The document discusses neurohumoral transmission, which is how nerves transmit messages through the release of chemical signals called neurotransmitters across synapses. There are five key steps in the process: 1) impulse conduction along nerve fibers, 2) transmitter release from nerve endings when an action potential occurs, 3) the transmitter binding and activating receptors on the postjunctional cell, 4) a response in the postjunctional cell such as muscle contraction, and 5) termination of the transmitter action through reuptake. The most common neurotransmitters are acetylcholine and norepinephrine. Neurohumoral transmission is important for autonomic drug actions and functions like muscle contraction.

1. NEUROHUMORAL
TRANSMISSION IN BODY
ACTION.
BY: RAJIB BISWAS.

2. NEUROHUMORAL TRANSMISSION
Neurohumoral transmission implies that nerves transmit their
message across synapses and neuroeffector junctions by the release of
humoral (chemical) messages.
Almost all autonomic drugs, which are used clinically, exert their
pharmacological actions by altering essential steps in the neurohumoral
transmission process.
The principal neurotransmitters released from the postganglionic
sympathetic and parasympathetic nerve endings respectively are
noradrenaline (NA or norepinephrine, NE) and acetylcholine (ACh),
whereas the transmitter released in ganglia from the preganglionic
nerve ending of both systems is acetylcholine.

3. STEPS IN NEUROHUMORAL TRANSMISSION
1. IMPULSE CONDUCTION:
A nerve impulse is the electric signals that pass along the
dendrites to generate a nerve impulse or an action potential. An
action potential is the movement of ions in and out of the cell. It
specifically involves sodium and potassium ions. They are
moved in and out of the cell through sodium and potassium
channels and sodium-potassium pump.
Conduction of nerve impulse occurs due to the presence of
active and electronic potentials along the conductors.
Transmission of signals internally between the cells is achieved
through a synapse. Nerve conductors comprise of relatively
higher membrane resistance and low axial resistance. The
electrical synapse has its application in escape reflexes, heart
and in the retina of vertebrates. They are mainly used whenever
there is a requirement of fast response and timing being crucial.
The ionic currents pass through the two cell membrane when the
action potential reaches the stage of such synapse.

4. 2. TRANSMITTER RELEASE:
Storage of the neurotransmitter in
storage granules or vesicles in the
axon terminal. Calcium enters the
axon terminal during an action
potential, causing release of
the neurotransmitter into the
synaptic cleft. After itsrelease,
the transmitter binds to and activates
a receptor in the postsynaptic
membrane.

5. 3. TRANSMITTER ACTION ON POSTJUNCTIONAL MEMBRANE:
The postjunctional
muscle cell
responds to
the transmitter by
depolarizing and this
results in
an action potential
in the muscle
cell membrane,
which triggers
muscle contraction.
The neuromuscular
junction is also
important as a
model synapse.

6. 4. POSTJUNCTIONAL ACTIVITY:
Visceral efferent
neurons innervate
smooth muscle,
cardiac muscle,
and glands, and
have the ability to
be either excitatory
or inhibitory in
function.
Neuroeffector
junctions are known
as neuromuscular
junctions when the
target cell is a
muscle fiber.

7. 5. TERMINATION OF TRANSMITTER ACTION:
The actions of these
chemical signals
are terminated through
active uptake by transporters
that are located in the plasma
membrane of neurons and
glial cells. Transporters
harness electrochemical
gradients to force the
movement
oftransmitter back into cells
against its concentration
gradient.

8. COTRANSMISSION:
Cotransmission,
defined here as the
control of a single
target cell by two or
more substances
released from one
neuron in response to
the same neuronal
event, does occur in
experimental
situations.

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