Nerve Impulses and Muscle Function
Ever wondered how your brain tells your muscles to move in milliseconds? It's all about action potentials - electrical signals that race along nerve cells at incredible speeds.
When a neuron is at rest, it maintains a resting potential of about -70mV. This happens because there are more positive ions outside the cell than inside. The key players are sodium and potassium ions, which create this electrical imbalance through the work of ion pumps.
Depolarisation kicks off when sodium channels open and Na+ floods into the cell, making it less negative. Once it hits the threshold of -55mV, there's no stopping it - the action potential fires and reaches +40mV. Then repolarisation occurs as potassium channels open and K+ leaves the cell, bringing the voltage back down.
Muscle fibres come in two main types: slow twitch (great for endurance, use oxygen efficiently) and fast twitch (powerful but tire quickly, perfect for explosive movements). Inside muscle cells, actin and myosin are the protein filaments that actually create contraction. The sarcoplasmic reticulum stores calcium ions that trigger this contraction process.
Quick Tip: Remember that Parkinson's disease occurs when dopamine-producing neurons die, causing tremors and movement problems. It's often treated with L-DOPA medication.
