B2.3.9 Adaptations of cardiac muscle cells and striated muscle fibres (HL) Notes

Cardiac and Striated Muscle Cells Are Adapted for Specialized Contraction and Force Generation

1. Muscle cells are highly specialized to allow movement and force generation.
2. Cardiac muscle cells and striated muscle fibres (skeletal muscles) have distinct adaptations suited to their respective functions.
3. While both types of muscles contain contractile myofibrils, they differ in structure and function, which reflect their specialized roles in the body.

Adaptations of Cardiac Muscle Cells

1. Branched Structure of Cardiac Muscle Cells

1. Cardiac muscle cells are branched, which allows them to form a network of interconnected cells.
2. The branching structure helps create a continuous pathway for electrical signals, ensuring synchronized heart contractions.
3. Function: The branching allows intercalated discs (specialized junctions) to form, facilitating the rapid transmission of electrical impulses from one cell to another, leading to coordinated heartbeats.

2. Presence of Single Nucleus

1. Cardiac muscle cells usually have a single nucleus located centrally within the cell.
2. This allows for more efficient control of contraction, as the nuclei direct the functions of the entire cell without the need for multiple control centers.

3. Myofibrils in Cardiac Muscle

1. Just like striated muscle fibers, cardiac muscle cells contain myofibrils made up of repeating sarcomeres, responsible for the contraction process.
2. These myofibrils allow for strong, controlled contraction necessary for pumping blood throughout the body.

Adaptations of Striated Muscle Fibers (Skeletal Muscle)

1. Long and Unbranched Structure

1. Striated muscle fibers, or skeletal muscle cells, are long and unbranched, which allows them to extend across large areas of the body.
2. These fibers are capable of generating significant force through the contraction of multiple units in parallel.

2. Multiple Nuclei

1. Skeletal muscle fibers are multinucleated, meaning they contain many nuclei per cell.
2. This is necessary because skeletal muscle fibers are so long that a single nucleus wouldn’t be sufficient to control all the activities within the cell.
3. The multiple nuclei allow for efficient coordination and regulation of contraction across the entire length of the fiber.

3. Myofibrils in Skeletal Muscle

1. Like cardiac muscle, striated muscle fibers also contain myofibrils.
2. These myofibrils consist of repeating sarcomeres, and the interaction between actin and myosin filaments enables the contraction that leads to voluntary movement.

Differences Between Cardiac Muscle Cells and Striated Muscle Fibers

Is a Striated Muscle Fibre a Cell?

1. Skeletal muscle fibers are not typical cells in the traditional sense.
2. Although they share many characteristics with cells (such as having nuclei and a membrane), they are multinucleated and long.
3. They are sometimes referred to as syncytial cells (multinucleated cells formed by the fusion of individual cells), rather than individual cells.
4. Despite being multinucleated, skeletal muscle fibers are still considered cells in the context of muscle function, but their structure and function make them distinct from typical, single-nucleus cells.