Sodium Potassium Pump

Resting Membrane Potential

• At rest, the insides of a neuron has a -70 mV charge comnpared to the outside of a the cell

• Neuron maintains a. stable voltage across its membrane called a resting membrane potential

1st factor that contribute to RMP

• Large negatively charged proteins are located inside the neurons

2nd factor that contribute to RMP

• Channels in the. membrane allow K+. (more open at rest) to diffuse postively out more easily than Na+

• Therefore more positive charges are outside the neuron vs inside

3rd. factor that contribute to RMP

• Na+/K+ pump moves these ions different ratios

• For every molecule of aTP that is hydrolyzed into ATP + Pi, 3 Na+ move out

• At rest the neuron is said to be polarized because there is a potenntial difference across the cell membrane

Sodium-Potassium Pump

• System uses ATP to move Na+ and K+ against their concentration gradient to maintain a -70mV charge

• As a result of the uneven movement in the K+ and Na+ and excess positive charge results outside the membrane

• Na and k+ also move via diffusion along their concentration gradients but because K+ can move out more easily there ends up being a -70mV charge inside the neuron

Action Potential

• change in charge that occurs when an euron has been stimulated and the threshold has been met

• Action potential is a nerve impulse

• During Action Potential, the k+ gates close and Na+ gates open

Depolarization

• Action potential causess it

• Charge reversal from -70mV to 40mV due to influx of Na+

• Only happens if the threshold is met and follolw the “All or Nothing Prinnciple” if a stimulus causes the threshold to be met, then an AP will occur

• If its not met, no AP will occur

AP 1ST Step

• If the threshold is met an action potentila is triggered

AP 2nd Step

• Voltage gated Na+ channels open, allowing sodium ions to move into the cell, causing +40mv, thus depolarization

AP 3rd Step

• Na+ channels close at 40mV and K+ channels open

• k+ exits rapidly and begins to repolraize then hyperpolarize the membrane (-90mV)

AP 4th Step

• At. -90mV K+ channels close

• Resting membrane potentiaal (polarizationn) is restored

Refracting Period

• For a few milliseconds during hyperpolarization, the membrane cant be stimulated preventing another AP from occuring

Synapse

• Connection between 2 neurons

• AP traavels along the axon to axon terminal

• AP cannot jump the gap, so chemicals are needed to keep the signal going

Chemical Transmission Across Synapse - Step 1

• Once an AP reaches the axon terminnal in the presynaptic cell, the AP trigges voltage gated Ca 2+ channels to open the presynaptic membrane

• Ca 2+ enters the presynaptic neuron and activates synaptic vesicles (sacs)

Chemical Transmission Across Synapse - Step 2

• Vesicles that contain neurotransmitters t hen fuse with the membrane

Chemical Transmission Across Synapse - Step 3

• Vesicles release the neurotransmitters inn the synaptic cleft through exocytosis

Chemical Transmission Across Synapse - Step 4

• Neurotransmitters bind to receptors on the post synaptic neuron and triggers an AP to occur by allowingn ion specific channnnels to openn

• Neurotransmitters can be excitatory which causes depolarization and AP which causes Na+ channels to openn

• Or can be inhibitory which causes hyperpolarization and no AP which causes K+ channels to open

Transporter Proteins

• Transporter proteins on the pre-synaptic membrane help with the reuptake of neurotransmitters from the synaptic back into the presynaptic neuron

  • Reverses the effects of neurotransmitters

Enzzymes

• Enzymes in the synpatic cleft break down neurotransmitters to be reabsorbed back into the pre-synaptic neuron

• Reverses the effects of neurotransmitters