Chapter 10,11,12 Continue Flashcards
The process in which nerve action potentials lead to muscle action potentials
Excitation
Events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract
Excitation- contraction coupling
step in which the muscle fiber develops tension and may shorten
Contraction
When its work is done, a muscle fiber relaxes and returns to its resting length
relaxation
Arrival of nerve signal
opens voltage- gated calcium channels
step 1
Acetylcholine (ACh) release
Calcium enters the cell thru gates, opened by voltage
Step 2
Binding of ACh to receptor
two ACh molecules bind to each receptor protein, opening Na and K channels
Step 3
Opening of ligand- regulated ion gates; creation of end- plate potential
Na enters; shifting RMP goes from -90 mV to + 75 mV then K exits (Action Potential) and RMP returns to -90 mV; quick voltage shift end of plate potential
Step 4
Quick voltage shift
end- plate potential (EPP)
Opening of voltage- regulated ion gates; creation of action potentials
Voltage change (EPP) in end- plate region opens nearby voltage- gated channels producing an action potential that spreads over muscle surface
Causing Action Potential after Action Potential
Step 5
Action potentials propagated down T tubules
Step 6
Calcium released from terminal cisternae
Ca gets diffused thru the muscles
Step 7
Binding of calcium to troponin in thin filaments
Step 8
Shifting of tropomyosin; exposure of active sites on actin
Troponin- tropomyosin complex changes shape and exposes active sites on actin
Step 9
Hydrolysis of ATP to ADP + P; activation and cocking of myosin head
“Pull hammer on gun back” on myosin which is pulled back by ATP
Step 10
Fermat ion of myosin -actin cross- bridge
Myosin comes back and attaches to Actin
Step 11
head binds to actin active site forming a
myosin- actin cross- bridge
Binding of new ATP; breaking of cross- bridge
Step 13
Power stroke sliding of thin filament over thick filament
Myosin fires= ATP molecules
Step 12
Cessation of nervous stimulation and ACh release
Relaxation; stop stimulation
Step 14
ACh breakdown by acetylcholinesterase (AChE)
Step 15
Reabsorption of Calcium ions by sarcoplasmic reticulum
Step 16
Loss of calcium ion from troponin
Give myosin one final ATP
Step 17
Return of tropomyosin to position blocking active sites of actin
Step 18
the amount of tension generated by a muscle and the force of contraction depends on how stretched or contracted it was before it was stimulated
Length- tension relationship
a weak contraction results in thick filaments too clos to Z discs and cannot slide
Overly contracted
a weak contraction results little overlap of thin and thick does not allow for very many cross- bridges to form
Too stretched
produces greatest force when muscle contracts
Optimum resting length
central nervous system continually monitors and adjusts the length of the resting muscle , and maintains a state of partial contraction
muscle tone
cause sarcoplasmic reticulum to break down quickly and release calcium molecules begin to break down
hardening of muscle and stiffening of body beginning 3-4 hours after death
Rigor mortis
a chart of the timing and strength of muscle’s contraction
Myogram
the response of a muscle to weak electrical stimulus seen in a frog gastrocnemius
Sciatic nerve preparation
what does a weak electrical stimulus do
causes no contraction
minimum voltage necessary to generate an action potential in the muscle fiber and produce a contraction
threshold
a quick cycle of contraction when stimulus is at threshold or higher
1-18 steps (1 time )
twitch
2 ms delay between the onset of stimulus and the onset of twitch response ; internal tension
time required for excitation- contracting coupling, and tension of elastic components of the muscle
everything before contraction
Latent period
force generated during latent period and no shortening of the muscle occurs
getting slack out
Internal tension
phase in which filaments slide and the muscle shortens
once elastic components are taut, muscle begins to produce external tension in muscle that moves a load
short- lived phase
Contraction phase
parts of body are moving
once elastic components are taut, muscle begin to
external tension
SR quickly reabsorbs Ca myosin releases the thin filaments, and tension declines
muscle returns to resting length
entire twitch lasts from 7- 100 ms
Relaxation phase
no contraction at all
didn’t get up to -55 mV
sub threshold stimulus
a twitch is produced
twitches caused by increased voltage are no stronger than those at threshold
threshold intensity and above
Do muscle fibers act the same to every spike no matter if its -55 or over ?
Yes
stimuli arriving closer together produce stronger twitches
stimulus frequency
in sarcoplasm can vary the frequency
concentration of Ca
Stimulus frequency Concentration of Ca stretch temperature PH State of hydration all influence what
how much force our muscles have
how much ___ muscle was before it was stimulated
stretched
___ of the muscles - warmed- up muscle contracts more strongly; enzymes work more quickly
Temperature
Lower than normal __ of sarcoplasm weakens contraction- __
pH; fatigue
___ of muscle affects overlap pH thick and thin filaments
State of Hydration
Stimulating the nerve and higher and higher voltages produces
use more muscle with stronger voltage
stronger contraction
the process of bringing more motor units into play
Recruitment or multiple motor unit (MMU)
each stimulus produces identical twitches and full recovery between twitches
up to 10 stimuli per second
Twitch
10-20 stimuli per second (staircase)
stimulus recovers fully between twitches but each twitch develops more tension than the one before
contraction get stronger and stronger and sarcoplasmic reticulum doesn’t have enough time to reabsorb Ca
Treppe
20 -40 stimulus per second
ca cant be reabsorbed fast enough and myosin and actin don’t have enough time to relax
each new stimulus arrives before the previous twitch is over
higher tension
Incomplete tetanus
muscle relaxes only partially between stimuli
produces a state of sustained fluttering contraction
Incomplete tetanus
40 -50 stimuli per second tasd muscle lock up
muscle had no time to relax between stimuli
rapid then flat lines
Complete tetanus
muscle is producing internal tension while an external resistance causes it to stay the same length or become longer
isometric muscle contraction
muscle changes in the with no change in tension
concentric contraction
eccentric contraction
Isotonic muscle contraction
muscle shortens as it maintains tension
Concentric contraction
muscle lengthens as it maintains tension
eccentric contraction
All muscles depend on what
ATP
___ supply depends on availability of : oxygen and organic energy sources such as glucose and fatty acids
ATP
__ is where production of ATP occurs
Mitochondria
Two main pathways of ____ synthesis
Anaerobic fermentation and Aerobic respiration
ATP
without oxygen
Enables cells to produce ATP in the absence of oxygen
yields little ATP and toxic lactic acid, major factor in muscle fatigue
ex. when running, hold breath
Anaerobic fermentation
With oxygen
produces far more ATP
Less toxic and produces
requires a continual supply of oxygen
Aerobic respiration
Oxygen need is briefly supplied by myoglobin for limited amount of aerobic respiration at onset- rapidly depleted
Muscle meet moser of ATP demand by borrowing phosphate groups from other molecules and transferring them to ADP
Short intense exercise (100m dash)
Two enzyme systems control these phosphate transfers
Myokinase
Creatine kinase
Transfer P from one ADP to another converting the latter to ATP
Myokinase
Obtain P from phosphate storage molecule creatine phosphate (CP)
Fast acting system that helps maintain the ATP level while other ATP generating mechanisms are being activated
Creatine kinase
ATP and CP collectively
Provides nearly all energy used for short bursts of intense activity
1 min, 6 seconds of sprinting or fast swimming, important in activities requiring brief but max effort
Ex football baseball weightlifting
Phosphagen system
As the phosphagen system is exhausted muscles shift to what
Anaerobic fermentation
Not getting oxygen to the tissue
Muscle obtain glucose from blood and their own stores glycogen
I absence of oxygen glycolysis can generate a net gain of 2 ATP for every glucose molecule consumed
Converts glucose to Latin acid
Anerobic fermentation
Short term energy
The pathway from glycogen to lactic acid
Glycogen lactic acid system
Anerobic fermentation produces enough ATP for how many seconds of max activity
Short term energy
30 to 40 seconds
To split sugar to make ATP
Glycolysis
After 49 seconds so the respiratory and cardiovascular systems catch up and deliver oxygen to the muscles fast enough for aerobic respiration to meet most of the ATP demands
Long term energy
Aerobic respiration produce 36 ATP per glucose
Efficient means of meeting the ATP demand sod prolonged exercise
Ones rate of oxygen consumption rises from 3 to 4 minutes and levels off to a steady state in which aerobic ATP production keeps pace with demand
Little lactic acid accumulates under steady state condition
Long term energy
Progressive weakness and loss of contractility from prolonged use of the muscles
Repeated squeezing of rubber ball
Holding textbook out level to the floor
Muscle fatigue
ATP synthesis declines as glycogen is consumed
ATP shortage slows down the Na K pumps compromises their ability to maintain the resting membrane potential and excitability of the muscle fibers
Lactic acid lowers pH sacroplasm
Inhibited enzymes involved in contraction ATP synthesis and other aspects of muscle function
More acidic less likely to contract will fatigue
Fatigue is thought to result from
Aerobic activity the ability to maintain high intensity exercise for more than 4 to 5 mins
Determined in large part by ones maximum oxygen uptake (VO2 max)
Endurance
Taking oral creatine increase level of creatine phosphate in muscle tissue and increases speed of ATP regeneration
Carbohydrate loading
Beating fatigue
Dietary regimen
Packs extra glycogen into muscle cells
Extra glycogen is hydrophilic and add 2.7 g water per gram of glycogen
Athletes feel sense of heaviness
Carbohydrate loading
Abundane mitchondria, myoglobin , capillaries deep red color
Adapted aerobic respiration and fatigue resistance
Relative long twitch lasting about 100 ms
Soules of calf and postural muscles of the back
Walking
Aerobic
Slow oxidative( SO) slow twitch red type T fibers
Fibers are well adapted for quick responses but not for fatigue resistance
Rich in enzymes of phosphagen and glycogen lactic acid systems generate lactic acid causing fatigue
Poor in mitchondria myoglobin and blood capillaries which gives pale appearance
Extrinsic eye muscles gastrocnemius and biceps brachi
Anaerobic respiration
Fast glycolysis (FG) fast twitch white type 2 fibers
Ratio of different fiber types have genetic predisposition
Muscles are a combination of both but may be more of one than the other
Born sprinter
Exists because of unequal electrolyte distribution between extracellular fluid and intercellular fluid
Results from combined effect of three factors
Ions diffuse down their concentration gradient through the membrane
Plasma membrane is selectively permeable and allows some ions to pass easier than others
Electrical attraction of cations and anions to each other
Resting membrane potential
Have the greatest influence of RMP
Plasma membrane is more permeable to K than any other ion
Leaks out until electrical charge of cytoplasmic anions attracts it back in and equilibriumvia reached and net diffusion of K stops
k is about 49 times as concentrated in the ICF as in the ECF
Potassium ion
Cannot escape due to size or charge( phosphates , sulfate a, small organic acids, proteins, ATP, and RNA )
Cytoplasmic anions
Point where a nerve fiber meets its target cell (intervates)
Synapse
When target cell is a muscle fiber (neuron and muscle cell)
Each terminal branch of the nerve fiber within the NMJ forms separate synapse with the muscle fiber
One nerve fiber stimulates the muscle fiber at several points within the NMJ
Neuromuscular junction (NMJ)
Swollen end of nerve fiber
Contains synaptic vesicles filled with acetylcholine (ACh)
Connects to muscle cell nuerotransmitter
Synaptic knob
Tiny gap between synaptic knob and muscle sacrolemma
Synaptic cleft
Envelopes and isolates all of the NMJ from surronding tissue fluids (insulation protect NMJ)
Schwann cell
Undergo Exocytosis releasing ACh into synaptic cleft
Synaptic vesicles
__ proteins incorporated into muscle cell plasma membrane
Junction folds
50 million ACh receptors
Of sacrolemma beneath synaptic knob
Increase surface area holding ACh receptors
Lack of receptors leads to paralysis in disease myasthenia graves
Junctional folds
Thin layer of collagen and Glycoprotein separates Schwann cell and entire muscle cell from surrounding tissues
Contains acetylcholinesterase (AChE) that breaks down ACh after contraction causing relaxation
Connective tissue layer that surrounds everything
Basal lamina
Slightly more K leaves the cell than Na entering
Drops the membrane voltage 1 or 2 mV more neg than the original RMP neg overshoot hyper polarization or after potential
K gates stay open longer than N gates
_ and _ switch places across the membrane during an action potential
Na and K
___ layers of the cytoplasm next to the cell membrane is affected
In reality very few ions are involved
Only a thin layer
Action potential is called __ because it happens fast
Spike
Out of 3 Na for every 2 K it brings in
Works continuously to compensate for Na and K leakage and requires great deal of ATP
70% of the energy requirement of the nervous system
Necessitates glucose and oxygen be supplied to nerve tissue
Pump contributes about -3 mV to the cells resting membrane potential of -70 mV
Na k pumps
__ concentrated outside of cell
Na
_ concentrated inside cell
K
__ is a rapid up and down shift in the membrane voltage
Depolarize the membrane
Threshold
Action potential
Critical voltage to which local potentials must rise to open the voltage regulated gates
-55 mV
Threshold
When threshold is reached neuron __ and produces and action potential
Fires
More and more Na channels open in the trigger zone in a positive feedback cycle creating a rapid rise in membrane voltage called
Spike
When rising membrane potential passes _ mV Na gates are inactivated
Begin closing when all closed the voltage peaks at + 35 mV
Membrane now positive on the inside and beg on the outside
Polarity reversed from RMP depolarization
0 mV
By the time the voltage gates peaks the slow ___ are fully open
K repelled by the positive intercellular fluid now exit the cell
Their outflow repolarizes the membrane shifts the voltage back to neg numbers retiring toward RMP
Slow K gates
