By Jacklyn Toms
Updated Mar 24, 2022

TL;DR

A muscle is a bundle of fibrous tissue that contracts to move bone. Muscles attach to bone at joints—such as the knee or elbow—and are controlled by nerves that send electrical signals from the brain. Together, the skeletal, muscular, and nervous systems give the body shape, support, and the ability to move.

What Is the Skeletal System?

The adult human skeleton is the primary support framework, comprising 206 distinct bones. It is divided into two main regions:

• Axial skeleton – the rib cage, spine, and skull, protecting the brain, spinal cord, heart, lungs, and other vital organs.
• Appendicular skeleton – the bones of the arms, legs, shoulders, and hips. This region contains 126 of the 206 bones.

Muscles attach to these bones at joints, enabling movement and maintaining posture.

What Is a Musculoskeletal Connection?

A musculoskeletal connection, commonly called a joint, is the site where muscle meets bone. Joints allow the body to assume an upright stance, walk, reach, and perform countless fine motor tasks. They vary in size and function—from large weight-bearing joints like the knee to small, precise joints in the fingers.

How Do Muscles Work?

Skeletal muscles contract voluntarily to move bones or stabilize them. For instance, lifting an arm requires the shoulder muscles to contract, pulling the humerus upward. Muscles remain contracted as long as the movement or hold is required.

Each skeletal muscle fiber is a long, multinucleated cell surrounded by connective tissue. Inside, myofibrils contain the actin and myosin filaments that slide past one another during contraction, a process described by the Sliding Filament Theory.

What Are Tendons and Ligaments?

Tendons and ligaments work alongside muscles to facilitate movement and maintain joint stability. They also guard against excessive joint extension or flexion.

• Tendons attach muscle to bone; they are strong, flexible, and not elastic.
• Ligaments connect bone to bone, providing joint support while allowing controlled flexibility.

How Do Nerves Help Muscles Move?

Signals from the nervous system travel via neuromuscular junctions, the synaptic connections where a motor neuron meets a muscle fiber. These junctions convert electrical impulses into chemical signals that trigger actin–myosin interactions, leading to muscle contraction.

For example, when you decide to stand, the brain sends a command through the nerves to the leg muscles. The signal reaches the neuromuscular junctions, causing the muscles to contract, which pulls the femur and tibia, allowing the body to rise upright.