Wk 5 – Membrane Potential, APs, Synapse & Reflexes

Question 1

What is an Action potential’s task?

Answer 1

• Changes a cell membrane’s voltage, which responds to a stimulus that results in communication of an electrical signal from the Neuron’s Cell body to Nerve terminal
• Briefly changes the charge inside of the cell by making it positive, which goes back to being negative again

Question 2

What does Ca^2+ do at the axon terminal?

Answer 2

When the Depolarization from an AP causes the VG Ca^2+ channels to open, a flood of Ca^2+ enter at the Axon terminal

Question 3

How does the Nervous system discontinue a Neurotransmitter’s signal?

Answer 3

• Presynaptic neuron should stop the release of a neurotransmitter
• Neurotransmitters need to be taken out from the Synaptic cleft by:
  • Enzymatic degradation of neurotransmitter: Synaptic cleft’s enzyme splits down Neurotransmitter, which changes its shape & can’t fit onto post-synaptic cell’s receptor
    
    • Reabsorbing the Neurotransmitter into the Pre-synaptic neuron or any other cell that’s a helper by Endocytosis

Question 4

Causes of the Resting membrane potential?

Answer 4

• Different ion concentrations inside vs. outside of cell:
  
  • Na+/K+ pump: ATP is used to pump 3 Na+ outside and 2 K+ inside of cell
    a. Inside of cell loses one (+) charge net every time it pumps
    b. Makes Na+ and K+ gradients
    i. Low [Na+] inside; High [Na+] outside of cell
    ii. High [K+] inside; Low [K+] outside of cell
    2. High Cl- outside; low Cl- inside of cell
    3. High Ca2+ outside; low Ca2+ inside of cell
• Selective permeability to different ions:
  
  • Membrane lets more K+ pass under RMP conditions
    a. K+ exit the cell through K+ leakage
    channels down its chemical gradient, which causes inside of cell to lose positive charge
• Existence of fixed anions:
  
  • Fixed anions: Big molecules with negative charges that aren’t able to leave cell
    (EX: DNA, proteins, ATP, & more)
  • Causes inside of cell to be more negative

Note: Other ions (e.g. Low Cl^- inside, Low Ca^++ inside of cell, & etc.) also impact RMP value

Question 5

What is Depolarization & its task?

Answer 5

• When inside of cell becomes more positive
• Task: Causes voltage-gate (VG) Na+ and K+ channels to open.

Question 6

What is Hyperpolarization & its task?

Answer 6

• When inside of cell becomes even more negative than during Resting membrane potential
• Task: Stops Neuron from sending electrical impluse/Action potential