The nervous system — Eduqas A-Level Biology

The nervous system enables rapid communication via electrical impulses along neurones, coordinating responses to stimuli. It comprises the central nervous system (brain and spinal cord) and peripheral nervous system, with synapses transmitting signals chemically using neurotransmitters.

The nervous system is a complex network of specialised cells called neurones that transmit electrical signals rapidly. It is divided into the central nervous system (CNS: brain and spinal cord) and the peripheral nervous system (PNS: nerves connecting CNS to the rest of the body). The system detects stimuli via receptors, processes information, and coordinates responses in effectors such as muscles and glands. Understanding the nervous system is fundamental to grasping how organisms interact with their environment and maintain homeostasis.

In WJEC A-Level Biology, you will explore the structure and function of neurones, the generation and propagation of action potentials, and synaptic transmission. Key topics include resting potential, depolarisation, repolarisation, the all-or-nothing principle, and the role of neurotransmitters. You will also study the reflex arc as a simple neural pathway and the effects of drugs on synaptic transmission. This topic links to homeostasis, the endocrine system, and muscle contraction.

Mastering the nervous system is essential for understanding neurological disorders, drug actions, and the integration of body systems. It also provides a foundation for further study in physiology, medicine, and neuroscience. Practical skills include interpreting graphs of membrane potential changes and calculating conduction velocities.

• →Resting potential: maintained by sodium-potassium pumps and potassium ion channels, typically around -70 mV.
• →Action potential: rapid depolarisation due to voltage-gated sodium channels opening, followed by repolarisation via potassium channels.
• →Saltatory conduction: rapid impulse propagation in myelinated neurones where action potentials occur only at nodes of Ranvier.
• →Synaptic transmission: release of neurotransmitters from presynaptic knob, diffusion across cleft, and binding to receptors on postsynaptic membrane.
• →Reflex arc: neural pathway involving receptor, sensory neurone, relay neurone, motor neurone, and effector, producing an automatic response.

• Components of a nervous response from receptor to effector
• Structure of the spinal cord including dorsal and ventral roots
• Mechanism of the simple reflex arc
• Comparison of nerve nets in Cnidaria with complex nervous systems
• Structure of a motor neurone
• Nature and transmission of the nerve impulse
• Analysis of oscilloscope traces for action potentials
• Factors affecting speed of conduction
• Structure and role of a synapse
• Process of synaptic transmission
• Effects of organophosphates and psychoactive drugs on impulse transmission

• 💡Be prepared to draw and label a motor neurone accurately
• 💡Practice interpreting oscilloscope traces to identify phases of an action potential
• 💡Ensure you can explain the sequence of events during synaptic transmission
• 💡Use precise terminology when describing the role of neurotransmitters
• 💡Use precise terminology: 'depolarisation' not 'firing', 'neurotransmitter' not 'chemical'. Marks are awarded for correct use of key terms.
• 💡In questions on synaptic transmission, always mention calcium ions and vesicle fusion. Many students miss this step.
• 💡When describing a reflex arc, explicitly state each component in order: receptor → sensory neurone → CNS (relay neurone) → motor neurone → effector.

• Confusing the roles of the dorsal and ventral roots in the spinal cord
• Inaccurate labeling of motor neurone diagrams
• Misinterpreting oscilloscope traces of action potentials
• Failing to distinguish between the structure and function of a synapse
• Misconception: The action potential moves along the axon like a wave of electricity. Correction: It is a wave of depolarisation caused by local currents; the impulse is regenerated at each point.
• Misconception: Neurotransmitters are always excitatory. Correction: Some neurotransmitters (e.g., GABA) are inhibitory, causing hyperpolarisation and reducing the chance of an action potential.
• Misconception: Myelination speeds up conduction because it insulates the axon completely. Correction: Myelin prevents ion leakage, but action potentials only occur at nodes; the impulse jumps, not flows continuously.

1. 1Week 1: Focus on neurone structure and resting potential. Draw and label a neurone, then explain how the sodium-potassium pump maintains the resting potential.
2. 2Week 2: Learn the stages of an action potential (depolarisation, repolarisation, hyperpolarisation). Practice drawing a graph and labelling each phase.
3. 3Week 3: Study synaptic transmission. Create a flow diagram of events from action potential arrival to neurotransmitter binding.
4. 4Week 4: Consolidate with past paper questions on reflex arcs and saltatory conduction. Review mark schemes to understand examiner expectations.

• 📋Multiple-choice questions on neurone types and functions (e.g., identify sensory neurone from a diagram).
• 📋Short-answer questions on the stages of an action potential (e.g., 'Explain how depolarisation occurs').
• 📋Data analysis questions involving graphs of membrane potential changes (e.g., calculate rate of depolarisation).
• 📋Extended response (6 marks) on synaptic transmission or the role of myelination.