Neve Tissue

Question 1

How is the resting potential established?

Answer 1

• Neuron adds organic anions, decreasing membrane potential
• Electrical force and diffusion acts on anion, trying to drive it out of neuron, but can’t leave because membrane highly impermeable to OAs
• Leak channels allow some ions to pass into and out of the cell
• ATP is used by Na-K pump to transport 3 Na ions out of neuron and 2 K ion into neuron,
• Decreases membrane potential
• Conc of K ions in neuron increases
• Conc of Na ions in neuron decreases
• Electrical force drives K ions into cell, Diffusion force trying to drive K ions out of the cell
• Diffusion force is much larger then electrical force, forcing the K ions to leave through leak channels
• This decreases membrane potential
• This continues to happen until the electrical force is same magnitude as diffusion force, therefore no net movement of K
• For Na, both Electrical and diffusion force driving Na ions into the neuron through leak channels
• But membrane permeability of Na smaller than K, it comes in at much smaller doses
• Resting membrane potential established

Question 2

How are action potentials established?

Answer 2

• In the axon
• Threshold potential determines whether VGCs open (Voltage Gated Channels)
• Temporal and spacial summation of excitatory potential spreads across the membrane of the soma into the initial segment of the axon (trigger zone)
• VGC has mechanism that sense the voltage change
• Threshold potential is crossed, VGCs of Na ion open
• Electrical and Diffusion forces trying to drive Na into axon through open VGCs
• That part of the membrane depolarises
• Trigger the next VGCs in the next part of axon to open
• More Na ions flow into axon
• Called the rising phase (more positive inside than outside the membrane)
• VGCs automatically close at high membrane potential value (+40 or soh
• Na stops flowing into neuron
• Membrane potential decreases rapidly until it’s lower than the resting potential
• Called falling phase
• During this phase, Electical and diffusion forces make K ions exit out of the neuron through leak channels
• K ions also exot through VGCs (slower to open than VG Na Cs)
• VGCs of K ion close when membrane potential lower than resting potential
• Hyperpolarisation (refractory period) occurs, causing membrane to return to resting state (slow because VGCs of K ion take longer to close)
• The movement of Na and K ions into and out of the cells start at the trigger zone, but then continues down the axon

Question 3

What is the natural resting potential of a neuron?

Answer 3

• Outside, more cations than anions
• Inside: more anions than cations
• 60mV usual resting potential
• Conc Potassium ions more inside than outside
• Conc Na ions more outside than inside
• Force of attraction acting on ions
• Potassium more attracted to inside of neuron
• Na also attracted to inside of neuron
• Force of diffusion trying to drive Potassium out of neuron
• Force of diffusion trying to drive Na+ into the neuron