The Muscular System

The Muscular System

1. Functions

   • 1. Mobility: Responsible for body movement. 2. Circulation: Involuntary cardiac and smooth muscles help heart beat and blood flow through body. 3. Respiration: Diaphragm is the main muscle at work during quiet breathing. During heavy breathing, it may require help from accessory muscle. 4. Digestion: Controlled by smooth muscles found in your gastrointestinal tract. 5. Urination: Smooth and skeletal muscles make up the urinary system where they work together to allow human to urinate.

2. Structures

   • Muscle fibers: composed of many fibrils, which give the cell its striated appearance.
     • Fascia: sheet of connective tissue, primarily collagen, beneath the skin that attaches, stabilizes, encloses, and separates muscles and other internal organs.
   • Tendons: a flexible but inelastic cord of strong fibrous collagen tissue attaching a muscle to a bone.
     • Example: Patellar tendon, Archilles tendon, Aponeurosis.

3. Types of Muscle Tissue

   • Skeletal Muscles: form of striated muscle tissue, which is under the voluntary control of the somatic nervous system.
   • Smooth Muscles: generally forms the supporting tissue of blood vessels and hollow internal organs, such as the stomach, intestine, and bladder.
   • Myocardial Muscle:an involuntary, striated muscle that constitutes the main tissue of the walls of the heart.

4. Muscle Contraction & Relaxation

   • Muscle Innervation: the simulation of muscle by impulse transmitted by motor nerve that control body's voluntary muscular contraction.
   • Antagonistic Muscle pairs: Antagonist and agonist muscles often occur in pairs, called antagonistic pairs. As one muscle contracts, the other relaxes.

5. Contrasting Muscle Motion

   • Abduction & Adduction: movements of limbs and other body parts toward or away from the center line of the body (a line that runs up and down the center of the human body) are termed adduction and abduction, respectively.
   • Flexion & Extension: Extension is the opposite of flexion, describing a straightening movement that increases the angle between body parts.
   • Elevation & Depression: Elevation: moving a body part up. Depression: moving a body part down.
   • Rotation & Circumduction: Circumduction – this is where the limb moves in a circle. This occurs at the shoulder joint during an overarm tennis serve. Rotation – this is where the limb turns round its long axis, like using a screw driver.
   • Supination & Pronation: Supination is the opposite of pronation and refers to the outward roll of the foot during normal motion.
   • Dorsiflexion & Plantar Flexion: refer to extension or flexion of the foot at the ankle.

6. How Muscles are Named

   • Named for their origin (less movable attachment) & Insertion (more movable attachment) (points of attachment)
     • Example: sternocleidomastoid, the muscle that attaches to sternum and tendons attches to mastoid process of the skull.
   • Named for their action
     • Example: (Flexion) flexor carpi muscles flex the wrist. (Extension) extensor carpi muscles extend the wrist.
   • Named for their location (position on body or organ near to it)
     • Example: tibialis anterior, is in front of tibia.
   • Named for fiber direction (direction which their fibers run)
     • Example: rectus abdominis muscle located in front of abdomen and its fibers are oriented in straight vertical direction.
   • Named for number of division
     • Example: biceps brachii formed from two divisions. Tricep brachii formed from three divisions.
   • Named for size and shape
     • Example: deltoid - resembles (-oid) a triangle (-delt). gluteus maximus , largest muscle of buttock.
   • Named for strange reason
     • Example: hamstrings, muscles which named due to reasons by which a butcher hangs a slaughtered pig.

7. Select Muscles and Their Functions

   • Muscles of Head
     • The frontalis muscle is a muscle located at the forehead of the skull that raises and lowers eyebrows.
     • Temporalis muscle is one of several chewing muscles that is necessary for crushing and grinding objects between the molars.
     • Masseter muscle a facial muscle that plays a major role in the chewing of solid foods
   • Muscle of Trunk
     • Pectoralis major is a thick, fan-shaped muscle, situated at the chest (anterior) of the human body.
     • External oblique and internal oblique muscles located in abdomen. External oblique muscles flex and rotate vertebral column. Internal oblique muscles flex the spine.
     • Rectus abdominis muscle, is a paired muscle running vertically on each side of the anterior wall of the human abdomen helps flex the trunk.
     • Transverse abdominis muscle is a very deep postural muscle that influences core strength and back health.
   • Muscle of Shoulders and Arms
     • Deltoid muscle is located on the outer aspect of the shoulder and is recognized by its triangular shape.
     • Trapezius muscle moves head and shoulder blade.
     • Biceps brachii found in anterior arm which flexes elbow.
     • Triceps brachii found in posterior upper arm which extends elbow.
   • Muscles of legs
     • Rectus femoris extends the leg at the knee.
     • Quadriceps femoris flex and extend the leg at knee.
     • Hamstring group helps in knee flexion and hip extension.
     • Gastrocnemius muscles flexes knee and bends foot downward.

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