Neural signalling: impulses and synapses
הוצג| English | משמעות |
|---|---|
| action potential/ˈækʃn pəˈtenʃl/ | פוטנציאל פעולה |
| synapse/ˈsɪnæps/ | סינפסה |
What would explain this observation?
- A stronger stimulus can increase impulse frequency while each action potential 动作电位 remains a similar size.
Build the model
- An action potential is a brief change in membrane potential involving voltage-gated ion channels.
- Depolarization followed by repolarization propagates along a neuron.
- At a chemical synapse 突触, transmitter release can alter the next cell membrane potential.
- action potential: A brief propagating change in membrane potential.
- synapse: A junction for communication between cells.
How can stimulus intensity affect an all-or-none signalling system?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Each action potential is all-or-none with fixed amplitude, so intensity is coded by how often impulses fire and how many neurons are recruited. Amplitude cannot grow, and removing ion gradients would abolish signalling.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- The all-or-none principle applies to an individual action potential.
- Stimulus information can be encoded by frequency and recruitment.
- Myelination permits saltatory conduction between nodes rather than making ions move freely through myelin.
In the lab: Interpret supplied voltage-time traces and compare time intervals. Identify threshold, rising phase and recovery before explaining ions. Use classroom models rather than electrical stimulation of people.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: 30 impulses occur in 0.50 s.
- Frequency = count/time = 30/0.50 = 60 Hz.
- This is impulse frequency, not an estimate of propagation speed.
Your turn: 24 impulses occur in 0.40 s. Find impulse frequency.
24 impulses occur in 0.40 s. Find impulse frequency.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 60 Hz. Known: 24 impulses in 0.40 s. Use frequency = count / time. Frequency = 24/0.40 = 60 Hz. This is firing frequency, not conduction speed along the axon.
Check the conclusion and its limits
- A neurotransmitter diffuses across the synaptic cleft; an action potential does not jump intact through the liquid gap.
- Excitatory input does not guarantee the postsynaptic cell reaches threshold.
Not true: A stronger stimulus always makes each action potential larger. Action potentials are all-or-none: once threshold is reached, the impulse has a fixed size set by the ion gradients. A stronger stimulus raises the frequency of impulses, not their amplitude.
- An action potential is a brief change in membrane potential involving voltage-gated ion channels.
- The all-or-none principle applies to an individual action potential.
- Watch for: A neurotransmitter diffuses across the synaptic cleft; an action potential does not jump intact through the liquid gap.
Write from an impulse frequency of 70 per second
- 21 impulses occur in 0.30 s.
- Find the frequency. This is not the propagation speed.
A stronger stimulus always makes each action potential larger.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Action potentials are all-or-none: once threshold is reached, the impulse has a fixed size set by the ion gradients. A stronger stimulus raises the frequency of impulses, not their amplitude.
A brief propagating change in membrane potential: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
action potential means A brief propagating change in membrane potential.
21 impulses occur in 0.30 s. What is the impulse frequency, and why is that not a propagation speed?
21 divided by 0.30 is 70. One action potential is all or none. The message can still vary in frequency.
What is the impulse frequency?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
21 divided by 0.30 is 70 per second.