MUSCLE PHYSIOLOGY CHAPTER 8 CONT….

What are muscles? Muscle Actions An organ composed of specialized cells that use the chemical energy stored in nutrients to contract. Skeletal muscle is composed of muscle, nervous, blood & connective tissue. Muscle Actions Provide muscle tone Propel body fluids and food (peristalsis) Generate heart beat Distribute heat

3 Types of Muscle Tissue 3 Types of Muscles 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 3 Types of Muscles Skeletal, smooth, cardiac

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)

Muscle Fiber Structures Sarcolemma (cell membrane) Sarcoplasm (cell cytoplasm) Sarcoplasmic reticulum (ER) – store calcium ions & activate muscle contraction Transverse tubules – channels that contain fluid which stimulates contractions Myofibrils (protein threads) 1. Myosin – thick thread, dark color, A bands, H zone, M line 2. Actin – thin thread, light color, I bands Both proteins form striations!!

(form repeating pattern units called sarcomeres) Sarcoplasmic reticulum : network of membranous channels that surround each myofibril and activates muscle contraction mechanism when the fiber is stimulated Actin and Myosin: Protein filaments. The organization of these filaments produces the alternating light and dark striations. (form repeating pattern units called sarcomeres)

Sarcomeres – repeating dark/light patterns (from z-line to z-line)

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 (thick). M line: holds myosin in place.

Relaxation vs. Contraction

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 (Contraction of Muscle) 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. http://www.youtube.com/watch?v=ren_IQPOhJc

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. Filament clip

Muscle Responses When one muscle fiber (cell) reaches 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+2 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

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)