Muscular System Flashcards
Describe skeletal muscle
attaches to skeleton
striated, voluntary
bundles of long, cylindrical, contractile, multinucleate cells that extend the length of the muscle
function: movement of body in relation to external environment
Describe cardiac muscle
found in the walls of the heart
striated, involuntary
contractile cells connected cell to cell by intercalated discs
function: pumping of blood out of the heart
Describe smooth muscle
unstriated, involuntary
loose network of short, contractile cells that rearranged in sheets
function: movement of contents within hollow organs
What are the layers of skeletal muscle?
epimysium
perimysium
fascicle
endomysium
muscle fiber
myofibril
thick and thin filament
myosin and actin
What does contraction allow?
- purposeful movement of the body
- manipulation of external objects
- propulsion of contents through hollow organs
- emptying the contents of certain organs to the external environment
isometric
contracting but not moving
isotonic
same tension, muscle moving and contracting
What are the isotonic movements?
concentric (muscle shortens against resistance)
eccentric (muscle lengthens against resistance)
titin definition and function
attaches myosin to the z-line
1. serves as scaffolding
2. acting as an elastic spring
3. participating in signal transduction
troponin + tropomyosin
Ca2+ binds to troponin and moves tropomyosin out of the way, exposing the binding site
sodium-potassium ATPase pump
(what is the sodium channel, and what is the potassium channel?)
High concentration of Na+ and Ca2+ on the outside
Concentration gradient, opposite charges attract and Na+ goes inside the cell
High to low concentration gradient, like charges repel and K+ goes outside the cell
action potential process
action potential causes the muscle to contract or cause a cell to perform its function
Na+ goes in and K+ goes out
sliding filament process
actin slides over myosin and elicits a contraction
muscle contraction steps
- alpha motor neuron stimulates muscles
- acetylcholine opens up Ca2+ and K+ channel in axon terminal
- nicotinic receptor stimulates the myofibril to contract
- transverse tubules send action potentials to all myofibrils rapidly to stimulate contraction
- DHP receptor senses a change in voltage and connects to the ryanodine
- ryanodine receptor detaches from the sarcoplasmic reticulum and Ca2+ leaves SR
- Ca2+ binds to tropinin and moves tropomyosin out of the body
- bonding site is exposed and myosin binds to actin
- Power stroke: ADP and inorganic phosphate come off the myosin and the head moves
- ATP that comes from the breakdown of various nutrients attaches to myosin and causes actin and myosin to unbind
- ATP hydrolysis splits ATP and inorganic phosphate and myosin heads get re-energized and bind to actin
rigor mortis
no ATP and cannot bind to actin or regulate sodium-potassium pump so myosin is bound to actin
motor unit
alpha motor neuron and all the fibers within the bundle
What tension influencing by?
- frequency of stimulation
- length of the fiber at the onset of contraction
- extent of fatigue
- thickness of the fiber
What happens to contractile activity at lengths less than I0?
- the thin filaments from the opposite sides of the sarcomere overlap, limiting the interaction between cross bridges and actin
- the ends of the thick filaments become forced against the z lines
- not as much Ca2+ is released and the ability for Ca2+ to bind to troponin is reduced at shorter muscle lengths
Four steps in the excitation, contraction, and relaxation process require ATP
- splitting of ATP by myosin ATPase provides the energy for the power stroke of the cross-bridge
- binding (but not splitting) of a fresh molecule of ATP to myosin less the cross bridge detach from the actin filament at the end of a power stroke so that the cycle can be repeated
- active transport of Ca2+ back into the lateral sacs of the SR during relaxation depends on energy derived from the breakdown of ATP
- The ATP dependent Na+ - K+ pump activity returns the ions that moved during the generation of a contraction-inducing action potential in the muscle cell
Type I fiber structural characteristics
small/endurance
Type I fiber contractile characteristics
slow twitch
Type I fiber energy substrate characteristics
high triglyceride content
Type I fiber enzymatic characteristics
metabolizing fat/high mitochondrial density
high capillary density
Type II fiber contractile characteristics
fast twitch
Type II fiber structural characteristics
large/stretch and speed has more myofibrils and can generate more tension
Type II fiber enzymatic characteristics
metabolizing glucose
low mitochondrial density
low capillary density
Type II fiber energy substrate characteristics
high glycogen content
hybrid fibers
can become one or the other depending on how you train
reflexes
activate muscle spindles that monitor muscle length
GTO (golgi tendon)
monitors muscle tension
inhibits the contraction to protect the muscle
Why do type II fibers fatigue easily?
pyruvate accumulates in cytosol and lactic acid is created
the acid causes fatigue because the buildup of H+ limits the amount of Ca2+ coming out of SR and less myosin binding to actin
explain hennemen’s size principle
type I recruited first and then type 2
type I recruited for endurance
type II recruited for strenght
what energy configuration does ADP + Pi have?
high energy configuration (ready to bind to actin)
what energy configuration does ATP have?
low energy configuration (myosin head disconnected from actin)
epimysium
surrounds whole muscle
perimysium
surrounds fasicle
endomysium
surrounds muscle fiber
myofibrils
protein structures that allow for muscle contractions
myosin
thick filament
t tubules
structure that reaches over the cell to allow all myofibrils to be stimulated
actin
think filament
