Functions of the Muscular System
skeletal muscle |
make up"flesh" of the body, maintain posture, voluntary movement, aid in breathing/eating/speech, provide facial expression, generate reflexes, produce body heat |
Skeletal muscle tissue development
Step 1 (embryonic mesoderm cells) |
Embryonic mesoderm cells undergo cell division (to increase number) and enlarge |
Step 2 (myoblasts) |
Several myoblasts fuse together to form a myotube |
Step 3 (myotube) |
Myotube matures into skeletal muscle fiber |
Step 4 |
Mature skeletal muscle fiber |
Connective Tissue of Skeletal
Endomysium |
around single muscle fiber |
Perimysium |
around a fascicle (bundle) of fibers |
Epimysium |
covers the entire skeletal muscle |
Fascia |
on the outside of the epimysium |
Tendon |
attachment, cord-like structure |
Aponeurosis |
attachment, sheet-like structure |
Connective Tissue of Skeletal
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Three Types of Muscle Fibers
Slow oxidative fibers (slow) |
Red color due to myoglobin, obtain energy from aerobic metabolic reactions, contain a large # of mitochondria, richly supplied w/ cappilaries, contract slowly and resist fatigue, fibers are small in diameter |
Fast oxidative fibers (intermediate) |
Have an intermediate diameter, contract quickly like fast glycolytic fibers, oxygen dependent, high myoglobin content and rich supply of capillaries, kinda fatigue resistant, more powerful than slow oxidative fibers |
Fast glycolytic fibers (fast) |
Contain little myoglobin and few mitochondria, about twice the diameter of slow-oxidative fibers, contain more myofilaments and generate more power, depend on anaerobic pathways, contract rapidly and tire quickly |
Overview of mus. contraction steps
Step 1 |
Nerve impulse travels down the axon and reach axon terminal |
Step 2 |
Calcium VGC open > calcium influx into axon terminal |
Step 3 |
Exocytosis of ACh into synaptic cleft (calcium dependent event) |
Step 4 |
ACh interaction with Na+/K+ channels on sarcolemma > opening of the channels |
Step 5 |
Na+ influx at higher rate than K+ efflux > leads to depolarization |
Step 6 |
Spreading of the depolarization in the muscle fiber through t-tubules |
Step 7 |
Opening of the calcium VGC associated with the T-tubules and release of calcium into sarcoplasm |
Step 8 |
Interaction of calcium with regulatory protein troponin |
Step 9 |
Eventual muscle contraction |
Main Steps of Muscle Contraction
1. |
Electrical impulse of neuron |
2. |
Electrical impulse in skeletal muscle |
3. |
Muscle contraction |
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Graded Muscle Response
Muscle response to changes in stimulus strength |
Recruitment works on size principle |
Motor units w/ smallest muscle fibers are recruited first |
Motor units with larger and larger fibers are recruited as stimulus intensity increases |
Largest motor units are activated only for the most powerful contractions |
Motor units in muscle usually contract asynchronously |
The Size Principle of Recruitment
Graded Muscle Response
Muscle response to changes in stimulus frequency |
If stimuli frequency increases, muscle tension reaches maximum |
Referred to as fused (complete) tetanus bcuz contractions "fuse" into one smooth sustained contraction plateau |
Prolonged muscle contractions lead to muscle fatigue |
Fused (complete) tetanus mus. response
The Muscle Twitch
Latent Period |
events if excitation-contraction coupling (no muscle tension seen) |
Period of Contraction |
cross bridge formation (tension increases) |
Period of Relaxation |
Ca2+ reentry into SR (Tension declines to zero) |
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Muscle Relaxation
Removal of ACh by AChE |
Electrical impulse from neuron must cease |
ATP? |
Calcium must be removed by pumps (active process vs. channel [passive]) |
Sliding Filament Model
What is it? |
The shortening of the sarcomeres in a myofibril produces the shortening of a myfribril |
I Band |
Narrows/shortens |
H zone |
Narrows/shortens |
A band |
Unaffected |
Z disk |
unaffected |
In Depth Relaxation
Step 1 |
ACh is broken down by AChE, ending action potential generation in the sarcolemma |
Step 2 |
The SR reabsorbs calcium ions, and the concentration of calcium ions in the sarcoplasm declines |
Step 3 |
When calcium ion concentrations approach normal resting levels, the troponin-tropomyosin complex returns to its normal position. This change re-covers the active sites and prevents further cross-bridge interaction |
Step 4 |
Without cross-bridge interactions, further sliding cannot take place, and the contraction ends |
Step 5 |
Muscle relaxation occurs, and the muscle returns passively to its resting length |
Unfused (incomplete) tetanus mus. stim
Action Terminology for Muscles
Dorsiflexion |
Lift up toes |
Plantarflexion |
move toes down |
Inversion |
when sole of foot point inward |
Eversion |
when sole of foot points outward |
Protraction |
to move anteriorly; shoulders, madible |
Retraction |
to move part posteriorly |
Elevation |
to raise part superiorly; shoulders |
Depression |
to lower part; open mouth |
Rotation |
pivot on an axis; shake head no, can rotate head and shoulder |
Circumduction |
to draw a circle with body part; shoulder, head |
Pronation |
turn hand downward |
Supination |
refers to arms; supinate; want a bowl of soup |
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