Presentation on theme: "MUSCLE TISSUE Muscle Contraction TYPES OF MUSCLE TISSUE A. Skeletal muscle -voluntary muscle, striated with light and dark bands, many nuclei per cell."— Presentation transcript:
MUSCLE TISSUE Muscle Contraction
TYPES OF MUSCLE TISSUE A. Skeletal muscle -voluntary muscle, striated with light and dark bands, many nuclei per cell. Found in limbs, trunk of body, jaws, face, eyes etc.
B. Smooth muscle —involuntary, visceral muscle forms muscular layer of organs. Has one nucleus per cell, contracts involuntarily, elongated. Rhythmic contractions. Digestive tract, bladder, ducts, arteries and veins.
C. Cardiac muscle -involuntary, similar to skeletal- striated but controlled by the autonomic nervous system. Branched cells with central nuclei. Intercalated discs assure impulses travel between cells. Heart muscle
S KELETAL M USCLE C OMPONENTS
MICROSOPIC ANATOMY OF SKELETAL MUSCLE A. Muscles contain bundles of fascicles that contain muscle fibers (cells). B. Muscle fibers contain Myofibrils which contain sarcomeres. Myofibrils play a key role in muscle contraction. C. Sarcomeres contain: Actin-thin filaments Myosin-thick filaments The organization between actin and myosin create the striations we see in muscle tissue.
T HE S ARCOMERE The sarcomere is the basic unit of the muscle fiber. A. I band- contain thin actin filaments B. Z lines-attach to the thin actin filaments C. A bands-thick myosin and thin actin filaments overlap Sarcomere Shortening Video
M USCLE C ONTRACTION The sarcoplasmic reticulum is a series of membrane channels that surround the myofibrils. The transverse tubules extend from the sarcoplasmic reticulum Together these structures help activate muscle contraction Neuromuscular junction
THE NEUROMUSCULAR JUNCTION A. Connects nerve cells called motor neurons with muscle cells at a specialized region on the muscle called the motor end plate. B. Neurotransmitters-chemicals released by the nerve cell which stimulate muscles to contract. For muscle contraction acetylcholine (ACh) is used. C. Target of neurotransmitters is the sarcomere in the muscle.
T HE N EUROMUSCULAR JUNCTION
S TEPS OF MUSCLE C ONTRACTION 1. Action potential-electrical signal from a motor neuron (nerve fiber) causes a change in the electrical charge of the membrane in the nerve cell (Na + rushes in). 2. The action potential causes a neurotransmitter (chemical that sends signals from the nervous system) called ACh ( acetylcholine) is released and bind to ACh receptors on muscle cell membrane, 3. This signals the muscle fibers in the sarcoplasmic reticulum which causes Ca ++ rushes in from surrounding sarcoplasmic reticulum.
4. Ca ++ binds to a molecule called troponin on actin which causes the shape to change. 5. Cross bridges attach and detach on actin and myosin causing contraction of muscle. The muscle fiber shortens. Myofilament Contraction video 6. For the muscle to relax, ACh, and Ca++ are taken up and chemical energy ATP is needed to break actin apart from myosin. Threshold stimulus-minimum stimulus needed for a muscle to contract. All or None Response-partial contraction does not happen, the muscle contracts when the threshold stimulus occurs. A stronger stimulus does not affect the contraction.
W HAT IS A DENOSINE T RIPHOSPHATE (ATP) ( SEE NEXT SLIDE FOR DIAGRAM ) ATP is the source of energy for muscle contraction/relaxation. Muscles store a very limited amount of ATP ( 4-6 sec. worth at most). ATP must be regenerated if contraction is to continue ATP can be generated by one of three pathways….
1. A EROBIC M ETABOLISM /C ELLULAR R ESPIRATION Occurs in mitochondria, requires oxygen, and involves a complex sequence of chemical reactions. Glucose + oxygen carbon dioxide + water+ energy ( 36 ATP ) When this system is used: Used during prolonged, endurance activities which maintain a constant heart rate As long as there is enough oxygen available relative to ATP demand, a muscle will utilize aerobic metabolism. Posture, most daily movements, marathon runs, bike riding
2.) A NAEROBIC M ETABOLISM /G LYCOLYSIS o Description: When muscles contract vigorously, the bulging muscles compress blood vessels within, impairing oxygen delivery. This pathway can occur in the absence of oxygen. Chemical Formula: Glucose lactic acid +energy ( 2 ATP ) When this system is used: When large amounts of ATP relative to available O 2 are needed. Usually for exercise about seconds long. Tennis, soccer, 100 meter swim
3. A NAEROBIC M ETABOLISM /C REATIN P ATHWAY 1. Description: Utilizes the molecule creatine phosphate to regenerate ATP, after stored ATP is depleted. 2. Chemical Formula: Creatine phosphate + ADP Creatine + ATP ( 1 ATP ) 3. When this system is used: Moblized at the beginning of exercise, before other pathways ‘kick in’. Creates enough energy for about 15 seconds of contraction. 100 meter dash, weightlifting
M USCLE F ATIGUE Definition: the state of physiological inability to contract Causes: 1. Occurs when ATP production fails to keep up with ATP use. Deficiency of ATP, as opposed to total absence of ATP which leads to a continuous state of contraction (rigor mortis, writers cramp) 2. Accumulation of lactic acid and ionic imbalances also contribute. decreases muscle pH causes burning sensation interferes with actin/myosin binding
S UMMARY OF M USCLE M ETABOLISM Creatine pathway Glycolysis Pathway Aerobic pathway Requires oxygenno yes Amount of ATP produced 1 ATP2 ATP36 ATP Duration15 seconds30-60 secondshours By productcreatinelactic acidCO 2 and H 2 O Advantages Rapid energy Easily mobilized Quick energy Does not require oxygen More ATP/glucose Waste products are easy to excrete Disadvantages Small amount of creatine available Small amount of ATP less ATP/glucose Lactic acid produces muscle fatigue Slower Limited by oxygen
F AST T WITCH VS. S LOW T WITCH M USCLES S PRINTER VS. M ARTHONER S PRINTER VS. M ARTHONER
S LOW T WITCH /F AST T WITCH Analogy: birds White meat-fast twitch, found in breast and wings, used for flying-quick movements. Dark meat-slow twitch, found in legs, used for walking. Fast TwitchSlow Twitch Lighter in color-less bloodDarker in color-rich in blood Few mitochondriaMany Mitochondria Mostly anaerobicPrimarily aerobic Easily fatigueFatigue slowly More forceful contractionsLess forceful contractions Increase in size with trainingDon’t increase in size with training SprintersDistance runners
M USCLE CONDITIONS Muscle cramps- (charley horse) sudden involuntary contraction of muscles due to injury, deficiency in calcium or phosphate, lack of blood flow, nerve tissue damage or dehydration. Muscle twitches -often cause by a single nerve, due to fatigue, lack of water, stress and anxiety. ALS-Lou Gehrig’s disease - damages motor neurons, leads to loss of motor movement. Muscular dystrophy -skeletal muscle progressively weaken.