Z 331 final Flashcards
motor unit
motor neuron and all the muscle fibers it supplies;
fibers spread throughout muscle;
contract asynchronously to prevent fatigue
muscle twitch
motor unit’s response to single action potential of motor neuron; simplest contraction observable in lab
3 phases of muscle twitch
latent: events of excitation-contraction coupling, no muscle tension
period of contraction
period of relaxation: tension declines to zero
graded muscle responses
contractions are smooth and vary in strength depending on demands
2 ways muscle contractions can be graded
changing frequency of stimulation, changing strength of stimulation
wave (temporal) summation
result of increase frequency of stimulation; muscle doesn’t completely relax between stimuli; second contraction of greater force; main function is smooth contractions
unfused (incomplete) tetanus
result of wave summation
fused (complete) tetanus
muscle reaches maximum tension, from very quick stimuli; no muscle relation, muscle fatigue
recruitment
multiple motor unit summation (from increased strenth of stimulus), controls force of contraction
size principle
motor units with smallest fibers recruited first, larger fibers recruited as stimulus intensity increases
isometric contraction
no shortening, tension increases but does not exceed load, cross bridges generate force but do not move actin filametns
isotonic contraction
muscle shortens, tension exceeds load
concentric contraction
muscle shortens and does work
eccentric contraction
muscle generates forces as it lengthens
muscle tone
constant slightly contracted state of all muscles, due to spinal reflexes
spinal reflexes
groups of motor units alternately activated in response to input from stretch receptors in muscles, responsible for muscle tone
force of muscle contraction depends on
number of myosin cross bridges attached.
- number of muscle fibers stimulated
- relative size of fibers
- frequency of stimulation
- degree of muscle stretch
the only energy source for contractile activities
ATP
3 ways ATP can be regenerated
direct phosphorylation of ADP by creatine phosphate
anaerobic glycolysis (glucose to lactic acid)
aerobic respiration
muscles store enough ATP to
start contraction
creatine kinase
catalyzes creatine phosphate + ADP –> creatine + ATP
creatine phosphate provides maximum muscle power for ? seconds
~15
where does CP come from?
some made from ATP at rest (reversible reaction with creatine phosphokinase), some stored in muscle
more pyruvate than mitochondria can use results in
lactic acid production from anaerobic pathway
aerobic respiration equations
glucose + oxygen –> carbon dioxide + water + ATP
aerobic respiration substrates can be
glucose (pyruvic acid), amino acids, or fatty acids
anaerobic threshold
point at which muscle metabolism converts to anaerobic glycolysis
muscle fatigue
inability to contract even though muscle may stil be receiving stimuli
causes of fatigue
ATP/CP shortage, depletion of metabolic reserves, damage to sarcolemma and SR, low pH (lactic acid) inhibits enzymes and effects CNS, motor nerve fibers deplete Ach, unable to release Ca, muscle exhaustion and pain
excess post-exercise oxygen consumption (EPOC)
extra oxygen the body must take in for restorative processes, difference between amount of oxygen needed for total aerobic activity and amount actually used
slow oxidative fibers
high endurance, aerobic metabolism, smaller, more mitochondria, little power, high blood supply, contain myoglobin, red
fast glycolytic fibers
quick, no oxygen, large, few mitochondria, large glycogen reserves, strong, fatigue quickly, little myoglobin, white
fast oxidative (intermediate) fibers
mid sized, intermediate power, contract quickly, oxygen dependent, some myoglobin, more capillaries than fast
muscle fibers of a motor unit are
same type
aerobic/endurance exercise
increase # of capillaries surrounding muscle, increase # of mitochondria, more myoglobin
may convert fast glycolytic fibers to fast oxidative
resistance exercise (high intensity/aerobic)
hypertrophy, increase size of fibers, more mitochondria, more myofilaments, store more glycogen, fast oxidative to fast glycolytic
2 layers of smooth muscle
longitudinal and circular
smooth muscle fibers
spindle shaped, thin, short, one nucleus, no striations/sacromeres, less developed SR, no myofibrils, no T tubules
Ca in smooth muscles from
SR, most through channels from extracellular space
caveolae
pouch like infoldings of sarcolemma, Ca infulx
longitudinal layer
fibers parallel to long axis, contraction dilates and shortens
circular layer
fibers in circumference of organ, contraction constricts lumen and elongates
varicosities
bulbous swellings of nerve fibers store and release neurotransmitters into diffuse junctions
innervation of smooth muscle
no NMJ, automatic nerve fibers at diffuse junctions
myofilaments in smooth muscle
ratio of thick to thin 1:13
spiraly arranged - contract like corkscrew
thick have long heads along entire length - as powerful as skeletal of same size
calmodulin
instead of troponin, binds Ca, interacts with myosin kinase to phosphorylate and activate myosin
intermediate filaments
resist tension, between dense bodies
dense bodies
proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals (like z disks)
gap junctions
actions potentials transfer from fiber to fiber
pacemakers (smooth)
some cells self-excitatory, depolarize without external stimuli
regulation of smooth muscle contraction
nerves, hormones, local chemical changes
stress-relaxation response
smooth muscle adapts to new length/stretch and relaxes, can still contract on demand
length and tension changes in smooth muscle
great force even when stretched, can stretch and relax to normal length
hyperplasia
smooth muscle cells can divide and increase numbers
types of smooth muscles
unitary (visceral) and multi unit
unitary (viseral) smooth muscle
hollow organs, opposing sheets, innervated by varicosities of autonomic nerve fibers, rhythmic spontaneous APs, gap junctions (no recruitment), respond to chemical stimuli; contract as single unit
multiunit smooth muscle
large airways, arteries, arrector pilli, iris; rare gap junctions, rare spontaneous depolarization, has independent muscle fibers, innervated by autonomic NS, graded contractions, motor units, responds to hormones
cardiac muscle cells
cardiocytes, cardio myocytes
cardiac cell characteristics
striated, short, branched, sacromeres, single nucleus, lots of mitochondria, t tubules, intercalated disks, aerobic
intercalated disks
anchor cardiac cells, myofibrils anchored together
desmosomes: prevent separation
gap junctions: ions pass from cell to cell, allow heart to be functional syncytium (single unit)
cardiac has long absolute refractory period to
prevent tetanic contractions
cardiac depolarization wave opens
slow Ca channel in sarcolemma, surge prolongs depolarization phase
pacemaker/autorhythmic cells
unstable resting membrane potentials, due to opening of slow Na channels, continuously depolarize
4 major functional characteristics of cardiac tissue
automaticity
variable contraction speed and tension
extended contraction time/longer refractory period
prevent wave summation and tetanic contractions
relative contraction speeds
fast-slow: skeletal, cardiac, smooth
sarcomeres?
skeletal and cardiac
require neural signal to contract?
skeletal, some smooth
t tubules?
skeletal, small in cardiac
Ca source for each
skeletal: SR
cardiac: 80 SR 20 ECF
smooth: SR and ECF
gap junctions to connect cells?
cardiac, some smooth
capable of tetanus?
skeletal and smooth
components of lever system
lever/fulcrum, effort, load
mechanical advantage
power lever, load close to fulcrum, effort far from fulcrum
mechanical disadvantage
speed lever, load far from fulcrum, effort close, load moved rapidly over large distance,
1st class lever
fulcrum between load and effort (load, fulcrum, effort)
ex: scissors, seesaw, raise head
2nd class lever
load between fulcrum and effort (fulcrum, load, effort)
ex: wheelbarrow, standing on toes
3rd class lever
effort between fulcrum and load (fulcrum, effort, load) most common in body, mechanical disadvantage, speed lever, tweezers
prime mover
agonist, major responsibility for movement
antagonist
opposes movement
synergist
help prime movers
fixator
immobilizes bone or muscle’s origin, stable base
circular arrangement
fascicles in concentric rings
ex: orbicularis oris
convergent arrangement
broad origin, converge towards tendon insertion
ex: pectoralis major
parallel arrangement
fascicles parallel to long axis
ex: sartorius
fusiform arrangement
spindle shaped, parallel fibers
ex: biceps brachii
pennate arrangement
short fascicles attached obliquely to central tendon running length of muscle unipennate - one side ex: extensor digitorum longus bipennate - opposite sides of tendon ex: rectus femoris mutipennate - feathers into one tendon ex: deltoid
