9.4 Skeletal Muscle Fiber Physiology

resting membrane potential

charge difference in an inactive cell due to more protein and K+ inside and more Na+ outside membrane, polarized cell

types of ion channels

ligand and voltage gated ion channels

ligand gated ion channels

specific neurotransmitter (acetylcholine) binds to a receptor part of the ion channel (motor end plate) in muscle, Na+ gate opens

voltage-gated ion channels

open and close in response to small voltage changes across sarcolemma (muscle plasma membrane), specific ions to specific gates (Na+, K+, Ca2+)

3 factors for resting membrane potential

increased K+ ions inside, increased Na+ ions outside, sarcolemma has more K+ leak channels than Na+ leak channels

sodium-potasium pump

active transport pump in sarcolemma that maintains distribution of Na+ and K+ ions

milivolts

The units used to measure the resting membrane potential

action potential

cell is stimulated and becomes more positive inside vs. outside

depolarization

Na+ channels open, more Na+ molecules diffuse inside cell and becomes more positive

threshold

Level of stimulation needed to trigger action potential, voltage gated Na+ channels open

Repolarization

Return of the cell to resting membrane potential (cell becomes polarized), Na+ gates close, K+ gates open and diffuse outside of cell making inside negatively charged compared to outside

all or none principle

Refers to the fact that the action potential occurs either full-blown or not at all.

propagate

the action to spread from one place to another, action potential occurs only in one region of cell membrane but creates stimulation in neighboring sections

action potential frequency

number of action potential produced per unit of time

Acetylcholinesterase

the enzyme that breaks down acetylcholine in the synaptic cleft