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
ligaments
hold bones together at joints
bone composition
organic components: collagen, glycoproteins, peptides; inorganic: calcium, phosphate, hydroxide ions which harden together to form hydroxyapatite crystals
Parathyroid hormone
released by parathyroid glands in response to low blood Ca2+, promotes break down of bone
calcitonin
hormone released by thyroid in response to high blood Ca2+, promotes bone formation
cartilage
composed of a firm but elastic matrix called chondrin, secreted by the chondrocytes; provides flexibility or cushioning; bones can be formed by hardening of cartilage (endochondral ossification)
immovable joints
bones fused together to form sutures or fibrous joints; found mostly in the skull
movable joints
allow bones to shift relative to one another; strengthened by ligaments
Origin
the end of the muscle with the larger attachment to bone
insertion
end of the muscle with the smaller attachment to bone
antagonistic pairs of muscles
one muscle relaxes while the other contracts
