Week 1 Lesson 5: Function of Muscles and tendons

What sarcomere structure defines the boundary of each sarcomere while anchors the thin filaments?

Z line

How do muscle cells (fibers) develop force or tension?

By contracting

What are the two major myofilaments are contained in muscle fibers?

Actin and myosin

How are myofilaments organized?

In a repetitive pattern of dark and light bands

What is the contractile functional structure of the skeletal muscle?

• Bundle of muscle fibers

• Myofibril

• Myofilaments

• Sarcomeres

What is the energy functional structure of the skeletal muscle?

Capillary

Mutochondrion

What is the excitability functional structure of the skeletal muscle?

Cell membrane

T-tubule

Where is the calcium stored in the functional structure of the skeletal muscle?

Sarcoplasmic reticulum

What is the functional unit of the skeletal muscle?

Sarcomere

What makes up the thick filament of the sarcomere?

Myosin

What are the two characteristics of Myosin?

Tail and 2 heads

What are the three components of the thin filament?

Actin

Tropomyosin

Troponin

What are the three subunits of troponin and their function?

C: binds to Ca

I: inhibitory, binds to actin

T: Binds to tropomyosin

What are formed by the interaction of myosin heads to active site in actin filaments?

Cross bridges

Why component of the thin filament inhibits the binding of actin sites to the myosin head?

Tropomyosin

When bound with Ca what component of the thin filament remove tropomyosin?

Troponin

What occurs to the A band during muscle contraction?

It remains the same length

All skeletal muscle fibers are innervated by what?

A neuron

What is it called when a single motor neuron communicates with serveral muscle fibers?

Motor unit

As tension in the muscles increase what also increases?

The number of motor units needed

What is the connection between two cells called?

Synapse

What is a synapse of a motor neuron with a muscle fiber called?

Neuromuscular junction

What is the Neuromuscular junction between the motor neuron and muscle fiber?

Chemical synapse

How is the Neuromuscular junction between the motor neuron and muscle fiber a chemical synapse?

it involves neurotransmitter release form the neuron that binds to muscle receptors at the motor end plate

Skeletal muscle fibers must be excited to contract , how does this happen?

Sarcolemma of the muscle fiber must experience an action potential

What is released from the motor neuron into the synaptic cleft that is between the neuron and muscle fiber?

Acetyl Choline (ACh)

ACh binds to what in the motor neuron end plate and allows Na to enter the muscle fiber?

Ligand gated Na Channel

With the entry of Na what happens to the sarcolemma?

It deporlarizes

What stimulates an action potentia; that will travel along rhe sarcolemma and down into the T-tubules?

The end-plate potential

How does the action potential move along the entire sarcolemma?

Propagates in a wave-like pattern

As a result of the action potential, the depolarization of one area of the membrane will depolarize other neighboring areas, stimulating what?

Opening of other voltage-gated Na channels along the muscle membrane

What refers to the connection of the depolarization of the sarcolemma and the contraction of the myofilaments?

Excitation-contraction coupling

What are deep invaginations of the muscle cell membrane into muscle fibers?

T-tubules

The T-tubules contact what organelle?

Sarcoplasmic reticulum

The wave of depolarization drives into the deep muscle fiber thanks to what?

The T-tubule

The t-tubules are directly linked to the cisternae of the sarcoplasmic reticulum were what is stored?

Calcium

When the depolarization wave runs through the t-tubules it stimulates the release of what from the SR?

Calcium

Where is Calcium released into from the SR?

The cytoplasm

Muscle contractions require many action potentials to occur repeatedly in this way the concentration of what increases with each one?

Calcium in the Cytosol

Calcium binds to what and triggers the sliding mechanism in the muscle?

Troponin

What curls around the thin filaments blocking the active sites of actin molecules, blocking the interaction with the myosin heads?

Tropomyosin

How does Ca ions binding to Troponin C allow for muscle contraction?

It initiates a mechanism that moves tropomyosin away from the actin active sites, allowing for the binding of the myosin head.

What are the 4 stages of the cross-bridge cycle?

1. ATP hydrolysis cocks the myosin heads

2. Myosin head binds to actin

3. Power stroke occurs

4. ATP breaks the attachment of myosin to actin and the cycle starts again

What does the term excitation-contraction coupling describe?

the process linking sarcolemma depolarization to myofilament contraction

At the end of each muscle, interdigiting collagen fibers merge and contribute to a connective tissue bundle called what?

Tendon

What is connected directly to the tendon creating a pull on the tendon attached to the bone?

Each individual muscle fiber

What is the function of tendons?

Transmit the tension

Store and release elastic energy

stabilize joints

What are the three steps of the sarcomere relaxation stage?

1. Stop ACh release

2. ACh left in the synaptic cleft must be broken down by acetylcholinesterase

3. Ca concentrations in the cytosol must decrease via active reuptake into the sarcoplsmic reticulum.

What is referred to the slight tension of the muscles?

Muscle tone

Muscle tone is the result from what?

The involuntary activation of motor units by the brain and spinal cord

What alternates motor units to activate so all can rest?

CNS

These contractions elicited by muscle tone are not strong enough for movement but the help maintain what?

Posture and stabilize joints

What is an intracellular enzyme present in high concentrations in the cytoplasm of skeletal and cardiac muscle fibers?

Creatine kinase (CK)

CK physiological role s the regenerate what and make it available for muscle contractions?

ATP

What will increase in the blood if there is muscle injury?

CK

What is a muscle protein that binds oxygen and stores it for use during muscle contractions?

Myoglobin

What is the clinical significance to myoglobin the blood?

When muscle finers are damaged myoglobin is also released into the bloodstream

Myoglobin is filtered by the kidneys, and elevated concentrations can lead to obstruction of the renal tubules, which can damage the kidneys.

Myoglobinuria

What contained in the myoglobin gives the urine that dark red or brown color?

Iron

Why can myoglobin appear in urine after muscle damage?

it leaks from damaged muscle cells into the bloodstream and filtered by the kidneys