C2.2  Neural Signaling

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How are electrical signals generated and moved within neurons?
• How can neurons interact with other cells?

​
​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• In what ways are biological systems regulated?
• How is the structure of specialized cells related to function?

Resources:

• At SHS, Topic C2.2 is taught in the Cellular Differentiation, Signaling Within Neurons and Signaling Between Neurons units. 
• Quizlet study set for this topic.  Coming soon!
• View the general sequence of the SHS course
• View the SHS units mapped to the IB Biology curriculum roadmap

C2.2.1— Neurons as cells within the nervous system that carry electrical impulses.  

• State the function of the following neuron cell parts:  dendrites, axon and cell body.
• Identify the cell body, axon and dendrites in diagrams of typical sensory and motor neurons. ​

C2.2.2— Generation of the resting potential by pumping to establish and maintain concentration gradients of sodium and potassium ions.

• Define membrane potential. 
• Define resting potential.
• Outline three mechanisms that together create the resting potential in a neuron.
• State the voltage of the resting potential.
• Outline the six steps of sodium-potassium pump action.

​C2.2.3— Nerve impulses as action potentials that are propagated along nerve fibers.

• Define nerve impulse.
• Define action potential.

C2.2.4— Variation in the speed of nerve impulses.

• Outline the correlation between conduction speed of nerve impulses and axon diameter.
• Explain the difference in nerve impulse speed for myelinated and unmyelinated fibers.
• State the correlation between conduction speed of nerve impulses and animal size. ​

C2.2.5-- Synapses as junctions between neurons and between neurons and effector cells.

• Define synapse, synaptic cleft and effector.
• List examples of effector cells.
• State that a signal can only pass in one direction across a typical synapse.
• State the role of neurotransmitters.
• State that neurotransmitters can either be excitatory or inhibitory.​​

C2.2.6- Release of neurotransmitters from a presynaptic membrane.

• Outline the mechanism of synaptic transmission occurring at a presynaptic cell, including the role of depolarization, calcium ions, exocytosis and diffusion.
• State that calcium functions as a chemical signal triggering exocytosis of neurotransmitter from a presynaptic cell.

C2.2.7- Generation of an excitatory postsynaptic potential.

• Outline the mechanism of synaptic transmission occurring at a post-synaptic cell, including the role of neurotransmitters, diffusion, receptors, gated ion channels, threshold potential and action potential. 
• State that acetylcholine is one of the most common neurotransmitters in both invertebrates and vertebrates and is used as the neurotransmitter in many synapses including between neurons and muscle fibers.
• Outline the digestion of acetylcholine by acetylcholinesterase.
  

AHL ​C2.2.8- Depolarization and repolarization during action potentials. 

• State that an action potential is only initiated if the threshold potential is reached. 
• Define depolarization. 
• Outline the mechanism of depolarization during an action potential using voltage gated sodium channels.
• Define repolarization. 
• Outline the mechanism of repolarization during an action potential using voltage gated potassium channels.

AHL ​C2.2.9- Propagation of an action potential along a nerve fiber/axon as a result of local currents.

• Describe the movement of sodium ions in a local current.
• State that local currents cause each successive part of the axon to reach the threshold potential.
• Explain how the movement of sodium ions propagates an action potential along an axon.
• Outline the cause and consequence of the refractory period after depolarization.

AHL ​C2.2.10- Oscilloscope traces showing resting potentials and action potentials.

• Outline the use of oscilloscopes in measuring membrane potential.
• Annotate an oscilloscope trace to show the resting potential, action potential (depolarization and repolarization), threshold potential and refractory period.
• Deduce the number of nerve impulses per second from an oscilloscope trace.

AHL ​​​C2.2.11- Saltatory conduction in myelinated fibers to achieve faster impulses.

• Describe the structure of a myelinated nerve fiber.
• Outline how the myelination of neurons allows for saltatory conduction, in which the differences in the distribution of electrically charged ions across the membrane can effectively jump from node of Ranvier to node of Ranvier.  
• State that in myelinated neurons, the gated and non-gated Na+ and K+ ion channels are clustered down the axon at nodes of Ranvier.

AHL ​​​C2.2.12- Effects of exogenous chemicals on synaptic transmission.

• Define exogenous chemicals.
• Outline the effects of neonicotinoids on synaptic transmission. 
• Outline the effects of cocaine on synaptic transmission.

AHL ​​​C2.2.13- Inhibitory neurotransmitters and generation of inhibitory postsynaptic potentials.

• Compare inhibitory and excitatory neurotransmitters.
• Outline the inhibitory mechanism of the neurotransmitter GABA.
• Outline the consequence of hyperpolarization by inhibitory neurotransmitters.

AHL ​​​C2.2.14- Summation of the effects of excitatory and inhibitory neurotransmitters in a postsynaptic neuron.

• Describe the effects of excitatory and inhibitory neurotransmitters on the ability of a postsynaptic cell to reach its threshold potential. 
• Define summation.
• Interpret graphical representations of the summation of combinations of excitatory and inhibitory neurotransmitters.

AHL ​​​C2.2.15- Perception of pain by neurons with free nerve endings in the skin.

• Describe the mechanism by which environmental stimuli are able to activate nerve endings in the skin, including the role of receptor proteins, ions channels, and threshold potential.
• List stimuli which can trigger a pain response. 
• Outline the flow of information during the pain response. ​

AHL ​​​C2.2.16- Consciousness as a property that emerges from the interaction of individual neurons in the brain.

• Define emergent property.
• State that new properties emerge at each level of biological organization.
• Outline consciousness as an emergent property.