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What do skeletal muscles do?
Move the bony levers of the skeletal system, enabling movement of the body
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What does the muscular system include?
- (SCS)
- Skeletal muscles;
- cardiac muscles
- smooth muscles
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What do smooth muscles do?
Assist in regulation of blood flow to various parts of the body
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Which type of muscle is controlled voluntarily and account for 50% of human body mass?
Skeletal muscles
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What is myofiber?
Skeletal muscle cells/fibers that are considered "excitable"
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What are the three layers of connective tissue in a skeletal muscle?
- (EPE)
- Epimysium
- Perimsysium
- Endomysium
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What is epimysium and where is it located?
- Outer layer of connective tissue that surrounds the entire muscle and separates muscle from surrounding tissue and organs;
- Converges at the end of the muscle to form the tendon that attaches to the bone
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What is perimysium?
Central layer of connective tissue w/in muscle that divides muscle into fascicles (singular = fasiculus)
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What is a fasciculus?
Group of as many as 150 myofibers lying in parallel and bundled together
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What is endomysium?
Inner layer of connective tissue w/in muscle that surrounds myofiber
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What are motor neurons and where do you find them?
- Controls each skeletal myofiber;
- Central Nervous System
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What is a motor unit?
A motor neuron and all the myofibers that it innervates.
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How do motor units work with muscle contraction?
All myofibers of a motor unit contract simulatneously and at maximal force
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What type of myofiber is contained in a motor unit?
All the same type (either Type II, Type IIa, or IIb)
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How is a muscle able to regulate its force production during contraction? How does this work for maximal force output?
- By controlling the number of motor units that are activated;
- By varying the firing rate of neural impulses delivered by the motor neuron to its myofibers
- For maximal force output, all of the muscles motor units have been recruited and each one is firing at it's highest possible rate
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What is a neuromuscular junction?
Junction where communication between a motor neuron and a skeletal muscle fiber occurs
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Where is a synaptic knob located, and what is the purpose of it?
- Located at the end of an axon of the motor neuron;
- Contains the neurotransmitter acetylcholine (ACh)
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What is the synaptic cleft?
Separates the synaptic knob from sarcolemma of the skeletal muscle fibers.
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How many nuclei can a myofiber contain?
More than one, and up to 200-300/mm of fiber length
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What is sarcolemma? What is it's purpose?
- The plasma membrane of the myofiber
- Contains chemically-gated sodium channels allow electrical stimulation of myofibers via action potentials
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What content is substantial in myofibers and what does it provide?
- Mitochondrial content;
- Provides ATP via oxidative pathway
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What is sarcoplasm?
Cytoplasm of the myofiber
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What are T-tubules (transverse)?
Extensions of the sarcolemma that form a network of tubules
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What is sarcoplasmic reticulum and what is it needed for?
- Richly developed in the myofiber to store calcium in special sacs called terminal cisterna;
- Needed to stimulate muscle contraction
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What do myfibirils contain?
myofilaments
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What do myofilaments consist of and how are they organized?
- Contractile proteins actin and myosin;
- Orgainzed in repeading functional units called sarcomeres;
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Functions of actin and myosin
- Account for 60% of protein content of myofiber;
- Form crossbridge to slide past one another during muscle contraction, shortening the sarcomeres
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Describe Myosin
Larger contractile protein sometimes called "thick filament"
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Describe Actin
Smaller contractile protein sometimes called "thin filament"
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What is tropomyosin?
- Covers the actin bridging site during resting condition;
- Attached to troponin
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What is the function of tropomyosin and troponin?
Regulate bridging of actin and myosin for muscle contraction and relaxation
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What is the most common method used to classify myofibers?
Based on the isoform of myosin expressed by the cell
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What are the 3 myosin isoforms? Describe them and when they used during exercise.
- Type I - slow twitch fibers w/ high oxidative capacity - exercise w/ low intensity and longer duration
- Type IIB - fast twitch fibers w/ low oxidative potential - exercise w/ high intensity and short duration
- Type IIA - intermediate fibers, both in twitch and oxidative capacity - exercise w/ high intensity and short duration
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What are essential to myofiber twitch?
Regulatory and contractile filaments
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What is the force generated by the whole musce a function of?
Function of both the number of myofibers within that muscle that are twitching and the rate at which the twitches occur
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What effect does training (both endurance and resistance) have on myofibers?
- Cause conversion of type IIB fibers to type IIA;
- Doesn't cause conversion between type I and Type II myofibers
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What does prolonged resistance training result in and what is in known as?
- Significant increase in myofiber size, particularty type II;
- Hypertrophy
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What is the Sliding-Filament theory? Describe it
- Explains how protein filaments interact to produce a twich of the myofiber
- 1) Nervous system excites myofiber's sarcolemma and T-Tubules
- 2) Calcium stored within sarcoplasmic reticulum releases into cell's cytosol
- 3) Calcium binds to troponin, causing associated tropomysin to change shape
- 4) Active sites of actin filament are exposed
- 5) Cross-bridge heads on myosin molecule bind to exposed active sites of actin
- 6) Adenosine triphosphatase (ATPase) cleaves ATP, resulting in "power stroke" that pulls actin towrad the center of the myosin molecule
- 7) Results in fiber shortening and force generation
- 8) When ATP binds to cross-bridge head, link between myosin and actin is broken, allowing process to repeat
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What is the Calcium pump?
Responsible for delivering cytosolic calcium back into sarcoplamic reticulum, returning myofiber to state of relaxation
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Describe muscle attachment locations
- - Begins at at proximal attachment (origin)
- - Ends at distal attachment (insertion)
- - Contracts to produce a specific action
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What is an agonist?
A prime mover, responsible for producing a particular movement
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What is an antagonist?
A primer mover that opposes the agonist
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What is a synergist?
Assists the prime mover but is not the primary muscle responsible for the action
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Why is identification of superficial landmarks of the skeletal muscles and other anatomic structures important?
Body composition and exercise testing
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Upper body anatomic structures important for exercise testing
- (SPBT)
- Sternocleidomastoid -- radial pulse;
- Pectoralis major;
- Biceps brachii;
- Triceps brachii
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Lower body anatomic structures important for exercise testing
- (GQG)
- Gluteus maximus;
- Quadriceps femoris;
- Gastrocnemius
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What is an important landmark for skinfold measurement and where is it located?
- Inguinal crease;
- Natural diagonal crease in the skin formed where the musculature of the thing meets the pelvic girdle
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