EXAM 2 Index cards

In this scenario, how is K+ most likely crossing the membrane?

Using a channel protein; K+ is charged and cannot pass directly through the phospholipid bilayer.

What is the name of the transport mechanism by which K+ would be crossing the membrane in this scenario?

Facilitated diffusion; K+ moves through a membrane protein down its electrochemical gradient without using ATP

Explain why it can be called “equilibrium” if the concentrations of K+ on the two sides of the membrane are different.

equilibrium occurs when the chemical force pushing K+ in one direction is balanced by the electrical force pushing it the opposite direction

Why does K+ reach equilibrium even though the concentrations are not equal in the two compartments?

Because there is no more net movement

Explain why the hydration she of K+ is not as big as the hydration shell for Na+

K+ has a larger ion radius and a lower charge density than Na+; Na+ is smaller, so its positive charge is concentration over a smaller area. It attracts water molecules more strongly and forms a larger hydration shell

One way to move ions across the membrane is the Na+/K+ pump. This is an example of:

Primary active transport; the pump directly uses ATP to move ions against their concentration gradients

One cycle of the Na+/K+ pump moves:

3 Na+ out and 2 K+ in

Which ion seems like it is more responsible for getting the membrane to a resting membrane potential of -70 mV

K+ because resting membrane is much more permeable to K+ so the resting potential is closer to K+’s equilibrium potential of about -90mV then to Na+s equilibrium

If the membrane is at resting membrane potential (-70mV), are Na+ and K+ still moving across the membrane?

yes, individual Na+ and K+ ions are still moving. The Na+/K+ pump maintains concentration gradients and prevents the ions from reaching equilibrium

If equal numbers of Na+ and K+ channels open at -70mV, which ion moves faster

Na+, because Na+ has a much larger electrochemical driving force.

Why are the chemical and electrical arrows for K+ not the same length?

The arrows represent forces with different strengths; The concentration gradient pushes K+ outward, while the electrical gradient pulls K+ inward. These forces are opposite but not necessarily equal in strength

If a voltage gated Na+ channel opens, how will membrane potential change?

It will become more positive

What type of feedback does this sound like?

Positive feedback

At the peak of the action potential (+30mV), what forces are acting on K+

Chemical driving force outward; electrical driving force outward. K+ concentration is higher inside the cell so the chemical force pushes K+ outward, and at ~ +30mV the inside of the cell is also positive, which electrically repels positive k+ outward

Which method of action potential propagation do you think will get the action potential to the axon terminals first?

Saltatory conduction; in myelinated axons the action potential jumps between node of Ranvier.

In a typical neuron, where would you find these neurotransmitter receptors

In the dendrites and cell body; they usually receive signals from other neurons. their receptors bind neurotransmitters and produce graded potentials

If a monovalent cation channel opens, which ion will move faster through it?

Na+ because it has a stronger electrochemical driving force than K+, so Na+ moves more rapidly through an open cation channel

Assume there is a large release of neurotransmitter at a synapse, leading to a large EPSP, big enough to get the postsynaptic membrane to -50mV will it fire a potential?

No it will not fire a potential, the membrane potential must reach threshold at the axon hillock or initial segment.

Would there be a limit to how frequent the action potentials can be?

Yes, during absolute refractory period potentials can’t overlap each other one must finished before another can fire

For this ion to reach equilibrium, the forces required to counterbalance the chemical gradient would be directed ______ and the equilibrium potential for this ion would be ______ number?

Outward;Negative. The chemical gradient pushed the negative ion inward to lover concentration. An electrical force directed outward must oppose it. A negative membrane potential inside the cell repels the negative ion outward

What is the mechanism by which a skeletal muscle cell contracts?

The sliding filament theory. Actin and myosin filaments slide past one another the sacromere become shorter as myosin pulls action toward the center

Where does calcium come from?

From the SR especially in the terminal cisternae, The SR stores Ca+ inside the muscle fiber. When the muscle is stimulated Ca+ is released into the cytoplasm and binds to troponin

What cause Ca+ to be released from the SR?

An action potential that travels along the muscle membrane and down the T-tubules, causing DIH receptors to activate the ryanodine receptors on the SR

We discussed how skeletal muscle contracts. How does the muscle relax?

Ca+ is actively pumped back into the SR by Ca+ ATPase pumps.

TTX blocks voltage gated Na+ channels. Which statement is true?

Upon receiving a stimulus, the neuron will produce a graded potential but cannot produce an action potential/ Graded potential cans till happen bcs they’re produced by ligand gated channels but Voltage gated channels require Na+

Autonomic preganglionic neurons are myelinated: What creates the myelin?

Schwann cells

Autonomic preganglionic neurons are myelinated: Where is the myelin found on the neuron?

Axons

Autonomic preganglionic neurons are myelinated: Describe the function of the myelin

It increases production go potentials; Saltatory Conduction

In a synapse, what is needed for the synaptic vesicle membrane to fuse with the cell membrane, allowing exocytosis of neurotransmitter from the presynaptic neuron?

Ca+ enters the neuron

In which case would action potentials propagate faster down a nerve fiber?

Larger diameter axon

What are the names of the two types of cholinergic receptors?

1. nicotinic

2. muscarinic

Where is nicotinic found in the parasympathetic nervous system?

Terminal ganglion; everywhere else

Where is muscarinic found in the parasympathetic nervous system?

On the final efferent organ; on the tissue

Which branch of the peripheral nervous system controls skeletal muscle:

Somatic nervous system

Which cholingeric receptor is found in the motor endplate of the NMJ on a skeletal muscle the effector organ

Muscarinic

During an action potential, the depolarization of the sarcolemma of a muscle fiber is the result of:

Sodium moving into the cell

Besides motor unit recruitment what other mechanics can adjust the tension in the skeletal muscle? explain how it works.

Twitch summation; It creates higher frequency of action potentials

In a synapse, if chloride ion channel opens and chloride enters the cell what would happen to the membrane potential?

Hyperpolarize

In a synapse, if chloride ion channel opens and chloride enters the cell what would happen to the membrane potential? Would the above synapse be excitatory or inhibitory?

Inhibitory