Question

1. Define an action potential. How are the Na+, K+, and Ca+ ions involved in an action potential? How does the myelin speed up its transmission?
2. Define a neurotransmitter. Where are they stored and how do they relay an action potential message from one cell to the next?
3. Define threshold. How do neurotransmitters bring target cells toward or away from threshold. What happens to the response of the target cell if threshold is not reached? What happens if threshold is reached? Once threshold is reached, can the target cell get turned “off”?

Answer 1

1. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential. The action potential is an explosion of electrical activity that is created by a depolarizing current. When an action potential happens, the sodium (Na+) ion channels (here shown in green) on the axon open and the Na+ rushes in. Since the Na+ (red) is positively charged, it makes the inside of the axon a little more positively charged. ... Now the positive potassium ions (blue) rush out, taking positive charges with them. Most nerve fibres are surrounded by an insulating, fatty sheath called myelin, which acts to speed up impulses. The myelin sheath contains periodic breaks called nodes of Ranvier. By jumping from node to node, the impulse can travel much more quickly than if it had to travel along the entire length of the nerve fibre.

2.  Chemicals known as neurotransmitters are stored in membrane-bound vesicles at the axon terminal of neurons.stored in pre synaptic cell. When a nerve impulse reaches the end of an axon, the axon releases chemicals called neurotransmitters. Neurotransmitters travel across the synapse between the axon and the dendrite of the next neuron. Neurotransmitters bind to the membrane of the dendrite