A Muscular System Guide

Human anatomy is a combination of several complex systems. Each system has its own major purposes, but also works with other systems to function properly and to take care of the body's needs. The muscular system's primary jobs are to give the body shape and enable it to move on the inside and the outside. To do this, the muscular system works with other systems, such as the skeletal system, which supports and protects the body. The human body has over 600 muscles.

The Muscular System

There are three kinds of muscle in the human body: smooth, cardiac (heart) and skeletal. When muscles contract, the movement is either voluntary (intentional, such as bending an arm) or involuntary (automatic, such as the heart beating). Smooth muscles and cardiac muscles are involuntary, while skeletal muscle is voluntary. A muscle is made up of cells, called fibers, which are long and thin, not unlike strands of hair. Nerves in the muscle fiber are what cause muscles to contract, causing movement. The muscles in the head, neck and trunk are called “axial muscles,” whereas “muscles of the extremities” are found in the arms and legs.

Muscular System: A guide that explains types of muscles, functions of muscles, and muscle tension.

List of Muscles: A resource on the origin, insertion, action and nerve of different muscles in the human body.

Muscular Tissue: A complete resource for understanding the functions and types of muscular tissue.

Face Muscles

Facial muscles allow us to express ourselves in a non-verbal way. Many facial muscles attach under the skin instead of attaching to bone, like most other muscles. Expressions are made by facial muscles contracting alone or in combination, which moves the skin to produce various configurations that signal our mood, intention, feelings or reaction.

Face Muscles: A straightforward guide that explains face muscles along with their associated nerves, as well as the facial artery and vein.
Facial Nerve Anatomy: An excellent resource for understanding facial muscles and nerves.

Neck Muscles

The neck muscles extend from the base of the skull to the back. They hold the head upright and allow it to move from side to side and up and down. Neck movement is broadly divided into four parts; rotation, lateral flexion, flexion, and hyperextension. A pain in the neck is actually a common occurrence and usually occurs if neck muscles are contracted for an extended length of time.

Neck Muscles: Physical and functional descriptions of each neck muscle, along with an illustration of their positioning,.

Muscles of the Neck: Explanation of neck muscles functions and positioning by group.
Posterior Neck Weakness: A complete resource to know more about posterior neck weakness.

Deltoid

The portion of the shoulder located at a 90-degree angle to the elbow and neck is known as the deltoid and it forms the round shape of the shoulder. The deltoid controls shoulder movement and has a great amount of control over movement of the arm. Shoulder movements include abduction, flexion and transverse abduction. Another important function of the deltoid is to prevent the dislocation of the upper arm bone when a person carries a heavy load.

Deltoid Muscle: Interactive illustrations of the deltoid muscle and the arm movements it facilitates. Other arm muscles are also illustrated.

Posterior Deltoid: Interactive table showing the location, movements and functions of the deltoid. Includes video clips that clearly illustrate arm and shoulder movements associated with the deltoid.

Biceps

The “biceps brachii” are located in the upper arm. Biceps are actually two bundles of muscles with different origins but the same insertion point. The primary functions are to bend the elbow, turn the forearm and bend the humerus head. The biceps also control three joints, the shoulder, elbow, and radioulnar, and so are said to be “triarticulate.”

Anatomical Terminology of the Muscular System: A diagram of the muscles of the upper extremities indicates the positioning of the biceps.

Biceps: A simple and brief guide on biceps.

Extensors of Wrists and Fingers

Finger extensor muscles allow free flowing movement of the hand. Without them, the fingers would be unable to grasp or extend. The wrist extensors allow the wrist and hand to bend forward and flex back. While the extensors are small compared to some other muscles, they are incredibly strong.

Muscles of the Wrist and Hand: The actions of the wrist and hand are categorized, along with a listing of the muscles responsible for those actions.
Extensor Muscles of the Forearm: Explanatory chart on the extensors of the forearm includes origin, insertion point, action and more.

Muscles of the Forearm: Description of forearm muscles grouped by location.

Chest Muscles

Muscles in the chest part are called the pectoral muscles and are divided into two types: pectoralis major and pectoralis minor. Pectoralis major is a large, fan-shaped muscle that is situated at the anterior part of the chest. Pectoralis minor is a triangular-shaped, thin muscle that is located just beneath the major muscle. The primary function of the pectoralis major is to move the shoulder joints, while pectoralis minor helps in moving the shoulder forward.

Muscle Atlas: A table of contents of the upper and lower extremities outlines medical terminology for the chest muscles, in addition to other anatomy.

Pectoral Region-Anatomy Table: A resource for understanding chest muscles in context of surrounding arteries, veins, lymphatics, nerves, and viscera.

Abdominal Muscles

The abdominal muscles are located between the ribs and the pelvis in the front and on each side of the lower abdomen. The important abdominal muscles are the external oblique, internal oblique, transverses abdominis, rectus abdominis, and pyramidalis muscle. These muscles cover and protect the organs and keep the body upright. Abdominal muscles also play an important role in supporting the back when heavy objects are lifted and with deep, heavy breathing.

Abdominal Muscles: A guide to the abdominal muscles and explanations of types of abdominal muscles, effective abdominal exercises, and muscle strain.

Abdominal Anatomy: This overview of the trunk muscles features a diagram with clear labels.

Quadriceps

The quadriceps are a group of four muscles located on the front of the thigh. This muscle grouping covers the side and front of the femur and is also the extensor of the knee. Often considered the strongest muscle in the body, quadriceps are divided into four parts: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. Quadriceps help the body move in any direction and allow the leg to flex and extend, thus playing a key role in in walking, squatting, jumping, and running.

Quadriceps Muscle: A thorough guide detailing the location, function, and other anatomical features of each of the four muscles that compose quadriceps.
Muscles of the Leg: Information on the origin, insertion, action, blood, and nerve of quadriceps and other leg muscles.

Groin Muscles

The groin muscles are called the adductors (adductor magnus, adductor longus, and adductor brevis), the pectineus, and the gracilis. The groin regions are the two bends near the junction of the trunk with the legs. The common injury called a “groin pull” or “groin strain” is usually the result of injury to the adductors. The main function of groin muscles is to move the leg back towards the body's midline, helping the body maintain balance during walking, running, and any sport requiring rapid changes in the body's direction of movement.

Illustration of Groin Muscles: A graphic showing the location of each groin muscle and a brief, straightforward description of the function of each muscle.
Pulled Groin Muscle: From Mount Sinai Medical Center, a diagram of groin muscles illustrating common injury to the area. Causes, risks, symptoms, diagnosis, treatment, and prevention is clearly explained.