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What is the structure of a skeletal muscle?
- Muscle fibers (muscle cells)
- Filament (actin/myosin)
What is fascia?
- Connective tissue that separates muscles (& muscle parts), holds them in place and allows each part of the muscle to move independtly.
- Has different names depending on where it is found
- Connect muscle to bone (tendon)
Fascia that surrounds skeletal muscle is called:
Fascia that surrounds fascicles is called:
Fascia that surrounds each individual muscle fiber (cell)
Sheetlike CT that attaches muscle to muscle OR muscle to bone (Very flat and broad)
Connects skin to ms below it, found just below the ski
What attaches bone to muscle?
Multi-nucleated/abundant michochondria (power supply)
The Cell of a muslce fiber
Cell (of a muscle fiber) membrane
Enlarged portion of SR
Cell cytoplasm "gel"
Function in muscle contraction, consist of two types of filaments, actin & myosin
Troponin & tropomyosin
Rounded, pearl necklace like - wraps around
Cross bridges (hockey stick with little head which attaches and pulls for contraction)
A segment of myofibrils between Z lines, repeating units
Motor neuron and the muscle it controls
Define Neuromuscular Junction
- Site where motor nerve fiber (axon) and muscle fiber meet
- Includes a motor end plate, a synaptic cleft, and a synaptic knob
Specialized area of muscle cell membrane, part of the neuromuscular junction
Motor end plate
Gap that separates muscle fiber and nerve fiber, part of a neuromuscular junction
Specialized area of nerve fiber (axon), part of the neuromuscular junction
How motor nerver impulse triggers a muscle to contract
- Acetylcholine (ACH)
- - NT that motor neurons use to control skeletal muscle
- - Stored in the snyaptic knob
- - Vesicles
- Released into the synapitic cleft when a nerve impulse reaches the end of an axon.
- ACH binds to receptors in sacrolemma
- Muscle impulse is transmitted into & around the muscle fiber
- Calcium ions released from SR into cytosol (sacroplasm retinaculum)
- High concentration of SR due to active transport (low concentratin to high concentration) when muscle cell is at rest
- Calcium binds to troponin
- Changes shape/position of troponin-tropomyosin complex
- Binding sites on actin are exposed
- Linkages form between actin and myosin
- Binding site and cross-bridges
During a contraction the sacromeres shorten and filaments slide past one another (pulling)
The Sliding Filament Theory
- 1) Myosin pulls actin (MCB) causing a breakdown of ATP (which provides energy)
- 2)MCB releases actin
- 3)MCB bind to another binding site father down actin
- 4)MCB pulls actin (until it shorten completely)
Skeletal muscle relaxation
- When the motor nerve impulses stop
- ACH in synaptic cleft is decomposed by enzyme (the calcium is gone and the muscle relxes)
- Calcium ions move back into SR (active transport/"calcium pump"
What is the energy source for a contraction?
- ATP - Adenosine triphosphate
- -Initial power source for contraction
- -ADP must be regenerated to ATP
- Creatin phosphate
- -Use to convert ADP - ATP
Within 10 seconds of intense muscle acitivy you use all the stored ATP and CP, so where does the muscle get more ATP?
- Cellular respiration of glucose
- Create more ATP using glucose
- Catabolism of glycogen = stored glucose
What happens to muscles after you die?
- Skeletal muscles contract, a few hours after death
- Results from an increase in membrane permeability to calcium ions, which promotes cross-bridge attachement and a decrease in ATP that is available to the muscle fiber
- Prevents cross-bridege release from actin
- Thus, actin and yosin filaments of the muscle fibers remain linked until the muscles decompse
Fun facts about Clostridium Botulinum (Botulism)
- It's a bacteria
- It can grow in unrefrigerated canned food
- It produces a toxin that prevents the release of ACH from nerve terminals
- If respiratory muscles are affected it is fatal
- Botox - paralyzes the muscles so they can't move and thus can't wrinkle.
What are the two types of cellular respiration?
- Not dependent of oxygen (O2)
- Breaks down glucose into a few molecules of ATP
- Glucose - ATP & lactic acid
- Not able to supply enough O2 to tissues (strenuous muscle activity)
- Cellular Repiration
- Requires O2
- Breaks down glucose into many molescules of ATP
Where does O2 come from? What is its source?
- Blood (hemoglobin in RBC)
- -myoglobin (muslce protein that holds onto or stores oxygen)
- -stores O2 in muscle tissue
What causes muscle fatigue?
- The muscle loses its ability to contract
- -lactic acid build up
- -decreased blood flow
The lowered PH from the lactic acid prevents muscle fibers from responding the stimulation (TP's or cramps)
What is oxygen Debt?
- The amount of O2 required to:
- Convert lactic acid back to glucose (liver)
- Restor original amounts of O2, ATP, & CP (muscle)
- Then the body shuts down
How does the body produce heat?
- Active cells = heat
- Heat = a by-product of cell metabolism
- Less than half of the energy released in cellular respiration is available for use in metabolic processes; the rest becomes heat.
- Threshold stimulus - twitch (minimal stimulus needed)
- Isolated muscle fiber
- All-or non response
- If a muscle fiber is exposed to a stimulus of threshold strenght or above, the muscle fiber will contract to its fullest extent
- Fully contracts or not at all
- A muscle fiber will not partially contract
What is a summation?
- A rapid series of stimuli (w/o allowing the fiber to relax in between stimuli) causes individual muscle twitches to combine
- -Sustained contraction - strong, smooth, sustained muscle contraction
- --muscle tone/smooth movement
- --walking/smooth movement
- --lifting weights/smooth movement
- --cramps/tetanic contraction (frozen state w/out relaxation)
What is motor unit recruitment?
- The greater the work the muscle belly must do, the greater the number of motor units need to be recruited (lifing a 50lb. barbell vs. lifting a pencil)
- Motor units respond in an all or non matter
- Same tone
- Length change during contraction
- -concentric (muscle shortens)
- -eccentric (muscle lengthens)
- Muscle length stays the same during contraction
- -i.e. postural muscles
- -occurs when person pushes against a wall, the tension in the muscle increases, but the wall does not move.
What is a variation on contraction speed?
Fast & slow twitch muscles
Slow twitch muscle (Type 1)
- AKA "red" fibers
- Resistant to fatigue
- Good blood supply
- A lot of myoglobin/mitochondria
- Aerobic respiration (produces oxygen)
- Postural muscles (don't burn out)
Fast twitch muscle (Type II A)
- AKA "white" fibers
- Higher rate fo fatigue
- Poorer blood supply (lighter color)
- Less myoglobin/mitochondria
- Extensive SR that allows muscle to contract very quickly
- i.e. eye muscles, certain hand muscles (ones that wear out)
Fast and slow twitch muscles
- Birds that migrate long distances have abundant dark, slow twitch muscles (this is why their meat is dark)
- Chickens that only flap around the barnyard have abundant fast-twitch muscles (mostly white meat)
- Distance runners have more slow twitch fibers
What are smooth muscles?
- GI tract, irish of eyse, walls of bladders, uterus, and blood vessels
- Single nucleus (per cell)
- Lack striations
- A type of smooth muscle
- Not well organized
- Function as separate units
- A type of smooth muscle
- Peristalsis - wave like contraction
- Single nucleus
- Syncytium - group of muscle cells contracts as a unit
- (cells are joined end to end with intercalcated disks - assist in transmitting force of contraction from muscle cell to muscle) (ex: the heart contracts and pumps blood)