muscle notes

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The Muscular System

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Muscle notes

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Page 1: Muscle notes

The Muscular System

Page 2: Muscle notes

Interesting Facts

• We have more than 600 muscles.

• By weight, the muscle system is the largest.

• Muscles use the majority of the body’s energy

• Muscles produce most of the body’s heat.

• You used more than 100 muscles to take out your notebook and write this.

Page 3: Muscle notes

Muscle Basics

• Muscles are made of muscle fibers (cells) and connective tissue.

• Muscle cells are made of various proteins.

• A muscle cell is as long as the muscle it is part of.

Page 4: Muscle notes

Organization

• Each muscle is separated from everything around it by a connective tissue “sac” called the fascia.

• Just deep to the fascia is a connective tissue layer called the epimysium.

• The epimysium holds together many packets of muscle fibers called fascicles.

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Page 6: Muscle notes

Organization

• Each fascicle is separately wrapped in a connective tissue layer called the perimysium.

• Within each fascicle, each individual muscle fiber is wrapped in a connective tissue called endomysium.

• Sattelite cells are found within the layer of endomysium

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Muscle Microanatomy

• Each muscle cell is composed of:– multiple nucleii– various contractile proteins– Sarcolemma (cell membrane)– Sarcoplasm (cytoplasm)– many mitochondria– sarcoplasmic reticulum and t-tubules

Page 9: Muscle notes

Micro-organization

• Muscles contain many fascicles

• Fascicles contain many muscle fibers

• Muscle fibers contain many myofibrils

• Myofibrils contain the contractile proteins actin and myosin (myofilaments).

• Actin and myosin form the contractile units called sarcomeres.

Page 10: Muscle notes

Muscle Microanatomy

• This tiny structure (2.25 um) is the moving force behind muscle contraction

Page 11: Muscle notes

The Sarcomere

• Is composed of actin and myosin fibers

• Has distinct areas– M-line-runs in the middle of the sarcomere– Z-disks-mark the borders (ends) of the

individual sarcomere– A-band in the area where myosin is found– I-band is the area where ONLY actin is found– H-zone is the area ONLY myosin is found

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MYOSIN

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THE NEUROMUSCLULAR

JUNCTION

The motor unit is a nerve and the muscle fibers that it stimulates. There are several muscle fibers connected to each nerve.

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Sliding Filament Animation

• lSliding Filament Animation

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The Junction

• The neuromuscular junction is where the nerve meets the muscle cell. There is not a direct connection, but rather a small space between the two.

Page 19: Muscle notes

The Synaptic Junction

• This space is called the synaptic cleft.

• The purple circles are called vessicles.

• Vessicles are like bags that hold a substance.

Page 20: Muscle notes

The Impulse

• The brain sends a nerve impulse through the motor neuron.

• This impulse causes little sacs called vesicles to release their contents.

Page 21: Muscle notes

The Neurotransmitters

• The vessicles burst open releasing a neurotransmitter called acetylcholine (Ach)

• The Ach travels across the empty space (synapse) to the special receptors on the other side.

Page 22: Muscle notes

The motor end plate

• There is a structure called a motor end plate across form the nerve.

• The receptors a re found on the motor end plate.

Page 23: Muscle notes

The role of calcium

• The receptors, once stimulated signal the sarcoplasmic reticulm to release calcium ions.

• These calcium ions travel down the T tubules to the sarcomere.

Page 24: Muscle notes

The Sliding Filament Theory

• Thin filament-actin-has active sites• Thick filament-myosin-has a head and a tail• The troponin-tropomyosin complex blocks

the active sites on the actin.• A site on the troponin has a receptor that

can bind a calcium ion, modifying the complex so that it no longer blocks the active site.

Page 25: Muscle notes

Sliding Filament Theory

• Once the active site is available, a myosin head attaches to it.

• The myosin head then pivots on its tail making the sarcomere shorter.

• As this happens in thousands of sarcomeres the entire muscle shortens or CONTRACTS.

Page 26: Muscle notes

All or none response

• A muscle fiber contracts fully or not at all. If the stimulus is not high enough, nothing happens, even if it is very close to the threshold. If it is over the threshold-even by just a little, maximum contraction occurs.