Muscular System Muscular System Functions 1 produce movement

Muscular System

Muscular System Functions: � 1. produce movement � 2. Maintain posture � 3. Stabilize joints � 4. Generate heat � 5. Move substances (fluid, food etc)

Properties of Muscles: �Excitability: capacity of muscle to respond to a stimulus �Contractility: ability of a muscle to shorten and generate pulling force �Extensibility: muscle can be stretched back to its original length �Elasticity: ability of muscle to recoil to original resting length after stretched

Muscular System · Muscles are responsible for all types of body movement – they contract or shorten and are the machine of the body · Three basic muscle types are found in the body · Skeletal muscle · Cardiac muscle · Smooth muscle

Skeletal Muscles: structure

· Muscle Coverings: Epimysium – Dense connective tissue that covers the entire skeletal muscle. Separates the muscle from all other organs · Fascicle–A group of muscle fibers �Perimysium- elastic cartilage surrounding a group a fascicle. Contains blood vessels and nerves. �Endomysium- Loose connective tissue that surrounds individual muscle fiber. Also has blood vessels and nerves.

Muscle Coverings:

Head and Neck Muscles

Muscles of the cephalic area:

Trunk Muscles

Muscles of the Anterior Trunk area:

Muscles of the Posterior Trunk area: latissimus dorsi

Posterior of leg Muscles of the Posterior and Anterior Leg: Anterior of leg

Anatomy of Skeletal Muscles: · Cells are multinucleate · Nuclei are just beneath the sarcolemma

Anatomy of Skeletal Muscles: · Myofibril- The smallest unit · Bundles of myofilaments · Myofibrils are aligned to give distinct bands · I band = light band · A band = dark band

Anatomy of Skeletal Muscles: · Sarcomere- one segment on a myofibril (from Z disc to Z disc) · Contractile unit of a muscle fiber (these are what allow the muscle to contract and move)

Anatomy of Skeletal Muscles: �Components of a Sarcomere: · Thick filaments = myosin filaments · Has ATPase enzymes ·(for energy to be broken down and used in order to move)

Anatomy of Skeletal Muscles: �Components of a Sarcomere: · Thin filaments = actin filaments

How skeletal muscles move or “slide” �Thin Actin slide past the thick Myosin so that the actin and myosin filaments overlap �In the relaxed state, thin and thick filaments overlap only slightly �In order for this process to start sodium must ender the cell (active transport) and the nervous tissue sends an action potential to begin contraction

· How skeletal muscles move or Step 1: “slide” Activation by nerve causes Calcium to be released. · Step 2: This allows the myosin heads to attach to binding sites on the actin. · Step 3: Myosin heads then bind to the next site of the actin filament. This shortens the Z line and they over lap. · Step 4; They continue until the muscle contracts and the two over lap more and more. · Step 5: To release the contracion the Calcium is taken back into the muscle fibers which covers the location so myosin can’t bind. · IF calcium doesn’t go back in the contraction is prolong and called a charlie horse or Cramp!

How skeletal muscles move or “slide”

Sliding filament Mechanism of Muscle contraction

How skeletal muscles move or “slide” �Within a skeletal muscle, not all fibers may be stimulated during the same interval · Muscle force depends upon the number of fibers stimulated · More fibers contracting results in greater muscle tension · Muscles can continue to contract unless they run out of energy

Energy for Muscle contraction and fatigue · Muscles use stored ATP for energy · Bonds of ATP are broken to release energy · Only 4 -6 seconds worth of ATP is stored by muscles

Energy for Muscle contraction and fatigue · 1. After this initial time, other pathways must be utilized to produce ATP · Muscle cells contain creatine phosphate (CP) · CP is a high-energy molecule · CP transfers energy to ADP, to regenerate ATP · CP supplies are exhausted in about 20 seconds

Energy for Muscle contraction and fatigue · 2. Anaerobic glycolysis · Reaction that breaks down glucose without oxygen · Glucose is broken down to pyruvic acid to produce some ATP · Pyruvic acid is converted to lactic acid · The lactic acid that builds up is what produces muscle fatigue

Muscle Fatigue and Oxygen Debt · When a muscle is fatigued, it is unable to contract · The common reason for muscle fatigue is oxygen debt · Oxygen must be “repaid” to tissue to remove oxygen debt · Oxygen is required to get rid of accumulated lactic acid · Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

Disorders relating to the Muscular System �Muscular Dystrophy: inherited, muscle enlarge due to increased fat and connective tissue, but fibers degenerate and atrophy �Duchenne MD: lacking a protein to maintain the sarcolemma �Myasthemia Gravis: progressive weakness due to a shortage of acetylcholine receptors