L25 Skeletal Muscle Structure and Function

Skeletal muscle is essential for movement, posture, and heat generation.

A muscle cell is made of myofilaments, and the sarcomeres within it are made of myofibrils.

Myofibrils have around 30,000 sarcomeres.

[blank_start]Sarcoplasmic Reticulum[blank_end]: The ER of the muscle. Stores calcium. [blank_start]T-tubule(Transverse tubule)[blank_end]: invaginated sarcolemma, enhances calcium transport. [blank_start]Triad[blank_end]: T-tubule in between two SR.

Troponin and tropomyosin attach to myosin, making them part of the thick filament.

If a motor neuron innervates a large number of muscle fibres, the action is precise. If a motor neuron innervates a small number of muscle fibres, the action is unprecise.

Choose the correct statements.

The mechanism of contraction of skeletal muscles begins with [blank_start]excitation[blank_end]. Here, the [blank_start]neuronal[blank_end] action potential is transferred to a [blank_start]muscular[blank_end] action potential via the neurotransmitter ACh. (This ACh is diffused through the NMJ when [blank_start]Ca++[blank_end] channels opening in the neuron trigger the release of vesicles.) Next, [blank_start]contraction[blank_end] occurs. ACh receptors open voltage gated [blank_start]Na+[blank_end] channels, which depolarises the muscle membrane ([blank_start]sarcolemma and T-tubules[blank_end]). Ca++ is released from the [blank_start]SR[blank_end] and diffuses into the firstly the [blank_start]sarcoplasm[blank_end], and then the [blank_start]myofilaments[blank_end]. Here it forms crossbridges with the myofilaments, allowing them to interdigiate. After, the muscle [blank_start]relaxes[blank_end] when Ca++ is taken up into the SR and the crossbridges [blank_start]uncouple[blank_end].

Choose the incorrect statement.

The sarcolemma depolarises when no new AP innervates it.

Ca++ ions diffuse back into the SR when the muscle relaxes, and can no longer bind to troponin.

When Ca++ leaves the myofilaments, they uncouple passively.