Lecture 27- Action Potentials And Synapses

Question 1

Refractory period

Answer 1

Period of time requires before neuron can generate another action potential

Question 2

Absolute refractory period

Answer 2

While Na+ channels are open, cell cannot respond to another stimulus

Question 3

Relative refractory period

Answer 3

Na+ channels are mostly reset, the cell is repolarizing and very strong stimulus can reopen Na+ channels and generate another action potential

Question 4

Synapse

Answer 4

Junction that mediates information transfer between two neurons or between a neuron and an effector

Question 5

Electrical synapse

Answer 5

Have neurons that are electrically coupled via protein channels

Allow direct exchange of ions from cell to cell
Gap junctions are fast enough to synchronize neuron activity

Question 6

Chemical synapse

Answer 6

Most common type of synapse

Specialized for release and reception of chemical neurotransmitters and have two parts

Question 7

Two parts of chemical synapses

Answer 7

Presynaptic neurons: secrete neurotransmitters

Postsynaptic neurons: listening for neurotransmitter, usually located on dendrites or cell body

Question 8

Steps in transfer across a chemical synapse

Answer 8

1. An action potential arrives at the axon terminal.
2. Voltage-gated channels open and Ca2+ enters the axon terminal.
3. synaptic vesicles release neurotransmitter by Exocytosis
4. Neurotransmitter diffuses across synaptic cleft and bind to postsynaptic membrane receptors.
5. ion channels open, creating graded potentials.
6. Neurotransmitters in synaptic cleft are removed by reuptake
7. Post-synaptic chemically-gated voltage channels close as neurotransmitter concentration in synapse drops.
8. Neurotransmitter effects are terminated.

Question 9

Excitatory synapses

Answer 9

Neurotransmitters bind to chemically gated ion channels

They cause depolarization and generation of excitatory postsynaptic potentials (EPSPs)

Can trigger action potentials if they are of adequate strength

Question 10

Inhibitory synapses

Answer 10

Neurotransmitter hyperpolarize membrane by making it more permeable to K+ or Cl-

Move membrane potential away from threshold (Inhibitory postsynaptic potentials or IPSPs)

Make generation of action potential less likely

Question 11

What does neurotransmitter effects depend on?

Answer 11

It’s receptor

Question 12

Neurotransmitter chemical classes

Answer 12

Acetylcholine, the biogenic amines (such as dopamine, serotonin, epinephrine and norepinephrine), amino acid-derived, peptides (such as endorphins), purines, and gases and lipids.

Question 13

Gamma amniobutyric acid (GABA)

Answer 13

primary inhibitory neurotransmitter in adult mammalian nervous system.
Neurons that release GABA are called GABAergic neurons.
In adult nervous system- GABA is an inhibitor that reduces neuron excitability.

In developing nervous systems- there is evidence that GABA excites neurons.

GABA receptors are also found in the pancreas, gastrointestinal tract, genital tracts, kidneys and airways, and may suppress immune inflammation.