Lecture 4 : Synapses and the Role of Neurotransmitters

Question 1

What is glia

Answer 1

Non-neuronal cells in brain that play a role in :
- Physical support
- Metabolic support
- Electrical insulation
- Guiding connections
- Signalling

Question 2

Notes about electrical synapse

Answer 2

• Fastest and most primitive
• Bi-direction transfer of information
• Gap junction
• Kinda rare in neurons in CNS, but present for glia-neuron and glia-glia communication

Question 3

Notes about chemical synapses

Answer 3

• The one i’m familiar with
• Unidirectional transfer of info

Question 4

How does neurotransmission occur across a synapse?

Answer 4

Action potential travels down presynaptic neuron and reaches axon terminal.

Depolarisation at axon terminal opens voltage gated Ca2+ channels in presynaptic membrane.

Ca2+ ions influx and enter axon terminal down a concentration gradient.

Increased concentration of Ca2+ stimulates synaptic vesicles containing neurotransmitters to move towards presynaptic membrane.

Vesicles dock at the active zones of the presynaptic membrane, and Ca2+ binds to proteins on vesicles and facilitates the vesicle’s fusion with the membrane through the SNARE complex membrane

Neurotransmitters are released into the synaptic cleft by exocytosis, and molecules diffuse across cleft and bind to specific receptors (either ionotropic or metabotropic) on postsynaptic membrane.

At an excitatory synapse, depolarisation via Na+ influx occurs, generating an excitatory postsynaptic potential. At an inhibitory synapse, hyperpolarisation (Cl- influx or K+ efflux) occurs generating an inhibitory post synaptic potential. If either are strong enough to reach threshold, a new action potential is triggered in post synaptic neuron.

Neurotransmitters are cleared from synaptic cleft to terminate the signal. They can be re-uptaken into the presynaptic neurone, degraded by enzymes or just diffuse away from cleft. Some components of neurotransmitters are recycled to maintain synaptic efficiency.

Question 5

What are ionotropic receptors? Examples?

Answer 5

Ligand-gated ion channels
- Very fast
- Direct effect (ion movement activated by neurotransmitter directly)
- AMPA/NMDA, GABA, Glycine receptors

Question 6

What are metabotropic receptors? Examples?

Answer 6

G-Protein-Coupled receptors.
- Slower action
- Indirect effect (Secondary messengers invomved, like cAMP)
- ACh receptors, glutamate receptors

Question 7

What are the major amino acid based neurotransmitters?

Answer 7

• Glutamate (major excitatory)
• GABA (major inhibitory)
• Glycine

Question 8

What are some major monoamine neurotransmitters?

Answer 8

• Noradrenaline
• Dopamine
• Serotonin

Question 9

What are neuroactive peptides?

Answer 9

Hundreds, opioids (endorphins), tachykinins (substance P, neurokinin A)