C2.2 Neural signalling

Question 1

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

Answer 1

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.

Question 2

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

Answer 2

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.

Question 3

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

Answer 3

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

Question 4

C2.2.4—Variation in the speed of nerve impulses

Answer 4

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.
Application of skills: 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.

Question 5

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

Answer 5

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.

Question 6

C2.2.6—Release of neurotransmitters from a presynaptic membrane

Answer 6

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

Question 7

C2.2.7—Generation of an excitatory postsynaptic potential

Answer 7

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

Question 8

C2.2.8—Depolarization and repolarization during action potentials

Answer 8

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.

Question 9

C2.2.9—Propagation of an action potential along a nerve fibre/axon as a result of local currents

Answer 9

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

Question 10

C2.2.10—Oscilloscope traces showing resting potentials and action potentials

Answer 10

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

Question 11

C2.2.11—Saltatory conduction in myelinated fibres to achieve faster impulses

Answer 11

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.

Question 12

C2.2.12—Effects of exogenous chemicals on synaptic transmission

Answer 12

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

Question 13

C2.2.13—Inhibitory neurotransmitters and generation of inhibitory postsynaptic potentials

Answer 13

Students should know that the postsynaptic membrane becomes hyperpolarized.

Question 14

C2.2.14—Summation of the effects of excitatory and inhibitory neurotransmitters in a postsynaptic neuron

Answer 14

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

Question 15

C2.2.15—Perception of pain by neurons with free nerve endings in the skin

Answer 15

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.

Question 16

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

Answer 16

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