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