Lec 17+ 18 Musculoskeletal System

Skeletal muscle

Responsible for locomotion, facial expressions, shivering, and breathing; it is striated.

Cardiac muscle

Makes up the heart and is responsible for pumping blood; it is striated.

Smooth muscle

Involuntary muscle that generates forces in hollow organs such as the gut, bladder, and blood vessels; it is not striated.

A skeletal muscle is made up of…..

a bundle of fibers

Each muscle fiber is….

multinucleated, containing numerous myofibrils

Myofibrils

Highly ordered assemblages of thick myosin and thin actin filaments found within each muscle fiber.

Sarcomeres

The functional unit of contraction in muscle fibers.

Only actin filaments

myofibril appears light

both actin and myosin

myofibril appears dark

Neuron

Nerve Cell

Nodes of Ranvier

a gap in the myelin sheath of a nerve

Dendrites

a neuron's bushy, branching extensions that receive messages and conduct impulses toward the cell body

Cell Body

integrates incoming signals and generates outgoing signal to axon

Axon

passes electrical signals to dendrites of another cell or to an effector cell

Axon Terminals

Branches at the end of the axon

Motor unit

A single motor nerve and the associated muscle fibers that are innervated upon stimulation.

Action potential

The electrical signal that begins at the dendrites and travels along the axon to initiate muscle contraction.

Myelin

Lipid-based structures that insulate axons, increasing signal speed.

Walk along or Ratchet Theory of Muscle Contraction

The theory that explains how myosin heads bind to actin during contraction via ATP binding and cleavage.

Troponin

A protein complex that binds calcium, causing exposure of myosin binding sites on actin.

Calcium pumps

Protains on the surface of the sarcoplasmic reticulum that actively transport calcium out of the cytoplasm and back into the SR.

In each A band, there is a H zone split down by

the M line

What is the M line made of

myomesin

What are the I bands split down the middle by?

The Z disc

one sarcomere runs from

one Z disc to the next

thick filaments

composed of myosin, across A band connected at M line

thin filaments

contain actin, extending across I band into the A band

elastic filaments

made of titin, spanning from Z discs to thick filament (core of thick filament)

myosin structure

head, tail, neck

myosin heads

Actin binding site
ATP binding site
where thick and thin filaments will interact by making cross bridges

tropomyosin

blocks myosin binding when muscle is relaxed

troponin

regulatory protein that binds to actin, tropomyosin, and calcium

What is the function of the sarcoplasmic reticulum?

It serves as the Ca++ corral prior to its release into the sarcoplasm.

What does the sarcoplasmic reticulum surround?

It surrounds a myofibril.

What triggers the release of Ca++ from the sarcoplasmic reticulum?

Depolarization of t-tubules.

SR function

stores and releases calcium

What are t tubules also called?

Transverse tubules

Where are t tubules found?

In skeletal and cardiac muscle cells

What is the function of t tubules?

They allow depolarization of the membrane to quickly penetrate to the interior of the cell.