Synaptic Transmission Flashcards
How do synapses help with the functional association of a neuron?
- with another neuron
- with effector organs (muscle or gland)
What are the 2 types of synapses?
- electrical
- chemical
What are electrical synapses?
- 2 neurons linked by gap junctions
- some between neutrons and glial cells
What are the 4 functions of electrical synapses?
- Rapid communication
- Ions or second messengers (through gap junctions)
- Bidirectional communication
- Excitation and inhibition (same synapse)
Give examples of excitation and inhibition in electrical synapses.
- retina
- cortex
- brainstem (breathing)
- hypothalamus (neuroendocrine neurons)
Describe chemical synapses.
- Pre & postsynaptic neuron
- Synaptic cleft
- Unidirectional
- Axodendritic (usual)
- Axosomatic
- Axoaxonic
- Dendrodendritic (unusual)
Describe the steps that occur at the synapse.
- Action potential
- Voltage-gated Ca2+ channels open
- Ca2+ entry triggers vesicle docking and secretion
- Neurotransmitter diffuses and binds to receptor
- Response in cell
- Response terminated by removal of neurotransmitter from the synaptic cleft
- Degradation by enzymes (multiple locations)
- Neurotransmitter reuptake into presynaptic terminal
- Degraded or recycled
- Diffusion out of synaptic cleft
What is synaptic delay?
Between arrival of an action potential and change in postsynaptic Vm = 0.5–5 msec delay
What is the reason for synaptic delay?
- Changes in [Ca2+] entry, vesicle docking, and release of neurotransmitter (NT)
- Not due to diffusion of NT across synaptic cleft
What is postsynaptic potential (PSP)?
- Response to receptor-neurotransmitter binding
- Membrane potential changes
What is excitatory postsynaptic potential (EPSP)?
- most common neurotransmitter: glutamate
- depolarization (AP produced)
- fast or slow
- Na+ and K+
- second messenger system
Describe fast EPSP.
neurotransmitter binds to channel and causes depolarization at that channel
Describe slow EPSP.
neurotransmitter binds to receptor that signals a cascade reaction (involves second messenger, enzyme activation) that eventually causes a response at another channel
What is inhibitory postsynaptic potential (IPSP)?
- Most common neurotransmitter: GABA
- Hyperpolarization
- Membrane stabilization (unlikely an AP produced)
- K+ or Cl- channels
An action potential is triggered if…
The membrane threshold at the axon hillock is depolarized to threshold
