8.1 - muscle phyisology

muscle twitch

contraction = response to stimulus = ap in 1+ muscle fiber, phases - lag/latent, contraction, relaxation

how are stronger contractions made

restim of muscle fiber before it completely relaxes, added to the first = causes a stronger contraction

tetanus

rapid arrival of ap causes twitches = peak level of contraction, sustatined muscle contraction evoked when motor nerve that innervates a skeletal muscle = emits ap at high rate

types of muscle fibers

slow muscle fibers - slow oxidative

fast aerobic - fast oxidative glycolytic fibers

fast anaerobic fibers - fast glycolytic fg

they diff in mitochondria and amt of atp produce

slow muscle fibers

small, weaker contractions- resist fatigue (postural muscles)

slow contraction as atp hydrolyzed on myosin head is slow, and has high amt of myoglobin = good supply of oxygen

fast aerobic fibers

intermed size and strength, with some fatigue, contract quick and powerful, but fatigue faster than slow muscle fibers = endurance

describe what fast anaerobic fibers are like

very strong contractions - fatigue fast, few mitochondria and myoglobin, anaerobic glycolysis = atp, but larger fibers = more force, for rapid movement for tiny amt of time, muscles has more type of a fiber than another

how do diff types of force excite diff fibers

gentle contractions - small muscle fibers

forceful contractions - generate strong contractions that will fatigue eventually but not fast

strong burst- largest muscle fibers

how is atp produced for muscle contractions

creatine phosphate, anaerobic respiration, aerobic respiration

creatine phosphate

accumulate in muscle tissue, used quickly, stores energy to make atp, where adp and creatine phosphate with a kinase make creatine and atp

anaerobic respiration

occurs without oxygen, breaks down glucose = atp and lactic acid, atp from creatine and anaerobic respiration = 3 mins

aerobic respiration

more efficient than anerobic = needs oxygen and breaks down glucose to make atp co2 and water

endruance training

fast muscle fibers from anaerobic to aerobic fibers

weight lifting

converts fast from aerobic to anaerboic, as anaerobic contract faster and more powerful, but fatigue faster

how does force correlate with motor units

skeletal muscles = functional motor units, and a group of muscle fibers activated by branch of single motor neuron, how total force = num of motor units activated (recruitment), and more motor units = more force

what is optimal length

maximal number of cross bridges needed for contractions = overlap between thick and thin filament without getting in the way,

if muscle fiber stretched too long, not much overlap and cross bridges

if extreme stretch = then no overlap what so ever

if length shorter than optimal = thin filaments overlap and get in the way, binding sites aren’t able to bind to all heads = less tension

why can’t we change the length as much

because our muscles are attached to our bones, and won’t stretch as far from optimal range

isomeric contraction

muscle = at same length, can contract but only exerts force or tension, like holding an object up, force = load

isotonic

muscle length changes - like lifting object at constant speed

two types 1:

concentric = shortening of muscles = generates forces

eccentric : causes muscles to elongate in response to greater opposing force

smooth muscle

found in bladder, reprodu tracts, gastroint tract, respiratory tract and surrounds blood vessels, mechnaically coupled to one another, contract of one cell = another cell, gap junctions couple adj cells chem and electrically = facilitating chemical and ap spread between cells

what is signif abt smooth muscles shortening

it can shorten greater than skeeltal as it surrounds structures that change in diameter, and contraction can be nonlinear, as fibers are slanted position

neural input for smooth muscle and hormonal

ANS can induce or inhibit contraction (either from sns or pns), hormones can stimulate a second messenger molecule = calcium release

how are smooth muscles activated by calcium

calcium enters from outside = voltage/ligand gated channels, others coem from sacroplasmic reticulum but has no t tubules, and calcium binds to calmodulin = and phosphorylates the cross bridges which can bind and pull on thin filaments

smooth muscle contractions

tend to be slower but not fatigued, like diameter of blood vessel will maintain like that for a long time

cardiac muscle

branched, connected through intercalated disks, and similar mechanism as skeletal muscle