1Define a transducer.
A cell that converts stimulus energy into an electrical impulse.
2What is the resting potential of a neurone?
-70 mV.
3How is the resting potential maintained?
By the sodium–potassium pump and potassium leakage channels.
4Define depolarization.
A reversal of membrane potential to about +40 mV.
5What causes depolarization?
Voltage-gated sodium channels open and sodium ions enter.
6What is repolarization?
Sodium channels close and potassium channels open, allowing potassium to leave.
7What is the refractory period?
A short time when the neurone cannot be stimulated.
8Define the all-or-nothing law.
An action potential only occurs if threshold is reached and is always the same size.
9What is saltatory conduction?
Impulse jumps between nodes of Ranvier in myelinated neurones.
10What are Schwann cells?
Cells that form the myelin sheath around axons.
11What is a synapse?
The junction between two neurones.
12Name a common neurotransmitter.
Acetylcholine.
13What is the role of calcium ions at a synapse?
They cause vesicles to fuse with the presynaptic membrane.
14What enzyme breaks down acetylcholine?
Acetylcholinesterase.
15What is summation?
The build-up of neurotransmitters to reach threshold.
16What is the difference between temporal and spatial summation?
Temporal is repeated impulses from one neurone; spatial is impulses from multiple neurones.
17Define a reflex arc.
The pathway of a nerve impulse in a rapid, involuntary response.
18List the components of a reflex arc.
Receptor → sensory neurone → relay neurone → motor neurone → effector.
19What is grey matter?
CNS tissue containing cell bodies and non-myelinated fibres.
20What is white matter?
CNS tissue containing myelinated axons.
21How does a nerve net differ from a vertebrate nervous system?
It is slower, non-myelinated, and impulses travel in both directions.
22Name an organism with a nerve net.
Hydra.
23What is an effector?
A muscle or gland that produces a response.
24What is hyperpolarization?
When membrane potential becomes more negative than resting potential.
25What is the function of the myelin sheath?
To insulate axons and increase transmission speed.
26What is the threshold potential?
The level of depolarization needed to trigger an action potential.
27What is the synaptic cleft?
The gap between presynaptic and postsynaptic membranes.
28How do organophosphates affect synapses?
They inhibit cholinesterase, causing continuous stimulation.
29What is the role of the sodium–potassium pump?
To maintain the resting potential by active ion transport.
30Why are impulses one-way across a synapse?
Neurotransmitters are released presynaptically and receptors are postsynaptic only.