Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 479–489 of the course textbook. Image credits are on slide 16.
When the membrane reaches the threshold (about −50 mV), voltage-gated Na+ channels open and Na+ diffuses in: the inside becomes positive (depolarization). At about +30 mV they close and voltage-gated K+ channels open; K+ diffuses out and the inside becomes negative again (repolarization). Below threshold, no action potential occurs: it is all-or-nothing.
Na+ that has entered diffuses along inside the axon, while Na+ outside diffuses towards the depolarized region. These local currents bring the next region to threshold, so its Na+ channels open and the impulse moves on.
An oscilloscope plots membrane potential against time: a flat resting potential near −70 mV, a steep rise to about +30 mV, a fall, a brief dip below rest, then recovery, all within a few milliseconds.
Myelin insulates the axon. Pumps and channels are clustered at the nodes of Ranvier, so the action potential jumps from node to node. Myelinated axons conduct many times faster than unmyelinated ones of the same width.
Neonicotinoid pesticides bind nicotinic acetylcholine receptors in insects and are not broken down, so transmission is blocked. Cocaine blocks the transporters that reabsorb dopamine, so dopamine stays in the cleft and keeps stimulating.
Neurotransmitters such as GABA open channels that let chloride ions in or potassium ions out. The postsynaptic membrane becomes hyperpolarized, an inhibitory postsynaptic potential, so an action potential is less likely.
A neuron receives many excitatory and inhibitory inputs. Their effects add together; only if the total reaches threshold does the neuron fire, and then fully.
Free nerve endings in the skin have channels for positive ions that open with heat, acid or chemicals such as capsaicin. Ions enter, threshold is reached and impulses travel to the brain, where pain is perceived.
Consciousness is an emergent property: it is not found in any single neuron but arises from the interactions of billions of neurons in the brain.
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Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
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A printable worksheet covering all nine statements, from quick recall to data questions and a longer answer. It has 40 marks and takes about 40 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Printed oscilloscope trace with scale, ruler
Safety: No practical hazards.
Carry this out with your teacher's supervision and follow your school's lab rules.
In 1921 Otto Loewi showed chemical transmission using two frog hearts. He later said that the idea came to him in a dream.
The idea may have come from a dream, but the evidence came from an experiment. Consider how discovery and justification differ.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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