Muscular System

Muscles: Designed for Motion How Muscles are Classified Muscles – The three main types of muscles are skeletal, smooth, and cardiac Voluntary Muscles – Muscles that are generally under conscious control (usually skeletal) Involuntary Muscles – Muscles that not under conscious control (smooth and cardiac)

Skeletal Muscles – Primary function is to move the skeleton, made of muscle fibers Muscle Fibers (Cells) – Bound together in parallel bunches, the contracting mechanism causes the muscle to be striated or striped. Striated Muscle – Another name for skeletal muscle

Smooth Muscle – Shorter, wider cells in a looser arrangement, specialized for long, slow, powerful contractions, used in circulatory and digestive systems, in the iris, and in women during birth

Cardiac Muscles – Similar to skeletal muscle but designed to contract continually, only found in the heart and is self stimulating

Important Muscles Sternocleidomastoid – Connect the temporal bones to the sternum and clavicle, Allows for movement of the head

Temporalis – Moves the lower jaw when it is chewing or talking Masseter – Located near your lower jaw and works with the Temporalis

Trapezius – Connected to the spine, head, and scapula, moves shoulders back and up, raises the head

Intercostal Muscles – Muscles between the ribs, used to raise the rib cage and expand the thoracic cavity when they contract Pectoralis Major – Connected to the sternum, extends across the chest and connects to the humerus, used when you push your hands in front of your body

Deltoid – Connected to your clavicle and humerus (shoulder), used in raising your arm away from your body

Latissimus Dorsi – Connects each humerus to the lumbar region, used for drawing your arms toward your body

Biceps Brachii – Located on the front of each upper arm, used to bend your forearm toward your body Triceps Brachii – Located on the back of each upper arm, used to straighten the arm

Fingers Flexed/Extended – Muscles in the forearm connected to tendons that run to the hands allow the fingers to be flexed and extended

Rectus Abdominus – (6-pack Abs) Extend from the bottom of the sternum to the top of the pelvic girdle, used when you sit up from reclining External Oblique – Connect the ribs to the pelvis, used for bending sideways (Laterally)

Erector Spinae – Extend vertically along the spine from the upper back to the pelvis, used to hold your body upright Gluteus Maximus – (butt) Largest and strongest muscle in the whole body, connected to pelvis and femur, used to move the leg downward and to the rear

Quadriceps Femoris – A group of four muscles on the front of the upper leg, used to straighten the leg Sartorius – Connects the outside of the pelvic bone to the inside of the tibia, used to lift the lower leg and turn it inward

Hamstrings – A group of three muscles on the back of the upper leg, used to bend the leg at the knee Gastrocnemius – Largest muscle on the back of the lower leg, used to extend the foot downward

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Engineered for Power The Design of Skeletal Muscle Fascia (8) (Epimysium) – The tough translucent sheath that covers the entire muscle The fascia tapers at each end into tendons (7) that connect the muscle to the bone

Fascicle (9) – Inside the muscle there are bundles of muscle cells called fascicles Perimysium (1) – The outer covering of a fascicle made of connective tissue Nerves and vessels (2) run between the fascicles to supply food and oxygen and signal the muscle to contract

Muscle Fiber (Cell) (4) – Inside the fascicle there are many muscle fibers that are made of many microfibrils Each muscle is made of millions of muscle fibers (cells) Each muscle cell has many nuclei and an unusually large amount of mitochondria

Microfibril (6) – Long tubes bunched together to make each muscle fiber; they are made of many sarcomeres Endomysium (3) – Tough connective tissue between the muscle fibers Sarcolemma (Cell Membrane) (5) - The outer covering of the muscle fiber (cell)

Sarcomere (12) – Overlapping protein fibers made of thick (myosin) and thin (actin) filaments that work together to contract the muscle (this is why skeletal muscles have a striated appearance)

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Muscle contraction Neuromuscular Junction – Where the nerve connects to the muscle, triggers the muscle to contract On average one nerve can stimulate 100 muscle cells

The group of muscle cells stimulated by a nerve cell is called a motor unit A motor unit allows there to be less nerve cells for every muscle cell

If there are less muscle cells per nerve cell, those muscles are more precise If there are more muscle cells per nerve cell, those muscles are less precise Each muscle has thousands of motor units, when you use a muscle some of the units contract while others are relaxed All-or-none Principle – When motor units are stimulated, they completely contract and completely relax until stimulated again

Muscles in Strength and Weakness Exercise is Healthy for Muscles Hypertrophy – The enlargement of muscles through use

Atrophy – The degeneration of muscles through the lack of use

Red Fibers – Muscle fibers that contain a large amount of mitochondria and myoglobin; have a pronounced red color Contract more slowly, but have more endurance, are called slow-twitch fibers Myoglobin – A protein that stores oxygen

White Fibers – Muscle fibers that contain smaller amounts of mitochondria and myoglobin; do not have a pronounced red color Have more myofibrils and contract faster and more strongly, are called fast-twitch fibers You can train your muscles to perform a certain task

A weightlifter and marathon runner have about the same amount of muscle cells, they are just trained for a different task. Weight Lifter Has more White Fibers

Marathon Runner Has more Red Fibers

Exercise We need to continue to exercise so the muscle will at least remain in the same condition If we do not exercise our muscles will deteriorate

Warming up – Allows muscle contraction and cellular respiration to occur more efficiently Cooling down – Allows excess lactic acid to be removed from the muscle to reduce soreness

If a muscle is strained, there is usually no noticeable strength loss after healing Muscle Fatigue – When a muscle becomes stiff, sore, and difficult to contract Caused by a build-up of waste products in the muscle Cramp – A sudden , painful, involuntary contraction, caused by a lack of ATP

Muscle Tone – A state of slight tension in a relaxed muscle, which a small number of cells are contracted Allows your muscles to be ready for action Needed for good posture

A Functioning Unit Both skeletal and muscular systems need all the other systems to be working together with them. Skeletal system gives the muscular system a support Nervous system sends electrochemical signals to the muscular system to contract

Muscle Sense – Sensors in the muscle tissue relay messages to the brain, informing it of location and tension