Muscular System Flashcards
activation gates
closed at rest; open with depolarization, allowing Na+ to enter cell
inactivation gates
open at rest; block channel once it is open to prevent more Na+ from entering cell
excitation-contraction coupling
- AP from motor end plate to t-tubules to sarcoplasm
- AP stimulate voltage gates open; linked to Ca channels in terminal cisternae (SR)
- Ca is released and diffuse out of cytoplasm
- Ca bind to troponin, cause troponin-tropomyosin to change shape and rest on actin
- actin activation sites now available to bind to myosin heads and contract
cross bridge movement
attach: lose P and ADP attaches to myosin head to actin
power stroke: myosin head attached to actin stroke forward from preexisting energy in the heads
release: ATP arrives and removes the myosin head from the actin
recovery: ATP broken into ADP and P; energy released stored in myosin heads
relaxation
- Ca back into sarcoplasmic reticulum via active transport (pay w ATP)
- use ATP to move Ca from troponin-tropomyosin complex
- troponin-tropomyosin complex reestablishes position and block binding sites
muscle twitch
Muscle contraction in response to a stimulus that causes action potential in one or more muscle fibers
-lag/latent phase
- contraction phase
- relaxation phase
lag (latent) phase
- AP arrive at presynaptic terminal and causes its permeability to increase
- Ca diffuse in and sends ACh vesicles across synaptic cleft to be received by ACh receptor molecules
-ACh binding to receptor = open Na ligand channels - Na diffuse in > depolarize > conduct AP
- acetylcholinestrease is working and causes presynaptic AP to cause postsynaptic AP
- AP in t tubules allows Ca in from SR to sarcoplasm
- Ca bind to troponin > change shape of troponin-tropomyosin complex > expose actin active sites
contraction phase
cross bridge formation and filament movement (attach, power stroke, release, recovery)
relaxation phase
- Ca actively transported from sarcoplasm to SR
- troponin-tropomyosin complex inhibits against cross bridge formation
- muscle fibers lengthen passively
titan
a protein the length of a sarcomere that allows muscle fiber to rebound to normal length after being stretched/compressed
contraction of whole muscle
- Strength of contraction is graded: ranges from weak to strong depending on stimulus strength
- multiple motor unit summation: strength of contraction depends on recruitment of motor units
(submaximal stimulus, maximal stimulus, supramaximal stimulus)
multiple wave summation
muscle tension increases as contraction frequencies increase
- incomplete tetanus: muscle fibers relax btwn contractions
- complete tetanus: no relax btwn contractions
treppe
each successive twitch contracts more forcefully than the previous one until all equal after a few stimuli
- occurs in long rested muscle
- Ca in sarcoplasm and not SR
isometric contraction
Muscle contracts but there is no movement, muscle stays the same length (“same” “length”)
- push/pull and hold
isotonic contraction
change in muscle fiber length but tension is constant (“same” “tension”)
- concentric: overcome opposing resistance, muscle shortens
- eccentric: tension maintained but muscle lengthens
muscle tone
the state of balanced muscle tension that makes normal posture, coordination, and movement possible
multiple wave summation
muscle tension increases as contraction frequencies increase
- incomplete tetanus: muscle fibers relax btwn contractions
- complete tetanus: no relax btwn contractions
Tetanus
Muscle contractions in smooth/organized way up until complete contraction
treppe
each successive twitch contracts more forcefully than the previous one until all equal after a few stimuli
- occurs in long rested muscle
- Ca in sarcoplasm and not SR
isometric contraction
Muscle contracts but there is no movement, muscle stays the same length (“same” “length”)
- push/pull and hold
- postural muscles
isotonic contraction
no change in length but muscle increases (postural muscles), stays the same
muscle tone
- Isotonic: change in length but tension constant, same tone
- Concentric: overcome opposing resistance and muscle shortens
- Eccentric: tension maintain but muscle lengthens
Muscle Tone
Constant tension by muscles for long periods of time (full motor unit recruitment)
active tension
force applied to an object to be lifted when a muscle contracts
- actively move weight (bicep curl)
passive tension
tension applied to load when a muscle is stretched but not stimulated
- pick up and hold weight (before action)
Total Tension
Sum of active and passive tension
Fatigue
decreased capacity to work; reduced performance efficiency
- psychological: depends on each person
- muscular: ATP depletion
- synaptic: not enough ACh in NMJ
Physiological contracture
State of fatigue where due to lack of ATP neither contraction nor relaxation can occur
- muscles cannot relax and stay contracted as not enough ATP is there to remove myosin head
Energy Sources
ATP made from:
- creatine phosphate: resting condt stores to make ATP
- anaerobic respiration: w/o oxygen break glucose down into lactic acid and ATP
- aerobic respiration: w oxygen, break glucose into ATP, CO, H2O
-oxygen debt
Slow twitch fibers
high-oxidative
-Lots of mitochondria
-Myoglobin stores oxygen in muscles (lots)
-Endurance > power
-Contract slowly
-Lots of blood supply (lots of capillaries)
-high aerobic capacity
-Postural muscles
- small fiber diameter
Intermediate Twitch Fibers
- intermediate fiber diameter
- medium myoglobin, mitochondria, capillaries, and aerobic capacity
- high anaerobic capacity
- lower body
- endurance activities
- traits of both fast and slow twitch fibers
fast twitch fibers
low-oxidative
- largest fiber diameter
- Contractile phase is fast; contract rapid
-Low myoglobin and low/fewer mitochondria
-Fatigue quickly
-Upper limbs for most people
- low aerobic capacity
- highest anaerobic capacity
- fasted ARP breakdown
- few capillaries
Hypertrophy
increase in:
- muscles size
- myofibrils
- nuclei due to fusion of satellite cells
- strength (better coordination)
- production of metabolic enzymes
- circulation
- less restriction by fat
Atrophy
decrease in muscle size
reverse of Hypertrophy except in severe situations cells die
Smooth muscle
-Not striated; small muscle fibers
-Spindle shaped; single and central nucleus (not produce a lot of ATP)
-no z disks
-more actin and less myosin
-Dense bodies are the z disk of smooth muscle; noncontractile intermediate filaments
Relaxation of Smooth muscle
is caused by enzyme myosin phosphatase (take P of myosin head so smooth muscle can relax)
Caveolae
indentations in sarcolemma; act similar to t tubule; electrical signal enter here
Ca makes contractions; bind to calmodulin to regulate myosin kinase
smooth muscle contraction
- Hormones create action potentials
- attach to G-protein + Alpha unit
- Alpha unit changes GTP to GDP
- Alpha unit w/ GTP opens Ca2+ channel + Ca2+ enters
- Ca2+ breaks to Calmodulin
- Calmodulin excites myosin kinase
- myosin kinase
dephosph ATP - P goes to myosin head
Myosin phosphatase remove P from myosin so the muscle can relax
visceral smooth muscle
-Cells in sheets; function as unit
-Digestive system ; respiratory tracts
-Work as group with lots of gap junctions
-All fire together (autorhythmic)
Multiunit smooth muscle
cells or groups of cells act as independent units
-Blood vessels (sheets)
-Arrector pili or iris (bundles)
-Capsule of spleen (single cells)
-Partial contractions (autorhythmic)
electrical properties of smooth muscle
- not all or none
- -60mV (reduced amplitude)
- Slow waves of depolarization and repolarization from cell to cell
-Depolarization = spontaneous diffusion of Na+ and Ca2+ into cell (none gated leakage channels)
-Does not follow all-or-none law
-May have pacemaker cells (spontaneous action potential)
-Contraction regulated by ANS and by hormones
cardiac and skeletal APs
- both have rapid depolarization
- both have all-or-none principle
skeletal: 2miliseconds long
cardiac: 500ms long - slow dispersal of CO2+ to bring it back into repolarization = long plateau phase = causes larger action potential
smooth muscle functional properties
- Some visceral muscle show autorhythmic contractions
-Tends to contract in response to sudden stretch but not to slow increase in length - constant tension (can maintain contraction for extended amount of period because not all-or-none)
smooth muscle regulation
*Innervated by ANS
*Neurotransmitters are acetylcholine and norepinephrine
*Hormones important are epinephrine and oxytocin
*Receptors present on plasma membrane which neurotransmitters or hormones bind determines response
cardiac muscle
- Found only in the heart and is striated with one nucleus
*Has intercalated disks and gap junctions (can excite adjacent cells)
*Autorhythmic cells
*Action potentials of longer duration and longer refractory period (500ms)
*Ca2+ regulates contraction
