Physiology- Muscle Physiology

What causes movement of skeletal muscle?

contraction

What do flexion and extension of skeletal muscle have in common?

both caused by muscle contraction

What do skeletal muscle cell nuclei look like?

Long, tube-shaped, multi-nucleiated, nuceli in perpiphery

What is a sarcomere?

contractile unit of skeletal muscle fiber made of actin and myosin

How many nerves innervate one skeletal muscle fiber?

ONE

What is the Z disc of a sarcomere?

end unit that anchors actin

What is the A band of the sarcomere?

dark area of BOTH actin and myosin

What is the M line of the sarcomere?

the middle of the sarcomere

What is the H zone of the sarcomere?

the zone of only myosin (thick letter, thick filament)

What is the I band?

only actin (thin filament)

Which muscle types have striations?

skeletal and cardiac

What does myosin look like?

intertwined helices

What does actin look like?

beaded string with tropomyosin string intertwined and troponin pearls at points of contact between the two

What does troponin bind to in order to pull tropomyosin off?

Calcium

What happens when calcium binds to troponin?

It pulls tropomyosin off the actin to reveal a myosin head binding site

What muscle fibers can be innervated by more than one nerve?

smooth muscle fibers

What muscle fibers can only be innervated by ONE nerve?

cardiac and skeletal

How can you increase contraction in skeletal muscle?

spatial or temporal summation

What is a type 1 skeletal muscle fiber also known as?

Slow-twitch

What is a type 2 skeletal muscle fiber also known as?

fast-twitch

What is a slow-twitch skeletal muscle fiber?

less powerful muscle fiber that fatigues slowly

What is a fast-twitch skeletal muscle fiber?

more powerful muscle fiber that fatigues quickly

How are fast-twitch skeletal muscle fibers more powerful?

extensive sarcoplasmic reticulum for increased calcium release

What are the two subclasses of type 2 (fast-twitch) skeletal muscle fibers?

2a and 2b

What is a type 2a skeletal muscle fiber?

in-between a slow and fast twitch

What is a type 2b skeletal muscle fiber?

classic fast-twitch

What kind of blood supply does a type 1 skeletal muscle fiber have?

rich blood supply

What kind of blood supply does a type 2 skeletal muscle fiber have?

less extensive blood supply

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine

What happens to a muscle fiber when acetylcholine is released at the NMJ?

causes NA+ to enter the muscle cell and depolarize the cell which starts an action potential

What does an initial action potential in a muscle fiber cause?

T-tubercles to release calcium from the sarcoplasmic reticulum

What happens when calcium is released from the sarcoplasmic reticulum?

calcium binds to troponin to lift tropomyosin

What happens after tropomyosin is removed from myosin head binding sites on actin?

enzymes cause ATP to be hydrolyzed while the myosin head is unattached

What happens after ATP is hydrolyzed in a sarcomere?

myosin head binds to the actin

What causes the myosin head to pull the actin filament?

The release of ADP+P

What causes the ADP+P to be released from the myosin head?

The myosin head binding to the actin filament causing a conformational change

How does myosin release from the actin?

when a new ATP binds

What are the four additional mechanisms by which smooth muscle is stimulated?

1. mechanical pressure
2. blood pH
3. Oxygen
4. Extracellular ion concentration

Do smooth muscles have actin and myosin?

Yes, just not as organized so no striations are formed

What are the cell characteristics of smooth muscle?

spindle-shaped with single, central nucleus

Compare/contrast the cell nuclei of skeletal, smooth, and cardiac muscle

1. skeletal- multiple nuclei in periphery
2. smooth- single, central nucleus
3. cardiac- single, central nucleus

What are the two types of smooth muscle cells?

1. multi-unit
2. single unit

What is a multi-unit smooth muscle cell?

has several autonomic neuronal axons spread like a network in between al of the cells for fine movement (being able to signal one cell at a time)

What is a single unit smooth muscle cell?

has one autonomic neuronal axon running near all the muscle cells and gap junctions for communication of ONE big uniform contraction

What special characteristic do cardiac muscle cells have?

intercalated discs

What are intercalated discs for?

communication

How is smooth muscle contraction initiated?

Calcium levels increase and bind to CaM (calmodulin)

How is skeletal/cardiac muscle contraction initiated?

Acetylcholine released at NMJ

What happens once calcium binds to calmodulin?

The calcium-calmodulin complex activated MLCK

What is MLCK?

myosin light chain kinase

What is the job of MLCK?

phosphorylate light chains of myosin heads to increase myosin ATPase activity (add ADP+P to myosin head)

What step is the first step to be the same in skeletal/cardiac and smooth muscle contraction?

ATP is hydrolyzed and cross-bridging begins