exam deck 4 Flashcards
Q: What is the typical resting membrane potential for most neurons?
Around -70 mV, mainly due to the activity of leaky K+ channels, with additional contributions from Na+ and Cl- channels.
What are the typical intracellular and extracellular concentrations of K+, Na+, and Cl-?
K+: 150 mM inside, 5 mM outside.
Na+: 15 mM inside, 150 mM outside.
Cl-: 10 mM inside, 110 mM outside.
Q: How does the Na+/K+ pump contribute to the resting membrane potential?
It is electrogenic, exchanging 3 Na+ out for 2 K+ in, making the cell slightly negative (about -5 mV). Its primary role is to establish ion gradients necessary for the resting potential, rather than generating the potential directly.
What would happen without the leaky K+ channels?
The Na+/K+ pump alone would only generate a small membrane potential; leaky K+ channels are needed to create a more substantial resting potential.
Which ion has the greatest influence on the resting membrane potential?
Potassium (K+), because the resting membrane is most permeable to K+.
Potassium (K+), because the resting membrane is most permeable to K+.
Because K+ leaks out of the cell down its concentration gradient, which is established by the Na+/K+ pump.
How does eating a large amount of potassium (e.g., >6 bananas) affect the resting membrane potential?
It increases extracellular K+ concentration, reducing the K+ concentration gradient and making the resting membrane potential less negative (depolarization).
What effect does this depolarization have on neurons?
The reduced resting potential can lead to spontaneous neuron firing and potentially cause seizures.
How does the blood-brain barrier protect the brain from changes in plasma K+ levels?
The capillaries in the brain are tightly sealed, preventing K+ and other polar substances from crossing easily and protecting brain neurons from changes in extracellular K+ levels.
what happens when two graded potentials occur at the same time on a neuron?
They can summate, or add together, to produce a larger graded potential.
Why is summation of graded potentials important?
Summation is critical for synaptic integration, influencing whether the neuron reaches the threshold to fire an action potential.
Which ion channels are mainly responsible for the resting membrane potential?
Leaky K+ channels, which set the resting potential close to the K+ equilibrium potential of -90 mV.
How are graded potentials generated?
By the opening or closing of specific ion channels, altering the flow of ions across the membrane.
What are some examples of graded potentials?
Generator potentials, postsynaptic potentials (PSPs), end plate potentials, and pacemaker potentials.
What is the function of graded potentials in neurons?
They help decide whether an action potential will be triggered by depolarizing or hyperpolarizing the membrane.
What ion movements generate excitatory postsynaptic potentials (EPSPs)?
EPSPs are generated by the opening of Na+ or K+ channels or the closing of leaky K+ channels, leading to depolarization.
What is the difference between fast and slow EPSPs?
Fast EPSPs are mediated by ionotropic receptors, while slow EPSPs are mediated by metabotropic receptors, leading to a more prolonged response.
How are inhibitory postsynaptic potentials (IPSPs) generated?
By opening Cl- channels or K+ channels, causing hyperpolarization and making the cell less likely to fire an action potential.
What is the difference between fast and slow IPSPs?
Fast IPSPs are mediated by ionotropic receptors, and slow IPSPs are mediated by metabotropic receptors, leading to sustained hyperpolarization.
List some key properties of graded potentials.
Graded potentials are variable in magnitude, decremental (decrease over distance), can be either depolarizing or hyperpolarizing, and are capable of summation.
What determines if a graded potential will trigger an action potential?
The summation of graded potentials must reach a threshold potential at the axon hillock to initiate an action potential.
What is the threshold property of action potentials?
An action potential is only generated if the membrane depolarizes to a specific threshold level.
What does “all-or-none” mean in terms of action potentials?
Once the threshold is reached, the action potential either occurs fully or not at all, with no partial responses.
What does it mean for action potentials to be self-propagating?
Once initiated, an action potential travels along the axon without losing strength.
What is the refractory period in action potentials?
It’s a period following an action potential during which a neuron cannot fire another action potential (absolute refractory) or requires a stronger stimulus to fire (relative refractory).
How is stimulus intensity encoded by action potentials?
Intensity is encoded by the frequency of action potentials, not their amplitude, as each action potential is the same size.
Do action potentials travel quickly or slowly?
Action potentials generally travel slowly compared to other forms of electrical signaling, though speed can vary with axon characteristics.
What types of ion channels are essential for action potential generation?
Voltage-gated ion channels, specifically Na+ channels for depolarization and K+ channels for repolarization and hyperpolarization.
How do voltage-gated Na+ and K+ channels contribute to the phases of an action potential?
Na+ channels open to cause the depolarizing phase, while K+ channels open to mediate repolarization and hyperpolarization.
How do action potentials differ from graded potentials in terms of channels?
Action potentials are mediated by voltage-gated channels, while graded potentials are generated by ligand-gated channels.
List the key properties of action potentials.
They have a threshold, are all-or-none, self-propagating, have a refractory period, encode intensity in frequency, travel slowly, and are mediated by voltage-gated channels.
What are the primary classes of nerve fibers, and how do they differ?
Nerve fibers are classified as Aα, Aβ, Aγ, Aδ, and C, varying in diameter, myelination, and conduction speed.
Describe the basic components of the neuromuscular junction (NMJ).
The NMJ includes the presynaptic terminal with vesicles of acetylcholine (ACh), the synaptic cleft, and the postsynaptic end plate on the muscle fiber.
What role does acetylcholinesterase play at the NMJ?
It breaks down ACh in the synaptic cleft to terminate the signal, allowing the muscle to relax.
Outline the steps in synaptic transmission at the NMJ.
Action potential arrives at the motor neuron terminal.
Voltage-gated Ca²⁺ channels open, triggering Ca²⁺ influx.
Ca²⁺-dependent exocytosis of ACh vesicles.
ACh diffuses across the synaptic cleft.
ACh binds to nicotinic receptors on the postsynaptic membrane.
Ligand-gated Na⁺/K⁺ channels open, generating an end plate potential.
Depolarization reaches threshold, opening voltage-gated Na⁺ channels.
Action potential is triggered, leading to muscle contraction.
What is unique about the end plate potential (EPP) at the NMJ?
The EPP is a large, graded potential (~40 mV) that always reaches threshold to trigger an action potential, thanks to the high density of voltage-gated Na+ channels near the end plate.
Does the NMJ integrate synaptic inputs?
No, the NMJ acts more like a switch, with a high safety factor to ensure reliable transmission and no integration of multiple synaptic inputs.
What is a compound action potential?
It’s a summated electrical signal from a bundle of axons in a nerve, recorded extracellularly, showing varied conduction speeds for different fiber types.
How does axon anatomy affect compound action potentials?
Axons with larger diameters and myelination conduct signals faster, which creates the complex waveform of a compound action potential.
What anatomical features increase action potential conduction speed?
Large diameter axons and myelination speed up conduction.
What are divergence and convergence in synaptic connectivity?
Divergence is when one neuron’s axon branches to contact multiple targets, while convergence is when multiple inputs synapse on a single neuron.
What is feedback inhibition?
Feedback inhibition occurs when an axon collateral activates an inhibitory interneuron, which then inhibits the original neuron to prevent repeated firing.
Differentiate between monosynaptic and polysynaptic reflexes.
Monosynaptic reflexes involve a direct connection between afferent and efferent neurons, while polysynaptic reflexes involve one or more interneurons.
What is synaptic plasticity?
synaptic plasticity refers to changes in the strength of synapses, often activity-dependent, including processes like long-term potentiation and long-term depression.
How do CNS synapses differ from the NMJ?
CNS synapses use a wide range of neurotransmitters and receptor types (EPSPs and IPSPs, fast and slow), allowing more complex arrangements and integration of inputs compared to the more straightforward NMJ.
What is the purpose of the Golgi tendon organ reflex?
It protects muscles from excessive tension, which could cause damage.
Describe the sequence of the Golgi tendon organ reflex.
Excessive tension activates the Golgi tendon organ.
B: Afferent fibers from the Golgi tendon organ activate inhibitory interneurons in the spinal cord.
C: These interneurons inhibit motor neurons supplying the muscle, causing it to relax.
Is the Golgi tendon organ reflex monosynaptic or polysynaptic?
Polysynaptic.
Which sensory receptors initiate the flexion reflex?
Nociceptors, which detect painful stimuli.
What is the function of the flexion (withdrawal) reflex?
It removes a limb from a harmful or potentially harmful stimulus.
Describe the response of the flexion reflex.
Activated nociceptors stimulate interneurons that:
Excite motor neurons to ipsilateral flexor muscles.
Inhibit motor neurons to ipsilateral extensor muscles.
What is the purpose of the crossed extensor reflex?
It maintains balance by activating the opposite limb when one limb is withdrawn from a harmful stimulus.
Describe the response in the crossed extensor reflex.
A: The reflex activates interneurons that:
Inhibit motor neurons to contralateral flexors.
Excite motor neurons to contralateral extensors.
Is the flexion and crossed extensor reflex a monosynaptic or polysynaptic reflex?
Polysynaptic, as it involves multiple interneurons and motor neurons.
