AVS331: Muscle tissue system

Muscle tissue

A body tissue that contracts or shortens, making body parts move

Neuromuscular junction (NMJ)

Synapse between nerve fiber and muscle fiber

Axon terminal

Swollen end of nerve fiber

Synaptic cleft

a gap into which neurotransmitters are released from the axon terminal (into sarcolemma)

Motor end plate

Sarcolemma of muscle fiver at synapse (post-synaptic membrane)

Acetylcholine

Neurotransmitter released at neuromuscular junction

Junctional folds

invaginations of the sarcolemma where ACh receptors are especially concentrated (millions of them)

Basal lamina

Thin layer of collagen and glycoprotein separating axon terminal and muscle cell from surrounding tissues

What does basal lamina contain?

Acetylcholinesterase (breaks down ACh to allow for muscle relaxation)

How do toxins interfere with synaptic function?

They paralyze muscles

What are 2 types of paralysis that can happen with toxins block the release of ACh?

Flaccid paralysis and botulism

Flaccid paralysis

A state in which muscles are limp and can't contract

Botulism

Type of food poisoning caused by a neuromuscular toxin secreted by bacterium (Clostridium botulinum)

Some pesticides contain _______

cholinesterase inhibitors

Cholinesterase inhibitors

Binds to acetylcholinesterase and prevent it from degrading ACh

Spastic paralysis

State of continual muscle contraction

What is the order of complexity for muscles? (go from most complex to most basic)

Muscle -> Muscle/Connective tissues -> Muscle cell/Muscle fiber/Myofiber -> Myofibrils -> Myofilaments

What does Skeletal muscle consist of?

muscular tissue, connective tissue, nerves, and blood vessels

What are 2 synonyms for muscle fiber?

Myofiber and skeletal muscle cell

Endomysium

Connective tissue surrounding a muscle fiber

Fascicle

bundle of muscle fibers

Perimysium

Connective tissue surrounding a fascicle (also has nerves, blood vessels, stretch receptors)

Muscle (organ)

consists of hundreds to thousands of muscle cells, plus connective tissue wrappings, blood vessels, and nerve fibers

Epimysium

a sheath of fibrous elastic tissue surrounding a muscle

Compartment

Groups functional muscles together

Fascia

a band or sheet of fibrous connective tissue that covers, supports, and separates muscle into their respective groups

What are the 2 cell types of muscle tissue?

Muscle fiber and myosatellite cells

Muscle fiber

Formed by fusion of myoblasts during embryogenesis (lots of nuclei and very long cells)

Myosatellite cells

Stem cell myoblast that didn't fuse (aid in muscle repair)

Sarcolemma

muscle cell membrane

T-tubules

tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side

What are the parts of muscle fiber?

Sarcoplasma, myoglobin, glycogen, mitochondria, myofibril, sarcoplasmic reticulum

Sarcoplasma

cytoplasm of a muscle cell

Myoglobin

An oxygen-storing, pigmented protein in muscle cells.

Glycogen

Nutrient stores

Mitochondria

Powerhouse of the cell, organelle that is the site of ATP (energy) production

Myofibril

A long, filamentous organelle found within muscle cells that has a banded appearance

Sarcoplasmic reticulum

Organelle of the muscle fiber that stores calcium (wraps around each myofibril)

Terminal cisterns

dilated end sacs of the sarcoplasmic reticulum (cross muscle fiber from one side to other)

Triad

T tubule + 2 terminal cisterns associated with it

How does a myofibril function?

Responsible for contraction, surrounded by sarcoplasmic reticulum (anchored to sarcolemma of muscle fiber

Myofilaments

bundles of protein filaments

What are the parts of myofilaments?

Contractile proteins, elastic filaments, regulatory proteins

Contractile proteins

Myosin and actin (do the work of shortening the muscle fiber)

Myosin

thick filaments (2 polypeptide chains interwined)

Actin

thin filaments

What are the types of thin filaments?

Fibrous actin, tropomyosin molecules, troponin molecule

Fibrous actin

2 intertwined strands

Tropomyosin molecules

Each blocking 6 or 7 active sites on G actin subunits when muscle is relaxed

Troponin molecule

small, calcium-binding protein on each tropomyosin molecule

Elastic filaments

Titin (provide elastic recoil after contraction and help stabilize and position thick filament)

Regulatory proteins

Tropomyosin and troponin (act like a switch that determins when fiber can/can't contract)

Dystrophin

Links thin filaments to proteins of endomysium

What is the purpose of dystrophin?

Transfers forces of muscle contraction to connective tissue that leads to tendon

Sarcomere

Contractile unit of muscle (made up of A band, H band, M line, I band, and Z disc)

A band

dark area (extends length of the thick filaments)

H band

not as dark (thick filaments only)

M line

Connection of neighboring thick filaments

I band

a light band composed of thin filaments only

Z disc

Provides anchorage for thin filaments and elastic filaments (bisects I band)

How do sarcomeres function?

Muscle cells shorten as individual sarcomeres shorten

During shortening, dystrophin and linking proteins also pull on _________

extracellular proteins