Neurons, synapses and brain systems
Introduced| English |
|---|
| all-or-none principle/ɔːl ɔː nɒn ˈprɪnsɪpl/ |
| reuptake/ˈruːpteɪk/ |
A decision before an answer
- A neuron cannot fire at half strength; the signal is all-or-none, and intensity travels in the firing rate.
- Your goal: Trace the action potential from trigger to synaptic release.
Trigger the spike
- The action potential begins at the axon hillock, where graded inputs sum; once the threshold is reached the neuron fires a complete spike (the all-or-none principle), and during the absolute refractory period it cannot fire again.
- Stimulus intensity is coded by firing rate and by how many neurons fire, not by spike size. Myelin insulates the axon and speeds conduction by saltatory conduction between the nodes of Ranvier; demyelinating disease slows or blocks conduction.
The action potential is triggered at which part of the neuron?
Graded potentials sum at the axon hillock; crossing threshold there launches the spike.
Cross the synapse
- At the synapse, the arriving spike opens calcium channels, vesicles release neurotransmitter into the cleft, and receptors on the postsynaptic cell convert binding into a new graded potential. Reuptake and enzymatic breakdown clear the transmitter.
- A drug can be an agonist (mimicking or enhancing a transmitter) or an antagonist (blocking receptors); SSRIs block serotonin reuptake, leaving more in the cleft.
The myelin sheath around an axon serves to:
Myelin enables saltatory conduction between nodes of Ranvier, speeding the impulse.
Map the structures
- Structure-function anchors: the amygdala supports emotion and fear learning; the hippocampus is needed to form new episodic memories; the hypothalamus regulates drives and homeostasis; the cerebellum coordinates movement; Broca's area supports speech production and Wernicke's area comprehension; the prefrontal cortex supports planning and control.
- Localisation is real but partial: most behaviours involve distributed networks.
A spike is triggered at the axon hillock once summed inputs cross threshold; after firing, the absolute refractory period enforces a pause. Blocking serotonin reuptake raises synaptic serotonin, which is the SSRI mechanism. Loss of dopaminergic neurons impairs movement in Parkinson's disease.
SSRIs raise synaptic serotonin by blocking its ____.
Blocking reabsorption leaves more transmitter in the cleft.
Follow the dopamine example
- Dopamine illustrates specificity: it supports movement and reward, its loss produces Parkinson's disease, and excessive dopaminergic signalling is linked to positive symptoms of schizophrenia, which many antipsychotics treat by blocking D2 receptors.
- One transmitter serves many systems, so a drug's behavioural effect depends on the pathway, not the molecule alone.
Describing a stronger stimulus as producing a bigger spike, or naming a single brain centre as the whole basis of a complex behaviour.
Which answer fits this case?
Trace the action potential from trigger to synaptic release
A stronger stimulus produces a proportionally larger action potential.
Spikes are all-or-none; intensity is coded by firing rate and neuron count.
Keep the distinctions
- all-or-none principle 全或无定律 — Once threshold is reached a neuron fires a complete spike; stronger stimuli raise rate, not spike size.
- reuptake 再摄取 — Reabsorption of neurotransmitter into the presynaptic cell, ending its action.
- Trace the action potential from trigger to synaptic release.
- Relate major brain structures to their behavioural functions.
- Distinguish neurotransmitter and drug actions at the synapse.
Match each term with its precise meaning in this lesson.
Keep the distinctions stated in the teaching example.
Put this lesson’s reasoning or event sequence in order.
The order follows the stated process; check each stage before the next.