Biology
The nervous system & neurons — quick study summary
The nervous system is the body's high-speed communication network. It's split into the central nervous system (CNS — brain and spinal cord) and the peripheral nervous system (PNS — all other nerves). Signals travel as electrical impulses (action potentials) along neurons and as chemical signals (neurotransmitters) across synapses. A resting neuron has a polarised membrane (~−70 mV); depolarisation triggers an all-or-nothing action potential that propagates down the axon.
Key points
- CNS = brain + spinal cord. PNS = everything else (sensory + motor)
- Resting potential ~−70 mV maintained by Na⁺/K⁺ pump and selective ion channels
- Action potential: depolarisation → repolarisation → hyperpolarisation → reset
- Myelin sheath speeds conduction via saltatory propagation between nodes of Ranvier
- Synapse: vesicles release neurotransmitter → binds postsynaptic receptors → new impulse
Practice quiz
Click each question to reveal the answer.
1. What is the approximate resting membrane potential of a typical neuron?
- +30 mV
- 0 mV
- −70 mV
- −40 mV
Answer: −70 mV
The inside of the cell is negative relative to the outside, maintained by the Na⁺/K⁺ pump and selective K⁺ leakage.
2. What is the role of myelin in nerve conduction?
Answer: Insulates the axon and speeds up signal conduction via saltatory propagation
Action potentials 'jump' between unmyelinated nodes of Ranvier, making conduction much faster than continuous propagation.
3. Across a synapse, signals are transmitted by which type of molecule?
Answer: Neurotransmitters
Electrical signals stop at the synapse. Vesicles release neurotransmitters that diffuse across the cleft and bind receptors on the next cell.
Last reviewed: May 2026