Muscles

The Muscular System Functions  Body Movement  Maintenance of Position  Respiration / organ volume  Production of Body Heat (Thermogensis)  Movement of substances (construction of organ and vessels)  Heart Beat

Characteristics of Skeletal Muscle   Contractility A muscle’s ability to shorten and generate force to do useful work at the expense of cellular energy.   Excitability Muscles need to be stimulated before contracting   Extensibility The way muscles can be stretched without damage   Elasticity Muscle’s return to their original length and shape after contracting Conductivity – conducts action / potential along plasma membrane

Skeletal muscle picture  Striated, multinucleated and voluntary

Skeletal Muscle  Each skeletal muscle fiber is a single cell containing numerous myofibrils  Myofibrils are composed of actin and myosin myofilaments  Myofibrils are joined end to end to form sarcomeres  Muscle fibers are organized into fasciculi and fasciculi are organized into muscles by associated connected tissue. Myofilaments Sacomere Myofibrils

Connective tissue components  Endomysium – separating individual muscle fibers  Perimysium – surround borders of 10 – 100 fibers (fascicles)  Epimysium – outlines the whole muscle  Deep fascia – dense irregular tissue, holds muscles together, separating into functional groups.

Smooth Muscles Smooth muscle is nonstriated (striped), uninucleated, and involuntary. Visceral organs (alimentary canal)

Cardiac Muscle *Cardiac: striated, uninucleated, branches, interculated discs, involuntary Both Cardiac and Smooth muscle are under involuntary control and is influenced by hormones, such as epinephrine.

Innervation of a Motor Unit and Muscle Fiber This neuron motors more than one muscle fiber. There may be 500 to 1,000 muscle fibers per neuron Muscle fiber is innervated by one single motor neuron

Neuroelectrical factors  Potassium ions (K+) are greater inside the muscle cell than outside, whereas sodium ions (Na+) are greater outside than inside  The inside of cell is negatively charged electrically, whereas outside is positively charged  (Neuromuscular junction) Nerve impulse reaching the neuromuscular junction causes and axon ending to release the neurotransmitter acetylcholine.

Neuronelectical factor con’t  This makes cell membrane permeable to Na+. They rush in creating an electrical potential. K+ begins to move out to restore resting potential (Not as Na+ comes in)  This causes muscles to generate its own impulse called the action potential  The sarcoplasm reticulum then release Ca++ into the fluids surrounding myofibrils.  Ca++ stops the action of the inhibitor substance troponin and tropomysin (which keep actin and myosin apart), causing contractile process to occur

Chemical factors  Ca++ combines loosely with myosin to form activated myosin.  Activated myosin reacts with ATP, attached to the myosin, and releases energy from the ATP to form actomyosin  Myosin filaments have cross bridges that now connect with the actin and pull the actin filaments in among the myosin filament  A sliding process occurs: The width of the A bands remain constant, but Z lines move closer. By now the sodium – potassium pump has kicked in to restore the resting potential. Ca++ gets reabsorbed and contraction ceases

Energy sources: ATP  Glycolysis: glucose to pyruvic acid, net gain of 8 ATP if O2 present, if no O2 then lactic acid (burn in muscles) forms with net gain of 2 ATP  Krebs’ citric acid cycle: pyruvic to CO2+H2O+30 ATP (28 ATP + 2 GTP)  Phosphocreatine in muscle cells: used in sprinting  Free fatty acid: fatty acids + H2O + ATP

Muscle Terms  Twitch A sudden uncontrollable muscle spasm A sudden uncontrollable muscle spasm  Threshold A very small detectable sensation A very small detectable sensation  All-or-none response A muscle will respond to stimulation completely or not at all A muscle will respond to stimulation completely or not at all  Lag phase The interval of time between stimulus and contractions The interval of time between stimulus and contractions

Muscle Terms (Cont.)  Contraction phase Tension rises to a peak Tension rises to a peak  Relaxation phase The phase of decreased tension after all or none The phase of decreased tension after all or none  Tetanus Calcium ions cause spasmodic / sustained contractions Calcium ions cause spasmodic / sustained contractions  Recruitment Patterns and corresponding change of muscle patterns, increase number of motor units activated Patterns and corresponding change of muscle patterns, increase number of motor units activated

Muscle Anatomy Terms   Tendon Tough fibers that connect muscle to bony structures; wide flat sheet called aponeurosis   Origin The head of the muscle, where it is located, stationary bone   Head Explains where the muscle begins   Insertion Muscle’s relationship with other muscles, moveable bone   Belly The fleshy part of the contracting muscle Resistance – force opposes movement Effort – force exerted to achieve movement

Anatomy of Skeletal Muscle  A single skeletal muscle, such as the triceps muscle, is attached at its origin to a large area of bone; in this case, the humerus. At its other end, the insertion, it tapers into a glistening white tendon which, in this case, is attached to the ulna, one of the bones of the lower arm.

Terms  Prime mover Muscle that contracts (pulls) mainly by itself Muscle that contracts (pulls) mainly by itself  Antagonist A muscle that works opposite of another, relaxing muscle A muscle that works opposite of another, relaxing muscle  Synergists Muscles working together Muscles working together REMEMBER: muscles only pull

Naming skeletal muscles  A. Direction of muscle fiber to midline  B. Location – structure near muscle is found  C. Relative SIZE of muscle  D. NUMBER of origins (tendons)  E. SHAPE of Muscles  F. Origin and insertion sites  G. Action – same as in joints. 2 new are Sphincter – decrease size of opening, Tensor – make body more rigid

Isometric / Isotonic Muscle Contraction  Isotonic contractions Tension on a muscle stays the same but the muscle shortens so things can be lifted, joints moves Tension on a muscle stays the same but the muscle shortens so things can be lifted, joints moves  Isometric contractions This is when the muscle does not shorten when contracting. This can happen when pushing on a wall or something else that will not move. This is when the muscle does not shorten when contracting. This can happen when pushing on a wall or something else that will not move.TONE This is a constant state of partial contraction maintained in a muscle This is a constant state of partial contraction maintained in a muscle

Muscle disorder  Symptoms: Paralysis, weakness, degeneration or atrophy, pain, spasms  Causes: Muscular tissue, Vascular system feeding muscle cells, nervous system connections, connective tissue surrounding cell bundles (fascicles)

Types of disorders  Fibromyalgia – muscle pain  Myasthenia gravis- muscle tiring / weakness, acetylcholine receptor destruction  Muscular dystrophy- inherited, males, muscles degenerate  Hernia – myocele – muscle breaks through sheath, Inguinal – bowel through abdominal muscle  Myoclonus – spasm / twitching of muscle, singultus – hiccup (myoclonus of diaphragm)  Botox – paralyze the muscle that causes wrinkles.