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2. Properties of Synapse Dr Ghulam Mustafa
3. Learning objectives Discuss the properties of synapse
Describe the factors affecting synaptic transmission
4. Decrement of Electrotonic Conduction in the Dendrites
5. Dales Law Only one type of neurotransmitter in released at one synapse
6. One-way conduction
Synapses generally permit conduction of impulses in one-way i.e.
from pre-synaptic to
7. Spatial Summation in Neurons Excitation of a single presynaptic terminal??
0.5 to 1 millivolt
10 to 20 millivolts - required to reach threshold
Many presynaptic terminals are usually stimulated at the same time.
Add to one another until neuronal excitation
Summing simultaneous postsynaptic potentials by activating multiple terminals on widely spaced areas of the neuronal membrane
8. Temporal Summation A presynaptic terminal fire
changed postsynaptic potential
lasts up to 15 milliseconds
Second opening of the same channels -increase the postsynaptic potential to - still greater level
Successive discharges from a single presynaptic terminal
Rapid enough- add to one another
This type of summation is called Temporal summation.
9. Facilitation of Neurons If the summated postsynaptic potential is excitatory.
But has not risen high enough to reach the threshold
The neuron is said to be facilitated.
Another excitatory signal - excite the neuron very easily
11. Fatigue of Synaptic Transmission. When excitatory synapses are repetitively stimulated at a rapid rate
Number of discharges by the postsynaptic neuron is at first very great
But the firing rate becomes progressively less in succeeding milliseconds or seconds.
Fatigue of synaptic transmission.
Against excess neuronal activity
Prevent over excitation
12. Mechanism Of Fatigue Exhaustion or partial exhaustion of the stores of transmitter substance
Progressive inactivation of many of the postsynaptic membrane receptors
Slow development of abnormal conc. of ions inside the postsynaptic neuronal cell
13. Effect of Acidosis or Alkalosis on Synaptic Transmission. Neurons are highly responsive to changes in pH
Alkalosis greatly increases neuronal excitability
8.0 often causes cerebral epileptic seizures
Acidosis greatly depresses neuronal activity;
a fall in pH from 7.4 to below 7.0
Severe diabetic or uremic acidosis,
15. Effect of Hypoxia Neuronal excitability is also highly dependent on an adequate supply of oxygen.
Cessation of oxygen for only a few seconds can cause complete inexcitability of some neurons
If Brains blood flow is temporarily interrupted,
Within 3 to 7 seconds, the person becomes unconscious.
16. Effect of Drugs Stimulants:
Caffeine, Theophylline, and Theobromine,
found in coffee, tea, and cocoa
By reducing the threshold for excitation of neurons.
Strychnine inhibits the action of some inhibitory transmitter substances
Most Anesthetics increase the neuronal membrane threshold for excitation
17. Synaptic delayIs the minimum time required for transmission across the synapse the synaptic delay 0.5 millisecond. This time is taken by
Discharge of transmitter substance by pre-synaptic terminal
Diffusion of transmitter to post-synaptic membrane
Action of transmitter on its receptor
Action of transmitter to ? membrane permeability
Increased diffusion of Na+ to ? post-synaptic potential
18. Convergence When many
19. Divergence Axons of most
pre-synaptic neurons divide into many branches that diverge
to end on many post-synaptic neurons.
20. Properties of synapse Dales Law
Summation in Neurons
Facilitation of Neurons
Fatigue of Synaptic Transmission
Effect of Acidosis or Alkalosis on Synaptic Transmission
Effect of Hypoxia & Drugs
Convergence & Divergence