1. Synaptic transmission

4. Synthesis and transport of neurotransmitter

6. Neurotransmitters 1.Small clear vesicles: Acetylcholine glycine
Glutamate
GABA (gamma-
amino butyric A.)
2. Small dense core vesicles: Catecholamines
3. Large dense core vesicles: neuropeptides:
hypothalamic
hormones, opioid
polypeptides

7. Synaptic Transmission of Impulse
Neural signals are transmitted over long distances through a chain of neurons.
A synapse is the junction between two neurons. Typically, the axon terminal divides into several branches and each branch terminates as a knob (synaptic knob) on the soma or a dendrite of another neuron. Ventral horn cells of the spinal cord have thousands of synaptic knobs of different neurons

8. Types of synapse
Axo -somatic
Axo - dendritic
Axo - axonic

10. Structure of a Synapse

11. Chemical Events at a Synapse

12. Electrical Events at a Synapse

13. EPSP and IPSP

14. Ionic Basis of EPSP and IPSP
The neurotransmitters that produce EPSP do so by combining with specific receptors on the post synaptic membrane and opening ligand -gated sodium channels.
Since a small part of the postsynaptic membrane is involved, the overall decrease in membrane potential of the post synaptic cell is small.
Mechanism of IPSP: Opening of ligand -gated chloride channels

16. 5. EPSP No threshold. Decreases resting membrane potential.
Closer to threshold.
Graded in magnitude.
Have no refractory period.
Can summate.

17. 6. Synaptic Summation EPSPs can summate, producing AP.
Spatial summation:
Numerous boutons converge on a single postsynaptic neuron (distance).
Temporal summation:
Successive waves of neurotransmitter release (time).

18. a. EPSP
b.Spatial summation
c.Temporal summation within 1-15msec

19. Generation of Action Potential
If due to spatial or temporal summation, the EPSP is strong enough, it generates an action potential in the axon hillock region of the post-synaptic neuron by current sink action. Axon hillock region has the highest conc. Of Na+ channels, and hence has the lowest threshold of excitation.
Axon potential travels down the axon as well as spreads in the soma to clear it of all previous influences

20. Fate of Neurotransmitters
Partly diffuses out of synaptic cleft
Partly degraded / hydrolyzed
Reuptake: more important : in case of NE
Dopamine
GABA
Glycine
Glutamate
Reuptake mechanism saves need for re-synthesis
Certain drugs can prevent reuptake of certain neurotransmitters. Given to prolong or increase its effect

22. Synaptic Inhibition
Post-synaptic inhibition
Pre-synaptic inhibition

23. 6. Presynaptic Inhibition
Post-synaptic inhibition
Presynaptic inhibition
Motor Neuron

25. Functional significance of Synaptic transmission
Synaptic transmission of impulse allows modulation of neural signals like:-
1.Inhibition.
2.Amplification.
3. Divergence.
4.Convergence
5.Interaction of multiple neural inputs