Unit 5 Flashcards
(24 cards)
Muscles
- biological motors of the body
- composed of multi nucleated muscle cells (fibers)
-uses contractile proteins to generate force
— actin and myosin
Skeletal muscles
- striated
—appears striped
—actin and myosin arranged arranged in regularly, repeating pattern
Cardiac muscle
Striated
Smooth muscle
- walls of arteries
- digestive and excretory systems
- actin and myosin arranged in irregular pattern
Organization of skeletal muscle
-composed of elongated cells called muscle fibers
—embedded in surrounding connective tissue
Myofibrils
-striated appearance
-contain thick (myosin) and thin (actin) filaments
Actin
-two molecules wound together
- composed of tropomyosin (green lines) troponin (yellow bundles)
Myosin
-two molecules wrapped around each other
- limitless hairs that stick off the filament
Muscle organization
- muscle -> muscle belly -> muscle bundle (contains muscle fibers) ~> muscle fibers -> myofibril
Sarcomere
- contractile unit of muscle
- defined as region between two z-discs
Titian
- prevents overstretching
- myosin attaches to titin
Sliding filament theory
- actin top and bottom while myosin in the middle
- the two sides come together
— lengths of actin and myosin do not change
— they change degree of overlap
Muscle shortening
-interaction between myosin and actin
— cause muscle fiber cells to shorten and produce force
Cross bridge cycle
- Myosin head binds to ATP
-detaches from actin - Myosin head catalyzes hydrolysis of ATP
-forms ADP and Pi
-cocks myosin head back - myosin head binds actin
- forming cross bridge - ADP and Pi are released
- produces power stroke that generates force
- causes thin filament to slide against thick
- sarcomere shortens
Excitation-Contraction Coupling
- muscle fibers are electrically excitable
- skeletal fibers are activated by impulses transmitted by motor nerves to skeletal muscle cells at fiber motor end plate
Fast twitch glycolytic fibers
- large diameter
- generate more force
- energy supplied by anaerobic glycolysis
—few mitochondria, capillaries, and myoglobin
-develop force rapidly
—but fatigue quickly
-think cheetah
Slow twitch oxidative fibers
- small diameter
- develop force slowly
— resist fatigue - aerobic respiration
-mitochondria well supplied with O2
— surrounded by capillaries
— contains abundant myoglobin
-think gazelle
Motor units
- motor neurons and the population of muscle fibers it innervates
- size determines how finely a muscles force can be controlled
- force depends on
1. Stimulation frequency
2. Number of motor units that are activated
Force summation and tetanus
- muscle force sums to higher level when action potentials stimulate the muscle at higher rates,
—reaching a tetanus
Depolarization leads to shortening (contraction)
- Action portential from motor neuron
- Depolarization spreads into inferior fiber via infoldings of cell membrane
- Leads to release of Ca2+
- Binds to troponin (little yellow things)
—causes movement of tropomyosin, exposing myosin binding cites on actin
— formation of cross bridges to generate force and produce contraction of muscles
Force and velocity are inversely related
- muscles shorten fastest when there is little force
- at higher rates contractions velocities:
— create fewer cross bridges
— reduces force
-large force production requires slow velocity
3 types of muscle contraction
- Shortening
- Lengthening
- generates greater force - Isometric
- staying same
Twitch contraction
- action potential from motor nerve with slight delay in force
- Occurs when
— Ca++ released and then pumped back into Sarcoplasmic reticulum
Super fast muscle
-evolved rapid cross bridging cycling
— but produce little force
-ex. Rattlesnake tails, toadfish mating calls
