muscles system part 2

number of pivoting cross-bridges depends on

amount of overlap between thick and thin filaments

optimum overlap

produces greatest amount of tension

too much or too little overlap results in

reduced efficiency
too much - stretched out so much there's no overlap
too little - no place for thin filaments to slide

twitch

result of a single stimulation to a single muscle fiber

myogram

graph of twitch tension development

3 phases of a twitch

1. latent period
2. contraction phase
3. relaxation phase

latent period

few milliseconds between nerve signal and generation of any tension

contraction phase

- tension rises to a peak
- attaching, pivoting, etc

relaxation phase

- calcium ion is pumped back to storage, etc
- tension falls to resting levels

treppe is german for

stairs

treppe

nerve signals drive just after relaxation phase

stimulation frequency of treppe

less than 50 signals per second

if each nerve signal is some strength, and they're received by same muscle cell, why/how is tension increasing with each signal?

1. nerve signals in calcium are released from storage
2. ion pumps start putting the calcium ion back into storage, but not enough time to put it all back before next signal arrives
3. calcium builds up with each signal that comes
4. more calcium in SR
5. more exposed active sites
6. more pivoting cross-bridges
7. more tension

wave summation

adding twitches together

frequency of wave summation

more than 50 signals per second

what occurs during wave summation

- repeating stimulation before end of relaxation phase
- less time to pump calcium into storage and tension rises faster

complete tetanus

- normal, smooth, sustained muscle contraction
- if frequency is high enough then muscle never begins to relax and is in continuous contraction

motor units

consists of a motor or neuron and all muscle fibers it controls

motor neuron

carries commands from CNS; opposite of sensory neurons

characteristics of large motor units

- up to 1000 muscle fibers
- good for less precise movements

example of large motor units

back or leg muscles

characteristics of small motor units

- around 5 muscle fibers
- precise movements

example of small motor units

eyes or fingers

recruitment

increasing the number of active motor units to increase tension

muscle tone

- natural tension and firmness of a muscle at rest
- motor units actively maintain body position, without movement

increasing muscle tone means

increase metabolic energy used (even at rest)

isotonic contraction

muscle length changes

types of isotonic concentration

concentric and eccentric

concentric contraction

tension is greater than the resistance and therefore muscle shortens

eccentric contraction

tension less than resistance and therefore muscle lengthens

example of isometric contraction

plants, wall sits, etc

isometric contraction

muscle develops tension but is prevented from changing length

sustained muscle contraction uses a lot of

ATP

how much energy is stored in muscles?

enough to start an activity and then muscle fibers must manufacture more ATP as needed

ATP means

adenosine triphosphate

ATP

only molecule cells can use to get energy they need for work

CP

- storage molecule for excess energy in resting muscle
- recharges ATP
- when gets used up, usual ways are used to make ATP

CP means

creatine phosphate

how does CP recharge ATP

- energy in CP can quickly recharge ADP back to ATP
- uses creatine phosphokinase (CPK)

two ways of ATP generation

1. aerobic metabolism of glucose or fatty acids in mitochondria
2. anaerobic glycolysis in cytoplasm

aerobic metabolism makes how much ATP per glucose

36

anaerobic glycolysis

- used during peak muscular activity
- makes 2 ATP/glucose
- break down glucose obtain from glycogen that's stored in skeletal muscle cells
- lactic acid is made as a byproduct

what happens when anaerobic glycolysis is at peak exertion

- muscles lack oxygen to support mitochondria
- rely on glycolysis for atp
- lactic acid builds up

muscle fatigue

when a muscle can no longer form a required activity

results of muscle fatigue

1. depletion of energy reserves (ATP, CP and glycogen)
2. low pH
3. damage to sarcolemma and SR (also due to lactic acid)
4. muscle exhaustion and pain

low pH of muscle fatigue

- due to buildup of lactic acid
- enzymes of cell can't work well
- cell becomes "sick"

recovery period

- time required after exertion for muscle to return to normal
- oxygen becomes available again
- mitochondrial activity resumes

oxygen debt

after exercise, body needs more oxygen than usual to get back to its normal resting state (homeostasis)

oxygen debt results in

heavy breathing

how to get back to normal after oxygen debt

- restore supplies of ATP, CP, and glycogen
- liver dealing with the lactic acid (cori cycle)

cori cycle

removal and recycling of lactic acid by the liver

steps of cori cycle

1. lactic acid carried by bloodstream from muscles to liver
2. liver converts lactic acid to glucose
3. glucose released from liver to bloodstream and may be used to recharge muscle glycogen reserves

active muscles produce

heat

what percent of muscle energy may be lost as heat?

up to 70%; raises body temp

muscle performance is divided into

power and endurance

power

amount of tension a muscle can produce

endurance

amount of time an activity can be sustained

both power and endurance depend on

- type of muscle fiber involved
- physical conditioning

3 types of muscle fibers

1. fast fibers
2. slow fibers
3. intermediate fibers

fast fibers

- very quick and strong contractions
- fatigue very quickly
- large diameter
- relatively few mitochondria (aka mostly make ATP using anaerobic)

why do fast fibers have a large diameter

because have a large amount of glycogen reserves

examples of muscles dominated by fast fibers

muscles that use eyes and hands (small motor units)

slow fibers

- slower to contract and fatigue
- lots of capillaries (so lots of oxygen)
- lots of mitochondria (so aerobic way of making ATP)
- contain myoglobin

myoglobin

- similar to hemoglobin
- red pigment binds to oxygen
- gives muscles their own private oxygen supply and reddish color

examples of muscle dominated by slow fibers

muscles in back and calves (large motor units)

intermediate fibers

- midsized
- have some myoglobin and mitochondria
- more capillaries than fast fibers (so better oxygen supply)

muscle types

white and red muscle

white muscle

- mostly fast fibers
- pale appearance
- like chicken breast

red muscle

- mostly slow fibers
- darker appearance
- like chicken legs

most human muscles

- mixture of fiber types
- appear pink

muscle hypertrophy

when cells get bigger

muscle hypertrophy occurs from

heavy training because diameter of individual muscle fibers increases

muscle hypertrophy means more of

everything (myofibrils, mitochondria, glycogen reserves, etc)

muscle atrophy

lack of muscle activity reduces size, tone, and power

physical conditioning improves

both power and endurance

anaerobic endurance

- uses fast fibers which fatigue quickly with strenuous activity
- improved by frequent, brief, repeated workouts
- results in muscle hypertrophy

examples of anaerobic activity

sprinting and weightlifting

aerobic activities

raise heartrate and breathing rate for a prolonged period of time (at least 30 minutes)

aerobic endurance

- prolonged exercise indicates that muscles are not using glycogen
- use ATP from mitochondria
- getting oxygen and nutrients from bloodstream
- improved by cardiovascular training
- also some fast fibers change and become more like intermediate fibers

aerobic endurance results in

growth of new capillaries to supply better blood flow to muscle cells

how cardiocytes differ from skeletal muscles

- normal cell size or strength
- single nucleus
- very aerobic (lots of myoglobin and mitochondria)
- intercalated discs

intercalated discs

- specialized contact points between cardiocytes
- structure includes gap junctions and desmosomes
- maintain structure of heart
- enhance molecule and electrical connections between cardiocytes
- conduct action potentials between cells

functional synctium

mass of merging cells that function as a unit

what makes cardiocytes a functional synctium

intercalated discs link cardiocytes mechanically, chemically, and electrically

4 functional characteristics of cardiac muscle

1. automaticity
2. variable heart rate and contraction tension
3. twitch length for cardiocytes is around 10x longer than skeletal muscle fibers and heart cells don't fatigue easily
4. prevention of summation and no tetanus

automaticity

contraction without neural stimulation; controlled by pacemaker cells

how does cardiac muscle have variable heart rate and contraction tension

nerves connect to heart and CVS can have effects (ex: if you get scared)

sustained tetanus means

no pumping of blood

smooth muscle forms around

other tissues

characteristics of smooth muscle

- non-striated
- actin and myosin filaments present but different arrangement
- cells are thin with tapered ends and single central nucleus
- no t-tubules, sarcomeres, myofibrils, or tendons/ aponeuroses
- scattered myosin filaments

thin filaments attached to

dense bodies

dense bodies

anchor thin filaments to cytoskeleton and attach adjacent smooth muscle cells

how do smooth muscle cells contract

thin filaments pull dense bodies to middle and "scrunch up"

other ways smooth muscles can be stimulated

1. hormones
2. stretching (ex: food in stomach)
3. irritation (ex: coughing from smoke)
4. signals from motor neurons (like with skeletal muscle)
5. pacesetter cells cause peristalsis
6. electrical signals can travel from cell to cell through gap junctions