axial muscles

Cardiac muscle

Striated, Y-shaped, involuntary, has intercalated discs

Skeletal muscle

Striated, voluntary

Smooth muscle

Not striated, involuntary

Contractility

Muscle cells can shorten

Excitability

Muscle cells are very responsive

Extensibility

Muscle cells can increase in length

Elasticity

Muscle cells can return to original length

Functions of skeletal muscle

Produce movement, maintain posture, support, generate heat, storage & movement of materials

Parallel (straight) muscle fibers

Fibers run parallel; central belly along midline

Convergent muscle

Fan-shaped; broad origin, narrow insertion; direction of pull can change

Pennate muscle

Fibers angled; uni-, bi-, multipennate; stronger than parallel of same size

Circular muscle

Sphincter; surround openings, close when they contract

Direct muscle attachment

Muscle appears fused to bone

Tendon attachment

Muscle connects via tendon to bone

Aponeurosis attachment

Muscle attaches via connective tissue sheet of tendon to bone

Orbicularis oris

Closes/puckers lips; attaches to skin around mouth

Orbicularis oculi

Closes eyelids; attaches to skin around eye

Zygomaticus major

“Smile” muscle; elevates corners of mouth; attaches to zygomatic bone & skin of mouth

Depressor anguli oris

“Frown” muscle; depresses corners of mouth; attaches to mandible & skin of mouth

Frontalis

Raises eyebrows; attaches to frontal bone & epicranial aponeurosis

Buccinator

Tightens cheeks; helps with chewing; attaches to mandible/maxilla & skin of face

Bell’s palsy

Facial nerve damage → muscles droop on one side of face; often temporary

Temporalis

Elevates & retracts mandible (closes jaw); attaches to lateral cranium & coronoid process of mandible

Masseter

Elevates & protracts mandible; strongest jaw muscle; attaches to zygomatic arch & mandible

Medial & Lateral Pterygoids

Elevate & protract mandible, side-to-side grinding; attach sphenoid to mandible

Genioglossus

Protracts (protrudes) tongue; attaches mandible to posterior tongue

Hyoglossus

Depresses tongue

Styloglossus

Retracts tongue

Palatoglossus

Elevates posterior tongue

Sternocleidomastoid (SCM)

Unilateral: flexes head laterally; Bilateral: flexes head/neck toward sternum; attaches mastoid process to sternum & clavicle

Torticollis

Asymmetrical head/neck position due to SCM shortening/overcontraction; congenital or acquired

Suprahyoid muscles

Elevate hyoid during swallowing & speaking; attach hyoid to mandible or temporal bone

Infrahyoid muscles

Depress hyoid at end of swallowing; attach hyoid to sternum

Clavicle fact

S-shaped, prone to fractures near curves; ligaments are strong so bone usually breaks instead of dislocating

Diaphragm

Primary muscle of inspiration; contracts to increase thoracic cavity; attaches to body wall & ribs, central tendon; has openings for aorta, IVC, esophagus

External intercostals

Elevate ribs during inspiration; fibers run inferomedially between ribs

Internal intercostals

Depress ribs during forced exhalation; fibers run superomedially (at right angles to external intercostals)

Rectus abdominis

Flexes trunk; attaches pubis to ribs & xiphoid process; enclosed in rectus sheath

External obliques

Flex & rotate trunk; attach lower ribs to pelvis & linea alba

Internal obliques

Flex & rotate trunk; deep to external oblique

Transversus abdominis

Compresses abdominal cavity; deepest ab muscle; fibers run horizontally; attach posterior to anterior body wall

Erector spinae (spinalis, longissimus, iliocostalis)

Bilateral: extend trunk, neck, head; Unilateral: laterally flex trunk, neck, head; attach pelvis, ribs, vertebrae, cranium

Levator ani

Supports pelvic viscera; openings for urethra, anus, vagina; attaches ischium/pubis to sacrum & coccyx

Coccygeus

Supports pelvic viscera; attaches ischium to sacrum