exam deck 4

Question 1

Q: What is the typical resting membrane potential for most neurons?

Answer 1

Around -70 mV, mainly due to the activity of leaky K+ channels, with additional contributions from Na+ and Cl- channels.

Question 2

What are the typical intracellular and extracellular concentrations of K+, Na+, and Cl-?

Answer 2

K+: 150 mM inside, 5 mM outside.
Na+: 15 mM inside, 150 mM outside.
Cl-: 10 mM inside, 110 mM outside.

Question 3

Q: How does the Na+/K+ pump contribute to the resting membrane potential?

Answer 3

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.

Question 4

What would happen without the leaky K+ channels?

Answer 4

The Na+/K+ pump alone would only generate a small membrane potential; leaky K+ channels are needed to create a more substantial resting potential.

Question 5

Which ion has the greatest influence on the resting membrane potential?

Answer 5

Potassium (K+), because the resting membrane is most permeable to K+.

Question 6

Potassium (K+), because the resting membrane is most permeable to K+.

Answer 6

Because K+ leaks out of the cell down its concentration gradient, which is established by the Na+/K+ pump.

Question 7

How does eating a large amount of potassium (e.g., >6 bananas) affect the resting membrane potential?

Answer 7

It increases extracellular K+ concentration, reducing the K+ concentration gradient and making the resting membrane potential less negative (depolarization).

Question 8

What effect does this depolarization have on neurons?

Answer 8

The reduced resting potential can lead to spontaneous neuron firing and potentially cause seizures.

Question 9

How does the blood-brain barrier protect the brain from changes in plasma K+ levels?

Answer 9

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.

Question 10

what happens when two graded potentials occur at the same time on a neuron?

Answer 10

They can summate, or add together, to produce a larger graded potential.

Question 11

Why is summation of graded potentials important?

Answer 11

Summation is critical for synaptic integration, influencing whether the neuron reaches the threshold to fire an action potential.

Question 12

Which ion channels are mainly responsible for the resting membrane potential?

Answer 12

Leaky K+ channels, which set the resting potential close to the K+ equilibrium potential of -90 mV.

Question 13

How are graded potentials generated?

Answer 13

By the opening or closing of specific ion channels, altering the flow of ions across the membrane.

Question 14

What are some examples of graded potentials?

Answer 14

Generator potentials, postsynaptic potentials (PSPs), end plate potentials, and pacemaker potentials.

Question 15

What is the function of graded potentials in neurons?

Answer 15

They help decide whether an action potential will be triggered by depolarizing or hyperpolarizing the membrane.

Question 18

What ion movements generate excitatory postsynaptic potentials (EPSPs)?

Answer 18

EPSPs are generated by the opening of Na+ or K+ channels or the closing of leaky K+ channels, leading to depolarization.

Question 19

What is the difference between fast and slow EPSPs?

Answer 19

Fast EPSPs are mediated by ionotropic receptors, while slow EPSPs are mediated by metabotropic receptors, leading to a more prolonged response.

Question 20

How are inhibitory postsynaptic potentials (IPSPs) generated?

Answer 20

By opening Cl- channels or K+ channels, causing hyperpolarization and making the cell less likely to fire an action potential.

Question 21

What is the difference between fast and slow IPSPs?

Answer 21

Fast IPSPs are mediated by ionotropic receptors, and slow IPSPs are mediated by metabotropic receptors, leading to sustained hyperpolarization.

Question 22

List some key properties of graded potentials.

Answer 22

Graded potentials are variable in magnitude, decremental (decrease over distance), can be either depolarizing or hyperpolarizing, and are capable of summation.

Question 23

What determines if a graded potential will trigger an action potential?

Answer 23

The summation of graded potentials must reach a threshold potential at the axon hillock to initiate an action potential.

Question 24

What is the threshold property of action potentials?

Answer 24

An action potential is only generated if the membrane depolarizes to a specific threshold level.

Question 25

What does “all-or-none” mean in terms of action potentials?

Answer 25

Once the threshold is reached, the action potential either occurs fully or not at all, with no partial responses.

Question 26

What does it mean for action potentials to be self-propagating?

Answer 26

Once initiated, an action potential travels along the axon without losing strength.

Question 27

What is the refractory period in action potentials?

Answer 27

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).

Question 28

How is stimulus intensity encoded by action potentials?

Answer 28

Intensity is encoded by the frequency of action potentials, not their amplitude, as each action potential is the same size.

Question 29

Do action potentials travel quickly or slowly?

Answer 29

Action potentials generally travel slowly compared to other forms of electrical signaling, though speed can vary with axon characteristics.

Question 30

What types of ion channels are essential for action potential generation?

Answer 30

Voltage-gated ion channels, specifically Na+ channels for depolarization and K+ channels for repolarization and hyperpolarization.

Question 31

How do voltage-gated Na+ and K+ channels contribute to the phases of an action potential?

Answer 31

Na+ channels open to cause the depolarizing phase, while K+ channels open to mediate repolarization and hyperpolarization.

Question 32

How do action potentials differ from graded potentials in terms of channels?

Answer 32

Action potentials are mediated by voltage-gated channels, while graded potentials are generated by ligand-gated channels.

Question 32

List the key properties of action potentials.

Answer 32

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.

Question 33

What are the primary classes of nerve fibers, and how do they differ?

Answer 33

Nerve fibers are classified as Aα, Aβ, Aγ, Aδ, and C, varying in diameter, myelination, and conduction speed.

Question 34

Describe the basic components of the neuromuscular junction (NMJ).

Answer 34

The NMJ includes the presynaptic terminal with vesicles of acetylcholine (ACh), the synaptic cleft, and the postsynaptic end plate on the muscle fiber.

Question 35

What role does acetylcholinesterase play at the NMJ?

Answer 35

It breaks down ACh in the synaptic cleft to terminate the signal, allowing the muscle to relax.

Question 36

Outline the steps in synaptic transmission at the NMJ.

Answer 36

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.

Question 37

What is unique about the end plate potential (EPP) at the NMJ?

Answer 37

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.

Question 38

Does the NMJ integrate synaptic inputs?

Answer 38

No, the NMJ acts more like a switch, with a high safety factor to ensure reliable transmission and no integration of multiple synaptic inputs.

Question 39

What is a compound action potential?

Answer 39

It’s a summated electrical signal from a bundle of axons in a nerve, recorded extracellularly, showing varied conduction speeds for different fiber types.

Question 40

How does axon anatomy affect compound action potentials?

Answer 40

Axons with larger diameters and myelination conduct signals faster, which creates the complex waveform of a compound action potential.

Question 41

What anatomical features increase action potential conduction speed?

Answer 41

Large diameter axons and myelination speed up conduction.

Question 42

What are divergence and convergence in synaptic connectivity?

Answer 42

Divergence is when one neuron’s axon branches to contact multiple targets, while convergence is when multiple inputs synapse on a single neuron.

Question 43

What is feedback inhibition?

Answer 43

Feedback inhibition occurs when an axon collateral activates an inhibitory interneuron, which then inhibits the original neuron to prevent repeated firing.

Question 44

Differentiate between monosynaptic and polysynaptic reflexes.

Answer 44

Monosynaptic reflexes involve a direct connection between afferent and efferent neurons, while polysynaptic reflexes involve one or more interneurons.

Question 45

What is synaptic plasticity?

Answer 45

synaptic plasticity refers to changes in the strength of synapses, often activity-dependent, including processes like long-term potentiation and long-term depression.

Question 46

How do CNS synapses differ from the NMJ?

Answer 46

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.

Question 47

What is the purpose of the Golgi tendon organ reflex?

Answer 47

It protects muscles from excessive tension, which could cause damage.

Question 48

Describe the sequence of the Golgi tendon organ reflex.

Answer 48

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.

Question 49

Is the Golgi tendon organ reflex monosynaptic or polysynaptic?

Answer 49

Polysynaptic.

Question 50

Which sensory receptors initiate the flexion reflex?

Answer 50

Nociceptors, which detect painful stimuli.

Question 51

What is the function of the flexion (withdrawal) reflex?

Answer 51

It removes a limb from a harmful or potentially harmful stimulus.

Question 52

Describe the response of the flexion reflex.

Answer 52

Activated nociceptors stimulate interneurons that:
Excite motor neurons to ipsilateral flexor muscles.
Inhibit motor neurons to ipsilateral extensor muscles.

Question 53

What is the purpose of the crossed extensor reflex?

Answer 53

It maintains balance by activating the opposite limb when one limb is withdrawn from a harmful stimulus.

Question 54

Describe the response in the crossed extensor reflex.

Answer 54

A: The reflex activates interneurons that:
Inhibit motor neurons to contralateral flexors.
Excite motor neurons to contralateral extensors.

Question 56

Is the flexion and crossed extensor reflex a monosynaptic or polysynaptic reflex?

Answer 56

Polysynaptic, as it involves multiple interneurons and motor neurons.