MUSCLE PHYSIOLOGY CHAPTER 8 CONT….

What are muscles? Muscle Muscle Actions An organ composed of specialized cells that use the chemical energy stored in nutrients to contract. Muscle Actions Provide muscle tone Propel body fluids and food Generate heart beat Distribute heat

3 Types of Muscles Skeletal, smooth, cardiac SKELETAL SMOOTH CARDIAC LOCATION (40% of body mass) Attached to bone Surrounds digestive organs and blood vessels In heart CONTRACTIONS Voluntary Involuntary involuntary STRIATED Yes No yes

Structure of Skeletal Muscle MUSCLE (COVERED BY EPIMYSIUM) FASCICLES (COVERED BY PERIMYSIUM) MUSCLE FIBERS(COVERED BY ENDOMYSIUM) MYOFIBRILS THICK AND THIN FILAMENTS (MYOSIN) (ACTIN) Fascia: layers of fibrous connective tissue that separates individual muscles and hold it in position; forms the tendon and attaches to bone’s periosteum (aponeuroses: broad sheets of connective tissue that may attach to bone or other muscles)

Sarcoplasmic reticulum : activates muscle contraction mechanism when the fiber is stimulated. Actin and Myosin: Protein filaments. The organization of these produces the alternating light and dark striations. (form repeating pattern units called sacromeres.)

I band: light band composed of actin attached to Z lines I band: light band composed of actin attached to Z lines. A band: dark band composed of myosin overlapping actin. H zone: has only myosin. M line: holds myosin in place.

Skeletal Muscle Contraction Motor Neuron: conducts impulse from brain and brings it to the muscle fiber. Neuromuscular Junction: connection between neuron and muscle. Neurotransmitter: chemicals at ends of connection that stimulates fiber.

Stimulus for Contraction Neurotransmitter (acetylcholine) is released at end of motor neuron. Acetylcholine diffuses into muscle fiber. Sarcolemma is stimulated and impulse travels deep into the sarcoplasmic reticulum. Ca+2 ions diffuse from sarcoplasmic reticulum into sarcoplasm.

Sliding Filament Theory When Ca+2 is present, actin binding sites are exposed. Myosin cross-bridges form a link at binding site. Myosin cross-bridges bend to pull on actin. Linkage breaks. Myosin cross-bridges forms to next binding site.

Relaxation of Muscle Acetylcholinesterase decomposes acetylcholine and the sarcolemma is no longer stimulated. Ca+2 is transported back to sarcoplasmic reticulum. Linkages between actin and myosin break. Filaments slide apart. Muscle fiber relaxes.

Muscle Responses When one muscle fiber (cell) reached its threshold stimulus and contracts it is called a twitch. MYOGRAM All - Or - Nothing (but muscles vary)

A. Normal contraction B. Summation contraction: series of stimuli with increasing frequency. C. Tetanic contraction: sustained contraction that lacks relaxation. (tetanus)

SMOOTH & CARDIAC CONTRACTIONS Essentially same as skeletal, difference include: (pg 190) SMOOTH CARDIAC Fibers can stimulate each other 2 neurotransmitters (acetylcholine & norepinephrine) and hormones for stimulation Contracts and relaxes slowly Produces more Ca+ in transverse tubules which makes twitches longer Contracts as a functional unit Single nuclei Self-exciting, rhythmic

Fatigue: caused by an interruption in Slow Twitch Fibers (fatigue resistant) & Fast Twitch Fibers (fatigable) Normal person ½ & ½ Sprinter 80% fast twitch Marathoner 90% slow twitch Fatigue: caused by an interruption in Blood supply Lack of acetylcholine Accumulation of lactic acid due to lack of O2 Cramp: sustained involuntary contraction from changes in extracellular fluid. Muscle tone: Partial sustained muscle contraction Important in maintaining posture

Muscle Strain: muscle fiber can be overstretched or even torn. Muscle pull: tendon of muscle tears away from bone. Shin splints: soreness due to straining the tibialis anterior Rigor mortis: partial contraction that fixes joints; actin and myosin remain linked until decomposition. Tendinitis: inflammation of tendon. Muscle hypertrophy: forcefully exercised muscle that causes increased size and shape. Muscle atrophy: unused muscle caused decrease in size and strength. Muscular dystrophies: missing or abnormal dystrophin (protein that holds fibers together); muscle will weaken and degenerate. Myoma: tumor composed of muscle tissue Myositis: inflammation of skeletal muscle tissue

Botox: toxin injected into the facial skin to temporarily smooth wrinkles preventing muscles from contraction. It prevents acetylcholine from being released. Too much can cause a frozen face Also causes botulism which is a serious form of food poisoning

Muscle movements Muscle is connected to bone or connective tissue at 2 main points. Origin: attachment to the immovable or less movable bone. Insertion: attachment to movable bone Moves toward origin during contraction Some muscles have interchangeable origins and insertions: (rectus femoris) Muscles can only pull (not push) as they contract. Prime mover: muscle that has main responsibility for a movement. (biceps) Antagonist: muscle that opposes or reverses movement. (triceps)