Chapter 8The Muscular

System

I. IntroductionA. There are over 600 skeletal muscles in the body.

B. 40-50% of your body weight is skeletal muscle

C. Muscles, along with the skeleton, determine the form and contour of the body

QUESTION….Two people wear the exact same

size in clothing. One of the two has 15% body fat (meaning they have 85% muscle) and the other person has 29% body fat. Who weighs more?

The person with the larger amount of muscle percentage will weight more. Muscle density is 1.06 g/ml and fat density is (about) 0.9 g/ml. Thus, one liter of muscle would weight 1.06 kg and one liter of fat would weight 0.9 kg. In other words, muscle is about 18% more dense than fat.

D. Skeletal Muscles are organsE. Function of muscles

1. Movement2. Heat production3. Posture

II. How muscles are named

A. Muscles are named using one of more of the following features1. Location (ie:subscapularis)2. Function (adductor muscle)

3. Shape (deltoid)4. Direction of the fibers or

muscle cells – (ie: “rectus” of rectus abdominus means “straight”)

5. Number of heads or divisions (ie: biceps, triceps, quadriceps)

6. Size of the muscle (ie: gluteus maximus, gluteus medius, gluteus minimus)

7. Attachment of musclesOrigin —point of attachment that does not move when muscle contracts

Insertion —point of attachment that moves when muscle contracts

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Location Brachialis Femoris Abdominal Dorsi Capitis

• Arm• Leg• Abdomen• Back• Head

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Function Adductor Abductor Supinator Flexor Extensor

• Adducts• Abducts• Supinates• Flexes• Extends

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Shape Deltoid Linea Trapezius

• Triangle• Line• trapezoid

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Number of Heads Biceps Triceps Quadriceps

• Two• Three• Four

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Direction of Fibers Oblique Rectus Transverse Circular Spiral

• Diagonal• Straight• Transverse• Around• Spiral

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Points of AttachmentExamples: sternocleidomastoid • Sternum

• Clavicle• Mastoid processes of the

temporal bone

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Relative Size Major Maximus Minor Minimus Longus Brevis Latissimus Longissimus Magnus Vastus

• Large• Largest• Small• Smallest• Long• Short• Very wide• Very long• Very large• Vast or huge

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Examples: Flexor carpi radialis Brachioradialis Three headed arm muscle Straight upper leg muscle Flexor pollicus longus

Vast side muscle of upper leg Adductor brevis

Adductor magnus

• Function/insertion/origin• Location/insertion• Triceps brachii• Rectus femoris• Long muscle that flexes the

thumb• Vastus lateralis

• Short muscle that adducts the leg

• Largest muscle that adducts the leg

III. Important Skeletal Muscles

A. Muscles of facial expression

—unique in that at least one point of attachment is to the deep layers of the skin over the face or neck

1. Corrugator supercilii (AKA: frontal muscle) – wrinkles forehead when frowning, and lifts eyebrows in surprise

2. Orbicularis oculi – encircles the eye and closes it

3. Zygomaticus major – draws the corner of the mouth upward (smiling or laughing)

4. Obicularis oris – puckers the mouth and presses the teeth to inside cheek (commonly referred to as the “kissing muscle”)

5. Buccinator – works with the above muscle to produce the kissing motion

B. Muscles of Mastication (chewing)

1. Masseter – closes jaw2. Temporalis – this works with

the above muscle to close the jaw

3. Pterygoids – grates teeth

C. Muscles that move the head

Muscles that move the head —paired muscles on either side of the neck are responsible for head movements 1. Sternocleidomastoid 2. Trapezius 3. Splenius capitis 4. Semispinalis capitis

C. Muscles of the Thorax

1. External intercostals – elevated ribs for inhalation

2. Internal intercostals – depresses ribs for exhalation

3. Diaphragm – enlarges thorax causing inspiration. Singers train this muscle so the viscera is pushing down which gives the lungs more room to expand. The can hold notes longer and have to inhale less often.

D. Muscles of the Abdominal Wall

1. External obliques – outermost layer

2. Internal obliques – middle layer3. Transversus abdominus –

innermost layer

4. Rectus abdominus – midline of the abdomen. “6 pack, washboard stomach” Muscles used to “push” in childbirth.

Aponeurosis –layers of flat, broad tendons

E. Muscles of the Back

Muscles of the back —bend or stabilize the back

Allow for rotation

2 “cap” muscles

3 muscles that move the scapula

4 muscles onthe scapula

2 serratus muscles

1 errector muscle

2 gluteal muscles

E. Muscles of the Upper Limb

1. Deltoid2. Rotator cuff muscles (SITS

muscles): a. Supraspinatus b. Infraspinatus c. Teres minor d. Subscapularis

3. Pectoralis major4. Opponens pollicus – thumb

muscles which allow thumb to be drawn across the palm

5. Biceps brachii6. Triceps brachii

F. Muscles of the Lower Limb

1. Gluteal group – posterior buttocksa. Gluteus maximusb. Gluteus mediusc. Gluteus minimus

2. Quadriceps group – anterior thigh3. Hamstring group – posterior thigh4. Gastrocnemius – calf muscles5. Soleus – underneath gastrocnemius

IV. Other Muscles“Involuntary

Muscles”

A. Cardiac 1. The heart 2. It is extremely striated with a series of

intercalated discs…..these are unique dark bands where the plasma membrane of other cardiac fibers come in contact with each other. The nature of the fibers helps the heart contract as a unit.

B. Smooth 1. These form the muscles of the hollow

organs (such as the intestines) 2. The cells of smooth muscles are tapered at

each end and have a single nucleus. They have no striations which gives them the appearance of being “smooth”.

V. Muscle Fiber Types

Each muscle contains both types of muscle fibers in

varying proportions

A. Slow (red) fibers

1. These contain large amounts of myoglobin (oxygen storage molecules), which give it its red color (red meat vs. white meat in animals).

2. “Slow” means they are slow to fatigue

3. Postural muscles that hold up a skeleton for prolonged periods have greater amounts of slow red fibers.

4. Studies show that marathon runners have a greater amount of red fibers than the general population

B. Fast (white) fibers

1. Muscle fibers that contain little myoglobin (hence the word white)

2. These muscles contract rapidly 3. But the price of rapid contraction is

rapid depletion of ATP. 4. Sprinters have a greater amount of white

fibers than the general population

VI. Muscle Contraction

A. Requires Energy

B. Comes from catabolism

Requires these two ingredients 1. Glucose (from food) – quick burst

fuel needed for muscle contraction 2. Oxygen

a. Aerobic respiration – produces maximum amount of energy using oxygen

b. Anaerobic respiration – the process that occurs when oxygen level is low. Lactic acid builds up in the muscle tissue during exercise and causes a burning sensation…..then remains in the muscle post-exercise and makes muscles sore.

VII. Muscle Fatigue

Loss of strength or endurance

A. Physiological fatigue1. Caused by a relative lack of

ATP due to: a. Depletion of oxygen or

glucose in the muscle fibers b. Inability to regenerate ATP

quick enough

c. Depletion of glycogen d. High levels of lactic acid e. Physiological fatigue rarely

happens – and if it does, the body will just “shut” itself off

B. Psychological fatigue

1. This is what produces the “exhausted” feeling

2. This will make you want to stop muscle activity long before the muscle has reached fatigue

C. Mind over matter

1. In physiological fatigue, we cannot contract our muscles any longer.

2. In psychological fatigue, we simply will not contract our muscles because we feel tired.

VIII. Problems Frequently

Associated with Muscles

A. Shoulder Joint Stability

1. The head of your humerus is twice the size of the scapula cavity that it rests in, which makes for great mobility (that it why it is the most mobile joint in the body)

2. This is also the reason it so easily dislocates (it is very unstable)

3. The SITS muscles help to strengthen this area

4. The muscles and tendons in this area fuse and are called the “rotator cuff”

B. Repetitive motions

1. Piano playing, meat cutting, typing (secretaries)

2. This causes inflammation of the tendon sheath that surrounds the tendons (like in the wrist)

3. If the inflammation causes compression on the median nerve in the tunnel of the wrist, carpal tunnel syndrome may result.

4. This produces tingling, muscle weakness, and pain in the radial side of the hand.

IX. Myopathies

Problems within the muscles

A. Muscular Distrophy1. This is an X linked genetic

disorder…..so it effects boys more than girls

2. The first sign appears at age 3 with leg weakness

3. By age 5-10, it is severe and usually fatal by the age of 21 die to heart weakness and respiratory muscles (Jerry’s Kids)

B. Hernias1. Weakness in the abdominal

muscle so that abdominal organ protrudes

2. If it becomes strangulated then the mass cannot manipulate itself back and blood flow is stopped to that area.

3. At worst, gangrene can occur

4. Usually requires immediate surgical intervention

X. Muscle Terms

A. Intramuscular injections

1. Shots given inside the muscle2. If less than 2 ml – given in

deltoid3. If greater than 2 ml – given in

gluteus maximus

B. Atrophy1. Shrinkage of muscle mass2. Usually caused by disease

or casting a bone break

C. Hypertrophy1. Increase in muscle size

D. Peristalsis1. The waves of action of

smooth muscle that cause the movement of food down the alimentary canal

E. Rigor mortis1. Latin for “stiffness of death”2. Skeletal muscles often stiffen

shortly after death3. This is because at the time of

death the postural muscle fibers are often in mid contraction.

4. But when death occurs, the muscles cease to be stimulated so they become stuck in the contracted position.

5. Basically muscle fibers run out of ATP required to turn off the muscle contraction and relax it

F. Treppe Staircase Phenomenon

1. Muscles contract more forcefully after they have contracted a few times (which is the reason you “warm up” before activity)

2. It works on the principle of increasing the temperature of the muscle to get the maximum amount of work out of it

G. Muscle Tone1. Continuous low level sustained

contraction by skeletal muscles (ie:posture)

2. Less muscle tone is called flaccid, more muscle tone than normal is known as spastic (disorder: movie – Awakenings)

H. Cramps1. Painful muscle spasms2. Can be symptoms of ion or

water imbalance (ie: leg cramps)

I. Convulsions1. Abnormal uncoordinated

muscular contractions2. May result from seizure

J. Fibrillation1. Flutter of muscle but no

movement2. Happens in the heart

muscle during “heart attack”

K. Myopathies1. Muscle disorders

L. Myoalgia1. Muscle pain

M. Muscle strain1. Overstretching or tearing

of muscle fibers

N. Muscle sprain1. Muscle strain that occurs in

the area of a joint or a ligament2. Takes weeks to heal because

soft tissue heals slower that hard tissue (like bone)

Ankle Sprain

O. Myositis1. Muscle inflammation2. Subside within a few hours or

days3. Could be caused by bacteria

in the system (like the flu) – that is why you are “sore” when you are sick with the flu

P. Myositis + tendon inflammation

AKA: Charley horse