muscles

Question 1

myofiber

Answer 1

muscle cell

Question 2

myofibril

Answer 2

collection of myofilaments

Question 3

myofilaments

Answer 3

actin and myosin

Question 4

thin filament

Answer 4

made of F-actin, 1um long, double helix, bound to tropomyosin and troponin

Question 5

thick filament

Answer 5

made of myosin, 1.6 um long

Question 6

sarcomeres

Answer 6

on myofibrils, mainly made of actin and myosin, muscles are repeating units of sarcomeres, myosin pulls the Z lines towards the center of the sarcomere by the pulling of thick filaments on thin filaments. One sarcomere is Z-line to Z-line

Question 7

skeletal muscle contraction

Answer 7

relaxed state, binding myosin to actin is prevented because the binding site is covered by tropomyosin, Ca2+ binds to troponin, troponin (bound to the end of tropomyosin) releases tropomyosin from actin, myosin can bind to actin, binding ATP allows myosin to dissociate from actin and hydrolysis of ATP puts myosin in high energy state

Question 8

molecular structure of sarcomere

Answer 8

contractile proteins are actin and myosin, troponin has calium sensor with 4 binding sights and rotates tropomyosin for myosin binding, tropomyosin: rod shpaed that binds 6-7 actin units, Titin: looks like a slinky is an elongatable component and keeps thick filaments centered in the sarcomere, nebulin runs along the actin, Z-line is alpha-actinin, M-line is myomesin and C protein on outside

Question 9

muscle conection to CT

Answer 9

sarcolemma is plasma membrane of myofiber, epi- peri- and endomysium are CTs that invest different muscle regions, epimysium = tough covering of muscle, perimysium = CT surrounding muscle fascicle, endomysium = CT within fasicles, surround and invest muscle cells. Vessels and nerves course these

Question 10

nerves and muscles

Answer 10

nerve synapse on center of muscle, AP spread toward tendon, each muscle innervated by group of motor neurons in spinal cord, damage to neurons produces paralysis, each neuron innervated one muscle and a subset of the total muscle fibers in said muscle, motor unit = muscle fibers innervated by motor neuron. when neuron fires AP activates all muscle fibers

Question 11

muscle contraction and relaxation

Answer 11

AP => Ach release => Ach receptor binds Ach => opens causing depolarization => AP propagates down fiber => AP and depol occur at t-tuble => protein links at t-tubles/Srjunction (triad) altered to allow Ca release from SR => Ca bind troponin, exposing myosin binding sites on actin => while Ca and ATP present the myosin-actin cycle continues => Ca ATPase pumps Ca back into SR => tropomyosin moves back into place and muscle relases

Question 12

transverse-tubule system (t-system) in skeletal and cardiac muscle

Answer 12

needed because extracellular Ca would take too long to diffuse to center of muscle cells, outside would contract before inside and muscle would tear apart. Each myofibril has Ca store it needs for contraction

Question 13

pathway for AP transmission to interior via t-tubule

Answer 13

depol in t-tubule doesn’t go directly to SR, no electrical continuity, AP goes toward tendon and inward toward t-system, membrane depols in t-system this translates to Ca release from SR (called E-C coupling).

Question 14

Excitation-contraction (E-C) coupling

Answer 14

DHPR is a voltage gated Ca channel, RyR is one of these with a channel in SR. depol causes conformational change in DHP receptor causing Ca release channel to open and Ca flows out of the SR

Question 15

skeletal muscle tension grading and regulation

Answer 15

Increase AP frequency or increase motor unit recruitment

Question 16

muscle fatigue

Answer 16

reduced perforance during prolonged or intense activity, decrease in force production and speed of contraction, in principle can be impairment at any point from motor neuron to SR. steps affected: 1) propagation of AP to t-tubule, 2) release of CA from SR, 3) effect of Ca on myofilament interaction, 4) force generation by myofilament

Question 17

sarcomere length in resting, contractile, and stretched

Answer 17

resting = 2.4 micrometer (um), contractile = shorter (close to 1.6 um), stretched to breaking point = 3.6 um

Question 18

muscle fiber classes

Answer 18

slow, fast and an intermediate. Have different myosin isoenzymes, different proportions of mitochondria and oxidative enzymes, different resistance to fatigue, and different speeds of contraction

Question 19

slow oxidative fibers

Answer 19

used for postual or relatively maintained contractions, reddish in color due to high myoglobin content

Question 20

intermediate fibers

Answer 20

fast with both glycolytic and oxidative enzymes

Question 21

fast twitch fibers

Answer 21

high in glycolytic content, used for rapid bursts of activity. Each motor unit is homogeneous

Question 22

satellite cells

Answer 22

stem cells, repair damaged muscles cells

Question 23

myofiber growth

Answer 23

number of cells don?t change, cell size increases by adding myofilaments as additional myofibrils so there is always a Ca store nearby

Question 24

Cardiac muscle

Answer 24

need Ca, have pacemaker, one nucleus, 50-100 um in length, are striated, 5-15 um in diameter, has SR, have t-system, yes troponin, use Ach and norepinephrine, no motor units, Na dependent (NaCh), fast tension development

Question 25

smooth muscle

Answer 25

no aligned filament, mononucleated, yes and no on gap junctions, 100s of um long, 2-5 um wide, some have SR, no t-system, no troponin, use Ach, norepinephrine, NO, many peptides, some have motor units, some CaCh, some no AP, have pacemaker, slow rate of tension development