Most of all movement of the human body is as a result of muscle contraction. Muscles are made up of fibres. The direction and composition of these fibres determine the appearance and strength of the muscle. All muscles are held together by connective tissue that is important to the characteristic of the skeletal muscle.
A moving muscle is attached to two different types of bones:
- Bones which are fixed in some way. The origin is often the proximal bone.
- Bones which move as a result of muscle contraction. The insertion point is often the distal bone.
What skeletal muscle is made up of
Skeletal muscle is a collection of many individual muscle fibres that are wrapped together by connective tissue to form individual bundles.
The anatomy of skeletal muscle is as follows:
- Facia which is connective tissue that covers the entire muscle.
- Epimysium which is connective tissue that covers the inner-most muscle fibres.
The fascia and epimysium help to form connective tissue between the muscle and the bone:
- The fascicle is the secondary muscle fibre inside the muscle.
- The perimysium is the connective tissue covering the fascicle.
- The endomysium is the0 connective tissue covering the inner-most muscle fibres.
All connective tissues in muscles play an important role in movement. They allow the forces that are generated by the muscle to be transmitted to create movement. Muscle tissue covers the entire length of the muscle to form tendons.
What are contractile elements of skeletal muscle fibres?
A single muscle cell is known as a muscle fibre. Under a microscope a distinct series of light and dark bands can be seen. Muscle fibres are enclosed by a membrane known as the sarcolemma. It contains typical cell components such as plasma that is called sarcoplasm which is a composed of glycogen, fats, minerals and oxygen-binding myoglobin.
Nuclei mitochondria transform energy into food. They are unlike other cells because they have structures made up of myofibrils. These contain myofilaments which are the contractile components of muscle tissue. Myofilaments are also known as actin and myosin which are thin and think filaments which form repeating sections within a myofibril.
Each one of these sections are known as a sarcomere. A sarcomere is the functional unit of the muscle that produces muscular contraction and consists of repeating sections of actin and myosin.
Tropomyosin and troponin are the two other protein structures that are important for the muscle contraction. Tropomyosin is found in the actin filament and blocks the myosin-binding sites located on the actin filament so prohibiting myosin from attaching to actin while the muscle is in a relaxed state. Troponin, also located on the actin filament, plays a role in muscle contraction by providing binding sites for both calcium and tropomyosin when the muscle needs to contract.
How to generate muscle force
A muscle generates force in a variety of different methods such as neural activation.
Neural activation is made possible by the communication between the nervous system and the muscular system. It makes muscle contraction and stabilisation possible. Where a connection is made with a motor neuron and the muscle fibres this is called the motor unit. The point where a single neuron meets a single fibre is called the neuromuscular junction. Impulses travel down from the central nervous system into the axon on the neuron. When the impulses reach the end of the axon, chemicals called neurotransmitters are released.
Neurotransmitters send messages between the neurons, nerves and muscle fibres. They fall into receptor sites on the muscle fibre. The neurotransmitter that is required by the neuromuscular system is called acetylcholine (Ach). Ach stimulates the muscle fibres to go through the necessary steps to produce a muscle contraction.
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