Topic 8: Neurons & Action Potentials

Spinal Reflex Arc

1. stimuli detected by receptors cells

2. impulse travels by sensory neuron through dorsal root ganglion

3. relay neuron send impulse to CNS where it’s processes and a new signal is sent out

4. impulse travels by motor neuron through ventral root to effectors to carry out the task

Resting Potential

• Na/K pump actively moves Na+/K+ outside the axon forming an electrochemical gradient

• K+ channels are open allowing K+ to diffuse back

outside axon: high [Na+], low [K+], more positive

inside axon: low [Na+], high [K+], less positive

depolarization

Na+ channels open allowing Na+ ions to diffuse back in

outside axon: low [Na+], high [K+], less positive

inside axon: high [Na+], low [K+], more positive

action potential triggered

re-polarization

Na+ channels close

K+ diffuse out

outside axon: high [Na+], low [K+], more positive

inside axon: low [Na+], high [K+], less positive

hyper-polarization

K+ diffuse out

Na+ & K+ exit

restoring resting potential

Refractory Period

neuron cannot be stimulated and an action potential cannot occur cause the ion channels are recovering so they can’t open it ensures that action potentials don’t overlap

Saltatory Conduction

myelin sheath acts as an insulator, so the ions can only move in the gaps (called nodes of ranvier) so the impulse to ‘jumps’ from node to node.