Muscle Tissue Types and Functions Overview

Skeletal Muscle

Attached to bones via tendons, found throughout the body.

Striated

Skeletal muscle fibers have a banded appearance due to the organized arrangement of actin and myosin filaments.

Multinucleated

Each muscle fiber (cell) contains multiple nuclei, located at the periphery.

Voluntary

Controlled consciously by the somatic nervous system.

Movement

Responsible for voluntary movements like walking, running, and lifting.

Posture

Maintains posture and body position.

Heat generation

Generates heat during contraction (e.g., shivering).

Cardiac Muscle

Found only in the walls of the heart (myocardium).

Single central nucleus

Cardiac muscle cells (cardiomyocytes) typically have one centrally located nucleus, though some may have two.

Intercalated discs

Specialized structures that connect cardiac muscle cells, allowing for synchronized contractions.

Involuntary

Controlled by the autonomic nervous system and hormones, without conscious effort.

Pump blood

Cardiac muscle contracts rhythmically to pump blood throughout the body.

Self-exciting

Has autorhythmicity, meaning the heart can initiate its own contractions due to pacemaker cells.

Smooth Muscle

Found in the walls of hollow organs (e.g., stomach, intestines, blood vessels, bladder) and other structures like the respiratory and reproductive tracts.

Non-striated

Smooth muscle fibers do not have visible striations because actin and myosin are arranged differently than in skeletal and cardiac muscle.

Spindle-shaped cells

Smooth muscle fibers are long, thin, and spindle-shaped.

Movement of substances

Smooth muscle controls movements like the contraction of blood vessels, peristalsis in the digestive tract, and regulation of airflow in the respiratory system.

Regulation of organ volume

Helps in controlling the diameter of blood vessels and hollow organs.

Sliding Filament Theory

Explains how muscles contract to produce movement, describing the interaction between actin and myosin within the sarcomere.

Sarcomere

The functional unit of muscle contraction, located between two Z-discs.

Myosin

Thick filaments with 'heads' that bind to actin during contraction.

Actin

Thin filaments that slide past myosin during contraction.

Tropomyosin

A protein that blocks the binding sites on actin.

Troponin

A protein that binds calcium and helps expose the active sites on actin by moving tropomyosin.

Power Stroke

The myosin head pivots, pulling the actin filament toward the center of the sarcomere.

Detachment

After the power stroke, ATP binds to the myosin head, causing it to detach from actin.

Re-cocking the Myosin Head

ATP is hydrolyzed into ADP and Pi (inorganic phosphate), re-cocking the myosin head into its original position.

Atrophy

Muscle shrinking.

Hypertrophy

Muscle growing.

Type I (Slow-Twitch Fibers)

Contraction speed: Slow; Fatigue resistance: High (good for endurance); Energy source: Aerobic (uses oxygen).

Type IIa (Fast-Twitch, Intermediate Fibers)

Contraction speed: Fast.

Type IIb (Fast-Twitch, Glycolytic Fibers, white fibers)

Contraction speed: Very fast. Fatigue resistance: Low (for short bursts of power). Energy source: Anaerobic (without oxygen). Example: Used in explosive activities like sprinting or weightlifting.

Agonist (Prime Mover)

The main muscle responsible for producing a specific movement. Example: The biceps brachii is the agonist for elbow flexion.

Antagonist

A muscle that opposes the action of the agonist, relaxing or lengthening during the movement. Example: The triceps brachii is the antagonist to the biceps during elbow flexion.

Synergist

Muscles that assist the agonist by stabilizing joints or adding extra force to the movement. Example: The brachialis assists the biceps in elbow flexion.

Orbicularis oris

Compresses lips, purses lips 'pout'.

Buccinator

Molar region of maxilla and mandible; compresses cheeks.

Mentalis

Mandible below incisors; elevates and protrudes lower lip.

Risorius

Lateral Fascia associated with masseter muscle; draws corner of mouth to the side.

Zygomaticus

Zygomatic bone; raises lateral corners of mouth upward (smiling muscle).

Depressor labii inferioris

Body of mandible lateral to its midline; draws lower lip down (pouting muscle).

Corrugator supercilii

Arch of frontal bone; pulls skin inferiorly and anteriorly; wrinkles brow.

Levator labii superioris

Zygomatic bone and infraorbital margin of maxilla; opens lips; raises and furrows upper lip.

Orbicularis oculi

Frontal and maxillary bones and ligaments around orbit; closes eye.

Occipitofrontalis

Epicranial aponeurosis; raises eyebrows, wrinkles forehead.

Platysma

Mandible & skin of cheek; tenses skin of neck, depresses mandible.

Masseter

Zygomatic arch; elevates mandible & closes jaw.

Temporalis

Temporalis fossa; elevates mandible & closes jaw.

Digastric

Inferior surface of mandible at chin; depresses mandible, opening mouth, and/or elevates larynx.

Sternocleidomastoid

Clavicular head; together they flex the neck; alone one side bends neck toward shoulder & turns face to opposite side.

Splenius

Ligamentum nuchae, spinous processes of C7-T6; extends or hyperextends head.

Erector Spinae

Spinalis group (medial); extends vertebral column.

Quadratus lumborum

Iliac crest & iliolumbar ligament; depresses ribs, lateral flexion of vertebral column.

Oblique and Rectus Muscles

The muscle of the oblique and rectus groups lie between the vertebral column and the ventral midline.

Origin

The point where a muscle attaches to a stationary bone.

Insertion

The point where a muscle attaches to a movable bone.

Action

The specific movement produced by a muscle when it contracts.

Scalenes

Muscles in the cervical region that elevate ribs and flex the neck.

External intercostals

Muscles that elevate ribs.

Internal intercostals

Muscles that depress ribs.

External oblique

Muscle in the abdominal region that compresses the abdomen and rotates the vertebral column.

Internal oblique

Muscle that compresses the abdomen and rotates the vertebral column to the same side.

Transversus abdominis

Muscle that compresses the abdomen.

Rectus abdominis

Muscle that depresses ribs, flexes the vertebral column, and compresses the abdomen.

Pectoralis Minor

Muscle that draws the scapula forward and downward.

Serratus anterior

Muscle that stabilizes and rotates the scapula.

Subclavius

Muscle that helps stabilize and depress the pectoral girdle.

Trapezius

Muscle that stabilizes, raises, retracts, depresses, and rotates the scapula.

Levator scapulae

Muscle that elevates and adducts the scapula.

Rhomboid major and minor

Muscles that stabilize the scapula.

Bulbospongiosus

Muscle that compresses the base of the penis/clitoris and ejects urine or semen.

Ischiocavernosus

Muscle that compresses and stiffens the penis or clitoris.

Deep transverse perineal

Muscle that supports the pelvic floor.

External urethral sphincter

Muscle that closes the urethra and compresses glands.

Pelvic diaphragm

Muscle group that supports the organs of the pelvic cavity and flexes the joints of the sacrum and coccyx.

Appendicular muscles

Account for roughly 40 percent of the skeletal muscles in the body.

Muscles of the pectoral girdle and upper limbs

One of the two major groups of appendicular muscles.

Muscles of the pelvic girdle and lower limbs

One of the two major groups of appendicular muscles.

Pectoralis major

Prime movers of arm flexion, rotates medial, adducts; originates from sternal and inferior portion of clavicle, body of sternum, cartilage of ribs 1-6, and aponeurosis of external oblique muscle.

Latissimus dorsi

Prime mover of arm flexion, rotates medially, adducts; originates from spinous process of inferior thoracic and all lumbar vertebrae, ribs 8-12, and thoracolumbar fascia.

Deltoid

Prime mover of arm abduction; originates from clavicle and scapula.

Teres major

Extends, medially rotates, adducts humerus; originates from inferior angle of scapula.

Coracobrachialis

Flexion and adduction of humerus; originates from coracoid process.

Subscapularis

Chief medial rotator of humerus; originates from subscapular fossa of scapula.

Supraspinatus

Initiates abduction of shoulder; originates from supraspinous fossa of scapula.

Infraspinatus

Rotates humerus laterally; originates from infraspinous fossa of scapula.

Teres minor

Rotates humerus laterally; originates from lateral border of dorsal scapular surface.

Triceps brachii

Powerful forearm extensor; long head originates from infraglenoid tubercle of scapula.

Anconeus

Abducts ulna during pronation; originates from lateral epicondyle of humerus.

Biceps brachii

Flexion at elbow and shoulder, supinates forearm; short head originates from coracoid process.

Brachialis

Major forearm flexor; originates from anterior, distal surface of humerus.

Brachioradialis

Synergist in forearm flexion; originates from lateral supracondylar ridge at distal end of humerus.

Pronator teres

Pronates forearm; originates from medial epicondyle of humerus and coronoid process.

Flexor carpi radialis

Powerful wrist flexor, abducts hand; originates from medial epicondyle of humerus.

Palmaris longus

Tenses skin and fascia of palm, hand movements; originates from medial epicondyle of humerus.

Flexor digitorum superficialis

Flexion at middle phalanges (2-5) + wrist; has four tendons into middle phalanges of fingers 2-5.

Flexor pollicis longus

Flexes distal phalanx of thumb; originates from anterior surface of radius and interosseous membrane.

Flexor digitorum profundus

Flexes distal interphalangeal joints; has four tendons into distal phalanges 2-5.

Pronator quadratus

Prime mover of forearm pronation; originates from distal portion of anterior ulnar shaft.

Extensor carpi radialis longus

Extends and abducts wrist; originates from lateral supracondylar ridge of humerus.