Transcript Powerpoint
DO NOW Label the parts of the neuron. Try not to look at your notes! NEURON Dendrites Dendrites – receive messages from other cells and conduct impulses toward the cell body NEURON Dendrites Cell Body Cell Body – the cell’s life-support center NEURON Dendrites Cell Body Axon Axon – the extension of a neuron through which messages are sent to other neurons or to muscles or glands NEURON Dendrites Cell Body Axon Myelin Sheath Myelin Sheath – a layer of fatty cells covering the axon, helps speed up neural impulses NEURON Dendrites Axon Terminals Cell Body Axon Myelin Sheath Axon Terminals – where impulses leave the neuron as neurotransmitters Video: How do nerves work? • https://www.youtube.com/watch?v=uU_4u A6zcE&list=PLhfdMF9uC2pAaqiNgm9tvRu9 gWbGVNwc4&index=18 Neurons – How do they work? • Neurons send messages to other neurons – this is what keeps every part of our body in communication with every other part. • Neurons “fire” – send an impulse (message) down their length dendrite Axon cell body cell body TYPICAL MOTOR NEURON synapse muscle tissue Action Potentials • This “firing” of impulse messages is called the action potential. • An action potential is a brief electrical charge that travels down the axon of the neuron. What causes an impulse to fire or not fire? • When a neuron is at rest, it is called the resting potential • There are electrically charged particles (ions) inside and outside of the neuron • During the resting potential, there is a negative charge on the inside of the neuron compared to the outside. Neuron Communication Resting Potential Action Potentials, cont. • Stimulation from inputs to dendrites causes the cell membrane to open briefly • Positively charged sodium ions flow in through the cell membrane • If resting potential rises above threshold, an action potential starts to travel from the cell body down the axon • Refractory period The “recharging phase” when a neuron, after firing, cannot generate another action potential Neuron Communication All-or-None Principle • The principle that if a neuron fires it will always fire at the same intensity • A strong stimulus can trigger more neurons to fire, and to fire more often, but all action potentials are of the same strength and speed. • A neuron does NOT fire at 30%, 45% or 90% but at 100% each time it fires. Just like a gun, there is no “part-way” firing How is a neuron firing similar to a toilet flushing? • Consider the following concepts: – All-or-none principle – Direction of impulse – Refractory period – Threshold – Resting potential – Action potential