11 - Types Of Skeletal Muscle Contractions. Taft College Human Physiology

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1 11 - Types Of Skeletal Muscle Contractions Taft College Human Physiology

2 Types Of Skeletal Muscle Contractions Isotonic Contractions: Tension produced and overall shortening of the muscle as a load is moved through the range of motion of the joint. Isotonic contractions serve to bring about movement or change in body position. Example = flexion, extension, adduction, abduction, etc. Isometric Contractions: Tension but no shortening of the muscle occurs. Energy is still used! Example:contractions that serve to keep the body fixed in position as in 1. maintaining posture, 2. maintaining balance, 3. fixing a proximal joint so a distal joint may move, 4. maintaining muscle tone. Most body activities involve both isotonic and isometric contractions. Twitch: A single isotonic response as a result of a single threshold (liminal) stimulus. (This is not the type of twitch you feel in your body due to being tired or a chemical imbalance). The muscle contracts quickly and then relaxes. A twitch can be demonstrated with an instrument that produces a myogram= a tracing of a muscle contraction or activity.

3 Types Of Skeletal Muscle Contractions Isotonic Contraction = Tension + Shortening of muscle Isometric Contraction = Tension, no Shortening of muscle

4 A Myogram of 3 Phases (Periods) of a Muscle Twitch 1. Latent Period the time from stimulation of the muscle until shortening of the muscle begins. The latent period is a lag time. Duration = about 2 ms. During this period of time the following events of muscle contraction are occurring: a. Depolarization b. Diffusion of Ca+2 c. Establishment of actin/myosin bonding 2. Contraction Period Tension and shortening of the muscle occurs. The upward tracing represents this phase. Duration = ms. 3. Relaxation Period Muscle goes back to it resting state. The Ca++ is actively transported back into the SR which results in relaxation. The downward tracing represents this phase. Duration = ms. Muscles differ in the amount of time it takes to through 3 phases. Ex. eye muscles 12 millisec = Fast Twitch Muscle gastrocnemius 36 millisec, soleus 100 millisec = Slow Twitch Muscle

5 3 Types of Skeletal Muscle Fibers In humans we see 3 types of skeletal muscle fibers classified based on : 1. How fast a muscle will twitch (due to how fast it splits ATP) and, 2. Metabolic pathway used to generate ATP (glycolytic (anaerobic) or oxidative). We will concentrate on only 2 fiber types a. slow twitch = slow oxidative fiber and b. fast twitch = fast glycolytic fiber.

6 Fast & Slow Twitch Muscle Fibers Fast Glycolytic Fast Twitch Slow Oxidative Slow Twitch Color White = Light Red = Dark Size Large fibers Small fibers few mitochondria more mitochondria Reaction Fast (anaerobic) Slow (aerobic) Function Speed Endurance Location Eye muscles & Postural muscles & upper appendages lower appendages Rate of fatigue Fast Slow Examples: eye muscles 12 millisec gastrocnemius 36 millisec soleus 100 millisec

7 Table of Characteristics of Skeletal Muscle Types Slow Twitch Fast Twitch Fast Twitch Structural Features Slow Oxidative Fast Oxidative Fast Glycolytic Diameter or Fiber Smallest Intermediate Largest Color/Myoglobin Red/large Red-pink/large White/small Mitochondria Many Many Few Functional Features Slow Oxidative Fast Oxidative Fast Glycolytic ATP Production Aerobic (O 2 ) process Aerobic (O 2 ) process Glycolysis (anaerobic) ATP use/velocity of Contraction Slow Fast Fast Resists Fatigue High Intermediate Low Glycogen Stores Low Intermediate High Order of recruitment 1 st 3 rd 2 nd

8 Skeletal Muscle Types Slow Oxidative: Maintain posture (anti-gravity muscles), endurance running. Back and neck muscles. Fast Oxidative: Walking, sprinting. Leg muscles. Fast Glycolytic: Rapid, intense movements of short duration. Ball throwing, weight lifting. Arm muscles.

9 Implications for Sports Number of red (slow twitch) vs. white (fast twitch) muscle fibers is hereditary Conditioning and training can do nothing to change the ratio (New research may show otherwise) E.g. Alberto Salizaar New York marathon winner had 92% red vs. 8% white. Other runners tend to have fewer red and more white in comparison. Sprinters contain about 60% fast oxidative. Weight lifters have about equal amounts fast glycolytic and slow oxidative Determination of muscle fiber ratios can be done by muscle biopsy.

10 Other animals use of muscle cell types Concentrations of fast and slow twitch muscles can be observed in other animals as well as humans. The light and dark meat of a chicken has to do with concentrations of different types of muscle fibers. A chicken uses it s breast muscle (white meat) for short flight if at all = fast twitch. The legs (dark meat) of a chicken serve for endurance = slow twitch. What type of meat would you expect to find in the breast of a migratory duck? Dark meat = slow twitch for endurance.

11 Physiology Assignment #4 Name Due Date Internet assignment (Attach article) What are the implications of fast/slow twitch muscle in sports (any sport you wish). Is it possible to change the percentage of fast twitch to slow twitch muscles you have or is it genetically determined?

12 Anabolic Steroid Abuse Testosterone (found in men) and human growth hormone influence muscle growth. Anabolic steroid drugs are testosterone-like and are abused by athletes to increase muscle size & strength and endurance. Moderate doses no better than optimal training. Large doses..damage to body.

13 Anabolic Steroid Abuse Problems: liver cancer, kidney cancer, heart disease, aggressive behavior, mood swings. Females: sterility, facial hair, deep voice, atrophy of breasts and uterus, menstrual irregularities. Males: testes atrophy, less sperm production, baldness.

14 Types of Skeletal Muscle (cont.) Tetanus sustained contraction of a muscle due to increased frequency of stimulation. Result of a summation of twitches (a normal muscle contraction) When the frequency of the stimulation is such that there is no hint of reduced tension or force between stimuli, it is called complete tetany or fused tetany stim/sec When the frequency of stimulation is reduced slightly, you can see partial muscle relaxation occurring between contractions, this is called incomplete tetany or unfused tetany stim/sec Incomplete tetany can result in trembling (shaky) movements of the limbs observed in some individuals. Normal muscle contractions with smooth movement are a result of complete tetanic contractions.

15 Twitches

16 Types of Skeletal Muscle (cont.) Treppe increased strength of contraction as muscle warms up due to identical stimuli too far apart for wave summation to occur. It is also known as the staircase effect, as the muscle steps up its strength with each contraction. Treppe How does this myogram differ from incomplete tetanus? Tension Increasing How do we know this is not wave summation? Hint Stimulus constant

17 Types of Skeletal Muscle (cont.) Treppe can be explained as follows: A progressive buildup of Ca ++ in the sarcoplasm probably accumulates because the stimuli release Ca ++ faster than the Ca ++ pump can move them back in to the SR. The troponin becomes saturated for maximum binding to myosin heads. Eventually the inflow and outflow of calcium ions equalize and the strength of contraction level off In your warming muscles, the sarcoplasm becomes less viscous. With more heat and the internal resistance of the muscle lessened it allows more energy to be directed to muscle shortening and less to overcome resistance. With heat from ATP splitting and other chemical reactions, the enzyme systems become more efficient. This is the basis for the warm-up period for athletes.

18 Muscle Tone Tone is a sustained partial state of contraction in the muscle. Tone is maintained in the body without fatigue by the alternation of different motor units. It serves to keep the body in a state of readiness for activity at all times. It is believed that the contractions are some type of involuntary spinal reflexes responding to activation of stretch receptors in muscles and tendons.

19 Muscle Tone Hypotonia Refers to decreased or lost muscle tone, resulting in flaccid (flattened) shape instead of round. Atrophy Wasting of muscle tissue where muscle fibers decrease in size as myofibrils are lost. Hypertrophy Opposite of atrophy. Refers to an increase in diameter of muscle fibers where myofibrils, mitochondria, and SR are increased. No increase in # of cells. Capillaries servicing muscle fibers are increased too. Due to forceful, repetitive strength training, which results in increased capacity for forceful contractions.

20 Muscle Tone Muscle tone can be lost quickly: If muscle usage is prevented by a cast (disuse atrophy), or by a severing of the nerves (denervation atrophy), the muscle fibers begin to atrophy in just a few days. Prolonged inactivity can lead to degeneration of the muscle fibers and potential replacement by scar tissue (C.T., including fat), which cannot be reversed when complete. Direct stimulation of the inactive muscle using a muscle stimulator may prevent atrophy until the muscle is removed from the cast or the severed nerve fibers can remake connections. The important thing to realize is that muscle health is maintained in part by utilization - use it, or lose it!

21 Smooth Muscle Smooth muscle is also called involuntary muscle (under ANS control) and nonstriated muscle (lacks organized sarcomeres). Actin and myosin myofilaments are present but are not regularly arranged leading to the absence of light and dark bands that cause the striations in skeletal muscle tissue. Characteristics of smooth muscle in comparison to skeletal muscle Smooth muscle has: 1. 7 times less actin & myosin in smooth muscle than skeletal muscle. 2. Lower levels of ATP & creatinine phosphate 3. Fewer number of mitochondria with slow contractions. 4. Smooth muscle cells lack T-tubules. Slower onset of contraction. 5. Have poorly developed sarcoplasmic reticulum. Takes Ca ++ longer to diffuse. Also delays in transport of Ca ++ for longer contraction. 6. Contraction stimulated by a. neurotransmitters (ACh, NE by ANS), b. hormones c. local chemical changes (ph, O 2, CO 2 ), d. stretching. So smooth muscle is designed for slow reacting, but prolonged contractions.

22 Abnormal Contractions Of Muscle Tissue Spasm A sudden involuntary muscle twitch (contraction of short duration), usually due to a chemical imbalance. Cramp A sustained, painful, spasmodic (tetanic) contraction of a muscle. Can last minutes to hours. Severe cramps usually occur when the muscle is shortened (when there is little pull on the tendons). Usually occurs at night or after exercise. It is not known what actually happens at the level of a sarcomere during a cramp. However, the pull on the tendons of muscles are constantly monitored by sense organs called golgi tendon organs

23 Abnormal Contractions Of Muscle Tissue Golgi tendon organs act to inhibit or apply the brakes to muscular contraction to prevent the development of too great of tensile force that could result in injury to the muscle or tendon. Learning how to disinhibit (keep the golgi tendon organs from working) may be an important part of strength training. Maximal vigorous contractions in a shortened position seems to increase the probability of cramping as you have maximal innervation with minimal inhibition. How can you relieve cramps in light of this information? Simply forcing the muscle into its longest position (stretching) will create tension on the golgi tendon organ. The inhibition caused by the golgi tendon organ will then stop the cramp.

24 Abnormal Contractions Of Muscle Tissue Convulsions Violent, involuntary contractions of whole groups of muscles. Convulsions occur when motor neurons are stimulated by factors such as fever, poisons, hysteria, and changes in body chemistry due to drug withdrawals. The stimulated neurons send seemingly senseless impulses to the muscle fibers. This is a nervous disorder not a muscular disorder.

25 Abnormal Contractions Of Muscle Tissue Fibrillation Uncoordinated contraction of individual muscle fibers so that the muscle fails to contract smoothly. Cardiac muscle is most prone to this type of activity and is recorded by electromyography.