Nearly Half Our Weight Comes from Muscle Tissue

MUSCULAR SYSTEM

“the power system”

·  Nearly half our weight comes from muscle tissue.

·  There are 650 different muscles in the human body.

·  Muscles give us form and shape.

·  Muscles produce most of our body heat.

THREE MAIN FUNCTIONS

1.  Responsible for all body movement.

2.  Responsible for body form and shape (posture)

3.  Responsible for body heat and maintaining body temperature.

SKELETAL

TYPES OF MUSCLES SMOOTH

CARDIAC

Skeletal Muscle

·  Attached to bone

·  Striated (striped) appearance

·  VOLUNTARY

·  Multinucleated muscle cell bundles (muscle cells = muscle fibers)

·  SARCOLEMMA = cell membrane

·  Contract quickly, fatigue easily, can’t maintain contraction for long period of time

Smooth Muscle

·  Visceral (organ) muscle

·  Found in walls of digestive system, uterus and blood vessels

·  Cells small and spindle-shaped

·  INVOLUNTARY

·  Controlled by autonomic nervous system

·  Act slowly, do not tire easily, can remain contracted for long time

Cardiac Muscle

·  Found only in the heart

·  Striated and branched

·  Involuntary

·  Cells are fused – when one contracts, they all contract

·  Involuntary

= special circular muscles in openings of esophagus and stomach, stomach and small intestine, anus, urethra and mouth.

CHARACTERISTICS OF MUSCLES

·  CONTRACTIBILITY – the ability of a muscle to reduce the distance between the parts of its contents or the space it surrounds.

·  EXCITEABILITY (IRRITABILITY) – the ability to respond to certain stimuli by producing impulses.

·  EXTENSIBILITY – the ability to be stretched.

·  ELASTICITY – ability of muscle to return to its original length when relaxing.

MOVEMENT

1.  Muscles move bones by pulling on them.

As a muscle contracts, it pulls the insertion bone closer to the origin bone. Movement occurs at the joint between the origin and the insertion.

Rule: A muscle’s insertion bone moves toward its origin bone.

2. Groups of muscles usually contract to

produce a single movement.

·  MOTOR UNIT – a motor neuron plus all the muscle fibers it stimulates.

·  NEUROMUSCULAR JUNCTION – the junction between the motor neuron’s fiber which transmits the impulse – and the muscle cell membrane.

·  ACETYLCHOLINE – chemical neurotransmitter, diffuses across the synaptic cleft (carries impulse across synaptic cleft)

·  MUSCLE FATIGUE – caused by the accumulation of lactic acid in the muscles.

·  OXYGEN DEBT – after exercise, the amount of oxygen needed by the muscle to change lactic acid back to glucose.

·  MUSCLE TONE - When muscles are slightly contracted and ready to pull.

·  DIAPHRAGM – Dome-shaped muscle that separates the abdominal and thoracic cavities, aids in breathing

Disorders and Related Terminology

ATROPHY – wasting away of muscle due to lack of use.

HYPERTROPHY – an increase in the size of the muscle cell.

STRAIN – tear in the muscle resulting from excessive use. Bleeding inside the muscle can result in pain and swelling. Ice packs will help stop bleeding and reduce swelling.

MUSCLE SPASM (cramp) – sustained contraction of the muscle, usually because of overuse.

MYALGIA – muscle pain

TENDONITIS – inflammation of a tendon