AP MUSCLE Exam 2

Origin

The fixed attachment point of a muscle.

Insertion

The movable attachment point of a muscle.

Gaster (muscle belly)

The thick, central part of the muscle.

Tendon

The structure that connects muscle to bone.

Dense connective tissue

The tissue type that tendons are made of (mostly collagen).

Antagonistic pair

Two muscles that work opposite each other (e.g., biceps and triceps).

Prime mover (agonist)

The main muscle responsible for a specific movement.

Antagonist muscle

The muscle that opposes the prime mover's action.

Synergist muscle

A muscle that assists the prime mover or stabilizes a joint during movement.

Naming of muscles

Muscles can be named based on location, shape, size, fiber direction, number of origins, attachments, or action.

Frontalis

An example of a muscle named by its location (over the frontal bone).

Deltoid

Means triangle-shaped in muscle naming.

Biceps

Means muscle with two heads (origins).

Rectus

Refers to straight fibers (parallel to midline) in muscle names.

Slow oxidative (Type I)

The muscle fiber type that contracts slowly but resists fatigue.

Fast oxidative-glycolytic (Type IIa)

The fiber type that uses both aerobic and anaerobic respiration.

Fast glycolytic (Type IIb)

The muscle fibers that contract quickly but fatigue easily.

Muscle atrophy

Decrease in muscle size due to lack of use or nerve damage.

Muscle hypertrophy

Increase in muscle fiber size from exercise and protein buildup.

Muscular dystrophy

Caused by a genetic defect in dystrophin protein leading to muscle degeneration.

Myasthenia gravis

An autoimmune disease that destroys acetylcholine receptors, causing weakness.

Muscle twitch

A single, quick contraction followed by relaxation.

Latent period

The time between stimulus and start of contraction.

Refractory period

The time after contraction when the muscle cannot respond to another stimulus.

Wave summation

Repeated stimuli cause stronger contractions before full relaxation.

Tetanus (in muscle physiology)

Sustained contraction with no relaxation between stimuli.

Muscle fatigue

Caused by ATP depletion and lactic acid buildup after prolonged activity.

Fasciculation

Visible, brief twitch of small muscle fibers.

Tremor

Rhythmic shaking due to alternating muscle contractions.

Cramps

Painful, prolonged contraction caused by dehydration or low electrolytes.

Spasm

Sudden, involuntary muscle contraction (short or sustained).

Muscle tone

Continuous, partial contraction that keeps muscles firm and ready.

Isometric contraction

Muscle contracts but does not change length (e.g., holding a position).

Isotonic contraction

Muscle changes length while maintaining tension.

Concentric contraction

Muscle shortens (lifting a weight).

Eccentric contraction

Muscle lengthens (lowering a weight).

What are the three types of muscle tissue?

Skeletal, cardiac, and smooth muscle.

Where is skeletal muscle found and what is its control type?

Attached to bones; voluntary control.

What are characteristics of skeletal muscle?

Striated, voluntary, multinucleated, and contracts quickly but tires easily.

Where is cardiac muscle found and what is its control type?

Found in the heart; involuntary control.

What are characteristics of cardiac muscle?

Striated, involuntary, branched fibers, single nucleus, intercalated discs.

Where is smooth muscle found?

In walls of hollow organs (stomach, intestines, blood vessels).

What are characteristics of smooth muscle?

Non-striated, involuntary, slow contractions, spindle-shaped cells.

What is the epimysium?

Outer connective tissue covering around the entire muscle.

What is the perimysium?

Connective tissue that surrounds each fascicle (bundle of muscle fibers).

What is the endomysium?

Thin connective tissue surrounding individual muscle fibers.

What is fascia?

A sheet of connective tissue that separates and supports muscles.

What is a muscle fiber?

A single muscle cell.

What is a fascicle?

A bundle of muscle fibers within a muscle.

What is the sarcolemma?

The plasma membrane of a muscle fiber.

What is the sarcoplasm?

The cytoplasm of a muscle cell that contains mitochondria and myofibrils.

What are myofibrils?

Long, thread-like organelles in muscle fibers made up of sarcomeres.

What are the two main types of filaments in muscle fibers?

Thin (actin) and thick (myosin) filaments.

What is a sarcomere?

The structural and functional unit of a myofibril, responsible for contraction.

What is actin?

The thin filament that provides sites for myosin to attach during contraction.

What is myosin?

The thick filament with heads that pull actin during contraction.

What is troponin?

A protein that binds to tropomyosin and helps regulate muscle contraction.

Tropomyosin

A protein that covers actin's binding sites when the muscle is relaxed.

Dystrophin

A protein that links the inside of the muscle fiber to the cell membrane, stabilizing it.

Sarcoplasmic Reticulum (SR)

The muscle cell's storage site for calcium ions needed for contraction.

T-tubules

Invaginations of the sarcolemma that carry the action potential deep into the fiber.

Sliding Filament Mechanism

Process where actin and myosin slide past each other, shortening the sarcomere.

Trigger for Muscle Contraction

Calcium release from the SR binds to troponin, shifting tropomyosin to expose actin sites.

Energy for Muscle Contraction

ATP, which allows myosin heads to detach and reattach to actin.

Muscle Relaxation

Calcium is pumped back into the SR, and actin's binding sites are covered again.

Motor Neuron

A nerve cell that carries impulses from the brain/spinal cord to a muscle.

Axon

The long fiber of a neuron that sends impulses away from the cell body to muscles.

Dendrites

Branch-like parts of a neuron that receive signals.

Neuromuscular Junction (NMJ)

The connection between a motor neuron and a muscle fiber.

Neurotransmitter

A chemical messenger that transmits signals between neurons or from neuron to muscle.

Acetylcholine (ACh)

The neurotransmitter released at the NMJ.

Action Potential Trigger

When ACh binds to receptors on the muscle fiber, it triggers an action potential in the sarcolemma, leading to contraction.

Creatine Phosphate

A quick source of energy to regenerate ATP during short bursts of activity.

Myoglobin

A red pigment in muscle cells that stores oxygen for aerobic respiration.

Muscle Structure Order

Muscle → Fascicle → Fiber → Myofibril → Filament (actin & myosin).

Muscle mechanics

The study of how muscles produce movement, force, and tension through contraction.

Muscle contraction

Depends on the number of fibers contracting, the frequency of stimulation, and the muscle's length and load.

Muscle twitch

A single, brief contraction and relaxation cycle in a muscle fiber after one stimulus.

Phases of a muscle twitch

Latent period, contraction period, and relaxation period.

Latent period

Time between stimulation and contraction; calcium is released from the SR, but no tension yet.

Refractory period

The short time after a muscle fiber contracts when it can't respond to another stimulus.

Importance of the refractory period

Prevents continuous, uncontrolled contractions and allows proper relaxation.

Wave summation

When a second stimulus occurs before full relaxation, increasing the strength of contraction.

Reason for wave summation

Because calcium stays in the sarcoplasm, allowing more cross-bridge interactions.

Tetanus (in muscle physiology)

A sustained, smooth contraction from rapid, repeated stimulation.

Types of tetanus

Incomplete tetanus (partial relaxation) and complete tetanus (no relaxation).

Muscle fatigue

The inability of a muscle to contract after prolonged activity.

Causes of muscle fatigue

Lack of ATP, buildup of lactic acid, and reduced calcium release.

Fasciculation

A brief, involuntary twitch of a small group of muscle fibers, visible under the skin.

Tremor

Involuntary, rhythmic shaking due to alternating muscle contractions.

Cramps

A painful, prolonged muscle spasm caused by low electrolytes or overuse.

Spasm

A sudden, involuntary muscle contraction, usually short and harmless.

Muscle tone

The constant, slight contraction of muscles that keeps them firm and ready to act.

Importance of muscle tone

Maintains posture and stabilizes joints even when not actively moving.

Isometric contraction

Muscle contracts but does not change length; tension increases (e.g., holding a weight still).

Isotonic contraction

Muscle changes length while maintaining tension (e.g., lifting or lowering a weight).

Types of isotonic contractions

Concentric: muscle shortens (lifting). Eccentric: muscle lengthens (lowering).