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Draw and label sufficient of two neurons to show a synaptic cleft - Leaving Cert Biology - Question 15 - 2004
Question 15
Draw and label sufficient of two neurons to show a synaptic cleft. Describe the sequence of events that allows an impulse to be transmitted across a synapse from on... show full transcript
Worked Solution & Example Answer:Draw and label sufficient of two neurons to show a synaptic cleft - Leaving Cert Biology - Question 15 - 2004
Step 1
Draw and label sufficient of two neurons to show a synaptic cleft.
Answer
To illustrate the synaptic cleft, draw two neurons with a gap between them.
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Neuron A: Depict the cell body with dendrites and an axon terminal.
- Label the following:
- Dendrites: The branching extensions receiving signals.
- Axon terminal: The end of the neuron where neurotransmitters are released.
- Label the following:
-
Synaptic Cleft: Draw the space between the two neurons and label it as the synaptic cleft.
- This gap is crucial for neurotransmission as it separates presynaptic neuron from the postsynaptic neuron.
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Neuron B: Illustrate another neuron receiving signals from the first neuron.
- Label the receptors on the postsynaptic neuron's dendrite, which bind to neurotransmitters.
Step 2
Describe the sequence of events that allows an impulse to be transmitted across a synapse from one neuron to the next.
Answer
- Arrival of Impulse: An electrical impulse (action potential) travels down Neuron A's axon to its terminal.
- Release of Neurotransmitters: Upon reaching the axon terminal, the impulse triggers synaptic vesicles to fuse with the membrane, releasing neurotransmitters into the synaptic cleft.
- Diffusion across the Synaptic Cleft: Neurotransmitters diffuse across the synaptic cleft towards Neuron B.
- Binding to Receptors: Neurotransmitters bind to specific receptors on the postsynaptic neuron's dendrites, initiating a change in its membrane potential.
- Start of New Impulse: If the signal is strong enough, it generates a new action potential in Neuron B.
- Deactivation of Neurotransmitter: The neurotransmitter is either reabsorbed by Neuron A or broken down by enzymes to prevent continuous stimulation.
Step 3
Suggest a possible role for a drug in relation to the events that you have outlined in (ii).
Answer
A drug could play various roles in neurotransmission processes, such as:
- Inhibition: Certain drugs might block receptor sites on Neuron B, preventing neurotransmitters from binding and inhibiting the transmission of the impulse, which could be useful in conditions like anxiety or seizure disorders.
- Enhancement: Alternatively, a drug could increase the release of neurotransmitters or mimic their action, leading to enhanced transmission. This is often the mechanism for antidepressants, which aim to boost serotonin levels in the synapse.
- Modulation: Some drugs may modulate the activity of enzymes that break down neurotransmitters, prolonging their effect.