Chapter 11 - Muscular and Skeletal Systems Flashcards
Three types of muscle
Skeletal - voluntary muscle
Cardiac - only in the wall of the heart. No conscious control.
Smooth - walls of hollow organs, responsible for GI motility, constriction of blood vessels, uterine contraction. No conscious control
Skeletal Muscle
Voluntary movement in response to somatic motor neurons.
Tendons
Attach muscle to bone.
Strong connective tissue formed primarily of collagen.
Directions of skeletal movement
Flexing - reducing the angle of the joint.
Extending - increasing the angle of the joint.
Abducting - moving away from the midline.
Adduction - move toward the body midline.
And others…
Origin
Point closest to the center of the body where skeletal muscle attaches.
Insertion
Point further away from the body center line where muscle attaches.
Curing contraction, the insertion point is brought closer to the origin.
Antagonistic Muscles
Muscles responsible for movements in opposite directions.
Synergistic Muscles
Muscles that move a join in the same direction.
Fascicles
Bundles of skeletal and connective tissue.
Connective tissue facilitates flexibility in the muscle.
Muscle Fibers
Also known as myofibers.
Refers to a single skeletal muscle.
Has a cell membrane called SARCOLEMMA.
Contain Myofibril.
Multinucleate Syncytia
Result of the fusion of individual cells during development.
Innervated by a single nerve ending.
Stretch the entire length of the muscle.
Sarcolemma
Composed of plasma membrane and an additional layer of polysaccharide and collagen.
Aids fusion with tendons.
Myofibril
Like a specialized organelle.
Causes striated appearance of muscle cell. Generates contractile force of skeletal muscle.
Actin and Myosin in skeletal muscle
polymerized and generate contraction.
Actin - forms thin filaments
Myosin - forms thick filaments
Sarcomeres
Many together form a myofibril.
Create the striated appearance due to the overlap of thin and thick filaments.
Each sarcomere is bounded by two Z-lines.
Thin filaments attach to Z-lines and overlap with thick filaments in the middle.
I bands
Sections of a sarcomere that are only thin filament.
A band
The full-length of the thick filament. (Includes overlapping regions with the thin filaments)
H-Zone
The region with only thick filaments. Only visible in resting sarcomeres.
Sliding Filament Model of Muscle Contraction
Filaments slide over eachother during contraction.
Myosin is an enzyme that uses ATP to create movement (ATP hydrolysis). Each Myosin monomer has a head and tail portion and can be referred to as myosin ATPase as it drives the ATP hydrolytic activity.
Myosin Binding Site
Specific site on thin filament where myosin binds actin.
When connected, they are said to form a CROSS BRIDGE.
Four steps of a contractile cycle
- Cross bridge formation. Myosin is ADP and Pi bound.
- Power Stroke. Myosin head moves to a low energy conformation. ADP is released.
- ATP binds. Release of Myosin head.
- ATP hydrolysis. Cocks the myosin head, putting it in a high energy conformation.
This occurs spontaneously if Myosin, Actin, and ATP in a beaker (with Mg2+)
Does contraction in myofibrils occur spontaneously?
No. Only when cytoplasmic [Ca] increases.
Why?
Because the actin filament also contains a troponin-tropomyosin complex.
Toponin-Tropomyosin Complex
Part of the actin filament and prevents contraction without [Ca] present.
Tropomyosin is long and fiborous. Wraps around actin and blocks all myosin binding sites.
Troponin is a globular protein that binds tropomyosin, but can also bind Ca. Binding of Ca creates a conformational change that results in a freeing of the myosin binding sites.
Neuromuscular Junction (NMJ)
the synapse between an axon terminus and a myofiber.
A long invagination of the cell membrane.
The axon terminus fills the entire cleft.
Allows for depolarization of a large region all at once.
Motor end plate
The long most synaptic region of the myofiber membrane of the NMJ.
Post-synaptic membrane ACh receptors in the NMJ
Are ligand-gated Na+ channels.
End plate potential (EPP)
The depolarization of the post-synaptic cell in the NMJ.
Miniature End Plate Potential (MEPP)
Depolarization resulting from the exocytosis of a single ACh vessicle.
Acetylcholinesterase
ACh degradation in the NMJ. Otherwise it will continue to activate.
An action potential in a myofiber
Only occurs when voltage-gated Na+ channels are activated upon reaching the threshold potential.
It must depolarize the entire myofiber before contraction can occur.
Transverse Tubules
Deep invaginations in the myofibers, that allow AP (which really only occur at the surface of a cell), to depolarize the interior.
Sarcoplasmic Reticulum
A specialized Smooth endoplasmic reticulum that enfolds each myofibril.
Specialized to release and sequester Ca rapidly into the sarcoplasm.
Ca is only realized upon depolarization of the myofiber.