NEURON AND NEURAL TRAMSMISSION:
ANATOMY OF A NEURON
created by Dr. Joanne Hsu
NEURON AND NEURAL TRAMSMISSION:
MICROSCOPIC VIEW OF NEURONS
A
A photograph
photograph taken
taken through
through aa light
light microscope
microscope (500x)
(500x)
of
of neurons
neurons in
in the
the spinal
spinal cord.
cord.
created by Dr. Joanne Hsu
NEURON AND NEURAL TRAMSMISSION:
RESTING POTENTIAL
When
When aa neuron
neuron isis at
at rest,
rest, the
the inside
inside of
of the
the neuron
neuron has
has aa
slight
slight negative
negative electrical
electrical charge
charge compared
compared to
to the
the outside.
outside.
created by Dr. Joanne Hsu
NEURON AND NEURAL TRAMSMISSION:
ACTION POTENTIAL
When
When aa neuron
neuron isis stimulated,
stimulated, more
more positively
positively charged
charged particles
particles
(sodium
(sodium ions)
ions) flow
flow into
into the
the cell,
cell, making
making the
the inside
inside suddenly
suddenly positive
positive
compared
compared to
to the
the outside
outside of
of the
the cell.
cell. This
This sudden
sudden reversal
reversal of
of the
the
electrical
the
potential.
electrical charge
charge isis called
calledcreated
the action
action
potential.
by Dr. Joanne Hsu
NEURON AND NEURAL TRAMSMISSION:
RESTING POTENTIAL AND ACTION POTENTIAL
created by Dr. Joanne Hsu
NEURON AND NEURAL TRAMSMISSION:
BIOCHEMICAL BASIS OF THE ACTION POTENTIAL
created by Dr. Joanne Hsu
(a)
(a) An
An action
action potential
potential occurs
occurs
when
when sodium
sodium gates
gates in
in the
the
membrane
membrane of
of aa neuron
neuron open,
open,
permitting
permitting sodium
sodium ions
ions to
to flow
flow
into
into the
the axon
axon (blue
(blue arrows).
arrows).
(b)
(b) After
After an
an action
action potential
potential
occurs,
occurs, the
the sodium
sodium gates
gates close
close at
at
that
that point,
point, but
but similar
similar gates
gates open
open
at
at the
the next
next point
point along
along the
the axon,
axon,
allowing
allowing the
the action
action potential
potential to
to
flow
flow along
along the
the axon.
axon.
(3)
(3) In
In the
the wake
wake of
of the
the action
action
potential,
potential, potassium
potassium gates
gates open
open
to
to let
let positively
positively charged
charged
potassium
potassium ions
ions flow
flow outward
outward
(purple
(purple arrows),
arrows), thus
thus
reestablishing
reestablishing aa negative
negative charge
charge
inside.
inside.
NEURON AND NEURAL TRAMSMISSION:
THE SYNAPSE
(1)Release:
(1)Release: When
When action
action
potential
potential reaches
reaches the
the axon
axon
terminal,
terminal, neurotransmitter
neurotransmitter
molecules
molecules stored
stored in
in synaptic
synaptic
vesicles
vesicles will
will be
be released
released into
into
synaptic
synaptic cleft.
cleft.
(2)
(2) Binding:
Binding: Some
Some
neurotransmitter
neurotransmitter molecules
molecules
will
will then
then bind
bind with
with the
the
matching
matching receptor
receptor sites
sites on
on the
the
next
next neuron.
neuron.
created by Dr. Joanne Hsu
(3)
(3) Inactivation
Inactivation or
or ClearingClearingOut
Out :: Neurotransmitter
Neurotransmitter
molecules
molecules will
will be
be removed
removed
from
from the
the receptor
receptor site
site after
after
binding.
binding.
NEURON AND NEURAL TRAMSMISSION:
THE SYNAPSE (SLIDE 2)
INACTIVATION OR CLEARING-OUT OF
NEUROTRANSMITTERS
After the binding at the receptor sites, neurotransmitter
molecules will be removed from the receptor sites in one of
the three ways:
•Some neurotransmitters will be destroyed by the
enzymes in the synaptic cleft.
• Some neurotransmitters will be broken down into its
component molecules which will be reclaimed by the
axon terminal.
•Some neurotransmitters will be reabsorbed by the axon
terminal as a whole, a process called reuptake.
created by Dr. Joanne Hsu
Afferent or Sensory Neurons:
relay messages from the sensory organs and receptors
(eyes, ear, nose, skin, etc.) to the brain and spinal cord.
Interneurons or Association Neurons:
carry information between neurons (most in the
central nervous system)
Efferent or Motor Neurons:
convey signals from the central nervous system to
the muscles and glands.
created by Dr. Joanne Hsu
ACTION
ACTION POTENTIAL:
POTENTIAL: THE
THE ALL-OR-NONE
ALL-OR-NONE LAW
LAW
The All-or-None Law:
A single neuron is either fires or does not fire. If fires,
it always fires at full speed and intensity.
Strength of a message is determined by:
• the number of neurons firing
•the rate of firing (number of times per second)
created by Dr. Joanne Hsu
GLIAL
GLIAL CELLS:
CELLS:
The
The Neurons’
Neurons’ Helper
Helper Cells
Cells
•Glial cells are specialized cells found throughout the nervous system
that provide structural support and insulation for neurons.
• Glial (“glue”) cells hold the nervous system together.
•They are smaller than neurons but outnumber neurons about nine to
one.
•They guide the formation of the nervous system during the prenatal
development.
•They provide nutritional and “housekeeping”functions for neurons.
•They are involved in the formation of the myelin sheath.
created by Dr. Joanne Hsu
NEUROTRANSMITTERS: TYPES
THREE TYPES OF NEUROTRANSMITTERS:
EXCITATORY:
INHIBITORY:
influence neurons to fire.
affect neurons not to fire.
EXCITATORY OR INHIBITORY:
depend on the receptors.
created by Dr. Joanne Hsu
NEUROTRANSMITTERS: EXAMPLES
SOME KNOWN NEUROTRANSMITTERS:
Acetylcholine
Acetylcholine
Dopamine
Dopamine
(Ach)
(Ach)
(DA)
(DA)
Norepinephrine
Norepinephrine
(NE)
(NE)
Serotonin
Serotonin
GammaGammaaminobutyric
aminobutyric
acid
acid (GABA)
(GABA)
created by Dr. Joanne Hsu
Endorphins
Endorphins
ACETYLCHOLINE
Acetylcholine
Acetylcholine (Ach)
(Ach) contributes
contributes to
to movement,
movement,
learning,
learning, memory
memory precsses,
precsses, and
and REM
REM sleep.
sleep. ItIt isis
the
the only
only transmitter
transmitter between
between motor
motor neurons
neurons and
and
voluntary
voluntary muscles.
muscles.
Excess:
Deficit:
Muscle paralysis or
convulsions, sometimes
death.
created by Dr. Joanne Hsu
Memory impairment,
Alzheimer’s disease.
DOPAMINE
Dopamine
Dopamine (DA)
(DA) isis used
used by
by neurons
neurons that
that control
control
voluntary
voluntary movements.
movements. ItIt isis also
also used
used by
by neurons
neurons that
that
are
are important
important for
for learning,
learning, attention,
attention, thought
thought and
and
emotion.
emotion.
Excess:
Deficit:
Schizophrenia
Parkinson’s disease
(irrational thought, delusion,
(tremors, muscular rigidity)
and/or hallucinations)
created by Dr. Joanne Hsu
DOPAMINE HYPOTHESIS FOR
SCHIZOPHRENIA
created by Dr. Joanne Hsu
SEROTONIN AND
NOREPINEPHRINE
Serotonin
Serotonin plays
plays aa prominent
prominent role
role in
in the
the regulation
regulation of
of
mood,
mood, sleep,
sleep, impulsivity,
impulsivity, aggression
aggression and
and appetite.
appetite.
Norepinephrine
Norepinephrine plays
plays aa role
role in
in eating,
eating, sleep,
sleep, and
and
mood.
mood.
Lower level of activity in serotonin and norepinephrine
is related to depression. Deficit in serotonin may lead
to increased aggressive behavior and suicide. Some
antidepressant drugs act to block the reuptake of
serotonin or norepinephrine.
created by Dr. Joanne Hsu
GABA
gamma-aminobutyric acid
GABA
GABA appears
appears to
to have
have inhibitory
inhibitory effects
effects at
at synapses.
synapses.
ItIt contributes
contributes to
to the
the regulation
regulation of
of anxiety
anxiety in
in humans.
humans.
Lower levels of activity in GABA activity is related to
anxiety. Antianxiety drugs (tranquilizers such as Valium)
facilitate GABA synapses and thereby reduce anxiety.
An abnormality in GABA neurons may cause epilepsy.
created by Dr. Joanne Hsu
ENDORPHINS
Endorphins
Endorphins (“endogenous
(“endogenous morphine”)
morphine”) are
are opiatelike
opiatelike
substances
substances produced
produced in
in the
the human
human body
body itself.
itself. They
They
provide
provide relief
relief from
from pain
pain and
and produce
produce feelings
feelings of
of
pleasure
pleasure and
and well-being.
well-being.
Drugs such as opium, morphine, and heroin bind with the
receptors for endorphins. Endorphins may explain the
“runner’s high” experienced by long-distance ruunners.
created by Dr. Joanne Hsu
Psychoactive drugs work on the nervous system in following ways:
Some affect the release of neurotransmitters:
Amphetamines (“Speed”) increase the release of dopamine,
norepinephrine, and perhaps serotonin.
Some bind with the receptor sites (acting like “pretenders”):
The opiates (opium, morphine, and heroin) bind with endorphins receptors.
Tranquilizers such as Valium bind with GABA receptors.
LSD binds to a specific subtype of serotonin receptor.
Marijuana (THC) attaches to anandamide receptors.
Some block out the receptor sites to make them ineffective:
Antipsychotic drugs used to treat schizophrenis block out dopamine receptors.
Some disrupt the reuptake or clearing process:
Cocaine and Amphetamine slow the reuptake of dopamine and
created
by Dr. Joanne Hsu
norepinephrine.