Muscle System

Muscular system: Sit less, move more.

Functions: generate movement, force, and heat.

Objectives: types of muscles, know steps of muscle contraction.

Gene myostatin: controls muscle growth. Defective myostatin gene does not control muscle growth, leads to excess muscle growth and their result is a super strong kid.

Types of muscle:
Cardiac- uninucleate, striated.

Skeletal- striated, voluntary, multinucleate.

Smooth- involuntary, uninucleate, not striated.

Muscles generate force through contraction.

Skeletal muscles are attached to bones by connective tissue and are controlled by neurons. Cardiac muscle causes the heart to pump blood throughout the body, not under nervous system control. Smooth muscle surrounds blood vessels and internal organs, not under nervous system control.

Muscle vocabulary:

Bicep muscle à bundle of muscle fibers à muscle fiber (with nuclei) à myofibril à sarcomere (actin and myosin filaments, thin thick thin).

Muscle is composed of bundles of fibers called fascicles, composed of muscle fiber (muscle cell), myofibrils (myofilaments), actin (thin fiber) and myosin (thick fiber) which become sarcomeres.

Muscle cell (muscle fiber) picture on slide 9. Membrane is called the sarcolemma; the fluid is sarcoplasm. Instead of having an endoplasmic reticulum they have sarcoplasmic reticulum which stores calcium. T tubule allows the action potential to quickly reach the interior of the cell.

Fast twitch: white, less myoglobin, less mitochondria, fast in speed.

Slow twitch: dark, lot of myoglobin, lot of mitochondria, slower in speed.

Acetylcholine neurotransmitter diagram on slide 11. Muscle fiber contraction diagrams on slides 12 and 13.

Sliding filament theory: sarcomere shortens because actin is pulled inward.

Motor unit: motor neuron + the muscle fibers innervated by the axon terminals of the motor neuron.

Small motor units for small movement, large motor units for larger movements.

Energy source for muscle: ATP. The process is cellular respiration, requires glucose and oxygen, organelle needed is the mitochondria.

Poisons like the ones produced by tetanus causing bacteria prevent the release of acetylcholine and bring about paralysis. Other toxins inhibit acetylcholinesterase (enzyme) and bring about paralysis.

Rigor mortis: stiffening of the body soon after death due to the lack of ATP. The muscles remain in a state of contraction.

Bell’s Palsy: nerve damage that controls the facial muscles.

Muscular dystrophy: X chromosome linked gene (females have XX, males have XY). If males have the defective X gene they will have muscular dystrophy, but in females one X could have it and the other X could not so they wouldn’t have the disease unless both X chromosomes are defective. More common in males.