Musculoskeletal system Flashcards
Skeletal muscle
voluntary movement, controlled by somatic nervous system; appears striped due to actin and myosin arrangement; contains red and white fibers; multiple nuclei
Sarcomeres
repeating units of actin and myosin that make skeletal muscle appear striated
Red fibers
slow-twitch fibers with high myoglobin content; derive most of energy aerobically- contain many mitochondria; muscles that slowly contract contain mostly red fibers
Myoglobin
oxygen carrier that uses iron in a heme group to bind oxygen, resulting in the red color found in red fibers
white fibers
fast twitch fibers, contain much less myoglobin and thus, less iron, resulting in a lighter color; muscles that quickly contract and are easily fatigued are mostly white fibers
smooth muscle
involuntary action, controlled by autonomic nervous system; not striated- contains actin and myosin but not as well-organized; capable of more sustained contractions such as a constant state of low-level contractions; can exhibit myogenic activity; a single nucleus
myogenic activity
contraction of muscle without nervous system input; can be accomplished by smooth or cardiac muscle
cardiac muscle
involuntary movement, ANS; striated; cells are connected by intercalated discs, which contain gap junctions for communication; can maintain their rhythm via myogenic activity; 1-2 nuclei per cell
Sarcomere
basic contractile unit of skeletal muscle, made of thick filaments (bundles of myosin) and thin filaments (made of actin, troponin, and tropomyosin)
Parts of the sarcomere
Z lines define ends of sarcomere (end of alpha)
M-middle of sarcomere
I band contains only thin filaments (thin letter)
H zone-only thick filaments (thick letter)
A band contains all the thick filament, including any overlap with thin filament
Sarcomere during contraction
H, I, and distance between Z lines and between M lines becomes smaller while A band stays the same size
sarcoplasmic reticulum
modified E.R. that contains a high concentration of calcium ions
myocytes
a muscle consists of muscle fibers (myocytes) that contain may myofibrils in parallel
sarcolemma
cell membrane of a myocyte that is capable of propagating an action potential to all sarcomeres in a muscle
initiation of muscle contraction
motor neuron signals at neuromuscular junction–ACh release into synapse–ACh binds receptors on sarcolemma–depolarization–action potential down sarcolemma to T-tubules into sarcoplasmic reticulum–Ca2+ release–Ca binds troponin causing change in tropomyosin–exposes myosin binding sites
shortening of sarcomere
heads of myosin bind with exposed sites on actin– shortens the sarcomere
Cycle: myosin carrying ADP+P binds myosin binding site; release of ADP and P provide energy for powerstroke and sliding of actin over the myosin filament- sarcomere contracts; ATP binds to myosin head, releasing it from actin; ATP hydrolyzed to ADP+P to start new cycle
relaxation of muscle
ACh degraded in synapse; termination of signl, allows sarcolemma to repolarize; stops Ca release which means myosin-binding sites are not accessible; ATP binds myosin heads, freeing them from actin
Simple twitch
single muscle fiber response; consists of latent period (time b/w reaching threshold and contraction during which Ca is released), contraction, and relaxation
Frequency summation
prolonged muscle stimulation giving the muscle little time to relax; if unable to relax at all, known as tetanus
Supplemental energy reserves in muscle
creatine phosphate produced during rest and can be hydrolyzed to form ATP; myoglobin keeps aerobic metabolism going due to it binding oxygen with high affinity
Axial skeleton
skull, ribcage, vertebrae, hyoid bone; central framework for body
Appendicular skeleton
bones of the limbs
Red bone marrow
filled with hematopoietic stem cells
tendons
attach muscle to bone
