Basics of Muscular System
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What are the four general functions of the muscular system?
1. Movement-skeletal & smooth muscle aid in movement or bones and fluids
2. Posture maintance-skeletal muscles contract to maintain the body in a sitting or standing position
3. joint stabilization-tendons that cross over joints stabilize joint as the muscle tone (constant low level contraction) places tension on the tendon
4. heat generation-muscular contractions generate heat influencing body temperature
What is the specialization of the muscular system?
1. able to contract - when long cells shorten with a pulling force created that contracts the muscle; may cause movement or stabilization
2. able to extend - at the end of a contraction the muscle may return to its original length by relaxing or extended with the aid of an opposing muscle
3. able to become excitable - muscle cells respond to nerve impulses by contraction
4. elasticity - muscles may be stretched beyond its normal size and recoil back to its normal size
What are the 3 classifications of the muscular system?
skeletal muscle, cardiac muscle, and smooth muscle
What is skeletal muscle?
- - multinucleated
- - striated
- - voluntary muscle that attaches to bones and causes skeletan to move
What is cardiac muscle?
- - binucleated
- - branched
- - striated involuntary muscle that makes up the wall of the heart
What is smooth muscle?
non-striated involuntary muscle that assists in the movement of internal viscera
- has capacity to stretch widely and contract powerfully
What is the epimysium?
the outer-most layer that is a sheath of dense connective tissue that externally surrounds the entire muscle
What are fascicles?
bundles within the muscle that is surrounded by a sheath of fibrous connective tissue called perimysium
What is perimysium?
a sheath of fibrous connective tissue with fascicles in it
What is endomysium?
a sheath of reticular fibers that surrounds the bundles within the fascicles
What are the three sheaths composed of connective tissue that help to organize a muscle?
epimysium, perimysium, and endomysium
What iare the jobs of the three sheaths?
- - help to organize a muscle
- - extend out of the muscle area to join ligaments
- - help to transfer the contracting force of the fiber over to the bone so the joint is moved
What are the jobs of nerves and blood vessels?
- nerves supply the excitability signals
- blood vessels bring in nutrients & remove waste
What are the muscle attachments?
origin - side of a muscle that attaches to a bone that does not move when the muscle contracts
insertion - the joint it crosses wioll move when the muscle contracts.
Note: insertion moves toward its origin
where does the nuclei lie in the skeletal muscle fiber?
lie on the sides of the cell right below the sarcolema (cells membrane)
What is the sarcolema?
cells membrane (same as plasma membrane, but the term is sarcolema for muscles)
What are sacomeres?
basic contraction unit formed by the arrangement of thin myofibrils called actin and a thick myofibril called myosin
What are myofibrils?
made up of sarcomeres and contain both actin and myosin
What is actin and what is myosin?
actin is thin and myosin is thick
What are myofilaments?
protein strands that make up myofibrils
What is the Z line (Z discs)?
where the sarcomere boundary is at. distance between a z line is the sarcomere. Actin extends from the z line to the middle of the sarcomere. In the middle of the sarcomere and in between actin strands lies myosin strands.
What is the A-band?
the myosin length, including the area where actin and myosin overlap, is the A-band
What is the H-zone?
is where only myosin is present
What is the I band?
the region where only actin is present
What is the m-line?
the m-line is down the middle of the sarcomere
What is the size order from largest to smaller for myofibrils, muscle fibers (muscle cell), and myofilaments?
- 1. Muscle fibers (muscle cell)
- 2. Myofibrils
- 3. Myofilaments
What do the myofibrils and sarcomeres do to the appearance of the skeletal muscle?
the visible stripes result from the arrangement of myofibrils in the sarcoplasm
What is the sliding filament theory?
explains how a muscle contraction happens
How does a muscle begin to contract?
by the release of calcium from the terminal cisternae once a nerve impulse is received
What does the calcium do?
calcium ions bind to troponin on actin where the troponin-tropomyosin complex moves exposing the myosin binding sites.
What is the job of ATP?
provides power for myosin to move by "energizing" the molecule and changing its conformation (cocked position)
What does the myosin head do?
attaches to the actin filament (cross bridge) and in a swivel action pulls the actin filament (power stroke).
What does the second ATP do?
binds the myosin head causing it to release actin and return to a ckocked position.
How does a muscle keep shortening and shortening?
the myosin binds multiple times pulling towards the center further and further down the actin strand. Ad the filaments slide past each other, the overall size shortens.
What happens to the calcium that was released?
the released calcium is re-absorbed by the terminal cisternae
What happens to the z lines, I bands, H bands, a band, and M line with the contraction of muscle?
Z lines come closer to each other
I and H bands become smaller
A band and M line remain the same
What causes muscle extension?
after a contraction, the muscle can be stretched to its original position by the action of an opposing muscle
What is the role of Titin?
molecules in sarcomeres that resist overstretching and attach to myosin
What is the sarcoplasmic reticulum?
smooth ER of muscle cells (muscle fibers) that run longituninal around myofibrils. It stores cacium which are released for contraction and reabsorbed
What are t-tubules?
a continuation of a sarcolemma is a triad
What are red slow twitch fibers?
high in myoglobin content and in mitochondria & is vascularized. Requires good oxygen and is not easily fatigued. these fibers do not generate a lot of power
What are white fast twitch fibers?
low myoglobin content and in mitochondria larger in diameter. greater capability to produce power.
What are intermediate fast-twitch fibers?
intermediate in all aspects between red and white
What is the muscle of the heart (cardiac muscle)?
myocardium is the muscle of the heart wall and contracts to pump blood.
How do the muscle cells of cardiac muscles connect?
by cell junctions called intercalated discs and have a branching pattern. Each cell has one-two nuclei in the center with sarcomeres as which makes the tissue looks striated.
What are the 6 areas of the body that smooth muscle is found?
- -blood vessel walls
- -respiratory tract
- -digestive tubes
- -urinary organs
- -reproductive organs
- -the eye
What are the 2 smooth muscle layers?
- Note: these layers have fibers running perpendicular to each other. As they alternate contractions they shorten and constrict the organ
- 1. longitudinal layer (parallel to the axis)
- 2. circular layer (perpendicular)
What does smooth muscle not have that cardiac and skeletal muscle have?
- - no striations and no sarcomeres
- - calcium ions signal contraction & forces are not high
- - can contract for a long time before fatiguing
What is muscle distrophy?
disorder in which muscle is destroyed and replaced with connective tissue (diagnosed during childhood)
What is duchenne muscular dystrophy?
muscle degeneration from pelvis to cranium, predominantly in men usually living to 20 years old.. It is related to the lack of production of a protein that influence cell structure
What is fibromyalgia?
chronic pain syndrome of lower back or neck muscles that affects 2% of people, mostly omen, treated with antidepressants, exercise, and pain relievers. Not truly a muscle disorder
When does cardiac muscle and skeletal muscle contact by?
- cardiac muscle - week 3 of development
- skeletal muscle - week 7 of development
When does skeletal muscle, smooth muscle, and cardiac muscle stop dividng?
skeletal - once formed (does have limited regerated capacity in case of injury though)
cardiac - by age 9
smooth - divides as needed & has great regenerative ability
What is muscle tissue replaced with as one ages and what is it called?
called sarcopenia that is reversible with exercise
muscle tissue is replaced with connective tissue as one ages
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