Muscular system

The muscular system provides support and facilitates movement of the body. Understanding how it works helps us see how the body performs physical activities and stays stable and strong. Use this resource to explore the components and roles of the muscular system.

The muscular system consists of all of the muscules in your body and the tissues that support them. It works with the skeletal system to help you move, maintain your posture and produce heat.

They also protect the internal organs and assist in critical functions like breathing and digestion.

Skeletal muscle

Skeletal muscle is a type of muscle that is attached to bones. It allows us to move voluntarily, like walk and lift things. It also helps us maintain our posture and generates heat to keep us warm.

Skeletal muscle is composed of fibres bundled together by connective tissues. It is striated, meaning that it is made of parallel light and dark bands. Rod-like microfibrils also run parallel to the muscle fibre. These are responsible for muscle contraction.

The contraction of muscles is controlled by the nervous system. The brain coordinates the motor neurons, which send signals to the skeletal muscle to contract. Muscles work in pairs, where one muscle contracts while the other relaxes to coordinate movement.

Examples of skeletal muscle include the triceps, which are at the back of your arm and the gluteus maximus, also known as the glutes or butt, which is the largest muscle in the body. You can go to this link to see a list of the skeletal muscles in the human body.

To make our skeletal muscle stronger, we need to exercise regularly. This improves flexibility and endurance.

Yoga class, by shushipu via Pixabay; Swimmer, by Johanna Steppan via Unsplash

Metabolism

Our skeletal muscles use ATP for energy during contraction. The body can generate this energy through two types of metabolism: aerobic respiration and anaerobic respiration

• Aerobic respiration occurs when there is a good supply of oxygen. Our muscles efficiently produce ATP by completely breaking down glucose and fat in the mitochondria to form carbon dioxide and water. It is helpful for slow, sustained energy production for activities where high endurance is needed.
• Anaerobic respiration occurs when oxygen levels are low. Our body quickly produces ATP through the breakdown of glucose alone in the cytoplasm, leading to lactic acid buildup. This can cause muscle fatigue, which explains why when you do intense activites like sprinting or lifting weights, you feel tired and sore more quickly. Anaerobic respiration is helpful for when you quickly need to obtain energy.

The process of ATP generation also produces heat, which the body can use to regulate its temperature.

Tendons

Tendons connect bones to skeletal muscle. They are mostly made up of collagen fibres, which make them tough and flexible.

Tendons work like cords, allowing muscles to pull bones effectively. They help transfer force and stabilise joints during movement.

Smooth muscle

Smooth muscle is found in the walls of organs like the stomach, intestines and blood vessels. Unlike skeletal muscle, it moves on its own, meaning that we don't control it consciously.

Smooth muscle contracts slowly to move substances through the digestive tract and regulate blood flow. It is particularly important for digestion and blood pressure regulation because it can stay contracted over longer periods of time. Smooth muscle can do this because it uses less ATP.

While skeletal muscles are made up of bundles of fibres that work together, smooth muscle is made up of individual cells that contract as one tissue in organs. Because of this, smooth muscle looks more uniform.

The smooth muscle is wrapped in neurons, meaning that it partly relies on the nervous system to coordinate its action. As well as this, it responds to hormones. For example, the hormone gastrin stimulates the contraction of smooth muscle in the stomach to help churn food.

Cardiac muscle

Cardiac muscle is found in the walls of the heart and is responsible for its rhythmic contractions. Like smooth muscle, it works involuntarily. It beats tirelessly, pumping blood throughout the body and is crucial for keeping our organs supplied with oxygen and nutrients.

Cardiac muscle has a unique structure. It is striated like skeletal muscle but forms interconnected networks called intercalated disks. This allows rapid transmission of electrical signals for the heart to contract efficiently and uniformly. They also have a high density of mitochondria to support constant contraction. Cardiac muscle is regulared by the sinoatrial node.

Summary

The components of the muscular system and their functions are outlined in the table.

Component	Function
Skeletal muscle	Attached to bones; enables voluntary movements like walking and lifting
Tendons	Connects muscles to bones; transfers force to move bones, stabilising joints
Smooth muscle	Found in organ walls; controls involuntary movements like digestion and blood flow
Cardiac muscle	Located in the heart; pumps blood continuously without conscious control

Exercise

See how well you understand the components and functions of the muscular system with a quick quiz.