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
If the potential is below threshold…
no action potential
What is graded potential summation?
adding effects of graded potentials
IPSPs and EPSPs…
- are graded potentials
- can be summed
What are the 2 types of summation?
- temporal
- spatial
What is temporal summation?
one synapse through time
What is spatial summation?
several synapses at the same time
Acetylcholine is found in …
PNS and CNS
What is the most abundant neurotransmitter in the PNS?
acetylcholine
Describe the synthesis of acetylcholine.
- Acetyl CoA + choline –> acetylcholine + CoA
- Synthesized in axon terminal
- Choline acetyl transferase (CAT) = enzyme for synthesis
