The Skeletal Muscles There are about 650 muscles in the human body The Skeletal Muscles There are about 650 muscles in the human body. They enable us to move, maintain posture and generate heat. In this section we will only study a sample of the major muscles. There are about 650 muscles in the human body. They enable us to move, maintain posture and generate heat. In this unit will only study a sample of the major muscles.  

Did you know that ? - more than 50% of body weight is muscle !

Three types of muscle Skeletal Cardiac Smooth

Skeletal Cardiac Smooth Voluntary Involuntary Striated Non-striated Very Strong Short Duration Long Duration Not Strong

Skeletal muscle Maintain posture Help with locomotion Found in antagonistic pairs Joined to bones by tendons Produce heat for body

Masseter & Orbicularis Oris Elevate Mandible The masseter is one of major chewing muscles. *The origin of the masseter is on the zygomatic arch. *The insertion is on the mandible. *Contraction of the masseter will elevate the jaw.

Sternocleidomastoid The first muscle we will learn is the sternocleidomastoideus. It is sometime called the sternocleitomastoid. It is the same neck muscle shown on the previous slide. * This muscle has two origins. The first origin is on the sternum manubrium. The second origin is on the clavicle. *The insertion is on the mastoid process of the skull. *Contraction of both sternocleidomastoideus muscles will flex the head. If just on of the muscles contracts, the head will rotate.

Trapezius \or Depress Scapula The trapezius is a large muscle in the upper back. It attaches to the skull, shoulder and vertebrae of the back. *When this muscle contracts it will cause the head to extend. It will also move the scapula. The direction the scapula moves depends on which part of the trapezius contracts. The trapezius may adduct elevate or depress the scapula.

Latissimus Dorsi The latissimus dorsi is a large muscle in the back. It is often referred to as a lat. *It has origins on the vertebrae, ilium ribs and scapula. *The insertion is on the humerus. When it contracts it moves the humerus. *It can extend, adduct and rotate the arm medially. This is the main muscle used in movement such as pounding a nail with a hammer.

Abduct, Flex & Extend Arm Deltoid Abduct, Flex & Extend Arm The deltoid covers the shoulder and has the shape of a delta. *It has origins on the scapula and clavicle. *The deltoid inserts on the deltoid tuberosity of the humerus. *Contraction of the deltoid will adduct the arm. If only the anterior fibers of the muscle contract it will flex the arm. Contraction of the posterior fibers will extend the arm.

Pectoralis Major The pectoralis major is a large muscle in the pectoral region of the body. *It has origins on the clavicle and sternum. *The insertion is on the greater tubercle of the humerus. *Contraction of the pectoralis major will flex the arm. It will also adduct and rotate the arm medially. The pectoralis major is used in movements such a climbing, throwing and doing pushups.

Biceps Brachii Flexes Elbow Joint The biceps brachii is located on the anterior side of the upper arm. It is often just called the biceps. There is a biceps femoris in the leg we will study shortly. *The biceps has two origins. One origin is on the corocoid process and the other on the Glenoid cavity of the scapula. The “bi” in biceps refers to the two origins. *It inserts on the radial tuberosity. *Contraction of the biceps will cause flexing at the elbow joint.

Triceps Brachii The triceps is on the back of the upper arm. *It has three origins. Two origins are on the back of the humerus and one on the scapula. *The triceps inserts on the olecranon. *Movement of the triceps will extend the elbow joint.  

Rectus Abdominus Rectus abdominus is a long muscle in the abdomen. *The muscle originates on the pubis. *It inserts on the xiphoid process of the sternum and also on cartilage of the ribs. *When rectus abdominus contracts it will flex the abdomen.  

External Oblique Another muscle in the abdomen is the external oblique. It has muscle fibers that run in an oblique direction across the abdomen. *Contraction of the external oblique will compress the abdomen.

External Intercostals Elevate ribs There are two groups of muscles that run between the ribs. The first are the external intercostals. *They will elevate the ribs.

Internal Intercostals Depress ribs The internal intercostals are also located between the ribs. *They will depress the ribs.

Gluteus Maximus The large muscle on the posterior side of the body at the top of each leg is the gluteus maximus. *The gluteus maximus originates on the ilium, sacrum and coccyx. *It inserts on the gluteal tuberosity of the femur. *This muscle will extend and rotate the thigh laterally.

Soleus

Gastrocnemius Gastrocnemius is commonly called the calf muscle. *It originates on the distal end of the femur. *The insertion is on the calcaneus bone of the foot. *It will cause plantar flexion of the foot and also flex the lower leg.