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Specialized plasma membrane that surrounds myofibrils and nuclei


Contractile organelles found in cytoplasm of muscle cells; have 2 bands


Thin band of muscle protein that joins other bands at z-disc; helical shape


Thick band of muscle protein that joins other bands at H zone; contains ATPase enzymes


Smallest contractile unit of muscle from one z-disc to the next

Cross bridges

Myosin heads that link thick and thin bands during muscle contraction

Sarcoplasmic reticulum

Muscle fiber organelle that surrounds each myofibril; stores calcium and releases when muscle is signaled to contract


Muscle's ability to receive and respond to a stimulus


Muscle's ability to shorten with an adequate stimulus


Muscle's ability to lengthen


Muscle's ability to recoil and resume resting length

Motor unit

One motor neuron and all the skeletal muscle cells stimulated by that neuron

Neuromuscular junction

Association site of the axon terminal of the motor neuron and muscle

Action potential

An electrical event occurring when a stimulus of sufficient intensity is applied to a neuron or muscle cell, allowing sodium ions to move into the cell and reverse polarity

Direct phosphorylation of ADP by CP

When ATP is depleted, it leaves ADP. CP transfers a phosphate group to ADP, regenerating more ATP; exhausted in ~15 sec.

Aerobic respiration

Respiration where oxygen is consumed and glucose is broken down into water, carbon dioxide, and 32 ATP; occurs in the mitochondria by a series of metabolic pathways that use oxygen. The reaction overall is slow and requires continuous oxygen

Anaerobic glycosis and lactic acid formation

Glucose breaks down in cytosol without oxygen, resulting in pyruvic acid that converts to lactic acid; creates 2 ATP per 1 glucose. Process is 2x faster than aerobic respiration

Isotonic contraction

When myofilaments are able to slide past each other during contractions; muscle shortens and movement occurs

Isometric contraction

When tension in the muscle increases but the muscle is unable to shorten or produce movement


Muscle attachment to an immovable bone


Muscle attachment to a moveable bone


Decreases the angle of a joint that brings 2 bones closer together


Increases the angle of a joint


Extension beyond 180 degrees


Movement of a bone around a longitudinal axis


Moving a limb away from the midline


Moving a limb toward the midline


A combination of flexion, extension, abduction, and adduction; proximal end is stationary and distal end is in motion

Prime mover

Muscle with the major responsibility for a certain movement


Muscle that opposes or reverses a prime mover


Muscle that aids a prime mover in a movement and helps prevent unnecessary movement


A specialized synergist that stabilizes the origin of a prime mover

Circular muscle

When the fascicles are arranged in concentric rings

Convergent muscle

The fascicles converge toward a single insertion tendon

Parallel muscle

Fascicles run parallel to the long axis of the muscle

Fusiform muscle

Fascicles run parallel to the long axis of the muscle, but have an enlarged belly; football shaped


Short fascicles attach obliquely to a central tendon


Unpaired muscle that covers the frontal bone, allows eyebrows to raise

Orbicularis oculi

Circular muscle around the eyes, allowing for blinks, winks, and squints

Orbicularis oris

Unpaired circular muscle around the mouth, allowing for puckering and kissing


Muscle on the face just inferior to the zygomaticus; allows for cheek flattening and chewing


Muscle on the face that allows for smiling


Muscle on the face that allows for the jaw to close


Muscle that covers the temporal bone and synergizes with the masseter to close the jaw


Unpaired muscle that covers the anterior surface of the neck, allowing for frowning


2-headed muscle found on either side of the neck; allows for neck flexion and lateral rotation

Pectoralis major

Convergent muscle covering the upper part of the chest; flexes and adducts the humerus

External intercostals

Muscles that lie between the ribs; allow rib cage to raise during inhalation

Internal intercostals

Muscles that lie deep between the ribs; allow rib cage to depress and exhale

Rectus abdominis

Paired, strap-like muscles most superficial on the abdomen; allows for flexion of vertebral column, compresses abdominal contents, and aids in childbirth, defecation, and forced breathing

External obliques

Muscles that make up the lateral wall of abdomen; flexes vertebral column, rotates trunk, allows for lateral bending

Internal obliques

Deep muscles with fibers running adjacent to and function with external obliques

Transverse abdominis

Deepest muscle of the abdominal wall; compresses abdominal contents


Most superficial muscles of the posterior upper trunk; extends the head, and moves the scapula

Latissimus dorsi

Large flat muscles that cover the lower back; extend and adduct the humerus

Erector spinae

Deep muscle group that is the prime mover of back extension; also stabilizes spine when bending over

Quadratus lumborum

Muscle that forms a small part of the posterior abdominal wall; flexes the spine laterally and together extend the lumbar spine


Prime mover of arm abduction

Biceps brachii

Prime mover of elbow flexion; also allows for supination of the forearm


Muscle that lies deep to biceps brachii; flexes elbow


Weak muscle in the brachial region

Triceps brachii

Prime mover of elbow extension, antagonist to biceps brachii

Gluteus maximus

Largest muscle; very powerful hip extensor

Gluteus medius

Lies deep to gluteus maximus; allows for thigh abduction and steadies pelvis when walking


Fused muscles on the lower limb; prime mover of hip flexion, keeps upper body from falling back when standing

Adductor muscles

Muscle group found on medial thigh; allows for thigh adduction and medial rotation

Hamstring group

Muscle group forming the mass of posterior thigh; prime movers of thigh extension and knee flexion


Thin strap-like muscle; weak hip flexor

Quadriceps group

Muscle group that forms the mass of the anterior thigh; extends knee, helps to flex hip

Tibialis anterior

Superficial muscle on anterior leg; allows for dorsiflexion and inversion

Fibularis muscles

Muscle group found on the lateral part of the leg; allows for plantar flexion and eversion


Muscle that forms the calf; prime mover for plantar flexion


Muscle deep to the gastrocnemius; helps in plantar flexion

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