ap chapter 11 Muscles

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ap chapter 11 Muscles

muscle cell structure (10)

1. Fiber = ("cell") entire length of muscle (skeletal)
2. Sarcolemma - plasma membrane
3. Sarcoplasm - cytoplasm
4. Sarcoplasmic reticulum - (like SER) stores calcium ions (need calium for muscles to contract - so it doesn't have to immediately go outside (mitochondria) to get it)
5. Multinucleated - more than 1 nucleus (muscles once smaller cells, now fused together)
6. Myofibril - protein strands combined
7. Myofilament - protein strands
8. Sarcomere - basic unit of contraction. where contraction happens
9. Striations - lines which are caused by sarcomere
10. T tubules - transverse, carry nervous impulse into muscle fibers (individual cells)

Myofilaments (3)

1. Myosin -thick
2. Actin - thin
3. Tropomyosin - thin, determine interaction
4. Troponin - thin, determine interaction

tropomyosin held in place by troponin

#2, 3 & 4 together allow muscles to contract


("cell") entire length of muscle (skeletal)






plasma membrane in muscle cell

sarcoplasmic reticulum

stores calcium lons in muscles


protein strands combined in muscle cells


protein strands in muscle cells


basic unit of contraction, where contractions happen in muscle cells


lines which are caused by sacromere in muscle cell

T tubules

carry nervous impulse into fibers (individual cells) in muscle cells


one single cell


bunches of neurons

neuromuscular junction (see paper slide) 1/

neuron tells muscle what to do. no contraction w/o it

1. Point of contact between neuron and muscle fiber
2. Muscles require innervation for contraction
3. Electrical message convert to chemical message
4. Neuron releases neurotransmitter - acetylcholine
5. Acetylcholine causes changes in sarcolemma
6. Impulse is carried into fiber by T tubules

neuromuscular junction (see paper slide) 2/

1. Synapse: synaptic knob resting in an invagination of the sarcolemma
2. Space between synaptic knob & sarcolemma - no actual contact
3. Neurotransmitter diffuses from synaptic knob across synapse to bind with receptors on sarcolemma


minimum level of stimulation for muscle to contract

Myofibril contraction (5) 1/3

1. Acetylcholine binds with receptors on membrane
2. Open sodium channels in membrane
3. Results in calcium release from sarcoplasmic reticulum in sacromere (thru diffusion)
4. Calcium binds to troponin in thin filament
5. Binding of troponin causes tropomyosin to shift and expose active sites on the actin

Note 1: using a lot of ATP & generating heat
Note 2: muscle fiber gets shorter in contractions, not the muscle

Myofibril contraction (5) 2/3

1. Exposed active sites can now bind with myosin heads (myosin binds w/action)
2. Sarcoplasmic reticulum begins to actively pump calcium back into SR (pumps)
3. Calcium ions removal from the troponin molecules lets tropomyosin to return to blocking action of actin
4. Ends the contraction

Myofibril contraction (5) 3/3

1. When stimulated muscle fibers either contract with all possible force or not at all
2. Muscle contraction is not all-or-none (you can do a little bit at a time)
3. Threshold stimulus

Myofibril relaxation (3)

1. Calcium moves back into sarcoplasmic reticulum by active transport.
2. Calcium moves away from troponin-tropomyosin complex
3. Tropomyosin moves back into position and blocks binding sites.

Note 1: now actin & myosin can't interact.
Note 2: muscle contraction is not chemical just interacting

sliding filament theory

1. Active sites on the actin are exposed
2. Myosin cross bridges will bind
3. Myosin heads pull thin filaments past them
4. Actin slides across myosin towards middle of sacromere
5. Each myosin head releases actin and binds to the next active site, and pulls again
6. Entire myofibril shortens

what is sliding in the contraction is actin. Actin slides across myosin.
Z line to Z line = one sacromere (functional unit of contraction)

Relaxed & contracted sarcomeres (3)

1. Muscle cells shorten because their individual sarcomeres shorten
- Pulls Z discs closer together
2. Neither thick nor thin filaments change length during shortening
3. Overlap changes as sarcomeres shorten

Note 1: no chemical changes

Excitation - Contractions Coupling

one has to happen in order for the other to happen

1. Coupling refers to the stimulation of neuron causes calcium to be released by SR and this results in contraction

Energy sources muscles

you need carbohydrates to make ATP. Mitochondria needs oxygen to make ATP.

1. Hydrolysis of ATP releases energy required for muscular contraction
2. Adenosine triphosphate (ATP) binds to the myosin cross bridge
3. Factors that help with energy production
a. Creatine phosphate - AA attached to the phosphate (high energy bond to make ATP w/o going to mitochondria)
b. Myoglobin - binds oxygen, carries oxygen
c. Glycogen - liver/carbs makes glycogen & ATP
d. Anaerobic respiration - results in oxygen debt
e. Aerobic respiration - mitochondria
4. Oxygen debt - mitochondria (ATP) & myoglobin (ATP) are gone. skeletan muscles. fatigue = muscle cramps

ex. chickens don't fly, don't need oxygen, therefore, use myoglobin.

motor unit (3)

one neuron going to numerous fibers

1. Neuron and all muscle fibers innervated
2. Small motor unit = precision (a couple of fibers) ex. fingers
3. Large motor unit = strength ( a lot of fibers. power/force) ex. thigh

contraction of muscle

1. Strength of contraction is graded: ranges from weak to strong depending on stimulus strength
2. Strength of contraction depends upon recruitment of motor units. A muscle has many motor units = summation

muscle twitch

Muscle contraction in response to a stimulus that causes action potential in one or more muscle fibers

tetanus = constant (sustained) contraction that you control. (ex. holding a book)

tetanus (lock jaw) = you can't relax your muscles (from toxins)


1. As the frequency of action potentials increase, the frequency of contraction increases
a. Incomplete tetanus: muscle fibers partially relax between contraction
b. Complete tetanus: no relaxation between contractions (carry)

Types of muscle contractions

1. Isometric (same length): no change in length (of muscle) but tension (pressure) increases (ex. carry something for a long time)
2. Isotonic: change in length but tension (pressure) constant (ex. moving muscle, keeping the pressure the same)
3. Muscle tone: constant tension by muscles for long periods of time (creates body heat)

Note 1: passed out = limp muscles (no muscle tone)
sleeping = some rigidity (muscle tone)

Length vs. Tension

Maximal strength muscle develops directly related to the initial length of its fibers.
Completely.fully contracted then any increase in movement, then increase in pressure is small

Strength of muscle contraction

1. amount of load (stretch reflex)
2. initial length of muscle fibers (length-tension relationship) -contracted or not
3. recruitment of motor units (#of fibers activated)
4. metabolic condition (fatigue, treppe)

Muscle size

1. Hypertrophy: increase in muscle size
a. Increase in myofibrils (by building myofilaments)
b. Increase in strength due to better coordination of muscles, increase in production of metabolic enzymes, better circulation (add blood vessels), less restriction by fat
2. Atrophy: decrease in muscle size (don't use it, lose it)

Rigor mortis

1. Stiffening of the body beginning 3 to 4 hours after death (b/c stop making ATP, muscles stay contracted
2. Deteriorating sarcoplasmic reticulum releases calcium
3. Calcium activates myosin-actin cross-bridging and muscle contracts, but can not relax.
4. Muscle relaxation requires ATP and ATP production is no longer produced after death
5. Fibers remain contracted until myofilaments decay

Note: after 12 hours you go limp b/c breaking down proteins

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