Chemical Neurotransmission+Synaptic plascity

Question 1

What is the sequence of events associated with synaptic transmission across chemical synapses?

Answer 1

1. action potential in presynaptic cell
2. depolarization of the cell membrane of the presynaptic axon terminal
3. release of the chemical transmitter by the presynaptic terminal
4. binding of transmitter to specific receptors on plasma membrane of postsynaptic cell
5. transient change in conductance of postsynaptic plasma membrane to specific ions
6. transient change in membrane potential of postsynaptic cell

Question 2

What is the mechanism of termination of synaptic transmission at neuromuscular junction?

Answer 2

-acetylcholinesterase at post junctional membrane hydrolyzes ACh

Question 3

What are hemicholiniums?

Answer 3

-inhibit uptake of choline by the presynaptic motor neuron. motor neurons can’t synthesize choline and must transport it in to make acetycholine

Question 4

Describe the molecular basis for myasthenia gravis

Answer 4

• density of functional nAChR (nicotinic acetylcholine receptor) is lower than normal
• antibodies to nAChR protein
• leads to smaller EPP, which may be too small to elicit an action potential in muscle
• leads to muscle weakness and fatigue

Question 5

Name members of the following classes of neurotransmitters: catecholamines, excitatory amino acids, inhibitory amino acids, neuropeptides, gases

Answer 5

• acetylcholine: in peripheral nervous system and brain
• catecholamines: dopamine, norepinephrine, epinephrine (serotonin, histamine).
• excitatory amino acids: glutamate, aspartate.
• inhibitory amino acids: gamma amino butyric acid (GABA), glycine. GABA in most CNS neurons.
• neuropeptides: endogenous opioids like endorphin, dynorphins, enkephalins. Substance P relays sensory info.
• Gases: nitric oxide

Question 6

Distinguish between EPSP and IPSP and know the ionic conductance changes that occur with each

Answer 6

• EPSP=excitatory postsynaptic potential. transient depolarization of postsynaptic neuron caused by action potential. transmitters that increase conductance of postsynaptic membrane to Na+ and reduce conductance of K+
• IPSP=inhibitory postsynaptic potential. transient hyper polarization caused by an action potential. increased conductance of postsynaptic cell to Cl- and/or K+

Question 7

Describe the action potential in terms of sequential changes in conductance of Na+ and K+

Answer 7

• Na+ channels open and Na+ flow in
• depolarization of membrane that causes neighboring Na+ gates to open
• Na+ voltage gated channels close
• K+ channels open, K+ leave cells and cause repolarizaion
• hyperpolarization before returning to resting level

Question 8

What is LTP and what are its properties?

Answer 8

-Long term potentiation is long lasting enhanced synaptic strength
Properties
-input specificity: input that has undergone high frequency stimulation express LTP
-associativity: weak input cannot be potentiated only, but coupled with strong input, can be potentiated together

Question 9

Describe the induction mechanism of LTP.

Answer 9

• needs high level stimulation. low level induces long term depression (LTD) instead
• Glutamate binds to AMPA–>depolarizaion and Na+ enters the cells
• NMDA: has Mg2+ block, so with glutamate alone, nothing happens, but glutamate+membrane depolarization (from AMPA stimulation), removes Mg++ block and Na+ flows in. Also permeable to Ca++, important secondary signal.

Question 10

Describe LTP expression mechanisms.

Answer 10

1. presynaptic changes: increase in quantity of neurotransmitters released
2. postsynaptic changes: increase in function and number of AMPA receptors
3. increase in receptor conductance via phosphorylation of AMPA receptor
4. increase in functional synapses: insertion of AMPA receptors into post synaptic membrane converting silent synapses (NMDA only) to functional ones
5. Increase in receptor number in functional synapses: more AMPA

Question 11

How is synaptic plasticity regulated?

Answer 11

1. metaplasticity: chronic activity leads to desensitization (harder to induce plasticity), prolonged inactivity increases sensitivity of synapses (lowers threshold for inducing plasticity)
2. Firing rate homeostasis: modifications of synaptic drive to maintain firing rate within a targeted functional range
3. Synaptic scaling: scaling back a cell’s firing scales to reduce strength of synapses to prevent unconstrained potentiation