Synapse Flashcards
Functional connection between a neuron and 2nd cell
Impulse are transmitted from one nerve cell to another to be able to react
Synapse
Type of Synapse
current flows directly
no synaptic delay
allow conduction in both directions rectification
cells that are joined by gap junctions useful in reflex pathways
Electrical Synapse
Type of Synapse
modify the transmission (plasticity)
terminal buttons
one-way conduction
0.5 second synaptic delay
Chemical Synapse
4 Functional Anatomy of Synapse
Dendrodentritic
Axo-somal
Axodendritic
Axo-axonic
The cell before the synapse/connection
Synaptic vesicles contain the neurotransmitters
Synaptic vesicles and plasma membrane contain several protein interactions
Mitochondria that supply energy to some
processes
Presynaptic Cell
The cell right after the synapse
Dendrites
Postsynaptic Cell
2 Types of Synapses
Electrical Synapse
Chemical Synapse
Current flows directly
No synaptic delay
No need to traverse the extracellular space
Ions that produce AP gets shared with the
postsynaptic cell; gap junctions
Allow conduction in both directions
Cells can share ions
Rectification
Cells that are joined by gap junctions - Connexins, connexons
Useful in reflex pathways
Examples: SA node, pacemaker cells of the heart and of GI
Share ions with cardiac muscle cells through
gap junctions
Electrical Synapse
Most abundant in our bodies
Modify the transmission (plasticity)
Postsynaptic cell can either be excited or inhibited
Dictates whether postsynaptic cell will discharge/fire or not
Involve ligands, neurotransmitters
End up on terminal buttons
One-way conduction
Mediator only on synaptic knobs not on postsynaptic cell
Once transmitted, there is no turning back
0.5 msec synaptic delay
Need to traverse the ECF before reaching the postsynaptic cell
Chemical Synapse
Functional Anatomy:
We name the pathways in the nervous system from its …
origin towards its destination
Originates from a dendrite and goes to another
dendrite
Will not conduct impulses to the postsynaptic
cell
Dendrites do not contain synaptic vesicles at the terminal button
NO synaptic vesicle = NO transmission of impulse
Dendrodentritic
Axon to body
From the axon of the presynaptic to the soma of the postsynaptic neurons
Axo-Somal
From the axon of the pre-synaptic to the
dendrite of the postsynaptic
Majority of synaptic connections are
axodendritic
Endings are commonly located on dendrites
Axodendritic
Axon of the presynaptic to the axon of the
postsynaptic
Presynaptic nerves terminate on the axon of
postsynaptic neurons
Axo-Axonic
One nerve will receive 10k synaptic
inputs (2k on soma; 8k on dendrites)
Dendrites expand surface area up to
90%
Principle of Convergence
In the cerebral cortex
__% on dendrites
__& on cell bodies
98%
2%
Takes time to traverse and be received by the
post synaptic cell
20-40 nm wide synaptic cleft
Highly specific for the neurotransmitters from the presynaptic cell
Proteins act as receptors
Receptor on postsynaptic cell
Proteins create this thickening
Proteins acting as receptors
Thickening on postsynaptic cell
Many mitochondria
Membrane enclosed vesicles (synaptic vesicles)
Presynaptic terminal
3 Kinds of Synaptic Vesicles
Small, clear which contains ACh, glycine, & GABA
Small vesicles with dense core which contains
catecholamines (granulated in appearance)
Large vesicles with dense core which contains neuropeptides
Where small vesicles are located
Darkened portion
Conglomeration/group of small clear synaptic vesicles in the presynaptic cell
Dense bars: conglomeration/group of receptors in the postsynaptic cell for small clear vesicles in
the active zones
Active Zones
When calcium enters, it becomes the key ion of exocytosis
Ca++ is the key for synaptic vesicle fusion
Restores Ca++ level
Calcium does not belong inside; therefore it has to be removed against its gradient in exchange for one sodium ion
Utilizes ATP (priming, anti-port, Na K pump)
Pumps in Ca2+ in exchange of sodium
Ca++ - Na+ antiport
Transient partial depolarization
Directly under the active synaptic knob
(exocytosis of neurotransmitter)
Not enough to drain off positive charges
Spatial & temporal summation
When a generator potential is produced within a synapse, it is now called an EPSP
Excitatory Postsynaptic Potential (EPSP)
0.5ms
It will traverse the extracellular space
Synaptic Delay
The postsynaptic cell adds all the excitatory impulses it receives
Stimulating the postsynaptic cell once at different sites/spaces
Stimulate A only or B only = EPSP
Stimulate both A and B = higher EPSP
Spatial Summation
Summing the potential when you frequently discharge a postsynaptic cell
Temporal = Time factor
Stimulate A or B twice = higher EPSP
Stimulate A or B 2x or 4x = action potential could
possibly occur
Temporal Summation
Inhibitory Postsynaptic Potential (IPSP)
Interneuron
Neurotransmitter: glycine
*dual function: inhibitory in the spinal cord but excitatory in the brain
Golgi Bottle Neuron: inhibits IPSP
Opening of ligand-gated Cl- channels
Opening of K+ channels
Closure of Na+ and Ca++ channels
Inhibitory Postsynaptic Potential (IPSP)
Directly inhibits ligand-gated channels
Direct Inhibition
Effects of previous postsynaptic cell discharge
Cell is in refractory period
After-hyperpolarization (point A or C of relative
refractory period)
Indirect Inhibition
golgi bottle neuron arrangement
neuron is in between main synapse
reciprocal innervation: one muscle contracts
and the other relaxes
postsynaptic inhibition
axo-axonal endings
interneuron synapses to the presynaptic cells
decreases action potential magnitude; only few EPSPs will happen in the motor neuron
presynaptic inhibition
3 mechanisms of Presynaptic Inhibition
Opens ligand-gated chloride channels (increase Cl- conductance)
Decrease Ca++ entry
K+ gates open (decreases magnitude of
action potential)
Neurotransmitter of Presynaptic Inhibition
GABA
Prolonged action potential; enhances EPSP
Presynaptic Facilitation
Calcium is the key ion for synaptic vesicle fusion and exocytosis
More calcium, more exocytosis
Prolonged opening of Ca++ channels
Increase in cAMP
Utilizes the secondary messenger system (G-protein); amplifies the signal
K+ closes; prolonging the action potential
Neurotransmitter: Serotonin
Alpha motor neuron gives off a branch that
synapses to an inhibitory interneuron
Inhibitory interneuron in turn synapses to the same alpha motor neuron and to another alpha motor neuron
Renshaw Cell
