Muscles and Motor Control

what is the purpose of tendons?

connect muscle to bone

what does origin mean?

closest to the trunk or more stationary bone

what does insertion mean?

more distal or mobile attachment

what does flexor mean?

brings bones together

what does extensor mean?

moves bones away

what does antagonistic muscle groups mean?

flexor-extensor pairs

what does muscle tension mean?

force created by muscle

what does load mean?

weight/force opposing contraction

what does contraction mean?

creation of tension in muscle

what does relaxation mean?

release of tension

what is the process of contraction and fatigue?

→ CNS: psychological effects, protective reflexes → through somatic motor neuron to neuromuscular junction → excitation-contraction coupling → Ca2+ signal → contraction-relaxation

what are muscle fibers?

muscle cells: fused cells with many nuclei

what are the components of muscle fibers?

satellite cells: differentiate into muscle cells bundled into fascicles surrounded by connective tissue

what is the sarcolemma?

muscle cell membrane

what is the sarcoplasm?

cytoplasm of a muscle cell

what is the sarcoplasmic reticulum and what does it do?

a) the endoplasmic reticulum of a muscle cell b) stores Ca2+ ion

what is the network of transverse tubules made up of?

T-tubules connected with the sarcolemma

what are myofibrils and what are its components?

a) contractile structures b) actin and myosin

what is actin?

thin filaments

what is a G-protein?

individual actin

what is titin?

elastic protein, keeps thick and thin filaments aligned

what is myosin?

thick filaments, motor protein

what is ATPase activity?

breaks down ATP

what are the 2 accessory proteins of myofibrils?

troponin, tropomyosin

what is a sarcomere?

contractile unit

what is the Z disc?

where actin attaches to

what is the I band?

actin only the section where actin in unbound will change depending on contraction

what is the A band?

actin and myosin overlap covering the entire length of the thick filament never changes

what is the M line?

middle of the sarcomere that cuts the A band in half where myosin attaches to

what is the sliding filament theory?

theory that actin and myosin slide past each other during contraction

what is the power stroke cycle?

myosin crossbridges move actin filament

what is the process of the power stroke cycle?

→ Ca2+ release from T-tubules → Ca2+ binds to troponin → troponin pulls tropomyosin from myosin-binding sites on actin → myosin binds tightly to and moves actin

what is rigor?

myosin stays tightly bound to actin until ATP binds to myosin and is released from actin

what happens during release?

myosin breaks down ATP → the energy rotates the myosin head that binds weakly to actin down the molecule → head of myosin is cocked ready for the next power stroke

what is rigor mortis?

muscles freeze if no ATP is available to release myosin

what occurs during relaxation?

Ca2+ ions are pumped back in sarcoplasmic reticulum

what is the process of excitation-contraction couple?

→ ACh is released from the somatic motor neuron and binds to receptors on the sarcolemma → Na+ and K+ ions flow in the cell → depolarization of the muscle fiber membrane creates an end-plate potential (EPP) at the motor end-plate → DHP receptor opens RyR Ca2+ release channels → Ca2+ is released from the sarcoplasmic reticulum and enters cytoplasm → Ca2+ binds to troponin, allowing avtin-myosin binding → power stroke → muscle twitch: single contraction-relaxation cycle

what is the latent period?

the short delay between the muscle action potential and the beginning of muscle tension development time required for Ca2+ release and binding to troponin

what are isotonic contractions and what are the 2 types?

a) create force and move a load b) concentric action: shortening eccentric action: lengthening

what are isometric contractions?

create force without moving a load sarcomeres shorten while elastic elements stretch, resulting in little change in overall length

what do the muscles do during a contraction force?

contract with optimum force if at optimum length before the traction begins the tension generated by a muscle fiber is directly proportional to the # of crossbridges formed between the thick and thin filaments

what is the summation of a contraction force?

stronger contraction when the muscle does not relax completely between action potentials

what is tetanus?

maximal contraction

what is a motor unit?

group of muscle fibers that function together and the somatic motor neuron that controls them

what increases contraction force?

recruitment of additional motor units by the nervous system

what does asynchronous recruitment do?

helps avoid fatigue as different motor units take turns maintaining tension

what is phosphocreatine breakdown?

a short burst of energy

what is anaerobic glycolysis?

produces lactate and acid quick, no oxygen required, small out of energy released

what is aerobic respiration?

citric acid cycle and electron transport chain slow, requires oxygen, large amount of energy release

what are slow-twitch fibers?

type 1 rely primarily on oxidative phosphorylation

what are fast-twitch fibers?

type 2 develop tension faster and split ATP more rapidly pump Ca2+ into sarcoplasmic reticulum more rapidly

what are glycolytic fibers?

type 2X/2B rely primarily on anaerobic glycolysis

what are oxidative-glycolytic fibers?

type 2A use oxidative and glycolytic metabolism

what is the cause of feeling tired and unmotivated?

central fatigue due to the CNS

what are the 2 types of peripheral fatigue?

extended submaximal exercise and short-duration maximal exertion

what is an effect of extended submaximal exercise?

depleted glycogen stores

what are the effects of short-duration maximal exertion

increased levels of inorganic phosphate slowed phosphorus and release from myosin decreased Ca2+ release

what are the effects of ion imbalances?

implicated in fatigue K+ leaves muscle fiber, leading to increased extracellular [ ], which can alter membrane potential changes Na+-K+-ATPase activity

what is a muscle cramp?

sustained painful contraction

what is a muscle strain?

stretching/tearing of a muscle/tissue connection/tendon

what are some muscle disorders?

overuse and disuse (atrophy) acquired and inherited disorders (dystrophy)

what muscle is the slowest to contract?

smooth muscle

what is the classification of smooth muscle by location?

vascular, gastrointestinal, urinary, repiratory, reproductive, ocular

what is the classification of smooth muscle by contraction pattern?

phasic (increased contraction) and tonic (decreased contraction) smooth muscles

what is the classification of smooth muscle by communication with neighboring cells?

single-unit, visceral, or multi-unit smooth muscle

what are the properties of smooth muscle?

must operate over a range of lengths layers may run in several directions contracts and relaxes much more slowly sustains contractions for extended periods uses less energy small, spindle-shaped cells with one nucleus

what are single-unit smooth muscle cells?

connected by gap junctions, and the cells contract as a single unit

what are multi-unit smooth muscle cells?

not electrically linked, and each cell must be stimulated independently

why is smooth muscle not skeletal muscle?

not arranged in sarcomeres contraction initiated by electrical/chemical signals or both controlled by the autonomic nervous system lacks specialized receptor regions Ca2+ is from the extracellular fluid and sarcoplasmic reticulum Ca2+ initiates a cascade ending with phosphorylation of myosin light chain and activation of myosin ATPase

how is smooth muscle regulated?

controlled by both sympathetic and parasympathetic neurons hormones and paracrines also control contraction

what constricts smooth muscle of airways?

histamine

what relaxes smooth muscles of blood vessels?

nitric oxide

what binds to G protein-linked receptors in smooth muscle?

hormones and paracrines

what second messenger pathways are there in smooth muscle?

cAMP, cGMP, IP3, DAG

how can Ca2+ enter the cell membrane of smooth muscle?

voltage-gated, ligand-gated, and stretch-activated Ca2+ channels

what is myogenic contraction?

opens when pressure or other forces distorts cell membrane

what are the anatomical differences of smooth muscles?

actin is more plentiful: attaches to the dense bodies and surrounds each myosin molecule lacks troponin less myosin: myosin filaments are longer and the entire surface of the filament is covered with myosin heads extensive cytoskeleton: intermediate filaments and dense bodies amount of SR varies and is less organized no T-tubules, but caveolae

what triggers smooth muscle contraction?

increased cytosolic Ca2+

what triggers relaxation in smooth muscle?

removal of Ca2+ from the cytosol