Muscular System. Student Learning Objectives: Identify the major muscles of the body Identify the action of major muscles of the body

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1 Muscular System Student Learning Objectives: Identify the major muscles of the body Identify the action of major muscles of the body Structures to be identified: Muscle actions: Extension Flexion Abduction Adduction Circumduction Head: Frontalis Orbicularis oculi Temporalis Zygomaticus major Orbicularis oris Masseter Risorius Neck and Trunk: Sternocleidomastoid Trapezius Pectoralis major Serratus anterior Latissimus dorsi External abdominal oblique Internal abdominal oblique Rectus abdominus Arms: Deltoid Biceps brachii Triceps brachii Legs: Gluteus maximus Gluteus medius Adductor group (Gracilis, Adductor magnus, and Adductor longus) Quadriceps group (Vastus lateralis, V. intermedius, V. medialis and Rectus femoris) Hamstring group (Biceps femoris, Semitendinosus, and Semimembranosus) Sartorius Tibialis anterior Gastrocnemius Achilles tendon Introduction The muscular system of the body provides movement. The skeletal muscles that you will be learning the names and actions of in this lesson are found attached to the bones of the skeleton. Muscle is a type of tissue that can contract. During contraction, the muscle shortens, pulling the attached bone along with it. This kind of action allows the individual to move around within his/her environment. In the last exercise, you looked at the skeleton. Remember the articulations? They had different shapes of bones and different abilities to move. The muscles that you will be looking at cross over these joints. Keep in mind the shape of the joint that is associated with the muscles that you are studying in this exercise. This will help you predict the type of movement that the muscle will cause during contraction.

2 Muscular Movements When you bend your arm to show off your muscle, the angle between the humerus and the radius and ulna gets smaller (i.e. the bones get closer together). Such a movement is known as flexion. Bending over at the waist, squatting down, and bending your knee would be additional examples of this type of movement. When you straighten that limb out again that the angle between the bones becomes greater (i.e. the bones move farther apart), the action is known as extension. If you move your arm or leg directly away from you to the side (i.e. away from the midline), this is known as abduction. When you return the limb to the original position (i.e. move it back towards the midline), the action is called adduction. When you do the exercise known as Jumping Jacks, you are doing combinations of abduction and adduction movements. Circumduction is a circular movement around a central pivot point. This type of movement is possible in ball-and-socket joints. When you do the exercise known as Windmills with your arms, you are doing circumduction. This can be done with your leg also is you move to draw a circle with your toe. Keep these kinds of movements in mind as you are looking at the muscles and studying their actions. Muscles of the Head Numerous muscles are found in the head region, especially in the face. These muscles are used in facial expressions, eating, and protection. The orbicularis oculi encircles the eye. Contraction of this muscle closes the eyelids to keep out debris or keep the eye moist. A similar, circularly arranged muscle surrounds the mouth. This muscle, the orbicularis oris, puckers the lips (as for a kiss). The zygomaticus major is also associated with the lips. This muscle connects the corner of the mouth to the zygomatic bone. Contraction of the zygomzticus major pulls the corners of the mouth upward (as in a smile). The risorius is also attached to the corners of the mouth and pulls the edges of the mouth laterally. The masseter is a large band of muscle tissue that begins at the temporal bone and covers over the ramus of the mandible. This muscle closes the jaw for chewing. The temporalis muscle also connects the temporal bone to the mandible and is involved in the chewing process.

3 The frontalis covers the forehead and raises the eyebrows, wrinkling the skin of the forehead in the process. Muscles of the Neck and Trunk The sternocleidomastoid lies on the lateral side of the neck. This strong band of muscle attaches to the sternum and clavicle in the front and the mastoid process of the temporal bone at the back. Contraction of the sternocleidomastoid muscle on one side of the head only will turn the head downward and towards that side. Contraction of both muscles at the same time will flex the head downward. Two large muscles cover the back. The trapezius attaches to the base of the occipital bone and then to the vertebra all the way down the back into the lumbar region and, finally, to the clavicle and the scapula forming a triangular-shaped muscle. Contraction of the trapezius pulls the scapula upwards (as when shrugging your shoulders), backwards (for good posture!), or downwards depending upon which part of the trapezius muscle is acting at a given time. In addition, the trapezius extends the neck, pulling the head upward. The latissimus dorsi is a large triangular muscle of the lower back. This muscle attaches to the vertebra from the mid-thoracic region all the way to the sacrum and then to the humerus. Contraction of this muscle adducts and rotates the arm moves it posteriorly.

4 The pectoralis major lies in the anterior shoulder region, beneath the breast. The muscle attaches to the sternum, clavicle, and humerus. Contraction of this muscle adducts the arm and pulls the shoulder forward. The serratus anterior lies beneath the upper arm and is partially covered by the pectoralis major and latissimus dorsi muscles. This muscle has multiple edges attaching to the ribs giving a jagged, stair-step appearance to the muscle, similar to the edge of a serrated knife. This muscle elevates the ribs and expands the size of the thorax. The abdomen is covered by a number of muscles that are arranged somewhat like the layers of plywood. The external abdominal oblique is the most superficial of the layers. Under this lies the internal abdominal oblique. These two muscles have fibers that run diagonally, in opposite directions. Sandwiched between the tendons of these two muscles near the midline at the front of the body is the rectus abdominus. The rectus abdominus muscles appear as the six-pack that shows up on the abdomen of many very physically fit individuals. Deep to the internal abdominal oblique is the transverses muscle that forms the innermost layer of the abdominal wall. This muscle cannot be seen on any of the model view that are included in this exercise. The muscles of the abdomen flex the spine (i.e. the rectus) so that you can touch your toes and compress the abdomen.

5 Muscles of the Arm There are numerous muscles of the arm, but we will focus strictly on three of them for this course. The deltoid muscle covers over the top of the shoulder joint. The deltoid causes numerous movements of the shoulder (depending upon which muscle fibers are involved) including flexion, extension, and abduction. This is the muscle used for giving intramuscular injections in the arm. The biceps brachii is the large muscle on the anterior part of the humerus. This is the muscle that contracts when you are showing off your muscle to impress everyone. The biceps brachii flexes the shoulder and elbow and rotates the hand. The triceps brachii is the large muscle on the posterior part of the humerus. This muscle has actions that oppose those of the biceps brachii. The triceps brachii extends the shoulder and elbow.

6 Muscles of the Legs Several large muscles are found in the buttocks region. The gluteus maximus is the largest and most posterior of the gluteal muscles. The gluteus medius lies just anterior and superior to this muscle, against the main portion of the ilium. The gluteus medius is the muscle used for intramuscular injections in buttocks region. The gluteal muscles abduct the hip and rotate the thigh. There several large muscle groups in the legs. The anterior thigh contains the muscle group known as the quadriceps. Four muscles make up this muscle group: vastus lateralis, vastus intermedius, vastus medialis, and rectus femoris. This muscle group extends the knee and flexes the hip. The vastus lateralis is the muscle used for intramuscular injections in the thigh, often used in infants and the elderly. Overlapping the quadriceps muscles is the sartorius. This strap-like muscle cuts diagonally across the thigh. The sartorius rotates the hip and flexes the hip and knee allowing you to cross your legs.

7 The hamstrings group lies at the back of the thigh. This group includes the bicep femoris, semitendinosus, and semimembranosus. This muscle group opposes the actions of the quadriceps causing flexion of the knee and extension of the hip, along with some rotation of the leg. A third muscle group lies on the medial thigh. The adductor group pulls the leg back to the midline. The gracilus, adductor magnus, and adductor longus make up this group. In the lower leg, the tibialis anterior muscle lies on the front of the leg in the area of the lateral shin. This muscle pulls the toes upward and turns the foot. On the posterior lower leg is the gastrocnemeus. This large, calf muscle is attached to the calcaneus bone by the Achilles tendon. Contraction of this muscle pulls the heel upward and points the toes.