• CT membrane that is wrapped/covers each skeletal muscle cell/muscle fiber
• Considered DELICATE

• Coarse CT membrane that wraps/covers a group of endomysium covered muscle fibers 
• Covers each fasicle- which is a group of enodmysium covered muscle fibers
• considered COARSE 

• CT membrane that covers/wrapps a group of fascicles 
• Considered to be TOUGH

• Consist of a group of endomysium coverd muscle fibers wrapped in a coarse CT membrane called perimysium 

• Connects the muscle to the bone and are important for indirect attachment and dense CT 

• The plasma membrane of muscle fiber

• Cytoplasm of the muscle fiber

• A red pigment that bind and stores oxygen 

• Structural units of a skeletal muscle
• repeated units arranged from end to end of each skeletal muscle
• the distance between 2 successive Z lines= a sarcomere
• It is composed of A band, M line, thin filaments, Z lines, H zone, I bands.

• aka Z discs
• anchor the thin filaments and the sarcomere is found between two of these consecutively 

• Middle region of the A band not overlapping with the thin filaments 
• When the sarcromere contracts the thin filaments are sliding into this section ( causes it to disappear along with the I bands) of the sacromere, which then pulls the Z discs towards the inside 

• Thick Filaments
• The middle of the sarcomere
• These are secured via expandable elements
• Remains the same length during muscle contraction

• Region of the thin filaments on a sacormere not overlapping with the A band/thick filaments
• Remain the same lenght during muscle constraction 

• composed of a tranverse tubule in between 2 terminal cisternae
• Terminal cisterna-Ttubule-Terminal cisterna
• Consist of 1 transverse tubule/ T- tubule in the center & 2 terminal cisternae on the outsides of the T tubules .
•  It's purpose is that when the sarcolemna depolarizes then it discharges calcium ions into the sarcoplasm 
   

• The motor neuron and all the skeletal muscle fibers that innerate via axonal terminals
• Consist of the motor neuron ( innervates the muscle to contract/shorten) & all skeletal fibers that it stimulates using it's axon terminal.
• These can vary in size

• The junction between the axon terminal of a motor neuron and a skeletal muscle fie seperated by a small space called the neuromuscular cleft( synaptic cleft)
• Each muscle fiber only has one neurmuscular junction 

• A motor end Plate is a highly folded region of the sarcolemma of the muscle fiber at the neuromuscular joint 
• Its function is to express acetylcholine receptors at the exterior (surface)

• 8mm in diameter; anchored by Z lines
• Contain 3 different proteins; actin, tropomyosin, troponin 

• ACTIN
• TROPOMYOSIN
• TROPONIN

• Contains the binding sites for the myosin heads 
• Structural protein help form the composition of the thin filaments 
• binding site for Troponinsubtype called TnI ( inhibotory troponin)

• a rod shaped regulatory protein that spirals around the actin and blocks myosin binding sites on actin in a relaxed skeletal muscle 
• regulatory protein
• causes actin to be spiral 
• Is a adaptable rod like protein 

• Regulatory protein 
• a Three polypeptide complex namely
• TnC- binds calcium ions
• Tnt- Binds to tropomyosin
• TnI- inhibatory subunit that binds to actin 

• Tropomyosin wraps around an actin filament to form a functional actin filament (thin filament).

• It's purpose is involved in the powerstroke of the myosin head. It does this by kind of like a hook. If you have a hook and you grab a long rope and pull it towards you, the hook is a thick filament (myosin) and the rope is a thin filament (actin).

• Tropomyosin will block the hook from latching onto the rope in normal resting phase. When it is released (by calcium), you can now freely hook the rope and pull it towards you.

The Three Subunits of Troponin are:

• Tnc: binds to calcium ions
• Tnt- Binds to tropomyosin
• TnI- Inhibitory subunit that binds to actin 

• Binding site for Actin, and ATP
• Activation A of myosin globular heads have sites for binding ATP and the heads contain enzyme ATPase. When ATPase hydrolyzes (splits) ATP into ADP and Pi with the ADP + Pi inorganic phosphate still attached to the myosin globular heads---> they are referred to as ACTIVATED GLOBULAR HEADS 
• They bind to their accessible sites on actin in an upright position ( at 90 degree angle)
• Activated Myosin globular heads attach to actin which is called CROSS BRIDGES

What is the Consequence of the Power Stroke? 

• The change in orientation of the crossbridges from an upright position to an oblique position when the (APP ppi) dissociate is referred to as the POWER STROKE
• The consequence of the POWERSTROKE is sliding of the thin filaments 
• After sliding of the thin filaments in other words after skeletal muscle contraction, the skeletal muscle relaxes

Describe how Skeletal Muscle Contraction Occurs

-Motor neuron is activated

-Axon of motor neuron generates and transmits action potential to the axonal terminals

-Results in the release of the neurotransmitter, ACETYLCHOLINE from vesicles in the axonal terminals into the neuromuscular cleft

-Acetylcholine binds to acetylcholine receptors on the motor end plate to cause depolarization which leads to the generation of action potential at the motor end plate

-The action potential spreads across the entire sarcolemma and into the T-tubules of the triads

-Results in the release of calcium ions from the terminal cisternae of the triads into the sarcoplasm

-Calcium ions bind to TnC which results in a conformational change and the removal of tropomyosin from blocking the myosin-binding sites on actin

-With the tropomyosin blockade ended, activated myosin heads = cross bridges bind to the accessible myosin-binding sites on actin

-Myosin heads are activated when the myosin heads are attached by ADP +Pi  (resulting from ATPase hydrolysis of ATP into ADP + Pi)

-When the ADP and Pi dissociate from the cross bridges, the attached cross bridges change their orientation termed the POWERSTROKE  from a right angle to a bent position pulling the attached

-Inward into the H zone toward the M line = sliding of thin filaments which results on skeletal muscle contraction

-Cross bridge detachment - NEW ATP molecules bind to the attached myosin heads to cause them to detach.

-Lack of new ATP results in skeletal muscle contracture termed RIGOR MORTIS- occurs when an individual dies and ATP synthesis ceases - actin and myosin are irreversibly cross linked and skeletal muscles remain contracted

-Muscle fatigue is a physiological inability of a stimulated skeletal muscle to contract due to ATP DEFICIT – rate of ATP production lags behind ATP demand.

• ATP is hydrolyzed by ATPase to produce ADP & Pi to activate myosin heads.

• ATP is required for cross bridge enhancement

• ATP is required for the sequestration of calcium ions back into the SR for storage (active transport)

• The sliding filament mechanism is when contraction( shortening) occurs when thin filaments "slide" into the H zone ( towards the M line) pulling the Z discs inward 

• Sliding of THIN FILAMENTS in sarcomere past A bands and towards M-lines in the H-zone causes shortening of sarcomeres as the Z-lines are pulled inward. Results in muscle contraction. So, Sarcomere length, H-zone, I-bands, and skeletal muscle shrinks.
• Skeleton muscle fibers
• skeletal mucle( the organ)
• The sacromeres
• Distance between Z discs shorten ( b/c they are being pulled inward)

• Lenghts of A bands
• Thin Filaments 

1) Size of motor units activated - larger motor units generate more force than smaller motor units.

2) Number of motor units activated - force increases as the number of motor units activated increases. Recruitment = smaller motor units are activated first followed by larger motor units.

3) Frequency of skeletal muscle activation - force increases as the rate of stimulation by motor neurons increases

4) The length of the sarcomeres prior to contraction - sarcomeres at the optimum length generate the maximum force; sarcomere length below the optimum length (shortened sarcomeres) results in decreased force; sarcomere length greater than the optimum length (stretched sarcomeres) results in decreased force of contraction.

1) Slow Oxidative Fibers - RED FIBERS

fatigue resistant, suited for endurance activities ex. marathons.

- uses aerobic respiration to generate ATP

-training at higher altitudes has an advantage - body makes more hemoglobin to compensate. Then coming to sea level to run a marathon will have an advantage. 1) efficient use of oxygen. 2) more slow oxidative fibers (red fibers).

2) Fast Oxidative Fibers - pink fibers (reddish-pink)

- Uses aerobic respiration.

3) Fast Glycogenic Fibers - white fibers.

- FATIGABLE(susceptible to fatigue)

- Are the largest fibers and use anaerobic respiration --> leads to lactic acid build up --> muscle fatigue.

- For intense but short activities such as weight lifting.

• Fast Glycogenic Fibers - white fibers.

  - FATIGABLE(susceptible to fatigue)

  - Are the largest fibers and use anaerobic respiration --> leads to lactic acid build up --> muscle fatigue.

  - For intense but short activities such as weight lifting.

  
  

• aka as Red Fibers because they hold most of the myoglobin 

• Arm is extend outward/straight 
• length of skeletal muscle remains contant with increasing tension
•