Muscular System mus means little mouse Called this

Muscular System --”mus” means little mouse --Called this because contraction of muscle looks like a mouse under the skin

4 functions of muscle: 1. Movement- ex. Move arm, smile 2. Generate heat 3. Maintain posture 4. Stabilize joints

Characteristics that allow muscle to function: 1. Contractibility- shortens with force 2. Excitability- Responds to a stimulus by a nerve 3. Extendable- Can be stretched back to the resting position and slightly beyond (ex. Calf muscle) 4. Recoilable- elastic- go to the original resting place after being stretched

Components of muscle Fibers- cells that make up muscle -They are elongated and are in bundles -They look and function like fibers that make up a cable

Muscle either functions automatically or we have it make it work 1. Voluntary muscle- must volunteer it to work - you control it - Ex. Walking muscles 2. Involuntary muscle- works automatically without you having to tell it to – Ex. heart

Muscles are divided into 3 groups: 1. Skeletal muscle- voluntary 2. Smooth muscle- involuntary 3. Cardiac muscle- involuntary 1 2 3

I. Skeletal Muscle: • Makes up to 40% of our body weight on average • Attaches to the skeleton (bone) • Contracts rapidly but tires quickly (ex. Running)

Skeletal muscle fibers (cells) have the following characteristics: 1. 2. 3. 4. Striated- appear to be striped/banded Multinucleated- more than 1 nucleus Long Voluntary- must tell to work

Structure of skeletal muscle: • Endomysium- delicate sheath that surrounds each cell • Perimysium- sheath that surrounds several fibers • (surrounds each bundle of cells) • Fascicle- bundle of fibers • Epimycium- sheath around several fascicles – Covers entire muscle – Connects muscle to tendons which connect to bone

Functions of tendon 1. Anchor muscle 2. Provide durability- stronger than muscle 3. Conserve space- more of these can pass through joints than muscle

Get prepared for this one!

II. Smooth muscle: --No striations-appears smooth --Involuntary --Found in the wall of hollow organs like stomach --Has 1 nucleus --Has slow contractions but last a long time (steady) Functions of smooth muscle -Propel substances along digestive tract

III. Cardiac muscle: --Found only in heart --Involuntary, striated and arranged in spiral --Cells branch and are joined together by interculated disc --Has sustained contractions at a fairly steady rate (lasts a long time) When these contractions stop-death occurs

How muscle accomplishes its functions: 1. Produce movement- skeletal muscle is the only muscle that causes locomotion (move from 1 place to another) -cardiac and smooth muscle- work to circulate blood -smooth muscle- forces fluids and other substances through channels (ex. Food, urine) 2. Maintain posture- skeletal muscle constantly makes adjustments to maintain the body erect against gravity

Muscle function Contd. 3. Stabilize joints- skeletal muscles pull on bone which stabilizes the joints -tendons work with muscle to do this 4. Generate heat- as all muscle contracts, chemical reactions are occurring that release heat (ATP powers contractions-as it is broken down it releases heat energy) ex. As exercise, burn ATP so temp. rises

Skeletal Muscle: (over 600 of these) • • Anatomy of skeletal muscle fibers Each skeletal muscle fiber has bands Each skeletal muscle fiber has organelles called myofibrils Myofibrils are made of units called sarcomeres (extends from 1 striation to another) Contraction occurs within the sarcomeres

Sarcomeres are made of 2 types of filaments 1. Myosin- Thick filament that extends entire length 2. Actin- Thin filament

What causes these striations (sarcomeres) in muscle to contract/shorten? • When a muscle is resting, the outside of it has a positive charge and the inside has a positive charge • The difference between the charges inside and outside the cell is called the resting membrane potential • An electrical current is sent by the nerve causing the charges to differ which produces a contraction

Parts needed for a contraction: • A nerve cell (neuron) stimulates muscle cell by an electrical current called and action potential • 1 nerve cell may stimulate several muscle fibers • 1 neuron plus the fibers it stimulates is called a motor unit • The junction where the neuron joins the muscle is called the neuromuscular junction

Energy for muscle contractions comes from ATP (adenosine triphosphate) adenosine plus 3 phosphates: There are 3 ways ATP is made: 1. Creatine phosphate- this substance in muscles gives ADP (adenosine diphosphate) a phosphate to make ATP -This is the substance you get from supplements -Quick energy for muscle contraction -Each ATP made depletes in 20 seconds ADP + P ATP

2. Aerobic respiration- requires oxygen and burns glucose to make ATP (1 glucose makes 36 ATP) C 6 H 12 O 6 CO 2 + H 2 O + 36 ATP 3. Anaerobic respiration- Uses no oxygen but it requires a lot of glucose to make ATP. It is much less efficient -If you contract muscle faster than glucose and oxygen can be made in muscle, lactic acid is made. This causes the muscle fatigue and soreness, burning C 6 H 12 O 6 pyruvic acid + 2 ATP

What caused fatigue (the muscles to not want to contract)? Strenuous muscle contraction in exercise Result: won’t contract even when stimulated Ex. Weight lifter, marathon runners Ideally, the muscle needs a good blood supply with a lot of oxygen. When contracted too fast to get enough oxygen, the muscle produces lactic acid instead of the needed ATP. No ATP= no contraction

In most cases, we don’t exercise to the extreme. Usually, we can breath heavy and replace oxygen and ATP True fatigue- complete stopping of contractions-rarely occurs except in marathon runners

2 types of muscle contractions: 1. Isotonic contraction- muscles shorten Ex. Bending of knee 2. Isometric contraction- a resistance occurs so no shortening can occur Ex. Weight lifting

What causes muscle tone? -As muscles are used a lot, some fibers will contract constantly (ex. Tight calf muscle) Causes the muscles to be toned -The less you exercise, the less the muscle is used so the less it contracts (flabby)

Effects of accidents on muscle: -If nerves to muscles are damaged, all fibers will relax because no signal is sent to stimulate them -Has no tone, called flacid ex. Damaged nerve to legs causes paralysis

Role of exercise in muscles: -Increases strength, size, endurance of muscle

2 Kinds of Exercise: 1. Aerobic exercise- called endurance exercise Ex. Biking, jogging, aerobics -results in stronger, more flexible muscle that resists fatigue Why? The muscle’s blood supply increases in each cell causing more mitochondria to form. Mitochondria are the place ATP is made. More ATP-more energy for muscle contraction -Muscles don’t increase much in size

2. Resistance exercise- strength training -Results in larger muscles because the muscle is made to contract against as much force possible Ex. Heavy weights -Fibers (muscles) enlarge because they make more filaments to become stronger *It is best to use both programs

Areas of a joint where muscle attaches: Origin- Attaches to less movable part of bone Insertion- Attaches to the more movable part of bone

5 major movements of muscle: 1. Flexion- Decreases the angle-2 bones get closer Ex. Bend elbow 2. Extension- Increases the angle-increase distance Ex. Straighten leg 3. Abduction- Move a limb away from midline of body Ex. Lift out arm 4. Adduction- Move limb toward body Ex. Fold knees toward stomach 5. Rotation- Occurs at ball and socket joint Ex. Swing arm