1) How is the nervous system transmitted along the axon of a nerve cell? Explain in detail.
2) How does the transmission across the junction between one neurone and the next happen? Explain your answer in detail.
3) How is the impulse transmitted across a neurone? Explain your answer in detail.
4) How does the impulse cross the synapse? Explain your answer in detail.
5) Draw a diagram for all of this and label it.
6) What happens along the axon and at a synapse? Explain your answer in detail. Structure your answer in a series of stages.
a) What happens at the end of one neuron? Explain your answer in detail.
b) What happens in the synapse itself? Explain your answer in detail.
c) What happens in the second neuron? Explain your answer in detail.
1) The nervous system transmits information along the axon of a nerve cell through electrical impulses, which are called action potentials. An action potential begins with the depolarization of the neuronal membrane due to the opening of voltage-gated sodium channels. This allows an influx of sodium ions, causing the membrane potential to become more positive. Once a threshold is reached, an action potential is generated, and it rapidly propagates along the axon via a chain-like sequence of events involving the opening and closing of voltage-gated ion channels. After the initiation of the action potential, voltage-gated potassium channels open, allowing potassium ions to exit the cell, repolarizing the membrane back to its resting potential. The action potential moves down the length of the axon until it reaches the axon terminal.
2) The transmission across the junction between one neuron and the next occurs at specialized structures called synapses. When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels, allowing calcium ions to enter the cell. The influx of calcium ions causes synaptic vesicles, which contain neurotransmitter molecules, to fuse with the presynaptic membrane and release their contents into the synaptic cleft. The neurotransmitters then diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane of the second neuron. These receptors are typically ligand-gated ion channels, which open in response to the binding of the neurotransmitter, allowing the flow of ions in or out of the cell. This results in a postsynaptic potential, which can either be excitatory (depolarizing) or inhibitory (hyperpolarizing), depending on the type of neurotransmitter and receptor involved. If the postsynaptic potential is strong enough to reach the threshold, an action potential will be generated in the second neuron, and the information will be transmitted to the next neuron in the chain.
3) The impulse is transmitted across a neuron by a process called saltatory conduction in which an action potential travels along the axon by jumping from one node of Ranvier to the next. In myelinated neurons, the myelin sheath acts as an insulator, preventing the leakage of ions across the cell membrane and speeding up the propagation of the electrical signal. The action potential is regenerated at each node of Ranvier, which are unmyelinated areas on the axon containing a high concentration of voltage-gated ion channels. This process ensures that the impulse remains strong and travels quickly across the neuron.
4) The impulse crosses the synapse through the release and binding of neurotransmitters. Once the action potential reaches the axon terminal, it causes voltage-gated calcium channels to open, allowing calcium ions to enter the cell. Calcium ions trigger the fusion of synaptic vesicles with the presynaptic membrane and the subsequent release of neurotransmitters into the synaptic cleft. The neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane, which results in the generation of postsynaptic potentials. If the combined postsynaptic potentials from multiple synapses reach the threshold, an action potential is triggered in the second neuron, allowing the impulse to continue along the neural pathway.
5) [I'm an AI language model and cannot draw images. However, I can describe it for you]
A diagram of this process would include:
- A presynaptic neuron with an axon, axon terminals, and synaptic vesicles containing neurotransmitters.
- A synaptic cleft, the space between the two neurons.
- A postsynaptic neuron with dendrites containing receptors for neurotransmitters.
- Arrows showing the direction of an action potential moving down the axon of the presynaptic neuron, the release of neurotransmitters, and the generation of postsynaptic potentials in the second neuron.
6) a) At the end of one neuron (the presynaptic neuron), the action potential arrives at the axon terminals, triggering the opening of voltage-gated calcium channels. The influx of calcium ions causes the synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft.
b) In the synapse, the neurotransmitters released into the synaptic cleft diffuse across the small gap and bind to specific receptors on the postsynaptic membrane of the second neuron (postsynaptic neuron).
c) In the second (postsynaptic) neuron, the binding of neurotransmitters to their receptors causes ligand-gated ion channels to open, either allowing positive ions to enter the cell (depolarizing, excitatory) or negative ions to enter/positive ions to exit (hyperpolarizing, inhibitory). Depending on the types and combinations of neurotransmitters and receptors, these postsynaptic potentials will either reach the threshold, generating an action potential and allowing the impulse to continue along the neural pathway, or not reach the threshold, meaning the impulse will not be transmitted any further.