Human Anatomy and Physiology: Muscle Histology, Contraction Physiology, and Muscular Anatomy

Comprehensive vocabulary flashcards covering skeletal muscle histology, contraction physiology, neuromuscular junction mechanisms, connective tissue sheaths, structural hierarchy, and muscular anatomy across all major body compartments.

Skeletal Muscle Tissue Functions

The four primary functions performed by skeletal muscles: movement, protection and support, regulatory functions, and thermoregulation.

Neuromuscular Junction

The microscopic site or synapse where a motor neuron's axon terminal meets the motor end plate of a muscle fiber.

Acetylcholine (ACh)

The neurotransmitter released from the motor neuron into the synaptic cleft that binds to chemical receptors in the sarcolemma to initiate an action potential.

Sarcolemma

The plasma membrane covering of a muscle cell/myofiber containing chemical receptors for acetylcholine.

T-tubules

Transverse tubules that extend deep into the myofiber to propagate the action potential depolarization wave toward the sarcoplasmic reticulum.

Sarcoplasmic Reticulum

The specialized organelle inside muscle fibers that releases calcium ions upon depolarization and actively pumps calcium back in when the signal ceases.

Troponin

The protein on the thin actin filament that binds calcium ions, causing it to move and expose the myosin-binding sites.

Cross Bridge Formation

The binding of energized myosin heads to exposed binding sites on the actin thin filaments.

Power Stroke

The mechanical action powered by ATP in which the myosin head pulls the thin actin filament toward the center of the sarcomere, shortening the muscle.

Cross Bridge Detachment

The release of the myosin head from the actin filament triggered by the binding of a new molecule of ATP.

Sarcomere

The functional contractile unit of a muscle fiber extending from one Z disc to the next adjacent Z disc.

Epimysium

The outermost, superficial connective tissue sheath covering the entire muscle.

Perimysium

The middle connective tissue sheath that encloses bundles of muscle fibers known as fascicles.

Endomysium

The deepest connective tissue sheath that surrounds each individual muscle fiber.

Skeletal Muscle Structural Hierarchy

The organizational hierarchy of skeletal muscle components: Muscle -> Fascicle -> Muscle fiber -> Myofibril -> Myofilaments (actin and myosin).

Origin

The point of muscle attachment on the immovable bone during contraction.

Insertion

The point of muscle attachment on the movable bone, which always moves toward the origin during muscle shortening.

Circular Muscle Pattern

A concentric fiber arrangement exemplified by the orbicularis oris that acts to purse the lips.

Parallel Muscle Pattern

A fiber arrangement running parallel to the long axis, exemplified by the rectus abdominis, producing trunk flexion or hip flexion.

Convergent Muscle Pattern

A broad-origin fiber pattern that converges to a single tendon, exemplified by the pectoralis major, producing adduction, hyperextension, abduction, and internal rotation.

Pennate Muscle Pattern

A feather-like fiber arrangement exemplified by the extensor digitorum, rectus femoris, and deltoid.

Occipitofrontalis

A muscle of facial expression that elevates the eyebrows.

Orbicularis Oculi

A circular muscle surrounding the eye responsible for squinting.

Orbicularis Oris

A circular muscle surrounding the mouth responsible for pursing the lips.

Buccinator

A facial muscle located behind the masseter responsible for whistling.

Masseter

A strong muscle of mastication on the side of the face responsible for chewing and closing the jaw.

Temporalis

A muscle of mastication situated over the temporal bone that assists in chewing.

Sternocleidomastoid

A neck muscle originating near the sternum/clavicle and inserting at the mastoid process; unilateral contraction causes lateral flexion and rotation to the opposite side; bilateral contraction causes cervical depression.

Erector Spinae

The primary back extensor group that extends the spine, composed of three columns: iliocostalis (lateral), longissimus (longest/intermediate), and spinalis (medial).

External Intercostals

Thoracic muscles angled inward toward the midline that elevate and open the ribs during inhalation.

Internal Intercostals

Thoracic muscles oriented from medial to lateral that depress and close the ribs during exhalation.

Diaphragm

A dome-shaped internal thoracic muscle that contracts to facilitate inhaling.

Transverse Abdominis

The deepest muscle of the abdominal wall that wraps entirely around like a blanket to hold organs in place and aid in trunk flexion.

Pectoralis Minor

An anterior thoracic muscle attaching to the 3rd, 4th, and 5th ribs and the coracoid process, responsible for protraction of the scapula.

Serratus Anterior

A finger-like muscle under the armpit attaching to the ribs and scapula, acting in scapular protraction and breathing/inhaling.

Trapezius

A superficial diamond-shaped posterior thoracic muscle responsible for cervical extension, scapular elevation, and horizontal extension/abduction.

Rhomboideus Major and Minor

Posterior thoracic muscles originating from the spine to the medial border of the scapula that perform retraction of the scapula.

Pectoralis Major

A major anterior chest muscle (O: clavicle and sternum, I: intertubercular groove of humerus) that performs shoulder horizontal adduction, shoulder flexion, and internal rotation.

Latissimus Dorsi

A large superficial V-shaped back muscle that performs shoulder adduction, extension, hyperextension, and internal rotation.

Deltoid

The primary shoulder muscle divided into anterior (flexion), middle (abduction), and posterior (adduction/horizontal extension) fibers.

Supraspinatus

A rotator cuff muscle (O: supraspinous fossa, I: greater tubercle of humerus) that performs arm abduction.

Infraspinatus

A rotator cuff muscle located below the scapular spine (O: infraspinous fossa, I: greater tubercle of humerus) responsible for external rotation of the arm.

Teres Minor

A rotator cuff muscle located below the infraspinatus (O: lateral border of scapula, I: greater tubercle of humerus) that performs external rotation of the arm.

Subscapularis

An anterior rotator cuff muscle (O: subscapular fossa, I: lesser tubercle of humerus) responsible for internal rotation of the arm.

Biceps Brachii

A superficial two-headed anterior arm muscle (O: shoulder, I: radius) that performs flexion of the elbow and shoulder, as well as supination.

Triceps Brachii

A three-headed muscle on the posterior humerus responsible for extension of the elbow and extension of the shoulder.

Pronator Teres

A short anterior forearm muscle located on the lateral side that pronates the forearm.

Flexor Digitorum Superficialis

An anterior forearm muscle lying between the palmaris longus and deeper layers that flexes digits 2–5 (excluding the thumb).

Supinator

A deep posterior forearm muscle located on the radial side responsible for supination of the forearm.

Iliopsoas

The primary anterior hip flexor group composed of the iliacus and psoas major muscles.

Sartorius

A long, strap-like anterior thigh muscle running from the hip to the medial knee that performs hip flexion, external rotation, and knee flexion.

Gracilis

A medial compartment thigh muscle that crosses the knee joint to perform knee flexion and hip adduction.

Rectus Femoris

An anterior thigh muscle (O: AIIS, I: tibial tuberosity) that extends the knee and flexes the hip.

Vastus Lateralis

An anterior compartment quadriceps muscle (O: lateral proximal femoral shaft, I: tibial tuberosity) that performs knee extension.

Piriformis

A lateral rotator muscle that extends horizontally across and over the sciatic nerve to produce external rotation of the hip.

Hamstrings

The posterior compartment thigh muscle group consisting of the biceps femoris, semimembranosus, and semitendinosus, which flex the knee and extend the hip.

Tibialis Anterior

An anterior lower leg muscle positioned directly lateral to the tibia that performs dorsiflexion and inversion of the foot.

Gastrocnemius

A superficial two-headed posterior calf muscle that performs plantar flexion (pointing toes) and knee flexion.

Soleus

A feathered-looking superficial posterior compartment muscle that attaches to the Achilles tendon and performs plantar flexion.

Fibularis (Peroneus) Longus and Brevis

Muscles of the lateral compartment of the leg that wrap around the ankle to perform eversion of the foot and plantar flexion.