Muscle Tissue

1
Muscle Tissue

• Chapter 11
• Part 2

2
Excitation (steps 1 and 2)

• Nerve signal opens voltage-gated calcium
  channels. Calcium stimulates release of synaptic
  vesicles containing ACh ACh release into
  synaptic cleft.

3
Excitation (steps 3 and 4)
ACh binds to receptor opens ______________________
__ changes RMP from _________________________
4
Excitation (step 5)
Voltage change opens nearby voltage-gated
channels producing an action potential
5
Excitation-Contraction Coupling (steps 6 and 7)

• Action potential spreading over sarcolemma
  enters ________________ -- channels open in T
  tubules causing ____________ to open in SR

6
Excitation-Contraction Coupling (steps 8 and 9)

• Calcium released by SR binds to _____________
• Troponin-tropomyosin complex changes shape and
  __________________________________

7
Contraction (steps 10 and 11)

• Myosin ATPase in myosin head hydrolyzes an ATP
  molecule, activating the head and cocking it in
  an extended position
• It binds to actin active site forming a
  _____________

8
Contraction (steps 12 and 13)

• __________________ myosin head releasesADP
  and phosphate it bends pulling the thin
  filament past the thick
• With more ATP, the myosin head attaches to a new
  active site
• Bound heads prevent slippage
• thin and thick filaments do not become shorter,
  just slide past each other (______________________
  ____)

Sliding Filament Theory
9
Relaxation (steps 14 and 15)

• Nerve stimulation ceases and
  ____________________ removes ACh from receptors.
  Stimulation of the muscle cell ceases.

10
Relaxation (step 16)

• __________________________________
  __________________________________
• ATP is needed for muscle relaxation as well as
  muscle contraction

11
Relaxation (steps 17 and 18)

• Calcium loss from sarcoplasm moves
  troponin-tropomyosin complex over active sites
• Muscle fiber returns to its resting length

12
________________________

• _________________________________________
• Deteriorating sarcoplasmic reticulum releases
  calcium
• Calcium activates myosin-actin cross-bridging and
  muscle contracts, but can not relax.
• ___________________________________ ATP
  production stops at death
• Fibers remain contracted until myofilaments decay

Cross Bridges
13
Length-Tension Relationship

• _______________________ _______________________
  _______________________
• Overly contracted (weak contraction results)
• thick filaments too close to Z discs and cant
  slide
• Too stretched (weak contraction results)
• little overlap of thin and thick not many cross
  bridges form
• Optimum resting length produces greatest force
  when muscle contracts
• cns maintains optimal length producing muscle
  tone or partial contraction

14
Muscle Twitch in Frog

• ____________________ ____________________
  ________________________________________
• a single brief stimulus produces a quick cycle of
  contraction and relaxation called a twitch
  (lasting less than 1/10 second)
• A single twitch contraction is not strong enough
  to do any useful work

15
Muscle Twitch

• Phases twitch contraction
• ________________________ (2 msec delay)
• no visible contraction occurs
• elastic components are being stretched
• contraction phase
• ___________________________________
• ________________________________
• loss of tension and return to resting length as
  calcium returns to SR

16
Contraction Strength of Twitches

• Threshold stimuli produces twitches
• _________________________________

17
Recruitment and Stimulus Intensity

• Stimulating the muscle with higher voltage
  produces stronger contractions
• More motor units are recruited
• multiple motor unit summation
• lift a glass of milk versus a whole gallon of milk

18
Twitch and Treppe Contractions

• Muscle stimulation
• low frequency (up to 10 stimuli/sec)
• each stimulus produces an identical twitch
  response
• moderate frequency (between 10-20 stimuli/sec)
• each twitch has time to recover but develops more
  tension than the one before (treppe phenomenon)
• __________________________________________
• heat of tissue increases myosin ATPase efficiency

19
Incomplete and Complete Tetanus

• Higher frequency stimulation (20-40
  stimuli/second) generates gradually more strength
  of contraction
• each stimuli arrives before last one recovers
• temporal summation or wave summation
• incomplete tetanus sustained fluttering
  contractions
• Maximum frequency stimulation (40-50
  stimuli/second)
• muscle has no time to relax at all
• twitches fuse into smooth, prolonged contraction
  called complete tetanus
• rarely occurs in the body

20
Isometric and Isotonic Contractions

• _________________________________________
• develops tension without changing length
• important in postural muscle function and
  antagonistic muscle joint stabilization
• _________________________________________
• tension while shortening or lengthening

21
ATP Sources

• Muscle contraction depends on ATP
• ATP synthesis
• ______________________ (ATP production limited)
• ______________________, produces toxic lactic
  acid
• _________________________ (more ATP produced)
• requires continuous oxygen supply, produces H2O
  and CO2

22
Immediate Energy Needs

• Short, intense exercise (100 m dash)
• oxygen supplied by ________________
• _______________ system
• myokinase transfers Pi groups to ATP
• creatine kinase transfers Pi groups from creatine
  phosphate to make ATP
• Result is power for a 1 minute brisk walk or 6
  seconds of sprinting

23
Short-Term Energy Needs

• ________________________ system takes over
• produces ATP for 30-40 seconds of maximum
  activity
• playing basketball or running around baseball
  diamonds
• muscles obtain glucose from blood and stored
  glycogen

24
Long-Term Energy Needs

• Aerobic respiration (prolonged exercise)
• Produces _____________ATPs/glucose molecule

25
Fatigue

• Progressive weakness from use
• ATP synthesis declines as glycogen is consumed
• sodium-potassium pumps fail to maintain membrane
  potential and excitability
• lactic acid inhibits enzyme function
• extracellular K accumulates hyperpolarizes the
  cell
• motor nerve fibers use up their acetylcholine

26
______________________

• Heavy breathing after strenuous exercise
• excess post-exercise oxygen consumption (EPOC)
• Purposes for extra oxygen
• __________________________ (myoglobin, blood
  hemoglobin)
• replenishes the phosphagen system
• ____________________________________

27
Slow- and Fast-Twitch Fibers

• __________________________________
• more mitochondria, myoglobin and capillaries
• adapted for aerobic respiration and ____________
  to fatigue
• soleus and postural muscles of the back
  (100msec/twitch)

28
Slow and Fast-Twitch Fibers

• Fast glycolytic, fast-twitch fibers
• rich in enzymes for phosphagen and
  glycogen-lactic acid systems
• __________________________________________________
  ____________________ (7.5 msec/twitch)
• extraocular eye muscles, gastrocnemius and biceps
  brachii
• Proportions genetically determined

29
Strength and Conditioning

• _______________________________
• muscle size and fascicle arrangement
• size of motor units and motor unit recruitment
• length of muscle at start of contraction
• Resistance training (weight lifting)
• stimulates cell enlargement (more myofilaments)
• Endurance training (aerobic exercise)
• ______________________________________
  ______________________________________

30
Cardiac Muscle

• __________________________________
• Linked by intercalated discs
• electrical gap junctions allow cells stimulate
  neighboring cells
• mechanical junctions hold cells together
• __________________________________________________
  ______________________

31
Cardiac Muscle

• _______________ due to pacemaker cells
• Uses aerobic respiration almost exclusively
• __________________________________________________
  ______________________
• vulnerable to interruptions in oxygen supply

32
Smooth Muscle

• __________________________
• no striations, sarcomeres or Z discs
• SR is scanty and has no T tubules
• calcium for contraction comes from extracellular
  fluid
• If present, nerve supply is autonomic
• releases either ACh or norepinephrine

33
Types of Smooth Muscle

• ________________________________
• largest arteries, iris, pulmonary air passages,
  arrector pili muscles
• terminal nerve branches synapse on myocytes
• independent contraction

34
Types of Smooth Muscle

• ______________________________
• most blood vessels and viscera as circular and
  longitudinal muscle layers
• large number of cells contract as a unit

35
Stimulation of Smooth Muscle

• Involuntary and contracts without nerve
  stimulation
• _______________________________________
• pacemaker cells in GI tract are autorhythmic

36
Features of Contraction and Relaxation

• Calcium trigger is extracellular
• Ca channels open ? voltage, hormones,
  neurotransmitters or cell stretching
• _____________________ _____________________
• shortens the entire cell in a twisting fashion

37
Features of Contraction and Relaxation

• Contraction and relaxation very slow in
  comparison
• slow myosin ATPase enzyme and slow pumps that
  remove Ca2
• Uses 10-300 times less ATP to maintain the same
  tension
• latch-bridge mechanism maintains tetanus (muscle
  tone)
• keeps arteries in state of partial contraction
  (vasomotor tone)