C2.2 Neural signaling_SL

C2.2 Neural signalling

Interaction and interdependence—Cells

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

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

Neurons: specialised cells that transmit electrical impulses within the nervous system

Myelin sheath: improves the conduction speed of electrical impulses along the axon

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

Membrane potential: the difference in charge across the cell membraneResting potential: difference in charge when a neuron is not firing

• The inside of the neuron is more negative than the outside (–70 mV)

• The maintenance is an active process (requires hydrolysis ofATP) controlled by sodium-potassium pumps (B2.1).

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

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

Nerve impulses: action potentials that are propagated along nerve fibres

Action potentials: rapid changes in charge across the membrane that occur when a neuron is firing due to the movement of positively charged ions (electrical change)

• Depolarisation:
• Sodium channels open
• Sodium ions move into the neuron, creating a positive membrane potential (+30 mV)
• Repolarization:
• Potassium channels open
• Potassium ions move out and re-establish the negative membrane potential

B2.1.14 Gated ion channels in neurons (AHL)

The sodium and potassium channels are examples of voltage-gated ion channels

• Ion channels are integral membrane proteins with an hydrophilic inner pore through which only specific ions may pass
• Allows ions to either enter or exit a cell according to the concentration gradient (facilitated diffusion)
• Voltage-gated ion channels: a change in voltage at one point of the axon will trigger their opening

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

Opening of voltage-gated ion channels produces depolarization of the next segment of the membrane and so on. The resting potential must afterwards be restored by the Na/K pump before a new action potential can occur, therefore, a refractory period exist where the membrane is not excitable. Consequently, transmission of the nerve impulse along the axon is unidirectional

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

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

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

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

Try this simulation:

C2.2.4 Variation in the speed of nerve impulses

Factors that affect conduction speed:

• Size of the organism: larger organisms have more complex neural pathways, with more synaptic gaps, creating a delay in transmission (negative correlation)

• Axon diameter: decreases longitudinal resistance, facilitating propagation (positive correlation)
• Myelin sheath (positive correlation)
• Temperature (positive correlation)

C2.2.4 Variation in the speed of nerve impulses

Giant squids have very large axon diameters and consequently have faster conduction speeds that other comparable animals, but the speeds are slower than most myelinated fibres

C2.2.4 Variation in the speed of nerve impulses

Application of skills: Correlations Correlation coefficient (r): a mathematical tool to determine the strength of correlation between two variables.

Coefficient of determination (R2): evaluates the degree to which variation in the independent variable explains the variation in the dependent variable.

C2.2.4 Variation in the speed of nerve impulses

Application of skills: Correlations

Complete the activity on Managebac

Open Day activity about reaction speed

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

Synapses: physical gaps that separate neurons from other cells Neurons transmit information unidirectionally across synapses by converting the electrical signal into a chemical signal (neurotransmitter)

C2.2.6 Release of neurotransmitters from a presynaptic membrane AND C2.2.7 Generation of an excitatory postsynaptic potential

C2.2.6 Release of neurotransmitters from a presynaptic membrane AND C2.2.7 Generation of an excitatory postsynaptic potential

C2.2.6 Release of neurotransmitters from a presynaptic membrane AND C2.2.7 Generation of an excitatory postsynaptic potential

C2.2.6 Release of neurotransmitters from a presynaptic membrane AND C2.2.7 Generation of an excitatory postsynaptic potential

C2.2.6 Release of neurotransmitters from a presynaptic membrane AND C2.2.7 Generation of an excitatory postsynaptic potential

C2.2.7 Generation of an excitatory postsynaptic potential

Acetylcholine is a neurotransmitter used in many synapses through the nervous system:

• In the neuromuscular junctions trigger voluntary muscular contractions

• In the autonomic nervous system to promote parasympathetic responses (‘rest and digest’)

B2.1.14 Gated ion channels in neurons (AHL)

Ligand-gated ion channels: Muscles contain nicotinic acetylcholine receptors that will trigger the opening of an ion channel when activated Binding of acetylcholine to these receptors results in the influx of ions into the muscle, triggering a cascade that results in muscular contraction (B3.3, AHL only)