300 |
A Handbook of Biology
Depolarised
Na+
+ + ++ + ++ + + + + + + +
+ + ++ + ++ + + + + + + +
+++
+++
Na+
Stimulus
applied
Excited axon
K+
K+
g
+ + +
+ + + +
+ + +
+ + + + +
++ +
Na+
Na+- K+ Pump
Resting axon
Polarised
membrane
K+
K+
K+
K+
K+
+ + + + + + +
+ + + + + + + + + +
+ + + +
+ + + + + + + + + + +
+ + + +
+ + +
+ + +
Polarised
De-polarised
Re-Polarised
Stimulus
applied
Excited axon
Na+
Na+
Na+
Na+
K+
K+
K+
K+
SÝÑÅPTÏÇ TRÅÑSMÏSSÏØÑ ØF ÏMPÜLSËS
Synapse is a functional junction between two neurons.
It is of 2 types: Electrical & Chemical.
1. ËLËÇTRÏÇÅL SÝÑÅPSËS
In
this,
the
membranes
of
pre-synaptic and post-synaptic
neurons are in close proximity. So
impulse transmission is similar to
the transmission along an axon.
Impulse transmission across an
electrical synape is always faster
than in chemical synapse.
Electrical synapses are very rare
in human system.
2. ÇHËMÏÇÅL SÝÑÅPSËS
In this, there is a fluid filled space (synaptic cleft) between the pre-
synaptic neuron and post-synaptic neuron.
The pre-synaptic regions have swellings called Synaptic knob
(buttons). They contain synaptic vesicles filled with neurotransmitters
(acetylcholine or adrenaline). (NEET 2017)
Impulse transmission through chemical synapse: Impulse reaches at
axon terminal ® synaptic vesicles bind on plasma membrane ® release
of neurotransmitter ® It diffuses across synaptic cleft ® bind with
receptors on the post synaptic membrane ® opening of ion channels
allowing entry of ions ® generates action potential.
This action potential may be excitatory or inhibitory.