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Questions and Answers
A ligand such as sugar, drug, or hormone opens the ligand-gated Na+ channel.
True
Na+ influx into the cell causes the membrane potential to decrease rapidly.
False
The activation of gated Na+ channels leads to the generation of a graded potential.
True
A decrease in extracellular Na+ would enhance the ligand-gated Na+ channel's opening.
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The membrane potential at rest is indicated as -70 mV.
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Ligand-gated channels for Na+ require a voltage change to open.
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Calcium ions (Ca2+) are primarily responsible for the initial depolarization of sensory cells.
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The influx of Na+ is an example of passive transport.
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The maximum membrane potential reached during an action potential is +40 mV.
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During the action potential, K+ channels open at a membrane potential of +30 mV.
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The Na+/K+ pump is responsible for maintaining a resting membrane potential of approximately +90 mV.
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The inflow of Na+ during an action potential occurs due to a small Na+ gradient and weak electrical gradient.
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In the context of action potentials, Na+ channels close at the peak of the action potential.
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The influx of Na+ into the cell leads to a decrease in membrane potential.
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Voltage-gated Ca2+ channels open in response to a decrease in resting membrane potential.
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A large stimulus generates a larger amount of neurotransmitter release compared to a small stimulus.
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If the threshold of -55 mV is not reached, a high frequency of action potentials is generated along the axon.
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Neurotransmitters released from the presynaptic cell bind to postsynaptic receptors which can be either ligand-gated or voltage-gated channels.
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The membrane potential must reach -60 mV for a nerve impulse to be sent along the axon.
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Calcium ions (Ca2+) play a crucial role in the fusion of neurotransmitter vesicles to the presynaptic membrane.
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Graded potentials are always sufficient to trigger an action potential.
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The arrival of an action potential triggers neurotransmitter release into the synapse.
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Sodium channels are primarily responsible for the repolarization phase of an action potential.
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Nerve impulses travel at a speed of 360 km/h.
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Copper wire transmits nerve impulses faster than 3 x 10^6 Km/h.
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Diffusion occurs at a speed of 0.000000008 Km/h.
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Nerve impulses are 4 x 10^10 times faster than the speed of diffusion.
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The speed of nerve impulses is 100 m/s.
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Nerve impulses take 1/100 second to travel 1 meter.
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The spinal cord is involved in transmitting nerve impulses to the toes.
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The speed of a nerve impulse is slower than 1 m/s.
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A nerve impulse can travel a maximum of 360,000 meters in one hour.
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Nerve impulses are transmitted slower than copper wire.
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Action potentials are small identical electrical changes occurring only in the axon of a neuron.
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Graded potentials can propagate without needing synapses.
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A high frequency of action potentials can be described as 'too sweet'.
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It takes 15 years for ions to achieve 99% equilibrium over a distance of one meter in a nerve.
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Synaptic transmission must occur through electrical changes in the nerve cell body.
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Resting membrane potential is at +30mV.
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The role of neuroglia is irrelevant to the propagation of action potentials.
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Graded potentials are only significant in sensory cells.
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The phrase 'Not enough!' refers to a high frequency of action potentials.
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Action potentials propagate in one direction because of the role of neuroglia.
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Study Notes
Sensory Cell Stimulation
- A ligand (e.g., sugar, drug, hormone) binds to a ligand-gated Na+ channel on the surface of a sensory cell
- This causes the channel to open
- Na+ rushes into the cell
- This generates a graded potential
- The increased membrane potential activates voltage-gated Ca2+ channels
- Ca2+ rushes into the cell
- This causes neurotransmitter-containing vesicles to fuse with the presynaptic membrane
- Neurotransmitters are released into the synapse
- The amount of NT released is proportional to the strength of the stimulus
Action Potentials
- Action potentials are small, identical, electrical changes in individual parts of a neuron.
- If the membrane potential at the axon hillock reaches the threshold of -55 mV:
- a low frequency of action potentials are generated and propagated along the axon
- If the threshold of -55 mV is maintained:
- a high frequency of action potentials are generated and propagated along the axon
Nerve Impulse Speed
- Nerve impulses travel at a speed of 100 meters per second
- This is much faster than diffusion which travels at 0.000 000 008 Km/h
Synapse Activity
- NTs bind to NT receptors on post-synaptic cells.
- NT receptors synapsed to sensory cells are ligand-gated Na+ channels.
- Na+ influx raises the membrane potential at the axon hillock
- When the threshold for an action potential is reached, a nerve impulse is sent along the axon.
Action Potential Propagation
- The influx of Na+ is extremely rapid because of the large Na+ gradient and the large electrical gradient.
- Na+ channels close at the peak of the AP.
- K+ channels open when the membrane potential reaches +30 mV.
- The efflux of K+ is extremely rapid because of the large K+ gradient and the large electrical gradient.
- The Na+/K+ pump helps reset the resting membrane potential (-70 mV)
- The action potential propagates in one direction because the Na+ channels become inactivated after they open, preventing the signal from traveling backward.
Neuroglia
- Neuroglia, also known as glial cells, are non-neuronal cells in the central nervous system (CNS) and peripheral nervous system (PNS) that provide support and protection for neurons.
- Myelin sheath is a fatty substance that insulates neurons and speeds up the transmission of nerve impulses.
- Myelin sheath is formed by a type of neuroglia called Schwann cells in the PNS and oligodendrocytes in the CNS.
Local Anaesthetics and Neurotoxins
- Local anaesthetics block the voltage-gated Na+ channels in nerve axons preventing the generation and propagation of action potentials.
- Neurotoxins are substances that interfere with the function of neurons, often by binding to and blocking neurotransmitter receptors.
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Description
Explore the fascinating mechanisms of sensory cell stimulation and action potentials in this quiz. Understand how ligands trigger graded potentials and the role of action potentials in nerve impulse transmission. Test your knowledge on the thresholds needed for action potentials and the dynamics of neurotransmitter release.
