graded potentials

For an open channel, what factors determine in which direction ions move through the channel?

1. Concentration gradient

2. Electrical gradient

3. Both – the electrochemical gradient

Describe the characteristics of a graded potential & give 3 examples

• Variable Amplitude: Strength of the potential depends on the stimulus strength.

• Decremental Spread: The potential weakens as it moves away from the point of origin.

• No Threshold or Refractory Period: Can occur without a minimum required stimulus, and no recovery period.

• Can Be Depolarizing or Hyperpolarizing: Can either make the cell more positive (depolarize) or more negative (hyperpolarize).

• Post-synaptic Potential (PSP)

• Receptor Potential

• Generator Potential

Describe 4 characteristics of voltage-gated ion channels

• Voltage Sensitivity: Open or close in response to changes in membrane potential.

• Ion Selectivity: Only allow specific ions (e.g., Na+, K+, Ca2+) to pass through.

• Rapid Activation and Inactivation: Open and close quickly, with many channels becoming inactivated after opening.

• Regulation of Electrical Signals: Essential for generating action potentials and transmitting signals in neurons and muscle cells.

Describe the changes that occur in the membrane potential during
an action potential with the aid of a diagram

• Resting Potential: -70 mV.

• Depolarization: Sodium enters, making the neuron positive.

• Repolarization: Potassium exits, making the neuron negative again.

• Hyperpolarization: Neuron gets a bit more negative than usual.

• Back to Resting: Neuron returns to -70 mV.

Describe the gating of the Na+ & K+ voltage-gated ion channels

Define the all-or-none law of the AP

The all-or-none law of an action potential (AP) states that once a neuron reaches a certain threshold level of stimulation, an action potential will be triggered. The key idea is that the action potential either occurs fully or not at all—there is no partial or incomplete action potential.

Describe the 2 ways by which an AP is propagated down a neurone

1. Continuous Conduction (in unmyelinated axons):

   • The action potential travels step-by-step along the entire axon.

   • Each segment depolarizes in sequence, which is slower.

2. Saltatory Conduction (in myelinated axons):

   • The action potential "jumps" from one node of Ranvier to the next, speeding up the signal.

   • Myelin insulates the axon, allowing the AP to only occur at the nodes, where there are high concentrations of sodium channels.

which method of AP propogation is faster

Saltatory conduction is much faster than continuous conduction.

Define the refractory period & describe the underlying mechanisms

• Absolute Refractory Period: The neuron cannot fire another action potential due to inactivation of sodium channels.

• Relative Refractory Period: A stronger stimulus is needed to trigger another action potential because the neuron is still in the process of returning to its resting potential, with potassium channels still open.

These refractory periods are essential for controlling the frequency of action potentials and ensuring that signals travel in only one direction along the axon.