Chapter 11: Skeletal Muscle Anatomy

Comprehensive practice flashcards defining essential anatomical terminology, muscle classifications, biomechanical levers, and functional groupings covered in Chapter 11 Skeletal Muscle Anatomy.

Tendons

Bands of connective tissue that attach muscles to bones, transferring the tension created by muscle contraction to produce movement.

Origin

The fixed or stabilized end of a skeletal muscle attachment.

Insertion

The moveable end of a skeletal muscle attachment where force is applied.

First-Class Lever

An uncommon lever system arranged as Load - Fulcrum - Effort; exemplified by the splenius capitis muscle lifting the anterior skull over the vertebral column.

Second-Class Lever

A lever system arranged as Fulcrum - Load - Effort; exemplified by a heel raise, where body weight acts between the metatarsophalangeal joint and the Achilles tendon.

Third-Class Lever

A lever system arranged as Load - Effort - Fulcrum; represents the majority of muscles in the body, such as the biceps brachii lifting the forearm.

Circular Fascicle Arrangement

A concentric arrangement of muscle fibers surrounding external body openings, such as the orbicularis oris and orbicularis oculi.

Convergent Fascicle Arrangement

A triangular or fan-shaped pattern where muscle fibers have a broad origin and converge toward a single, small tendon of insertion (e.g., pectoralis major).

Fusiform Fascicle Arrangement

A spindle-shaped parallel muscle arrangement with an expanded central belly and tapered ends, exemplified by the biceps brachii.

Pennate Fascicle Arrangement

A feather-like arrangement where short fascicles attach obliquely to a central tendon, including unipennate, bipennate, and multipennate patterns.

Prime Mover (Agonist)

The principal muscle directly responsible for producing a specific movement.

Antagonist

A muscle that produces the opposite action of an agonist, relaxing or stretching while the prime mover contracts.

Synergist

A muscle that assists the prime mover by adding extra force or stabilizing intermediate joints during movement.

Fixator

A specialized synergist that stabilizes the origin of the prime mover so that force is directed efficiently to the intended movement.

Muscle Compartment

A grouping of skeletal muscles along with their associated nerves and blood vessels in the limbs, enclosed and separated by a tough connective tissue membrane called fascia.

Compartment Syndrome

A condition where injury-induced inflammation elevates pressure within an enclosed fascial compartment, compromising blood flow and causing pain, pallor, paresthesia, pulselessness, and paralysis.

Anterior Compartment of the Leg

The most common site for compartment syndrome injury; contains the extensor muscles of the toes, tibialis anterior, deep peroneal (fibular) nerve, and tibial artery.

Bell's Palsy

A disorder causing unilateral drooping of the facial muscles due to damage or dysfunction of Cranial Nerve VII (facial nerve).

Orbicularis Oris

A circular sphincter muscle surrounding the mouth that controls the shape of the lips, assisting in eating, whistling, and drinking through a straw.

Orbicularis Oculi

A circular muscle surrounding the eye that functions to blink and close the eyelids.

Occipitofrontalis

A muscle of the scalp with a frontal belly and an occipital belly connected by the epicranial aponeurosis that moves the forehead and eyebrows.

Buccinator

A deep cheek muscle that compresses the cheek against the teeth to aid in chewing, whistling, and drinking from a straw.

Extrinsic Eye Muscles

Six skeletal muscles (superior, inferior, medial, lateral recti; superior and inferior obliques) originating on the sphenoid or maxillary bones and inserting onto the sclera to direct gaze.

Masseter

The primary and most powerful muscle of mastication that elevates the mandible to close the jaw.

Temporalis

A fan-shaped muscle located over the temporal bone that assists in mastication by elevating and retracting the mandible.

Extrinsic Muscles of the Tongue

Four paired muscles (genioglossus, hyoglossus, styloglossus, palatoglossus) that originate outside the tongue and insert into it to aid in chewing, deglutition, and speech.

Platysma

A thin, broad, superficial muscle covering the front and sides of the neck that depresses the lower jaw and pouts the lower lip.

Suprahyoid Muscles

A group of muscles situated superior to the hyoid bone (digastric, stylohyoid, mylohyoid, geniohyoid) that elevate the hyoid, floor of the mouth, and larynx during swallowing.

Infrahyoid Muscles

A group of strap muscles positioned inferior to the hyoid bone (omohyoid, sternohyoid, sternothyroid, thyrohyoid) that depress the hyoid bone and larynx during swallowing and speech.

Sternocleidomastoid (SCM)

A major neck muscle originating on the sternum and clavicle and inserting on the mastoid process; unilaterally turns the face to the opposite side and bilaterally flexes the cervical spine.

Scalenes

A lateral neck muscle group (anterior, middle, posterior) originating on cervical transverse processes and inserting onto ribs to flex the neck and elevate the ribs.

Splenius (Capitis and Cervicis)

Posterior neck muscles originating from the midline spine that insert into the head or cervical vertebrae, acting to rotate the head toward the same side and extend the neck.

Diastasis Recti

A clinical condition involving the splitting or separation of the linea alba between the rectus abdominis muscles, commonly occurring during pregnancy.

Diaphragm

The primary muscle of respiration separating the thoracic and abdominal cavities; flattens upon contraction to expand thoracic volume during inhalation and relaxes during exhalation.

External Intercostals

Superficial thoracic muscles between ribs whose contraction elevates the ribs, expanding the thoracic cavity to facilitate inhalation.

Internal Intercostals

Intermediate thoracic muscles between ribs whose contraction depresses the ribs, constricting the thoracic cavity during forced exhalation.

Levator Ani

The principal pelvic floor muscle group composed of the puborectalis, pubococcygeus, and iliococcygeus; supports pelvic organs, maintains continence, and relaxes during defecation.

Pelvic Floor Dysfunction (PFD)

Weakness of pelvic floor muscles that can result in urinary incontinence during coughing or sneezing, commonly developing during or after pregnancy.

Erector Spinae

A deep back muscle complex consisting of the spinalis, longissimus, and iliocostalis that extends and laterally flexes the vertebral column, head, and neck.

Rotator Cuff (SITS)

A group of four scapulohumeral muscles (Supraspinatus, Infraspinatus, Teres minor, Subscapularis) that stabilize the head of the humerus in the shoulder joint.

Supraspinatus

A rotator cuff muscle originating in the supraspinous fossa and inserting on the greater tubercle of the humerus; abducts the arm and stabilizes the glenohumeral joint.

Subscapularis

An anterior rotator cuff muscle originating in the subscapular fossa and inserting on the lesser tubercle; medially rotates the humerus and depresses the humeral head during elevation.

Coracobrachialis

An arm muscle originating from the coracoid process of the scapula and inserting onto the anteromedial shaft of the humerus.

Brachialis

A deep anterior arm muscle originating on the distal humerus and inserting onto the coronoid process of the ulna; acts as a major flexor of the forearm.

Brachioradialis

A superficial muscle of the lateral forearm originating on the distal humerus and inserting on the radial styloid process; acts as a synergist in forearm flexion.

Flexor Retinaculum

A fibrous connective tissue band at the wrist that holds the tendons of anterior forearm flexor muscles in place over the carpal bones.

Iliopsoas

A composite muscle consisting of the psoas major and iliacus that serves as the prime flexor of the hip.

Gluteus Medius

A gluteal muscle responsible for hip abduction that serves as a common anatomical site for intramuscular injections.

Piriformis

A deep gluteal muscle that externally rotates the hip; the sciatic nerve runs directly beneath it, and tightness here can lead to sciatica.

Quadriceps Femoris

The anterior thigh muscle group (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) that extends and stabilizes the knee via the patellar ligament inserting on the tibial tuberosity.

Sartorius

A long strap-like anterior thigh muscle originating on the ASIS and inserting on the medial proximal tibia; flexes, abducts, and laterally rotates the hip and flexes the knee.

Hamstrings

A posterior thigh muscle group (biceps femoris, semitendinosus, semimembranosus) sharing a common origin at the ischial tuberosity; responsible for hip extension and knee flexion.

Tibialis Anterior

An anterior leg muscle originating on the lateral surface of the tibia that produces dorsiflexion and inversion of the foot.

Plantar Fascia

A dense connective tissue band supporting the longitudinal arch along the bottom of the foot, extending from the calcaneus to the toes.

Plantar Fasciitis

An inflammatory condition of the overstretched plantar fascia that produces localized pain in the heel at its calcaneal origin.