chapter 9: muscular system. types and functions of muscles skeletal usually attached to bone,...

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

Copyright © 2007 by Saunders, an imprint of Elsevier Inc.

All rights reserved.

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Types and Functions of Muscles (cont’d.)



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Muscle Structure



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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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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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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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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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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


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


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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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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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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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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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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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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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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Muscles from Head to Toe

Anterior view



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Muscles from Head to Toe (cont’d.)

Posterior view



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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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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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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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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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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.

chapter 9: muscular system. types and functions of muscles skeletal usually attached to bone,...

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