5 and 6 - Synaptic Transmission Flashcards
What is an electrical synapse?
A conductive link between two neurons that is formed at a narrow gap between the pre and post synaptic neurons, known as the gap junction
What is the morphology of an electrical synapse?
Each cell contributes a “half channel” called a connexon
What is a connexon formed by?
Six protein subunits called connexoins
What is a gap junction?
A connection between two cells that is formed by the connexon channels
A signal is passed from cell to cell via connexon channels
Is synaptic transmission bidirectional or unidirectional?
Mostly bidirectional, but it can be unidirectional
What is the function of a gap junction?
Rapid transmission of a signal with little or no delay
Groups of neurons that are interconnected by gap junctions have ___________ activity
Synchronous
What is a chemical synapse?
- Specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands.
- Allow for the formation of circuits with the CNS (muscle control, perception, etc.)
What is the morphology of a CNS chemical synapse?
A synaptic cleft forms (10-20 nm space)
- Pre-synaptic density (docking complex)
- Postsynaptic density
- Active zone
What is the active zone?
Part of the presynaptic membrane that is specialized for vesicular release of the transmitter
What is the morphology of a CNS neuromuscular junction?
A synapse between a motor neuron and a muscle fiber
- presynaptic structure
- postsynaptic membrane
Describe the presynaptic structure of a neuromuscular junction
The motor neuron axon approaches its termination, loses its myelin sheath and divides into a number of terminal “boutons”
Describe the postsynaptic membrane of a neuromuscular junction
You will find junctional folds and the motor end plate
What is a synapse?
The site of functional apposition between neurons where an impulse is transmitted from one neuron to another
What is a pre-synaptic neuron?
A neuron before or proximal to the synapse
What is a post-synaptic neuron?
A neuron after a synapse
What does “one-way conduction” mean?
Signals are transmitted from pre-synaptic neurons to post-synaptic neurons ONLY - never vice versa
Describe the mechanism by which an action potential causes transmitter release
- Action potential causes depolarization of the membrane of the pre-synaptic terminal
- This action potential causes Ca++ channels to open
- Ca++ flows into the cell
- This increases the probability that the synaptic vesicles in the active zone will fuse with the pre-synaptic membrane
- Once synaptic vesicles fuse, they release the transmitter
What is the role of SNARE proteins?
- A transmembrane protein that comes together with other SNAREs to form a helical docking complex
- Located on the presynaptic neuron and holds the synaptic vesicle to the membrane until Ca++ release
- Upon Ca++ release the vesicle fuses to the membrane to release the neurotransmitter
What is the SNARE protein of clinical relevance?
It is a vulnerable target for neurotransmitter inhibitors (medications/drugs)
What is the active zone of a chemical synapse?
Part of the presynaptic membrane that specializes in vesicular release of the transmitter
What is the docking complex?
The high concentration of vesicles that “dock” at the tip of the presynaptic neuron
Where does the SNARE complex function?
Near the docking complex because it holds the vesicles close to the membrane so they can be easily released upon Ca++ signaling
What is a synaptic delay?
A pause in the transmission of a signal