Muscle - Lectures 10-11-12 Flashcards
(67 cards)
1
Q
what are the 3 types of muscle
- 2 similarities
A
- Skeletal muscle
- cardiac muscle
- smooth muscle
SIMILARITIES:
- excitability! membrane potential can be changed
- all use actin and myosin –> 2 major proteins responsible for contractability
2
Q
describe each type of skeletal muscles:
- size?
- pattern/striation?
- how many nucleus?
- intercalated disk?
- T-tubules?
A
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
3
Q
how can there be multiple nuclei in one muscle cell?
A
stem cells during embryonic development form myoblasts (1 nucleus per cell) –> merge together to form myocytes/muscle fibers = many nuclei per cell
4
Q
what are antagonistic muscles?
- what are the 2 movements?
A
- move bones in opposite directions
- flexion moves bones closer together (arm curl)
- extension moves bones away from each other (push-up)
5
Q
- 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 _______
A
- 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
6
Q
what are the 3 layers of connective tissue that surround muscle vs fascicles vs myocytes?
- what does the connective tissue provide? (3)
A
- myocytes surrounded by endomysium
- fascicles surrounded by perimysium
- entire muscle surrounded by epimysium
- fluid, blood, nerves
7
Q
Z-line vs M-line vs A band vs I-band vs H-zone
- dark or light?
A
- 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
8
Q
what is a sarcomere?
A
functional unit of muscle
9
Q
muscle fiber anatomy:
- sarcolemma?
- sarcoplasm?
- sarcoplasmic reticulum? describe structure + function?
A
- sarcolemma: cell membrane
- sarcoplasm: cytoplasm
- sarcoplasmic reticulum: endoplasmic reticulum: longitudinal tubes with enlarged ends called terminal cisternae
- concentrates and sequesters Ca2+
10
Q
What are t-tubules?
- what forms a triad?
- function?
A
- 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
11
Q
muscle fibers also contain
1. all sarcomeres linked together
2. energy source
3. powerhouse
A
- myofibrils
- glycogen granules
- mitochondria
12
Q
- thin filament = which protein?
- thick filament = which protein? heavy vs light chains
- regulatory proteins (2)
- accessory proteins (2)
- crossbridges
A
- 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
13
Q
myosin heads contain 3 parts
A
- actin binding site
- ATP or ADP/P+ binding site
- ATPase enzyme –> break down ATP into ADP + P
14
Q
what are the 3 subunits of troponin?
- when troponin binds with ____ –> 2 things happen
- repeated as long as what?
A
- 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
15
Q
what is the important component of actin?
- actins are all linked together by _______
A
- 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)
16
Q
when myosin binds with actin, myosin heads move towards _______ –> sarcomere becomes longer/shorter
- A-band, H-zone, I band stay the same lengths?
A
- M-line –> sarcomere becomes shorter
- A band stays same
- I band and H-zone become shorter
17
Q
- titan spans distance from _______ to the neighbouring ________
- nebulin attaches to a _______ but does not extend to the ________
- role of titn?
A
- 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
18
Q
- muscle tension = what?
- load = what?
- contraction = what?
- relaxation = what?
A
- muscle tension = force created by muscle
- load = weight or force opposing contraction
- contraction = creation of tension in muscle
- relaxation = release of tension
19
Q
5 major steps leading up to skeletal muscle contraction
A
- events at the neuromuscular junction
- excitation-contraction (E-C) coupling
- Ca2+ signal
- contraction-relaxation cycle
- muscle twitch + sliding filament theory
20
Q
do length or thick and thin filament change during contraction? –> what is this theory called?
A
- no!
- sliding filament theory of contraction –> overlapping actin and myosin fibrils
- fibrils are fixed length
- slide past each other in energy-dependant process
21
Q
- what is a powerstroke?
- what happens at the end of a powerstroke (2)
A
- 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
22
Q
rigor state vs rigor mortis
A
- 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
23
Q
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!
A
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
24
Q
explain steps from neuron to contraction of muscle to relaxation (10 steps)
A
- 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
25
Timing of Excitation-Contraction coupling --> 3 steps
1. motor neuron AP --> releases ACh --> binds Nm --> induces 2
2. muscle fiber action potential --> Ca2+ released --> induces 3
3. development of tension during 1 muscle twitch (latent period + contraction phase + relaxation phase)
26
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)
27
1. anaerobic glycolysis produces (2)
- quick or slow?
- oxygen required?
- quantity of energy released?
2. aerobic respiration (biochemistry pathways (2))
- quick or slow?
- oxygen required?
- quantity of energy released?
1. anaerobic glycolysis produces lactate and acid
- quick!
- no oxygen
- small amount of E released
2. aerobic respiration (TCA cycle + ETC)
- slow
- oxygen required
- large amount of E released
28
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)
29
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
30
oxidative fibers have more _________ --> why?
- myoglobin!
- because myoglobin binds oxygen in muscle so it is readily available for aerobic processes
31
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
32
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!
33
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
34
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)
35
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
36
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
37
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
38
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
39
- 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
40
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
41
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
42
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!
43
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
44
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
45
- 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
46
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
47
what is the role of muscle spindles vs golgi tendon organs?
- muscle spindles: prevents too much stretching
- GTO: prevents too much contraction
48
why do intrafusal fibers contract if they cannot generate force?
because they keep muscle fibers sensitive to stretch! to prevent too much stretching!
49
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)
1. vascular, gastrointestinal, urinary, respiratory, reproductive, ocular
2. 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)
3. 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
50
do multi-unit smooth muscle cells have gap junctions?
- how are they stimulated?
- no!
- stimulated independently through neurotransmitters released by caricosities
51
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
52
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+)
53
how do smooth muscles hold integrity if no sarcomeres?
have an extensive cytoskeleton --> intermediate filaments and dense bodies
54
do smooth muscles have a z-line? where do actins attach?
no z-line
- actins attach to dense bodies which links to plasma membrane
55
explain contraction of smooth muscle (5 steps)
1. Autonomic nervous system --> AP opens Ca2+ channels on plasma membrane
2. increase in cytosolic Ca2+ initiates contraction (Ca2+ comes from SR and extracellular fluid)
3. Ca2+ binds calmodulin
4. Ca2+-calmodulin activates myosin light chain kinase (MLCK) --> MLCK phosphorylates Myosin light chain which enhances myosin ATPase activity (myosin become active)
5. phosphorylated MLC can remove tropomyosin --> myosin can bind actin and induce contraction = increase muscle tension
56
Explain relaxation in smooth muscle (10)
1. free Ca2+ in cytolsol decreases when Ca2+ is pumped out of cell or back into SR
2. Ca2+ unbinds from calmodulin. MLCK activity decreases
3. 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
5. less myosin ATPase activity results in decreased muscle tension = relaxation
57
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
58
what is calmodulin?
a calcium binding protein that binds to calcium and activates myosin light chain kinase
59
4 channels to release sarcoplasmic Ca2+
1. ryanodine receptor (RyR) calcium release channel
2. IP3 - receptor channel
3. calcium-induced calcium release (CICR) --> Ca from outside cell can induce Ca release from SR
4. store-operated Ca2+ channels (on plasma membrane)
60
electromechanical coupling vs pharmacomechanical coupling
- electromechanical coupling --> contraction caused by electrical signaling
- pharmacomechanical coupling --> contraction caused by chemical signaling
61
3 ways for calcium to enter cell membrane (from extracellular fluid)
1. voltage-gated Ca2+ channels (opens when AP from ANS comes)
2. ligand gated Ca2+ channels (opens when hormones come) or receptor-operated calcium channels (ROCC)
3. stretch activated calcium channels --> open when pressure or other force distorts cell membrane (ie blood vessel stretching) --> myogenic contraction
62
what are 2 types of unstable membrane potentials?
1. slow wave potential --> not stable resting membrane potential --> once it reaches threshold, activates AP
2. pacemakker potentials: unstable but will always reach threshold and induce AP (mostly in cardiac muscle)
63
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
64
- 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
65
- 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!
66
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!
67
excitation-contraction coupling in cardiac contractile cells (7 steps)
1. AP in cardiac contractile cell --> travels down T-tubules
2. 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
3. increase cytosolic Ca2+
4. troponin-tropomyosin complex in thin filaments pulled aside
5. cross-bridge cycling between thick and thin filaments
6. thin filaments slide inwards between thick filaments
7. contraction
