anatomy 12 unit 4 (part 3 action potential) (copy)

relation between neurons and electrical signals

neurons generate electrical signals through brief, controlled, changes in permeability of their cell membranes of particular ions

trait in axoplasm which causes negative polarity

large negative anions (organic proteins) in axoplasm

distribution of ions during resting potential of neuron

na/k pump pushes 3 Na+ out for every 2K+ brought in

action potential definition

• electrochemical change that moves in one direction along length of nerve fiber

• changes in ion concentrations cause changes in voltage

cause of action potential

nerve stimulation: sensory stimuli which leads to message being sent to muscle or gland, thought, electric shock, pH change

depolarisation axomembrane actions

• Na+ protein channels open, Na+ moves from outside to inside

• membrane potential changes from -60mV to +40mV

repolarisation axomembrane actions

• Na+ channels close FIRST

• K+ protein channels open SECOND, K+ move from inside to outside

• membrane potential changes from +40mV to -60mV

recovery/refractory period actions

• protein CARRIER transports na/k across membrane

• 3 Na+ go outside, 2 K+ ions go inside, against gradient

order of action potential process

1. resting potential

2. DEpolarisation

3. REpolarisation

4. recovery/refractory period

myelin sheath function in transmission speed

allows rapid speed of nerve impulses to occur

• 200m/s myelinated vs. 0.5m/s non-myelinated nerve fibers

saltatory conduction (myelinated fibers)

nerve impulses jumps from node of ranvier to next node

non-myelinated fibers process

nerve impulse depolarise and repolarise at each point along fiber