Chapter 11

The Muscular System

 

Lecture Outline

INTRODUCTION

•      The voluntarily controlled muscles of the body make up the muscular system.

•      The muscular system and muscle tissue contribute to homeostasis by producing movement, stabilizing body position, regulating organ volume, moving substances within the body, and producing heat.

•      This chapter discusses how skeletal muscles produce movement and describes the principal skeletal muscles.

Chapter 11
The Muscular System

•       Skeletal muscle major groupings

•       How movements occur at specific joints

•       Learn the origin, insertion, function and innervation of all major muscles

•       Important to allied health care and physical rehabilitation students

HOW SKELETAL MUSCLES PRODUCE MOVEMENT

Muscle Attachment Sites:
Origin and Insertion

•       Skeletal muscles shorten & pull on the bones they are attached to

•       Origin is the bone that does not move when muscle shortens (normally proximal)

•       Insertion is the movable bone (some 2 joint muscles)

•       Fleshy portion of the muscle in between attachment sites = belly

Tenosynovitis

•      Inflammation of tendon and associated connective tissues at certain joints

–   wrist, elbows and shoulder commonly affected

•      Pain associated with movement

•      Causes

–   trauma, strain or excessive exercise

Lever Systems and Leverage

•      A lever is a rigid structure that moves around a fixed point, the fulcrum (F)

•      The lever is acted on by two different forces: (Figure 11.1b).

–   resistance (load) (L), which opposes movement

–   effort (E) which causes movement Bones serve as levers and joints serve as fulcrums.

•      Leverage, the mechanical advantage gained by a lever, is largely responsible for a muscle’s strength and range of motion (ROM), i.e., the maximum ability to move the bones of a joint through an arc.

Levers

Levers are categorized into three types –

•      First class levers (EFL) e.g. a seesaw – the head on the vertebral column (Figure 11.2a)

•      Second-class (FLE)  eg. a wheelbarrow(Figure 11.2b)

•      Third-class (FEL) (Figure 11.1b) e.g.  forceps  - the elbow joint (Figure 11.2c).

Lever Systems and Leverage

•      Muscle acts on rigid rod (bone)
that moves around a
fixed point called a fulcrum

•      Resistance is weight of body
part & perhaps an object

•      Effort or load is work done
by muscle contraction

•      Mechanical advantage

–   the muscle whose attachment is farther from the joint will produce the most force

–   the muscle attaching closer to the joint has the greater range of motion and the faster the speed it can produce

First - Class Lever

•      Can produce mechanical advantage or not depending on location of effort & resistance

–   if effort is further from fulcrum than resistance, then a strong resistance can be moved

•      Head resting on vertebral column

–   weight of face is the resistance

–   joint between skull & atlas is fulcrum

–   posterior neck muscles provide effort

 

Second - Class Lever

•      Similar to a wheelbarrow

•      Always produce mechanical advantage

–   resistance is always closer to fulcrum than the effort

•      Sacrifice of speed for force

•      Raising up on your toes

–   resistance is body weight

–   fulcrum is ball of foot

–   effort is contraction of calf muscles which pull heel up off of floor

Third - Class Lever

•       Most common levers in the body

•       Always produce a mechanical disadvantage

–    effort is always closer to fulcrum than resistance

•       Favors speed and range of motion over force

•       Flexor muscles at the elbow

–    resistance is weight in hand

–    fulcrum is elbow joint

–    effort is contraction of biceps brachii muscle

 

Fascicle Arrangements

•       A contracting muscle shortens to about 70% of its length

•       Fascicular arrangement represents a compromise between force of contraction (power) and range of motion

–    muscles with longer fibers have a greater range of motion

–    a short fiber can contract as forcefully as a long one.

 

Coordination Within Muscle Groups

•       Most movement is the result of several muscle working at the same time

•       Most muscles are arranged in opposing pairs at joints

–    prime mover or agonist contracts to cause the desired action

–    antagonist stretches and yields to prime mover

–    synergists contract to stabilize nearby joints

–    fixators stabilize the origin of the prime mover

•    scapula held steady so deltoid can raise arm

HOW SKELETAL MUSCLES ARE NAMED

•      The names of most of the nearly 700 skeletal muscles are based on several types of characteristics.

•      These characteristics may be reflected in the name of the muscle.

•      The most important characteristics include the direction in which the muscle fibers run, the size, shape, action, numbers of origins, and location of the muscle, and the sites of origin and insertion of the muscle

•      Examples from Table 11.2

–   triceps brachii -- 3 sites of origin

–   quadratus femoris -- square shape

–   serratus anterior -- saw-toothed edge

 

PRINCIPLE SKELETAL MUSCLES

•      Exhibits 11.1 through 11.20 list the principle skeletal muscles in various regions of the body.

•      Figure 11.3 shows general anterior and posterior views of the muscular system.

•      The exhibits contain objectives, an overview which provides a general orientation to the muscles, muscle names, origins, insertions, and actions, “relating muscles to movements,” innervation, and Figures (11.4-11.23) that show the muscles under consideration.

Muscles of Facial Expression

•      Arise from skull & insert onto skin

•      Encircle eyes, nose & mouth

•      Express emotions

•      Facial Nerve (VII)

•      Bell’s palsy = facial paralysis due

Muscles of Facial Expression

•      Orbicularis oculi closes the eye

•      Levator palpebrae superioris opens the eye

•      Orbicularis oris puckers the mouth

•      Buccinator forms the muscular portion of the cheek & assists in whistling, blowing, sucking & chewing

 

Extrinsic Muscles of the Eyeballs

•      Extrinsic muscles insert onto white of eye

•      Fastest contracting & most precisely controlled

•      Cranial nerves 3, 4 & 6 innervate the six muscles

–   4 Rectus muscles & 2 obliques

•      Intrinsic muscles are found within the eyeball

•      Levator palpebrae superioris raises eyelid

Muscles that Move the Mandible

•      Masseter, temporalis & pterygoids

•      Arise from skull & insert on mandible

•      Cranial nerve V (trigeminal nerve)

•      Protracts, elevates or retracts mandible

–   Temporalis & Masseter elevate the mandible (biting)

–   temporalis retracts

Jaw Muscles -- Deep Dissection

•      Lateral pterygoid protracts mandible

–   sphenoid bone to condyle of mandible

•      Medial pterygoid elevates & protracts mandible

–   sphenoid bone to angle of mandible

•      Together move jaw side to side to grind food.

Muscles that Move the Tongue

•       4 extrinsic mm arise
elsewhere, but insert
into tongue

–    Genioglossus

•    from inside tip of mandible

–    Styloglossus

•    from styloid process

–    Palatoglossus

•    from hard palate

–    Hyoglossus

•    from hyoid bone

•       Together move tongue in various directions

•       Intubation is necessary during anesthesia since Genioglossus relaxes & tongue falls posteriorly blocking airway

 

Muscles of the Floor of the Oral Cavity

•       Suprahyoid muscles lie superior to hyoid bone.

–    Digastric m. extends from mandible to mastoid process

•    used to open the mouth

–    Mylohyoid m. extends from hyoid to mandible

•    supports floor of mouth & elevates hyoid bone during swallowing

–    Stylohyoid & Geniohyoid elevate the hyoid during swallowing

 

Muscles that Move the Head

•       Sternocleidomastoid muscle

–    arises from sternum & clavicle & inserts onto mastoid process of skull

–    innervated by cranial nerve XI (spinal accessory)

–    contraction of both flexes the cervical vertebrae & extends head

–    contraction of one, laterally flexes the neck and rotates face in opposite direction

Muscles of Abdominal Wall

•       Notice 4 layers of muscle in the abdominal wall

Muscles of Abdominal Wall

•       4 pairs of sheetlike muscles

–    rectus abdominis = vertically oriented

–    external & internal obliques and transverses abdominis

•    wrap around body to form anterior body wall

•    form rectus sheath and linea alba

•       Inguinal ligament from anterior superior iliac spine to upper surface of body of pubis

•       Inguinal canal = passageway from pelvis through body wall musculature opening seen as superficial inguinal ring

•       Inguinal hernia = rupture or separation of abdominal wall allowing protrusion of part of the small intestine (more common in males)

 

Transverse Section of Body Wall

•      Rectus sheath formed from connective tissue aponeuroses of other abdominal muscles as they insert in the midline connective tissue called the linea alba

Muscles Used in Breathing

•       Breathing requires a change in  size of the thorax

•       During inspiration, thoracic cavity increases in size

–    external intercostal lift the ribs

–    diaphragm contracts & dome is flattened

•       During expiration, thoracic cavity decreases in size

–    internal intercostal mm used in forced expiration

•       Diaphragm is innervated by phrenic nerve (C3-C5) but intercostals innervated by thoracic spinal nerves (T2-T12)

 

Female Pelvic Floor & Perineum

•       Both the pelvic diaphragm ( coccygeus & levator ani) and the muscles of the perineum fill in the gap between the hip bones

–    supports pelvic viscera & resists increased abdominal pressure during defecation, urination, coughing, vomiting, etc

–    pierced by anal canal, vagina & urethra  in females

–    levator ani may be damaged during episiotomy during childbirth (urinary incontinence during coughing)

Muscles of Male Perineum

•      Perineum contains more superficial layer of muscle

–   urogenital triangle contains external genitals

•   muscle arrangement forms urogenital diaphragm assists in urination (external urethral sphincter) and ejaculation (ischiocavernosus, bulbospongiosus)

–   anal triangle contains anus

•   external anal sphincter

Stabilizing the Pectoral Girdle

•       Anterior thoracic muscles

–    Subclavius extends from 1st rib to clavicle

–    Pectoralis minor extends from ribs to coracoid process

–    Serratus anterior extends from ribs to inner surface of scapula

•       Posterior thoracic muscle

–    Trapezius extends from skull & vertebrae to clavicle & scapula

–    Levator scapulae extends from cervical vertebrae to scapula

–    Rhomboideus extends from thoracic vertebrae to vertebral border of scapula

 

Axial Muscles that Move the Arm

•      Pectoralis major & Latissimus dorsi extend from body wall to humerus.

Muscles that Move the Arm

•       Deltoid arises from acromion & spine of scapula & inserts on arm

–     abducts, flexes & extends arm

•       Rotator cuff muscles extend from scapula posterior to shoulder joint to attach to the humerus

–    supraspinatus & infraspinatus: above & below spine of scapula

–    subscapularis on inner surface of scapula

Flexors of the Forearm (elbow)

•      Cross anterior surface of elbow joint & form flexor muscle compartment

•      Biceps brachii

–   scapula to radial tuberosity

–   flexes shoulder and  elbow & supinates hand

•      Brachialis

–   humerus to ulna

–   flexion of elbow

•      Brachioradialis

–   humerus to radius

–   flexes elbow

Extensors of the Forearm (elbow)

•      Cross posterior surface of elbow joint & forms extensor muscle compartment

•      Triceps brachii

–   long head arises scapula

–   medial & lateral heads from humerus

–   inserts on ulna

–   extends elbow & shoulder joints

•      Anconeus

–   assists triceps brachii in extending the elbow

Cross-Section Through Forearm

•      If I am looking down onto this section is it from right or left arm?

Muscle that Pronate & Flex

•      Pronator teres

–   medial epicondyle to radius so contraction turns palm of hand down towards floor

•      Flexor carpi muscles

–   radialis

–   ulnaris

•      Flexor digitorum muscles

–  superficialis

–  profundus

•      Flexor pollicis

Muscles that Supinate & Extend

•      Supinator

–   lateral epicondyle of humerus to radius

–   supinates hand

•      Extensors of wrist and fingers

–  extensor carpi

–  extensor digitorum

–  extensor pollicis

–  extensor indicis

Retinaculum

•       Tough connective tissue band that helps hold tendons in place

•       Extensor & Flexor retinaculum cross wrist region attaching from bone to bone (carpal tunnel syndrome = painful compression of median nerve due to narrowing passageway under flexor retinaculum

 

Intrinsic Muscles of the Hand

•      Origins & insertions are within the hand

•      Help move the digits

•      Thenar muscles move the thumb

•      Hypothenar muscles move the little finger

•      Opposition, flexion, extension, abduction & adduction

Muscles that Move the Vertebrae

•       Quite complex due to overlap

•       Erector spinae fibers run longitudinally

–    3 groupings

•    spinalis

•    iliocostalis

•    longissimus

–    extend vertebral column

•       Smaller, deeper muscles

–    transversospinalis group

•    semispinalis, multifidis & rotatores

–    run from transverse process to dorsal spine of vertebrae above & help rotate vertebrae

Scalene Muscle Group

•      Attach cervical vertebrae to uppermost ribs

•      Flex, laterally flex & rotate the head

Muscles Crossing the Hip Joint

•       Iliopsoas flexes hip joint

–    arises lumbar vertebrae & ilium

–    inserts on lesser trochanter

•       Quadriceps femoris has 4 heads

–    Rectus femoris crosses hip

–    3 heads arise from femur

–    all act to extend the knee

•       Adductor muscles

–    bring legs together

–    cross hip joint medially

–    see next picture

•       Pulled groin muscle

–    result of quick sprint activity

–    stretching or tearing of iliopsoas or adductor muscle

Adductor Muscles of the Thigh

•      Adductor group of muscle extends from pelvis to linea aspera on posterior surface of femur

–   pectineus

–   adductor longus

–   adductor brevis

–   gracilis

–   adductor magnus (hip extensor)

 

Muscles of the Butt & Thigh

•       Gluteus muscles

–    maximus, medius & minimus

–    maximus extends hip

–    medius & minimus abduct

•       Deeper muscles laterally rotate femur

•       Hamstring muscles

–    semimembranosus (medial)

–    semitendinosus (medial)

–    biceps femoris (lateral)

–    extend hip & flex knee

•       Pulled hamstring

–    tear of origin of muscles from ischial tuberosity

Cross-Section through Thigh

•       3 compartments of muscle with unique innervation

–    anterior compartment is quadriceps femoris innervated by femoral nerve

–    medial compartment is adductors innervated by obturator nerve

–    posterior compartment is hamstrings innervated by sciatic nerve

Muscles of the Calf (posterior leg)

•       3 muscles insert onto calcaneus

–    gastrocnemius arises femur

•    flexes knee and ankle

–    plantaris & soleus arise from leg

•    flexes ankle

•       Deeper mm arise from tibia or fibula

–    cross ankle joint to insert into foot

•    tibialis posterior

•    flexor digitorum longus

•    flexor hallucis longus

–