Term
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Definition
-Muscles are specialized masses of tissue that are able to contract, relax and change their length
-More than 700 skeletal muscles make up the muscular system, and technically each one is an organ because they are composed of muscles tissue, CT, and nervous tissue
-Muscle accounts for about 40% of body weight |
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Term
| Functions of the Muscular System |
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Definition
-Movement of the body
-Maintenance of posture
-Production of body heat
-Communication
-Constriction of organs and vessels
-Contraction of the heart |
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Term
General Properties of Muscle Tissue:
5 main functions shared by 3 muscles types |
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Definition
1. excitability
2. contractility
3. extensibility
4. elasticity
5. conductivity |
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Term
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Definition
| ability to respond to neural stimulation |
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Definition
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Term
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Definition
| ability to contract over a range of resting lengths |
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Definition
| ability of a muscle to return to its original length after contraction |
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Term
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Definition
| ability of the muscle cells to transmit a stimulus |
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Term
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Definition
-3 different muscle tissues, all with different functions and different histochemical and metabolic characteristics
-Skeletal
-Cardiac
-Smooth |
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Term
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Definition
-Found only in the heart; involuntary; acts to constantly pump blood through blood vessels
-Appearance: striated like skeletal muscle, but myocytes are short and branching, and connected by intercalated disks
-Metabolically: cannot fatigue; therefore, rich in glycogen, myoglobin and 25% of the cell is mitochondrial reticulum. Also uses lactic acid directly as fuel with other fuels
-Vulnerable to any interruption in O2 delivery
-Calcium stores are within the cell and delivered from the extracellular fluid |
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Term
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Definition
-Involuntary
-Found in visceral organs and vasculature (to move fluids/solids along)
-Fusiform in shape; no striations, but it does contain actin and myosin fibers; dense bodies that attach thin filaments to the cytoskeleton
-Calcium source primarily from ECF |
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Term
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Definition
-More than 700 muscles in the human body
-They are contractile in function (when active)
-Attached to bone. Their attachment determines their function in the human body |
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Term
| Skeletal Muscle Structure |
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Definition
| -Each muscle is a complete organ consisting of cells (skeletal muscle fibers) with associated connective tissue, nerves, vasculature (arteries and veins) |
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Term
| Connective Tissue of Muscles |
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Definition
-Allows connection between muscles fibers/cells (forming muscle cells), separation from other muscles or bone, and attachment to other structures in strong fashion
-Muscle has 3 types of surrounding CT that exist in different layers:
1. Endomysium
2. Perimysium
3. Epimysium
4. Muscular Fascia |
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Term
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Definition
-innermost layer
-surrounds each muscles fiber/cell, connects them to other cells and contributes to the insertion of tendon of muscle |
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Definition
-middle layer
-surrounds bundles of muscle fibers (fascicles); vasculature and nervous supply traverse her; also contributes to the tendon of the muscle |
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Definition
-outer layer
-covers the outside of the entire muscle; also contributes to the tendon of muscle |
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Definition
| surrounds epimysium, used to be considered part of the deep fascia; it separates muscle from surrounding tissue or bone |
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Term
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Definition
-Generally, at each end of muscle, the CT comes together and extends to form tendons (which are cord-like) or sponeuroses (which are flat sheets of fibrous tissue)
-Allows for an indirect attachment of muscle to bone or other fibrocartilage
-Some muscle epimysium has direct attachment to bone periosteum (one example of muscle cells in contact with bone) |
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Term
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Definition
-nerves travel in both the epimysium and perimysium to innervate muscle fibers (voluntary), vasculature (ANS) and sensory organs of the muscles
-these voluntary skeletal muscle fibers are innervated by axons from motor neurons from the ventral horn of spinal cord (CNS)
-Connection between muscle fiber and motor neuron is known as a synapse or neuromuscular junction |
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Term
| Vascular Supply of Muscle |
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Definition
-vessels (arteries and veins) are found traveling predominantly in perimysium and epimysium
-this is the delivery system for nutrients of oxygen and fuel sources (for ATP production)
-works as a removal system for metabolic waste products
-contains a large capillary network coiled around each muscle fiber within the endomysium
-vessels are not affected by the length changes in muscles
-vasculature and nerves generally travel together |
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Term
| Skeletal Muscle Fiber (Cell) Anatomy |
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Definition
-Muscle cells are similar to typical cells in some ways, and differs from typical cells in other ways
-Vary in size and nucleus |
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Term
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Definition
-muscle cells/fibers are very large and often 14-16 inches long in the appendicular skeleton
-cells/fibers are relatively thicker than other cells
-extend the length of muscle, generally
-number of cells varies considerably in each muscle depending on the muscle size and type (genetically determined) |
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Term
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Definition
| Muscle cells are multinucleated; each cell has hundreds of nuclei that exist just under the sarcolemma membrane |
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Term
| The Origin of Muscle Cells |
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Definition
-Embryologically, individual myoblasts fuse together to form muscle fibers- by fetal week 17, the contractile elements are functional
-satellite cells are myoblasts that don't fuse, but exist between cells and function to aid in injury repair
-mitosis exists up to about 1 year of age, then no further new fibers are added |
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Term
| Histology of Muscle Cells |
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Definition
-plasma membrane of muscle cells is called a sarcolemma
-2 layered system: innermost is called the External lamina(comprised of collagen fibers) and outer layer is called the endomysium(thickest layer, also collagen)
-surrounds the cytoplasm of muscle cells which is called the sarcoplasm. the sarcoplasm surrounds individual myofibrils of muscle cells
-CT which contributes to the muscle tendons at either ends of the muscle. therefore, each fiber is really attaced to bone via tendon and transmits its generated force to the bone through the tendon |
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Term
| T-tubules of Muscle Cells |
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Definition
-transverse tubules of t-tubules are a network of tubules that extend inward at right angles to the sarcolemma
-part of the sarcoplasmic reticulum, an outer, organized network of membraneous channels that extends throughout the sarcoplasm
-they interconnect to surround myofibrils on path to opposite sides of the cells and allows for: 1. nerve impulses to be transmitted rapidly to individual myofibrils(contracted elements) for simultaneous action and 2. the transport of nutrients along with extracellular fluid to inner parts of muscle fiber |
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Term
| Components of the Muscle Sarcoplasm |
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Definition
-these muscle cell specific components show unique characteristics from a typical cell and are important in generating the unique contractile action of muscle cells
-components include:
1. a large quantity of stored glycogen
2. a large quantity of stored myoglobin (similar to hemoglobin in RBC's -> an oxygen binding/transport molecule)
3. sarcoplasmic reticulum- longitudinal network of tubules that serves as a storage site for calcium; it is essential for muscle contraction
4. mitochondrial reticulum- a network of structures for the energy producing biochemical "Krebs Cycle" which produces ATP through oxidative phosphorylation |
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Term
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Definition
-sarcoplasm of each muscle fiber surrounds 100's to 1000's of myofibrils
- myofibrils are the contractile elements of the muscle fiber
-they are cylindrical and as long as the muscle fiber in length and are connected to the sarcolemma through elastic filaments along the length of the myofibril; therefore, contraction of the myofibrils will act to shorten the entire cell
-myofibrils are made up of long strands of repeating subunits called sarcomeres |
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Term
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Definition
-bounded by Z-disc
-Sarcomeres are the most basic and smallest functional units of the myofibril
-Sarcomeres are composed of bundles of myofilaments which are responsible for muscle contraction
-extend from one Z-Disc to an adjacent Z-disc
-2 types of myofilaments composing the sarcomeres are myosin and actin |
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Term
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Definition
-thickest of the 2 types of myofilaments
-many myosin molecules bind parallel to one another with globular heads protruding around the circumference
-each molecule is 2 protein strands twisted together forming a tail end and a 2 globular head end: on each head is an ATPase enzyme
-Molecule bunches are also bound tail end to tail end to form one myosin myofilament
-myosin myofilaments are centered in the sarcomere, but are connected to the Z-discs by elastic filaments called Titin: also acts as a spring, allowing the sarcomere to stretch and recoil
-myosin heads have 3 important properties: 1. bind to active sites on Actin, 2. able to bend and straighten, 3. break down ATP |
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Term
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Definition
-thinner myofilament
-composed of actin, tropomyosin and troponin
-2 F-actin protein strands are twisted together as the base structure: strands are made of protein globule called G-actin
-2 thinner tropomyosin strands are twisted around the outer surface of the actin strands
-at specific sites on the F-actin strands, a tri-globular troponin molecule sits on top of the tropomyosin (which sits on top of actin active site)
-Troponin is tri globular to allow for: 1.attachment to G-actin 2.attachment to tropomyosin 3. binding of Calcium
-Attaches to the sarcoma via a Z-disc: the other end extends into the midline of the sarcomere |
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Term
| Appearance of Skeletal (and Cardiac) Muscles |
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Definition
-striations or a banded appearance is present in both skeletal and cardiac muscles
-this appearance is caused by the alignment of actin: myosin in a 2:1 ratio within the sarcomere (although 2/3 of muscle protein is myosin) and the alignment of myofibrils within the fiber
-I-Band: lighter regions are where there are only actin myosin filaments
-A-Band: darker regions contain both actin and myosin
-H-Zone: center of A-band, consists of only myosin myofilaments
-M-Line: center of H-Zone that attaches to the myosin myofilaments (like the Z-disc holds onto Actin) |
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Term
| Contractile Action Within Muscle |
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Definition
-when stimulated, the muscle cell always attempts a concentric contraction(i.e. producing tension by shortening the length of the muscle cell through interactions between the thick and the thin filaments in each sarcomere
-this process of shortening and having the thick and thin filaments articulate with one another is called the Sliding Filament Theory
-It is important to note that although the sarcomere, myofibrils and muscle fibers shorten, the myofilaments do NOT |
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Term
| Physiology of Skeletal Muscle Fibers |
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Definition
Steps in Achieving Contraction of a Muscle Fiber
-In order for a contraction to occur in a muscle fiber, certain processes must occur
1.Action Potential from motor neuron, stimulating contraction
2. Excitation-Contraction coupling within the muscle fiber, causing contraction
3. Cross-bridge movement of the myofilaments, the process of contraction |
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Term
| Action Potentials and the NeuroMuscular Junction(NMJ) |
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Definition
-there must be innervation: each muscle fiber receives neural input from a single motor neuron at one or more neuromuscular junctions
-assuming innervation to stimulate contraction:
1.an action potential arrives at the pre-synaptic terminal at the end of the neuron, releasing Ca2+ into the pre-synaptic membrane
2. calcium ions enter the pre-synaptic terminal and initiate the release of the Neurotransmitter ACh(acetylcholine)
3. ACh is released into the synaptic cleft
4. ACh binds to Na+ channels on the post-synaptic membrane (on the sarcolemma)
5. Na+ channels open and Na+ enters into the post-synaptic membrane causing depolarization: if a threshold is met, the action potential will continue along the sarcolemma (this is an Obligatory response of All or Nothing principle, meaning if threshold is not met, nothing happens, but if threshold is met, the action potential must continue)
-ACh unbinds and is rapidly broken down into Acetic acid and Choline by the enzyme Acetylcholinesterase
-Choline is recycled into the pre-synaptic membrane and bound with acetic acid taken from byproducts of glucose metabolism to form more ACh: this recycling process
1. Increases efficiency of the Action Potential (1 pre-synaptic action potential yields 1 post-synaptic action potential)
2. requires less energy to form more ACh
3. Takes less time to form more ACh |
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Term
| Cross-Bridge Movement (Sliding Filament Theory) |
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Definition
-Once attached, the myosin head will continually tilt, move and release, moving the actin and myosin myofilaments toward each other in the following steps:
1. there is a high energy complex of ADP + P in the unattached myosin head waiting for an actin binding site to open.
-when it binds, it releases the P, initiating the power stroke, causing the actin to past the myosin
-The remaining ADP is then released
-An ATP attaches to the myosin-actin complex, causing conformation change in the myosin head (it releases from the active binding site on actin)
-The binding-release process mediates the partial hydrolysis of ATP by myosin ATPase, reforming the high-energy complex of ADP + P in the myosin head
-Myosin head returns to its resting position and then looks for another open actin active site and repeats the process (if possible)
-This process continues for as long there is:
1. nervous stimulation
2. calcium release
3. available binding sites
4. ATP |
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Term
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Definition
-Most ATP is produced in the mitochondria through oxidative metabolism
-ATP energy is required for this contraction process and for the process leading to relaxation (release of cross-bridges) |
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Term
| Ending Muscle Contraction |
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Definition
-Muscle action ends when calcium is fully pumped out (via the Ca2+ pump) of the sarcoplasm back into storage in the sarcoplasmic reticulum
-however, when there is no available ATP (e.g. in fatigue, death or starvation), Ca+ pump is unable to return the Ca2+ to the SR and thus, there is no release of the cross-bridges. This leads to contractures or rigor mortis (seen in death) |
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Term
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Definition
-includes motor neurons, its axon, and the set of muscle fibers it innervates (vary in number, but always all in the same muscle and, if they exist, in the same neuromuscular compartment)
-Motor units will vary in terms of:
1. number of muscle fibers they contain
2. sensitivity to stimuli
-size (innervation ratio) ranges from 1:1 to 1:2-3,000, and indicates both:
1.ability to control precision of movement
2.type of muscle fiber innervated |
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Term
| Stimulation of motor neurons |
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Definition
-when motor neurons are stimulated sufficiently, a contraction effort will be made by muscle fibers.cells in a given muscle (obligatory response)
-the amount of tension produced when a muscle is stimulated to contract depends primarily on:
1.frequency & rate of stimulation: the smound of nercous stimulation and ultimately amount of Ca2+ released and how long it stays in sarcoplasm
2. the number and size of motor units stimulated: allows precise control of contractions so that as more fibers are recruited, greater tension/force is produced; smooth, steady increase in force production/whole muscle contraction created through summation of stimulated muscle fibers
-Resting tension (initial overlap of myofilaments): most important |
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Term
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Definition
| all motor units contracting at maximum rate/frequency of stimulation (note: contraction won't last long due to ATP shortage) |
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Term
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Definition
| motor units are alternated (so muscle won't fatigue as fast) to maintain force production at given level |
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Term
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Definition
always present (i.e. muscle tone); there is random stimulation of motor units creating isometric contraction for position, stability, balance, joint stability, etc
-ready to go |
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Term
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Definition
-the sarcomere can produce force (tension) in various ways
1. isotonic contraction
2. isometric contraction
3. isokinetic contraction |
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Term
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Definition
change of length but the force generated remains the same
1. concentric contraction- shortens space between Z-discs
2. eccentric contraction- either returns sarcomere to original (or resting) length or longer |
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Term
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Definition
no change in length, but a constant coupling/decoupling of cross-bridges (without shortening)
-produces a force |
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Term
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Definition
| contraction with a change in length and the force generated varies throughout the range of motion |
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Term
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Definition
-Fatigue is the decreased capacity to do work and the reduced efficiency of performance that follows activity/training
-Development of fatigue varies person to person, but occurs at 3 possible locations:
1. the nervous system (psychological fatigue): most common
2. within muscles (muscular fatigue: second most common
3. At the neuromuscular junction(synaptic fatigue): least common, except in cases of extreme exertion |
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Term
| Muscle Training/Plasticity |
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Definition
-muscle plasticity can be defined as how muscle can be shaped/affected by or adapt to various factors
-with training (e.g. repeated stimulation to produce near-max force, with an increase in the size of myofibrils, greater number of glycolytic enzymes and greater amount of stored glycogen, etc.): hypertrophy results
-enlargement intra-cellularly, which serves to increase amount and speed of force development by that fiber |
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Term
| Muscle Plasticity with no use |
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Definition
-with lack of stimulation:
1. see muscular atrophy or loss of both muscle tone and mass
2. smaller, weaker, lower force production
3. can be reversed for some time, but after a long time of no stimulation, dead muscle fibers/cells (and they are not replaced- this is why physical therapy is so important) |
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Term
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Definition
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Term
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Definition
| increase in the number of cells |
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Term
| Muscle plasticity with age |
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Definition
-Age will reduce size and power output of muscle via:
1. lower fiber diameter (smaller myofibrils; lower levels of myoglobin, glycogen, ATP)
2. less blood flow due to lower cardiovascular delivery and decreased capillary density (during exercise and rest; less ability to dissipate heat generated by muscle action)
3. Increased inelasticity: more fibrous tissue(i.e. fibrosis), less flexibility, restricts movement
4. Reduction in the surface area of the NMJ
5. Decrease in number of motor neurons innervating a given muscle fiber
- with these changes we see:
1.rapid fatigue of muscle- lower tolerance for exercise
2. plasticity lowers- recovery slower from injury- lower number of satellite cells available, increased fibrous tissue, and damage repair will be primarily scar tissue
3. decreases work capacity
4. muscles become less elastic- more fibrous tissue (fibrosis), less flexibility, restricts movement |
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Term
| Muscle plasticity and fitness |
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Definition
| rate of muscle function decline is similar in all people, but if you start from a higher level of fitness, there won't be such a dramatic change with age |
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Term
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Definition
-during movement or exercise, endurance and speed of movement is largely dependent upon muscle's ability to produce energy and force, respectively
-primary determinant of these characteristics is related to fiber type composition of the muscle (thought to be from different forms of myosin)
-There are 3 major fiber types in skeletal muscle:
1. type 1: slow twitch or slow oxidative
2. type 2a: fast-oxidative (glycolytic)
3. type 2b or 2x: fast twitch or fast glycolytic |
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Term
| Type 1: slow-twitch or slow-oxidative |
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Definition
-endurance activity
-smaller diameter fibers: takes approximately 50-150 milliseconds to reach peak tension (speed low, strength low)
-more myoglobin, more oxygen
-more capillaries, more oxygen/glucose
-fatigue resistant, more mitochondria
-ATP produced more slowly; aerobic
-Red in color
-Found in postural muscles: long muscles of the back and legs |
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Term
| Type II a: fast-oxidative (glycolytic) |
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Definition
-reddish-pink in color
-intermediate fiber size and characteristics
-resistance to fatigue, assets of power and endurance
-aerobic |
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Term
| Type II b(or IIx): fast-twitch or fast glycolytic |
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Definition
-white in color; large diamter, dense myofibrils, greater number of sarcomeres; thus relatively high strength.
-more developed sarcoplasmic reticulum: increased delivery of calcium when stimulated and re-uptake
-fast contraction; peak tension in 10-50 msec
-highly glycolytic: more glycogen stored
-not fatigue resistant: relatively few mitochondria; considered anaerobic
-associated with fast, powerful movements (think gastrocnemius) |
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Term
| Muscle Fiber Type Distribution |
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Definition
-motor neuron determines to a large extent whether the fiber is slow-twitch or fast-twitch in nature
-e.g. type II/fast-twitch connected to larger cell body in CNS which in turn innervates many more muscle fibers: so motor units are larger also
- most muscles contain a mix of fast, slow, and intermediate fiber types, but some are much more dominated by either fast or slow fibers
-genetically determined, so there are variations from person to person, as well as within an individual |
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Term
| What you can change in muscle fibers |
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Definition
-intermediate fibers can be increased with endurance/ power training
-involves conversion of fast-twitch glycolytic fibers to fast-twitch oxidative fibers (can convert back as well with retraining)
-more power and endurance produced by increasing intermediate fibers (permanent conversion with time)
-**it is not known to occur in any other direction, such as fast-oxidative initially being converted to fast-glycolytic |
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Term
| Types of Skeletal Muscle in body |
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Definition
-bundles of muscle fibers (fasciculi) within a muscle can vary in their relationship to one another (even though fibers within fasciculi do run parallel to each other) and to the muscle tendon
-several important fasciculi organizations are:
1. parallel muscles
2. convergent muscles
3. pennate muscles
4. circular or annular muscles |
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Term
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Definition
-Fasciculi run parallel to long axis of muscle
-most skeletal muscles are parallel in form (rectus abdominus), though may be shaped differently (i.e., flat bands such as the gluteus maximus; fusiform or spindle-shaped, composed of a belly and 2 cord-like tendons, such as the biceps brachii)
-with spindle-shaped especially:
1. power output ability can be estimated by cross-sectional area of muscle. Good endurance but not too strong
-Not the most effective (efficient) contractile setup for power output but is, however, best setup for moving the bony levers the most distance and creating speed in levers |
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Term
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Definition
-Origin or proximal end is wider
-Stronger than parallel muscles
-fibers converge in the tendon insertion distally (e.g. pectoralis major)
-different neuromuscular compartments of muscle can work separately/independently to provide pull or foce in different directions
-but when the whole muscle is stimulated, relatively less efficiency or force generated compared to parallel or pennate muscles |
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Term
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Definition
-decent power output
-feather-like shape; they tire quickly
-there are several types: all have tendons (1 or more) running through the muscle body
-in each, the fasciculi attach obliquely on the tendon, like parking on an angle: allows for more muscle fiber attachment than parallel muscles
-leads to more contractile strength/power output (though doesn't move tendon or bone as far as parallel muscle since pulling on angle)
-Types:
1. Unipennate: extensor digitorium
2. Bipennate: more common; rectus femoris
3. Multipennate: tendon branches with the muscle; deltoid |
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Term
| Circular or Annular Muscles |
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Definition
-sphincter-like, e.g. orbicularis oris(mouth) and oculi(eye)
-concentrically arranged around an opening
-contraction reduces the diameter of the opening |
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Term
| Skeletal Muscles and the skeletal system |
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Definition
- all skeletal muscles are directly or indirectly associated with the skeletal system, and movement is produced by muscles acting on skeletal lever systems
-levers(bones) move around axes or fulcrums(joints)
-capaciry for force, speed, distance and direction in the produced movement of the lever are interrelated and highly determined by the:
1. nature of the muscle attachment(e.g. broad or small attachments, sites of attachment)
2. muscle characteristics (e.g. muscle architecture, fiber type %, metabolic characteristics) |
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Term
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Definition
- 3 classes of mechanical lever setups that describe joint systems in the human body
-1st class levers: seesaw, e.g. neck W>F>P
-2nd class levers: wheel barrel P>W>F
-3rd class levers: W>P>F
-**Not all muscles are part of the lever system(e.g. rectus abdominis) |
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Term
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Definition
- fulcrum or join lies between the applied force and the resistance
-e.g. neck/head around cranium and atlas or C0(occiput)/C1 joint(seesaw) |
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Term
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Definition
-resistance is located between the applied force and the axis(wheelbarrow)
-need less force to overcome the resistance but the resistance moves slower and goes a shorter distance: favors effective force development
-not seen in the human body generally, except at the elbow with triceps attachment, calcaneal attachment, and in dropping the jaw with the digastric muscle at the temporomandibular joint |
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Term
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Definition
-force is applied between the point of resistance and the fulcrum
-most common in the human body
- reverse of 2nd class, but at the expense of force development
-since resistance is farther away, the effective force produced by the muscle is proportionately reduced (relative to 2nd class levers)
-speed and distance are favored; movement of the resistance proportionately increased |
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