Muscular System Structure, Function, Adaptation, and Disorders

Comprehensive practice flashcards covering muscle anatomy, tissue types, sliding filament contraction, hypertrophy, atrophy, neural adaptation, and muscular disorders from Muscular System lecture notes.

How many muscles are in the human body, and what portion of an average person's body mass do they comprise?

The human body contains more than $600$ muscles, which make up more than $40\%$ of an average person's body mass.

What are the cellular characteristics, joint attachments, and control type of skeletal muscles?

Skeletal muscles are voluntary muscles attached to bones by tendons at synovial joints, consisting of long, multi-nucleate parallel cells that are striated perpendicularly.

Where are smooth muscles found in the body, and what are their structural and control features?

Smooth muscles are found in the walls of hollow structures such as blood vessels and the stomach; they are composed of short, tapered cells that function involuntarily.

What are the anatomical and cellular features of cardiac muscle?

Cardiac muscle is found exclusively in the walls of the heart to pump blood involuntarily, exhibiting striated cells with $1$ nucleus per cell.

How do tendons function mechanically with bones during muscle contraction?

Tendons attach muscle to bone and pull on the bones, making them act like levers that move when the corresponding muscle contracts.

What three characteristics typically determine a muscle's name?

A muscle's name usually describes its shape, location, or job (such as the Frontalis on the forehead, Deltoid moving the shoulder, Biceps bending the arm, and Rectus abdominus on the stomach).

Why do skeletal muscles operate in opposing pairs, and what are the roles of the agonist and antagonist?

Muscles can only pull on bones and cannot push; therefore, they work in opposing pairs where the agonist (prime mover) contracts to cause movement and the antagonist relaxes.

How is a single muscle fiber structurally distinguished from a fascicle?

A muscle fiber is a single muscle cell that contracts when stimulated by a nerve signal, whereas a fascicle is a bundle of muscle fibers wrapped together.

What is the structural hierarchy among myofibrils and myofilaments?

Myofibrils are tiny threads inside muscle fibers that aid contraction, containing protein filaments called myofilaments (actin and myosin) that carry out the contraction.

What are the distinct structural roles of actin and myosin during contraction?

Actin is the thin filament that is pulled inward during contraction, while myosin is the thick filament that utilizes ATP to pull actin.

What is a sarcomere, and how does it relate to the Z-line?

A sarcomere is the functional contractile space between Z-lines, which serve as the attachment points for actin and myosin.

What is required for the sliding filament model of muscle contraction, and how much energy is consumed per engagement?

Contraction requires ATP and calcium ($\text{Ca}^{2+}$), consuming $1$ ATP molecule each time a myosin filament engages with an actin filament.

What causes muscle fatigue and soreness during intense exercise under oxygen debt?

When oxygen is insufficient to produce ATP efficiently, cells switch to lactic acid fermentation; this yields less ATP, and the buildup of lactic acid lowers blood pH, causing muscles to stop contracting.

What are the definitions of a muscle's origin, insertion, and belly?

The origin is the tendon attachment to the more stationary bone, the insertion is the attachment to the more movable bone, and the belly is the middle region of the muscle.

What physiological mechanism accounts for initial strength increases before muscle hypertrophy occurs?

Initial strength gains result from neural adaptation, where the brain and motor neurons improve motor unit recruitment, inter-muscular coordination, and signal synchronization.

What morphological change occurs during muscle hypertrophy, and what three stimuli are required for it?

Muscle cells enlarge rather than multiply, thickening fibers by adding myofibrils (actin and myosin); this growth requires mechanical tension, muscle damage, and metabolic stress.

Why is overtraining detrimental to muscle growth, and what hormone mediates this effect?

Overtraining without adequate recovery causes fatigue, decreased performance, and hormonal imbalance, during which elevated cortisol (stress hormone) promotes muscle breakdown.

What is muscle atrophy, and in what common situations does it occur?

Atrophy is the shrinking of muscle fibers and loss of protein content caused by disuse, injury, or disease; common examples include immobilized limbs in casts, sedentary lifestyles, and astronauts in microgravity.

What cellular mechanism allows previously trained individuals to regain muscle faster during re-training?

Re-training is faster because muscle nuclei acquired during prior training do not disappear when the individual becomes de-trained.

What are the defining characteristics and most common demographic for fibromyalgia?

Fibromyalgia is a muscular disorder of unknown cause (possibly genetic) characterized by chronic widespread muscle pain, sleep disorders, and fatigue, affecting women more often than men.

What is Duchenne muscular dystrophy (DMD), and what is its typical age of onset and patient demographic?

DMD is a genetic muscular disorder marked by progressive weakness and muscle loss; symptom onset occurs in early childhood between ages $2$ and $3$, primarily affecting males.

Why is Cerebral Palsy classified as a neurological disorder rather than a muscular disorder?

It is caused by damage to the part of the brain that controls movement, rather than damage to the muscular tissue itself, appearing in early childhood and affecting motor control in one, half, or all limbs.

What physiological triggers cause muscle cramps, and what dietary remedies are effective at relieving them?

Muscle cramps are triggered by electrolyte imbalances or excessive muscle loading; they can be reduced using electrolyte tablets, salt tablets, and pickle juice (which is very effective).

What is the typical recovery timeline for minor tendon tears compared to complete surgical ruptures?

Minor tears take $2\text{--}6\text{ weeks}$ to heal, while complete ruptures requiring surgery take $6\text{--}12\text{ months}$; simple movements return around $3\text{ months}$, but returning to $100\%$ strength can take up to $2\text{ years}$.

What injury is illustrated in this diagram, and what are the four most common anatomical sites where tendon ruptures occur?

The diagram shows an Achilles tendon rupture; the four most common sites are the Achilles tendon, rotator cuff, biceps tendon, and quadriceps tendon.