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Muscular System 2 Cheat Sheet by

muscular system overview

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

around single muscle fiber
around a fascicle (bundle) of fibers
covers the entire skeletal muscle
on the outside of the epimysium
attach­ment, cord-like structure
attach­ment, sheet-like structure

Connective Tissue of Skeletal


Energy Sources


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

Electrical impulse of neuron
Electrical impulse in skeletal muscle
Muscle contra­ction

Action Potential Graph


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)

Isometric Twitch Myogram


Muscle Relaxation

Removal of ACh by AChE
Electrical impulse from neuron must cease
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
H zone
A band
Z disk

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

Lift up toes
move toes down
when sole of foot point inward
when sole of foot points outward
to move anteri­orly; shoulders, madible
to move part poster­iorly
to raise part superi­orly; shoulders
to lower part; open mouth
pivot on an axis; shake head no, can rotate head and shoulder
to draw a circle with body part; shoulder, head
turn hand downward
refers to arms; supinate; want a bowl of soup


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