Download 6 BIO Neurotransmitters - Appoquinimink High School

Neuroanatomy
Neuroanatomy
refers to the
study of the parts and
function of neurons.
Neurons are individual nerve
cells.
The entirety of the human
body’s neurons make up the
nervous system, from the
brain to the tips of the toes.
Neuron
The
basic building block of the
nervous system -- a nerve cell
Neurons perform three basic tasks
–Receive information
–Carry the information
–Pass the information on to the next
neuron
The Basic Parts of a Neuron
A.
Dendrites
– Thin, branching fibers lined with
receptors at which the dendrite receives
information from other neurons. The
greater the surface area, the greater
the amount of information. Some
dendrites are covered with spines which
greatly increase its surface area.
B.
Cell Body/Soma
–Contains the (C) nucleus
and other parts of the cell
needed to sustain life
D.
Axon
–Wire-like structure ending
in the terminal buttons that
extends from the cell body
 E.
Myelin Sheath
–An insulating, fatty covering around
the axon that speeds neural
transmissions. Axons that are
myelinated appear white. Known as
“white matter.”
F. Schwann Cells
 Provide
sheath.
for the growth of the myelin
 G.
Nodes of Ranvier
– Regularly spaced gaps in the myelin
sheath around an axon or nerve fiber.
This is where depolarization takes
place.
H.
Terminal Buttons
–The branched end of the
axon that contains
neurotransmitters
Neural Transmission
Synapse
–The space between the
terminal buttons on one
neuron and dendrites of the
next neuron
Neurotransmitters
Chemicals
contained in the
terminal buttons
that enable
neurons to
communicate.
Neurotransmitters fit
into receptor sites on
the dendrites of
neurons like a key
fits into a lock.
Neurotransmitters
 At
the terminal
buttons,
neurotransmitters
are released into
the synapse and
passed along to
the dendrites of
the next neuron.
If
enough
neurotransmitters have
been sent, the next
neuron will fire. If not,
the message ends. This is
called the all-or-nothing
principle.
 After
a neuron fires its message,
there is a brief period of time
before it can fire again. This is
called a neuron’s refractory
period.
 During the refractory period,
excess neurotransmitters are
reabsorbed by the sending
neuron, called re-uptake, as well
as the cell becoming polarized
once again.
Resting Potential
 While
in resting potential, a
neuron is said to be “Polarized”
 negative ions are within the cell.
Surrounding the cell are
positively charged ions.
 The ions cannot mix while in this
stage
A
neuron has a pre-set level
of stimulation that needs to
be met or exceeded in order
for it to pass the received
impulses on to the next
neuron. This is called a
neuron’s threshold.
 If
the threshold has been met or
exceeded, a chain reaction begins.
 With threshold being met, the cell
becomes depolarized and allows
positively charged ions into the
axon at the nodes of ranvier. This
mix of positive and negative ions
causes an electrical charge to form
(an action potential). At 120
meters per second, the action
potential travels to the terminal
buttons.
Axon – inside and out
Resting Potential
 The
state of a neuron when it is at rest
and capable of generating an action
potential
 The neuron is set and ready to fire
Action Potential
A
brief electrical charge that travels
down the axon of the neuron.
 A neural impulse
 Considered an “on” condition of the
neuron
Refractory Period
The
“recharging phase” when
a neuron, after firing, cannot
generate another action
potential
Once the refractory period is
complete the neuron can fire
again
Neuron firing like a Toilet
1.
Like a Neuron, a toilet has an
action potential. When you
flush, an “impulse” is sent down
the sewer pipe
Neuron firing like a Toilet
2. Like a neuron, a toilet
has a refractory period.
There is a short delay
after flushing when the
toilet cannot be flushed
again because the tank
is being refilled
Neuron firing like a Toilet
3.
4.
Like a Neuron, a toilet has a
resting potential. The toilet is
“charged” when there is water
in the tank and it is capable of
being flushed again
Like a Neuron, a toilet operates
on the all-or-none principle – it
always flushes with the same
intensity, no matter how much
force you apply to the handle
All-or-None Principle
The
principle that if a neuron fires it
will always fire at the same intensity
All action potentials are of the same
strength.
A neuron does NOT fire at 30%,
45% or 90% but at 100% each time
it fires.
Click here to see a neuron in
action!
Click here to see a quick summary!
Depending
on what type
of neurotransmitter has
been released, the next
neuron will react
differently.
….so, since the entire body is
a connection of nerves, …
Inhibitory vs Excitatory
 Inhibitory
neurotransmitters
decrease the likelihood of the
firing action potential of a cell
while
 Excitatory
neurotransmitters
increase the likelihood of action
potential
Acetylcholine (ACh)
Excitatory
Involved
in muscle action,
learning, and memory
Undersupply - Alzheimer’s
disease
Inhibitory:
Dopamine
Pleasure,
Reward and
Motivation, Motor Control
over Voluntary Movements
Excessive
dopamine linked to
schizophrenia;
Serotonin
Inhibitory
Affects
mood, hunger,
sleep, and arousal
Undersupply
is linked to
depression; Prozac and
other anti-depressants
raise serotonin levels
Epinephrine and
Norepinephrine
Excitatory:
Used for arousal
in the flight/fight response,
plays a role in learning and
memory retrieval
Adrenaline Burst of Energy
(small amounts in brain)
Undersupply can depress
mood
GABA
Inhibitory:
offsets
excitatory messages
(see Glutamate); helps
regulate daily sleep-wake
cycles
Undersupply linked to
anxiety, seizures, tremors,
and insomnia
Glutamate
Excitatory
Involved
in memory,
learning and movement
Oversupply
can
overstimulate the brain,
producing migraines or
seizures (epilepsy)
Endorphins
Inhibitory:
Natural opiates
that are involved in pain
perception and positive
emotions
released in response to pain
and vigorous exercise
Drugs and Chemicals
Interact with Neural
Transmission
Some
drugs that people
put into their bodies are
classified as agonists.
Agonists
may either speed
up the neural process,
cause an over-release or
absorption of a
neurotransmitter, or block
the re-uptake process.
Prozac blocking the
re-uptake of
Serotonin
 Some
agonists mimic the effects of a
naturally occurring neurotransmitter
Agonist (like
morphine – replacing
natural endorphines)
Dendrite of
receiving
Neuron
After
a neuron fires, if reuptake is blocked, the
lingering neurotransmitters
in the synapse will
continue to be absorbed by
the receiving neuron until
it is gone.
Therefore, a lingering
feeling will occur
Examples of Agonists
Cocaine
– blocks the reuptake of dopamine
MDMA (Ecstasy) – blocks
the reuptake of serotonin
–Repeated use destroys
serotonin producing cells
Some
drugs that people
put into their bodies are
classified as antagonists.
Antagonists
may slow or stop
the transmission of a
neurotransmitter, or they may
bind themselves to receptors
on a neuron’s dendrite, thus
not allowing a message to be
passed on.
Examples of Antagonists
 Curare
– a poison that stops the flow
of Ach – causes paralysis
Antagonist
(like
curare)
Neurotransmitter
(such as Ach)
Dendrite of
receiving
Neuron
Types of Neurons
There
are three types of
neurons:
–Afferent Neurons
(Sensory Neurons)
–Interneurons
–Efferent Neurons
(Motor Neurons)
Types of Neurons
Afferents, or “sensory neurons”,
carry information from the body
to the brain
Types of Neurons
Interneurons,
found in the spinal
cord and the brain
 interpret incoming information
and determine the next course of
action
Types of Neurons
or “motor neurons”,
carry information from the spinal
cord or the brain to the rest of the
body in order to initiate behavior
Efferents,
The
exceptions to
the “general
pathway” of neural
activity are
reflexes.
•Reflexes are
controlled by the
spinal cord
without any
conscious effort
on behalf of the
brain.
Reflexes
are
primitive responses
protect
our
bodies
from
danger

Coughing
Blinking
Yawning (too
much carbon
dioxide in the
blood)
….etc…….
Reflex
Reflex
Spinal Cord
 Sensory
to spinal cord to motor…
 no brain processing involved….