The Structure of Skeletal Muscle

Skeletal muscle has several important functions within the human body. One of these is movement, which occurs when skeletal muscle attaches to bone, which they pull against in order to enable movement. Another function is to enable support and posture, this is due to the fact that skeletal muscles are rarely fully relaxed. They are in a constant state of slight contraction. Skeletal muscles also produce heat. This is due to when the muscles contract, it involves the production of breaking down glycogen in order to provide this energy, which in turn, releases heat.This causes the body to get hot when we exercise. When our bodies are cold, the muscles often go through a series of involuntary muscle contractions, which in turn, releases heat to help keep the body warm.Skeletal muscle is completely surrounded by a thick connective tissue, which is known as epimysium.

Epimysium is continuous and eventually forms tendons, which helps joint the muscle onto bones. Each pert of the muscle is covered by connective tissue, which helps to provide shape and strength. The muscle belly is made up of lots of fibre bundles, which are known as fasiculi, and are covered in perimysium. Each fibre within a fasciculus is encompassed by a membrane, which is known as the sarcolemma. This contains many smaller fibres called myofibrils which provide the contractile unit of the muscle. These myofibrils are covered by endomysium and have striations, which represent a sarcomere. The myofibrils are a pattern of separate units connected end on to form long strands. These units are called sarcomeres and are the contractile units of the muscle. This pattern is repeated along the length of the m yofibril. yofibril.

There are three different types of skeletal muscle fibers, which are: Red/slow Type I fibers “slow twitch fibers’; Red/fast Type IIa fibres “fast oxidative fibres’; White/fast IIb fibres “fast glycoltic fibres.” Each of these muscle fbres have different functions and characteristics which define them.Type I muscles fibres main characteristics are that they have slow ATPase activity. They also have a high capacity for ATP production via oxidative phosphorylation. Type I muscle fibres also very phosphorylation. Type I muscle fibres also very dense capillary networks. Due to these three characteristics the main pathway for ATP production is aerobic cellular respiration, the final stage of which is oxidative phosphorylation. Type 1 fibres also produce high levels of intracellular myoglobin. Due to this and the fact that the capillary networks are dense, their predominant colour is red.

The main characteristics of fast contracting muscle fibre Type IIa are, that have higher myosin ATPase activity than Type 1 muscle fibres. They also have a high capacity for ATP production via oxidative phosphorylation. Their capillary network is also dense. These characteristics mean that the main pathway for ATP production is aerobic cellular respiration, the final stage of which is oxidative phosphorylation. They also have high levels of intracellular myoglobin. Which also means - the same as Type I - their predominant colour is red.