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100 Cards in this Set
- Front
- Back
From where does the energy come to shorten muscles?
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Muscle cells convert the chemical energy of ATP into mechanical energy.
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Three types of Muscle Tissue
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- Skeletal
- Cardiac - Smooth |
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Two Visual Categories of Muscle Tissue
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- Striated: Skeletal & Cardiac
- Unstriated: Smooth |
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Two Functional Categories of Muscle Tissue
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- Voluntary: Skeletal
- Involuntary: Cardiac & Smooth |
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Four Functions of Muscle Tissue
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- Movement of body parts & organ contents
- Control of passageways & openings - Prevent movement - Communication - Body heat production |
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Universal Characteristics of Muscle
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- Excitability: responds to chem, stretch, elec. signals
- Conductivity: electrical change triggers excitation wave - Contractility: Shortens when stimulated - Extensibility - Elasticity |
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Describe Skeletal Muscle
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- Voluntary striated muscle attached to bones
- Alternating light and dark transverse bands |
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What are those Alternating light and dark transverse bands in Skeletal Muscle?
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- Overlapping arrangement of internal contractile proteins
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Three Parts of Skeletal Muscle
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- Origin: Attachment to stationary end of muscle
- Body: thicker middle region of muscle - Insertion: attachment to mobile end of muscle |
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Connective Tissue Elements of Muscle
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- Endomysium, Perimysium, epimysium, fascia, tendon
- Not excitable or contractile - Somewhat extensible & elastic - Called Series-elastic components |
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What Do Series-Elastic Components Do?
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- Are connected to each other in linear series
- Help return muscles to their resting lengths - Add Significantly to muscle power output and efficiency |
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Describe Epimysium
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- Covers whole body of muscle
- Blends into connective tissue that separates muscles |
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Describe Perimysium
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- Slightly thicker layer of CT than Epimysium
- Surrounds a bundle of muscle cells called a fascicle |
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Describe Endomysium
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- Thin layer of areolar tissue surrounding each cell
- Allows room for capillaries and nerve fibers |
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Location of Fascia: a fibrous connective tissue
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- Deep Fascia between adjacent muscles
- Superficial fascia (= hypodermis) found between skin and muscles. Contains adipose tissue |
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Four Muscle Attachments
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- Direct (fleshy) attachment to bone
- Indirect bone attachment: epimysium - tendon - bone - Attachment to dermis - Attachment to other muscles |
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Three Coordinated Muscle Actions
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- Prime Mover (antagonist): produces most force
- Synergist: aids PM, stabilizes joint, modifies direction - Antagonist: Opposes PM, prevents excess movement & injury |
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Describe Intrinsic & Extrinsic Muscles
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- Intrinsic: contained within region of movement
-- muscles of hand moving fingers - Extrinsic: found outside region of movement -- muscles of forearm moving fingers |
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Skeletal Muscle Anatomy (8 major parts)
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- Muscle Belly - Fascicle
- Muscle Fiber/Cell - Myofibril - Thick Filaments - Thin Filaments - Actin - Myosin |
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Sliding Muscle Theory
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- Muscle contraction is the result of thin filaments sliding past thick filaments.
- Pull on Z lines & shorten the sarcomere & the cell as a whole. |
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Skeletal Muscle Fiber Anatomy
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- A band - H band - I band - M band - Z band - Z disc
- Nucleus - Mitochondria - Myofibrils -Sarcoplasm - Sarcoplasmic reticulum - Sarcolemma - Triad: - 2 Terminal cisternae - 1 Transverse tubule |
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Muscle Fiber
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- Single skeletal muscle cell (up to 2.5 feet long)
- Multiple Mitochondria for ATP production - Made of multiple myofibrils and nuclei from fused cells |
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Parts of Muscle Fiber
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- Sarcoplasm: may contain glycogen & myoglobin
- Sarcolemma: Plasma membrane - T (Transverse) -tubules: infoldings of sarcolemma |
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Triad
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- 2 terminal cisternae & 1 Transverse Tubule
- Connects electrical signal on sarcolemma to release Ca from Sarcoplasmic reticulum |
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Myofibrils
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- Specialized contractile element
-- 80% of muscle cell -- 100s lie in parallel in a muscle cell - Appears banded (striated) by thick & thin filaments |
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Myofilaments
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- Thick filaments made of myosin with titin core
- Thin filaments made of Actin, Tropomyosin & Troponin |
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Thick Filaments
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- 200 to 500 myosin molecules
-- 2 entwined polypeptides - Core of titin recoils after stretching - Arranged in bundle w/ heads out and bare zone |
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Myosin Protein Making Thick Filament
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- 2 subunits with tails intertwined
- Globular head (paddle) has actin binding site and myosin ATPase site |
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Thin Filaments
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- "String" of Balls of actin each with active site
- Double bands of tropomyosin (blocking protein) - Troponin: Regulating protein of 3 subunits: Ca Binding, Actin binding, Tropomyosin binding |
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3-D Actin-Myosin Interaction
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- Cross bridging: 16B thick & 32B thin filaments/fiber
- Geometric relationship: 1 thick surrounded by 6 thin |
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Neuromuscular Junction
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- Where nerve fiber makes functional connection with a target muscle cell
- Acetylcholine (Ach) opens ligand-gated channels on muscle cells |
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Motor End Plate
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- Specialized muscle cell membrane under terminal button
- Has ACh receptors, ligand-gated channels, ion channels - Electrical change = end plate potential |
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Nerve-Muscle Relationships
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- Cell bodies of somatic (alpha) motor neurons in brainstem or ventral horn of spinal cord
- Axons of SMN are called somatic nerve fibers - Each branches to supply 200 fibers (motor units) |
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Motor Unit
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- One motor neuron & innervated fiber
- Weak contraction over wide area - Motor units take turns (asynchronous recruitment) - Small and Large motor units |
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Small Motor Unit for Fine Control
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- Contains as few as 20 muscle fibers per nerve fiber
- Small, controlled movements - e.g. eye muscles |
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Large Motor Unit for Strength
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- Large contractions - e.g. posture
-- gastrocnemius has 1000 fibers per nerve fiber |
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Acetylcholinesterase: The OFF Signal for the Neuromuscular Junction
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- Enzyme inactivates ACh by degrading it
- Always present in synaptic cleft - Stops end plate potential (& muscle contraction) - Keeps contraction proportional to nerve stimulation |
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Toxins and Paralysis: Cholinesterase Inhibitors
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- Bind to AChesterase to prevent Ach degradation
-- Spastic paralysis, possible suffocation -- Contracted muscles unable to relax -- Used in some pesticides |
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Toxins and Paralysis: Tetanus or Lockjaw
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- Spastic Paralysis caused by Clostridium bacteria toxin
- Blocks glycine release in the spinal cord |
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Toxins and Paralysis: Curare
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- Competes w/ ACh: Binds to ACh receptors
- Prevents contraction, causing flaccid paralysis - Can lead to respiratory arrest |
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4 Actions Involved in Muscle Contraction and Relaxation
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- Excitation: APs in Nerve lead to APs in muscle fiber
- Excitation-contraction coupling link AP to myofilament activation (via Ca) -Contraction of muscle fibers - Relaxation of muscle fiber to resting length |
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Excitation of Muscle Fiber: Steps 1 & 2
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- Nerve signal (AP) stimulates voltage-gated calcium channels
- Causes exocytosis of synaptic vesicles containing ACh - ACh released into synaptic cleft |
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Excitation of Muscle Fiber: Steps 3 & 4
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- ACh binds to ligand-gated channels on muscle cell
-- Allows Na and K to diffuse -- Results in an end-plate potential (EPP) --- local/graded potential |
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Excitation of Muscle Fiber: Step 5
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- Voltage change in end plate region (EPP) opens nearby voltage-gated channels in plasma membrane
--Produces AP on muscle cell (sarcolemma - Whole sarcolemma gets action potential |
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Excitation-Contraction Coupling
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- Links muscle APs and contraction
- ACh stimulates APs over the surface of whole fiber - Transverse (T-) tubule: sarcolemma extention conducts AP along SR deeply into cell (triad) between A & I bands |
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Sarcoplasmic Reticulum
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- Modified ER
-- Stores Ca++ -- Terminal cisternae sacks sit at junction of A & I bands |
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Excitation-Contraction Coupling: Steps 6 & 7
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- 10,000x more Ca++ in SR than in sarcoplasm
- AP spreads over sarcolemma - Enters T-tubules where Voltage-gated channels open - Opens Ca gates in SR & Ca released to sarcoplasm |
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Excitation-Contraction Coupling: Steps 8 & 9
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- Ca release by SR into sarcoplasm
- Ca binds to Troponin - Troponin-tropomyosin complex changes shape and exposes active sites on actin - regulates contraction |
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Contraction: Steps 10 & 11
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- Myosin ATPase in Myosin head hydrolyses ATP
-- Activates head and cocks it in extended position -- Energy is now stored in myosin head - Myosin binds to active site on actin |
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Contraction: Steps 12 & 13
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- Power Stroke: head releases ADP and P as it flexes and pulls thin filament
- Binds more ATP, releases thin filament & attaches to new active site further down thin filament |
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Power Stroke
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- Ca++ binds Troponin, which slides tropomyosin over, allowing Myosin to bind actin
- Binding causes conformational change: myosin bends inward, new ATP causes release, returns to original form |
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Role of ATP
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- Myosin ATPase splits ATP, Energy stored (cocking)
- Ca allows power stroke: release of ADP & P from myosin - New ATP binds to myosin/Mg complex for release (or else rigor mortis) |
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Single Contraction
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- Shortens muscle by 1%
- Each head 5 strokes per second = 5 ATP - Skeletal muscle can shorten up to 40% |
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Relaxation: Steps 14 & 15
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- Nerve stimulation ceases
- AChesterase removes ACh from receptors -- Ends stimulation of the muscle cell |
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Relaxation: Step 16
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- Ca moved to Sr from sarcoplasm via active transport pumps
- ATP needed for relaxation as well as contraction - Ca binds to calsequestrin in SR |
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Relaxation: Steps 17 & 18
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- Loss of Ca from Carcoplasm results in troponin-tropomyosin complex moving back over the active sites
- Muscle fiber returns to resting length by stretching series-elastic components & antagonistic contractions |
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Rigor Mortis
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- Begins in 3-4 hrs. Peak at 12 hrs. Next 48 to 60 hours
- Deteriorating SR releases Ca, activating contraction - Relaxation needs ATP - Fiber contraction continues until myofilaments decay |
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Sarcomere: The Functional Unit of Skeletal Muscle
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- Z-line to Z-line
- Smallest component of muscle that can contract |
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Striations: Organization of Filaments
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- Dark anisotropic (A) bands / Light isotropic (I) bands
- A band of thick filaments end to end - H band: lighter central area without thin filaments - I band: light region, thin filaments w/ Z-line & connectin |
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A Band (Dark Band)
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- Thick filaments
- Part of thin filaments - H zone where thin filaments do not reach - Support Proteins of M-line anchoring thick Filaments |
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I Band (Light Band)
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- Contains only thin filaments, but not their whole length
- Space between thick filaments - Z-line: Cytoskeletal structure, protein called connectin, anchoring elastic & thin filaments |
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Elastic Filaments
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- Titin: Huge springy protein runs through core of each thick filament, connects thick filament to Z disc structure
- Functions: keep thick & thin aligned, resist overstretching, help cell recoil to resting length |
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Sarcomere Contraction: Muscle Cells Shorten Because Their Individual Sarcomeres Shorten
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- Sliding filaments: thin slide closer together
-- I band shorter, A band unchanged, H zone shorter - Filaments don't change length, only overlap increases |
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Twitch
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- contraction produced by one action potential on one muscle fiber
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Tension
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- amount of contraction per fiber
-- number of muscle fibers contracting |
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Recruitment
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- turning on more and more motor units
-- to increase tension in whole muscles |
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Length-Tension Relationship
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- Amount of tension generated depends on length of muscle before it was stimulated
- Central Nervous System maintains optimal length -- muscle tone |
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Phases of a Twitch Contraction
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- Latent period: between stimulus and contraction start
-- only elastic components, so no shortening - Contraction: external tension develops/muscle shortens - Relaxation: tension loss, returns to resting length |
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Twitch Summation
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- incomplete tetnus
- next signal to contract comes before muscle has fully relaxed - Each stimulus creates identical response 10/sec max |
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Complete Tentus
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- Sustained maximal contraction
-- increased cytosolic Ca++ - twitchs fuse into smooth prolonged contraction; no relaxation; 40-50 stimuli per second |
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Treppe
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- Each twitch has time to recover but develops more tension than the one before; 10-20 stimuli per sec
- Ca++ not completely back into SR - Heat of tissue increases myosin ATPase efficiency |
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Incomplete Tetnus
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- sustained fluttering contractions generates gradually more strength of contraction
- higher frequency 20-40/sec -- each stimulus arrives before recovery of the previous |
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Recruitment & Stimulus Intensity
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- stimulating the whole nerve with higher and higher voltage produces stronger contractions of motor units
- multiple motor unit summation: more motor units are being recruited as more work is done |
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Isometric & Isotonic Muscle Contractions
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- Isometric: develops tension without changing length
- Isotonic: -- Equal tension while shortening: Concentric -- Equal tension while lengthening: Eccentric |
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Muscle Sensors: Muscle Spindles
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- monitor change in muscle length
- has own efferent and afferent nerve supply (gamma motor neurons) to keep spindles taut - annulospiral and flowerspray sensory nerve endings |
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Muscle Spindle Nerve Endings: Annulospiral
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- Wrapped around intrafusal fiber
- Sense length and rate of stretch |
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Muscle Spindle Nerve Endings: Flowerspray
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- at end of intrafusal fiber
- senses length |
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Muscle Sensors: Proprioception
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- Sense of body position and movement
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Stretch Reflex
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- Stretch sensed by muscle spindles
-- activate alpha motor neurons -- cause contraction --- e.g. patellar tendon reflex |
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Golgi Tendon Organs
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- Located in tendons
- Sense muscle tension; tension stretches receptors - Reaches conscious level: proprioception -- ability to weight objects |
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Muscle Metabolism
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- Need ATP for power stroke, release of actin/myosin cross bridge, active transport of Ca into SR
- 3 major sources: Phosphagens (1-20 seconds), Glycolysis (10-120 secs), Aerobic Respiration (2+ min) |
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Phosphagen System
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- Provide energy for immediate needs
- Transfer phosphate groups to ATP - Myokinase system: P from ADP to ADP = ATP + AMP - Creatine kinase sys: P from creatineP = ATP + creatine |
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Glycolysis
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- Anaerobic: makes 3 ATP net
- Pyruvic acid converted to lactic acid |
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Aerobic Respiration
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- Citric Acid Cycle in mitochondria
- Aerobic - 36 to 38 ATP net - limits: glycogen depletion and fluid/electrolyte loss |
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Fatigue
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- Progressive weakness and loss of contractility from prolonged use
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Endurance
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- Ability to maintain-intensity exercise
- Depends on the supply of organic nutrients |
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Slow & Fast Twitch Fibers
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- Slow oxidative fibers: more mitochondria, myoglobin & capillaries
- Fast glycolytic fibers: phosphagen enzymes & glycogen lactic acid systems SR releases Ca quickly |
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Oxygen Supply
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- Slow Red Fibers rich in Myoglobin
- Fast White Fibers poor in Myoglobin |
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Oxygen Debt
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- Excess Post Exercise Oxygen Consumption
- Replaces Oxygen reserves - replenishes phosphagen system - reconverts lactic acid to glucose |
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Muscle Efficiency
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- At rest: 58% of energy lost to body heat
- Active skeletal muscle: 85% loss to body heat |
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Smooth Muscle
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- Around tube and hollows
- Sheets of spindle-shaped cells; no Z-lines or banding - No troponin or tropomyosin; little SR; No T-tubules - Very slow cycles; uses 10 to 300x less ATP |
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Smooth Muscle
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- Dense Bodies: Same protein as Z-lines
- 10 - 15 thin per thick filaments - Huge contractility |
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Smooth Muscle Contraction
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- Ca++ from ECF binds to calmodulin
- complex binds to myosin light chain kinase - MLCK uses an ATP to phosphorylate cross-bridge - Cross-bridges bind to actin |
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Smooth Muscle Response to Stretch
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- Opens mechanically gated calcium channels
- Tissues briefly contract then relax |
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Types of Smooth Muscle
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- Multiunit: Nerves to individual myocytes in motor unit
- Single Unit |
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Multi Unit Smooth Muscle
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- Neurogenic contraction
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Cardiac Muscle
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- Combination of features from skeletal and single unit smooth muscle
- Involuntary & striated |
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Single Unit Smooth Muscle
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- Electrically linked via gap junctions
- self excitable - Autonomic Nervous System |
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Cardiac Muscle
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- Cells are shorter, thicker, have anastamoses
- linked at intercalated discs - Autorhythmic due to pacemaker cell - Use Aerobic Respiration |
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Spontaneous Depolarization
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- Pacemaker Potentials
- Slow wave potentials: in digestive tract |