1.2.1 HBS Human Body Systems PLTW WCHS Mr. Alasti

What forms the cross bridge?

Myosin head

What is the basic functional unit of muscle?

The sarcomere

What is the sarcomere made of?

Thick myosin filaments and thin actin filaments 

What do myosin and actin filaments do within the sarcomere?

Slide past each other

Neuromuscular junction

The specialized synapse where a motor neuron communicates with a muscle fiber to control muscle contraction

What are Z lines ?

Thin actin filaments that are attached to the ends of the sarcomere 

What are M lines?

Thick myosin filaments that are attached to the center of the sarcomere 

The sliding filament theory

Explains muscle contraction, stating that the thin actin filaments and thick myosin filaments within a sarcomere slide past each other, causing the sarcomere to shorten and the muscle to contract

What do the thick and thin filaments do when a muscle contracts?

Slide past each other so the muscle shortens, but the filaments stay the same length

What is the main responsibility of the myosin head?

To generate movement

How are thick filaments made?

The myosin’s tail attaches to tails of other myosin molecules

How are thick filaments held in place?

By a spring like molecule called titin

What happens from changes to the myosin head’s ATP?

Repeated cross bridging with actin filaments 

What happens during each ATP binding, hydrolysis, and release?

The head moves along the actin filament in one direction to the next binding site 

Hydrolysis

A chemical reaction where water breaks down a compound into smaller parts by inserting its hydrogen and hydroxyl groups across a bond

True or False: Heads are only attached to actin for a very short time in each cycle?

True

Label the image

1. Muscle Fiber

2. Myofibrils

3. Endoplasmic Reticulum (ER)

4. Plasma Membrane

Label the image

Action potential

Label the image

Tubules

Label the image

1. Myofibrils (relaxed)

2. Sarcomere

Label the image

1. Myofibrils (contracted)

2. Sarcomere

What level of biological organization is muscle?

Organ

Muscle

An organ composed of one of the three types of fibrous tissue (skeletal, cardiac, and smooth), specialized for contraction to produce voluntary and involuntary movements of parts of the body

How are muscles attached to bones?

Through tough cords or sheets of connective tissue called tendons, and these bones meet at other joints

What process pulls on bones and moves the body?

Contraction or shortening of muscles

Contraction

A process leading to shortening and/or development of tension in muscle tissue 

What are the three types of muscle tissue?

Skeletal, smooth, and cardiac

Skeletal muscle tissue

An organ specialized for contraction, composed of striated muscle fibers (cells), supported by connective tissue, attached to bone by a tendon, and stimulated by somatic motor neurons

Cardiac muscle tissue

Striated muscle fibers that form the wall of the heart. They are stimulated by the intrinsic conduction system and autonomic motor neurons 

Smooth muscle tissue

A tissue specialized for contraction, composed of smooth muscle fibers, located in the walls of hollow internal organs, and innervated by the autonomic motor neurons

Which muscle tissues are striated?

Skeletal and cardiac

Which muscle tissues are voluntary control?

Skeletal 

Which muscle tissues are involuntary control?

Smooth and cardiac

How many nuclei does skeletal muscle tissue have?

Many

How many nuclei does smooth muscle tissue have?

One 

How many nuclei does cardiac muscle tissue have?

One

What type of tissue is this?

Skeletal

What type of tissue is this?

Smooth muscle tissue 

What type of tissue is this?

Cardiac muscle tissue

What generates the needed force to move the skeleton?

The contraction of a muscle

What triggers a muscle contraction?

A series of molecular events known as the cross bridge cycle

What takes place when a sarcomere shortens?

Myosin heads within thick myofilaments form cross bridges with actin molecules in thin myofilaments

What initiates the formation of a cross bridge?

When calcium ions (released from the sarcoplasmic reticulum) bind to troponin, which causes the troponin to change shape

What happens when troponin connects with a calcium ion?

Tropomyosin moves away from the myosin binding sites on actin, which allows the myosin head to bind with the actin, forming a cross bridge

True or false: The myosin head must be activated before a crossbridge cycle can begin

True

How does a myosin head become activated?

ATP binds to the myosin head, and is hydrolized to ADP and an inorganic phosphate. The energy taken from the hydrolysis of ATP activates the myosin head, which forces it into the cocked position

What are the four steps of the cross bridge cycle?

1. Cross Bridge Formation- activated myosin head binds to actin, forming a cross bridge, phosphate is released, and the binding between myosin and actin becomes stronger

2. Power Stroke- ADP is released, and the activated myosin head pivots, sliding the thin myofilament toward the center of the sarcomere

3. Cross Bridge Detachment- Another ATP binds to the myosin head, and the link between the myosin head and actin weakens, causing the myosin head to detach 

4. Reactivation of Myosin Head- ATP is hydrolyzed to ADP and inorganic phosphate, and the energy released during hydrolysis reactivates the myosin head, returning it to the cocked position

What has to stay exposed for the cross bridge cycle to repeat?

The binding sites on actin

What happens as the cross bridge cycle repeats?

The myofilaments are pulled toward each other, and the sarcomere shortens, causing the whole muscle to contract

When does the cross bridge cycle end?

When calcium ions are actively transported back into the sarcoplasmic reticulum

What happens when troponin returns to its original shape?

Tropomyosin can glide over and cover the myosin binding site on actin

ATP

A compound composed of adenosine and three phosphate groups that supplies energy for many biochemical cellular processes

What do muscle fibers need in order to shorten or contract?

ATP and salt

What is the equation of percent contraction?

Original length- final length/ original length x 100

Is this muscle fiber relaxed or contracted?

Relaxed

Is this muscle fiber relaxed or contracted?

Contracted

What are the main proteins that make up a sarcomere?

Myosin and actin

About how many sarcomeres does each muscle fiber contain?

Over 2000 sarcomeres, but that number can vary depending on an individual’s muscle mass and age

Location of skeletal muscle tissue

Attached to bones via tendons 

Location of smooth muscle tissue

Make up the walls of the hollow internal organs

Location of cardiac muscle tissue

Walls of the heart

Describe the differences between the three types of muscle tissue

Cardiac and smooth muscle tissue have only one nucleus while skeletal has thousands. Cardiac and skeletal tissue are striated, while smooth tissue has no striations. Cardiac tissue looks almost like channels, skeletal looks like cylinders, and smooth is tightly packed together

What is happening within cells when muscle fibers shorten?

Sarcomeres shorten due to actin and myosin sliding over each other and overlapping which is mainly driven by ATP

What happens inside your muscle when you get a muscle cramp?

A nerve that controls the muscle sends an abnormal sign, which causes the muscle fibers to begin contracting. The fibers then shorten and generate force, and pain and discomfort are then caused from the muscles being contracted for an extended amount of time 

What are common causes of involuntary muscle cramps?

Electrolyte imbalances, dehydration, overexertion, muscle strain, and certain medications

What must be gained for the troponin to slide from the tropomyosin and to reveal the active sites?

Calcium

If one sarcomere is contracting, are all of them?

Yes; the neuron stimulates the entire muscle fiber

True or false: Neurons do not physically touch the muscle fibers, but must be close to be stimulated

True

What happens to a muscle fiber if the neuron is too far away?

The muscle fiber gets smaller and never gets stimulated 

Neuromuscular junction

The spot in which the muscle fiber and neuron are close

What is the chemical stimulus called that neurons create?

Acetylcholine

What does acetylcholine do?

It swims across the space between the neuron and muscle cell membrane (synaptic cleft), and there are receptors that accept the chemical. As soon as it lands, it creates an electric potential, causing calcium ions to be released into the sarcoplasm

How does acetylcholinesterase stop muscle contractions?

It grabs as many acetylcholine receptors as it can to stop contraction by eventually breaking it down, or returning it to the synaptic cleft of the neuron to be packaged and used again. Sarcoplasmic reticulum pumps calcium back, and the troponin doesn't have calcium anymore, placing the tropomyosin back over the active site

What has to take place for neurons to fire?

There has to be a change inside and outside that is achieved by sodium and potassium channels

What are the functions of skeletal muscles?

1. Produce skeletal movement

2. Maintain body position

3. Support soft tissues

4. Guard body openings

5. Maintain body temperature

How does heat get produced from skeletal muscles?

Heat that gets produced gets distributed throughout the cardiovascular system and all throughout the body

What level of organization are muscles? How?

Muscles are organs since they are made up of 2 or more tissue types (nervous, muscular, and connective)

What are the red dots within the muscle fibers?

Myofibrils

What is the blue lacy glove made up of that surrounds each sarcomere?

Sarcoplasmic reticulum

Why do muscles need more mitochondria?

Because muscles use lots of energy 

When does calcium get released into the sarcoplasm?

When electrical impulses are released