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Synapse (to connect)

How two neurons communicate/How they exchange information

2 types of synapse

1. electrical

Electrical synapse

* simple synapses-cells have direct connections with each other
* Neurons are connected via gap junction-simplest type of cell to cell communication
*No Delay-very fast synapse of exchange of ions between the neurons

Gap Junction

*made of proteins referred to as connexon-which are 6 sided channels

gap junction

During _______ communication ions can diffuse from one cell to the next cell.

Electrical synapses are found in....

1. escape reflex neurons (invertebrates)
2. Epithelial cells (gut)
3. Cardiac muscle cells (heart)

Chemical Synapse

* Has more stages of activity (3 components) and is more complicated than electrical synapse

3 components of Chemical Synapse

1. Presynaptic component or stage
2. Posynaptic component or stage
3. Inbetween these two components or stages is a cleft called synaptic cleft

Chemical Synapses are found in....

* almost all mammalian neurons

Presynaptic Stage

(chemical synapse)
1. invasion of the synaptic terminal by an action potential
2. depolarization of the terminal(cell) - this depolarization results in influx(increase) of calcium ions into the cell
3. Ca++ influx (opening of voltage-gated Ca++ channels)
4. neurotransmitter release (Ca++ dependent, exocytosis of vesicles)
5. diffusion of the neurotransmitter across the synaptic cleft
(from the cell membrane)


(chemical synapse)
*Presyanptice stage
*the entrance of calcium(Ca++) ions into the cell triggers this process which releases the contents of small structures in the cell called vesicles


(chemical synapse)
* contain neurotransmitters -during exocytosis they release their neurotransmitters into the synaptic cleft-this starts the postsynaptic stage

Postsynaptic stage

(chemical synapse)
6. binding of the neurotransmitter to postsynaptic receptors of the cell membrane
7. Binding of neurotransmitters result in the opening of postsynaptic ion channels
8. entrance of the neurotransmitter to postsynaptic neuron
9. changes in postsynaptic membrane potential
10. re-uptake or break down of neurotransmitter to presynaptic, postsynaptic, or other neurons


(Chemical synapse)
When the neurotransmitters go to the vesicles in the presynaptic membrane

Ligand gated channels

open chemical synapse

voltage gated channels

open electrical synapse

graded potential=

can add up-IPSP and EPSP

Sodium Potasssium Active Pump

*active transport pump
*Pump is an electrogeneric pump that generates electricity
**Pumps 3 Na+ ions out of the cell
**Pumps 2 K+ ions into the cell

synaptic bouton

axon terminal

List of neurotransmitters

*serotonin (sleep cycle)
*melatonin (sleep cycle)
* adensoine

Excitatory neurotransmitters in the nervous system

* glutamic acid
*acetylcholine (associated with the heart)
*Aspartic acid

Inhibitory neurotransmitters in the nervous system


Electrical and chemical synapses operational differences

Operational Differences
1. no delay 1. delay
2. bidirectional 2. unidirectional
3. no amplification 3. amplification
4. no sensitivity to 4. sensitivity to
metabolic rate, metabolic rate,
pharmacology, pharmacology,
and temperature and temperature

Electrical and chemical synapses morphological differences

Electrical Chemical
Morphological Differences
5. needs size match 5. no size match needed
6. direct connection 6. synaptic cleft
7. gap junction 7. vesicles
8. no receptors 8. receptors

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