Skeletal muscle Flashcards
skeletal muscle tissue (fiber)
-this tissue that we need to make up skeletal muscles
-the cells making up that organ are as long as the organ itself
-look like soda straws and are parallel to each other
-skeletal muscle tissue, a cell is a fiber (1 cell and 1 soda straw)
-is striated and multinucleated, come out of the plasma (sarcolemma) like a pimple
-our muscles have capacity of being anaerobic
sarcolemma
-plasma membrane of a muscle cell
-different from other plasma membrane because it has a junction box (special place for nervous system to plug in) and always towards the middle of the cell
-need that to spill the chemical to reach the sarcolemma and open the sodium gate forming an action potential along it
-is capable of impulse
sarcoplasm
cytoplasm of a muscle cell
skeletal muscle cells
-will not contract on their own, has to be innervated by a motor neuron has to form something equivalent to a synapse (neuromuscular junction)
What jobs can the skeletal muscle tissue do?
-works with skeletal system to cause motion to happen
-the muscle tie onto the skeleton
-also work to stabilize joints and produces heat
List what is in a connective tissue coverings
- epimysium
- fascicle
- perimysium
- endomysium
- tendon
- aponeuroses
epimysium
-connective tissue wrap that covers the skeletal muscle
-made of DFCT
tendon
-a continuation of the epimysium
-all of this is DFCT
-looks like a rope and ties muscle to bone
aponeuroses
-touch muscle to a muscle that looks like a white flat sheet
-flat band of DFCT
What does a tendon and an aponeuroses have in common?
-both made of DFCT
-both continuations of epimysium
-both bind the muscle to something else
fascicle
-bundles of fibers within the organ wrapped with perimysium (DFCT)
endomysium
-the filler in stuff
-where you find the axon endings, and blood vessels
-made of LFCT
-above the sarcolemma
perimysium
-wraps the fascicles and made of DFCT
Generation of muscle contraction requires what?
-this is a mechanical function and requires ATP from mitochondria
-need ATP to attach and de-attach for muscle contractions
myofibrils
-thinner than muscle fiber, run through each cell the entire length
-can have hundreds
-gets broken up into “apartments” by structural proteins
Z line (disk)
-structural protein
-from z line to z line its going to make up one sarcomere (one apartment)
sarcomere
-made up of connecting z-lines (disk), along a myofibril
-functional unit of a skeletal muscle fiber, responsible for contraction
-every sarcomere is identical
-composed of myofilaments
What are the two kinds of myofilaments
- thin myofilaments (actin)
- thick myofilaments (myosin)
Thin myofilaments
- thin filaments that are composed of the protein actin
thick myofilaments
-thick filaments that are composed of hundreds of protein mysoin
-looks like a two headed golfclub, one head has a certain shape to it that attaches to actin
-this head goes up and forms a cross bridge with actin. The other head is used for ATP
What causes striations in muscles?
the thick and thin filaments alternating
I band
-in the sarcomere is the light area
-composed of actin filaments
A band
-in the sarcomere is the dark area
-region of striated muscle that contains thick filaments (myosin)
-another region in this area that is only thick called H zone
H-zone
-the center of the A band where there is no overlap between thick and thin filaments
-under trained eye can see a bright spot which correlates to this zone and this can be used during autopsy to determine if muscle is in its relaxed state or contracted
crossbridge
-during contraction the linkage of thin and thick filaments
sliding filament theory of muscle contraction
-attach to the thin filaments and slide over the thick and because the thick are attached to the z-line (disk) you are pulling them with you. So the sarcomere is
-myosin filaments use energy from ATP to “walk” along the actin filaments with their cross bridges. This pulls the actin filaments closer together. The movement of the actin filaments also pulls the Z lines closer together
When a muscle is relaxed, can you see the H zone?
Yes. every sarcomere is at max length you see a clear H zone
Benefits of stretching before physical exercise
makes for a very efficient contraction
What are overstretched muscles
- you pulled the sarcomeres so wide they have no points of contact
What are the portions of a thin filament
- troponin complex
- tropomyosin
- actin
actin molecules
ball like structures, that twist together
- important in forming the myosin crossbridge form
G-actin
globular actin, the actin monomer that is assembled into networks that provide structural support
How do you stop a actin crossbridge from forming
cover up the active actin site
tropomyosin
regulatory protein that covers up the active site on the actin
troponin
regulatory protein (used to be called TT complex)
- troponin and tropomyosin are all components of the thin myofilaments (block active site)
sarcoplasmic reticulum
-channels within the sarcoplasm
-looks like crochet sleeve
-located all around the myofibrils
-when a muscle fiber is resting calcium ions are stored in the SR
neuromuscular junction
-is a motor neuron and a muscular cell
-axon and synaptic bulbs have neurotransmitters
-and one place along sarcolemma where we can plug in which holds receptors for neurotransmitter, the motor end plate has the receptors for it and open sodium gate
motor end plate
-spot that has the receptors for acetylcholine and opens up first sodium gate and start action potential
acetylcholinesterase
-enzyme that clears the gap of the neurotransmitter
job of motor neuron
to produce the neurotransmitter and have in there in the synaptic bulbs ready to be spilled into the gap (clef)
-will always be acetylcholine
what is acetylcholine
a neurotransmitter
where is acetylcholine produced
motor neuron
what is the function of acetylcholine
transmitting action potential from neuron to muscle
motor unit
1 motor neuron and all motor fibers it innervates at the same time
-ex: 1 motor neuron to 7 or 10 fibers
-if you do not have enough you recruit more until you maximize for that particular organ
-each organ has a different max recruitment
-this is how you adjust the strength
t- tubules
circular openings
-like taking the plasma membrane and continuing it down, so now the action potential can come down into the depts of the cell
-has sarcoplasm reticulum around it (which releases the calcium ions into sarcoplasm)
Energy sources for contraction are
1.ATP
2. Creatin phosphate
3. myoglobin (muscle hemoglobin)
4. oxygen debt
5. muscle fatigue
ATP
-glucose is turned into this, needed for muscle contraction to occur
-this is the currency
-in the cytoplasm of the cell the glucose is changed into two ATP
-has to be broken down in the mitochondria and needs oxygen
creatin phosphate
-chemical made in the liver and hangs out in skeletal muscle cells
-when you get elevated creatin in your blood, your muscles are ripping and tearing (Rabdo) which can cause kidney failure
-creatin phosphate is a high energy molecule, which can be made more than ATP
-a resting muscle cell can make a lot of this
-can remove phosphate and make creatin into ATP (first way to get additional ATPA for short term)
myoglobin
-holds onto oxygen
muscle fatigue
is a state of physiological inability to contract even though the muscle is still receiving stimuli
-this is done to preserve the ATP you still have left
-buildup of lactic acid
Latent period
first few milliseconds following stimulation when excitation-contraction coupling is occurring. During this period, cross bridges begin to cycle but muscle tension is not yet measurable so the myogram does not show a response.
-do not see until power stroke happens then a period of contraction happens
period of contraction
cross bridges are active, from the onset to the peak of tension development, and the myogram tracing rises to a peak. This period lasts 10–100 ms.
myograms
-picture of muscle tension building
-the greater the tension the higher it will go
twitch
one threshold stimulus and 1 latent period, 1 contraction and 1 period of relaxation
not realistic in terms of muscles just a way to study steps
treppe (staircase effect)
-very important for athletes
-have a latent period, then period of contraction, then let the whole thing relax. Then hit it again causing greater tension until you peak the tension for that
-you do not take back all the calcium ion this causes greater tension every time
-start your event at maximum tension
what is in a twitch
- latent period
- period of contraction
- period of relaxation
- refractory period
period of relaxation
due to pumping of Calcium back into the SR. Because the number of active cross bridges is declining, contractile force is declining. Muscle tension decreases to zero and the tracing returns to the baseline. Notice that a muscle contracts faster than it relaxes
tetanus (sustained contraction)
-allowed no time for relaxation and requires a lot of energy
-almost all activity we do is a sustained contraction
-this is exhaustion
direct phosphorylation
coupled reaction of creatine phosphate (CP) and ADP
-CP is turned into creatine
-ADP uses creatin kinase to turn into ATP
-no oxygen is used and this last 15 seconds
What is the energy source for direction phosphorylation
creatine phosphate
End products for direct phosphorylation
1 ATP per CP, creatine
Anaerobic pathway
glycolysis and lactic acid formation
-the energy source is glucose
-glucose is broken down from glycogen or delivered from blood by glycolysis in cytosol (2 ATPs). Next pyruvic acid is made, then lactic acid which is released into the blood
-oxygen is not required, last 60 sec or more
* White meat
Aerobic pathway
-aerobic cellular respiration
-energy source: glucose, pyruvic acid; free fatty acids from adipose tissues; amino acids from protein catabolism
-glucose is broken down from glycogen or delivered from blood. Then pyruvic acid is made which turns into aerobic respiration in mitochondria which needs fatty acids and amino acids which then releases CO2 and H2O and 32 ATP
-requires oxygen and last hours
End Products from anaerobic pathway
2 ATP per glucose and lactic acid
end products from aerobic pathway
32 ATP per glucose, CO2 and H2O
