Anatomy

Chapter 9Muscular System

PowerPoint Presentation to accompany Hole’s Human Anatomy and Physiology, 10th edition, edited by S.C. Wache for Biol2064.01

You are responsible for the following figures and tables:

Part I. Fine Structure and Function.Tab. 9.2 - Muscular System Function Fig. 9.1 - Muscular System Organs – Fig. 9.2 - 9.11 - Fine structure and function of muscles.Fig. 9.2 - Skeletal muscle organization.Fig. 9.4 – Myofibrils.Fig. 9.6 - Troponin, Tropomyosin, Actin and Myosin.Fig. 9.8 NMJ, neuromuscular junction.Fig. 9.10 - Calcium from the SR binds troponin.Fig. 9.12 – ATP; creatine-phosphate. Fig. 9.13, 9.14 - Oxygen debt.Fig. 9.15 - Muscle twitches can be recorded.Fig. 9.16 - Different types of muscle contractions.See Glossary, p. 994.[see the table in the attached lecture handout]

You are responsible for the following figures and tables:

Part II. Skeletal Muscle Identification.[see tables in the attached lecture handout ]

Tab. 9.5 - Sternocleidomastoid Fig. 9.24 - Trapezius and Deltoid are named by their shape.Tab. 9.7 - Pectoralis major – Tab. 9.8 - Forearm muscles: Biceps brachii/agonist;Triceps brachii/antagonist.Tab. 9.10 - Muscle of the abdominal wall. Tab. 9.13 - Muscles that move the leg. Tab. 9.14 – Gastrocnemius.

MUSCLE STRUCTURE TYPE OFCONTROL

LOCATION FUNCTION

SKELETAL long, thin, striated muscle fibers / cells with many nuclei

voluntary attached to bones

move bones

CARDIAC network of striated cells with a centrally located nucleus; are connected via intercalated discs

involuntary heart pump blood to lungs and body

SMOOTH spindle shaped cells with one centrally located nucleus, lacking striations

involuntary walls of visceral hollow organs, irises of eyes, walls of blood vessels

helps move substances through ducts or vessels (i.e. food, urine, semen, blood)

Note: This chapter focuses on skeletal muscle fine structure and skeletal muscle identification.

Skeletal Muscle (Fig. 9.1)

• A muscle is composed of skeletal muscle tissue, nervous tissue, blood vessels, and connective tissue.

• Individual muscles are held in place by fascia, dense connective tissue.

• Tendons are extensions of the fascia that connect muscle to bone by intertwining with the fibers in the periosteum of the bone.

• Aponeuroses are sheets of connective tissue that connect muscle to muscle.

• Epimysium: connective tissue that surrounds a skeletal muscle.

• Perimysium: connective tissue that extends inward from the epimysium and separates fascicles (bundles of muscle fibers also called muscle cells).

• Endomysium: Connective tissue that separates muscle cells within a fascicle.

• Each muscle cell contains many myofibrils.

Skeletal Muscle Structure and Connective Tissue Coverings

Figure 9.2

Skeletal Muscle Fibers (Fig. 9.2)

• A muscle fiber is a multinucleated muscle cell that attaches to connective tissue.

• Sarcolemma is the muscle cell membrane.• Sarcoplasm is the cytoplasm containing

nuclei, mitochondria, and myofibrils.• Myofibrils are composed of protein

filaments, predominantly myosin and actin.

Protein Filaments• Myosin: Thick filament of twisted protein strands

with globular ends called cross-bridges.• Actin: Thin filament protein which can be found in

a complex with two other muscle proteins, tropomyosin and troponin.

• The close association of these proteins makes muscle contraction possible.

• Organization of these protein filaments leads to light and dark striations seen in skeletal muscle under the light microscope which denote each sarcomere.

Figure 9.6

Thin and Thick Filaments

Sarcomere StructureStriations form a repeating pattern along themuscle fiber called sarcomeres.• Z Line – separates sarcomeres.• I bands (light bands) are composed of actin

filaments attached to Z lines.• A bands (dark bands) are composed of myosin

overlapping actin attached to Z lines by titin.• A central region (H zone) consists of myosin

only with a thick line, the M line.

Figure 9.4

Intracellular Structure of Muscle• Sarcoplasmic reticulum: network of membranous

sacs surrounding myofibrils.• Transverse tubules (T-tubules) extend deep into

the sarcoplasm and contain extracellular fluid. These transverse tubules allow a multinucleated muscle fiber to be stimulated simultaneously.

• Cisternae: enlarged portions of the sarcoplasmic reticulum.

• These three structures form a triad where the actin and myosin overlap.

Figure 9.7- Sarcoplasm content of a muscle cell = muscle fiber

Motor neuron axons join the skeletalmuscle at the neuromuscular junction. • Neurotransmitters are chemicals stored in vesicles

of the motor neuron axon. Acetylcholine controls skeletal muscle contraction.

• Motor end plate is a specialized region of the sarcolemma at the neuromuscular junction.

• Synaptic cleft is a space between the neuron and the motor end plate.

• A amotor unit consists of the motor neuron and the muscle fibers it controls.

Events of Muscle Contraction

Figure 9.9 – Neuromuscular Junction

Figure 9.9

Molecular Events of Muscle Contraction• Motor neuron axon releases acetylcholine.• Acetylcholine diffuses across synaptic cleft.• This stimulates the sarcolemma. The impulse travels over

the muscle fiber surface and down the T-tubules to the sarcoplasmic reticulum (SR).

• Calcium ions diffuse out of the SR into the sarcoplasm and bind to troponin.

• Tropomyosin moves and exposes sites on actin filaments.• Actin and myosin form linkages.• Actin filaments are pulled inward by myosin cross-bridges

(sliding filament theory).• Muscle fibers shorten as contraction occurs.

Figure 9.10 – a) resting relaxed muscle; b) excited contracted muscle.

Note the change in the actin/ troponin/ tropomyosin complex by binding of Ca 2+

Figure 9.12 – Sliding filament theory explains how actin moves along myosin filament thereby causing the shortening of the muscle.

It explains how actin moves along myosin filament thereby causing the shortening or contraction of the muscle.• See Fig. 9.11 to envision the shortening of muscle in the course of actin sliding or walking alongside the myosin thick filament as it makes a bond with a myosin head, then breaks it, then remakes it with the next myosin head.• Imagine how tension and muscle strength increase as the muscle shortens.

Sliding Filament Theory

Events of Muscle Relaxation

• Acetylcholine is degraded by the enzyme acetylcholine-esterase and the muscle is no longer stimulated.

• Calcium ions are actively transported back into the SR.

• Actin-myosin linkages break.• Troponin and tropomyosin cross-bridges

reform.• Troponin and tropomyosin interaction inhibits

the interaction between myosin and actin.

Energy Sources• ATP, generated by cellular respiration, is enough

for a brief contraction.• In the mitochondria, excess energy is stored as

creatine phosphate. Creatine Phosphate has a high energy phosphate

bond that can regenerate ATP from ADP (ADP + P ATP). Creatinine is excreted in the urine.

It is generated by phosphokinase when there is excess ATP.

• Muscles store excess glucose, needed for cellular respiration, in the form of glycogen in muscle tissue and liver .

Figure 9.12

Oxygen and Cellular Respiration• Initially, oxygen is transported bound to blood

hemoglobin inside RBC in the lung. • In muscle tissue, it is transferred to myoglobin,

an oxygen binding protein found in muscle.• Glycolysis: early phase of metabolism that

partially breaks down glucose and does not require oxygen (anaerobic phase).

• Citric acid cycle: complete breakdown of glucose which requires oxygen (aerobic phase).

Oxygen Debt

• During strenuous exercise there may not be enough oxygen to maintain aerobic metabolism.

• Anaerobic metabolism maintains ATP levels while lactic acid=lactate levels increase.

• This causes muscle cramps.• Fig. 9.14 - Liver cells convert lactic acid to

glucose using ATP energy.• Definition oxygen debt: It is the amount of

oxygen needed for the liver to convert the accumulated lactic acid into glucose.

Muscle Fatigue• Fatigue occurs when a muscle is exercised for a prolonged

period and loses its ability to contract.• It is often due to lactic acid accumulation that lowers pH

and prevents muscle fibers from responding.• It can also be caused by decreased blood flow, ion

imbalances, and psychological causes.• Cramps can occur with fatigue: decreased electrolyte

concentrations trigger uncontrolled stimulation.• Physically fit people make less lactic acid due to better

circulation and increased oxygen carrying capacity.• Some muscle fibers are more likely to become fatigued.

Heat Production

• Heat is a by-product of cellular respiration.• Muscles are a major source of heat.• Blood transports heat throughout the body.

* Remember that one response of the body to a low body temperature is shivering or muscle contraction which results in raising body temperature (Chapter 1).

Types of Muscular ResponsesTo get a muscle twitch, a threshold stimulus (=minimal stimulus required to cause contraction) is required. A twitch isthe millisecond response of a muscle to a one stimulus. Phasesof a single muscle twitch:• Latent period is the time between stimulus and response.• Period of contraction is when the muscle pulls at its

attachments.• Period of relaxation is when the muscle stretches to its

former length.• Refractory period is a brief period when the muscle remains

unresponsive.• All-or-none response: a muscle that does not reach threshold

will not contract. Once threshold stimulus is reached, the muscle contracts completely.

Types of Muscular Responses

Figure 9.17 – a) series of twitches; b) summation; c) tetanic contraction

Types of Muscular Responses• A series of single twitches is the result of multiple stimuli,

that are far apart allowing the muscle to relax in-between each stimulus.

• Summation: each successive contraction increases to maximum. The staircase effect is due to a net increase in available calcium ions.

Summation is the process of combining twitches into a sustained contraction.

• A tetanic contraction is a forceful sustained contraction. • A tetanus is a prolonged contraction of a muscle resulting

from a series of motor impulses following one another too rapidly to permit intervening relaxation of the muscle.

Sustained Contraction Through Activation of Many Motor Units

• Definition motor unit: It is a motor neuron and the muscle fibers it controls.

• Definition sustained contraction: Multiple motor unit summation or recruitment is an increase in the number of activated motor units leading to sustained contraction.

• Muscle tone is a low level of sustained contractions in a muscle that appears at rest.

Further Differentiation of Muscle Contractions

• Isotonic: involve a change in length during contraction.

Concentric: occur when the muscle shortens. Eccentric: occur when the muscle lengthens.

• Isometric: do not involve a change in length.

Figure 9.17

Figure 9.17

Fast and Slow Muscle Fibers

• Slow-twitch (type I) fibers are oxidative and resistant to fatigue. They are called red fibers because they contain myoglobin.

• Fast-twitch (type II a) are glycolytic and easily fatigue. They are called white fibers.

Fast-twitch (type II b) are intermediate fibers, oxidative and fatigue-resistant.

Cardiac Muscle (Heart)• Cells have a single nucleus, sarcoplasmic reticulum, T

tubules, and mitochondria. However, they are connected with each other by intercalated disks.

• This connection allows cardiac muscle to act in unison, as a functional syncytium.

Note: A syncytium is a multinucleated cell. While cardiac muscle cells are not multinucleated, functionally they appear as if they are multinucleated.

• Intercalated disks are gap junctions.• Cardiac muscle is involuntary in action and self-

exciting with the help of a natural pacemaker called the sinoatrial node. It has rhythmicity.

Smooth Muscle (Glands, Vessels, and Organs)

• They lack striation and T- tubules.• Multiunit smooth muscle fibers function

as separate units.• Single-unit smooth muscle (visceral

smooth muscle) consists of sheets of cells joined by gap junctions. The fibers respond as a unit. The muscle displays rhythmicity.

Smooth Muscle Contraction• In part, triggered by nerve impulses and release of calcium.• Uses ATP and actin-myosin reactions.• Smooth muscle lacks troponin and uses calmodulin to

bind calcium ions.• Calcium diffuses in from extracellular fluid.• Norepinephrine or acetylcholine can function as a

neurotransmitters.• Contraction can be affected by hormones.• Stretching can trigger contractions.• Smooth muscle is slower to contract and relax, but can

forcefully contract longer with the same amount of energy expended.

• Muscle fibers can change length without changing tautness.

• Supplies of myoglobin, ATP, and creatine phosphate begin to decline by age 40. Ultimately, this will lead to atrophy of muscle tissue.

• Muscles shrink and become less elastic.• Muscles become smaller and capable of less

forceful contraction.• By age 80 half of the muscle of young

adulthood has atrophied.• Exercise can combat and delay these events.

Life-Span Changes

Identification of Major Skeletal Muscles

Focus will be on the following skeletal muscles:• Chest and abdominal wall muscles• Upper limb muscles• Lower limb muscles

Note: For arms and legs, identify the prime movers of flexion and any synergists as well the antagonist.

Skeletal Muscle Position and Function

Positioning of skeletal muscles between bones:• Origin: immovable end of a joint• Insertion: movable end of a joint

Skeletal muscles work in groups:• Prime mover or Agonist: major muscle involved in action• Synergists: assist the prime mover• Antagonists: resist the prime mover

•SKELETAL MUSCLE NAMING • VOCABULARY • EXAMPLES OF NAMES

•Direction of fascicles relative to midline

•rectus = parallel•transverse = perpendicular•oblique = at 45o angle

•Rectus abdominis•Transversus abdominis•External Oblique

•Location (bone or body part that a muscle covers)

•frontal bone•tibia

•Frontalis•Tibialis Anterior

•Relative Size •maximus = largest•longus = longest•brevis = shortest

•Gluteus maximus•Palmaris longus•Peroneus longus

•Number of Origins (Heads) •biceps = 2 origins•triceps = 3 origins

•Biceps brachii•Triceps brachii

•Shape •deltoid = triangle•trapezius = trapezoid•serratus = saw-toothed•orbicularis = circular

•Deltoid•Trapezius•Serratus anterior•Orbicularis oris

•Location of Origin and/or Insertion

•2 origins = sternum, clavicle•insertion = mastoid process of the temporal bone behind the ear that is well developed and of somewhat conical form in adults but inconspicuous in children

•Sternocleidomastoid =a thick superficial muscle on each side that arises by one head from the first segment of the sternum and by a second from the inner part of the clavicle, that inserts into the mastoid process and occipital bone, and that acts especially to bend, rotate, flex, and extend the head

•Action of Muscle •flexion•extension•adduction

•Flexor carpi radialis•Extensor digitorum•Adductor longus

NAME OF MUSCLE LOCATION/ DESCRIPTION ACTION

EpicraniusFrontalisOccipitalis

Covers craniumover foreheadover occipital

elevates eyebrow

Orbicularis oris circular muscle around the mouth closes lips (“kissing muscle”)

Zygomaticus (*)Origin: zygomatic arch Insertion: orbicularis oris

muscle that connects zygomatic arch to corner of mouth

elevates corners of mouth (“smiling muscle”)

Buccinator hollow of cheek compresses cheeks “trumpeter’s muscle”

Platysma over lower jaw to neck depresses mandible

Orbicularis oculi circular muscle around eye closes eye

Muscles of Facial Expression

NAME OF MUSCLE LOCATION/ DESCRIPTION

ACTION

MasseterOrigin: Zygomatic ArchInsertion: Lateral Mandible

over lateral mandible elevates mandible

Temporalis convergent muscle over temporal bone

elevates mandible

Muscle that moves the Head NAME OF MUSCLE LOCATION/

DESCRIPTION ACTION

Sternocleidomastoid(*)Origin: sternoclavicular Insertion: mastoid process of temporal bone

Major neck muscle flexion of head toward chest (both contracted)rotation/abduction of head (as antagonists)

Muscles of Mastication

Muscles That Move the Head

Fig.9.25- Sternocleidomastoid: pulls head to one side, flexes the neck

Muscles That Move the Head

Fig. 9.23- Splenius capitis: rotates head, bends head, extends neck

Fig. 9.23 - Semispinalis: extends and bends head to one side, rotates head; Longissimus capitis: extends and rotates head.

Muscles that move the Pectoral Girdle

NAME OF MUSCLE LOCATION/ DESCRIPTION

ACTION

Trapezius (*)Origin: occipital bone & spines of C7-T12Insertion: clavicle and acromion process of scapulae

Trapezoid shaped muscle in posterior neck and upper back

elevates pectoral girdle (“shoulder shrug”)

Pectoralis minor Muscle deep to Pectoralis major

scapula fixator

Serratus anterior Saw-toothed lateral thoracic muscle

scapula fixator

Muscles that move the Arm (Humerus)

NAME OF MUSCLE LOCATION/ DESCRIPTION ACTION

Pectoralis major (*)Origin: clavicle, sternum, & costal cartilages of ribs 1-6Insertion: Greater tubercle of humerus

Large, convergent chest muscle flexes arm medially (pull arms forward and together)

Latissimus dorsi Large, back muscle adduction of humerus

Deltoid Triangular shaped shoulder muscle abduction of humerus

Muscles that move the Forearm (Radius and Ulna)

NAME OF MUSCLE LOCATION/ DESCRIPTION ACTION

Biceps Brachii (*)Origin: Coracoid processInsertion: Radial tuberosity

fusiform, parallel, anterior upper arm muscle (2 origins)

flexion of arm at elbow (prime mover)

Brachialis muscle beneath biceps brachii flexion of arm at elbow (synergist)

Brachioradialis lateral muscle between upper and forearm

flexion of arm at elbow (synergist)

Triceps brachii posterior upper arm muscle (three heads)

extension of arm at elbow(antagonist)

Figure 7.14

Muscles of the Forearm

Fig. 9.29- Biceps brachii: flexes forearm, rotates hand; Brachialis, Brachioradialis: flexes forearm; Triceps brachii: extends forearm

Muscles of the Forearm

Fig. 9.29- Supinator: rotates forearm laterally; Pronator teres: rotates forearm medially; Pronator quadratus: rotates forearm medially

Muscles that move Wrist, Hand, Fingers NAME OF MUSCLE LOCATION/

DESCRIPTIONACTION

Flexor carpi Radialis anterior, lateral forearm muscle

flexion of wrist

Flexor carpi Ulnaris anterior, medial forearm muscle

flexion of wrist

Palmaris longus anterior forearm muscle located between two above

flexion of wrist

Extensor digitorum posterior forearm muscle extension of wrist/fingers

Muscles that tense the Abdominal Wall

NAME OF MUSCLE LOCATION/ DESCRIPTION

ACTION

Rectus abdominis (*)Origin: pubic crest/symphysisInsertion: xiphoid process & costal cartilages of 5-7th ribs

strap like muscle from costal cartilages to ilium

tenses abdominal wall

External Oblique superficial/lateral oblique abdominal muscle

tenses abdominal wall

Internal Oblique deep oblique abdominal muscle tenses abdominal wall

Transversus abdominis deep abdominal muscle; runs perpendicular to rectus abdominis

tenses abdominal wall

Muscles that move the Thigh (Femur)

NAME OF MUSCLE LOCATION/ DESCRIPTION

ACTION

Gluteus Maximus (*)Origin: dorsal ilium, sacrum, coccyxInsertion: posterior femur

buttocks, largest muscle in body

extension of hip at thigh(as in walking or climbing stairs)

Gluteus Medius lateral hip muscle abduction of femur

Adductor Longus medial thigh muscle adduction of femur

Muscles that move the Tibia & Fibula

NAME OF MUSCLE LOCATION/ DESCRIPTION ACTION

Rectus femoris anterior thigh; quadriceps extension of leg at knee

Vastus lateralis lateral anterior thigh; quadriceps extension of leg at knee

Vastus Medialis medial anterior thigh; quadriceps extension of leg at knee

Vastus intermedius deep anterior thigh; quadriceps extension of leg at knee

Sartorius (*)Origin: iliac spineInsertion: medial tibia

parallel strap-like muscle; crosses thigh flexion of knee forward

Biceps femoris posterior thigh; hamstring flexion of leg at knee

Semitendinosus posterior thigh; hamstring flexion of leg at knee

Semimembranosus posterior thigh; hamstring flexion of leg at knee

Muscles that move the Foot & Toes

NAME OF MUSCLE LOCATION/ DESCRIPTION

ACTION

Tibialis anterior anterior to tibia dorsiflexion

Peroneus longus lateral to fibula eversion

Gastrocnemius (*)Origin: condyles of femurInsertion: calcaneus

posterior lower leg (i.e. calf muscle); two origins

plantar flexion (prime mover)

Soleus deep to gastrocnemius plantar flexion (synergist)

Note the location of the Calcaneal Tendon Fig 9.40, p324.

Life-Span Changes

• 40’s: First signs of aging in the muscular system• 80’s: Decline in motor neuron activity leads to

muscle atrophy, diminished muscular strength, and slower reflexes

• Exercise: Can help maintain a healthy muscular system (strength training and aerobics)