Chapter 12 muscles

What triggers the contraction of muscles at the cellular level?

Neural activity causes changes in the membrane potential of muscle cells, leading to internal changes in calcium release, which then causes muscle contraction.

What causes change in the membrane potential of muscles ?

Neural activity causes change in the membrane potential of muscles

How are changes in membrane potential of muscles linked to muscle contraction

Changes in the membrane potential of muscles are linked to internal changes in calcium release which triggers contraction

What is sliding filament mechanism ?

The process in which myosin filaments bind to and move actin filaments, leading to muscle contraction

What role does calcium play in muscle contraction ?

Calcium release inside the muscle is responsible for initiating the contraction process

What is the basic mechanism for muscle contraction when stimulated ?

Sliding filament mechanism, where myosin binds to and moves actin filaments

How are myosin and actin interactions regulated in all three types of muscle (skeletal, cardiac, and smooth )

Regulated by the availability of calcium ions

What involuntary function does smooth muscle perform ?

Regulation of blood pressure and movement of material in the gut

What is the primary function of cardiac muscle ?

Contraction and relaxes spontaneously to move blood through the body

Where is cardiac muscle found ?

only in the heart

What roles does calcium play in smooth, cardiac, and skeletal muscle function ?

All three muscle types calcium ions regulate the interactions between myosin and actin, which are essential for muscle contraction

What is the structure of skeletal muscle in terms of muscle fiber ?

Skeletal muscle typically contains many muscle fibers which are group into fascicles

What are myofibrils? Where are they found ?

Structures found within muscle fibers and they contain myofilaments (proteins)

Why is a skeletal muscle cell called a muscle fiber ?

Due to its elongated shape

How long can a skeletal muscle fiber be ?

20 cm long

What is the diameter range of a skeletal muscle fiber ?

Range from 10 to 100 micrometers

Why do muscle fibers have multiple nuclei?

Because they result from the fusion of multiple cells during development

What is a muscle composed of ?

Multiple skeletal muscle fibers bound together with connective tissue

How is muscle attached to bone?

By tendons which are bundles of connective tissue consisting of collagen fibers

What happens when a muscle contracts?

It generates tension on the tendon which moves the bone at a joint

What do myofibrils contain ?

myofilaments which are proteins in muscle contraction

Where does the neuromuscular junction occur ?

The location is where a muscle fiber and a motor neuron meet

What causes an action potential in muscle fiber ?

An action potential in a motor neuron causes an action potential in the muscle fiber

What neurotransmitter is released at the neuromuscular junction ?

acetylcholine

What is the role of acetylcholine in muscle contraction ?

ACh binds to nicotinic ACh receptors on the muscle fiber membrane, which triggers an action potential (AP) in the muscle fiber resulting in muscle contraction

What is a motor unit ?

A motor neuron and all the muscle fibers it innervate

What is the neuromuscular junction role in muscle contraction ?

The neuromuscular junction is the point of synaptic contact between the axon terminal of a motor neuron and the muscle fiber, where acetylcholine is released leading to muscle contraction

What is the neuromuscular junction?

The point of synaptic contraction between an axon terminal of a motor neuron and the muscle fiber it controls

What happens after acetylcholine is delivered to the muscle fiber?

Contraction follows the delivery of acetylcholine (ACh) to the muscle fiber

What is a motor unit?

Consists of a motor neuron and all of the muscle fiber it controls

How many motor units are typically found in a muscle ?

Each muscle contains hundreds of motor units, each controlling many muscle fibers

How do smaller motor units contribute to muscle control

Smaller motor units allow for finer muscle control because they involve fewer muscle fiber per neuron

What is recruitment in muscle physiology ?

Recruitment is the process of increasing the number of motor units that are active in a muscle at any given time as needed to increase muscle tension

How does activation of more motor neuron affect muscle tension ?

The activation of more motor neurons lead to increase muscle tension

How does the brain control muscle movement through recruitment ?

The brain recruits more motor units until the desired movement is accomplish smoothly

How is greater strength and muscle tension produced ?

By activating more and larger motor units

Each skeletal muscle fiber is packed with what and what does it cause ?

Packed with myofibrils and it extends the length of the fiber

What are myofibrils packed with and what do they produce ?

Packed with myofilaments, actin, and myosin which produce a striated appearance

The interaction of myofilaments cause what ?

Muscle fiber contraction

What is a myofibrils

Cylindrical bundles of myofilaments, 1-2mm in diameter

What are the sections in myofibrils called ?

sarcomeres

What are myofilaments?

Striations in a myofibrils are due to the arrangement of thick and think protein

What does thick filament have ?

myosin

What is a myofibrils and how large is it in diameter ?

A myofibrils is a cylindrical bundle of myofilaments and its is 1-2mm in diameter

What are sections of a myofibrils called ?

sarcomeres

What causes the striations in a myofibrils ?

The striations in a myofibrils are caused by the arrangement of thick and think protein filaments

What is the function of the thick filament in a sarcomere ?

The thick filament is made of myosin and its globular heads form cross-bridges with active during muscle contraction

What is the primary protein component of thin filament in a scaromere ?

The primary protein is actin

What are the three subunits of troponin and what do they bind to ?

The three subunits are

Troponin C (bind to calcium)

Troponin T ( binds to tropomyosin)

Troponin I (binds actin)

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What is the role of tropomyosin in muscle contraction ?

Tropomyosin blocks the myosin binding site n active preventing muscle contraction uniting calcium binds to troponin and shifts the tropomyosin

What is a sarcomere and what is its role in muscle structure ?

A sarcomere is the basic contractile unit in striated muscle structure and it is a section of the myofibrils

What structure marks the ends of a sarcomere ?

Z discs

Where is actin anchored in a sarcomere ?

Z disc

How is myosin anchored in a sarcomere ?

Myosin is anchored to the Z line by Titian in a sarcomere

What are the A bands and I band in a sarcomere ?

The A bands and I bands are parts of the scaromere with A bands containing the thick myosin filament and I bands containing the thin actin filament

What are the two types of filament that compose a sarcomere ?

Thick filaments called myosin and thin filaments called actin

How is myosin anchored in the sarcomere ?

Myosin is anchored in place by Titian fibers in the sarcomere

Where is actin anchored in the sarcomere ?

Z disk

What forms between myosin and actin during muscle contraction ?

Cross-bridges form between myosin and actin during muscle contraction

What must happen for muscle contraction to occur ?

For muscle contraction to occur, myosin must bind to actin to form cross-bridges

In a relaxed muscle, what prevents myosin from binding to actin ?

The binding site on active is blocked by tropomyosin

What is the function of troponin in a relaxed muscle ?

Troponin holds tropomyosin in a block position, preventing myosin from binding to actin

What is the structure of troponin and what are the roles of its subunit ?

Troponin is a heterotrimer ( a molecule with three subunits). The subunits:

C (binds Ca2+)

T(binds tropomyosin)

I (binds actin)

What happens during muscle contraction when the muscle fiber is depolarized ?

When muscle fiber is depolarized an action potential (AP) travels down the transverse tubules, leading to the release of Ca2+ from the sarcoplasmic reticulum

How does Ca2+ contribute to muscle contraction ?

Ca2+ binds to troponin C causing a conformational change in troponin T which moves tropomyosin out of its blocking position and allows the myosin cross bridges to bind to actin

What occurs between the filaments during muscle contraction?

During muscle contraction, the thick myosin filaments and thin actin filaments slide past each other.

Where are skeletal muscle located in the body ?

Skeletal muscles are attached to bones

What is the appearance of skeletal muscle cells and why do they have that appearance ?

What type of control is responsible for skeletal muscle contraction ?

Is under voluntary control, managed by the somatic nervous system

Where are smooth muscle cells located in the body ?

In the walls of internal organs and the skin

What is the appearance of smooth muscle cells ?

-do not have striations

-long and flat with spindle-shaped pointed ends and a single centrally located nucleus

What type of control is responsible for smooth muscle contraction ?

Involuntary controlled by the autonomic nervous system

Where are cardiac muscle cells located in the body ?

Heart only

What is the appearance of cardiac muscle cells and how does it compare to skeletal muscle cells ?

They are striated similar to skeletal muscle cells, but they are in voluntary unlike skeletal muscle cells

What happens when a muscle fiber is depolarized ?

When a muscle fiber is depolarized an action potential (AP) travels down the transverse tubules in the fiber resulting in the release of Ca2+ from the sarcoplasmic reticulum

What role does Ca2+ play in muscle contraction ?

Ca2+ binds to troponin C, causing a confrontational change in troponin T which moves tropomyosin out of its blocking position. This allows the myosin cross bridge to bind to actin

What structural change occurs when tropomyosin moves out of its blocking position ?

When tropomyosin moves out of its blocking position it allows the myosin cross-bridge to bind to actin facilitating the process of muscle contraction

What happens to the filaments during muscle contraction ?

During muscle contraction, the filament slide past each other

What is necessary for muscle contraction to occur at the molecular level ?

For muscle attraction to occur myosin must bind to actin to form cross bridges

What is the primary action during muscle contraction

The activation of the force generating sites in muscle fibers generates tension

What is the sliding filament mechanism ?

Overlapping thick (myosin) and thin (actin) filaments in a sarcomere move past each other to contract a muscle fiber

What happens when myosin binds to active during muscle contraction ?

When myosin binds to actin it slides the actin filament pulling the Z-lines closer together and reducing the width of the I-band and H band

What is the result of myosin pulling the actin filament during muscle contraction ?

The Z lines are pulled closer together and the width of the I-bands and H-bands is reduced

What is the role of ATP in the activation of the myosin head ?

ATP binds to the myosin head, and the myosin head acts as a ATPase to split ATP into ADP and Pi

What happens when myosin binds to actin ?

muscle contraction

What occurs during the cross bridge power stroke ?

Pi released from the myosin head, and a conformational change occur, causing the myosin head to slide the actin filament (sliding filament mechanism )

What is required for cross bridge to release and the muscle fiber to relax ?

A new ATP must bind to the myosin head to release the cross bridge and allow the muscle fiber to relax

What is tension in muscle contraction ?

Tension is the force exerted on an object by a contracting muscle

What is load in muscle contraction ?

Load is the force exerted on a muscle by an object

How are tension and load related during muscle contraction ?

Tension and load are opposing forces during muscle contraction

What is a twitch in muscle contraction ?

The mechanical response (contraction) of a muscle fiber to a single action potential (AP)

What is summation in muscle contraction ?

Summation is the increase in muscle tension in a fiber due to successive action potential or stimuli occurring during contraction

What is recruitment in muscle contraction ?

The increase in muscle tension in a fiber due to the activation of more motor units or increase stimulation

What is tetanus in muscle contraction ?

A sustained maximal contraction that results from repetitive stimulation

Can you give an example of tetanus or tetany in everyday activities ?

Exp include crouching, maintaining posture holding up a heavy box

What is tension ?

Force exerted on an object by a contracting muscle

What is load ?

Force exerted on a muscle by an object

What is the relationship between tension and load ?

They are opposing forces

What is a twitch ?

Mechanical response (contraction) of a muscle fiber to a single AP

What is summation ?

Increase in muscle tension in a fiber, due to successive AP occurring during contraction