Muscle - Lectures 10-11-12 Flashcards
what are the 3 types of muscle
- 2 similarities
- Skeletal muscle
- cardiac muscle
- smooth muscle
SIMILARITIES:
- excitability! membrane potential can be changed
- all use actin and myosin –> 2 major proteins responsible for contractability
describe each type of skeletal muscles:
- size?
- pattern/striation?
- how many nucleus?
- intercalated disk?
- T-tubules?
SKELETAL:
- large fibers
- striped or striated
- multiple nuclei –> advantage = can produce many proteins
- no intercalated disks
- T-tubules
CARDIAC:
- smaller than skeletal, branched
- striations
- 1 nucleus per cell
- cells are joined in series by intercalated disks (to squeeze at the same time)
- T-tubules!
SMOOTH:
- small
- no striations
- 1 nucleus per cell
- no intercalated disks
- no T-tubules
how can there be multiple nuclei in one muscle cell?
stem cells during embryonic development form myoblasts (1 nucleus per cell) –> merge together to form myocytes/muscle fibers = many nuclei per cell
what are antagonistic muscles?
- what are the 2 movements?
- move bones in opposite directions
- flexion moves bones closer together (arm curl)
- extension moves bones away from each other (push-up)
- muscle cells are called muscle _______- –> shape (2)
- what kind of cells differentiate into muscle for growth and repair?
- amount of muscle cells already decided at birth? what changes?
- muscle ____A____ –> bundle into _______ which bundle into _______
- connective tissues hold muscle to bone with _______
- muscle fibers –> long and cylindrical
- satellite cells/stem cells
- yes! when you exercise, you change diameter and length BUT stem cells can repair and replace damaged muscles
- muscle fibers bundle into fascicles which bundle into entire muscle
- tendon
what are the 3 layers of connective tissue that surround muscle vs fascicles vs myocytes?
- what does the connective tissue provide? (3)
- myocytes surrounded by endomysium
- fascicles surrounded by perimysium
- entire muscle surrounded by epimysium
- fluid, blood, nerves
Z-line vs M-line vs A band vs I-band vs H-zone
- dark or light?
- Z line/Z-disk: separates each sarcomere (btw 2 actins of different sarcomeres)
- M-line: middle of myosin
- A-band: entire length of myosin, has some overlap with actin –> dArk
- I-band: only covers actin (from 2 sarcomeres ish) –> light!
- H-zone: only myosin! bit lighter than A band
what is a sarcomere?
functional unit of muscle
muscle fiber anatomy:
- sarcolemma?
- sarcoplasm?
- sarcoplasmic reticulum? describe structure + function?
- sarcolemma: cell membrane
- sarcoplasm: cytoplasm
- sarcoplasmic reticulum: endoplasmic reticulum: longitudinal tubes with enlarged ends called terminal cisternae
- concentrates and sequesters Ca2+
What are t-tubules?
- what forms a triad?
- function?
- continuous with the sarcolemma, invaginations of the sarcolemma that allows action potentials to get closer to SR
- t-tubule + 2 flanking terminal cisternae = triad
- allow AP to penetrate nearer to the internal structures of the fiber
muscle fibers also contain
1. all sarcomeres linked together
2. energy source
3. powerhouse
- myofibrils
- glycogen granules
- mitochondria
- thin filament = which protein?
- thick filament = which protein? heavy vs light chains
- regulatory proteins (2)
- accessory proteins (2)
- crossbridges
- thin = actin –> each can interact with 3 myosin
- thick = myosin –> each can interact with 6 actin: heavy chains = motor domain = myosin ATPase VS light chains = regulatory fcts
- reg proteins: tropomyosin and troponin
- acces: titin and nebulin
myosin heads contain 3 parts
- actin binding site
- ATP or ADP/P+ binding site
- ATPase enzyme –> break down ATP into ADP + P
what are the 3 subunits of troponin?
- when troponin binds with ____ –> 2 things happen
- repeated as long as what?
- troponin I –> binds with actin
- troponin C –> binds with Ca2+
- troponin T –> binds with tropomyosin
- when troponin C binds with Ca2+ released by SR (from terminal cisternae), troponin pulls tropomyosin from myosin-binding sites of actin –> myosin binds tightly to and moves actin
- repeated as long as binding sites are uncovered and ATP is available
what is the important component of actin?
- actins are all linked together by _______
- myosin binding site! binds with myosin head and forms crossbridge
- myosin binding site usually covered by tropomyosin when not a lot of calcium
- linked together by tropomyosin ish (which covers myosin binding sites)
when myosin binds with actin, myosin heads move towards _______ –> sarcomere becomes longer/shorter
- A-band, H-zone, I band stay the same lengths?
- M-line –> sarcomere becomes shorter
- A band stays same
- I band and H-zone become shorter
- titan spans distance from _______ to the neighbouring ________
- nebulin attaches to a _______ but does not extend to the ________
- role of titn?
- from Z-disk to M-line (ie half a sarcomere)
- Z-disk but doesn’t extend to M-line
- titin provides elasticity and stabilizes myosin
- muscle tension = what?
- load = what?
- contraction = what?
- relaxation = what?
- muscle tension = force created by muscle
- load = weight or force opposing contraction
- contraction = creation of tension in muscle
- relaxation = release of tension
5 major steps leading up to skeletal muscle contraction
- events at the neuromuscular junction
- excitation-contraction (E-C) coupling
- Ca2+ signal
- contraction-relaxation cycle
- muscle twitch + sliding filament theory
do length or thick and thin filament change during contraction? –> what is this theory called?
- no!
- sliding filament theory of contraction –> overlapping actin and myosin fibrils
- fibrils are fixed length
- slide past each other in energy-dependant process
- what is a powerstroke?
- what happens at the end of a powerstroke (2)
- myosin crossbrige swivels and pulls actin toward M-line
1. myosin releases actin and resets and binds another actin
2. heads are not released in unison - then powerstroke is repeated many times
rigor state vs rigor mortis
- rigor state = occurs when no ATP or ADP are bound to myosin –> very brief
- rigot mortis: muscle freezes if no ATP is available to release myosin
Start: rigor state where myosin is tightly bound to ______ after a ______ _______ (needs what to detach?)
1. ATP binds and myosin ________ –> ATP increases/decreases myosin affinity to actin
2. _______ of ATP provides energy for myosin head to do what?
- how is energy provided?
3. ______ _______
- begins in response to ____ binding ______
- release of ____ allows head to swivel, pulling ____ toward ______
4. myosin releases ____ –> makes room for next ____
*CHECK SCHÉMA!
start: myosin bound to actin after a power stroke (needs ATP to detach!)
1. ATP binds to ATP binding site on myosin head and myosin detaches –> ATP decreases myosin affinity to actin
2. hydrolysis of ATP provides E for myosin head to rotate and weakly bind to actin
- E is provided by myosin ATPase that breaks down ATP into ADP and Pi
3. Power stroke
- to Ca2+ binding to troponin
- release of Pi allows head to pull actin towards M-line
4. myosin releases ADP –> makes room for next ATP
explain steps from neuron to contraction of muscle to relaxation (10 steps)
- somatic motor neuron releases Ach at neuromuscular junction
- ACh binds to Nm receptor –> opens Na+ channels –> depolarization -> EPP –> Action potential into T-tubules!
- AP in T-tubules alters conformation of DHP (L-type Ca2+ channel) receptor (voltage gated channel)
- DHP receptor opens RYR (Ca2+ channel on SR) in SR and Ca2+ from SR is released and enters cytoplasm
- Ca2+ binds to troponin C + expose myosin binding site
- myosin heads execute power stroke
- actin filament slides toward center of sarcomere
- sarcoplasmic Ca2+ ATPase pumps Ca2+ back into SR
- decrease in [Ca2+] in cytosol causes Ca2+ to unbind from troponin
- tropomyosin recovers binding site. when myosin heads release, elastic elements pull filaments back to their relaxed position
Timing of Excitation-Contraction coupling –> 3 steps
- motor neuron AP –> releases ACh –> binds Nm –> induces 2
- muscle fiber action potential –> Ca2+ released –> induces 3
- development of tension during 1 muscle twitch (latent period + contraction phase + relaxation phase)
skeletal muscle contraction requires a steady supply of ____
- what breakdown produces short burst of energy? using what enzyme?
- ________ are the most rapid and efficient store of energy?
- ATP!
- phosphocreatine breakdown –> creatine kinase
- carbohydrates (glucose)
- anaerobic glycolysis produces (2)
- quick or slow?
- oxygen required?
- quantity of energy released? - aerobic respiration (biochemistry pathways (2))
- quick or slow?
- oxygen required?
- quantity of energy released?
- anaerobic glycolysis produces lactate and acid
- quick!
- no oxygen
- small amount of E released - aerobic respiration (TCA cycle + ETC)
- slow
- oxygen required
- large amount of E released
what are the 3 types of skeletal muscles?
- slow-twich fibers (ST or type 1)
- fast twitch oxidative-glycolytic fiber fibers (FOG or type IIA)
- fast twitch glycolytic fibers (FG or type IIB/X)
SLOW TWITCH FIBERS:
- rely primarily on what?
- ie what type of activity?
- increase (3)
FAST TWITCH FIBERS:
- does 3 things faster
- 2 types? difference?
SLOW TWITCH FIBERS:
- oxidative phosphorylation
- marathon running
- increases mitochondria, myoglobin and blood vessels/capillaries to muscle
FAST TWITCH FIBERS:
- develop tension faster + split ATP more rapidly + pumps Ca2+ into sarcoplasmic reticulum more rapidly
- oxidative-glycolytic –> uses oxidative AND glycolytic metabolism (ie weightlifting)
- glycolytic fiber –> relies primarily on anaerobic glycolysis
oxidative fibers have more _________ –> why?
- myoglobin!
- because myoglobin binds oxygen in muscle so it is readily available for aerobic processes
how to visually differentiate slow twitch vs fast twitch?
- slow twitch oxidative has large amounts of red myoglobin, numerous mitochondria + extensive capillary blood supply
- fast twitch: larger diameter, pale color, easily fatigued
what affects tension in muscle?
- sarcomeres contract with optimum force if it is at optimum _________ before contraction begins
- tension generated directly proportional to number of __________
- resting fiber length!
- optimum force at optimum length
- tension proportional to number of crossbridges!
force of contraction increases with _____A____ –> what is ____A_____
- what is tetanus?
- with summation!
- summation = stronger contraction when the muscle does not relax completely btw action potentials
- tetanus = maximal contraction
what is a motor unit? small or big? examples
- contraction depends on the ______ and _________ of motor units –> explain (2)
- motor unit = one motor neuron and its muscle fibers
- can be small (ie eyelids) = good control, or big (ie back muscle) = less precise
- depends on type and number of motor units
1. recruitment of additional motor units increases contraction force (increase load = increase motor units mobilized)
2. asynchronous recruitment of motor units helps avoid fatigue (ie not all leg muscles are contracted when standing to avoid fatigue)
length-tension relationship:
- very big overlap between thick and thin filament = what?
- almost no overlap btw thick and thin = what?
- optimal resting length = what?
- BIG overlap = less tension
- NO overlap = no crossbridges can be formed = no contraction
- optimal length = maximum force
can AP have summations? can graded potentials have summations? can contractions have summations? + explain!
- 1 EPP = 1 what?
- AP –> no
- graded potential –> yes! spatial and temporal
- contractions –> yes! stimuli closer together do not allow muscle to relax fully
- 1 EPP = 1 contraction/twitch/power stroke
summation leading to unfused tetanus VS leading to complete tetanus
- unfused: stimuli are far enough apart to allow muscle to relax slightly between stimuli
- complete tetanus: muscle reaches steady tension = complete tetanus –> if muscle fatigues, tension decreases rapidly
isotonic contractions vs isometric contractions?
- what stays the same?
- 2 types of isotonic contractions
- what allows isometric contractions?
ISOTONIC contractions move loads!
- muscle force stays the same ish
- concentric action = shortening action
- eccentric action = lengthening action
ISOMETRIC contractions create force without movement –> load does NOT move –> tetanus below the force required to move load
- muscle length stays the same
- sarcomeres shorten while elastic elements (ie tendons) stretch, resulting in little change in overall length
- in an isometric contraction, sarcomeres lengthen/shorten, generating ______, but elastic elements ________, allowing muscle length to ________ _________
- in isotonic contractions, sarcomeres lengthen/shorten more, but because elastic elements are ________ _______, the muscles _______
- isometric –> sarcomeres shorten, generating force, but elastic elements stretch, allow muscle length to remain the same
- isotonic –> sarcomeres shorten more –> elastic elements are already stretched –> muscle shortens
bones and muscles around joints form ___A___ and _______
- what is a ____A______
- what forms ____A____ and what forms _____B_____
- form levers and fulcrums
- lever = rigid bar that pivots around a point called a fulcrum
- bones = lever
- flexible joints = fulcrums
human forearms = lever
- what is the fulcrum?
- what is the lever?
- where is the applied force?
- where is the load?
- fulcrum = elbow joint
- lever = forearm bone
- applied force = bicep attached to forearm bone
- load = in your hand/ gravity acting on mass of forearm and hand
to lift up a 2 kg book using your bicep (bicep curl), is more than 2kg of bicep force needed?
- what is advantageous of the human body?
- yes! 6kg!
- small movement of the biceps becomes a much larger movement of the hand! –> biceps contracts and shortens 1 cm, hand moves upward 5 cm!
Golgi tendon organs (GTO)
- where are they found (2)
- composed of what?
- found in junction of tendons and muscle fibers (so between tendons and muscle fibers)
- composed of free nerve endings that wind between collagen fibers inside connective tissue capsule
what is the role of golgi tendon organs?
- how does it do it? (4)
- goal = prevents too much contraction of muscle
- when a muscle contracts, its tendons act as a series elastic element during isometric phase –> activates GTO –> GTO sends sensory info to CNS/spinal cord –> spinal cord sends back signal to muscle to decrease muscle contraction
- what are muscle spindles?
- muscle spindle capsule encloses a group of what? known as what?
- innervation of muscle spindles from what neurons?
- muscle spindles = stretch receptors that encode signals about muscle length and changes in muscle length
- group of small muscle fibers known as intrafusal fibers
- from gamma moror neurons
what is alpha-gamma coactivation?
- def
- 3 steps
- result
- simultaneous activation of alpha and gamma motor neurons
1. alpha motor neurons fire, innervates extrafusal muscle fibers = muscle shortens, tension released
2. gamma motor neurons fire, intrafusal fibers contract, maintains stretch —> sends info to spinal cord/CNS
3. spinal cords sends back signal to contract extrafusal fibers but not TOO much stretching - result: spindle remains active
what is the role of muscle spindles vs golgi tendon organs?
- muscle spindles: prevents too much stretching
- GTO: prevents too much contraction
why do intrafusal fibers contract if they cannot generate force?
because they keep muscle fibers sensitive to stretch! to prevent too much stretching!
3 different ways to classify smooth muscles
1. by location (6)
2. by contraction pattern: 2 types + examples
3. by their communication with neighboring cells (2 types)
- vascular, gastrointestinal, urinary, respiratory, reproductive, ocular
- phasic smooth muscles –> alternate contraction and relaxation (mostly GI tract)
VS tonic smooth muscles –> always a bit of contraction (esophageal and urinary bladder sphincters + blood vessels) - single-unit smooth muscle or unitary smooth muscle or visceral smooth musche –> around empty cavities + contract together! function as 1 unit through gap junctions!
VS multiunit smooth muscles –> each muscle cell receive different neuron signals
do multi-unit smooth muscle cells have gap junctions?
- how are they stimulated?
- no!
- stimulated independently through neurotransmitters released by caricosities
smooth vs skeletal vs heart muscle –> which has fastest/slowest muscle twitch duration?
- how fast depends on (2)
- skeletal = fastest (less than 0.5sec)
- cardiac = middle (1 sec)
- smooth = really slow! (5 sec) –> slow contraction AND slow relaxation!
1. ATPase (actin-myosin dissociation)
2. amount of Ca2+ –> how fast it can go in/out
smooth muscles lack _________
ACTIN:
- ratio with myosin?
- associated with _______ but not _________
MYOSIN:
- filaments are _________
- myosin heads along what?
SR:
- amount of SR _______ and is more/less organized
- no _________ but has _________
- sarcomeres!
ACTIN: - 10-15 actin for 1 myosin (vs 6 actin per myosin for skeletal)
- with tropomyosin (blocks myosin binding site) but not troponin
MYOSIN: - longer!
- entire surface of filament covered with myosin heads
SR: - amount varies and is less organized
- no t-tubules but has caveolae (indentation in plasma membrane, has lots of Ca2+)
how do smooth muscles hold integrity if no sarcomeres?
have an extensive cytoskeleton –> intermediate filaments and dense bodies
do smooth muscles have a z-line? where do actins attach?
no z-line
- actins attach to dense bodies which links to plasma membrane
explain contraction of smooth muscle (5 steps)
- Autonomic nervous system –> AP opens Ca2+ channels on plasma membrane
- increase in cytosolic Ca2+ initiates contraction (Ca2+ comes from SR and extracellular fluid)
- Ca2+ binds calmodulin
- Ca2+-calmodulin activates myosin light chain kinase (MLCK) –> MLCK phosphorylates Myosin light chain which enhances myosin ATPase activity (myosin become active)
- phosphorylated MLC can remove tropomyosin –> myosin can bind actin and induce contraction = increase muscle tension
Explain relaxation in smooth muscle (10)
- free Ca2+ in cytolsol decreases when Ca2+ is pumped out of cell or back into SR
- Ca2+ unbinds from calmodulin. MLCK activity decreases
- myosin phosphatase/myosin light chain phosphorylase (MLCP) removes phosphate from myosin light chains, which decreases myosin ATPase activity –> dephosphorylated myosin may remain attached to actin for a period of time during latch state
- less myosin ATPase activity results in decreased muscle tension = relaxation
what controls Ca2+ sensivity in smooth muscle contraction?
- low vs high = sensitize or desensitizes myosin?
myosin light chain phosphorylase (MLCP) (same as phosphatase)
- low phosphatase activity sensitizes myosin –> needs less calcium to generate force
- high phosphatase activity desensitizes myosin –> needs more calcium to generate force
what is calmodulin?
a calcium binding protein that binds to calcium and activates myosin light chain kinase
4 channels to release sarcoplasmic Ca2+
- ryanodine receptor (RyR) calcium release channel
- IP3 - receptor channel
- calcium-induced calcium release (CICR) –> Ca from outside cell can induce Ca release from SR
- store-operated Ca2+ channels (on plasma membrane)
electromechanical coupling vs pharmacomechanical coupling
- electromechanical coupling –> contraction caused by electrical signaling
- pharmacomechanical coupling –> contraction caused by chemical signaling
3 ways for calcium to enter cell membrane (from extracellular fluid)
- voltage-gated Ca2+ channels (opens when AP from ANS comes)
- ligand gated Ca2+ channels (opens when hormones come) or receptor-operated calcium channels (ROCC)
- stretch activated calcium channels –> open when pressure or other force distorts cell membrane (ie blood vessel stretching) –> myogenic contraction
what are 2 types of unstable membrane potentials?
- slow wave potential –> not stable resting membrane potential –> once it reaches threshold, activates AP
- pacemakker potentials: unstable but will always reach threshold and induce AP (mostly in cardiac muscle)
where does the extra Ca2+ go after contraction?
- consequence? (3 steps)
- goes back to extracellular fluid (and not SR)
- SO we need to replenish depleted Ca2+ stores of SR –> use store-operated Ca2+ channels that are on plasma membrane –> will increase Ca2+ entry from ECF and replenish SR
- 2 similarities between cardiac and skeletal muscle (shape/structure)
- 3 differences between cardiac and skeletal muscle
SIMILARITIES:
- striated
- sarcomere structure
DIFFERENCES:
- cardiac muscle fibers are shorter
- cardiac muscles may be branched
- cardiac muscle have single nucleus
- 3 similarities btw cardiac and smooth muscles (function/properties)
- 1 difference
SIMILARITIES:
- electrically linked to one another (just like single unit smooth muscles –> gap junctions!
- some exhibit pacemaker potentials
- under sympathetic and parasympathetic control as well as hormone control
DIFFERENCES:
- cardiac muscle: gap junctions in intercalated disks!
desmosome vs gap junction vs intercalated disk?
- desmosome = connecting junction –> links 2 cells together, allows some flow of (nutrients/water?) between cells
- gap junction: forms channel between 2 muscle cells to electrical signal can quickly move between cells
- intercalated disk –> junction between 2 cells –> contains desmosome and gap junctions!
excitation-contraction coupling in cardiac contractile cells (7 steps)
- AP in cardiac contractile cell –> travels down T-tubules
- entry of small amount of Ca2+ from ECF through L-type Ca2+ channels –> induces release of large amount of Ca2+ from SR through ryanodine Ca2+ release channels
- increase cytosolic Ca2+
- troponin-tropomyosin complex in thin filaments pulled aside
- cross-bridge cycling between thick and thin filaments
- thin filaments slide inwards between thick filaments
- contraction
