Chp 4 Muscles

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Muscle construction

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Constructed like a sturdy rope, tiny thousands of parallel threads called myofibrils squish together to form muscle fiber( muscle cells) with mitochondria, sarcolemma, nuclei, those muscle fibers then form larger string like bundles called fascicles and they combine to form a larger rope like bicep.

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Myofibrils contruction

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The myofibrils that combine to form muscle fiber are divided lengthwise into segments called sarcomere.

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Sarcomere contains

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2 proteins. 2 kinds of myofilaments called Actin and Myosn

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Overall

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Smallest to largest

Myofibril -Muscle fiber(muscle cell) (with mitochondria, sarcolemma, nuclei-fascicles-bicep.

Within the myofibril is: so even smaller

Within the myofibrils segments are divided called sarcomere- sarcomere contain myofilaments-called actin and myosin.

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Sarcomere contains

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myofirbrils

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The myofibrils contain two kinds of protein called

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Action and Myosin

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Thick filaments

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Myosin(dark bands)

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Thin filaments

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Actin(light bands), troponin, and tropomyosin

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Myosin has

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heads

think of male

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Actin

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has the binding sites

think of female

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cell membrane

cytoplasm is called

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is called sarcolemma

sarcoplasm

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Neuromuscular junction

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is the gap where a motor nerve and myofibril meet called the synapse

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At the end of the motor nerve

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acetycholine is stored in snynaptic vessicles which will release this neurotransmitter using exocytosis upon stimulation of a nerve impulse

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Across the synapse the surface of the myofibril contains receptors that can bind with

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the neurotransmitter

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Contraction process

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1. The distal end of a motor neuron releases acetylcholine.

2. Acetycholine diffuse across the gap at the neuromuscular junction.

3. The gap is between motor nerve and a myofibril

4. The sarcolemma is stimulated(sarcolemma is in muscle fiber) and a muscle impluse travels over the surface of the muscle fiber and deep into the fiber through transverse tubules and reaches sarcoplasmic reticulum.

5. Calcium ions diffuse from the sarcoplasmic reticulum into the sarcoplasm=binding to troponin molecules

6. Tropomuson molecules move and expose specific sites on actin filament.

7. Actin and Myosin link

8. Actin filaments are pulled inward by myosin cross bridges

9. Muscle fibers shortens as the muscle contracts

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Muscle Relaxation

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1. Acetylcholinestrase decomposes acetycholine and the muscle fiber membrane is no longer stimulated.

2. Calcium ions are actively transported into the sarcoplasmic reticulum

3. ATP causes linkage between actin and myosin to break

4. Cross bridges re open

5. Troponin and Tropomysosin molecules inhibit the interaction between myosin and actin filaments

6. Muscle fiber remains relaxed until ready to be stimulated again

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I band

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Light band consisting of Actin

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A band

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is the dark band, consisting only myosin overlapping actin

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Myosin filaments are held together by

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Z band

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H zone

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in center, consisting of only thick filaments.

also called central region

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A band consists

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of a region where thick and thin filaments overlap, and a region called central region (H zone)

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In the center of the A band is

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a dark band called M line

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Sarcomere

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The segment of myofibrils that extends from one Z line to the next.

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A muscle repsonse

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is all-or-none response

if it contracts at all, it will contract completely

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Threshold stimulus

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is the minimal stimulus needed to elicit a muscular contraction

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Twitch

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single short contraction reflecting stimulation needed to elicit a muscular contraction

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Latent Period

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the time between stimulus and responding muscle contraction

IT TAKES MILLISECONDS__AMAZING

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Refractory Period

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During this period immediately following contraction a muscle cannot respond

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Summation

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A rapid series of stimuli may produce summation of twitches and a sustained contraction

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Tetanic contraction

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Forceful sustained contraction without relation

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Tetany is a result of

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Low Ca2+ concentration

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Types of Contractions

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Isotonic

Isometric

Isokinetic

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Isotonic

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when a muscle contracts and and its ends are pulled closer together

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Isometric

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When a muscle contracts but its attachments do not move

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Isokinetic

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when the force a muscle generates is less than that required to move or lift an object

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White or fast skeletal muscle fibers

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have few mitochondria, reduced ability to carry on aerobic respiration and tend to fatigue rapidly

(ex. extra oscular muscles) Desgined for speed and fatigue easily

AKA EYE MUSCLES

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Red or slow skeletal muscle fibers

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have many mitochondria, are designed for endurance and can contract for long periods of time.

ex: Solues

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Muscle fatigue

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A fatigued muscle loses its ability to contract.

Muscle fatigue is due to accumulation of lactic acid and ATP exhaustion

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Oxygen Debt

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The amount of O2 needed to convert accumulated lactic acid to glucose and restore supplies of ATP and creatine phosphate

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During rest of moderate exercise

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O2 is sufficient to support aerobic exercise using many ATP molecules

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During strenuous exercise

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o2 deficieny may develop and lactic acid may accumulate as a result of anaerobic exercise

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Anaerobic

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Shorting lasting high intensity workout

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Role of Calcium in contraction

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promotes neurotransmitter release

triggers Ca2+ release from SR

Triggers sliding of myofilaments and ATPase activity

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Slding filament theory

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insertion to origin of the muscle

2. Shortening of myofibrils is caused by shortening of sarcomere or distance between Z lines reduced.

Sarcomere shortens but each filaments remains the same during contraction

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Sliding is caused by

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power strokes of myosin cross bridges which pull thin actin over thick myosin

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NEED TO STUDY WAY MORE

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