CHAPTER 7: THE MUSCLE

SYSTEMKaryn BorregoTyler CorreaSabrina Cardona Nicholas Jacinto

THE THREE TYPES OF MUSCLE

• Three types of muscle exist in the human body: smooth, cardiac, and skeletal.• Each fiber is surrounded by a thin layer or areolar connective tissue called

endomysium. • Smooth: located in the walls of hollow internal organs and blood vessels;

moves materials through organs and regulates blood flow in blood vessels; the fibers of this muscle are narrow, tapered root shaped cells; can sustain prolonged contractions and does not fatigue easily; involuntary

CARDIAC MUSCLE• Forms the heart wall.• Fibers are uninucleated , striated, tubular, and branched• Relaxes completely between contractions, which prevents fatigue• Contractions are involuntary

SKELETAL MUSCLE• Fibers are tubular, multinucleated, and striated • Contractions always simulated • Supports the body• Makes bones and body parts move, constant body temperature and

protection; usually found attached to tendons

IN THE LABORATORY • Muscles can be studied in the lab • When a muscle fiber is isolated and provided with ATP, it

contracts completely along its entire length • Result from the all or nothing law: Law that states that muscle

fibers contract maximally or not at all• In contrast, a whole muscle shows a degree of contractions

• Isolated and stimulated electronically • Mechanical force of contraction is recorded as a visual pattern

called myogram

MUSCLE TWITCH • Muscle twitch: A single

contraction that last for only was fraction of a second• Three parts:

1.Latent period: period of time between stimulation and initiation of contraction

2.Contraction period: When the muscle shortens

3.Relaxation period: When the muscle returns to its former length

MYOGRAM• A. Series of twitches• B. Summation

• Increased muscle contraction• C. Tetanic Contraction

• Maximal sustained contraction• No longer shows individual twitches;

rather the twitches are fused and blended completely into a straight line

• Continues until the muscle reaches fatigues: Failure of a muscle fiber to continue to contract due to the exhaustion of ATP

FATIGUE • Gradual weakening that occurs after repetitive use• Reasons why muscles become fatigue

1. ATP is depleted during constants use2. Lactic acid by fermentation3. Muscles run out of neurotransmitter, acetylcholine4. The brain itself signals a person to stop exercising

even if the muscles aren’t fatigued

IN THE BODY• In the body, muscles are innervated to contract by nerves• Each axon stimulates a number of muscle fibers • Motor Unit: A nerve fiber together with all of the muscle fibers it innervates.

• Obeys all-or-none law because the muscles in the motor unit are all stimulated at once; they either contract or do not contract

• Tetanic contractions ordinarily occurs in the body because , as the intensity of nervous stimulation increase, more and more motor units are activated • This is known as recruitment

• While some muscles are contracting, other are relaxing, which is why muscles rarely experience fatigue

• Even when some muscles appear to be resting, they exhibit tone, in which fibers re always contracting. • Muscle tone is important in posture

EXERCISE AND SIZE OF MUSCLES

• Muscles not used or used for weak contraction decrease in size or atrophy. • Atrophy: Occurs when a limb is placed in a cast or when the nerve serving a

muscle is damaged.• Can cause muscle fibers to shorten, leaving body parts in contorted positions • If nerve stimulation is not replaced, muscle fibers are replaced by fat & fibrous

tissue • Forceful muscular activity causes muscles to increase in size as the number of

myofibrils within the muscle fibers• Hypertrophy: occurs only if the muscle contracts to at least 75% of it

maximum tension • Athletes take anabolic steroids, either testosterone or related chemicals, to

promote muscle growth. This causes undesirable side effects

SLOW-TWITCH MUSCLE FIBERS • Muscle fibers metabolize both aerobically and anaerobically but some

muscle fiber utilizes one method more than the other to provide myofibrils with ATP

• Slow-twitch fibers tend to be aerobic and is referred as Type I fibers • Steadier tug and more endurance despite having motor units with a smaller

number of fibers • Helpful in sports such as running, biking, jogging• Tire when fuel supply is gone• Have many mitochondria and are dark in color because they contain

myoglobin, respiratory pigment found in muscles • Resistant to fatigue because they have a substantial reserve of glycogen and

fat

FAST TWITCH MUSCLE FIBERS• Fast-twitch fibers tend to be anaerobic and is referred as Type II fibers

• Designed for strength because their motor units contain many fibers • Provide an explosion of energy and are helpful in sport activities such as

sprinting, wrestling and swinging a golf club• Light in color because they have fewer mitochondria, little to no myoglobin,

and fewer blood vessels • Develop maximum tension more rapidly than slow twitch fibers and their

tension is greater • Vulnerable to an accumulation of lactic acid that causes them to fatigue

quickly

BASIC PRINCIPLES• Muscle contracts at a joint, one bone remains stationary and the other

moves• The origin of a muscle is on the stationary bone and the insertion of a

muscle is on the bone that moves • A body part is moved by a group of muscles working together. A prime

mover is the muscle that does most of the work. • The assisting muscles are the synergist• Muscles contract, the shorten. Therefore they can only pull; they cannot

push. However, muscles have antagonist. Antagonist pairs work opposite one another to bring about movement in opposite directions

NAMING MUSCLES 1. Size 2. Shape3. Direction of fibers 4. Location 5. Attachment 6. Number of attachments 7. Action

SKELETAL MUSCLE GROUPS • The muscles of the body will be grouped according to the region• Try to correlate its name with muscles location and action

MUSCLES OF THE HEAD• Facial expression and mastication (chewing)• Neck allows the head to move

MUSCLES OF FACIAL EXPRESSION

• Located in scalp and face • Insert into and move the skin • These muscles communicate emotions to others

MUSCLES OF FACIAL EXPRESSIONS

• Frontalis: Raises the eyebrows• Skin and muscles around the eye

• Orbicularis oculi: Closes eye or to blink • Skin around the eye

• Orbicularis oris: Closes and protrudes the lips• Skin around the mouth

• Buccinator: Compresses cheek inward• Outer surface of maxilla and mandible

• Zygomaticus: Raises corner of the

mouth • skin and muscle around mouth

MUSCLES OF MASTICATION • Muscles of mastication are used

when we chew and bite • Both Masseters and Temporalis

insert on the mandible, are synergist and are prime movers for elevating the mandible• Masseters: Closes jaw

• Located in the zygomatic arch • Temporalis: Closes Jaw

• Located in the temporal bone

• Fan-shaped muscle

MUSCLES OF THE NECK • Swallowing • Moving the head

SWALLOWING • The tongue (a muscle) & the buccinators squeeze the food back along the roof of the mouth

to the pharynx• Hyoid: important bone that functions in swallowing , does not articulate with another bone

and is attached to the larynx • Suprahyoid Muscles: Lie superior to the Hyoid

• Pulls hyoid forward and upward toward the mandible • Infrahyoid Muscles: Lie inferior to the hyoid

• Moves the hyoid• Moves hyoid and larynx to their original positions

• Epiglottis: Closes the respiratory passages• Small Palatini Muscles: Closes nasal passages • Pharyngeal Constrictor Muscles: Pushes the food into the pharynx; widens the surahyoid

muscle

MUSCLES THAT MOVE THE HEAD TERMS

• Flexion: Movement that closes the angle at a joint • Extension: Movement that increases the angle at a joint • Abduction: Movement away from the midline of the body • Adduction: Movement towards the midline of the body • Rotation: Movement of a part around its own axis

MUSCLES THAT MOVE THE HEAD • Sternocleidomastoid:

Flexes and rotates the head• Located in the sternum and

clavicle • Trapezius: Extends the head

and adducts the scapula • Located in the Occipital bone C7

vertebra, all of thoracic vertebra

MUSCLES OF THE TRUNK: THORACIC WALL

• Primarily involved in breathing 1. External Intercostal: Elevate rib

cage for inspiration during breathing • Located in the superior rib

2. The Diaphragm: Depress rib cage for forced expiration • Located in the inferior rib

3. Internal Intercostal: Tenses abdominal wall; lateral rotation of trunk • Located in the lower eight rib

MUSCLES OF THE TRUNK: ABDOMINAL WALL

• Protect and support organs within the abdominal cavity

1. External: Tenses abdominal wall; lateral rotation of trunk • Located in the lower eight ribs

2. Internal obliques: Tenses abdominal wall; lateral rotation of trunk • Located in the Iliac crest

3. Transverse abdominis: Tenses abdominal wall• Located in the lower six

4. Rectus abdominis: Flexes and rotates the vertebral column• Located in the pubic symphysis

MUSCLES OF THE SHOULDER • The muscles of the shoulder attach the scapula to thorx• Move the scapula • Also attach the humerus to the scapula and move the arm

MUSCLES THAT MOVE THE SCAPULA

• Serratus anterior: Depresses the scapula and pulls it forward; elevates arm above horizontal • Located in the upper nine ribs

MUSCLES THAT MOVE THE ARM• Deltoid: Abducts arm to horizontal

• Located in the upper nine ribs• Pectoralis major: Flexes and adducts

arms • Located in the spine of scapula and

clavicle • Latissimus dorsi: Extends and

adducts arm • Located in the lliac crest

• Rotator cuff: Angular and rotational movements of arms • Located in the scapula

MUSCLES THAT MOVE THE FOREARM

• Biceps brachii: Flexes and supinates the forearm• Located in the scapula

• Triceps brachii: Extends the forearm • Located in the scapula and

proximal humerus • Brachialis: Flexes the forearm• Located in the anterior

humerus

MUSCLES THAT MOVE THE HAND AND FINGERS

• Flexer carpi and extensor carpi: Move wrist and hand • Located in the humerus

• Flexer digitorum and extensor digitorum: Move fingers• Located in the humerus, radius and

ulna

MUSCLES THAT MOVE THE THIGH

• lliposoas: Flexes the thigh • Located in the lumbar

vertebrae • Gluteus maximus: Extends the

thigh • Located in the Posterior ilium

• Gluteus medius: Abducts the thigh• Located in the llium

• Adducts group: Adducts the

thigh • Located in the Pubis

MUSCLES THAT MOVE THE LEG • Quadriceps femoris group:

Extends the legs • Located in the Ilium and femur

• Satoruis: Flexes, abducts and rotates leg laterally • Located in the Iiium

• Hamstring group: Flexes and rotates leg medially and extends thigh • Located in the Ischial tuberosity

MUSCLES THAT MOVE THE ANKLE AND FOOT

• Gastrocnemius: Plantar flexion and eversion of foot • Located in the Condyles of Femur

• Tibialis anterior: Dorsiflexion and inversion of foot • Located in the Condyles of Tibia

• Fibularis group: Plantar flexion and enversion of the foot • Located in the Fibula

• Flexor and extensor digitorum longus: Moves toes • Located in the Tibula

EFFECTS OF AGING• Muscle mass and strength decrease with age. At first, muscle is replaced

by connective tissue, and then eventually fat. Endurance decreases. Degenerate changes take place in the mitochondria.

• Changes in cardiovascular systems begin to occur, which affect muscle function. If elderly people undergo training, muscle mass and strength can increase.

• When exercising, regardless of age, muscle buildup is stimulated. Exercise also improves the cardiovascular system and reduces the risk of diabetus and glycation, excess glucose molecules stick to body proteins so that the proteins no function properly.

• Exercise burns glucose, which prevents muscle deterioration.

HOMEOSTASIS• On page 151, the illustration titled Human Systems Work Together tells how the

muscular system works other systems of the body to maintain homeostasis.• Contractions in the cardiac muscle is what a heart beat is. It creates blood

pressure, the force that sends blood through the arteries and arterioles. The walls of the arteriols. The walls of the arteries and arteriols are smooth muscle.

• Constrictions of arteriol walls is regulated to help maintain blood pressure. Arteriols branch into capillaries where exchange takes place that creates and cleanses tissue fluid. Blood and tissue fluid are the internal environment of the body, and without cardiac and smooth muscle contraction, blood would never reach the capillaries for exchange to take place.

• Blood is retuned to the cardiovascular system within lymphatic vessels. Skeletal muscle contraction presses on the cardiovascular veins and lymphatic vessels, normal blood pressure could not be maintained.

HOMEOSTASIS (CONTINUED)• The contraction of sphincters composed of smooth muscle fibers temporarily prevents the

flow of blood into capillary. This is an important homeostatic mechanism because in times of emergency it is more important, or example, for blood to be directed to the skeletal muscles than to the tissues of the digestive tract.

• Smooth muscle contraction also account for peristalsis. The process that moves food along the digestive tract. Without this action, food would never reach all the organs of the digestive tract where digestion releases nutrients that enter the bloodstream. Smooth muscle contraction assists the voiding of urine, which is necessary for ridding the body metabolic wastes and for regulating the blood volume, salt concentration, and pH of internal fluids.

• Skeletal muscles protect internal organs, and their strength protects joints by stabilizing their movements. Skeletal muscle contraction raises and lowers the rib cage and diaphragm during the active phases of breathing. As we breathe, oxygen enters the blood and is delivered to the tissues, including the muscles, where ATP is produced by skeletal muscle contraction allows the body temperature to remain within the normal range for human beings.

• Finally, skeletal muscle contraction moves bones and allows us to perform those daily activities necessary to our health and benefit. Although it may seem as if movement of our bodies not affect homeostasis, it does so by allowing us to relocate our bodies to keep the external environment within favorable limits for our experiences.