Neurotransmitters
NEUROTRANSMITTERS
Summary
Excitatory vs Inhibitory
- Neurotransmitters can be either excitatory or Inhibitory
Excitatory
- Excitatory – pushes membrane potential closer to depolarization
Inhibitory
- Inhibitory – pushes membrane potential farther from depolarization (hyperpolarization)
Both Excitatory & Inhibitory
- Based on the channel activated, not the neurotransmitter itself (some neurotransmitters can be both excitatory or inhibitory)
Direct vs Indirect
- Neurotransmitters can perform direct or indirect activation.
Direct Activation
- Bind to and open ligand-gated ion channels
Indirect Activation
- Signal through intracellular second messenger pathways
6 Classes with examples
- Acetylcholine – Acetylcholine (first neurotransmitter discovered)
- Biogenic Amines – Dopamine and Serotonin
- Amino Acids – GABA (gamma aminobutyric acid) and Glutamate
- Peptides – Endorphins and Substance P
- Purines – ATP and Adenosine
- Gasses and Lipids – Nitric oxide and endocannabinoids
Neurotransmitter Fate
- Reuptake – Channel proteins take neurotransmitters back up into cells
- Degradation – Enzymes in the synaptic cleft break down the neurotransmitters
- Diffusion – Neurotransmitters eventually diffuse away from the synapse
Axonal Transport
Retrograde Transport
From axon to cell body
- Fast – 50-250mm per day and uses dynein
- Viruses (rabies, polio, herpes simplex) and tetanus toxin use it to transport themselves to the cell body
Anterograde Transport
From cell body to axon
- Slow – ~1mm per day though the mechanism is unclear
- Fast – 100-400mm per day and uses kinesin
- Nerves use slow anterograde transport to heal themselves