Neurotransmitters are the brain chemicals that
communicate information throughout our
brain and body.
They relay signals between nerve cells, called
The brain uses neurotransmitters to tell heart
to beat, lungs to breathe, and stomach to
They can also affect mood, sleep, concentration,
weight, and can cause adverse symptoms when
they are out of balance.
Neurotransmitters are chemicals found and
produced in the brain to allow the transmission
of impulses from one nerve cell to the next
across synapses. They aid in the conduction of
information throughout the body. These
chemicals fit into specific receptor cells
embedded in the membrane of the dendrite
that either fuel up or excite action in the cells
(excitatory) or stop or inhibit an action
The impulse moves through the nerve in a long
and slender cellular part called the axon.
As the impulse travels through the axon it
travels the presynaptic membrane. It is in this
area that neurotransmitters are released in the
free space called the synaptic cleft.
The receptors located in the postsynaptic
membrane of another nearby neuron pick up
the free flowing neurotransmitters.
The molecule is adapted in the next nerve cell
and the impulse continues to the next nerve cell
until the message is relayed throughout the
After they served their purpose of being
released into the synapse and relaying the
messages to the receptor cells, they are
transported back from the synapse to the axon
to be stored for later use which is a process
called reuptake. If the neurotransmitters will
not undergo reuptake, they will be metabolized
and inactivated by enzymes, primarily
1) synthesized in the presynaptic neuron
2) Localized to vesicles in the presynaptic neuron
3) Released from the presynaptic neuron under
4) Rabidly removed from the synaptic cleft by
uptake or degradation
5) Presence of receptor on the post-synaptic neuron.
6) Binding to the receptor elicits a biological
Neurotransmitters released from a presynaptic
neuron bind to neurotransmitter receptors in
the plasma membrane of a postsynaptic cell.
Each type of neurotransmitter receptor has one
or more neurotransmitter binding sites where
its specific neurotransmitter binds.
When a neurotransmitter binds to the correct
neurotransmitter receptor, an ion channel
opens and a postsynaptic potential (either an
EPSP or IPSP) forms in the membrane of the
Neurotransmitter receptors are classified as
either ionotropic receptors or metabotropic
receptors based on whether the
neurotransmitter binding site and the ion
channel are components of the same protein or
are components of different proteins.
the neurotransmitter binding site and the ion
channel are components of the same protein.
In the absence of, the ion channel component of
the ionotropic receptor is closed.
When the correct neurotransmitter binds to the
ionotropic receptor, the ion channel opens, and
an EPSP or IPSP occurs in the postsynaptic cell.
When cation channels open, they allow passage
of the three most plentiful cations (Na, K, and
Ca2) through the postsynaptic cell membrane,
but Na inflow is greater than either Ca2 inflow
or K outflow and the inside of the postsynaptic
cell becomes less negative (depolarized).
When Cl channels open, a larger number of
chloride ions diffuse inward. The inward flow
of Cl_ ions causes the inside of the postsynaptic
cell to become more negative (hyperpolarized).
contains a neurotransmitter binding site, but
lacks an ion channel as part of its structure.
metabotropic receptor is coupled to a separate
ion channel by a type of membrane protein
called a G protein.
When a neurotransmitter binds to a
metabotropic receptor, the G protein either
directly opens (or closes) the ion channel or it
may act indirectly by activating another
molecule, a second messenger, in the cytosol,
which in turn opens (or closes) the ion channel.
When K channels open, a larger number of
potassium ions diffuses outward. The outward
flow of K ions causes the inside of the
postsynaptic cell to become more negative
The same neurotransmitter can be excitatory at
some synapses and inhibitory at other
synapses, depending on the structure of the
neurotransmitter receptor to which it binds.
For example, at some excitatory synapses
acetylcholine (ACh) binds to ionotropic
receptors that contain cation channels that open
and subsequently generate EPSPs in the
Excitatory Acetyl co-A +
Broken by acetyl
some CNS cells
alpha α &
through COMT &
MAO in liver
endings to body
For details refer
ANS. e.g. fight or
flight, on heart,
controls attention &
ii.Norepinephrine Excitatory Tyrosine, found
nerve ending is
iii. Dopamine Excitatory Tyrosine CNS,
bic and tubero-
D1 to D5
Same as above Decreased dopamine
Excitatory Tryptophan CNS, Gut
5-HT1 to 5-HT
5-HT 2 A
MAO to form 5-
pineal body it is
Mood control, sleep,
temperature, BP, &
4. Histamine Excitatory Histidine Hypothalamus Three types H1,
H2 ,H3 receptors
tissues & the
pressure, blood flow
in sensation of itch)
5. Glutamate Excitatory
in the brain
Brain & spinal
Three types of
It is cleared from
the brain ECF by
Na + dependent
uptake system in
involved in memory
and learning by
causing Ca++ influx.
6. Aspartate Excitatory Acidic amines Spinal cord Spinal cord
Aspartate & Glycine form an excitatory /
inhibitory pair in the ventral spinal cord
7. Gama amino
of glutamate by
GABA – A
increases the Cl
GABA – B is
works with G –
GABA – C
succinate in the citric
GABA – A causes
Anxiolytic drugs like
increase in Cl- entry
into the cell & cause
GABA – B cause
of K+ into the cell.
8. Glycine Inhibitory
Is simple amino
and a carboxyl
to a carbon
permeable to Cl-
Deactivated in the
synapse by simple
active transport back
into the presynaptic
Glycine is inhibitory
transmitted found in
the ventral spinal
cord. It is inhibitory
1. Diffusion. Some of the released
neurotransmitter molecules diffuse away from
the synaptic cleft. Once a neurotransmitter
molecule is out of reach of its receptors, it can
no longer exert an
2. Enzymatic degradation. Certain
neurotransmitters are inactivated through
enzymatic degradation. For example, the
enzyme acetylcholinesterase breaks down
acetylcholine in the synaptic cleft.
3. Uptake by cells. Many neurotransmitters are
actively transported back into the neuron that
released them (reuptake). Others are
transported into neighboring neuroglia
(uptake). The neurons that release
norepinephrine, for example, rapidly take up
the norepinephrine and recycle it into new
synaptic vesicles. The membrane proteins that
accomplish such uptake are called
Found in sensory neurons, spinal cord
pathways, and parts of brain associated with
pain; enhances perception of pain.
Inhibit pain impulses by suppressing release
of substance P; may have a role in memory
and learning, control of body temperature,
sexual activity, and mental illness.
Inhibit pain by blocking release of substance
P; may have a role in memory and learning,
sexual activity, control of body temperature,
and mental illness.
May be related to controlling pain and
Hypothalamic releasing Produced by the
regulate and inhibiting hormones the release of
hormones by the anterior pituitary.
Stimulates thirst; may regulate blood pressure
in the brain. As a hormone causes
vasoconstriction and promotes release of
aldosterone, which increases the rate of salt
and water reabsorption by the kidneys.
Found in the brain and small intestine; may
regulate feeding as a “stop eating” signal. As a
hormone, regulates pancreatic enzyme
secretion during digestion, and contraction of
smooth muscle in the gastrointestinal tract.