The Muscular System

Muscles in the Body There are over 650 muscles in the human body. They are named due to many factors.

Naming Skeletal Muscles (1) Location of muscle  Bone or body region associated with the muscle Shape of muscle  Ex: deltoid (triangular) Relative size  Ex: maximus (large), minimus (small), longus (long) Direction of fibers  Ex: rectus (fibers run straight), transversus, oblique (fibers run at angles to an imaginary defined axis.

Naming Skeletal Muscles (2) Number of origins  Ex: biceps (2 origins) and triceps (3 origins) Location of attachments  Named according to point of origin or insertion. Action  Ex: flexor or extensor, as in the names of muscles that flex or extend.

Muscles of the Scalp Epicranius  2 part muscle consisting of the following:  Frontalis Primary function is to raise the eyebrows.  Occipitalis Works with the frontalis

Temporalis Located on the side of your forehead. One of the major muscles of mastication (chewing)  Allows you to raise your cheeks

Sternocleidomastoid Muscles Anterior muscles of the neck that act to flex and rotate the head.

Trapezius Large muscle that extends from the neck to a person’s back. Responsible for:  Shrugging  Turn head side to side.  Drawing the shoulder bones toward the midline.  Pulling the shoulder blades down.  Elevate the scapula  Rotate the scapula

Deltoid Muscle forming the round contour of the shoulder. Responsible for:  Shoulder abduction  Lifts the arm from to the side of the body. Flexion Extension

Biceps Brachii Muscles in the upper arm Have several functions:  Flex the elbow  Rotate the forearm

Triceps Found in the upper arm. An extensor muscle, unlike the biceps which act as flexors. Allows for elbow extension, which allows for pressing activities.

Pectoralis Major Also known as the “pecs.” Thick, fan-shaped muscle at the upper front of the chest wall. Actions:  Flexes the humerus (upper arm)  Draws the scapula anteriorly (back) and inferiorly (down)

Rectus Abdominis Paired muscle running vertically on each side of the anterior wall of the human abdomen. Commonly known as the “abs” Functions  Key postural muscle Responsible for flexing the lumbar spine as when doing a “crunch.”  Can play a role in respiration

Oblique Muscles Located on the sides of the abdomen. Allow you to twist.

Latissimus Large flat dorso-lateral muscle of the trunk. Also known as the “lat.” Responsible for:  Extension, adduction, transverse extension, and internal rotation of the shoulder joint.  It also has a synergistic role in extension and lateral flexion of the lumbar spine.

Gluteus Maximus It is a large muscle in the butt. One of the strongest muscles in your body. Responsible for:  Extends the femur  Keeps body upright when motion is occurring and when motion stops.

Rectus fermoris One of the four quadriceps muscles Located in the middle, front of the thigh. Functions:  Hip flexion  Knee extension

Sartorius A long, thin muscle that runs down the length of the thigh. Longest muscle in the human body. Responsible for:  Abduction, flexion, and lateral rotation of the hip  Medial rotation of the knee

Hamstrings Located in the back of your leg. Responsible for:  Flexion of the knee  Walking, running, jumping, and controlling some movement of the trunk.

Gastrocnemius Located in the back part of the lower leg. Also called the calf. Involved in:  Standing, walking, running, and jumping.

Tibialis anterior Muscle in the shin that spans the length of the tibia. Functions to stabilize the ankle and foot.