The Muscular System

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Chapter 11

• The Muscular System
• Lecture Outline

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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.

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Chapter 11The 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

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HOW SKELETAL MUSCLES PRODUCE MOVEMENT
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Muscle Attachment SitesOrigin 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

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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

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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 muscles
  strength and range of motion (ROM), i.e., the
  maximum ability to move the bones of a joint
  through an arc.

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Levers
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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).

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Lever Systems and Leverage

• Muscle acts on rigid rod (bone)that moves around
  a fixed point called a fulcrum
• Resistance is weight of bodypart perhaps an
  object
• Effort or load is work doneby 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

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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

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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

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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

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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.

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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

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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

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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.

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Muscles of Facial Expression

• Arise from skull insert onto skin
• Encircle eyes, nose mouth
• Express emotions
• Facial Nerve (VII)
• Bells palsy facial paralysis due

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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

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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

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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

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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.

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Muscles that Move the Tongue

• 4 extrinsic mm ariseelsewhere, but insertinto
  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

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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

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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

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Muscles of Abdominal Wall

• Notice 4 layers of muscle in the abdominal wall

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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)

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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

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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)

Quadratus lumborum fills in space between 12th
rib iliac crest to create posterior body wall
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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)

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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

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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

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Axial Muscles that Move the Arm

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

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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

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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

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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

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Cross-Section Through Forearm

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

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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

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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

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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

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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

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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

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Scalene Muscle Group

• Attach cervical vertebrae to uppermost ribs
• Flex, laterally flex rotate the head

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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

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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)

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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

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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

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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
• flexing ankle joint toes

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Muscles of the Leg and Foot

• Anterior compartment of leg
• extensors of ankle toes
• tibialis anterior
• extensor digitorum longus
• extensor hallucis longus
• tendons pass under retinaculum
• Shinsplits syndrome
• pain or soreness on anterior tibia
• running on hard surfaces
• Lateral compartment of leg
• peroneus mm plantarflex the foot
• tendons pass posteriorly to axis of ankle joint
  and into plantar foot

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Muscles of the Plantar Foot

• Intrinsic muscles
• arise insert in foot
• 4 layers of muscles
• get shorter as go into deeper layers
• Flex, adduct abduct toes
• Digiti minimi muscles move little toe
• Hallucis muscles move big toe
• Plantar fasciitis (painful heel syndrome) chronic
  irritation of plantar aponeurosis at calcaneus
• improper shoes weight gain

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Compartment Syndrome

• Skeletal muscles in the limbs are organized in
  units called compartments.
• In compartment syndrome, some external or
  internal pressure constricts the structures
  within a compartment, resulting in damaged blood
  vessels and subsequent reduction of the blood
  supply to the structures within the compartment.
• Without intervention, nerves suffer damage, and
  muscle develop scar tissue that results in
  permanent shortening of the muscles, a condition
  called contracture.

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IM injection

• Intramuscular injection penetrates the skin,
  subcutaneous tissue and enters the muscle.
• They are given when rapid absorption is
  necessary, for large doses, or when a drug is
  irritating to subcutaneous tissue.
• Common sites of injection are the gluteus medius,
  vastul lateralis, and deltoid.
• Intramuscular injections are faster than oral
  medications, but slower than IV.