The Synapse (3 Components)
- Presynaptic cell
- Synaptic cleft
- Post synaptic cell
Presynaptic Cell
carries the signal to the synapse
Synaptic Cleft
The space in between the pre- and post-synaptic cells 3-30 nm across
Post-synaptic Cell
Neurons, muscles, and endocrine glands
The neurotransmitter junction is the synapse between a motor neuron and a muscle cell
Transfer info between cells by direct ionic coupling via
gap junctions
The connexon proteins of gap junctions
Narrow the gap and lower the resistance between cells
Current decays between neurons just like passive spread of a local:
Na+ current
Chemical Synapses
Transfer info between cells indirectly via neurotransmitters
Electrical Synapse
- Rare in complex animals
- Comparatively fast
- Bi-directional
- Postsynaptic signal is similar to presynaptic
- Excitatory
Chemical Synapse
- Common in complex animals
- Comparatively slow
- Unidirectional
- Postsynaptic signal can be different
- Excitatory/Inhibitory
Neurotransmitters are released by:
Ca2+ - dependent exocytosis
AP frequency determines Ca 2+ concentration and therefore: how much neurotransmitter is released
how much neurotransmitter is released
Fast vs. Slow Chemical Synaptic Transmission:
Differentiated by their post-synaptic mechanisms, NOT by their neurotransmitters
Fast Chemical Synapses
Act through ionotropic receptors (ex. ligand-gated ion channels) found on the post-synaptic membrane
Slow Chemical Synapses Act:
Through meta trophic receptors (ex. G-protein coupled receptors) found on the post-synaptic membrane
The Neuromuscular Junction: Structural Specialization
- APs are conducted to skeletal muscles via large myelinated motor neurons
- The neuromuscular junction includes pre- and post-synaptic specializations
