C2.2  Neural Signaling

Theme:  Interaction and Interdependence

In neural signaling, interaction occurs between ions, neurotransmitters, and specialized membrane proteins.

• The action potential is driven by the interaction between Na+ and K+ ions and voltage-gated channels. When the membrane potential reaches a threshold, these channels interact with the electrical field to change shape, allowing ions to move across the membrane.
• At the synapse, interaction is chemical. Neurotransmitters are released from the presynaptic neuron and interact with ligand-gated ion channels on the postsynaptic membrane. This specific binding event converts a chemical signal back into an electrical one.

The nervous system relies on the interaction of multiple cells and structures to create a functional response.

• A sensory neuron, an intermediate neuron (relay), and a motor neuron are mutually dependent. If any one "link" in this chain fails, the organism cannot respond to a stimulus.
• The brain depends on constant feedback from sensory organs to adjust its output response.
  
• Neurons are highly dependent on myelin (produced by Schwann cells). Myelination allows for saltatory conduction; without this interdependence, neural signaling would be too slow for complex coordination .
• Neural signaling is interdependent with the muscular system. The nervous system provides the command, but it depends on the musculoskeletal system to execute the action. 

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?

Key Terms to Know: * higher level only

Acetylcholine
Acid*
Action Potential
Adenosine Triphosphate (ATP)
Axon
Axon Diameter
Brain*
Calcium Ion
Capsaicin*
Cell Body
Cocaine*
Coefficient of Determination (R^2)
Concentration Gradient
Conduction Speed
Consciousness*
Cytoplasm
Dendrite
Dependent Variable
Depolarization
Diffusion
Effector Cell
Electrical Impulse
Emergent Property*
Excitatory Neurotransmitter*

Excitatory Postsynaptic Potential
Exogenous Chemical*
Free Nerve Ending*
Hyperpolarize*
Independent Variable
Inhibitory Neurotransmitter*
Inhibitory Postsynaptic Potential*
Ion Pump
Local Current*
Membrane Polarization
Membrane Potential
Myelinated
Negative Correlation
Neonicitinoid*
Nerve Fibre
Nervous System
Neurotransmitter
Neurotransmitter Reuptake*
Node Of Ranvier*
Non-Myelinated
Nucleus
Neuromuscular Junction
Neuron
Oscilloscope Trace*

Pain*
Pesticide*
Plasma Membrane
Positive Correlation
Postsynaptic Cell*
Potassium Ion
Presynaptic Cell
Repolarization*
Resting Potential
Saltatory Conduction*
Signaling Chemical
Skin*
Sodium Ion
Squid
Stimulus*
Summation*
Synapse
Synaptic Cleft
Temperature*
Threshold Potential*
Transmembrane Receptor
Variation
Voltage-Gated Channel*

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 gap 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.​​​

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 action potential can effectively jump from node of Ranvier to node of Ranvier. 
  
• ​State that in myelinated neurons, the 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.

• ​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.