Transcript Neurotransmitters

Neuroanatomy
• Neuroanatomy refers to the
study of the parts and
function of neurons.
• Neurons are individual
nerve cells that combine to
create the body’s nervous
system (communication
system).
Types of Neurons
• There are three types of
neurons:
–Afferent Neurons
(Sensory Neurons)
–Interneurons
–Efferent Neurons
(Motor Neurons)
•Afferent Neurons
are responsible for
taking information
from the senses TO
the brain.
• Interneurons are located
in the spinal cord and the
brain, and are primarily
responsible for
processing information.
•Efferent Neurons are
responsible for taking
information FROM the
brain and the spinal
cord, and back to the
rest of the body.
• Most information travels from
the body, up the spinal cord, is
processed by the brain, sent
back down the spinal cord,
and then back to the body with
behavior instructions. The
exception to this general
pathway is reflexes.
•Reflexes are
controlled by the
spinal cord without
any conscious effort
on behalf of the brain.
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
C. Nucleus
• The function of the nucleus is to control
the activities of the cell
• 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.
Made of Schwann cells.
– Axons that are myelinated appear white.
Known as “white matter.”
F. Schwann Cells
• Provide for the growth of the myelin
sheath.
• 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
• I. 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.
Neural Transmission
• In its resting state (resting
potential or polarization), a
neuron has a negative charge
because mostly negative ions are
within the cell. Surrounding the
cell are positively charged ions.
The ions cannot mix because in
its resting stage, the cell
membrane is semi-impermeable.
• 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.
• 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.
• Depending on what type of
neurotransmitter has been
released, the next neuron will
react differently. Since nerve cells
are connected to the brain,
muscles, glands, etc., the entire
human body reacts different
depending upon what type of
neurotransmitter has been
released.
Neurotransmitters
Acetylcholine (ACh)
• Enables muscle action, REM
sleep, and memory
• Undersupply, as AChproducing neurons deteriorate,
marks Alzheimer’s disease
Dopamine
• Reward and Motivation, Motor Control
over Voluntary Movements
• Excessive dopamine receptor
activity is linked to schizophrenia;
a lack of dopamine produces the
tremors and lack of mobility of
Parkinson’s disease
Serotonin
• Affects mood, hunger,
temperature regulation, sleep,
and arousal
• Undersupply is linked to
depression; Prozac and other
anti-depressants raise serotonin
levels
Norepinephrine
• Helps to control alertness,
dreaming, waking from sleep,
reactions to stress
• Undersupply can depress
mood
GABA
• Neural inhibitor with a
tranquilizing effect.
• Undersupply linked to
seizures, tremors, and
insomnia
Glutamate
• Involved in memory
• Oversupply can
overstimulate the brain,
producing migraines or
seizures
Endorphins
•Natural opiates that
are released in
response to pain and
vigorous exercise
Endorphins
Epinephrine
• Adrenaline Burst of
Energy (small amounts in
brain)
Drugs and Chemical Interactions
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.
• 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) –
excessive release of
serotonin
• 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