Physiology-Neuromuscular Junction

Question 1

What can physiologically produce an action potential?

Answer 1

Synaptic transmission from another cell, spontaneously within the cell, another action potential and peripheral receptors.

Question 2

Where do action potentials typically begin in an axon?

Answer 2

The axon hillock, its threshold is only about -45mV so any depolarization hits the axon hillock 1st.

Question 3

What is an EPSP?

Answer 3

Excitatory Postsynaptic Potential. They depolarize the membrane to get it to threshold.

Question 4

What are IPSPs?

Answer 4

Inhibitor Postsynaptic Potential. They hyper polarize the membrane to inhibit action potential

Question 5

What are the two types of synapses?

Answer 5

Electrical and chemical

Question 6

Where are electrical synapses used and why?

Answer 6

Cardiac muscle, smooth muscle and gut. Rapid modification of the muscle is not necessary in these places.

Question 7

What makes up an electrical synapse?

Answer 7

Gap junctions made up of connexons. Na+ traveling through the channel depolarizes the adjacent cell.

Question 8

What is the mediating agent of electrical synapse?

Answer 8

Ionic current

Question 9

Where is chemical synapse used?

Answer 9

CNS where behavior must be flexible depending on the circumstances.

Question 10

What channels are present at the synaptic cleft?

Answer 10

*

Question 11

How are vesicles brought close to fuse with the presynaptic membrane?

Answer 11

Ca VGCs allow Ca to come in and control the amount of neurotransmitter released.

Question 12

What are the different types of channels?

Answer 12

Ionotropic: directly opens or closes postsynaptic channel. Metabotropic: releases a messenger that may activate enzymes, transcription or secondary membrane channels

Question 13

What creates and EPSP/IPSP?

Answer 13

Ionic current flowing through the open channels in the synaptic cleft?

Question 14

What is happening here?

Answer 14

It is a motor endplate. An axon is innervating different muscle fibers. Eventually the myelin will go away and form synaptic clefts

Question 15

What creates an end plate potential?

Answer 15

ACh is released. Channels open that are permeable to both Na and K. More Na goes in than K goes out and the end plate potential is produced. The more channels that open, the greater the end plate potential.

Question 16

If ACh opens a channel that allows Na and K to flow through, why does more Na enter?

Answer 16

It has a greater driving force than K because its electrical potential is further from the resting potential.

Question 17

What do crabs have that humans don’t?

Answer 17

Inhibitory end plate potentials. Humans only have excitatory end plate potentials.

Question 18

When does the end plate potential initiate an action potential?

Answer 18

Once it depolarizes the membrane to threshold (60mV)

Question 19

How does the presynaptic membrane recover after synapse?

Answer 19

Choline is taken back into the cell via Na+ anti port transport. Choline buds off as a vesicle into the cell and is re-acetylated.

Question 20

Why does the site of action potential generation need to be close to the end plate potential?

Answer 20

End plate potentials do not propagate.

Question 21

How do action potentials and EPSP/EPP/IPSPs differ? (Activating mediators, propagation, permeability sequence and summation)

Answer 21

Action potentials are activated by voltage and EPSP/EPP/IPSP are activated by neurotransmitters. APs propagate, EPSPs do not propagate. APs have sequential changes in permeability to Na and K, EPSPs have simultaneous changes. APs are not summative and EPSPs can sum.

Question 22

How does the CNS utilize ionotropic channels to produce action potentials?

Answer 22

Very similarly to neuromuscular junctions but only about 2mV depolarization. EPSPs must be added together to produce an action potential.

Question 23

How does the CNS produce IPSPs?

Answer 23

Hyperpolarization via increasing permeability to Cl- or K+

Question 24

How does action potential initiation take place via temporal summation in the CNS take place?

Answer 24

Before all ACh is degraded at the synaptic cleft transmitter is continually spilled out until the membrane potential reaches threshold.

Question 25

How does action potential initiation take place via spatial summation in the CNS take place?

Answer 25

Multiple synapses are stimulated at the same time to generate enough neurotransmitter to depolarize the membrane to threshold.

Question 26

Why does summation not take place at the neuromuscular junction?

Answer 26

A single synapse depolarizes the membrane enough to generate an action potential

Question 27

How do EPSP and IPSP signals effect action potential generation at the axon hillock?

Answer 27

IPSPs produce a hyperpolarization, which requires greater depolarization by EPSP in order to generate an action potential.

Question 28

How do electrical and chemical synapses differ in their properties? (Continuity, mediating agent, synaptic delay, directionality, behavior and extracellular space).

Answer 28