Muscular System Muscle Contraction

Movement requires muscle Three types: skeletal, smooth, cardiac Skeletal will be our focus Long fibrous tissue Muscle fibers are enclosed in layers of connective tissue

From Largest to smallest Muscle Bundle of fibers called a fascicle Muscle fiber (one cell) Bundle of myofibrils Filaments arranged in sarcomeres Actin and myosin are the proteins of the myofilament

Terms Cytoplasm is called sarcoplasm Inside the muscle fiber (muscle cell) are myofibrils They contain 2 proteins: actin and myosin

A sarcomere The space from one Z line to the next Z line Striations (stripes) are caused by the proteins of the myofilament Sarcomere is the contracting unit of the muscle fiber Z lines

Contraction Contractions means getting smaller The myofibril can contract because actin and myosin move This movement is described in the sliding filament theory

Sliding Filament Theory Head of myosin attaches to the actin This can happen only if calcium is present Myosin head pulls the actin filament in Makes the sarcomere shorter

Neuromuscular Junction Connection between a motor neuron and a muscle

Neuromuscular Junction A nerve fibers comes from the brain or spinal cord to the muscle. The nerve and the muscle do not actually touch The gap between them is called the synaptic cleft

Neuromuscular Junction At the end of the neuron, many tiny vesicles are present These vesicles store chemicals called neurotransmitters The neurotransmitter will go across the gap (synaptic cleft)

Neuromuscular Junction The muscle fiber on the other side of the gap is stimulated by the neurotransmitter The muscle fiber contracts The neurotransmitter is called acetylcholine

After contraction, relaxation Acetylcholinesterase (an enzyme) destroys the remaining acetylcholine Calcium ions are taken away Without these actions, the muscle would stay contracted

Related Conditions Nerve gas works by inhibiting acetylcholinesterase Breathing muscles cannot relax Botulism prevents the release of acetylcholine, so muscles cannot contract

Related Conditions Rigor mortis Ca++ pumps run out of ATP Ca++ cannot be removed continuous contraction eventually tissues break down

Contraction Facts Threshold stimulus must be reached to cause a contraction Enough acetylcholine must reach the receptors All or none response Either the fiber (and its motor unit) contracts or it doesn’t

Contraction Facts A motor neuron comes from the brain or spinal cord and connects to a group of muscle fibers, called a motor unit. When a motor neuron transmits an impulse, all the fibers in the motor unit contract (If threshold was reached)

Contraction Facts A motor unit exhibits an all or none response How, then, can some muscle contractions be more forceful than others? Determined by the number of motor units stimulated

Contraction Facts Where does the energy come from to power muscle contraction? ATP (adenosine tri-phosphate) If extra energy is available, it is stored in creatine phosphate Creatine phosphate is converted to ATP when needed.

Origin and Insertion One end of a skeletal muscle is attached to an immovable end, like an anchor. This is the ORIGIN. The other end is attached to a movable part, called the INSERTION.

Biceps Brachii Two origins Insertion

Contraction Facts Muscle Twitch cycle of contraction and relaxation Contraction only lasts a fraction of a second

Contraction Facts Tetany is sustained contraction Lacks even partial relaxation Tetanus bacteria can cause this Lockjaw

Contraction Facts Muscle cramps ATP depletion dehydration ion imbalance massage or stretching increase circulation

Which are You? A sprinter or an endurance performer? Why do some people excel at one, but not the other? Read the article and find out!

Use It or Lose It! Muscle inactivity will lead to weakness and wasting Aerobic exercise will result in stronger, more flexible muscles with greater resistance to fatigue. Resistance (isometric) exercise will result in increased size of muscles.

Which type should you do? Resistance: body building; enlarges individual muscle cells. Aerobic: endurance, increases strength in other systems as well. YOU NEED BOTH!

Contraction Facts Muscle fatigue lack of carbohydrate source (glucose)   Contraction Facts Muscle fatigue lack of carbohydrate source (glucose) lack of ATP to restore membrane potential lactic acid drops pH which interferes with protein function

Oxygen Debt Happens later, while you are resting or sleeping Body cannot supply muscles with enough oxygen during strenuous exercise Muscles must switch to anaerobic respiration This produces lactic acid, which the liver will destroy later Oxygen debt is the amount of oxygen liver cells need to convert the lactic acid into glucose