A brief overview of Synaptic integration, Types of Synapses and Excitatory and inhibitory post synaptic potentials.

1. SYNAPTIC INTEGRATION
TYPES OF SYNAPSES
EPSP & IPSP
M.Rajagopalan
V M.Sc Life sciences

2. SYNAPTIC INTEGRATION
• Neurons in the brain receive thousands of
synaptic inputs from other neurons.
• Synaptic integration is the term used to
describe how neurons ‘add up’ these inputs
before the generation of a nerve impulse, or
action potential.
• The ability of synaptic inputs to effect
neuronal output is determined by a number of
factors

3.  Size, shape and relative timing of electrical
potentials generated by synaptic inputs
 the geometric structure of the target neuron,
 the physical location of synaptic inputs within
that structure
 expression of voltage‐gated channels in
different regions of the neuronal membrane.

4. SYNAPTIC INTEGRATION AND ITS
MECHANISM
Neurons within a neural network receive information from,
and send information to, many other cells, at specialised
junctions called synapses.
Synaptic integration is the computational process by which an
individual neuron processes its synaptic inputs and converts
them into an output signal.
Neurons are specialised for electrical signalling, with the main
neuronal input signal (synaptic potentials) and the main
neuronal output signal (action potentials)

5. Synaptic potentials occur when neurotransmitter binds to and
opens ligand‐operated channels in the dendritic membrane,
allowing ions to move into or out of the cell according to their
electrochemical gradient.
Synaptic potentials can be either excitatory or inhibitory
depending on the direction and charge of ion movement.
Action potentials occur if the summed synaptic inputs to a
neuron reach a threshold level of depolarisation and trigger
regenerative opening of voltage‐gated ion channels.
Synaptic potentials are often brief and of small amplitude,
therefore summation of inputs in time (temporal summation)
or from multiple synaptic inputs (spatial summation) is usually
required to reach action potential firing threshold.

7. TYPES OF SYNAPSES
• Types of synapses
• there are two types of synapses:
– electrical synapses
– chemical synapses

8. Electrical synapse
• electrical synapses are a direct electrical coupling between two
cells
– mediated by gap junctions, which are pores (as shown in the
electron micrograph) constructed of connexin proteins
– essentially result in the passing of a gradient potential (may be
depolarizing or hyperpolarizing) between two cells
• very rapid (no synaptic delay)
• passive process --> signal can degrade with distance-> may
not produce a large enough depolarization to initiate an
action potential in the postsynaptic cell
• bidirectional
– i.e., "post"synaptic cell can actually send messages to
the "pre"synaptic cell

9. Chemical synapse
• Chemical synapses coupling between two cells
through neuro-transmitters, ligand or voltage
gated channels, receptors.
• Influenced by the concentration and types of
ions on either side of the membrane.
• Glutamate, sodium, potassium, calcium are
positively charged.
• GABA, chloride are negatively charged.

10. Chemical synapse
• Ionotropic receptors are single protein
complexes that combine two functions.
• They have recognition sites on their surfaces
extending into the extracellular fluid that
allow them to interact with neurotransmitter
molecules.
• They also have the ability to open and close,
allowing ions to move across the neural
membrane.
• ionotropic receptors respond very quickly.

11. Chemical synapse
• Metabotropic receptors are made up of
multiple protein complexes embedded in the
neural membrane.
• One complex has the capacity to recognize
neurotransmitter molecules but cannot open
and close.
• Instead, the metabotropic receptor binds
molecules of neurotransmitter
• It releases a G protein, or "second
messenger," from its surface extending into
the intracellular fluid of the neuron

12. Chemical synapse
• This G protein travels away from the receptor
where it can interact with adjacent ion
channels, which can then open and close like
the ionotropic receptor.
• The eventual opening of ion channels is
slower than it is with ionotropic receptors.

13. • in contrast, chemical synapses are
• slow
• active (require ligand-gated channels)
• pseudo-unidirectional

15. IPSP AND EPSP
• An electrical charge (hyperpolarisation) in the membrane of a
postsynaptic neuron caused by the binding of an inhibitory
neurotransmitter from a presynaptic cell to a postsynaptic
receptor; makes it more difficult for a postsynaptic neuron to
generate an action potential.
• An electrical change (depolarisation) in the membrane of a
postsynaptic neurone caused by the binding of an excitatory
neurotransmitter from a presynaptic cell to a postsynaptic
receptor; makes it more likely for a postsynaptic neurone to
generate an action potential

17. EPSP
• Consider, for example, a neuronal synapse
that uses glutamate as receptor.
• Receptors open ion channels that are non-selectively
permeable to cations.
• When these glutamate receptors are
activated, both Na+ and K+ flow across
the postsynaptic membrane.
• The reversal potential (Erev) for the post -
synaptic current is approximately 0 mV.

18. EPSP
• The resting potential of neurons is
approximately -60 mV.
• The resulting EPSP will depolarize the post
synaptic membrane potential, bringing it
toward 0 mV.

19. IPSP
• As an example of inhibitory post synaptic
s action, consider a neuronal synapse that
uses GABA as its transmitter.
• At such synapses, the GABA receptors typically
open channels that are selectively permeable
to Cl-.
• When these channels open, negatively
charged chloride ions can flow across the
membrane.

20. IPSP
• Assume that the postsynaptic neuron has
a resting potential of -60 mV and an action
potential threshold of -40 mV.
• If ECl is -70 mV, transmitter release at this
synapse will inhibit the postsynaptic cell.
• Since ECl is more negative than the action
potential threshold.
• It reduces the probability that the
postsynaptic cell will fire an action potential.

21. • Some types of neurotransmitters, such as
glutamate, consistently result in EPSPs
• Others, such as GABA, consistently result in
IPSPs.
• The action potential lasts about one msec, or
1/1000th of a second.
• In contrast, the EPSPs and IPSPs can last as
long as 5 to 10 msec. This allows the effect of
one postsynaptic potential to build upon the
next and so on.

22. THANK YOU ALL