SL Content Statements

• C2.2.1

  Neurons as cells within the nervous system that carry electrical impulses

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  Students should understand that cytoplasm and a nucleus form the cell body of a neuron, with elongated nerve fibres of varying length projecting from it. An axon is a long single fibre. Dendrites are multiple shorter fibres. Electrical impulses are conducted along these fibres.
  

• C2.2.2

  Generation of the resting potential by pumping to establish and maintain concentration gradients of sodium and potassium ions

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  Students should understand how energy from ATP drives the pumping of sodium and potassium ions in opposite directions across the plasma membrane of neurons. They should understand the concept of a membrane polarization and a membrane potential and also reasons that the resting potential is negative.
  

• C2.2.3

  Nerve impulses as action potentials that are propagated along nerve fibres

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  Students should appreciate that a nerve impulse is electrical because it involves movement of positively charged ions.
  

• C2.2.4

  Variation in the speed of nerve impulses
  

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  Compare the speed of transmission in giant axons of squid and smaller non-myelinated nerve fibres. Also compare the speed in myelinated and non-myelinated fibres.
  AOS: Students should be able to describe negative and positive correlations and apply correlation coefficients as a mathematical tool to determine the strength of these correlations. Students should also be able to apply the coefficient of determination (R2) to evaluate the degree to which variation in the independent variable explains the variation in the dependent variable. For example, conduction speed of nerve impulses is negatively correlated with animal size, but positively correlated with axon diameter.
  

• C2.2.5

  Synapses as junctions between neurons and between neurons and effector cells
  

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  Limit to chemical synapses, not electrical, and these can simply be referred to as synapses. Students should understand that a signal can only pass in one direction across a typical synapse.
  

• C2.2.6

  Release of neurotransmitters from a presynaptic membrane

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  Include uptake of calcium in response to depolarization of a presynaptic membrane and its action as a signalling chemical inside a neuron.
  

• C2.2.7

  Generation of an excitatory postsynaptic potential

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  Include diffusion of neurotransmitters across the synaptic cleft and binding to transmembrane receptors. Use acetylcholine as an example. Students should appreciate that this neurotransmitter exists in many types of synapse including neuromuscular junctions.
  

AHL Content Statements

• C2.2.8

  Depolarization and repolarization during action potentials
  

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  Include the action of voltage-gated sodium and potassium channels and the need for a threshold potential to be reached for sodium channels to open.
  

• C2.2.9

  Propagation of an action potential along a nerve fibre/axon as a result of local currents

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  Students should understand how diffusion of sodium ions both inside and outside an axon can cause the threshold potential to be reached.
  

• C2.2.10

  Oscilloscope traces showing resting potentials and action potentials

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  AOS: Students should interpret the oscilloscope trace in relation to cellular events. The number of impulses per second can be measured.
  

• C2.2.11

  Saltatory conduction in myelinated fibres to achieve faster impulses

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  Students should understand that ion pumps and channels are clustered at nodes of Ranvier and that an action potential is propagated from node to node.
  

• C2.2.12

  Effects of exogenous chemicals on synaptic transmission

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  Use neonicotinoids as an example of a pesticide that blocks synaptic transmission, and cocaine as an example of a drug that blocks reuptake of the neurotransmitter.
  

• C2.2.13

  Inhibitory neurotransmitters and generation of inhibitory postsynaptic potentials

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  Students should know that the postsynaptic membrane becomes hyperpolarized.
  

• C2.2.14

  Summation of the effects of excitatory and inhibitory neurotransmitters in a postsynaptic neuron

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  Multiple presynaptic neurons interact with all-or-nothing consequences in terms of postsynaptic depolarization.
  

• C2.2.15

  Perception of pain by neurons with free nerve endings in the skin

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  Students should know that these nerve endings have channels for positively charged ions, which open in response to a stimulus such as high temperature, acid, or certain chemicals such as capsaicin in chilli peppers. Entry of positively charged ions causes the threshold potential to be reached and nerve impulses then pass through the neurons to the brain, where pain is perceived.
  

• C2.2.16

  Consciousness as a property that emerges from the interaction of individual neurons in the brain

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  Emergent properties such as consciousness are another example of the consequences of interaction.