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Questions and Answers
The gaps between myelin where Na+ & K+ channels cluster are called nodes of ______
The gaps between myelin where Na+ & K+ channels cluster are called nodes of ______
Ranvier
Multiple Sclerosis is an autoimmune disease where myelin is ______
Multiple Sclerosis is an autoimmune disease where myelin is ______
absent
Nerve diameter is directly proportional to conduction ______
Nerve diameter is directly proportional to conduction ______
rate
Sensory synapses link cells that detect changes in the body's ______ and external environment.
Sensory synapses link cells that detect changes in the body's ______ and external environment.
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Voltage-gated ______ channel activation causes the release of neurotransmitters.
Voltage-gated ______ channel activation causes the release of neurotransmitters.
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The ______ fluid surrounding certain cells in the ear has a high potassium concentration.
The ______ fluid surrounding certain cells in the ear has a high potassium concentration.
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In synaptic transmission, neurotransmitters diffuse across the ______ to bind to receptors.
In synaptic transmission, neurotransmitters diffuse across the ______ to bind to receptors.
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If Ca2+ channels are blocked, there is no ______ release, leading to impaired synaptic transmission.
If Ca2+ channels are blocked, there is no ______ release, leading to impaired synaptic transmission.
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The action potential 'arrives' through the influx of ______ ions from the final Na+ channel in the axon.
The action potential 'arrives' through the influx of ______ ions from the final Na+ channel in the axon.
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The direction of action potential propagation is towards the ______ neuron.
The direction of action potential propagation is towards the ______ neuron.
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Graded potentials occur when the membrane potential increases to _____ mV.
Graded potentials occur when the membrane potential increases to _____ mV.
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The inside of the cell is negative relative to the outside at _____ mV.
The inside of the cell is negative relative to the outside at _____ mV.
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When reaching _____ mV, Na+ channels start to open.
When reaching _____ mV, Na+ channels start to open.
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Voltage-gated Na+ and K+ channels are crucial for the generation of _____ potentials.
Voltage-gated Na+ and K+ channels are crucial for the generation of _____ potentials.
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During action potentials, the membrane potential can rise to as high as _____ mV.
During action potentials, the membrane potential can rise to as high as _____ mV.
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Graded potentials affect the _____ of a neuron by altering the membrane potential.
Graded potentials affect the _____ of a neuron by altering the membrane potential.
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The flow of _____ ions is primarily responsible for the depolarization during action potentials.
The flow of _____ ions is primarily responsible for the depolarization during action potentials.
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Resting membrane potential is maintained by the _____ of ions across the cell membrane.
Resting membrane potential is maintained by the _____ of ions across the cell membrane.
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The ______ in the skin of the hand detects heat.
The ______ in the skin of the hand detects heat.
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The brain sends action potentials to block the reflex ______ inter-neuron.
The brain sends action potentials to block the reflex ______ inter-neuron.
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When the brain perceives the plate is hot, the output reflex is to ______ the plate.
When the brain perceives the plate is hot, the output reflex is to ______ the plate.
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The conscious decision made by the brain was to ______ the pain.
The conscious decision made by the brain was to ______ the pain.
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The motor neuron to the muscle in the hand helps to maintain ______.
The motor neuron to the muscle in the hand helps to maintain ______.
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Spatial summation occurs when 1 Yes and 1 ______ equals No AP.
Spatial summation occurs when 1 Yes and 1 ______ equals No AP.
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The brain makes a decision based on incoming ______.
The brain makes a decision based on incoming ______.
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Inhibition of an inhibitor leads to ______, allowing the grip to be maintained.
Inhibition of an inhibitor leads to ______, allowing the grip to be maintained.
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The brain is aware of the value of the plate, noting it is a family ______.
The brain is aware of the value of the plate, noting it is a family ______.
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When the plate is recognized as deadly hot, the brain must ______ the decision.
When the plate is recognized as deadly hot, the brain must ______ the decision.
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The influx of ______ is extremely rapid because the gradient is large.
The influx of ______ is extremely rapid because the gradient is large.
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______ channels open at +30 mV during an action potential.
______ channels open at +30 mV during an action potential.
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The maximum potential during an action potential is approximately ______ mV.
The maximum potential during an action potential is approximately ______ mV.
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The voltage-regulated Na+ channel has three states: closed, ______, and inactivated.
The voltage-regulated Na+ channel has three states: closed, ______, and inactivated.
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The ______ period occurs after the activation of sodium channels, during which a new action potential cannot be initiated.
The ______ period occurs after the activation of sodium channels, during which a new action potential cannot be initiated.
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Na+ channels at site A are in ______ state, making it inactive during the action potential.
Na+ channels at site A are in ______ state, making it inactive during the action potential.
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The membrane potential is reset to ______ mV by the Na+/K+ pump after an action potential.
The membrane potential is reset to ______ mV by the Na+/K+ pump after an action potential.
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The action potential at site B is caused by the activation of Na+ channels, resulting in rapid ______.
The action potential at site B is caused by the activation of Na+ channels, resulting in rapid ______.
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During an action potential, K+ channels lead to an efflux of ______, reducing the membrane potential.
During an action potential, K+ channels lead to an efflux of ______, reducing the membrane potential.
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The biological timer switch keeps the Na+ channel open for ______ msec.
The biological timer switch keeps the Na+ channel open for ______ msec.
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Na+ will enter cells if Na+ channels are open – ______
Na+ will enter cells if Na+ channels are open – ______
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K+ will leave cells if K+ channels are open – ______ or hyperpolarise
K+ will leave cells if K+ channels are open – ______ or hyperpolarise
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Depolarisation in post-synaptic cell is called an ______: Excitatory Post-Synaptic Potential
Depolarisation in post-synaptic cell is called an ______: Excitatory Post-Synaptic Potential
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Hyperpolarisation in post-synaptic cell is called an ______: Inhibitory Post-Synaptic Potential
Hyperpolarisation in post-synaptic cell is called an ______: Inhibitory Post-Synaptic Potential
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Slow response involves ligand binding and conformational changes that lead to channel ______
Slow response involves ligand binding and conformational changes that lead to channel ______
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Study Notes
Graded Potentials
- Graded potentials occur when a stimulus causes a change in membrane potential.
- The magnitude of the change is proportional to the strength of the stimulus.
- The change in membrane potential is localized to the area of the stimulus.
- Graded potentials can be either depolarizing (more positive) or hyperpolarizing (more negative).
- The change in membrane potential is caused by the influx or efflux of ions.
Action Potentials
- Action potentials are rapid changes in membrane potential that travel along the axon of a neuron.
- Action potentials are triggered when a graded potential reaches threshold at the axon hillock.
- Threshold is the membrane potential at which voltage-gated sodium channels open, allowing an influx of sodium ions.
- The influx of sodium ions causes a rapid depolarization of the membrane, creating an action potential.
- Action potentials are "all-or-nothing" events, meaning that they either occur with full amplitude or not at all.
- The rapid depolarization of the membrane causes the opening of voltage-gated potassium channels.
- The efflux of potassium ions causes the membrane to repolarize, returning to its resting membrane potential.
- The repolarization phase is followed by a brief hyperpolarization, known as the after-hyperpolarization.
- The action potential is then propagated along the axon, triggering the opening of voltage-gated sodium channels in the adjacent section of membrane, setting off a chain reaction.
- This propagation of action potentials ensures that information is transmitted along the axon without loss of strength.
Refractory Period
- Sodium channels are inactivated for a brief period of time after they have opened, during the refractory period.
- This prevents the action potential from traveling backward along the axon.
- The refractory period also ensures that action potentials are separated from each other, allowing for clear transmission of information.
Role of Myelin Sheath
- The myelin sheath is a fatty substance that wraps around the axon of a neuron, providing insulation.
- The myelin sheath speeds up the conduction of action potentials by reducing the loss of current across the membrane.
- Action potentials jump from one node of Ranvier to the next, a process called saltatory conduction.
Synaptic Transmission
- When an action potential reaches the end of the axon, it triggers the release of neurotransmitters into the synaptic cleft.
- Neurotransmitters are chemicals that bind to receptors on the postsynaptic neuron.
- The binding of neurotransmitters to receptors can cause either an excitatory or inhibitory postsynaptic potential (EPSP or IPSP).
- EPSPs depolarize the postsynaptic membrane, increasing the likelihood of an action potential.
- IPSPs hyperpolarize the postsynaptic membrane, decreasing the likelihood of an action potential.
- The sum of all EPSPs and IPSPs determines whether an action potential is triggered in the postsynaptic neuron.
Local Anaesthetics
- Local anaesthetics block the voltage-gated sodium channels, preventing the generation of action potentials.
- This results in a loss of sensation in the area where the anaesthetic has been applied.
Neurotoxins
- Neurotoxins can disrupt the normal function of the nervous system by interfering with the release or uptake of neurotransmitters, or by blocking the activity of specific receptors.
- This can lead to a wide variety of symptoms, depending on the specific neurotoxin and its mechanism of action.
Propagation of Action Potentials
- Action potentials are propagated in one direction due to the refractory period.
- Sodium channels that have recently been activated are inactivated for a brief period of time.
- This means that the action potential cannot travel backward along the axon.
- Instead, the action potential travels forward along the axon, triggering the opening of voltage-gated sodium channels in the adjacent sections of membrane.
Axon Hillock
- The axon hillock is the region where the axon joins the cell body of a neuron.
- The axon hillock is the site of action potential initiation.
- The axon hillock has a high density of voltage-gated sodium channels, making it more sensitive to depolarization.
- When a graded potential reaches threshold at the axon hillock, it triggers the opening of voltage-gated sodium channels, initiating an action potential.
Nodes of Ranvier
- Myelin sheaths cluster sodium (Na+) and potassium (K+) channels in discrete regions along the axon.
- These gaps between myelin sheaths are called nodes of Ranvier
- Nodes of Ranvier allow for efficient propagation of action potentials (APs)
- Multiple Sclerosis (MS) is an autoimmune disease that destroys myelin sheaths, leading to inefficient AP transmission
- Nerve diameter affects conduction rate; the larger the diameter, the faster the conduction rate.
Action Potentials
- Action potentials propagate in only one direction because of the refractory period of the sodium (Na+) channels.
- Local anesthetics block voltage-gated sodium (Na+) channels, preventing APs from travelling along a neuron
- Neuroglial cells (myelin sheath) insulate the axons of neurons, speeding up the rate of conduction.
Sensory Synapses
- Sensory synapses connect specialized sensory cells to the nervous system.
- Sensory cells detect changes in the body's internal and external environment.
- Stimulus triggers the opening of voltage-gated calcium (Ca2+) channels, causing the release of neurotransmitters.
- These neurotransmitters diffuse across the synapse and bind to receptors on the afferent neuron.
- If the stimulus is strong enough, this triggers the generation of action potentials that propagate along the neuron to the central nervous system (CNS).
Hearing
- Sensory cells in the ear are bathed in endolymph, a fluid with a high potassium (K+) concentration.
- Stimulation of these cells causes the release of neurotransmitters, which then activate the afferent neuron.
Vision
- Photoreceptor cells in the eye are stimulated by light.
- This stimulation activates voltage-gated calcium (Ca2+) channels, leading to the release of neurotransmitters.
- Neurotransmitters then act on the afferent neuron, triggering APs that travel to the CNS.
Neuronal Synaptic Transmission
- Signals are transmitted across synapses by neurotransmitters.
- Stimulation of the presynaptic neuron triggers the release of neurotransmitters.
- Neurotransmitters diffuse across the synapse and bind to receptors on the postsynaptic neuron, either triggering or inhibiting AP generation.
- The signal must be terminated when the APs stop.
- This termination is achieved by recycling neurotransmitters, enzymatic degradation, or diffusion away from the synapse.
Synaptic Transmission - Signal Termination
- The release of neurotransmitters from the presynaptic neuron triggers the depolarization of the postsynaptic neuron.
- If the stimulus is strong enough, the postsynaptic neuron will fire an action potential.
- Excitatory post-synaptic potentials (EPSPs) make it more likely that an AP will be generated.
- Inhibitory post-synaptic potentials (IPSPs) make it less likely that an AP will be generated.
- In some cases, the nervous system can override reflex responses.
- The brain can send signals to block inhibitory neurons, allowing the reflex action to continue despite the original stimulus.
- An example of this is the grip reflex.
Fast Excitatory Response
- Excitatory responses are usually fast, occurring within milliseconds.
- An example of this is the binding of neurotransmitters to ionotropic receptors, which directly open ion channels.
- This allows sodium (Na+) ions to enter the cell, causing depolarization and an EPSP.
Fast Inhibitory Response
- Inhibitory responses are also usually fast, occurring within milliseconds.
- They are mediated by the opening of potassium (K+) channels, allowing potassium (K+) ions to leave the cell, causing hyperpolarization and an IPSP.
Slow Response
- Some synaptic responses are slow, taking several seconds to occur.
- These are typically mediated by metabotropic receptors that do not directly open ion channels.
- Instead, binding of neurotransmitters to metabotropic receptors activates a signaling cascade within the cell, leading to the opening of ion channels and a change in membrane potential.
Calcispetin
- This protein blocks calcium (Ca2+) channels, preventing the release of neurotransmitters.
- This can result in death, as signals are not transmitted between neurons.
Local Anaesthetics
- These drugs block voltage-gated sodium (Na+) channels, preventing the propagation of APs in neurons.
- This results in a loss of sensation.
Neurotoxins
- Some neurotoxins, such as tetrodotoxin, also block voltage-gated sodium (Na+) channels, leading to paralysis and death.
Neuronal Circuits
- Synapses play a crucial role in neuronal circuits.
- These circuits are based on interconnected neurons that transmit information throughout the body.
- Some circuits are involved in simple reflex actions, while others are involved in more complex functions such as learning and memory.
Spatial Summation
- Several presynaptic neurons can synapse on a single postsynaptic neuron, allowing the integration of multiple signals.
- The sum of signals from all the presynaptic neurons determines whether an AP will be triggered in the postsynaptic neuron.
- If the combined effect of multiple EPSPs is not sufficient to trigger an AP, the neuron will remain inactive.
Revision Notes on Voltage-gated Ion Channels
- Voltage-gated ion channels are responsible for the opening and closing of specific ion channels in response to changes in membrane potential.
- Sodium (Na+) channels open during depolarization, allowing an influx of sodium (Na+) ions and bringing the membrane potential closer to the threshold potential.
- Potassium (K+) channels open during repolarization, allowing an efflux of potassium (K+) ions that returns the membrane potential to its resting state.
- Potassium (K+) channels can also contribute to hyperpolarization, making it less likely to fire another AP.
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Description
This quiz tests your understanding of graded and action potentials in neuroscience. It covers the mechanisms, characteristics, and differences between these key electrical signals in neurons. Prepare to explore the dynamics of membrane potential changes related to stimuli and threshold effects.
