11.7 muscular system Flashcards
protozoa and amoeba
move via power stroke, recovery stroke and amoeba move via pseudopodia
flatworms
hydrostatic skeleton. with longitude and circle muscles. contraction moves it
annelids
hydro skeleton but also setae, and peristalsis
Skeletal muscle structure
(striated muscle) – voluntary movement, fibers are multinucleated cells
- made of myofibrils, sarcomeres, sarcoplasmic reticulum, etc.
Myofibrils
filaments divided into sarcomeres
Sarcomeres
– individual contractile units separated by a border (Z-line)
Sarcoplasmic reticulum
– stores Ca2+; surrounds myofibrils
Sarcoplasm
cytoplasm
Sarcolemma
– plasma membrane of muscle cells; can propagate action potential
i. Invaginated by T-tubules- channels for ion flow
ii. Wraps several myofibrils together to form a muscle cell/muscle fiber
Mitochondria
present in large amounts in myofibrils
sarcomere structure
actin thin filaments, myosin thick filaments
- Z line – boundary of a single sarcomere; anchor thin filaments
- M line – center of sarcomere
- I band – region containing thin filaments (actin) only (on ends, only purple above)
- H zone – region containing thick filaments (myosin) only (in middle, only green above)
- A band – actin and myosin overlapping (one end of overlap to the other end of overlap)
o H and I reduce during contraction, while A does NOT
- Note: striations are the result of alternating thin actin + thick myosin (I bands and A bands)
contraction
- Action potential of neuron releases acetylcholine when meets neuromuscular jxn
- Action potential then generated on sarcolemma and throughout T-tubules
- Sarcoplasmic reticulum releases Ca2+
- Myosin cross bridges form – result of Ca2+ binding to troponin on actin helix
Note: at the end of each contraction cycle, Ca2+ is actively pumped back into the sarcoplasmic reticulum
sliding filament model of contraction
ATP binds to myosin head. myosin and actin unbind, then mysin head is cocked back.
- Ca+ exposes binding sites on actin. binds troponin and pulls back tropomyosin
- cross bridges between myosin and actin forms
- ADP is released, sliding motion of actin brings z lines together
- new ATp attaches, and myosin bridges unbind
strength of muscle contraction
single muscle fiber cannot be increase, but strength of overall contraction
can be increased by recruiting more muscle fibres
Motor unit:
the neuron + muscle fibers it innervates. Each muscle fiber (cell) forms synapses with only
one motor neuron, but each motor neuron typically synapses with many muscle fibers.
recruitment
when a greater quantity of muscle fibers are activated by the
brain rather than an increase in frequency of action potentials that stimulate muscle fiber contraction. used for slow to fast twitch
small vs large motor units
Intricate movements tend to use smaller motor units (e.g. finger), whereas muscles requiring greater
force (e.g. back) have larger motor units.
simple twitch
response of a single muscle fiber to brief stimulus; latent, contraction, relax
1. Latent period – time between stimulation and onset of contraction; lag
o Action potential spreads on sarcolemma and Ca2+ ions released
2. Contraction
3. Relaxation (absolute refractory period) – unresponsive to stimulus
summation
– contractions combine and become stronger and more prolonged
(repeated APs summate)
tetanus
continuous sustained contraction; muscle cannot relax; will release if maintained (in tetanus, rate of muscle stimulation so fast that twitches blur into one
smooth constant)
tonus
state of partial contraction; muscle never completely relaxed
Subthreshold:
no motor units respond
Threshold:
one motor unit responds.
Submaximal:
increasing #’s of motor units respond.
Maximal:
all motor units respond.
Supramaximal:
all motor units respond.
- Speed and amplitude remain constant during an action potential. As stimulus intensity increases, the # of AP’s goes up.
Type I: Skeletal muscle
slow-twitch, lots of myoglobin, lots of mitochondria, aerobic endurance [they split ATP at a slow
rate, result: slow to fatigue but slow contraction velocity. Appear red, small in diameter.
Type IIA: skeletal muscle
IIA: fast-twitch, endurance by not as much as type 1 (can use aerobic + anaerobic equally) [split
ATP at high rate: contract rapidly]. Lots of myoglobin. Resistant to fatigue but not as much as Type 1.
Appear red to pink, intermediate in diameter.
Type IIB: skeletal muscle
IIB: fast-twitch, low myoglobin, lots of glycogen, generate power. Few myoglobin, use glycolysis
(anaerobic primarily). Split ATP at a fast rate. Appear white, large in diameter.
(hyperplasia)
increase in size adult muscle
(hypertrophy)
which sees an increase in: diameter of muscle
fibers, # of sarcomeres and mitochondria, sarcomere length adult muscle
smooth muscle
involuntary. one nucleus no striation, autonomic NS. slow to contract.
Thick & thin filaments attached to IFs, contract
IF’s pull dense bodies together. smooth muscle length shrinks.
* no sarcomere org
Single-unit: Smooth Muscle
visceral, connected by gap jxns, contract as single unit (stomach uterus,
urinary bladder)
Multiunit: Smooth Muscle
each fiber directly attached to neuron; can contract independently (iris, bronchioles, etc)
Note: smooth muscle does not have
T-tubules, striations, troponin, or tropomyosin. It instead
uses myosin light change kinase to overcome lack of troponin.
Cardiac Muscle
striated, one or two central nuclei; cells separated by
intercalated discs that have gap jxn to allow AP’s to chain flow via electrical synapse; involuntary; lots of
mitochondria. Grows by hypertrophy.
Both smooth and cardiac muscle are ____
myogenic – capable of contracting without stimuli from nerve cells
