Muscular System Help

By — McGraw-Hill Professional
Updated on Apr 25, 2014

Muscle Terminology

Muscles are named according to various features of the muscle.

  • Muscle Nomenclature
Feature Example
Shape Deltoid (like a triangle)
Location Pectoralis (chest region)
Attachment(s) Sternocleidomastoid
Orientation Rectus (straplike)
Relative position Lateralis; medialis
Function Abductor, flexor

The function (or action) of a muscle is described using the terms below.

Action Definition
Flexion Decreases the joint angle
Extension Increases a joint angle
Abduction Movement away from the midline
Adduction Movement toward the midline
Elevation Raises a body structure
Depression Lowers a body structure
Rotation Turns a bone around its longitudinal axis
Supination Rotates the forearm so palm faces anteriorly
Pronation Rotates the forearm so palm faces posteriorly
Inversion Turns the sole inward
Eversion Turns the sole outward

Muscles of the Axial Skeleton

The muscles of the axial skeleton include those used in facial expression (not discussed here), mastication, neck movement, and respiration; those that act on the abdominal wall and those that move the vertebral column.

The muscles of mastication that close the jaw are the:

The muscles of neck movement include:

The muscles of the abdominal wall all function to compress the abdomen, some act in lateral rotation and flexing the vertebral column.

The muscles of the vertebral column include a group of muscles collectively called the erector spinae muscles. These muscles are longitudinally directed muscles that function to extend the vertebral column.

Muscles of the Appendicular Skeleton

The muscles of the appendicular skeleton include those of the pectoral girdle, brachium (arm), antebrachium (forearm), manus (hand), thigh, leg, and pes (foot).

The muscles of the pectoral girdle attach the pectoral girdle to the axial skeleton and are involved in movements of the scapula.

The muscles that move the humerus at the shoulder joint function to flex, extend, rotate, abduct or adduct the humerus. The function of each muscle can be determined by the origin, insertion of each muscle.

The ventral muscles that act on the antebrachium (forearm) function to flex the elbow; the dorsal muscles function to extend the elbow.

There are numerous muscles that act on the wrist, hand, and fingers. They can be divided into three general groups:

  1. Pronators and Supinators, function to pronate or supinate the forearm;
  2. Flexors, flex the wrist and digits; and
  3. Extensors, extend the wrist and digits.

The pronator and all the flexors arise from the medial epicondyle of the humerus; the supinator and extensors all originate from the lateral epicondyle of the humerus.

The anterior muscles that move the thigh at the hip all function to flex and laterally rotate the hip. The posterior muscles extend, abduct, and some medially rotate the hip.

The medial muscles that move the thigh at the hip all function to adduct the thigh.

The muscles of the thigh that move the leg are divided into an anterior group that primarily function to extend the leg at the knee (the exception is sartorius, which flexes the leg and thigh), and a posterior group (the hamstrings) that functions to extend the thigh at the hip and flex the leg at the knee.

The muscles of the leg that move the ankle, foot, and toes are separated into (1) an anterior group (including tibialis anterior) that dorsiflexes the foot and extends the digits, (2) a lateral group (the peroneal muscles) that aid in dorsiflexion and eversion, and (3) a posterior group (including gastrocnemius and soleus) that plantar flexes the foot and flexes the toes. Only a few are described here.

Practice problems for these concepts can be found at:

Muscular System Practice Problems

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