Muscular system

A band

The dark bands in skeletal and cardiac muscle cells under the microscope, made up primarily of myosin filaments

Abductor muscle

A muscle that moves a body part away from the midline of the body

Actin filament

The thin protein filament in muscle cells that slides past myosin during contraction to create movement.

Adductor muscle

A muscle that moves a body part toward the midline of the body.

Adenosine diphosphate (ADP)

A molecule with two phosphate groups that must be recharged to ATP to provide energy for muscle contraction.

Adenosine triphosphate (ATP)

The energy molecule that powers all muscle contraction and relaxation by releasing energy when it loses a phosphate group. Often called the "energy currency" of cells.

Aerobic metabolism

Energy production that uses oxygen to create ATP efficiently without producing harmful byproducts.

Agonist

The primary muscle that performs a specific movement by contracting.

Anaerobic metabolism

Energy production without oxygen that creates lactic acid as a byproduct and can only sustain brief, intense activity.

Antagonist

A muscle that opposes the action of the agonist muscle to provide smooth, controlled movement. From Greek meaning "opponent."

Aponeuroses

Flat, broad sheets of fibrous connective tissue that attach muscles to bones or other muscles.

Autorhythmic

The ability of cardiac muscle to generate its own electrical impulses and contract rhythmically without external nerve stimulation.

Biceps brachii

The two-headed muscle of the upper front leg that flexes the elbow joint.

Brachium

The upper arm region between the shoulder and elbow, containing the humerus bone.

Brachiocephalicus

A muscle that extends from the humerus to the skull, allowing both head extension and front leg movement. The name means "arm-to-head muscle."

Cardiac muscle

The specialized involuntary striated muscle found only in the heart that contracts rhythmically throughout life.

Creatine phosphate

A high-energy molecule stored in muscles that quickly regenerates ATP during intense muscle activity.

Cross-bridge

The connection formed when myosin heads attach to actin filaments during muscle contraction, creating the pulling force that generates movement.

Cutaneous muscle

Thin, broad muscles attached to the skin rather than bones that allow animals to twitch their skin to remove insects.

Deltoid muscle

The triangular shoulder muscle that abducts the front leg and helps flex the shoulder joint.

Dense body

Anchoring structures in smooth muscle cells that allow the muscle to contract effectively by providing attachment points for contractile filaments.

Diaphragm

The dome-shaped muscle that separates the chest and abdominal cavities and serves as the primary breathing muscle

Endomysium

The delicate connective tissue that surrounds each individual muscle fiber and contains capillaries that supply nutrients

Epimysium

The tough outer covering that surrounds an entire muscle and separates it from adjacent muscles.

Expiratory muscle

Muscles that actively push air out of the lungs during forced breathing, including the internal intercostals and abdominal muscles.

External abdominal oblique

The outermost layer of abdominal muscle with fibers running diagonally, helping support internal organs and assist with breathing.

Fascicle

A bundle of muscle fibers wrapped together by connective tissue, visible as the "grain" in meat

Fixator

A muscle that stabilizes a joint or body part so that other muscles can create controlled movement

Gastrocnemius muscle

The large calf muscle that extends the hock (ankle) joint and provides propulsion during movement.

Gluteal muscles

The large, powerful muscles of the hip region that extend the hip joint and propel the body forward during movement.

H band

The lighter zone in the center of the A band in striated muscle where only myosin filaments are present, with no actin overlap.

Hamstring group

The muscles on the back of the thigh (biceps femoris, semimembranosus, semitendinosus) that extend the hip and flex the stifle joint.

I band

The light bands in striated muscle containing only actin filaments, which shorten during muscle contraction.

Inspiratory muscle

Muscles that draw air into the lungs during breathing, primarily the diaphragm and external intercostal muscles.

Intercalated disc

Specialized cell junctions in cardiac muscle that connect heart muscle cells and allow electrical impulses to pass between them.

Internal abdominal oblique

The middle layer of abdominal muscle with fibers running diagonally opposite to the external oblique, providing core stability and breathing assistance.

Intramuscular

Within or into a muscle, most commonly referring to injection technique where medication is delivered directly into muscle tissue.

Involuntary muscle

Muscle tissue that contracts without conscious control, including cardiac and smooth muscle. "

Involuntary striated muscle

Another name for cardiac muscle, which has striations like skeletal muscle but contracts automatically without conscious control.

Lactic acid

The byproduct of anaerobic metabolism that accumulates in muscles during intense exercise and can cause fatigue and soreness.

Latissimus dorsi

The broad, triangular muscle of the back that pulls the front leg backward and helps propel the body forward.

Linea alba

The white fibrous band running down the ventral midline where abdominal muscles meet, commonly used as a surgical entry point. The name means "white line."

Masseter

The powerful jaw muscle located in the cheek area that provides most of the force for chewing

Motor unit

A single motor nerve fiber and all the muscle fibers it controls, working together as one functional unit.

Multi-unit smooth muscle

Smooth muscle consisting of individual cells or small groups that require specific nerve signals to contract, allowing precise control.

Muscle

Contractile tissue that generates force and creates movement by shortening and lengthening in response to nerve signals.

Myofibril

The long, thread-like contractile structures inside muscle cells that contain actin and myosin filaments and perform the actual work of contraction.

Myoglobin

An oxygen-storing protein in muscle cells that gives muscle its red color and provides oxygen during intense activity.

Myosin filament

The thick protein filament in muscle cells that has heads which pull on actin filaments to generate the force of muscle contraction.

Neuromuscular junction

The specialized connection where a motor nerve meets a muscle fiber, allowing nerve signals to trigger muscle contraction.

Nonstriated involuntary muscle

Another name for smooth muscle, which lacks the striped appearance of skeletal and cardiac muscle but works automatically.

Pectoral muscles

The chest muscles that adduct the front legs and prevent them from splaying outward, also serving as common injection sites.

Perimysium

The connective tissue that wraps bundles of muscle fibers into fascicles and contains larger blood vessels and nerves.

Quadriceps femoris

The four-headed muscle group on the front of the thigh that extends the stifle (knee) joint and supports body weight.

Rectus abdominis

The paired strap-like muscles forming the "six-pack" abs that flex the spine and support the abdominal contents.

Sarcolemma

The specialized cell membrane of a muscle fiber that receives nerve signals and triggers muscle contraction

Sarcomere

The basic contractile unit of striated muscle between two Z lines, containing the actin and myosin filaments that create contraction.

Sarcoplasm

The cytoplasm inside a muscle cell that contains ATP, enzymes, and other substances needed for muscle contraction.

Sarcoplasmic reticulum

The calcium-storing network inside muscle cells that releases calcium to trigger contraction and reabsorbs it to allow relaxation.

Sinoatrial node

The natural pacemaker of the heart located in the right atrium that generates electrical impulses to control heart rhythm.

Skeletal muscle

Voluntary striated muscle attached to bones that creates movement and maintains posture under conscious control.

Skeletal muscle fiber

An individual skeletal muscle cell that can be several inches long and contains multiple nuclei to support its large size.

Smooth muscle

Involuntary non-striated muscle found in organ walls and blood vessels that works automatically to control internal functions.

Striations

The alternating light and dark bands visible in skeletal and cardiac muscle that result from organized arrangement of contractile proteins.

Synergist

A muscle that assists the agonist muscle in performing a movement, helping to produce smooth and efficient motion

Tendon

The fibrous connective tissue that attaches muscle to bone, transmitting the force of muscle contraction to create movement.

Transverse tubule

Tubular extensions of the muscle cell membrane that carry electrical signals deep into the muscle fiber to ensure complete contraction.

Transversus abdominis

The deepest layer of abdominal muscle with fibers running horizontally, providing core stability and assisting with forced expiration.

Triceps brachii

The three-headed muscle on the back of the upper front leg that extends the elbow joint and supports weight bearing.

Twitch contraction

A single, brief contraction and relaxation cycle of a muscle fiber in response to one nerve impulse.

Viscera

The internal organs, particularly those within the thoracic and abdominal cavities.

Visceral smooth muscle

Smooth muscle arranged in large sheets in organ walls that contracts in coordinated waves and works automatically.

Voluntary striated muscle

Another name for skeletal muscle, emphasizing that it's under conscious control and has a striped appearance under the microscope.

Z line

The boundary structure of a sarcomere where actin filaments attach, appearing as dark lines that move closer together during muscle contraction.