Traffic - week 8 Flashcards
3 types of muscle
- skeletal (striated, voluntary, multinucleate) a. movement of whole body or parts
- cardiac (striated, involuntary, one nucleus) a. pump blood
- smooth (unstriated, involuntary, one nucleus) a. movement of substances through hollow
organs
skeletal muscle (long)
functional anatomy
- whole muscle
a. made up of long cells bundled with connective tissue
b. connective tissue extends to form tendons attaching muscle to bone
muscle cell
contains myofibrils (specialized organelles) which are made up of protein filaments (myofilaments)
thick filaments
(1) made of myosin molecules, each of which has a head and tail end
(2) heads form cross bridges, have an actin binding site and ATPase site
thin filaments
(1) made mostly of actin molecules, each of which has a myosin binding site (cross bridge binding site)
(2) tropomyosin blocks binding sites when cell at rest
(3) troponin holds tropomyosin in place, has Ca2+ binding site
thick and thin filaments arranged into…
sarcomeres (functional units that contract) this arrangement results in striations
plasma membrane of muscle fiber also called
sarcolemma (1) forms T tubules, which project into cell (continuous with surface membrane, allowing electrical activity at cell surface to be transmitted throughout cell)
sarcoplasmic reticulum is modified..
smooth ER
(1) network of tubules surrounding myofibrils
(2) ends of each portion expand into sacs called terminal cisternae (a.k.a. lateral sacs, stores Ca2+)
other important points during contraction (gg)
during contraction, at any given time, only some cross bridges are attached - as they release others attach so thin filaments don’t slide backward
b. latent period is time between AP and contraction
c. contraction and relaxation last about 100 m sec
d. contraction of an individual cell is an all-or- none response
Skeletal muscle mechanics (car battery)
gradation of whole muscle tension
- a single AP to a muscle fiber results in a weak contraction (twitch) - muscle cells work together to produce more force
- recruiting more motor units➝ more tension (more force, stronger contraction)
a. a motor unit is a motor neuron plus all the fibers it innervates (fibers spread throughout muscle)
smaller motor units in muscles..
needing precise control (eyes, fingers)
asynchronous recruitment of motor units
prevents fatigue - alternate motor units (e.g., postural muscles, holding a heavy object)
influencing tension in each fiber..
increased frequency of stimulation➝ increased tension
if there is no relaxation between APs,
tetanus occurs (a smooth, sustained contraction of maximal strength)
length-tension relationship
maximal force possible at optimal length - myosin cross bridges have maximal access to actin binding sites. less fatigue ➝ increased tension
types of contractions
isotonic and isometric
isotonic
tension constant, muscle changes length
(1) concentric contraction - muscle shortens (lifting a load)
(2) eccentric contraction - muscle lengthens (lowering load)
isometric
tension develops, length stays the same (trying to lift too heavy a load, pushing against a wall)
muscles accomplish work…
(force x distance), but most of the energy muscles use (about 75%) converted to heat
lever systems
muscles provide force to move bones (levers) around joints (fulcrum)
2. depending on construction of system, allows a given effort to move a heavier load, or to move it farther and faster
Skeletal muscle metabolism (arms and legs)
- muscle cells have enough ATP reserves to last 4-6 seconds of strenuous activity
3 ways to form ATP
creatine phosphate, oxidative phosphorylation and anaerobic glycolysis
anaerobic glycolysis
fast but not as efficient as with O2, pyruvic acid➝lactic acid, which contributes to soreness and fatigue b. good for short term (high intensity)
oxidative phosphorylation (mito)
in mitochondria,needsO2
(1) fueled by fatty acids (during rest or light exercise, slow) or glucose (during more intense exercise, from blood and glycogen stores)
b. high yield of ATP but relatively slow
c. constant supply of O2 facilitated by myoglobin (stores O2, increases O2 transfer from blood) d. good for long term (endurance)
creatine phosphate (tu)
contains high energy phosphate group
CP + ADP ➝ creatine + ATP (with enzyme creatine kinase) b. very fast
c. enough stores to last 15-20 sec
fatigue (pie)
muscle fatigue: muscle no longer responds with same degree of contraction
a. increase in Pi from the breakdown of ATP is primary cause (interferes w/power stroke, decreases sensitivity of regulatory proteins to Ca2+, decrease amount of Ca2+released)
b. depletedCa2+levels(leaks from cell after periods of intense exercise)
c. depleted glycogen reserves
neuromuscular fatigue
ACh synthesis too slow to keep up with high intensity exercise. wouldn’t happen in a normal healthy body
psychological fatigue
CNS does not activate motor neurons due to pain or tiredness
oxygen debt
oxidative phosphorylation allows restoration of energy reserves
a. breaks down lactic acid, replenishes stores of creatine phosphate and glycogen
b. takes minutes to whole day
fiber types
most muscles have varying percentages of fiber types
fiber type - slow-oxidative (sloth)
a. small, contract slowly (low ATPase activity)
b. use oxidative phosphorylation (lots of
mitochondria, myoglobin, capillaries)
c. good for low intensity endurance,resist
fatigue (postural muscles in back and legs)
fast-glycolytic
large (more myofilaments), contract quickly (lots
of force, high ATPase activity)
b. use anaerobic glycolysis (few mitochondria, little myoglobin, lots of glycogen & glycolytic
enzymes)
c. good for short duration high intensity movement (arms for lifting)
fast-oxidative (ox)
medium sized, contract quickly (lots of force)
b. mostly oxidative phosphorylation, some
anaerobic glycolysis (characteristics of slow-ox and fast-gly)
c. good for intermediate activities
endurance exercise…
converts fast-glycolytic to fast- oxidative, weight lifting does the opposite
a. changes in amount of mitochondria, blood supply, size, etc.
typically cannot convert between slow and fast fibers…
depends on nerve supply
skeletal muscle input in… (SCM)
SCM
spinal cord, corticospinal (pyramidal) motor system, multineuronal (extrapyramidal) motor system
spinal cord
spinal reflexes
corticospinal (pyramidal) motor system (cork)
a. from primary motor cortex
b. activity planned by premotor and supplementary motor areas, and cerebellum (pcs)
c. mainly precise movements, especially of hands/fingers, face
multineuronal (extrapyramidal) motor system (PPRCBTS)
PPRCBTS
a. complex pathways including primary motor cortex, reticular formation, cerebellum, basal nuclei, thalamus, premotor and supplementary motor areas
b. mainly regulation of posture and large muscle groups (subconscious)
afferent signals (change coming)
- necessary for coordinated activity
- muscle proprioceptors sense changes in length and tension
a. inform brain
b. local spinal reflexes
muscle spindles
a. in middle of muscle, monitors muscle length and speed of stretching
b. when whole muscle stretched, afferent fibers sense stretch in spindle fibers (respond with increased AP frequency)
c. when whole muscle contracts, gamma motor neurons signal ends of intrafusal fibers to contract (takes up slack so receptors maintain sensitivity to stretch)
golgi tendon organs (alf-fire)
in tendons, monitor tension
b. when whole muscle contracts, afferent fibers fire in response to the stretch of the tendon (increased APs directly related to amount of tension)
c. can inhibit alpha motor neurons of that muscle to prevent damage
smooth muscle (sheets)
small cells arranged in sheets 2. thick and thin filaments a. no troponin b. tropomyosin does not block binding sites 3. no myofibrils or sarcomeres (no striations)
contraction (sign contract)
Ca2+ enters mostly from ECF (voltage-gated Ca2+ channels), then some from sarcoplasmic reticulum
- Ca2+ acts as second messenger, activating myosin kinase which phosphorylates myosin
- cross bridge cycling occurs until Ca2+ no longer available (actively pumped back to ECF and SR)
multiunit smooth muscle (hair)
- groups of cells function independently
- innervated by ANS, which initiates contractions
- large blood vessels, large airways, eye, hair follicles
single-unit smooth muscle (most)
- cells electrically linked (gap junctions)
- clusters of cells are self-excitable and pass activity to rest of cells (myogenic activity)
a. no resting potential-cells gradually depolarize with automatic changes in channel permeability
b. ANS controls gradation of contraction by influencing amount of intracellular Ca2+
smooth muscle designed for sustained…(stomach)
contractions with low energy use and no fatigue
- a single contraction can be 3 sec long (cross bridge cycling and Ca2+ removal slow)
- uses oxidative phosphorylation
a. ATP use slow
b. can use anaerobic glycolysis if needed - can develop tension even when stretched to about 2.5 times resting length (filaments still overlap)
larger motor units in muscles
designed for power (legs)
twitch summation occurs when…
fiber does not relax completely between APs, greater cross bridge cycling from prolonged availability of Ca2+
if there is no relaxation between APs,
tetanus occurs (a smooth, sustained contraction of maximal strength)
thicker fibers…
equals increased tension, more myofilaments in cell
muscle spindles in spinal cord (omega-long)
synapse on alpha motor neuron supplying that muscle, causing stretch reflex (muscle contracts) which resists passive changes in muscle length
z line defines
ending and beginning of sarcomere (thick and thin filament arrangement)
excitation-contraction
the neuromuscular junction and the sliding filament theory combined - end result is muscle contraction
