Synapses and Synaptic Transmission Flashcards
Synaptic Transmission:
• Chemical transmission of one neuron to another
Electrical Synapses:
- Faster than chemical synapses due to gap junctions (connect pre and post synaptic neuron)
- Pre and post synaptic neurons are touching (membrane coupling)
- Allows for direct transmission of small molecules and ions (no need for neurotransmitter release)
- Passive spread of depolarization
- Common in invertebrates, not common in mammals due to complex nervous systems
- Only Excitatory, can’t have inhibitory electrical synapse
Gap Junctions
- Set of channels
- 6 connexins-> 1 connexons
- 2 connexons-> 1 gap junction
Neurotransmitter Synthesis
• One neuron can release several different types of neurotransmitters
• Early synthesis occurs in soma, but not completed
• Polypeptides
o Somal vesicle packaging, active axoplasmatic transport (40 cm/day)
• Small molecules
o Axonal travel (passive)
o Button vesicle packaging (in terminal)
Non Directed Synapse
- Action potential causes neurotransmitter release from varicosities
- Can stimulate larger number of neurons in that area as opposed as one to one transmission
Release of Neurotransmitters:
- Action potential reaches synaptic terminal
- Voltage activated Ca channel open
- Ca ion inters cell, promotes docking
- Presynaptic vesicles dock (dock) with cell membrane
- Neurotransmitter released into synaptic cleft
Snare Proteins
- Small proteins imbedded in terminal membranes and in synaptic membranes
- Allow docking because snare proteins come together
Receptor
- Protein that contains binding site for a specific neurotransmitter
- Neurotransmitter can bind to several different receptors
Ionotropic Receptor:
- Ligand activated channel
- Fast effect
- Causes EPSP or IPSP
- Transmembrane protein
Metabotropic Receptor:
- Associated with signal proteins and G proteins
- Slower effect
- Longer lasting
- Varied responses
- Ligand binds, receptor protein changes shape, G protein stimulated
G Protein
G protein is a GTP activated peripheral membrane protein
• Signal protein winds back and forth through bilayer 7 times
• 3 parts- alpha, beta, gamma
• Each part can go do different things in response to receptor binding
• G protein stimulates enzyme, activated second messenger (neurotransmitter was first messenger), can activate ion channels, activate other messengers, influence gene expression
Autoreceptors:
- Negative feedback to reduce neurotransmitter release
- Metabotropic receptor on pre synaptic neuron
- Neurotransmitter bind and tell pre synaptic neuron to stop releasing neurotransmitter
- Reduces chances of overstimulation, but doesn’t actually remove molecule from synapse
Heteroreceptors:
- A neuron releases a neurotransmitter, binds to heteroreceptor on second cell, which prevent that cell from releasing neurotransmitter to a third cell
- Cell 1 influences cell 3 indirectly through cell 2
Post Synaptic Inhibition and Facilitation:
- 2 neurons communicating with a third neuron
- Facilitation if they both release same kind of neurotransmitter (inhibitory or excitatory)
- Inhibitation if they release different kinds
- Type of spatial summation
Intracellular Receptors:
- Receptors for liposoluble neurotransmitters
* Hidden in cell, activated only by lipid soluble ligand
