Anatomy & Physiology

Chapter 6: The Muscular System

Five Golden Rules of Skeletal Muscle Activity

Movement can occur because muscles attach to our bones

Muscles are attached to at least two points known as:Origin

Attachment to a moveable boneInsertion

Attachment to an immovable bone

Muscles and Body Movements

TYPES OF BODY MOVEMENTSFlexion

Decreases the angle of the joint

Brings two bones closer together

Typical of hinge joints like knee and elbow

ExtensionOpposite of flexionIncreases angle

between two bones

TYPES OF BODY MOVEMENTSRotation

Movement of a bone around its longitudinal axis

Common in ball-and-socket joints

Example is when you move atlas around the dens of axis (shake your head “no”)

Internal Rotation: Moving towards the midline around an axis of rotation

External Rotation: Moving away from the midline around an axis of rotation

TYPES OF BODY MOVEMENTSAbduction

Movement of a limb AWAY from the midline

AdductionOpposite of

abductionMovement of a limb

TOWARD the midline

CircumductionCombination of flexion, extension, abduction,

and adductionCommon in ball-and-socket jointsMoving in a “circular” motion

TYPES OF BODY MOVEMENTS

These movements are only specific to the ankle:Dorsiflexion

Lifting the foot so that the superior surface approaches the shin

Plantar flexionDepressing the foot (pointing the toes)Moving foot downward as if you’re pushing on a gas pedal.

InversionTurn sole of foot medially/inwards/towards body

EversionTurn sole of foot laterally/outwards/away from body

Special Movements

Special MovementsThese movements

are specific to the elbow joint

SupinationForearm rotates

laterally so palm faces anteriorly

PronationForearm rotates

medially so palm faces posteriorly

Special MovementsThis movement is

specific to the phalanges

OppositionMove thumb to

touch the tips of other fingers on the same hand

Prime mover—muscle with the major responsibility for a certain movement i.e. biceps brachii is mainly responsible for flexion of the

elbow jointAntagonist—muscle that opposes or reverses a prime

mover i.e. triceps does the opposite of flexion and helps extend

the elbow jointSynergist—muscle that aids a prime mover in a

movement and helps prevent rotation i.e. biceps brachii also does shoulder flexion and receives

help from the anterior deltoidFixator—stabilizes the origin of a prime mover

Terms of Muscle Descriptors

NAMING OF SKELETAL MUSCLESBy direction of muscle

fibersExample: Rectus (straight)

By relative size of the muscleExample: Maximus

(largest)By location of the muscle

Example: Temporalis (temporal bone)

By number of originsExample: Triceps (three

heads)

By location of the muscle’s origin and insertionExample: Sterno (on

the sternum)By shape of the muscle

Example: Deltoid (triangular)

By action of the muscleExample: Flexor and extensor (flexes or extends a bone)

ARRANGEMENT OF FIBERS

Facial muscles Frontalis—raises eyebrows Orbicularis oculi—closes eyes, squints, blinks, winks Orbicularis oris—closes mouth and protrudes the lips Buccinator—flattens the cheek, chews Zygomaticus—raises corners of the mouth

Chewing muscles Masseter—closes the jaw and elevates mandible Temporalis—synergist of the masseter, closes jaw

Neck muscles Platysma—pulls the corners of the mouth inferiorly Sternocleidomastoid—flexes the neck, rotates the head

Head and Neck Muscles

Anterior musclesPectoralis major—adducts and flexes the

humerusIntercostal muscles

External intercostals—raise rib cage during inhalation

Internal intercostals—depress the rib cage to move air out of the lungs when you exhale forcibly

Muscles of Trunk, Shoulder, Arm

Anterior Muscles of Trunk, Shoulder, Arm

Muscles of TrunkMuscles of the abdominal

girdleRectus abdominis—flexes

vertebral column and compresses abdominal contents (defecation, childbirth, forced breathing)

External and internal obliques—flex vertebral column; rotate trunk and bend it laterally

Transversus abdominis—flexes trunk diagonally

Muscles of the Shoulder and ArmPosterior muscles

Trapezius—elevates, depresses, adducts, and stabilizes the scapula

Latissimus dorsi—extends and adducts the humerus

Erector spinae—back extension

Quadratus lumborum—flexes the spine laterally (side-to side)

Deltoid—arm abduction

Biceps brachii: flexes shoulder and elbow jointBrachialis: flexes the elbow joint

Think “reverse curls”

Brachioradialis: helps with elbow flexion in conjunction with radial deviation

Triceps brachii—elbow extension (antagonist to biceps brachii)

Muscles of the Upper Limb

Muscles of the Lower LimbGluteus maximus—hip

extensionGluteus medius—hip

abduction, steadies pelvis when walking

Iliopsoas—hip flexion & knee extension, keeps the upper body from falling backward when standing erect

Adductor muscles—adduct the thighs

Muscles of the Lower LimbMuscles causing

movement at the knee and hip jointHamstring group—

hip extension and knee flexionBiceps femorisSemimembranosusSemitendinosus

Muscles of the Lower LimbMuscles causing

movement at the knee jointSartorius—flexes the

hip and externally rotates

Quadriceps group—extends the kneeRectus femorisVastus muscles (three)

Vastus medialisVastus lateralisVastus intermedius

Muscles of the Lower LimbMuscles causing movement at

ankle and foot Tibialis anterior—dorsiflexion

and foot inversion Extensor digitorum longus—

toe extension and dorsiflexion of the foot

Soleus—plantar flexion Fibularis muscles are

commonly known as Peroneals Peroneus brevis Peroneus longus Peroneus tertius

*Perform eversion of the foot/ankle

Anterior Muscles

Posterior Muscles