Propagation of the Action Potential and the Chemical Synapse

Question 1

propagation of action potential

Answer 1

at the peak of the action potential the inside of the membrane is positive (about + 30 mV)

nearby regions are still negative since they are still at rest

the current flow of postive charges repel each other and attract torwards the negative regions

depolarization of the membrane potential ahead of and behind the action potential

when the membrane potential of the adjacent membrane reaches threshold, the Na⁺ voltage-gated channels found there will open and an action potential is generated

the action potential therefore propagates along the membrane without losing strength

Question 2

describe the propagation of an action potential down an axon

Answer 2

1. Depolarizing graded potential arrives at axon hillock and is above threshold. Na+ VG open
2. That Na+ that enters is attracted to the next region that is still at -70mV because ”opposites attract”
3. Those Na+ VG open. AP fires in next segment, while repolarization/ hyperpolarization happens in segment behind it

Question 3

why are action potentials unidirectional?

Answer 3

the absolute refractory period prevents the initiation in the other direction that had just produced the AP

the potassium voltage-gated channels are slow to inactivate, potassium goes out the cell which makes the cell

Question 4

speed of propagation

Answer 4

1. influenced by membrane resistance to ion leakage (myelination) (increased ion leakage = slower action potential)
2. axon diameter (larger diameter = faster propagation)
   - > not all action potentials travel at the same speed in neurons

Question 5

myelin sheath (saltatory conduction)

Answer 5

• > node of ravier to next node of ravier
• > makes action potentials faster by myelin sheath that acts like insulation
• > reduces ion leak preventing depolarization

Question 6

multiple sclersis

Answer 6

Question 7

label the neurons

Answer 7

Question 8

what happens when the action potential reaches the axon terminal?

Answer 8

once the action potential reaches the axon terminal, it triggers Calcium gated channels to open

this triggers vesicles with neurotransmitters to fuse to the plasma membrane and release the neurotransmitters into the synaptic cleft to bind to receptors on the post-synapse

Question 9

The chemical synapse

Answer 9

synapse is made of axon terminal of the pre-synaptic neuron and the plasma membrane of the post-synaptic neuron

at axon terminal depolarization triggers Ca²⁺ to enter the axon terminal through Ca²⁺ voltage-gated channels, causing neurotransmitters to release into the synaptic cleft from synaptic vesicles

these neurons bind to receptors on the post-synaptic neuron by opening chemically-gated ion channels

Question 10

how are neurotransmitters removed?

Answer 10

neurotransmitters are removed from

1. recycled back into axon terminal
2. enzymes in synaptic cleft
3. diffuse away from cleft

Question 11

post synaptic potentials (type of graded potential)

Answer 11

when neurotransmitters bind to the post-synaptic receptors, it opens a chemically-gated ion channel depending on what the receptor is linked with (ex, chemically gated sodium, chlorine or potassium channel)

excitatory postsynaptic potential (EPSP) - event of depolarization of the post-synaptic neuron

inhibitory postsynaptic potential (IPSP) - event of hyperpolarization of the post-synaptic neuron

Question 12

excitatory postsynaptic potential (EPSP)

Answer 12

the post-synaptic neuron becomes depolarized from neurotransmitter-receptor and ion channel gate (chemically-gated ion channel)

if depolarization is large enough it can trigger another action potential (to continue)

Question 13

inhibitory postsynaptic potential (IPSP)

Answer 13

event of hyperpolarization of the post-synaptic neuron

the post-synaptic neuron gets hyperpolarizated from the neurotransmitter-receptor ion channel (chemically-gated ion channel)