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Chapter 9:
Muscular System
Types and Functions of Muscles
Skeletal Usually attached to bone, produce movement, maintain
body posture, stabilize joints Voluntary, striated
Smooth Found in the walls of organs (viscera), airways and blood
vessels Involuntary, not striated
Cardiac Found only in the heart Involuntary, striated, branching
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3
Types and Functions of Muscles (cont’d.)
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4
Muscle Structure
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6
Whole Muscle Structure
Belly: fleshy body of muscle between slender points of attachment
Fascia: layers of tough connective tissue surrounding large skeletal muscles Endomysium: surrounds individual muscle fibers Perimysium: surrounds small bundles of fibers Fascicles: bundles of muscle fibers Epimysium: outer layer of fascia Tendon: strong, cordlike fascia that extends toward
and attaches to bone
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7
Muscle Compartments
In the limbs, fascia separates muscles into isolated compartments
Each compartment has its own blood supply and nerves
Damage to the muscles causes inflammation and leakage of fluid into the space; increases pressure and can cause muscles and nerves to die (from being compressed)
Results in compartment syndrome (or crush syndrome)
Muscle Compartments
Compartment Syndrome
Muscle Attachments
Tendons Dense fibrous connective tissue connects muscle
to bone; extension of the epimysium Direct attachment to bone or soft tissue Aponeurosis
Flat, sheet-like fascia; connects muscle to muscle or muscle to bone
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11
Muscle Fiber Structure
Sarcolemma: cell membrane of a muscle fiber Transverse tubules: points of cell membrane that
penetrate deep into interior of muscle fiber Sarcoplasmic reticulum: specialized endoplasmic
reticulum within muscle fiber Myofibrils: long cylindrical structures in each muscle
fiber Sarcomeres: contractile units formed of proteins
actin and myosin
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12
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13
Sliding Filament Theory
Muscles contract because sarcomeres shorten Sarcomeres shorten because actin and
myosin filaments slide past each other Myosin heads make contact with actin when
stimulated Crossbridges form Myosin heads rotate, pulling actin toward the center
of the sarcomere and causing the actin to slide past myosin
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14
Role of Calcium and ATP
Contraction and relaxation of muscle: ATP allows the actin and myosin to interact in the
presence of calcium Calcium: stored in sarcoplasmic reticulum, away
from actin and myosin
Skeletal Muscles & Nerves
Muscles contract only when stimulated by a nerve
Somatic motor nerves (composed of many cells called motor neurons) arise from the spinal cord and travel to skeletal muscle
Neuromuscular junction (NMJ): area where motor nerve meets muscle fibers
Motor Unit
A single motor neuron and all the muscle fibers it innervates
Each muscle has many motor units Strength of contraction depends on number
of units that are stimulated; more strength, more motor units used. This process is called recruitment
Motor Unit
Neuromuscular Junction
Muscle Contraction
The electrical signal (nerve impluse) travels down the nerve to the terminal and causes the release of the neurotransmitters ACh (acetylcholine)
The ACh diffuses across the neuromuscular junction and binds with the receptor sites
Muscle Contraction
Muscle Contraction
Stimulation of the receptor sites causes an electrical impulse to form in the muscle membrane (sarcolemma). The electrical impulse travels along the muscle membrane and penetrates deep into the muscle through the transverse tubules (T-tubules)
The impulse causes the release of calcium from the sarcoplasmic reticulum
Muscle Contraction
The calcium allows actin, myosin and ATP to interact, causing crossbridge formation and muscle contraction.
Muscle relaxation occurs when calcium is pumped back into the sarcoplasmic reticulum and away from the actin and myosin
Impairment at the NMJ
Myasthenia Gravis Damaged receptor sites on the muscle cell
membrane- cannot bind with ACh Muscle contraction is impaired and person
experiences extreme muscle weakness Patient will display easy fatigability, drooping of
the eyelids and eventually difficulty breathing (remember the diaphragm is skeletal muscle)
Serial pictures to demonstrate fatigue of eyelid muscles as the patient keeps looking up.
After a few minutes of rest, the eyelids have returned to near-normal position.
Myasthenia Gravis
Impairment at the NMJ
Curare and neuromuscular blockade Blocks the receptor sites on muscle membrane Muscle contraction is prevented because ACh
cannot bind with receptor sites Person is paralyzed and cannot breathe
spontaneously; synthetic skeletal muscle blockers are often used during surgical procedures
Patient maintains awareness
Impairment at the NMJ
Clostidium botulinum Prevents the release of ACh; muscle cells are not
stimulated to contract- result is paralysis Has medical use- Botox
Clostridium tetani Causes excessive nerve firing and excessive
release of ACh; muscle is constantly stimulated and severe muscle spasm results- tetanus
Often affects the jaw muscles first, hence the term lockjaw
Botox
Tetanus
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30
Responses of a Whole Muscle
Partial muscle response If little force needed, few fibers contract If more force needed, additional fibers contract Recruitment: process of using additional muscle
fibers to achieve greater muscle force
All or nothing rule
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31
Responses of a Whole Muscle (cont’d.)
Twitch: single muscle response in which muscle contracts and then fully relaxes
Tetanus: sustained muscle contraction caused by repeated stimulation (necessary to maintain posture)
Tonus: normal, continuous state of partial muscle contraction; due to contraction of different groups of muscle fibers within a whole muscle (alternating contraction and relaxation)
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32
Responses of a Whole Muscle (cont’d.)
ATP is energy source for muscle contraction After ATP is consumed, it is replaced in three
ways: Metabolism of creatine phosphate (storage form
of energy) & ATP (15 sec) Glycolysis (anaerobic metabolism of glucose);
enough ATP for 30-40 sec (results in lactic acid) Aerobic metabolism of glucose; after 40 sec;
requires O2
Muscle Fatigue
Inability of a muscle to contract forcefully following prolonged activity
Results from decreased release of Ca++, depletion of nutrients, oxygen, glycogen or creatine, and/or a build-up of waste (lactic acid)
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Muscle Terms
Muscle attachments Origin: attaches to the stationary bone Insertion: attaches to the more movable bone
Muscle groups and cooperation Prime mover: muscle responsible for most of the
movement of a muscle Synergists: assist the prime mover Antagonists: muscles that oppose the action of
another muscle
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35
Muscle Terms (cont’d.)
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Muscle overuse and underuse: Hypertrophy: growth in response to overuse Atrophy: wasting in response to disuse Contracture: abnormal fibrous formation in
muscle that “freezes” muscle in flexed position
Muscle Terms (cont’d.)
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37
Hypertrophy Atrophy
Contracture vs. Contraction
Contracture- abnormal bending of a joint in a fixed position
Contraction- shortening of muscles fibers to produce movement
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39
How Skeletal Muscles Are Named
Characteristics of skeletal muscles: Size Shape Direction of fibers Location Number of origins Identification of origin and insertion Muscle action
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40
Muscles from Head to Toe
Anterior view
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41
Muscles from Head to Toe (cont’d.)
Posterior view
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42
Muscles of the Head
Facial muscles Frontalis Orbicularis oculi Orbicularis oris Buccinator Zygomaticus Platysma
Muscles of the Head
Chewing muscles Masseter Temporalis
Masseter
Sternocleideomastoid
Muscles of the Neck
Sternocleidomastoid Scalene (3) Trapezius
Trapezius
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46
Muscles of the Trunk
Muscles involved in breathing Intercostal
muscles Diaphragm
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Muscles of the Trunk (cont’d.)
Muscles of the abdominal wall
External oblique Internal oblique Transversus abdominis Rectus abdominis Linea alba* (aponeurosis)
(rectus- straight)
Muscles of the Trunk
Muscles that move the vertebral column Erector spinae
Muscles that move the Shoulder and Arm
Trapezius Serratus anterior Pectoralis major Latissimus dorsi Deltoid Teres major Rotator cuff
Subscapularis Supraspinatus Infraspinatus Teres minor
Teres major
Pectoralis Major
Deltoid
Latissimus dorsi
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54
Muscles That Move theForearm
Biceps brachii Triceps brachii Brachialis Brachioradialis Flexor and extensor
carpi groups Flexor and extensor
digitorum groups
Biceps Brachii Triceps Brachii
Brachialis Brachioradialis
(Both are synergistic to the biceps brachii- assist in elbow flexion)
Muscles that move the wrist, hand and fingers
Flexors Flexor carpi radialis Flexor carpi ulnaris Flexor digitorum
Extensors Extensor carpi radialis longus Extensor carpi ulnaris Extensor digitorum
“Puppet string” configuration
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59
Carpal Tunnel Syndrome
Anatomy of the carpal tunnel
Muscles That Move the Thigh
Gluteus maximus Gluteus medius Gluteus minimus Adductor group
Adductor longus Adductor brevis Adductor magnus Gracilis pectineus
Tensor fascia latae Iliopsoas Sartorius
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Iliopsoas
Muscles That Move the Leg
Quadriceps femoris Rectus femoris Vastus lateralis Vastus medialis Vastus intermedius
Sartorius
Hamstrings Biceps femoris Semitendinosus Semimembranosus
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Quadriceps Femoris
Hamstring Muscles
Muscles That Move theAnkle and Foot
Tibialis anterior Peroneus longus Gastrocnemius Soleus Calcaneal tendon
(Achilles tendon)
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Peroneus longus
Tibialis Anterior
Gastrocnemius
Achilles Tendon
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72
Special Muscles
NCLEX Question
When assessing a patient’s range of motion, the nurse notices that the patient has trouble extending his right arm out from his side. Moving a body part away from the midline is called
1. Flexion2. Abduction3. Adduction4. Extension
Rationale
2. Abduction is movement away from the midline of the body.
NCLEX Question
Connective tissue that connects muscle to bone is
1. Ligament
2. Osseous
3. Cartilage
4. Tendon
Rationale
4. Tendons are extensions of epimysium, dense fibrous connective tissue, that connects muscle to bone.