Midterm 2 Flashcards
skeletal muscle features
striated and multi-nucleated
cells are organizes into long sections
cardiac muscle features
mono nucleated and striated
smooth muscle features
not striated but multi-nucleated, can contract in multiple directions
functions of muscles (6)
- produce skeletal movement
- maintain posture and body position
- support soft tissues
- guard entrances and exits
- maintain body temperature
- store nutrient reserves
muscle characteristics (4)
contractility, excitability, extensibility, and elasticity
contractility
ability to shorten with force, only creates pulling forces
excitability
capacity to respond to a stimulus
extensibility
ability to be stretched beyond normal resting length
elasticity
ability to return to normal resting length after being stretched due to PEC
organization of connective tissue in muscle
epimysium - surrounds entire muscle
perimysium - surround muscle fascicules, group of muscle fibres, functional unit of muscle
endomysium - surrounds muscle fibre, a group of myofibrils
myofibrils
- contain bundles of protein filaments called myofilaments
- two types of protein filaments: thin (actin) and thick (myosin)
- myofibrils actively shorten > contraction
sarcoplasmic reticulum
- tubular network that surrounds myofibril, have openings into sarcolemma forming a passageway from inside to outside
- store calcium ions needed for contraction cycle
sarcomere
- basic contractile unit of muscle fibre
- arrangement of thick and thin filaments creates a banded appearance
- have A band, I band, and H band, and M line and Z line
A band
region from end to end of myosin filaments
I band
region of only actin filaments, actin filaments end connect to form Z line
H band
region of only myosin filaments
M line
where the myosin ends are bound to each other
Z line
where actin filaments ends and bound to each other
titin
attached myosin to Z line or actin, helps with elasticity
tropomyosin
2-chained helical coil protein, that in complex with troponin, covers the active sites on actin
troponin
associated with tropomyosin, blocks the binding site on actin
myosin features
- can hinge
- head can connect to actin
- has ability to breakdown ATP to generate energy for head
myosin
multiple strands make up thick filament, has a long tail and head that can hinge
sliding filament mechanism
- during muscle contractions, actin and myosin filaments slide over each other
- creates tension (pulling force)
- muscles always pull, they never push
excitation-contraction coupling
- neuromuscular junction (NMJ) stimulates muscle to shorten, motor nerve that synapse on muscle, somatic nervous system
- sarcoplasmic reticulum, stores Ca2+
- troponin, tropomyosin undergo conformational change exposing active sites on actin allowing myosin heads to bind
- myosin crossbridge formation
steps of excitation-contraction coupling
- ACh is released into synaptic cleft, ACH can bind to receptors on motor end plate
- action potential travels along length of axon
- action potential reaches axon terminal causing release of ACh into synaptic cleft
- ACh molecules bind to receptors on surface of motor end plate, causing increased permeability to Na+
- Na+ rush into cells causing action potential propagation along sarcolemma, ACh is broken down by AChE
- action potential travels along sarcolemma until it reaches a T tubule, where it enters muscle fibre
- action potential in muscle fibre triggers release of Ca2+ from sarcoplasmic reticulum
- contraction cycle can begin
contraction cycle basics
binding site on actin exposed > myosin cross-bridge is formed > myosin head pivots > cross-bridge separates > myosin is reactivated
contraction cycle detailed
starts with arrival of Ca2+
- arrival of Ca2+ within zone of overlap in sarcomere
- Ca2+ binds to troponin, moves troponin-tropomyosin complex out of the way, exposing binding site on actin allowing interaction with energized myosin heads
- energize myosin heads binds to active sites forming cross-bridges
- myosin head pivots toward M line, called the power stroke, bound ADP and phosphate are released
- when another ATP binds to the myosin head, the cross-bridge is broken
- myosin head is energized when the free myosin head splits ATP into ADP+P, head is recocked
length of contraction depends on…
- period of stimulation at the NMJ (repeated stimulations)
- amount of calcium in the sarcoplasm
- availability of ATP
muscle relaxation details
- return to resting conditions after contraction
- two mechanisms:
- active transport of Ca2+ across sarcolemma into ECF
- active transport of Ca2+ into sarcoplasmic reticulum
muscle relaxation steps
- ACh is broken down by AChE, which ends the action potential generation
- sarcoplasmic reticulum reabsorbs Ca2+, their concentration in cytosol decreases
- active sites covered, and cross-bridge formation ends, tropomyosin returns to its normal position and active sites are covered again
- without cross-bridge formation, contraction ends
- muscle relaxation occurs, muscle returns passively to its resting length
rigor mortis
- after death circulation stops and the muscle is deprived of nutrients and oxygen
- after a few hours, muscle fibres run out of ATP
- muscle can’t pump Ca2+ out of the cytosol and Ca2+ levels rise
- without ATP, cross-bridge cannot be released and the muscles become “locked in the contracted position”
- begins 2-7 hours after death and can last 1-6 days depending on conditions
muscle tension factors
- tension = force
- determined by the number of pivoting cross-bridges
- dependent on: muscle fibre length and frequency of stimulation
length-tension relationship
- when the thick filaments contact the Z lines, the sarcomere cannot shorten - the myosin heads cannot pivot and tension cannot be produced
- at short resting length, thin filaments extending across the center of the sarcomere interfere with the normal orientation of thick and thin filaments, decreasing tension production
- maximum tension is produced when the zone of overlap is large but the thin filaments do not extend across the sarcomere’s center
- if the sarcomeres are stretched too far, the zone of overlap is reduced or disappears, and cross-bridge interactions are reduced or cannot occur
- when the zone of overlap is reduced to zero, thin and thick filaments cannot interact at all. The muscle fibre cannot produce any active tension, and a contraction cannot occur
muscle twitch
one single stimulation-contraction-relaxation sequence
duration of stimulation-contraction-relaxation sequence
- takes about 40 ms to go through the stimulation-contraction-relaxation sequence
- not the same in all parts of the body, eye muscle is a fast twitch muscle, gastrocnemius is intermediate and soleus is slow twitch
latent period
muscle doesn’t respond right away to stimulation take 2.5 ms, caused by action potential propagation and Ca2+ release into muscle cells
treppe
an increase in peak tension with each successive stimulus delivered shortly after the completion of the relaxation phase of the preceding twitch
wave summation
occurs when successive stimuli arrive before the relaxation phase has been completed, leads to greater force generation with each successive stimulus
incomplete tetanus
occurs if the stimulus frequency increases further, tension production rises to a peak, and the periods of relaxation are very brief
complete tetanus
the stimulus frequency is so high that the relaxation phase is eliminated, tension plateaus at maximum levels
muscle tension summation
- whole muscle tension is determined by: tension produced by individual muscle fibres, and the number of muscle fibres stimulated
- sum of tensions generated by each muscle fibre is the total tension in the muscle
motor unit
- motor neuron and all of the muscle fibres that it innervates
- varies in size (4-6 fibres to 1000-2000 fibres)
- recruitment -> must recruit enough motor units to generate an appropriate contraction level
- asynchronous motor unit summation
asynchronous motor unit summation
- trying to get all motor neurons to work at the same time is impossible
- recruit motor units in succession, helps to increase duration for maintaining a level of strength
- the tension applied to the tendon remains the same, even though individual motor unit cycle between contraction and relaxation
muscle tone
- muscle tone = resting tension
- stabilizes bones and joints
- allows muscles to act as shock absorbers
- greater muscle tone = higher metabolism
isotonic contraction
- equal tension, length changes
- two types: concentric and eccentric
isometric contraction
- equal tension, equal length
- tension never exceeds the load
concentric contraction
muscle tension excess load and muscle shortens
eccentric contraction
muscle tension is less that the load and muscle lengthens
slow-twitch fiber
- type I, slow fatigue, slow twitch oxidative, red fibers
- small diameter, small glycogen reserves, many mitochondria to generate energy, rich capillary supply, myoglobin, fatigue resistant
- half the diameter of fast-twitch and three times slower to reach peak tension
fast-twitch fiber
- type II-X, fast fatigue, fast-twitch glycolytic, white fibers
- able to reach peak tension very quickly
- large diameter, many myofibrils, large glycogen reserves, few mitochondria, low capillary supply, fatigue easily
intermediate muscle fiber
- type II-A, fatigue resistance, fast-twitch oxidative
- closely resembles fast-twitch in appearance
- intermediate diametes, intermediate mitochondria supply, intermediate capillary, somewhat fatigue resistant
size principle
- describes recruitment pattern during muscle contraction
- small motor unites have lowest threshold and are recruited first
- as force requirements increase, larger motor units are recruited
- small motor units are associated with slow-twitch fibers, large motor units are associated with fast-twitch
- never overshoot contraction needed by only recruiting as many motor units as needed
- recruit slow-twitch first then intermediate, then fast-twitch
stretch-shortening cycle
- eccentric contraction -> transition period (amortization) -> concentric contraction
- leads to increased propulsive forces and a reduction in the metabolic cost of movement
3 components of the muscle are responsible for generating force
- contractile component: actin and myosin
- elastic components: PEC (titin, sarcolemma, and muscle fascia), and SEC (tendons)
storage of elastic energy (EE) during eccentric phase of SSC
- EE is mostly stored in the tendon
magnitude of EE is directly proportional to the applied force - EE acts as an additional force that can be used during the concentric phase
transition (amortization) phase of SSC
- cross bridges can be maintained for approx. 15-120 ms
- amortization period must be as short as possible to maximize energy return
- slow-twitch vs fast-twitch
muscle stiffness in SSC
- important for storage of EE in the tendon
- muscle stiffness is developed by training (strength and plyometrics)
- strength training develops strength which prevent injury
- plyometrics creates the environment for structural adaptations in the muscle
afferent information
- feedback with respect to your body position is critical
- two types of receptors: muscle spindles and Golgi tendon organs
muscle spindle
- monitors muscle length and speed
- includes: intrafusal fibers, efferent fibers, and afferent sensory endings
- embedded in the center of the muscle
- if muscle stretches too fast and too much we get stretch reflex causing contraction
stretch reflex, patellar tendon
- striking of the patellar tendon indicates stretching of the quadriceps muscle leading to contraction of the muscle to protect it
Golgi tendon organ
- located in the tendons
- tells us how much muscle is shortening, muscle shortening causes tendon to lengthen
- respond to changes in muscle tension
- afferent fiber endings entwined in bundles of connective tissue that make up tendon
- when muscle contracts, there is a pull at the tendon, tightens connective tissue in tendon and Golgi tendon organ is stretched
- afferent nerve fibers are fired at a frequency that is directly related to the tension developed
effects of exercise on fiber type
- training can increase size and capacity of both types (I and II)
- high intensity training increase muscular strength and mass in type II fibers
- endurance training enlarges type I fibers
- endurance training can also convert some type II-X fibers to type II-A
hypertrophy
- increase in muscle size
- due to increase in number of myofibrils
- also results in increase in blood supply and mitochondria
atrophy
decrease in muscle size
effects of exercise - muscle strength
- strength increases from hypertrophy are not only achieved by increase in muscle size
- increases in muscle strength is also achieved by changes in the nervous system, gets better at recruiting motor units
- the nervous system in a trained person can recruit large number of motor units than an untrained person
- neural factors account for rapid and significant strength increases early in training
- often occurs without an increase in muscle size and cross-sectional area
neural factors that modify human strength
neural factors:
- greater efficiency in neural recruitment patterns
- increased central nervous system activation
- increased motor unit synchronization
- lower neural inhibitory reflexes
effects of exercise - muscle endurance
- improved metabolism
- increased number of capillaries
- more efficient respiration
- greater cardiac output
aging and muscle mass
- changes can begin as early as 25 years old
- capacity reduced 30-50% by 80 yeas old (3-5% per decade after age 30)
- lifting weight can slow this process
1. changes occur due to faster loss of fast-twitch fibers, contributing to loss of strength and speed
2. surface are of neuromuscular junction decreases resulting in fewer action potentials produced in muscle fibers
3. number of motor units also decreases, remaining motor units take up extra fibers (may result in less precision)
4. decrease in the density of capillaries in skeletal muscle, reduced blood flow to muscles and longer recovery period following exercise - many of these changes can be slowed dramatically by remaining active
energetics
the study of the flow of energy and its change(s) from one form to another
metabolism
all the chemical reactions that take place in an organism
adenosine triphosphate
high energy compound used in cells, main energy currency of the body
catabolism
- breakdown of organic molecules
- releases energy that is used to synthesize ATP
- proceeds in a series of steps
- most ATP in formed in mitochondria
anabolism
- synthesis of new organic molecules
- carry out structural maintenance and repairs
- support bone and muscle growth
- store nutrient reserves, glycogen, triglycerides
carbohydrate metabolism
- always has ratio of 1C, 2H, and 1O
- glucose C6H12O6
- used to generate new ATP
- breakdown of glucose in steps releases energy that is used to convert ADP to ATP
- catabolism of 1 glucose molecule = 38 ATP
glycolysis
- breakdown of glucose to pyruvate
- occurs in a series of seven metabolic steps
- requires: glucose, enzymes, ATP and ADP, inorganic phosphate and NAD
- anaerobic process occurring in the cytoplasm
- net gain of 2 ATP
steps of glycolysis (7)
1 and 2. phosphorylation: costs the cell 2 ATP molecules
3. split: creates two 3C fragmetns
4. 2 NAD -> 2NADH
5. formation of 2 ATP molecules
6. formation of 2 H2O
7. formation of 2 ATP
end point of glycolysis is reached and 2 molecules of pyruvate are formed, 2 NADH, 2 H2O, and net 2 ATP
pyruvate
- pyruvate still contains additional energy in its bonds
- in order to capture the energy… oxygen must be available
- if oxygen is available, we now move into the mitochondria for more metabolism
pyruvate to acetyl CoA
- occur in mitochondrion
- results in a molecule of acetyl CoA, a CO2 and a 1 NADH
- aerobic process
citric acid cycle
- also know as tricarboxylic acid cycle, TCA cycle or Kreb’s cycle
- goal is remove hydrogen atoms from molecules and transfer them to coenzymes (NAD and FAD)
- aerobic process
- 8 steps that start and end at the same place, produce 2 ATP, 6 NADH, and 2 FADH2per acetyl CoA
- acetyl CoA is added to oxaloacetate to form citrate
electron transport chain (ETC)
- series of reactions that occur in the inner mitochondrial membrane
- produces more than 90% of the body’s ATP
- primarily produces ATP from NADH and FADH2, transport electrons to ETC to produce ATP
- ATP generation is limited by the availability of either oxygen or electrons (NADH, FADH2)
- no oxygen -> no ATP production in the mitochondria
- each molecule of FADH produces 3 ATP while each FADH2 produces 2 ATP
lipid metabolism
- 95% of lipids in our diet are triglycerides
- most acetyl CoA enters the citric acid cycle
- lipids are responsible for 99% of the body’s energy storage
- during rest, nearly 60% of the energy supply is provided by the metabolism of fats
- to lose fat during exercise want to do low intensity exercise so they don’t end up using anaerobic energy production
triglycerides
- divided into saturated and unsaturated fats
- get energy from fatty acid side chains not glycerol backbone
- free fatty acids (FFA) are metabolized by a beta oxidation, breaking it into 2C fragments to form acetyl CoA
- always have even number of carbons, each with 4 bonds to it
- acetyl CoA enters citric acid cycle to generate 120 ATP per fatty acid chain, which is 3x120 ATP = 360 ATP per triglyceride
saturated fat
all carbon bonds are occupied by hydrogen, except to other carbons
unsaturated fat
has double bonds on carbons, not fully bound to hydrogen
how is percentage of fat in food calculated?
- 1 gram fat = 9 calories
- total grams of fat x 9 = total fat calories
- represent total fat calories as a % of total calories
proteins
- chains of amino acids
- 20 different amino acids, 9 essential AAs we get from diet and 11 non-essential AAs- used to synthesize protein in the body
- also used as an energy source
- excess AAs are stored as glycogen or fat
- different AAs are fed into different points of citric acid cycle to generate ATP
cellular respiration
- can be either aerobic or anaerobic
- not either/or, both systems work concurrently
- when we refer to exercise, anaerobic and aerobic refer to which energy system predominates
the energy continuum
- the ATP-PC system predominated in activities lasting 10 seconds or less, continues to provide small amounts of energy for maximal activities up to 2 minutes
- anaerobe system (ATP-PC and LA) predominates in supplying energy for exercise lasting less than2 minutes, continues to provide energy requirements for exercise as long as 10 minutes
- the aerobic system is the dominant system 5 minutes into exercises, the longer the exercises, the more important it becomes
lactate
- lactate is produced in muscle cells
- in the absence of oxygen, NADH transfer its hydrogen to pyruvate forming lactate
- lactic acid -> lactate + H+
- amount of lactate depends on the balance between its production and its removal into bloodstream
- the more you exercise at a high intensity where you can’t provide enough oxygen, lactate will build up because pyruvate can’t be turned into acetyl CoA so it ends up being turned into lactate
why is lactate a problem?
- it is the H+ that comes from lactic acid that is the problem
- normally we buffer excess H+ to maintain pH
- when H+ levels exceed buffering capacity, the pH becomes acidic causing pain to be perceived and performance suffers because muscle can’t function in acidic environment
lactate removal
- lactate is removed from the bloodstream relatively quickly following exercise
- generally, half of the total lactate is removed in about 15-25 minutes
- near-resting levels can be achieved in 30-60 minutes
- can enhance removal of lactate using easy exercise, which increases blood flow to muscle, intensity of exercise should not exceed 40% VO2 max
- higher intensities of exercises during recovery can deplete glycogen stores and delay resynthesis
glucose from lactate
- lactate enters the blood and travels to the liver
- with oxygen, lactate is converted to glucose using the Cori cycle and gluconeogenesis
- glucose enters blood and is used by cells as an energy source
training the anaerobic system
- anaerobic training (sprint/power training):
- increases resting levels of ATP, CP, creatine and glycogen
- increases strength
- increases numbers of enzymes that control glycolysis
- increases capacity to generate high levels of lactate
measuring anaerobic power and capacity
- use Wingate anaerobic power test
- lactate threshold
Wingate anaerobic power test
- uses Monark Cycle Ergometer
- all out for 30 seconds
- resistance based on body weight
- flywheel revolutions are measured
- three variable calculated: peak power (peak for 5 seconds), mean power (average for 30 seconds), and fatigue index (best 5 seconds/worst 5 seconds)
lactate threshold (LT)
- also known as anaerobic threshold, ventilatory threshold (VT), onset of blood lactate accumulation (OBLA), or maximal lactate steady state (MLSS)
- points on lactate accumulation curve that indicate sharp rise are the LT, marathoners would higher LT than a middle distance runner or sprinter
lactic acid steady-state
- lactic acid does not accumulate in the blood under steady state conditions
- steady state is different for different people
- depends on: capacity to deliver oxygen to muscles and ability of the muscles to use the oxygen
aerobic metabolism
- aerobic system provides long-term energy
- occurs in mitochondria
- includes citric acid cycle, and electron transport chain
training the aerobic system
- aerobic training (endurance training):
- large, more numerous mitochondria in muscle
- enhanced breakdown of fat during sub maximal exercise (spares glycogen)
- enhanced ability to breakdown CHO during maximal exercise
- delays onset of blood lactate during exercises of progressively increasing intensity
- body composition and performance changes
- psychological benefits
