Neuromuscular Junction

Motor End Plate

The motor end plateThe part of the muscle fiber membrane involved in neuromuscular transmission. is a specific region on the sarcolemma (cell membrane) of the skeletal muscle fiber. This is where the skeletal muscle must have receptorsProteins located on the surface or inside cells that bind specific molecules (e.g., neurotransmitter for the neurotransmitterChemicals that transmit signals across synapses. that the neuron puts into the synapse. These ligand-gated receptors are also channelsProtein passages in the cell membrane that allow specific molecules to pass through. that open upon connection with the specific excitatory neurotransmitter called acetylcholinealso know as ACh A neurotransmitter that stimulates muscle contraction. (ACh).

Once ACh connects to these ligand-gated receptorA structure that detects stimuli./channels, they open. This allows sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function. to move into the muscle fiber at the motor end plate. At first, this depolarizationThe loss of electrical charge across a membrane, triggering an action potential. is limited to the motor end plate. If enough sodium diffuses through these ligand-gated receptor/channels, voltage-gated channels in the sarcolemma surrounding the motor end plate will depolarize. The wave of depolarization spreads out from the motor end plate like a single ripple in a pond. Then it moves into the T tubules.

Figure 1: Muscle fibers, Golgi colloidal gold stain, 20X Slide 071-2A
Figure 2: Muscle fibers, Golgi colloidal gold stain, 20X Slide 071-2A
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.