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

• Weight LifterHas more White

Fibers

• A weightlifter and marathon runner have about the same amount of muscle cells, they are just trained for a different task.

• Marathon RunnerHas

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