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# of skeletal muscles in human body?
- 40-50% total body weight
skeletal muscle functions
- 1.force generation for movement & breathing
- 2. " " support
- 3.produce heat
- 1. voluntary, controlled consciously
- 2.involuntary, controls itself w/ assistance from the nervous & endocrine systems
- 3.involuntary, controlled by local factors and n&e
2.motor neuron function
- 2a. single muscle to contract
- 2b. voluntary control
10000 to more than__ per muscle.
1 fiber has _
1 million fibers
many nuclei (multinucleated)
muscle fiber enclosed by a plasma membrane_.
form a network around fibers
extensions of sarcolemma
*sarcoplasmic reticulum (SR) stores _?
~Control center of muscle fiber
-found near membrane
-control protein synthesis
-RNA to DNA to protein
- ~important for regeneration and repair
- ~muscle 'stem' cells
- ~look like myonuclei
sarcomeres placed end to end
- -smallest functional unit of a muscle
- -made of thick (myosin) & thin (actin) filaments
- -contracts muscles & is striated
- -2/3 of muscle protein
- -molecular motor w/ globular head at one end
Thin Filament Proteins
- 1. Actin
- 2. Troponin
- 3. Tropomyosin
Thick Filament Proteins
- 1. Myosin
- a. head region
- b. tail ' '
motor neuron & the muscle fibers it connects to.
motor end plate
junction for sarcolemma 'pocket" from muscle fiber innervation from an alpha motor neuron.
- -place where nerve connects to muscle fiber
- -signals by neurotransmitter acetylcholine (ACh)
- -shape maximizes contact for ACh release & capture
released -> muscle contracts
- depolarization of T-tubule
- opening of SR channels, release of Ca2+
Skeletal Muscle Organization (6)
Muscle Fiber Structures (5)
- Transverse Tubules
- Sarcoplasmic Reticulum
- Thin filament (actin)
- Thick filament (myosin)
Motor Neuron Structure (5)
- Cell body
- Myelin sheath
- Nodes of Ranvier
Ryanodine (RyR) Receptor
signals calcium to be released from the Sarcoplasmic Reticulum.
Sliding Filament Theory
- -Myosin cross-bridge activates, binds w/ actin, cross-bridge changes.
- -The change makes myosin head 'tilt' toward arm of cross-bridge and drags actin and myosin filaments in opposite directions.
tilt of myosin head
How does the muscle shorten and generate force?
- -actin filament is pulled past myosin 5nm
- -ADP is released
- -ATP binds myosin
- -Myosin detaches from actin
- -Myosin head moves farther down actin
- -Break ATP into ADP and Pi (ATPase action)
- -Myosin head pivots back into its "cocked" position
Muscle Fiber Type
- 1. Type I Fibers "slow-twitch"
- 2. Type II Fibers "fast-twitch"
- a. Type IIa
- b. Type IIx
Muscle fiber types are influenced by...
- Blood levels of hormones
- Individual exercise habits and training status
Altered Neuromuscular Control
- Exercise-induced muscle fatigue ->
- -increased muscle spindle activity
- -decreased GTO activity
What relieves muscle cramping?
inverse stretch reflex
Muscle Fiber Type (cont.)
- -Type I: also called "slow oxidative"
- -Type IIa: ' ' "fastoxidative, glycolytic"
- -Type IIx: ' ' "fast glycolytic"
Electrolyte Depletion & Dehydration theory
- -cramps happen from electrolyte imbalances in blood and extracellular fluid-exercise-induced loss of body water and sodium through heavy sweating causes an electrolyte imbalance.
Def. of Fatigue
Decrease in power output
Build up of _ disrupts homeostasis.
- 1. Myosin attaches to Actin
- 2. Power stroke
- 3. Cross-Bridge Detachment
- 4. ATP Hydrolysis
What 5 things influence fatigability of muscle?
- 1. individuals state of fitness
- 2. nutritional status
- 3. fiber type
- 4. intensity
- 5. duration
Causes of exercise-induced muscle fatigue are __ & ____
complex & not entirely understood
Oxidative capacity of a muscle fiber is determined by the number of __, __, __.
- Capillaris around the fiber,
- amount of myoglobin ' '
Large number of mitochondria helps produce more __.
High number of capillaries around a muscle fiber ensures that the fiber will receive __.
Specific Force formula...
- Specific Force (tension) = Force
- Fiber CSA
What are the 4 characteristics that influence muscle fiber performance?
- maximal force production
- Seed of contraction
- maximal power output
- muscle fiber efficiency
Fibers with high myosin activity...
possess a high Vmax
Maximal Power Output equation...
Power= Force x shortening velocity
a measure of the muscle fiber's economy
muscle fiber efficiency
- Energy used
- Force produced
Type I Fibers
- Oxidative capacity - High
- Anaerobic ' ' - Low
- Contractile speed - Slow
- Motor unit size - small
- ' ' strength - Low
- Fiber size - small
Type IIa & IIx Fibers
- Oxidative capacity - Moderate, Low
- Anaerobic ' ' - High
- Contractile speed - Fast
- Motor unit size - Large (300 - 800 fibers)
- ' ' strength - High
- Fiber size - Large