Nerve Impulse Quiz

A: A nerve impulse is an electrochemical message that travels quickly along a nerve fiber, allowing the body to respond rapidly to changes in the internal or external environment.

A: A nerve impulse is electrochemical because it involves both an electrical voltage change and chemical shifts, specifically the movement of ions across the neuron cell membrane.

A: Membrane potential is the potential difference across a cell membrane due to ion concentration differences between the extracellular and intracellular fluids. In unstimulated neurons, this resting membrane potential is about -70 mV, with the inside of the cell being more negatively charged than the outside.

<p>A: Ions cannot directly diffuse through the cell’s phospholipid bilayer and must pass through protein channels. Some, like leakage channels, are always open, while voltage-gated channels open only when the nerve is stimulated.</p> Signup and view all the answers

<p>A: The sodium-potassium pump is a carrier protein that actively transports ions against their concentration gradients using ATP, moving three Na+ ions out and two K+ ions into the cell, resulting in a net reduction of positive ions inside the cell and maintaining the negative resting membrane potential.</p> Signup and view all the answers

<p>A: Depolarization is a rapid increase in membrane potential due to a strong enough stimulus that opens ligand-gated sodium channels, allowing Na+ ions to flow in and making the intracellular space less negative. If the membrane reaches -55 mV, voltage-gated Na+ channels open fully, leading to a positive charge inside the cell.</p> Signup and view all the answers

<p>A: During repolarization, Na+ channels close, and K+ channels open, allowing K+ to exit the cell and restoring the negative membrane potential. Hyperpolarization occurs when the membrane potential briefly drops below the resting level due to prolonged K+ channel opening.</p> Signup and view all the answers

<p>A: The refractory period is a phase following depolarization when the neuron cannot respond to another stimulus. This period ensures that nerve impulses travel in one direction along the neuron.</p> Signup and view all the answers

<p>A: In unmyelinated fibers, the action potential moves continuously along the membrane. In myelinated fibers, the impulse jumps between nodes of Ranvier in a process called saltatory conduction, which allows faster transmission—up to 140 m/s compared to 2 m/s in unmyelinated fibers.</p> Signup and view all the answers

<p>A: A nerve impulse is always the same size, regardless of stimulus strength, provided it meets the threshold. A strong stimulus, however, can depolarize more fibers and generate more impulses in a given time, enabling the brain to distinguish intensity.</p> Signup and view all the answers

<p>1 When the nerve impulse reaches the axon terminal, it activates voltage-gated calcium ion channels.</p> <p>2 As there is a higher concentration of calcium ions in the extracellular fluid, they flow into the cell at the pre-synaptic axon terminal.</p> <p>3 This causes synaptic vesicles to fuse with the membrane, releasing special chemicals called neurotransmitters by exocytosis.</p> <p>4 The neurotransmitters diffuse across the gap and attach to receptors on the membrane of the next neuron.</p> <p>5 This stimulates ligand-gated protein channels to open, which allows the influx of sodium ions and initiates an action potential in the post-synaptic membrane.</p> Signup and view all the answers

<p>A: Chemicals can enhance or inhibit nerve transmission at synapses. Stimulants like caffeine boost transmission, while depressants like anesthetics inhibit it. Certain toxins, like those in nerve agents, disrupt neuromuscular junctions by causing acetylcholine buildup, leading to muscle paralysis.</p> Signup and view all the answers