Transcript Synaptic transmission

Learning objectives of Today’s Lecture

Describe the physiological basis of Resting
membrane potential of a neuron

Enlist the sequence of events in
synaptic transmission

Differentiate between Excitatory Post
Synaptic Potential EPSP and Inhibitory
Post Synaptic Potential IPSP
Synaptic
transmission
Dr Ghulam Mustafa
Resting Membrane Potential of the
Neuronal Soma.

Resting Membrane Potential -65 millivolts.

Less negative than the -90 millivolts

Lower voltage is important:

Allows both positive and negative control of
the degree of excitability of the neuron.
 Decreasing
the voltage - less negative value
- neuron more excitable
 Increasing
the voltage - more negative
value - neuron less excitable.
Resting Membrane Potential of the
Neuronal Soma
40 nm vesicles formed in GA of cell body-
Motor neuron
Vesicles transported---axoplasmic streaming
to nerve terminal
Acetylcholine synthesized in terminal parts of
nerve - stored
Action potential opens calcium channels
Calcium bind with protein molecules (Release sites)
Exocytosis of Acetylcholine vesicle
2000 and 10,000 molecules of acetylcholine are
present in each vesicle
Enough vesicles in the Presynaptic terminal
To transmit more than 10,000 action potentials.
Acetylcholine.
Acetyl cholinesterase
Vesicles
reformation
Acetate
Choline
Reabsorbed BACK
Coated pits - Clathrin
New vesicles
ACETYLCHOLINE (NT) IN SYNAPTIC CLEFT
Transmitter substance activates
Ion Channel
Second Msgr System
If transmitter substance activates an
Ion Channel
opens within a fraction of
a millisecond
Cation channel
Sodium Ions
Anion Channel
Chloride ions
Excitatory Transmitter
Inhibitory Transmitter
“Second Messenger” System in the
Postsynaptic Neuron.
G Protein activation
Alpha
Beta
Alpha
Gamma
G Protein mediated actions
1.
Opening specific ion channels
2.
Activation of cAMP or cyclic cGMP in the
neuronal cell.
3.
Activation of one or more intracellular
enzymes.

Activation of gene transcription.
Excitation

Opening of Sodium Channels

Depressed conduction through Chloride
or Potassium channels, or both.

Various changes in the internal
metabolism of the postsynaptic neuron
Effect of Synaptic Excitation on
the Postsynaptic Membrane



Increase the membrane’s permeability to
Na+
Neutralizes part of the negativity of the
RMP
Positive increase in voltage above the RMP
 Excitatory Postsynaptic Potential
(or EPSP)
 20 millivolts more positive than RMP
 simultaneous discharge of many terminals —
about 40 to 80
EPSP
EPSP
Inhibition

Opening of Chloride ion channels through the
postsynaptic neuronal membrane.

Increase in conductance of potassium ions out
of the neuron.

Activation of receptor enzymes that
 Inhibit
cellular metabolic functions
the number of inhibitory synaptic
receptors or
 Increase
 Decrease
the number of excitatory receptors.
Electrical Events During Neuronal
Inhibition

Open mainly Chloride channels

Potassium efflux
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Increase the degree of intracellular negativityHyperpolarization

Inhibitory Postsynaptic Potential (IPSP)
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More negative value of -70 millivolts
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IPSP of -5 millivolts
IPSP

Ensure impulse to pass in one
direction

Prevent damage of effectors due to
over stimulation

Act as junctions for dividing up and
merging of neurons
Resting Membrane Potential of the
Neuronal Soma
EPSP
IPSP