENTIAL



A neuron is stimulated by an increase in positive ions
Regenerative
 Sudden, massive change in charge in the neuron
 Chain reaction down the whole axon
 When this happens the axon has “fired”
Either all or nothing
 Occurs when depolarization reaches the threshold of
excitation and the movement of positively charged atoms in
and out of channel
 400 ft per second (Myelinated) to 3 ft per second
Action Potential
+
+
+
-
+
+
+
-
-
+
+
Continues Down
+
+
+
+
THE NEURAL IMPULSE

Refractory Period
 The
time it takes for
the positive ions to
be pumped out.

Threshold

the level of
stimulation required
to trigger a neural
impulse
THE NEURAL IMPULSE


Absolute refractory period
 Period immediately
after an action potential
when another action
potential cannot occur
 1/1000th of a Second
Relative refractory period
 Period following
absolute refractory
period when a neuron
will only respond to a
stronger than normal
impulse
ABSOLUTE REFRACTORY PERIOD
 Limits the maximal firing rate
+
+
+
+
-
+
+
+
+
-
+
+
+
SUMMARIZE
Axon has – molecules
inside, + molecules outside
 + and – want to be together
 + molecules rush in and
axon becomes stimulated,
creating an action potential
 ‘telegraph’ sends signal
down the line
 Refractory period brings
things back to normal

WHAT’S THE POINT OF THE ACTION POTENTIAL?
HOW DOES THE ACTION POTENTIAL
INFLUENCE BEHAVIOR?
MOVE!
MOVE!
MOVE!
MOVE!
What’s happening
here?
THE MESSAGE HAS REACHED THE END OF THE
NEURON – WHERE DOES IT GO?
Synaptic
cleft
Pre-synaptic Neuron
Post-synaptic Neuron
Synaptic
vesicles
TRANSMISSION BETWEEN NEURONS – THE
NEURAL IMPULSE



Synaptic vesicles
 Sacs in terminal button that
release chemicals into synaptic
space
Neurotransmitters
 Chemicals released by synaptic
vesicles
Receptor sites
 Location on receptor neuron for
specific neurotransmitter
The Message Sender
SYNAPTIC VESICLES
Pre-synaptic Membrane
(Axon terminal of the neuron)
SYNAPTIC
CLEFT
Post-synaptic Membrane
(Dendrite on other site)
The Message Receiver
HOW NEURONS TALK
Step 1:
 Action potential reaches the end of the
presynaptic neuron
Electrical WITHIN
neuron
HOW NEURONS TALK
Step 2:
 Triggers the release of neurotransmitters from
synaptic vesicles into the synaptic gap
Chemical BETWEEN neuron
HOW NEURONS TALK
Step 3:
 Neurotransmitters attach to specific receptor sites
on the postsynaptic neuron
HOW NEURONS TALK
Step 4 (part 1):
 Reuptake (recycling) of non-binded
neurotransmitters
HOW NEURONS TALK
Step 4 (part 2):
 Chemical breakdown of neurotransmitter causes
an electrochemical signal on the postsynaptic
neuron
Synaptic
Vesicles
Neurotransmitters
Receptor Sites
1) Release of NT into
synaptic cleft.
2) NT binds to receptor
site.
3) NT breaks down or
there is reuptake
RECEPTOR SITES

Bind with specific
neurotransmitters
based on their
shape, like a lock
and key

Can be tricked by
chemical
“lookalikes”
NEUROTRANSMITTERS
Neurotransmitters
(chemicals) released from
the sending neuron travel
across the synapse and
bind to receptor sites on the
receiving neuron, thereby
influencing it to generate
an action potential.
THERE ARE FOUR CRITERIA BY WHICH
NEUROTRANSMITTERS ARE DEFINED.
1. It must be synthesized in the presynaptic cell.
 2. It must be released by the presynaptic
terminal in sufficient quantities to produce a
measurable effect on the postsynaptic cell.
 3. When administered artificially, it mimics
natural release.
 4. A specific, known mechanism exists for it to be
removed from the synaptic cleft.

REUPTAKE
Neurotransmitters in
the synapse are
reabsorbed into the
sending neurons
through the process of
reuptake. This process
applies the brakes on
neurotransmitter
action.
LOCK & KEY MECHANISM
Neurotransmitters bind to the receptors of the
receiving neuron in a key-lock mechanism.
TYPES OF NEUROTRANSMITTERS

Acetylcholine (ACh)





Released at the neuromuscular junction
Plays an important role in arousal and attention
Loss of ACh producing cells is linked to Alzheimer’s Disease
Too much = Spasms / Too Little = Paralysis
Dopamine



Affects neurons associated with voluntary movement and
pleasure
Plays a role in learning, memory, and emotions
Implicated in Parkinson’s Disease and Schizophrenia

Serotonin – “prozac”






Found throughout the brain
Appears to sets an “emotional tone”
Affects mood, hunger, sleep, and arousal
Low serotonin levels are implicated in depression
Some antidepressant drugs raise serotonin
Endorphins – “Natural Opiates”



Shield the body from pain
Reduce pain by inhibiting or “turning down” neurons that
transmit pain information
“runner’s high”
TYPES OF NEUROTRANSMITTERS

Oxytocin – Love and Social Bonding



Hormone released when mothers give birth that stimulates lactation
and breast feeding.
Released during sexual orgasm and plays a role in pleasure and
emotional attachment to romantic partners.
Can be a stress mechanism in women


“tend and befriend” response
Glutamate – involved in learning and memory, as its key
role is exciting neurons to fire
 Too much can cause migraines and seizures
 A factor in anxiety, depression, schizophrenia, Alzheimer,
Parkinsons

Norepinephrine (Adrenaline)
 Helps
control alertness and arousal
 Undersupply can depress mood
 Oversupply leads to hyperactivity

GABA (Gamma-aminobutyric acid)
A
major excitatory neurotransmitter; involved in
memory
 Oversupply linked to seizures, tremors, and
insomnia
PSYCHOPHARMACOLOGY
Most psychoactive drugs (and toxins) work by
blocking or enhancing synaptic transmission
 Botulism

 Blocks
release of ACh at the neuromuscular
junction, causing paralysis
 “Botox” is botulism toxin used to prevent facial
muscles from making wrinkles
PSYCHOPHARMACOLOGY

Curare


Can stun or kill prey quickly
Blocks ACh receptors causing paralysis

Cocaine

Prevents re-absorption of dopamine
 Leads to heightened arousal of entire nervous system
Antipsychotic medications




Block dopamine receptors
Reduces schizophrenic hallucinations
Caffeine

Increases the release of excitatory neurotransmitters by blocking
the inhibitory neurotransmitter adenosine (a-den-oh-seen)
AGONISTS
ANTAGONISTS