CHAPTER 6 THE MUSCULAR SYSTEM—PART C

Muscles and Body Movements Movement is attained due to a muscle

moving an attached bone Muscles are attached to at least two points

OriginAttachment to an immoveable bone

InsertionAttachment to a movable bone

During contraction, insertion moves toward origin

Muscles and Body Movements

Types of Ordinary Body Movements Flexion

Decreases the angle of the joint Brings 2 bones closer Ex: hinge joints like knee & elbow Ex: ball & socket joints like hip & shoulder

Extension Opposite of flexion Increases the angle between two bones Ex: Straightening knee or elbow

Hyperextension

Line of appendage is over 180° when straightened

Ex: Tip head posteriorly

Types of Ordinary Body Movements

Types of Ordinary Body Movements

Rotation Movement of

bone around its longitudinal axis

Common in ball & socket joints

Ex: Move atlas around the axis (shake your head “no”)

Types of Ordinary Body Movements

Abduction Movement of a limb

away from the midline Adduction

Opposite of abduction Movement of a limb

toward body midline Circumduction

Combination of flexion, extension, abduction, adduction = circular

Common in Ball & socket joints

Special Movements Dorsiflexion –

Lifting the foot so that the superior surface approaches the shin

Plantar flexion Depressing the

foot (pointing the toes)

Special Movements

Inversion Turn sole of foot medially

Eversion Turn sole of foot laterally

Special Movements Supination

Forearm rotates laterally so palm faces anteriorly

Radius & Ulna are parallel

Pronation Forearm rotates

medially so palm faces posteriorly

Radius & Ulna form “X” shape

Special Movements

Opposition Move thumb to

touch the tips of other fingers on the same hand

Types of Muscles Prime Mover – muscle with the major

responsibility for a certain movement Antagonist – muscle that opposes or

reverses a prime mover Muscle can be both:

Biceps – prime mover flexes elbowTriceps – prime mover extends elbow

Synergist – muscle that aids a prime mover in a movement and helps prevent rotation

Fixator – stabilizes the origin of a prime mover Allows all tension to move insertion

bone

Naming of Skeletal Muscles Based on direction of muscle fibers

Example: Rectus (straight) Based on relative size of the muscle

Example: Maximus (largest) Minimus – smallest Longus - long

Based on location of the muscleExample: many muscles are named for

bones Temporalis (temporal bone)

Naming of Skeletal Muscles Based on number of origins

Example: Triceps (three heads)Bi – 2Quad -4

Based on location of the muscle’s origin and insertion Example: sterno (on the sternum)

Naming of Skeletal Muscles Based on the shape of the

muscle Example: deltoid --triangular

Based on the action of the muscle Examples: flexor and extensor --flexes or extends a bone

Arrangement of Fascicles

Figure 6.14

FasciclesCircular – rings of muscle that open and close areas

Sphincters Orbicularis oris – around mouth

Convergent – muscles come together to a single insertion point—usually a tendon

Fan or triangle shaped Pectoralis major

Parallel – length runs parallel to long axis of muscle

Straplike

Fusiform – spindle shaped, long Biceps brachii

Pennate – fascicles attach obliquely (at a slanted position) to central tendon

Head and Neck MusclesFacial 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

mouthChewing muscles

Masseter—closes the jaw and elevates mandible

Temporalis—synergist of the masseter, closes jaw

Head and Neck Muscles

Neck muscles Platysma—pulls the corners of

the mouth inferiorly Sternocleidomastoid—flexes

the neck, rotates the head

Head and Neck Muscles

Figure 6.15

Muscles of Trunk, Shoulder & Arm

Anterior muscles Pectoralis major—adducts and

flexes the humerus Intercostal 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

Figure 6.16

Anterior Muscles of Trunk, Shoulder, Arm

Muscles of Trunk, Shoulder, ArmMuscles of the Abdominal Girdle:

Rectus 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—compresses abdominal contents

Anterior Muscles of Trunk, Shoulder, Arm

Figure 6.17

Muscles of Trunk, Shoulder, Arm

Posterior 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

Deltoid—arm abduction

Muscles of Posterior Neck, Trunk, Arm

Muscles of Posterior Neck, Trunk, Arm

Muscles of the Upper Limb

Biceps brachii—supinates forearm, flexes elbow

Brachialis—elbow flexion; lifts ulna

Brachioradialis—weak muscle Triceps brachii—elbow extension

(antagonist to biceps brachii)

Anterior Muscles of Trunk, Shoulder, Arm

Muscles of the Lower Limb Gluteus maximus—hip extension Gluteus medius—hip abduction,

steadies pelvis when walking Iliopsoas—hip flexion, keeps the

upper body from falling backward when standing erect

Adductor muscles—adduct the thighs

Muscles of the Pelvis, Hip, Thigh

Posterior view of hip and thigh

Muscles of the Lower Limb

Muscles causing movement at the knee joint: Hamstring group—thigh extension and

knee flexionBiceps femorisSemimembranosusSemitendinosus

Muscles of the Lower Limb

Muscles causing movement at the knee joint Sartorius—flexes the thigh Quadriceps group—extends the

kneeRectus femorisVastus muscles (three)

Muscles of the Pelvis, Hip, Thigh

Anterior view of pelvic & thigh muscles

Muscles of the Lower Limb

Muscles causing movement at ankle and foot: Tibialis anterior—dorsiflexion and

foot inversion Extensor digitorum longus—toe

extension and dorsiflexion of the foot

Fibularis muscles—plantar flexion, everts the foot

Soleus—plantar flexion

Muscles of the Lower Leg

Muscles of the Lower Leg

Superficial Muscles: Anterior

Superficial Muscles: Posterior

Developmental Aspects Nervous system must mature before

muscle control can be achieved. Gross movements develop before

precise control is possible. Maximum development of nervous

system achieved in mid-teens—athletes often notice an increased level of performance.

Homeostatic Imbalances Muscular Dystrophy – group of inherited

muscle-destroying diseases that affect specific muscle groups Muscles enlarge due to fat and connective

tissue deposits, but muscle fibers degenerate

Caused by lack of the protein dystrophin that is found in the sarcolemma

Duchenne’s Muscular DystrophyPrimarily affects malesDo not live beyond young adult

Homeostatic Imbalances Myasthenia gravis

Characterized by drooping of eyelids, difficulty in swallowing and talking, generalized muscle weakness

Shortage of acetylcholine receptors at the neuromuscular junction

Autoimmune disease

Homeostatic Imbalances Effects of Aging

Connective tissue increases, muscle mass decreases

Body weight decreases Strength decreases These effects can be countered by regular exercise, including weight training