Muscles - sliding filament theory

What is muscle made up of?

Each muscle fibre is a single muscle cell

What does multinucleate mean and why are cells multinucleate?

During [blank_start]prenatal[blank_end] development, several cells [blank_start]fuse[blank_end] together forming an [blank_start]elongated[blank_end] muscle fibre. Muscle cells are also [blank_start]striped[blank_end] which is related to their ability to [blank_start]contract[blank_end].

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muscle fibres are bound together by connective tissue, which is continuous with the tendons

Each muscle [blank_start]fibre[blank_end] may be up to 2cm long, but less than 0.1mm in diameter. Inside the muscle fibre is the cytoplasm containing [blank_start]mitochondria[blank_end] and the other organelles found in a cell. Within each muscle fibre there are also numerous [blank_start]myofibrils[blank_end]; each is composed of [blank_start]repeated contractile units[blank_end] called sarcomeres.

Sarcomeres are made up of myofibrils

What is the name of the protein that makes up the thinner filament in a sarcomere?

What is the name of the protein that makes up the thicker filament in a sarcomere?

[blank_start]Contractions[blank_end] are brought about by co-ordinated sliding of these protein filaments within the muscle cell [blank_start]sarcomeres[blank_end]. The proteins overlap and give the muscle fibre its characteristic [blank_start]striped[blank_end] (striated) appearance under the microscope. When the muscle contracts, the [blank_start]actin[blank_end] moves between the [blank_start]myosin[blank_end] - this [blank_start]shortens[blank_end] the length of the sarcomere and hence the length of the [blank_start]muscle[blank_end].

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How are myosin molecules shaped?

What are troponin and tropomyosin?

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What is sarcoplasm?

What is sarcoplasmic reticulum?

What is the sarcolemma

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When a [blank_start]nerve impulse[blank_end] arrives at a neuromuscular junction, [blank_start]calcium[blank_end] ions are released from the [blank_start]sarcoplasmic[blank_end] reticulum. The calcium ions [blank_start]diffuse[blank_end] through the sarcoplasm. This initiates the movement of protein filaments. Calcium ions attach to the [blank_start]troponin[blank_end] molecule causing it to move. As a result, the [blank_start]tropomyosin[blank_end] on the actin filament shifts its position, exposing [blank_start]myosin-binding sites[blank_end] on the actin filaments. Myosin heads bind with myosin-binding sites on the actin filament, forming [blank_start]cross-bridges[blank_end]. When the myosin heads bind to the actin, [blank_start]ADP and P[blank_end] on the myosin head [blank_start]are[blank_end] released. The [blank_start]myosin[blank_end] changes shape, causing the [blank_start]myosin head[blank_end] to nod forward. This movement results in the relative movement of filaments; the attached [blank_start]actin[blank_end] moves over the myosin. An [blank_start]ATP[blank_end] molecule binds to the myosin head - this causes the myosin head to [blank_start]detach from[blank_end] the actin. An [blank_start]ATPase[blank_end] on the myosin head hydrolyses the ATP, forming ADP and P. This [blank_start]hydrolysis[blank_end] causes a change in the shape of the myosin head. It returns to its upright position. This enables the cycle to start again

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When a muscle [blank_start]relaxes[blank_end], it's no longer being stimulated by nerve impulses. Calcium ions are [blank_start]actively pumped[blank_end] out of the muscle [blank_start]sarcoplasm[blank_end], using [blank_start]ATP[blank_end]. The troponin and tropomyosin move back, once again blocking the [blank_start]myosin-binding sites[blank_end] on the actin.

What happens in the absence of ATP?