muscular system chapter 8. introduction muscles are responsible for movement –contraction &...

Muscular System

Chapter 8

Introduction

• Muscles are responsible for movement– Contraction & relaxation

• Muscles make up 40 – 50 % of a human’s total body weight

Characteristics of Muscle Tissue

• Excitability– Can receive & respond to stimuli

• Contractility– Can shorten & thicken

• Extensibility– Can be stretched

• Elasticity– Can return to its original shape

Functions of Muscle Tissue

• Motion

• Maintenance of posture

• Heat production

Kinds of Muscle Tissue

• Skeletal Muscle

• Cardiac Muscle

• Smooth Muscle

The Muscular System

• Muscle tissue = all contractile tissue

• Muscular system = – Skeletal muscle tissue– Connective tissue

Human Anatomy, 3rd editionPrentice Hall, © 2001

Skeletal Muscle Tissue

• Fascia– Sheet or band of

fibrous connective tissue around muscles and other organs

• Fascia of skeletal muscle– Surrounds muscle

– Subdivides muscle

Human Anatomy, 3rd editionPrentice Hall, © 2001

Structural Organization of Skeletal Muscle

Human Anatomy, 3rd editionPrentice Hall, © 2001

Tendons

• Cord of connective tissue that attaches a muscle to the periosteum of a bone

• Extensions of fascia

Human Anatomy, 3rd editionPrentice Hall, © 2001

Nerve & Blood Supply• Each skeletal muscle is well-supplied with nerves and blood

vessels– Related to contraction

• Contraction requirements– Stimulation by impulse from a nerve cell

– Energy

– Waste products eliminated

Human Anatomy, 3rd editionPrentice Hall, © 2001

Skeletal Muscle Fiber

• Muscle fibers = elongated cells– Sarcolemma– Sarcoplasm– Sarcoplasmic reticulum– T tubules

• Muscle fibers consist of myofibrils

• Extend length of fiber

Human Anatomy, 3rd editionPrentice Hall, © 2001

Histology of Skeletal Muscle Tissue

• Myofibrils consist of myofilaments - proteins that cause contraction– Thick filaments

– Thin filaments

Human Anatomy, 3rd editionPrentice Hall, © 2001

Myofilaments

• Myofilaments do not extend entire length of fiber.

• Stacked in compartments = sarcomeres

Human Anatomy, 3rd editionPrentice Hall, © 2001

Thick and Thin Filaments• Thin filaments

– Composed mostly of actin

– Contain tropomyosin and troponin

– Double-stranded coil

• Thick filaments

– Composed mostly of myosin

– Rod-shaped (tail) with head

• Cross bridges

Human Anatomy, 3rd editionPrentice Hall, © 2001

Contraction – Sliding Filament Theory

• Thin filaments slide inward

• Sarcomere shortens

• Lengths of myofilaments do not change

• Sliding of myofilaments and shortening of sarcomeres causes the shortening of muscle fibers

Human Anatomy, 3rd editionPrentice Hall, © 2001

Neuromuscular Junction• Contraction requires a stimulus from a neuron• An axon comes into close contact with a muscle membrane =

neuromuscular junction• Small vesicles in end of axon release acetylcholine (Ach)

• Acetylcholine transmits nerve impulse to the muscle fiber– Initiates contraction

Human Anatomy, 3rd editionPrentice Hall, © 2001

Physiology of Contraction – Relaxed Muscle

• Sarcoplasm is low in calcium

• ATP is bound to myosin cross bridges

• Tropomyosin-troponin complex is attached to actin

Physiology of Contraction – Muscle is Stimulated

– Nerve impulse reaches neuromuscular junction– Neuron releases ACh– Electrical charge travels along sarcolemma– Electrical charge travels down T tubules– Electrical charge travels to S.R.– S.R. releases calcium into sarcoplasm

Physiology of Contraction – Activation of Myosin

• Calcium binds to troponin – Frees receptor sites of actin for myosin cross bridge

• Cross bridges attach to actin• Calcium acts as an enzyme

– Breaks down ATP to ADP + P

• Myosin cross bridges move• Sarcomere shortens• Muscle shortens

Physiology of Contraction – Relaxation of Muscle

• Nerve impulse ends• ACh is broken down by acetylcholinesterase• Calcium is actively transported back into S.R.• ADP + P = ATP

– Binds to cross bridges

• Myosin cross bridges separate from actin• Binding sites on actin are covered• Thin myofilaments slip back to resting position• Sarcomeres return to resting length• Muscle fiber returns to resting length

Human Anatomy, 3rd editionPrentice Hall, © 2001

Physiology of Contraction

Disorders

• Fibrosis

• Fibrositis

• Fibromyalgia

• Muscular dystrophy

• Myasthenia gravis

Abnormal Contractions

– Spasm– Cramp– Convulsion– Fibrillation– Tic

Anatomy of the Muscular System

How Skeletal Muscles Produce Movement

• Exert force on tendons• Attached to articulating bones forming a joint• When muscle contracts, one bone moves toward

the other• Attachments

– Origin = attachment to stationary bone– Insertion = attachment to moveable bone– Belly = fleshy portion of muscle between

tendons

Group Actions

• Agonist or prime mover– Causes desired action

• Antagonist– Effect is opposite to agonist

• Synergist– Assists agonist

Naming of Skeletal Muscles

• Direction of muscle fibers

• Location

• Size

• Number of origins

• Shape

• Origin & insertion

• Action

Human Anatomy, 3rd editionPrentice Hall, © 2001

Muscles of the Anterior Trunk and Shoulder

– Sternocleidomastoid– Pectoralis major– Rectus abdominus– External oblique– Deltoid

Human Anatomy, 3rd editionPrentice Hall, © 2001

Muscles of the Posterior Trunk and Shoulder

• Trapezius• Latissimus Dorsi• Deltoid

Human Anatomy, 3rd editionPrentice Hall, © 2001

Muscles of the Arm

– Deltoid– Biceps brachii– Brachioradialis– Triceps brachii

Human Anatomy, 3rd editionPrentice Hall, © 2001

Muscles of the Forearm– Flexors - anterior side– Extensors – posterior side

Human Anatomy, 3rd editionPrentice Hall, © 2001

Muscles of the Anterior Thigh

– Gracilis– Adductor longus– Sartorius– Quadriceps

• Rectus femoris

• Vastus lateralis

• Vastus medialis

Human Anatomy, 3rd editionPrentice Hall, © 2001

Muscles of the Posterior Thigh

– Gluteus maximus– Hamstrings

• Biceps femoris

• Semitendinosis

• Semimembranosis

Human Anatomy, 3rd editionPrentice Hall, © 2001

Muscles of the Anterior and Lateral Leg

– Tibialis anterior– Peroneus longus– Extensor

digitorum longus

Human Anatomy, 3rd editionPrentice Hall, © 2001

Muscles of the Posterior Leg

– Gastrocnemius– Soleus– Achilles tendon

(nonmuscular)