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Bio 273 - Human Physiology > Unit 3 - Muscle > Flashcards

Unit 3 - Muscle Flashcards

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Biology 101 flashcards
1
Q

what are the functions of muscles?

A

to produce motion and force
- they can only contract and cannot expand
- generate heat and control body temp through homeostasis

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2
Q

what are the 3 main muslce types?

A

skeletal: attached to bones to control body movements, contract only in response to somatic motor neuron signals, striations, long cylinder cells with lots of nuclei
smooth: primary muscles of internal organs and tubes, influence the movement of materials through the body, no stations, each cell has its own nucleus
cardiac: found only in the heart and pump blood around the body, striations, each cell has its own nucleus but close contact with other cells for communication

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3
Q

what are the main characteristics of skeletal muscles?

A
  • responsible for positioning and movement of the skeleton/bones
  • attached to bones via tendons (composed of dense regular connective tissue with collagen, a cable-like protein fibre)
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4
Q

what is the structure of skeletal muscles?

A

sarcolemma: cell membrane of skeletal muscle
epimysium: outer connective tissue
fascicles: bundles of msucle tissues
Perimysium: cover fascicles, connect tissue sheath
muscle fibres: found within each fascicle
endomysium: innermost connective tissue sheath that covers muscle fibres
myofibrils: functional units of skeletal muscles, within each muscle fibre
cytosol: within the muscle fibres, contains glycogen granules for energy storage and mitochondria for ATP synthesis

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5
Q

what is the structure of a muscle fibre?

A
  • inner most of part of muscle
  • long, cylindrical cell
  • contain hundreds of nuclei on the surface of the fibre
    myofibrils: majority of the space is taken up by these, they are contractile and elastic protein bundles
    sacroplasmic reticulum: specialised endoplasmic reticulum, form net around
    t-tublues/tranverse tubules: associated with the SR, branching tubes, lumen is continuous with ECF that goes into the tubes and surrounds the cell, associated with the terminal cisternae (sequester Ca), creates the triad, the tubules allow for rapid action potential diffusion into the muscle fibres
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5
Q

what are the characteristics of the myofibril?

A
  • occupy most of the space in a muscle fibre
  • highly organized budles of contractile elastic proteins
  • contractile proteins: actin and myosin
  • regulatory protein: troponin and tropomyosin
  • accessory proteins: nebulin (aligns filaments of sarcomere) and titin (maintains spatial structure)
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5
Q

what are the 2 contractile protiens of myofibril?

A

myosin: motor protein consisting of two coil protein molecules that a head and tail region that are joined by a flexible hinge, around 250 myosin molecules create a thick filament where the heads are at the end and the tails are together

actin: subunits g-actin that polymerized to form chain/F-actin that create filamentous, two f-acting chains twins together to form a part of the the thin filament along side the regulatory protiens

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6
Q

what are the 3 regulatory proteins of the myofibril?

A

troponin: pull tropomyosin away to show the binding site
tropomyosin: regulate is the binding site is available or not, looks like a robe on the thin filament

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7
Q

define the sarcomere

A
  • creates the striated pattern seen on skeletal muscles, repeated banding pattern in the myofibril (organization of think and thin filaments)

z-line/disks: site of attachment for thin filaments (each acromere has 2 fo these)
I band/isotropic: region containing only thin filaments, light can pass through, z line is in the middle of the I band (each 1/2 of the I band is part of a different sacromere)
A band/anisotropic: contains thick and thin filaments that overlap at the outer edges of the A band, center is think filaments only
H zone: part of the A band, region containing only thick filaments, central region is a bit lighter than the outer edges
M line: site of attachment for the thick filaments, center of sacromere

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8
Q

what is the basis of muscle contraction?

A
  • tension is the force created by contracting muscle whereas the load is a weight or force that opposes the contraction
  • muscles shorten when they contract
  • Huxley and Neideigerka created the sliding filament theory of contraction
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9
Q

define the sliding filament theory of contraction

A
  • at rest, the ends of thick and thin filaments slightly overlap within each sarcomere
  • thick and thin filaments will slide past each other, with no change in their length when contracting
  • think will slide along the thick towards the M line of the sarcomere, bringing the Z disks closer to each other
  • each think filament is surrounded by 6 thin
    changes in length: sarcomere shortens, I band shortens, H zone shortens
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10
Q

what are the basic steps of muscle contraction?

A
  • excitation-contraction coupling is the series of electrical and mechanical events in a muscle that create the contraction
    1. ACh from neuromuscular junction binds to nicotinic receptor (Na and K)
    2. binding of ACh causes Na and K ions to move across the membrane
    3. Ach is removed by acetylcholinesterase
    4. influx of Na is more than efflex of K and causes depolarization called End plate potentail/ EPP
    5. EPP moves down the T-tubule system
    6. dihydropyrdine receptros/DHP are located within the tubules are change in chape when depolarization occurs
    7. DHP are mechanically linked to Ca channels of the SR called ryanodine receptors/RyR
    8. DHP changes RyR which results the opening of Ca channels of the SR, and Ca leaves
    9. increase in Ca in the cyotsol will bind to troponin on thin filament and will move tropomyson into the on positive
    10. moving of the tropomysoin reveals the actin binding site where myosin will bind and create the cross bridge cycle
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11
Q

what are the basic steps of the cross-bridge cycle?

A
  • myosin is the motor protein that is involved in converting ATP into movement
  • cross bridge is the activation of myosin on actin
  • start myosin in rigor state where the head is bounded to G-actin, no ATP/ADP is bound)
    1. active site on actin becomes open when Ca binds to troponin
    2. myosin head with bind to the actin and form the cross bridge
    3. hydrolysis of ATP occurs and inorganic phosphate is released
    4. release of P cause the head of myosin to pivot, 45 degrees, towards the centre of the sarcomere and this is called the power stroke (movement of mysoin head that is the basis for contraction)
    5. this action pulls the thin filament towards the M line, ADP is released after the P
    6. new molecule fo ATP will attache to myosin head causing the crossbridge to detach, shifting back to 90 degrees
    7. myosin head will hydrolysed the ATP and return the head into its cocked position, return to step 2
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12
Q

how do skeletal muscles relax?

A
  • this is caused from when Ca is pumped back into the SR through the Ca-ATpase
  • decrease in CA in cytosol causes tropinin and CA to unbin and switching tropomyosin to its off position to cover the actin binding site
  • myosin heads can no loner bind to action, cannot produce crossbridge to crease movement
  • elastic elements pull filaments back to relaxes positions when myosin unbinds
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13
Q

what are the basic things about msucle contraction with ATP

A
  • muscles convert biochemcail energy into mechaincal work
  • Ca controls muslce contractions and is removed from the cell by CaATPase
  • Na and K ions are pumped back into and out of the cell by using ATP and the NA/K pump
  • Myosin and actin interaction uses ATP
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14
Q

define ATP

A
  • main energy currency of the cell
  • muscle contraction requires a steady supply of ATP
  • energy from nutrients is transferred to create ATP (erobic or anaerobic)
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15
Q

what are the 3 ways that we produce ATP for our bodies?

A
  1. glycolysis: occurs in aerobic and anaerobic environments, provides a limited amount of ATP (2), generates unwanted metabolites when no oxygen is present (lactic acid), occurs in the cyotsol
  2. Oxidative metabolism: main way, requires oxygen, produces 15x more ATP per glusoce molecules, does not produce toxic end products, occurs in the mitochondria
  3. creatine phosphate: it is a high energy phosphate molecules, muscles have high concentration of this, provides a rapid source of energy for the muscles, easily doantes inorganic phosphate to ADP to create ATP, limited supply of ATP, used as a buffer over short time scales, reaction is: creatine phosphate + ADP = ATP + creatine, catalyzed by creatine kinase (CK)
16
Q

what are the two important time periods regarding muscle contraction?

A
  1. twitch: single contraction-relaxation cycle
  2. latent period: short delay between AP and beginning of the muscle tension (time it takes for excitation-contraction coupling to occur)
17
Q

what are the 3 general types of muscle fibres?

A
  1. slow twitch oxidative
  2. fast twitch oxidative-glycolysis
  3. fast twitch glycolytic
18
Q

define the differences in muscle fibres

A

oxidative or glycolytic: refers to the primary source of ATP
- oxidative are usually red due to myoblogin (oxygen carrier protein_
- oxidative are smaller and have numerous mitochondria and are better vascularized
Fast or slow: refers to the rate of myosin ATPase activity (what hydrolyzes ATP into ADP and Pi)
- fast can split ATP quickly and contract tension quicker
- result of the presence of different isoforms of myosin
duration of contraction:
- fast have a shorter twitch period (determined by removal of Ca from cytosol, higher rate of removal = quicker contract/relax)
- twitch period sets the speed of the which the muscle will then relax
short duration is useful for small rapid contraction
- long durations are good for sustained mvoemnets

19
Q

what is the ideal length of the fibre for muscle contraction?

A
  • depends on the msucle type
  • sarcomere length at the start of the contraction
    –> too little overlap: few cross-bridges, little force can be generated
    –> too much overlap: actin starts to interfere with each other, less force generated
    –> way too much overlap: thick filaments collide with Z disk, force rapidly decreases
20
Q

define summation

A
  • increase in force generated by a muscle
  • due to repeated stimulating from AP that occur before the muscle has fully relaxed
21
Q

define tetanus

A
  • state of the muscle when it reaches maximum force of contraction
    Incomplete/unfused: slow stimulation rate, fibre relaxes slight between stimuli
    Complete/fused: fast stimulation rate, fibre does not get any time to relax
22
Q

define the motor unit

A
  • basic unit of contraction in an intact skeletal muscle
  • composed of a group of muscle fibres (# will vary) and a somatic motor neuron that will control them
  • all muscles fibres are of the same skeletal muscle fibre type
  • an AP in a somatic motor neuron causes contractions of all muscle fibres in each motor unit
  • each motor unit operates in an all-or-none fashion
23
Q

how can the contraction of muscle cells vary?

A
  • changing the type of motor unit that is being activated
  • chanign the number of motor units that are active
  • slow oxidative have a low threshold for stimulation while fast have a high
24
Q

what are the 2 types of muscle contraction?

A
  • isotonic: creates force to move a load, load is constant and muscle length changes
  • isometric: creating force without movement, muscle length is constant, load is greater than the force applied (series elastic element = elastic fibers in the muscle that stretch during isometric contraction)
25
Q

where is smooth muscles found in the body?

A
  • walls of hollow organs and tubes
  • not attached to bones
  • ex. bladder sphincter, intestine, walls of blood vessels
26
Q

what are the 2 ways taht smooth muscles can be arranged?

A

Single unit:
- cells are coupled by gap junctions (important for cell-cell communication)
- each fibre does not need to be stimulated
- found on walls of internal organs

Mutli-unit:
- no gap junctions
- each individual fibre is separately innervated (individually acted on by their own branch of a neuron)

27
Q

what are the difference on smooth and skeletal muscles on a whole muscle level?

A
  • contracting smooth muscle withh cahnge its shape
  • smooth develops tension slowly
  • smooth can maintain contraction for much longer without fatiguing (some are contracted all the time)
28
Q

what are the difference on smooth and skeletal muscles on a cellular level?

A

Smooth:
- much smaller
- no straitions for smooth (actin and myosin are not arranged into sarcomeres)
- actin and myosin are arranged in long bundles diagonally periphery of the cell
- actin is anchored at cell membrane structure (dense bodies)
- no t-tubulues, not much for SR
- have specialised vesicles (caveolae) that sequester Ca and are meant for cell signalling
- force of contraction is related to mhow much Ca is released

29
Q

how does not having t-tubulues affect smooth muscles?

A

there is no direct coupling of teh AP to CA release from the SR through DHP. instead Ca eneters through the cell membrane causing Ca release from SR (Ca dependent CA release is how smooth muscle starts to contract)

30
Q

what are the difference on smooth and skeletal muscles on a molecular level?

A
  • less myosin per unit of actin in smooth
  • actin and myosin are longer and overlap more in smooth
  • myosin ATPase activity is much slower in smooth
  • mysoin heads are located along parts of myosin molecular in smooth
  • no troponin (open up binding site for mysoin = creating crossbridge)
31
Q

how does the specific properties of myosin contribute to how smooth muscles function?

A
  • contract more slwoly and for longer periods of time due to slower myosin ATpase activity
  • longer actin and myosin filamnets allow longer connection and allow smooth to be stretched yet still be able to contract
32
Q

what are the 3 kinds of channels Ca can enter in from in smooth?

A
  • voltage gated: open when cell depolarizes
  • stretch activated: open when membrane is stretched
  • chemically gated: open in response to hormones
33
Q

what are the roles of Ca in the contraction of smooth muscles?

A
  1. signal to initatie contraction (increase in cytosolic Ca)
  2. Ca binds to calmodulim (CaM)
  3. Ca/CaM activates the enxyme myosin light chain kinase (MLCK)

finished in notes here

34
Q

define flexor and extensor

A

a msucle that brings connected bones closer together when it contract and a muscle that moves bones away from each other when contracting

35
Q

define antagonisitc muscle groups

A

flexor-extensory pairs of muscles attached to the same set of bones

36
Q

what are the 2 states of the crossbridge?

A

low-force is for relaxed muscles and high-force is for contracting muscles

37
Q

define fatigue

A

reversible condition in which an exercising muscle can no longer generate or sustain expected power output

38
Q

define recruitment

A

addition of motor units to increase the force of contraction in a muscle

39
Q

define dystrophin

A

muscle protein that links actin to the cell membrane

Bio 273 - Human Physiology (4 decks)

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