THE MUSCULAR SYSTEM What do you already know about muscle tissue? What is the definition of an organ?

Types of muscle tissue Skeletal muscle Cardiac muscle Smooth muscle

Functions Producing body movements by changing chemical energy into mechanical energy Stabilizing body positions Generating heat Moving substances Within the body

Skeletal muscle anatomy Connective tissue around muscle (epimysium) Extends to form tendon (dense regular connective tissue) – connects muscle to periosteum of bone

Nerves and blood vessels Muscles: bundles of fascicles (group of fibers – cells) surrounded by perimysium Nerves and blood vessels At least 1 capillary per muscle fiber

Myofibrils= contractile organelles  stripes Sarcoplasmic reticulum - encircles myofibrils= similar to smooth ER; function = stores calcium Filaments (thin and thick)– inside myofibrils; don’t extend length of fiber; contained in sarcomeres

Anatomy of muscle fiber No mitosis Growth: hypertrophy due to hormones (testosterone, HGH) Sarcolemma = cell membrane Sarcoplasm = cytoplasm (glycogen!!) Myoglobin – a protein = binds with/release O2 for the mitochondria Mitochondria = many!

Review: Sarcolemma Sarcoplasm Sarcoplasmic reticulum Myofibrils Don’t write Review: Sarcolemma Sarcoplasm Sarcoplasmic reticulum Myofibrils filaments

HOW A MUSCLE CONTRACTS http://www.youtube.com/watch?v=ren_IQPOhJc&list=PL7DDED4766451C09D

A neuron connects to a muscle fiber [called the neuromuscular junction (NMJ)] Arrival of nerve impulse causes release of acetylcholine (ACh: a neurotransmitter – a chemical). ACh diffuses to receptors on muscular membrane (sarcolemma), opening a Na+ ion channel, causing Na+ to enter the muscle fiber

Muscle contraction cont Causes muscle action potential due to change in membrane potential (b/c of addition of Na+ ) Sarcoplasmic reticulum releases stored Ca+2 into sarcoplasm Causes muscle contraction (sliding filament mechanism): Unblocks actin (thin) so myosin (thick) heads can bind to them Filaments slide past one another, shortening the muscle

Sliding filament mechanism

Sliding filament mechanism Lengths of filaments do not change Sarcomere shortens Causes shortening of muscle fiber and muscle

Plants/drugs effect NMJ Botulinum toxin from bacterium Clostridium botulinum blocks exocytosis of ACh Curare – plant derivative – used on arrow/blowgun darts. Binds to/blocks ACh receptors

Muscle physiology Muscles tug on tendons which pull on bones One bone is pulled towards another Insertion towards origin Most cross a joint

Muscle groups Prime mover and antagonist Opposite actions Switch roles Opposite sides of bone/joint

Lever systems Most of the bones of the limbs (arms & legs) act as levers. These levers are powered by muscles. A lever is a rigid rod able to rotate about a fixed point known as a fulcrum, formed by the joint. Any force applied to the lever is called the effort. A force that resists the motion of the lever, such as the downward force exerted by a weight on the bar, is called the load or the resistance. The contraction of the muscles is the effort and the part of the body concerned is known as the resistance or load. Bones of the body act as levers (a mechanical device) which create a mechanical advantage of strength or speed.

Muscle contraction Muscle fibers: all-or-none Strength of muscle contraction: depends on # of contracting fibers Affects energy usage

Providing energy ATP broken down during contraction Store little ATP, must produce it 3 ways: Aerobic respiration: slow, requires O2, lots ATP Anaerobic glycolysis and lactic acid formation: faster, no O2 needed, less ATP Creatine phosphate and ADP: CP not found in other cells, very fast, doesn’t last

Muscle fatigue no contraction even with stimulation - occurs from oxygen debt (lactic acid builds up and ATP runs low)

Types of muscle contractions Isotonic: with movement Isometric: muscle against immovable (or almost) object

Effect of exercise Aerobic (endurance): results in muscles with resistance to fatigue. Resistance (isometric) training: enlarged muscles

In review……… (don’t write) Lifting weights is an example of resistance or endurance training? The reaction of creatine phosphate and ADP generates ATP quickly or slowly? The ability of your body to use oxygen to produce ATP is _____ respiration. True or False: The strength of a muscle contraction is determined by the amount of muscle fibers that are contracting.

The strength of a muscle contraction depends on what? Don’t write The strength of a muscle contraction depends on what? What is the relationship between the strength of a muscle contraction and energy usage? Muscle fatigue is due to ____ debt

example Running a 100 yd dash in 12 seconds requires 6L of oxygen. But the max amount that could be delivered and used by your muscles (VO2 max) would be 1.2 L Oxygen debt? = 4.8L

THE POINT The more oxygen your body can take in and use determines your endurance

Why are some people better at endurance activities? DON’T WRITE Why are some people better at endurance activities? Why are some people FAST? Is it genetic? Is it training?

Types of muscle fibers 1. Slow oxidative fibers Little power (small in diameter); fatigue resistant; many mitochondria. Adapted for maintaining posture & endurance activities 2. Fast oxidative-glycolytic fibers Intermediate in diameter, faster than #1 but briefer in duration. Adapted for: walking/sprinting 3. Fast glycolytic fibers Large diameter (contract strongly/quickly); tire quickly; large amount lactic acid build up Short, rapid, intense movement Adapted for intense anaerobic movements of short duration: weight lifting/throwing a ball

muscle fibers in muscles Muscle are a combo of different fibers Proportion of fibers is individual