Human Anatomy: Unit 2 Notes - Temecula Valley Unified ...



Human Anatomy A: Unit 5 Notes Name:

Ch. 8: The Muscular System Per. #

See the Video (on website) Human Body: Strength. Pushing the Limits:

Motion results from the contraction and relaxation of muscle. Approximately 40-50% of the body weight is muscle…usually a little more for males.

Types of Muscle Tissue

1. Skeletal: Attached mostly to the bones of the skeleton, it is striated or striped (has alternating dark and light bands), under voluntary control and has many nuclei.

2. Cardiac: Forms the bulk of the heart wall, it is also striated with a criss- cross pattern, involuntary, it has a single central oval nucleus

3. Smooth: muscle of internal organs and structures such as the organs of the digestive tract and blood vessels… lacks striations.

Smooth muscle fibers are smaller than skeletal muscle fibers. They are thick in the middle and taper at each end. There is a single, centrally located oval nucleus.

Functions of Muscle Tissue:

1. Motion

2. Movement of body substances: Blood, food, bile, urine (this regulates organ volume too.)

3. Stabilizing body positions: Postural muscle display sustained contraction

to keep us in stable positions.

4. Heat production: Muscle contractions generate as much as 85% of all body heat.

Characteristics of Muscle Tissue:

1. Excitability: The ability to receive and respond to stimuli

2. Contractility: The ability to shorten and thicken

3. Extensibility: The ability to stretch and extend

4. Elasticity: The ability to return to original shape

Skeletal Muscle Tissue

Connective Tissue Components

“Fascia” is a sheet or broad band of connective tissue beneath the skin and around the muscles and organs (2 types)

1. “Superficial Fascia” is the subcutaneous layer.

2. “Deep Fascia” holds muscles together, separating them into groups.

Underneath the deep fascia, skeletal muscles are covered with:

Epimysium: wraps the entire muscle (See a color diagram here!)

Perimysium: wraps the bundles of muscle fibers (“fascicles”)

Endomysium: wraps each individual muscle fiber (cell)

[pic]

Epimysium, perimysium, and endomysium extend beyond the muscle as a “tendon”… a cord of connective tissue that attaches the muscle to the bone.

Certain tendons, like those in the wrist and ankle are enclosed in tubes called “tendon sheaths” for protection and to allow it to slide more easily. An “aponeurosis” is a broad flat tendon that looks like a sheet of white tissue.

Histology: Fig. 8.2

Skeletal muscle is composed of long cylindrical cells called muscle fibers (myofibers). The membrane of a fiber is called the “sarcolemma” and the cytoplasm is called “sarcoplasm.”

Each muscle fiber has many nuclei, mitochondria and “myoglobin,” a

red pigment that holds O2 until needed.

Within each fibers are cylindrical structures called “myofibrils”

Myofibrils contain even smaller structures called “thin myofilaments” (made of the protein actin) and “thick myofilaments” (made of the protein myosin).

Myofilaments are arranged in compartments called “sarcomeres.”

Within one sarcomere, the area composed of thick myofilaments is called the “A band.” (The ends of the A band are darker because of overlapping thin myofilaments.)

The “H zone” is the center area of the band that contains only thick myofilaments. The “I band” is the area where there are only thin myofilaments. Show IP Module “Anatomy Review: Skeletal Muscles”

[pic]

The Sliding Filament Mechanism

During muscle contraction, thin myofilaments slide inward toward the center of the sarcomere. The sarcomere shortens, but the filaments themselves do not shorten.

Extending off the thick myofilaments are structures called “myosin heads” or “cross bridges.” (See microscopic view of skeletal muscles)

It is thought that the myosin heads pull on the thin myofilaments sliding them inward during muscle contraction. The Z discs are drawn toward each other and the sarcomere shortens.

[pic]

see sliding filaments here:

The Neuromuscular Junction

For a skeletal muscle fiber to contract, it must be stimulated by a nerve cell called a “motor neuron.”

A single motor neuron connects to many muscle fibers. A “motor unit” is composed of a motor neuron and all the muscle fibers it stimulates.

Muscles that control precise movements (ex. Eye) have fewer that 10 muscle fibers in each motor unit, but many motor units. Gross body movements (ex: arms, legs) have as many as 2000 muscle fibers in each motor unit, but fewer motor units. Show IP Module “Contraction of Motor Units”

Stimulation of one motor neuron contracts all the fibers in that motor unit simultaneously!

“Recruitment” refers to the number of motor units activated by the brain at any one time to bring about a desired action.

After contraction, a muscle fiber relaxes briefly (the refractory period) and cannot contract. Other motor units relieve one another so smoothly that a contraction can be sustained.

The all-or-none principle:

(see the video “Know Your Muscle, Grow your Muscle)

The “threshold stimulus” is the weakest stimulus from a neuron that causes muscle contraction.

According to the all-or-none principle, if a stimulus reaches the threshold or greater, individual muscle fibers will contract to their fullest extent. There is no partial contraction of a single muscle fiber!

However, the strength of contraction is influenced by the cell’s lack of nutrients or oxygen.

Remember, the muscle as a whole can contract to a greater or lesser degree depending upon the number of the motor units recruited.

Oxygen Debt:

During exercise, blood vessels dilate to increase blood flow to the muscles, bringing oxygen and nutrients and ridding wastes.

If muscle exertion is great, oxygen cannot be supplied fast enough to produce all the ATP needed. Additional ATP is produced anaerobically, with the by-product being lactic acid.

“Oxygen debt” refers to the additional oxygen that must be taken into the body to restore all systems back to their normal state. Oxygen debt is usually paid back by heavy, labored breathing.

“Muscle fatigue” (related to oxygen debt)…the inability for of a muscle to maintain its strength.

Muscle Phenomena:

“Treppe”… a condition in which a skeletal muscle contracts more forcefully to the same stimulus after it has contracted several times. (Time is allowed between stimuli for relaxation)

“Isotonic Contraction”…is where the muscle shortens while under tension to produce movement.

“Isometric Contraction”…the muscle does not shorten, but the tension on the muscle is increasing.

“Muscle tone”…sustained contraction of portions of a skeletal muscle. (tone is essential for maintaining posture)

“Muscular atrophy”…The wasting away of muscles; individual muscle fibers decrease in size due to a progressive loss of myofibrils.

Raw world Bench Press record is 722 lbs. See here:

The “assisted” record with a bench press shirt is 1102 pounds, see here:

“Muscle hypertrophy”…growth in size of a muscle; individual muscle fibers become bigger with more myofibril and nutrients.

How skeletal muscles produce movement:

Skeletal muscles produce movements by pulling on tendons which in turn pull on bones. Most muscles cross at least one joint and are attached to the articulating bones that form the joint

“Point of Origin”… the point of attachment of a muscle tendon to the stationary bone.

“Point of Insertion”… The point of attachment of the muscle tendon to the moveable bone.

Most movements require several skeletal muscles acting in groups. Also, most skeletal muscles are arranged in opposing pairs.

Ex: Flexor-Extensor, abductor-adductor

The muscle that that causes a desired action is called the “agonist” or “prime mover.” The opposite muscle, the antagonist, must relax for the prime mover to work.

Here is a great website that lists all the major muscle groups and exercises to build that muscle(s):

Naming Skeletal Muscles

The names of the nearly 700 skeletal muscles are based on specific characteristics:

1. Direction of the muscle fibers may indicate the muscle name:

➢ Rectus: fibers run parallel to body midline

➢ Transverse: fibers perpendicular to midline

➢ Oblique: fibers are diagonal to the midline

2. Location May determine the name of the muscle

3. Size: Maximus = large, Minimus = small, longus = long, brevis = short

4. Number of origins: biceps have 2 origins, triceps have 3 origins

5. Shape: deltoid = triangular, rhomboid = diamond, serratus = sawtooth

6. Origin and/or insertion: Ex. Sternocleidomastoid originates on the sternum and clavicle and inserts on the mastoid.

7. Action:

Flexor: Decreases the angle at a joint

Extensor: Increases the angle at the joint

Abductor: Moves a bone away from the midline

Adductor: Moves a bone closer to the midline

Supinator: Turns the palm upward

Pronator: Turns the palm downward

The major muscles that you need to know for the test are on pages 184-185. Here is a similar diagram.

Crash Course Muscular System Review here: 12 min.

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To see all of the major muscle actions, click here:



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