Action Potential and Membrane Permeability Quiz

Nerve Stimulation and Action Potential

• A weak stimulus applied to a nerve trunk will not elicit a response due to the threshold being unmet.
• During the Absolute Refractory Period (A.R.P.) of a nerve fiber, no stimulus, regardless of strength, can evoke another action potential as the sodium channels are inactivated.

Nerve Conduction

• The velocity of nerve conduction is primarily influenced by the diameter of the nerve fiber and the presence of myelin.
• Saltatory conduction describes the process of impulse propagation in myelinated nerve fibers, where the nerve impulse jumps from one node of Ranvier to the next.

Nerve Excitability

• During the Relative Refractory Period (R.R.P.), excitability increases, but a stronger stimulus is needed to trigger an action potential.
• Stimulation of a nerve fiber in an unmyelinated nerve fiber causes depolarization at the stimulation site, and the impulse travels along the fiber in a continuous wave.

Stimulus and Strength-Duration Curve

• Electric stimuli are the preferred type for stimulating nerve fibers.
• The strength-duration curve displays the relationship between the strength of the stimulus and the duration needed to elicit a nerve fiber's response.
• Rheobase represents the minimum strength of stimulus required to elicit an action potential regardless of duration.
• Chronaxie indicates the time needed for a stimulus twice the rheobase to trigger an action potential.

Resting Membrane Potential and Action Potential

• The resting membrane potential of a nerve cell is typically around -70 mV, where the inside of the cell is more negative than the outside.
• The strength-duration curve demonstrates that a strong stimulus with a shorter duration can evoke an action potential while a weak stimulus requires a longer duration.

Neuromuscular Junction

• The junction between a nerve and a muscle is called the neuromuscular junction.
• The potential required to trigger the action potential in neuromuscular transmission is known as the end-plate potential (EPP).
• Acetylcholine, after triggering muscle contraction, is broken down by acetylcholinesterase (AChE).

Calcium and Acetylcholine Release

• Calcium ions (Ca++) play a crucial role in the release of acetylcholine at the neuromuscular junction.

Motor Unit

• The motor unit is the functional unit of muscle contraction, consisting of a motor neuron and all the muscle fibers it innervates.
• During the negative after potential, nerve fibers are hyperpolarized, hence exhibiting reduced excitability.

Nerve Fiber Types and Properties

• Type A nerve fibers have the highest velocity of conduction.
• Type C nerve fibers have very high excitability.
• The sodium-potassium pump is responsible for restoring normal ionic distribution in a nerve fiber after an action potential.

Proprioception and Positive After Potential

• Type Ia and Ib nerve fibers, associated with proprioception, relay information from muscle spindles and Golgi tendon organs.
• During the positive after potential, nerve fibers become hyperexcitable and experience an increased conduction velocity.

Resting Membrane Potential and Ion Permeability

• The resting membrane potential is primarily established by the movement of potassium ions (K+) across the cell membrane, as the membrane is more permeable to K+ than Na+.
• Depolarization involves the movement of sodium ions (Na+) into the cell, making the inside of the cell less negative.

Properties of Action Potential

• One property of action potential is its "all-or-none" nature, meaning it either occurs fully or not at all.
• Repolarization, marking the end of depolarization, occurs due to the movement of K+ ions out of the cell.
• The movement of Na+ ions into the cell during depolarization is driven by the sodium-potassium pump and electrochemical gradients.

Test your knowledge on action potential, membrane permeability, ionic distribution, and after potentials in neuron physiology.