(NS) Synapses and Neurotransmitters

Question 1

What is an action potential?

Answer 1

A uniform and propagated change in the electrical potential (membrane potential) across the cell membrane.

Question 2

An action potential results from?

Answer 2

The changes in the cell permeability (p) to Na+ and K+

Question 3

Permeability is the result of ?

Answer 3

Voltage-gated (VG) channels

Question 4

The activation gate closes the channel

Answer 4

At the resting membrane potential

Question 5

Activation gate opens when

Answer 5

When depolarizing stimulus arrives to
the channel

Question 6

With the activation open gate

Answer 6

Na+ enters the cell

Question 7

Inactivation gate closes and

Answer 7

Na+ entery stops

Question 8

During repolarization caused by K+ leaving the cell

Answer 8

The two gates reset to their original positions

Question 9

Voltage gated Na+ channels are completely blocked. What are the resulting effects on resting membrane potential, the ability to fire an action potential, and the resulting action potential ( if there is one)?

Question 10

Voltage gated Na+ channels are partially blocked. What are the resulting effects on resting membrane potential, the ability to fire and action potential, and the resulting action potential ( if there is one)?

Question 11

Propagation of and AP (action potential)

Answer 11

1. resting membrane potential
2. Depolarizing stimulus
3. Membrane depolarizes to threshold. Voltage-gated Na+ and K+ channels begin to open
4. Rapid Na+ entry depolarizes cell
   5.Na+ channels close and slower K+ channels open
   6.K+ moves from cell to extracellular fluid
5. K+ channels remain open and additional K + leave cell, hyper-polarizing it
6. Voltage-gated K+ channels close, less K+ leaks out of the cell
7. Cell returns to resting ion permeability and resting membrane potential

Question 12

How does an injection of KCL cause the heart to stop?

Answer 12

Potassium chloride is mixture is lethal which immediately stops the heart

Question 13

You are told that the Ek is -85mV, the ENa+ is +65mV, and the resting membrane potential of the cell is 70mV. What is the magnitude of the net electrochemical force in the resting cell for both K+ and Na+, respectively?( assume permeability of the ion)

Answer 13

+15 and -135

Question 14

When two or more graded potentials arrive at the trigger zone (axon hillock), what events could potentially occur?

Question 15

Trigger zone?

Answer 15

Axon Hillock

Question 16

IPSPs

Question 17

EPSPs

Question 18

IPSPs are likely to be produced in a typical neuron if (assume typical ECF and ICF ion concentrations)

Answer 18

The membrane permeability to K+ increases

Question 19

If a stimulus electrode is placed in the middle of a resting axon and an above-threshold voltage is applied to the electrode action potentials?

Answer 19

Will start at that point and proceed only towards the axon terminal

Question 20

How would the absolute refractory period of a neuron be impacted if voltage gated sodium channels remained inactivated? Defend your answer with a mechanistic explanation.