Download Ch. 6 The Muscular System Notes Function: To provide movement

Ch. 6 The Muscular System Notes
Function: To provide movement (for all body parts including heart and lungs), maintain posture,
stabilizes joints and generates heat.
All muscles are made of muscle fibers (long muscle cells). All muscles shorten (contract) using
myofilaments. All muscle terms have one of the following prefixes: myo, mys, sacro.
Can you give examples of each?
Three types of Muscle tissue:
1. Skeletal Muscles. – Attach to the body’s skeleton, they are long, striated, and
multinucleated. Also known as striated or voluntary muscles. They are the only muscle type
subject to conscious control but can be activated by reflexes as well.
Skeletal muscle parts:
- Endomysium - surrounds each individual muscle fiber (cell)
- perimysium - surrounds a bundle of fibers
- Fascicle - the bundle of fibers
- Epimysium - surrounds the entire muscle
- Tendon - attaches the bone to the muscle
Muscle Movements
Flexion - Contraction (decreases angle of joint)
Extension - relaxation (increases angle of joint) opposite flexion
Abduction - moving away from midline
Adduction - moving toward from midline
Rotation - movement of bone around its axis
Circumduction - moves in a circle
Supination - moving palm from posterior to anterior position
Pronation - moving palm from anterior to posterior position
Eversion - moving foot laterally - outward
Inversion - moving foot medially - inward
Dorsiflexion - moving foot up
Plantar flexion - moving foot down
2. Smooth Muscles - No striations and is involuntary. Found in hollow organs like the
bladder, stomach, lungs. Also known as visceral, nonstriated or involuntary. They have only
one nucleus and are arranged in sheets or layers one circularly and one long.
3. Cardiac Muscles – Found only in the heart it pumps blood into blood vessels and body
tissues. It is striated and involuntary and branched. They are arranged in a figure 8 or spiral
around the heart.
Microscopic Anatomy of a Muscle fiber (one muscle cell)
sarcolemma - the plasma membrane of the muscle cell
myofibrils - long ribbon like organelles
Light - I bands
Z line - darker area of the I band
Dark - A bands
H zone - lighter area of the A band
Sarcomere - tiny contractile units of the myofibril (from one Z line to the next)
Myosin filament - Thick. Contain myosin protein and enzymes that provide the energy
for muscle contraction. Contain the myosin heads (oars) that link to the actin
during contraction
Actin filament - Thin. What slide in during a muscle contraction.
How a Muscle Contracts
1. A nerve impulse must stimulate a contraction. A motor neuron comes into contact
with a muscle fiber.
2. At the axon terminal a neurotransmitter (acetylcholine Ach) is released and diffuses
into the space between the muscle and the axon terminal (Synaptic cleft).
3. This causes Calcium ions to rush into the muscle cell giving it a positive charge that
generates an action potential.
4. The action potential goes down the entire muscle fiber and causes the muscle to
contract.
Sliding Filament Theory
1. Muscle fibers are activated by the nervous system (Acetylcholine)
2. The myosin heads (oars) attach to the actin and pull the actin in toward the H zone
3. ATP keeps energizing it so that the myosin heads can release and attach several times
4. The attachment of the myosin to the actin requires Calcium
Muscle Fatigue: When muscles quit because they come too weak or tired.
Oxygen debt - occurs when muscles run out of oxygen and instead use anaerobic respiration
to get the energy needed for muscle contraction. This builds up lactic acid which must be
gotten rid of as the muscle starts to receive the oxygen it needs.
Types of Muscle Contraction:
Isotonic - Movement
Isometric - No movement - Tension
Muscle Diseases and Disorders:
Muscular Dystrophy – gradual weakness of muscles. Genetic, caused by lack of a certain
protein needed to keep muscles healthy.
Fibromyalgia – tenderness of muscles especially due to pressure.
Restless leg syndrome – muscles become irritated if not moving and so the individual feels the
need to move their muscles.
Spasmodic Torticollis – causes muscles of neck to move and turn involuntarily.