Ch. 6: The Muscular System

Chapter Overview
Describe similarities and differences in the structure and function of the three types of muscle tissue, and indicate where they are found in the body
Define muscular system
Define and explain the role of the following: endomysium, perimysium, epimysium, tendon, and aponeurosis
What is the function of the Muscular System?
The muscular system provides for movement of the body and its parts, maintains posture, generates heat, and stabilizes joints.
Name the three types of muscle tissue
Skeletal, cardiac, and smooth
What are muscle fibers?
The types of muscle (i.e. skeletal and smooth muscle) cells that are elongated
What are some characteristics of muscles?
1. Muscle cells are elongated
2. Contraction of muscles is due to the movement of microfilaments
3. All muscles share some terminology: myo-, mys- ("muscle"), sarco- ("flesh")

Ex: sarcoplasm - in muscle cells the cytoplasm is called thiss
What are some skeletal muscle characteristics?
1. Most attached by tendons to bones
2. Cells are multinucleate
3. They have visible banding (striated)
4. They are subject to conscious control
5. Cells are surrounded and bundled by connective tissue
What is endomysium?
These are connective tissue wrappings of skeletal muscle around single muscle fiber
What is perimysium?
These are connective tissue wrappings of skeletal muscle around a fascicle (bundle) of fiber
What is epimysium?
These are connective tissue wrappings of skeletal muscle that covers the entire skeletal muscle
What is fascia?
These are connective tissue wrappings of skeletal muscle on the outside of the epimysium
The epimysium blends into either of the these two connective tissue attachment
tendons or aponeuroses
What is tendon?
This is a cordlike structure cartilages or connective tissue coverings
What is aponeuroses?
This is a sheet-like structure cartilages or connective tissue coverings
What are some smooth muscle characteristics?
1. has no striations
2. they are spindle-shaped cells
3. they are single nucleus
4. They are involuntary - no conscious control
5. They are found mainly in the walls of hollow organs
What are some cardiac muscle characteristics?
1. has striations
2. usually has a single nucleus
3. they are joined to another muscle cell at an intercalated disc
4. They are involuntary
5. These are found only in the heart
What are some functions of muscles?
1. Produce movement
2. Maintain posture
3. Stabilize joints
4. Generate heat
Describe the microscopic structure of skeletal muscle and explain the role of actin- and myosin-containing myofilaments
What is a multinucleate cell?
These are cells that have multiple nucleus. This is true for the skeletal muscle cells
What is called the sarcolemma?
This is the specialized plasma membrane where the nuclei can be seen just beneath it
What is the sarcoplasmic reticulum and its major role?
These are muscle fiber organelle which are specialized smooth endoplasmic reticulum. The major role (a part of) of this elaborate system is to store calcium and to release it on demand when the muscle fiber is stimulated to contract
What is the myofibril?
These are long ribbonlike organelles. They are bundles of myofilaments. They are aligned to give distinct bands.

I-band and A band (These bands give the muscle cell as a whole a striped appearance)
What is a myofilaments?
These are threadlike proteins and have two types: The thick filaments and thin filaments
What is an I band?
This is the light band
What is an A band?
This is the dark band
What is Sarcomere?
These are myofibrils that are chains of tiny contractile units of a muscle fiber
What is the organization of the sarcomere?
They have the thick filaments and the thin filaments
What are the thick filaments and their properties?
These are myosin filaments and is composed of the protein, myosin, and has ATPase enzymes
What are cross bridges?
These projections, or myosin heads, that are found on the thick filaments
What are the thin filaments and their properties?
These are actin filaments and is composed of the protein actin
Describe how an action potential is initiated in a muscle cell
What are some special functional properties that enable the muscle cells to perform their duties?
Excitability, or responsiveness; contractility; extensibility; elasticity
What is irritability?
The ability to receive and respond to a stimuls
What is the motor unit?
One neuron and all the skeletal muscle cells it stimulates is considered this
For the nerve of the skeletal muscles to contract, what must be done?
The skeletal muscles must be stimulated
What is a neurotransmitter?
This is a chemical that fills the vesicles contained in the neuromuscular junctions. This is the transmission of nerve impulse to muscle
What is acetylcholine or ACh?
This is the specific neurotransmitter that stimulates skeletal muscle cells
What is the sliding filament theory of muscle contraction?
1. Activation by the nerves causes myosis heads (cross bridges) to attach to binding sites on the thin filaments
2. Myosin heads then bind to the next site of the thin filament
3. This continued action causes a sliding of the myosin along the actin
4. The result is that the muscle is shortened (contracted)
In skeletal muscles, this law of muscle physiology applies to the muscle cell, not to the whole muscle
This law is the "all-or-non" law. This states that a muscle cell will contract to its fullest extent when it is stimulated adequately; it never partially contracts
What are graded responses and what two ways can they be produced??
These are different degrees of shortening.

The graded muscle contractions can be produced generally in two ways:
1. By changing frequency of muscle stimulation
2. By changing the number of muscle cells being stimulated at one time
What are some types of graded responses?
Twitch, tetanus, unfused tetanus, fused (completed) tetanus
What is a muscle twitch?
This is a single, brief contraction and not a normal muscle function
What is tetanus (tet'ah-nus)?
This is the summing of contractions. One contraction is immediately followed by another. The muscle does not completely return to a restin gstate
What is fused, or complete, tetanus?
This is when a muscle is stimulated so rapidly that no evidence of relaxation is seen and the contractions are smooth and sustained
What is unfused, or incomplete, tetanus?
Some relaxation occurs between contractions. The results are summed
What are muscle response to strong stimuli?
1. Muscle force depends upon the number of fibers stimulated
2. More fibers contracting results in greater muscle tension
3. Muscles can continue to contract unless they run out of energy
Describe three ways in which ATP is regenerated during muscle activity
Working muscles use these three pathways for ATP regeneration
1. Direct phosphorylation of ADP by creatine phosphate
2. Aerobic respiration
3. Anaerobic glycolysis
What is direct phosphorylation?
1. Muscle cells contain creatine phosphate (CP)
2. CP transfers energy to ADP, to regenerate ATP
3. CP supplies are exhausted in about 20 seconds
What is aerobic respiration?
1. Series of metabolic pathways that occur in the mitochondria
2. Glucose is broken down to carbon dioxide and water, releasing energy
What is anaerobic glycolysis?
1. Reaction that breaks down glucose without oxygen
2. Glucose is broken down to pyruvic acid to produce some ATP
3. Pyruvic acid is converted to lactic acid
4. Lactic acid produces muscle fatigue
Define oxygen deficit and muscle fatigue, and list possible causes of muscle fatigue
What is muscle fatigue?
This is when a muscle is unable to contract even through it is still being stimulated
What is the common reason fatigue is oxygen debt?
1. Oxygen must be "repaid" to tissue to remove oxygen debt
2. Oxygen is required to get rid of tissue to remove oxygen debt
What is oxygen deficit?
This is when oxygen is not taken in fast enough to keep the muscles supplied with all oxygen they need when they are working vigorously. Muscle fatigue is believed to result from this deficit
What causes the muscle to contract less?
The increasing acidity from lactic acid and lack of ATP
What are the types of muscle contractions?
Isotonic and Isometric contractions
What are Isotonic contractions?
1. Myofilaments are able to slide past each other during contractions
2. The muscle shortens

Ex: Bending the knee, rotating the arms, and smiling
What are Isometric contractions?
1. Tension in the muscled increases
2. The muscle is unable to shorten

Ex: Muscles are contracting isometrically when you try to life a 400 lb dresser alone. When you straghten a bent elbow, the triceps muscle is contracting isotonically. But when youpus against a wall with bent elbows, the wall doesn't move, and the triceps muscles, which cannot shorted to straighten the elbows, are contracting isometrically
What is muscle tone?
1. Some fibers are contracted even in a relaxed muscle
2. Different fibers contract at different times to provide muscle tone
3. The process of stimulating various fibers is under involuntary control
Describe the effects of aerobic and resistance exercise on skeletal muscles and other body organs
What are the results of increased muscle use?
1. Increase in muscle size
2. Increase in muscle strength
3. Increase in muscle efficiency
4. Muscle become more fatigue resistant
Define origin, insertion, prime mover, antagonist, synergist, and fixator as they relate to muscles
Demonstrate or identify the different types of body movements
Name the five golden rules of skeletal muscle activity
1. With a few exceptions, all skeletal muscles cross at least one joint
2. Typically, the bulk of a skeletal muscle lies proximal to the joint crossed
3. All skeletal muscles have at least two attachments: the origin and the insertion
4. Skeletal muscles can only pull; they never push
5. During contraction, a skeletal muscle insertion moves toward the origin
How is movement attained?
This is attained due to a muscle moving an attached bone
Muscles are attached to at least two points
Origin and insertion
What is the origin point?
This is attachment to a moveable bone
What is the insertion point?
The attachment to an immovable bone
What are some general types of body movements?
Flexion, extension, rotation, abduction, adduction, circumduction
What is flexion and give an example?
This is a movement, generally in the sagittal plane, that decreases the angle of the joint and brings two bones closer together. This is typical of hinge joints, but it is also common at ball-and-socket joints

Ex: bending the knee or elbow or bending forward at the hip
What is extension and give an example?
This is opposite of flexion, so it is a movement that increases the angle, or the distance, between two bones or parts of the body

Ex: straightening the knee or elbow
What is rotation and give an example?
This is movement of a bone around its longitudinal axis. Rotation is a common movement of ball-and-socket joints and describes the movement of teh atlas around the dens of the axis

Ex: Shaking your head "no"
What is abduction and give an example?
This is moving a limb away (generally on the frontal plane) from the midline, or median plane, of the body

Ex: fanning movement of the fingers or toes when they are spread apart
What is adduction and give an example?
opposite of abduction

Ex: The movement of a limb toward the body midline
What is circumduction and give an example?
This is a combination of flexion, extension, abduction, and adduction commonly seen in ball-and-socket joints such as the shoulder

Ex: The proximal end of the limb is stationary, and its distal end moves in a circle
What are some special body movements?
Dorsiflexion, plantar flexion, inversion, eversion, supination, pronation, opposition
What is Dorsiflexion and plantar flexion?
Up and down movements of the foot at the ankle
What is dorsiflexion?
This is the lifting the foot so that its superior surface approaches the shin

Ex: Standing on your heels
What is plantar flexion?
This is depressing the foot

Ex: Pointing your food (pointing the toes)
What is inversion and eversion?
To invert the foot, turn the sole medially
To evert the foot, turn the sole laterally
What is supination and pronation?
Supination is turning backwards while pronation is turning forward

Ex: Supination - drinking a cup of soup
Ex: Pronation - turning the palms so that it faces posteriorly
What is opposition?
The saddle joint between metacarpal 1 and the carplas allows opposition of the thumb

This is the action by which you move the thumb to touch the tips of the other fingers on the same hands
What are the roles of muscles?
1. Prime mover
2. Antagonist
3. Synergist
4. Fixator
What is a prime mover?
Muscle with the major responsibility for a certain movements

Ex: biceps and arms are prime mover of elbow flexion
What is an antagotist?
Muscles that oppose or reverses a prime mover

Ex: biceps of the arm is antagonized by triceps (a prime mover of elbow of extension)
What is synergist?
Muscles that aids a prime mover in a movement and helps prevent rotation

Ex: When making a fist, the synergist muscles prevent the wrist from bending. The muscles stabilize and allow the prime mover to act on the finger joints
What is fixator?
Stabilizes the origin of a prime mover

Ex: They hold the bone still
List some criteria used in naming muscles
Muscles are named on the basis of these several criteria, each of which focuses on a particular structural or functional characteristic
1. Direction of the muscle fibers
2. Relative size of the muscles
3. Location of the muscles
4. Number of origins
5. Location of the muscle's origin and insertion
6. Shape of the muscle
7. Action of the muscle
Name some examples of muscle names that are associated with when the direction of the muscle fiber is known
Rectus (straight); Oblique (at a slant)
Name some examples of muscle names that are associated with the relative size of the muscle
Maximus (largest); Minimus (smallest); and Longus (long)
Name some examples of muscle names that are associated with the location of the muscle
Temporalis and Frontalis Muscles overlie the temporal and frontal bones of the skull, respectively
Name some examples of muscle names that are associated with the number of origins
Biceps (two); Triceps (three); quadriceps (four)
Name some examples of muscle names that are associated with when the location of the muscle's origin and insertion is known
Sternocleidomastoid muscle

Origin on the seternum (Sterno) and clavicle (cleido) and inserts on the mastoid process of the temporal bone
Name some examples of muscle names that are associated with the shape of the muscle
Deltoid (means "triangular")
Name some examples of muscle names that are associated with the action of the muscle
Flexor, extensor, adductor.

Adductor muscles of the thigh all bring about its adduction, and the extensor muscles of the wrist all extend the wrist