Skeletal Muscle Contraction

Question 1

Epimysium

Muscle

Perimysium

Answer 1

• Connective tissue surrounding entire muscle
  
  • connected to ends of the muscle, bones, tendons(defines a typical muscle )
• Made up of multiple fascicles
• Connective tissue surrounding individual fascicle
  
  • thinner then the epimysium and visible with the naked eye

Question 2

Fascicle

Endomysium

Sacrolemma

Answer 2

• A bundle of myofibers
• Delicate connective tissue around each myofiber
  
  • encloses the tiney myofibers in each fascicle
  • created from multinucleated muscle cells
• (plasmalemma) cell membrane of muscle fiber

Question 3

Myofiber

Myofibirl

Myofilament

Answer 3

• (muscle cell)individual multinucleated muscle cell
• A chain of sacrcomeres within a myofiber
• Actin and myosin filaments that make up a sacromere

Question 4

Sacrolemma

Answer 4

• =Plasmalemma
• T-tubules
  
  • invaginations of sarcolemma
  • lie close to cisternae of sacrcoplasmic reticulum
  • fom triads with cisternae
    
    • t-tubule plus two cisternae
    • two of these traids per sarcomere
  • Two per sarcomere
• Sarcoplasmic reticulum
  
  • =endoplasmic reticulum
• Sarcomeres

Question 5

Sarcomere binding

Z lines

I bands

A bands

H bands

Answer 5

Z lines

• Anchor actin filaments
• located at each end of a sarcomere

I bands

• Composed entirely of actin
• width changes during contraction

A bands:

• composed of actin and myosin
• width does not change during contraction

H bands

• Composed entirely of myosin
• width chagnes during contraction
• band disappears completely during maximum contraction( replaced by the M line)

Question 6

Sarcomeric arrangement

Answer 6

• sarcomeres align to produce banding pattern charecteristic of striated muscle
• nuclei of skeletal muscle are pushed to the periphery of the muscle

Question 7

Sliding filament mechanism events

Answer 7

• Arrival of action potential at terminal end of nerve fiber
• Opening of voltage gated calcium channels on nerve fiber ending
• Release of neurotransmitter(Ach) from synaptic vesicles into synaptic cleft
• Opening of ligand gated sodium channels of sarcolemma
• Generation of action potential on sarcolemma
• voltage gated channels on T tubuels(DHP-dihydropyridine-channels) interact with ryanodine receptors on SR membrane
  
  • DHP do not allow calcium to pass across the membrane , thier function is to function with ryanodine
• Opening of ryanodine-sensitive calcium ion release channels
• Increase in calcium ion concentration in cytosol
• activation of sliding filament mechanism
• Release calcium ions bind to troponin
• Tropomyosin uncovers myosin binding sites on actin
• ATPase heads of myosin molecuels split ATP and bind to actin
• stored energy in myosin head causes deformtion such that thick and thin filaments slide past one another
• A second ATP binds to myosin and causes it to release actin(process repeated over and over)
• Contraction stops when ATP dependent calcium pump sequesters calcium ions back into SR

Question 8

Skeletal muscle contraction

Answer 8

Question 9

Calsequetrin

Answer 9

• help return calcium back to the cisternae and moniter the concetration in this cavity

Question 10

Dihydropyridine(DHP) receptors

Answer 10

• Voltage sensitive L-type calcium channels arranged in quadruplets
• Located on the sarcolemma T-tubules
• Cause a conformational change in the ryanodine receptors
• A minute amount of calcium flows into the cytosol via these channels

Question 11

Ryanodine receptors(RyRs or Ca2+ release channels)

Answer 11

• Located on the cisternae of the sacrboplasmic reticulum
• open in response to conformaional change in DHP receptors
• Allow calcium into the cytosol from the SR
• SERCA* uses ATP to pump calcium back into the SR
  
  • Sarcoplasmic Reticulum Calcium ATPase
• Calsequestrin in the SR maintains an optimum calcium concentration gradient t ofacilitate return of calcium to SR

Question 12

Actin filament

Answer 12

• troponin complex has three binding sites, one is or actin adn oen for troponin

Question 13

Preload

Answer 13

• Definition:load on a muscle in the relaxed state(before it contracts)
• Results
  
  • Preload stretches hte muscle which stretches the sacromere
  • Preload generates passive tnesion in the muscle
  • Muscle resists the tension in the muscle
  • muscle resists he tension applie to it
  • Force of the resistance is measured as passive tension
  • The greater the preload,greater the passive tension in the muscle

Question 14

Afterload

Answer 14

Definition:load the muscle works against

Results:

• if the muscle gernates more force than the afterload, an isotonic contraction occurs
• If the muscle generation less force than the afterload , an isometric contraction occurs
• Isotonic contraction-same tone,length of hte muscle chagnes two types
  
  • concentric-muscle shortens because it generates more force in the afterload
• Isometric-same length generates same force but lenght doesn’t chagne

Question 15

Cross Bridge cycling

Answer 15

• Cross bridge cycling starts when free calcium is available and attaches to troponin
• contraction is the continuous cycling of cross bridge
• a top is not required to form the cross bridge linking to actin but is required to break the link with actin

Question 16

Length tnesion diagram explain points

Answer 16

• A: actin filaments overlap
  
  • Sarcomere length < 1.65um
• B:Actin filaments touch
  
  • sarcomere length=1.65
  • Tension=maximum
• C.Actin filament has overlapped all the cross bridges
  
  • Sarcomere length=2.2um
  • tension=maximum
• D.Actin filament pulledo ut all the way with no overlap
  
  • Sarcomere length=3.5um

Question 17

Relation of muscle length to tension

Answer 17

• Resting length of muscle is a sarcomere length of 2.0 um
• Increase in tension(active) decreases as muscle is stretched beyond its normal length
  
  • Sarcomere length>2.2um

Question 18

Where is ATP required ofr muscle contraction?

Answer 18

• Most is used for sliding filament mechanism
• Pumping calcium ions from sarcoplasm back into sarcoplasmi reticulum
• Pumping sodium and potassium ions through the sarcolemma to reestablish resting potential

Question 19

Concentration of ATP in muscle fiber

Answer 19

• about 4 mmol
• Enough to maintain contraction for 1-2 seconds

Question 20

Phosphocreatine

Answer 20

• Releases energy rapidly
• reconsitutes ATP
• ATP+ phosphocreatine provdies enough energy for 5-8 seconds of contraction

Question 21

Glycolysis

Answer 21

• Lactic acid build up
• Can sustain contraction for 1 minute

Question 22

How much energy does oxidative metabolism provide for rephosphorylation?

Answer 22

• Provdies more than 95% of all energy needed for long term contraction

Question 23

Isometric

Answer 23

• An isometric contraction occurs when there is an increase in tension but not in length

Question 24

Isotonic

Answer 24

• Muscle length chagnes in an isotonic contraction
  
  • Eccentric:
    
    • An eccentric contraction occurs when the muscle lengthens
  • Concnetric
    
    • A concnetric contraction occurs when the muscle shortens

Question 25

Myofiber type

Answer 25

* Myofiber type is detrmined by the innervating neuron * Fiber types are classified mainly on endurance(resistance to fatigue) and speed of contraction * Types: * Dark,slow fibers(red fibers) * Light,fast fibers(white fibers) * Can change within classes * can't change from one type to another * After birth , then umber of myofibers cannot be increased * number of myofibrils can be increased;thereofre * mass of a myofiber and a muscle may be incrased * Lost muscle tissue will be replaced by scar tissue(fibrous connective tissue) * increase mass by increasing nubmer of myofbirils

Question 26

Fiber type:fast(white)

Answer 26

* Fast twitch fibers contract rapidly but have less endurance * Charecteristics include: * Fewer mitochondria * Primarily use anearboic respiration resutling in a buildup of pyruvic acid and lactic acids * Little myoglobin * Similiar to hemoglobin except its a monomer rather then a dimer and binds oxygen * Larger concetration of ATPase

Question 27

Fiber types:slow(red)

Answer 27

* Slow twtich fibers contract more slowly but have more endurance * charecteristics include: * more mitochondria * primarily use aerobic respiration * more myoglobin * smaller concentration of ATPase * most muclse are made up a combination of both * Gastrocnemuis-mostly made up of fast * Soleus-muscle made up slow

Question 28

motor units

Answer 28

* A single nerve cell(neuron) may innervate from a few to several hundred myofibers * A neuron and the myofibers it innervates consittue a motor unit * when a neuron fires, all the myofibers in the motor unti contract * all or none really refers to a motor unit * When an alpha motor neuron fires , its all or none and same for the motor unit which is all or none and can contract

Question 29

Summation

Answer 29

* Electrical events occur faster than mechanical events: * An additional spike can occur before the previous calcium ions have been returned to the SR * This increase the toal amount of calcium ion in the cytosol and increases the rate of cycling between the myosin and actin corss bridges * This incrases muscle tnesion * EAch additional spike adds to the effects of the previous spikes * Mechanical events refer to the actin and myosin heads sliding

Question 30

Tetany

Answer 30

* If the frequency of spikes is fast enough , there is no time for relaxation between spikes * The muscle remains at maximal contraction

Question 31

Muscle as levers

Answer 31

* Machines transmit forces from one place to another * machiens invovle two forces: * Forces applied to the machine(in-force(fi) or effort) * Force derived form the machine(out-force(Fo) or resistance) * Bone-muscle systems often transmit forces by levers * A lever is a rigid body(bone) that rotats around a pivot(joint) or fulcrum * Distance from the in force(muscle attachement) to the fulcrum is the in lever arm * The distance form the out force to the fulcrum is hte otu lever arm

Question 32

Explain the below Diagram

Answer 32

* Bone Muscle systems as levers: * Force X its lever arm is a moment * Thus, a functional lever must have at least two moments: * Mi=FiLi(M=moment;F=force;L=lever arm) * Mo=FoLo * at equiliubrm FiLi=FoLo * This type of lever system is really good at increasing speed * takes a small contraction at the joint to increase our distance at the distal end

Question 33

What types of levers are there and how are they classified?

Answer 33

* Classified according to hte position of the fulcrum in relation to the in-force and the out-force * First class; fulcrum in the middle * Ex-raising chin using sternocleidomastoids or similar muscles(fulcrum=atlas/axis complex) * In-force and out force move in opposite directions * Second class; resistance(out force) is in the middle * Ex:raising the body on the ball of the foot * Fulcrum-ball of foot * both in and out ofces are on the same side of the fulcrum * Third class;effort(in force) is in the middle * Ex.lifiting a wieght in the palm of your hand * Both in and out forces are on the same side of the fulcrm * Both forces move in same direction