Muscular System Flashcards

Flashcards on the Muscular System

Functions of Skeletal Muscle

Support & movement, provides protection, gives body form, communication, temperature regulation

Skeletal muscles

≈ 650-700 named; more still discovered

Tendons

Cord-like; attach muscle to bone

Aponeuroses

Flattened tendon sheets; attach muscle to bone or muscle to muscle

Skeletal Muscle Tissue

Linear cells, multinucleated, striations, voluntary & strong; attaches bone to bone; provides movement

Cardiac Muscle Tissue

Only in heart; highly branched fibers; mono-nucleated, faint striations, involuntary

Intercalated discs

Spot desmosomes = strong cell-to-cell links; Gap junctions = shared cytoplasm → functional syncytium

Smooth Muscle Tissue

No striations, single nucleus, propeller-shaped cells; woven like fabric; lines hollow organs

Motor Unit

All muscle cells responding to the same nerve fiber

Synaptic vesicles

Store acetylcholine (ACh)

Synaptic cleft

Gap where ACh diffuses

Sarcolemma

Folded for ↑surface; houses ACh receptors

Motor end plate

Specialized postsynaptic membrane

AChE (acetylcholinesterase)

Enzyme breaking down ACh

Depolarization

Voltage change when Na enters

Creatine-P Key Reaction

Creatine P → creatine + P + energy = ADP → ATP

Aerobic Resp. Key Reaction

Glucose → ATP + CO₂ (or Glycogen → Glucose → …)

Myoglobin

O₂-storage pigment (red-brown)

Anaerobic Key Reaction

Glucose → Pyruvic acid → Lactic acid

Fast-Twitch (White) Muscle Fibers

No myoglobin, few mitochondria → low ATP; contracts & fatigues quickly

Slow-Twitch (Red-brown) Muscle Fibers

Myoglobin-rich, many mitochondria; contracts slowly, high endurance

Threshold

Minimum stimulus

Recruitment

Stronger stimulus → more units

Graded response

Force is proportional to units engaged

All-or-None

Each fiber fires completely once threshold reached

Absolute Refractory Period

No response

Relative Refractory Period

Needs supra-threshold stimulus

Tetanus

Summation of twitches

Multiple motor-unit summation

↑frequency + ↑strength = max force

Asynchronous activation

Units rotate for sustained hold

Rigor Mortis

ATP depleted post-mortem → stiffness, resolves after decomposition

Latent Phase

Stimulus, no shortening

Contraction Phase

Fiber shortens

Relaxation Phase

Returns to length

Refractory Phase

Unresponsive

Isotonic Contraction

Muscle shortens, constant load

Isometric Contraction

Length constant, tension rises

Tetanus

Sustained contraction

Muscle tone

Baseline partial contraction

Prime mover (agonist)

Main muscle for movement

Antagonist

Opposes agonist

Synergist

Assists prime mover

Fixator

Stabilizes origin

Origin

Immovable point

Insertion

Movable point (pulled toward origin)

Action

Movement produced (muscle can only move insertion toward origin)

Muscle Fiber

A single muscle cell; specialized for contraction, poor at healing.

Motor Unit

A single motor neuron and all the muscle fibers it stimulates.

Tendon

A cord-like structure that connects muscle to bone.

Aponeurosis

A flat sheet-like tendon that connects muscle to bone or muscle to muscle.

Origin

The fixed, immovable attachment point of a muscle.

Insertion

The movable attachment point of a muscle, pulled toward the origin during contraction.

Action

The movement produced when the muscle contracts and the insertion moves toward the origin.

Skeletal Muscle

Voluntary muscle with striations and multiple nuclei; responsible for body movement and posture.

Cardiac Muscle

Involuntary muscle found only in the heart; branched fibers with faint striations and a single nucleus.

Smooth Muscle

Involuntary muscle with no striations and a single nucleus; found in walls of hollow organs.

Intercalated Disc

A structure between cardiac muscle cells that contains desmosomes and gap junctions for strength and communication.

Functional Syncytium

A condition in which cardiac muscle cells contract together as a unit due to communication through gap junctions.

Sarcolemma

The plasma membrane of a muscle cell; folded to increase surface area for receptors.

Synaptic Vesicle

A small sac in the axon terminal that contains neurotransmitters like acetylcholine (ACh).

Synaptic Cleft

The small space between the nerve ending and muscle membrane where neurotransmitters are released.

Acetylcholine (ACh)

A neurotransmitter released by nerve cells that triggers muscle contraction.

Acetylcholinesterase (AChE)

The enzyme that breaks down acetylcholine in the synaptic cleft.

Depolarization

A change in electrical charge across a membrane that initiates an action potential.

Creatine Phosphate

A high-energy compound that quickly regenerates ATP in muscle cells.

Myoglobin

An oxygen-binding protein in muscle cells; gives muscle its red-brown color.

Aerobic Respiration

ATP production using glucose and oxygen; slower but efficient.

Anaerobic Respiration

ATP production without oxygen, resulting in lactic acid build-up.

Oxygen Debt

The amount of oxygen required to restore the muscle to its resting state after activity.

Fast-Twitch Fiber

Muscle fibers that contract quickly with little endurance; few mitochondria, no myoglobin.

Slow-Twitch Fiber

Muscle fibers that contract slowly but are fatigue-resistant; rich in mitochondria and myoglobin.

Threshold Stimulus

The minimum stimulus strength needed to cause a muscle fiber to contract.

All-or-None Response

Once threshold is reached, a muscle fiber will contract fully.

Recruitment

The process of increasing the number of active motor units to lift a heavier load.

Graded Response

The varying degree of muscle contraction based on stimulus strength.

Twitch

A single brief contraction followed by relaxation.

Summation

Repeated stimulation of a muscle before it fully relaxes, leading to a stronger contraction.

Tetanus

A sustained muscle contraction from rapid stimulation.

Complete Tetanus

No relaxation occurs between contractions.

Incomplete Tetanus

Partial relaxation occurs between contractions.

Refractory Period

The time during which a muscle fiber cannot respond to a second stimulus.

Absolute Refractory Period

The muscle fiber absolutely cannot respond.

Relative Refractory Period

The muscle fiber can respond to a stronger-than- normal stimulus.

Asynchronous Motor Unit Activation

Switching between motor units during sustained contraction to prevent fatigue.

Rigor Mortis

Stiffening of muscles after death due to lack of ATP.

Isotonic Contraction

Muscle tension stays the same, and the muscle shortens.

Isometric Contraction

Muscle length stays the same, but tension increases.

Muscle Tone

A continuous state of partial contraction in resting muscles.

Prime Mover (Agonist)

The main muscle responsible for a specific movement.

Antagonist

The muscle that opposes the prime mover.

Synergist

A muscle that assists the prime mover.

Fixator

A muscle that stabilizes the origin of the prime mover.