Muscle Anatomy and Function Quiz

Skeletal Muscle Classification

• Skeletal muscles are classified by fascicle organization: parallel, convergent, circular, and pennate.
• Parallel muscles have fibers running parallel to the muscle's long axis. Examples include sartorius and biceps brachii (fusiform).
• Convergent muscles have a broad origin that converges on a single tendon. Examples include pectoralis muscles.
• Circular muscles, also called sphincters, surround body openings. Examples include orbicularis oris and external anal sphincter.
• Pennate muscles have fascicles attaching obliquely to a central tendon. These are further divided into unipennate, bipennate, and multipennate types. Examples include extensor digitorum (unipennate), rectus femoris (bipennate), and deltoid (multipennate).

Origin, Insertion, and Action

• Origin: fixed point of attachment
• Insertion: moving point of attachment
• Most muscles originate or insert on the skeleton. Origin is usually proximal to insertion, but exceptions exist.
• Action: movement produced by muscle contraction. Examples include flexion, extension, adduction, and various specific movements.

Types of Muscles Based on Action

• Agonist (prime mover): produces a particular action.
• Synergist: assists the larger agonist, helping to start or stabilize. A synergistic muscle can also be a fixator.
• Antagonist: opposes the action of the agonist.

Muscle Opposition

• Agonists and antagonists work in pairs. When one contracts, the other relaxes. Examples include flexors-extensors, abductors-adductors, etc.

Muscle Terminology

• Correct muscle names often include the term "muscle." Examples include platysma and diaphragm.
• Muscle names can be determined by location, origin/insertion, fascicle organization, relative position, and structural characteristics.

Naming Skeletal Muscles

• Muscles are named based on various factors including: location in the body, origin and insertion points, fascicle organization, relative position, and structural characteristics.

Location in the Body

• Muscle names often reflect their location. Examples include temporalis (temporal bone) and frontalis (frontal bone).

Origin & Insertion

• The first part of a muscle's name often indicates its origin, while the second part indicates its insertion. Sternocleidomastoid muscle is an example (originating at sternum and clavicle, and inserting at the mastoid process).

Fascicle Organization

• Fascicle orientation within a muscle is described using terms like rectus (straight), transversus (across), and oblique (slanted).

Relative Position

• Muscles are classified as superficial (externus), deep (internus), extrinsic (outside an organ), or intrinsic (inside an organ) depending on their location relative to other structures or organs.

Structural Characteristics

• Factors such as the number of tendons (heads), shape (e.g., deltoid, trapezius), and size (e.g., longus, brevis) can be used to name and differentiate muscles.

Action

• Muscle actions are described by the specific movement they produce, such as flexion, extension, adduction, etc. Sartorius is an example, with a specific special action.

Combined Names (Example)

• Some muscles have combined names that describe their action and location. Flexor digitorum superficialis muscle is an example (flexes the fingers; located superficially).

Divisions of the Muscular System

• Axial muscles compose 60% of skeletal muscles. These muscles are involved in positioning the head and vertebral column, and moving the thoracic cage.
• Appendicular muscles (40% of skeletal muscles) support the pectoral and pelvic girdles, and move the upper and lower limbs.

Muscles of the Head & Neck

• Facial muscles control facial expressions and originate on the skull
• Muscles of mastication move the mandible.
• Extrinsic eye muscles control eye position.
• Muscles of the tongue have names ending in glossus.
• Muscles of the pharynx initiate swallowing.

Muscles of Facial Expression

• Occipitofrontalis (epicranius) is separated into frontal and occipital bellies by the epicranial aponeurosis. It raises the eyebrows.
• Orbicularis oculi closes the eyelids.
• Orbicularis oris constricts the mouth.
• Buccinator moves food within the cheeks.

Muscles of Mastication

• Masseter is the strongest jaw muscle.
• Temporalis helps lift the mandible.
• Buccinator moves food around the cheeks.
• Pterygoids (medial and lateral) assist jaw movements.

Extrinsic Muscles of the Eye

• 4 rectus muscles (superior, inferior, medial, lateral) control eye movement.
• 2 oblique muscles (superior, inferior) assist in complex eye movement.
• Note that the abducens and trochlear nerves control some eye muscles.

Muscles of the Neck

• Sternocleidomastoid muscle: flexes the neck (exceptions exist: origin is distal to insertion).

Muscles of the Abdominal Wall

• Oblique muscles (external and internal) help compress the underlying structures and rotate the vertebral column.
• Rectus muscles (rectus abdominis) flex the vertebral column and oppose the erector spinae muscles, helping control the spine.

Muscles of the Pelvic Floor

• Support pelvic organs, flex the sacrum and coccyx, and control urination and defecation. The external anal sphincter/urethral sphincter muscles are essential in this control.
• Perineum is an area of skin anterior to the anus; it extends to the vagina or base of the testicles.
• The perineum is rich in nerve endings

Muscles of Pectoral Girdle

• Trapezius, rhomboids, and levator scapulae are involved in moving the scapula.
• Serratus anterior muscle moves the scapula

Muscles Move Upper Limbs

• Muscles move the arm, forearm, and hand in various ways.
• Examples include, Deltoid, Latissimus dorsi, Pectoralis major, Subscapularis, Teres major, Infraspinatus, Teres minor

Muscles Move the Arm

• These muscles are generally involved in moving the arm in multiple directions, including: adduction, medial rotation, extension, etc.
• Specific examples include Pectoralis major, Latissimus dorsi, Deltoid, Supraspinatus, Infraspinatus, Subscapularis

Rotator Cuff

• The rotator cuff is composed of 4 muscles, including subscapularis, supraspinatus, infraspinatus, and teres minor.
• It forms a cuff to stabilize and rotate the upper arm.

Rotator Cuff Tear

• Possible causes that lead to tears include acute injuries (sports), or repetitive overhead work.

Muscles Move the Leg

• Extensors (e.g., quadriceps femoris) originate on the femoral surface and are important for knee extension
• Flexors (e.g., hamstrings) originate on the pelvic girdle are crucial for flexing the knee.

Extensors of the Knee

• Quadriceps femoris muscle (rectus femoris, vastus medialis, vastus lateralis, vastus intermedius) are important for extending the knee.
• Share one tendon
• Enclose the patella and insert at the tibial tuberosity

Flexors of the Knee

• Semitendinosus, semimembranosus, biceps femoris, and sartorius flex the knee and assist with hip flexion.
• Popliteus rotates the tibia to unlock the knee.

Muscles Move Foot & Toes

• Muscles like Gastrocnemius, Soleus, Peroneus longus, and brevis perform plantarflexion at the ankle.
• Tibialis anterior muscle opposes these extensors performing dorsiflexion.
• There are extensor and flexor muscles involved in movement of the toes.

Intrinsic Muscles of the Foot

• Located within the foot; help with fine motor control of the foot (e.g., toe movements).

Tendon Sheaths

• Wide bands of connective tissue, including the extensor and flexor retinaculum; protect the tendons as they move.

Carpal Tunnel Syndrome

• Thickening of flexor retinaculum; narrows the carpal tunnel, compressing the median nerve.

Hernia

• Protrusion of an organ through an abnormal opening (e.g., inguinal, umbilical, diaphragmatic).

Effects of Aging on Skeletal Muscles

• Skeletal muscle fibers diminish in size and elasticity due to fibrosis.
• Decreased exercise tolerance and recovery from injuries.

Skeletal Muscle Integration with Other Systems

• Skeletal muscles interact with other organ systems to maintain homeostasis and perform various bodily functions. Integration with other systems includes the urinary, nervous, endocrine, digestive, respiratory, circulatory systems.