Tissue Mechanics Exam #2

What are the structures that make up muscle from smallest to largest?

thick and thin filaments-> myofibril-> muscle fiber-> muscle fascicle-> muscle

What are the connective tissues of the muscle?

epimysium, perimysium, endomysium

What is the epimysium?

surrounds the entire muscle

What is the perimysium?

surrounds the muscle fascicles, blood vessels and nerves lie in this layer

What is the endomysium?

surrounds the individual muscle fibers, just outside the sarcolemma

What is the basal lamina?

scaffolding that surrounds the muscle cell ("basement membrane of the muscle")

What kind of cells are in the muscle?

muscle cells and satellite cells

What are muscle cells and where are they located in the muscle?

they create contractile forces, they are located on the outer edge of the muscle

What are satellite cells and where are they located in the muscle?

they divide, one daughter cell will enter the muscle and the other remains on the outside, they are outside of the basal lamina

Where does energy come from for muscle?

mitochondria producing ATP

What is the z-line on a sarcomere?

end of sarcomere

What is the I-band on a sarcomere?

contains only thin filaments (actin)

What is the A-band on a sarcomere?

entire length of thick filament, may overlap with the actin

What is the H-zone on a sarcomere?

contains only thick filament (myosin)

What do thin filaments do?

myosin binds to actin to generate force and shorten the sarcomere

What does tropomyosin do?

stabilizes the actin filament

What does troponin do?

influences the position of tropomyosin with a bond of Ca++

What does the troponin/tropomyosin complex do at rest (no calcium)?

covers up the myosin binding site

What does heavy chain of myosin do?

molecular motor for muscle contraction

What does light chain of myosin do?

influences the contraction velocity of the sarcomere

What protein anchors the terminal end of the muscle to the musculotendinous junction?

dystrophin and dystrophin associated proteins

What protein stabilizes the actin by acting like a length regulator?

nebulin

What protein connects myosin to the z-lines to prevent overstretching and to return to resting length after stretch or contraction?

titin

What is functions of non-contractile proteins?

-generate passive tension when stretched

-provide internal and external support and alignment of muscle fibers

-help transfer the active forces of the muscle

What is the physiology of a muscle cell?

-muscle is an excitable tissue

-membranes of all living cells have the ability to separate charged ions through membrane receptors and ion channels

What are the three types of protein channels?

chemical dependent, voltage dependent, and potassium channels

What are the steps to a muscle contraction?

1) motor neuron releases neurotransmitter (Ach)

2) neurotransmitter interacts with muscle membrane receptor

3) receptor opens sodium channel allowing Na+ to move into cell

4) voltage channels open allowing Na+, dropping the voltage potential and opening up the rest of the Na+ channels

5) Na+ floods the cell, changing the electrical potential and creating an action potential (depolarization)

6) depolarization spreads across muscle membrane to t-tubules

7)when t-tubules are depolarized, they release Ca++

8) Ca++ diffuses through muscle cell membrane to interact with troponin, causing tropomyosin on actin to uncover the myosin binding site

9) myosin interacts with the myosin binding site and forms a cross-bridge, pulling the actin and myosin closer to one another

10) Shortening of the myofibrils, causing the entire muscle to shorten

What is summation rate coding?

increase in overall force when individual twitches overlap and come together

What is tetanus rate coding?

increase in overall force to maximal force when twitch force frequency is increased to an amount that maxes out the muscles

What characteristics do type I muscle fibers have?

oxidative system (more mitochondria), smaller fibers, endurance based muscle fibers, more ATP= able to last longer, but not able to produce as much force

What characteristics do type II muscle fibers have?

glycolytic or phosphate creatine system, not as much mitochondria, higher level of force production

What does the size principal state?

smaller fibers will be recruited first, then larger.

When you have muscle memory of a stimulus, how is the size principal affected?

the fiber types recruited can skip to get to what they need to counteract the stimulus (can skip past type I straight to type II)

What characteristics do fusiform muscles have?

fibers are going in one direction, since they are going in one direction, they aren't as packed in, so they have a greater ROM but less force production. In line with the tendon, contracting in one direction

What characteristics do pennate muscles have?

fibers are going in multiple directions, so they pack in fibers, at an angle to the tendon (usually between 10-30 degrees), when that happens, more sarcomeres means more force, but not as much ROM (this is because overall fibers are shorter in pennate muscles, so the actin and myosin bump into one another quicker because the sarcomeres are shorter).

T/F: do pennate muscles produces less force at the angle, but more force overall because there are more fibers

true

How is muscle length measured?

from distal tendon to proximal tendon

How can we find pennation angle?

angle between the tendon and the fiber orientation

What factors affect the force production of a muscle?

-pennation angle

-physiological cross-sectional area

-type of muscle orientation (fusiform, unipennate, bipennate, multipennate)

What does the active length-tension curve show us?

-Deals with the contractile components of a muscle contraction (concentric)

-The myosin and actin have optimal lengths

What is passive insufficiency?

when the muscle is stretched too far, the muscle will have limited movement

What is active insufficiency?

when the muscle is contracted too far, the muscle will have limited movement

What does the passive length-tension curve tell us?

The connective tissues (series and parallel components) can be "stretched" or lengthened similar to a rubber band

What does the total length-tension curve tell us?

-Below resting length the active contraction is all that can create force

-Once the passive tension begins to be applied the total force that can be formed flattens and then increases (due to active dropping off)

Why do we have maximum force production at mid-range of a movement?

because that is typically when the external moment arm is the largest

What is the force-velocity relationship?

-Concentric contraction- produce more force at "slower" speeds, no time to make cross-bridges= no force to produce

-Eccentric contraction- produce more force at "higher" speeds, because of protective mechanisms and passive components

What is power?

the maximum amount of force we can produce at the maximum velocity

How should we train muscles?

based on what they do architecturally (ROM, force, etc.)

What is the primary purpose of stretching?

To increase the extensibility of the musculotendinous unit or other soft-tissue structures.

What components must lengthen to achieve a permanent change in muscle length?

Both the contractile and non-contractile components of the muscle.

What are the connective tissues associated with muscles?

Joint capsule, ligament, skin, fascia, and retinaculum.

What is neural mobilization in the context of stretching?

Neural gliding, which should be done carefully to avoid paresthesia.

What is the effect of acute stretching?

It leads to relaxation of cross bridges, allowing for temporary 'sarcomere give'.

What happens during chronic muscle lengthening?

It can lead to a change in stretch tolerance and structural lengthening by adding sarcomeres in series.

What is myofibrillogenesis?

The process of adding sarcomeres in series to achieve structural lengthening of muscle.

What is the threshold of stretching stimulus?

It triggers physiological adaptations by adding sarcomeres in series.

What is stretch weakness?

Weakness due to excessive chronic lengthening of a muscle, affecting its force production.

What is tight weakness?

Weakness due to chronic shortening of a muscle, limiting its force generation when stretched.

What are the characteristics of viscoelastic behavior in connective tissues?

Creep, stress relaxation, and hysteresis.

What is creep in the context of stretching?

Tissue length increases under a constant load.

What is stress relaxation?

The load decreases when the length of the tissue remains constant.

What is hysteresis in stretching?

The phenomenon where the tissue returns to its resting length after being stretched.

What is required for permanent changes in connective tissue?

Micro failure of the collagen fibrils must occur.

How can passive stretching be made more effective?

By ensuring the muscle is relaxed during the stretch, often through breathing techniques.

What is the impact of multiple bouts of stretching?

It can increase range of motion (ROM) temporarily but does not change muscle stiffness.

What is the role of parallel and series elastic components during stretching?

Parallel components move with the muscle, while series components (tendons) move opposite to the muscle.

What is the effect of stretching on athletic performance?

It can enhance performance by improving the economy of motion and restoring mobility.

What is the relationship between stretching and injury prevention?

Stretching can help prevent or reduce the incidence of injuries.

How long do the effects of a single bout of stretching last?

The effects typically last for only 10-20 minutes.

What is the role of muscle spindles?

Muscle spindles detect changes in muscle length and respond to stretching.

What are the two types of afferents associated with muscle spindles?

Type Ia afferents respond to quick stretch, while Type II afferents respond to tonic stretch.

Describe the process of muscle contraction in response to stretching.

Stretching stimulates intrafusal fibers, activating Type Ia afferents, which send signals to the spinal cord, leading to the contraction of the same muscle via alpha motor neurons.

What type of stretching is generally considered best for passive stretching?

Slow, low-intensity, long-duration stretching is best to avoid activating the muscle.

Where are muscle spindles located?

Muscle spindles are located in series with muscle fibers.

What is autogenic inhibition?

Autogenic inhibition refers to the inhibition of a muscle's stretch due to the activation of the Golgi tendon organ.

How does the Golgi tendon organ function?

When stretched, it inhibits muscle stretch as a protective mechanism, sending signals through Ib fibers to inhibit alpha motor neurons.

What force activates the Golgi tendon organ?

Active force of 30-90 mN or passive force of 2N activates the Golgi tendon organ.

What is reciprocal inhibition?

Reciprocal inhibition occurs when the activation of the agonist muscle inhibits the opposing muscle during stretching.

What is static stretching?

Static stretching involves applying a slow, sustained force to the muscle-tendon unit and holding it for a specified period.

What are the principles of creep and stress relaxation in stretching?

Creep involves a constant load leading to increased range of motion, while stress relaxation involves a constant range of motion leading to decreased load.

What is manual stretching?

Manual stretching is a technique where an external force is applied to stretch the muscle.

What is ballistic stretching?

Ballistic stretching involves cyclic, rhythmic movements and is usually not recommended due to the risk of muscle injury.

What are potential effects of ballistic stretching?

Ballistic stretching may increase strain rate, stiffness, energy storage, and require more force to rupture.

What is disinhibition in the context of muscle physiology?

Disinhibition refers to overriding the inhibition of a muscle, such as in a drop jump.

What is the role of inhibitory interneurons in muscle response?

Inhibitory interneurons receive input from muscle spindles, joint afferents, and cutaneous afferents to modulate muscle activity.

What is the function of alpha motor neurons?

Alpha motor neurons innervate extrafusal fibers and are responsible for muscle contraction.

What is the relationship between muscle spindles and joint afferent neurons?

Muscle spindles and joint afferent neurons provide sensory feedback to the central nervous system regarding muscle and joint position.

How does the body respond to forceful muscle contraction?

Muscle spindles respond to forceful contractions by sending signals that can lead to muscle inhibition.

What is the purpose of dynamic stretching?

To prepare the muscle for movement through a slow, steady motion without holding at end-range.

What is the primary benefit of dynamic stretching?

It reduces hysteresis and lubricates muscle proteins, preparing the nervous system for movement.

What does PNF stand for in stretching techniques?

Proprioceptive Neuromuscular Facilitation.

Describe the Hold Relax technique in PNF stretching.

Lengthen the target muscle until a slight stretch is felt, contract it isometrically for 5-10 seconds, then passively stretch to a new barrier.

What is the difference between Hold Relax and Contract Relax in PNF stretching?

Hold Relax uses isometric contraction, while Contract Relax uses a slight concentric contraction of the target muscle.

What is the Agonist Contract Relax technique?

A passive stretch of the target muscle followed by active contraction of the opposing muscle to facilitate reciprocal inhibition.

What is the Slow Reversal Hold Relax technique?

Combines Hold Relax followed by Agonist Contract Relax to enhance both agonist and reciprocal inhibition.

What factors affect stretching?

Velocity of stretch, intensity of stretch, duration of stretch, and frequency of stretching.

What is the recommended intensity of stretch for safety?

Generally low intensity to minimize muscle guarding and risk of injury.

What is the minimum hold time for static stretching to be effective?

30 seconds.

What is the recommended frequency for stretching to increase range of motion?

At least 1 time per week for a minimum of 6 weeks.

What are some contraindications to stretching?

Bony block, unstable fracture, joint instability, severe pain during stretching, and recent steroid injection in a joint.