Neural signalling and muscle contraction

Learning objectives

Describe the structure of a motor neuron, and (HL) explain how the myelin sheath and the nodes of Ranvier produce saltatory conduction that greatly increases the speed of an impulse

Explain the resting potential as a negative potential across the axon membrane maintained by the sodium–potassium pump and by differences in membrane permeability to sodium and potassium ions

(HL) Explain an action potential as a wave of depolarisation caused by the opening of voltage-gated sodium channels followed by repolarisation through voltage-gated potassium channels, and explain the threshold, the all-or-nothing response and the refractory period

Describe transmission across a chemical synapse: the arrival of the impulse, the entry of calcium ions, the release of neurotransmitter by exocytosis, binding to receptors on the postsynaptic membrane and the subsequent breakdown of the neurotransmitter

(HL) Distinguish excitatory from inhibitory postsynaptic potentials, explain spatial and temporal summation at a synapse, and explain how substances such as neonicotinoid pesticides interfere with transmission at cholinergic synapses

(HL) Explain the sliding filament model of muscle contraction using the structure of a sarcomere, the cross-bridge cycle between myosin heads and actin, the roles of ATP, calcium ions, tropomyosin and troponin, and the action of antagonistic muscle pairs across a joint