A&P Structure and Function of Muscles

The main functions of Muscle is:

Movement

Heat Production

Posture

Joint Stabilization

3 types of muscle:

Skeletal: Voluntary Striated Muscle

Cardiac: Involuntary Striated Muscle

Smooth Muscle: Involuntary Unstriated Muscle

40-50% of body weight is:

Skeletal muscles

Muscles, along with the skeleton determines the:

form and contour of the body.

Skeletal muscles vary considerably in:

size, shape, and fiber arrangement

Examples of shapes of the muscles:

broad, narrow, long, tapering, short, etc.

Origin:

Point of attachment that does not move when the muscle contracts

Insertion:

Point of attachment that moves when the muscle contracts.

Basic Structures of a muscle organ:

Endomysium

Fascicles

Perimysium

Epimysium

Aponeurosis

Fascia

Muscle Fiber is the same as a:

Muscle Cell

Endomysium:

Fine connective tissue that covers muscle fibers

Fascicles:

Group of muscle fibers

Perimysium:

Thick connective tissue that covers fascicles.

Epimysium:

Coarse sheath that covers entire muscle.

Aponeurosis:

Broad, flat sheet of connective tissue.

Fascia:

Fibrous connective tissue surrounding muscle and outside the epimysium and tendon.

Epimysium, Perimysium, & Endomysium may:

Join with fibrous tissue that extends from the muscle as a tendon.

Isotonic Contraction:

Contraction which the tone or tension within muscle remains the SAME as the length of the muscle changes.

Types of Isotonic Contraction:

Concentric & Eccentric

Concentric:

Muscle shortens as it contracts; lifting a cup or pushing a door.

Eccentric:

Muscle lengthens while contracting; setting objects down, walking, or running.

Isotonic means:

Same tension

All energy of contraction is used to:

Pull on thin myofilaments and thereby change the length of a fibers sarcomeres.

Isometric Contraction:

Contraction in which muscle length remains the same while muscle tension increases.

Isometric means:

Same length

Isometric contraction is important to maintain:

Upright posture & when muscles act as fixators.

Most body movements occur as a result of both types of:

Contractions.

Prime Mover:

A muscle that directly performs a specific movement.

Agonists:

Any “mover” muscle that directly performs a movement, including prime mover.

Antagonist:

Muscle that, when contracting, directly oppose prime movers, relax while the prime mover is contracting to produce movement; provide precision and control during contraction of prime movers.

Synergist:

Muscles that contract at the same time as the prime movers; facilitate prime mover actions to produce a more efficient movement.

Fixator Muscles:

Joint stabilizers through isometric contraction (type of synergist)

A particular muscle can be any of the above under:

differing conditions.

Motor Unit:

Motor neuron plus the muscle fibers to which it attaches.

The smaller the number of fibers in motor unit:

The more precise the movements available.

The larger the number of fibers in a motor unit:

The more powerful the contraction available.

Characteristics of Skeletal Muscles Cells include:

Excitability

Contractility

Extensibility

Excitability:

Ability to be stimulated by nervous & endocrine systems.

Contractility:

Ability to contract, or shorten, and produce body movement.

Extensibility:

Ability to extend, stretch, thereby allowing muscles to return to resting length.

Muscle cells are called:

Fibers because of their threadlike shape.

Sarcolemma:

Plasma membrane of muscle fibers.

Sarcoplasmic Reticulum: SR

Opens to allow calcium to enter for muscle contraction.

T-tubules:

Network of tubules & sacs found within muscle fibers that let signals move deeper into cell.

Membrane of the SR continually pumps:

Calcium ions from the sarcoplasm and stores the ions within the sacs or later release.

What is equivalent to cytoplasm in other cells.

Sarcoplasm

Muscle fibers contain many:

Mitochondria & several Nuclei

Myofibrils:

Numerous fine fibers packed close together in sarcoplasm that extend lengthwise along a skeletal muscle fiber.

Sarcomere:

Segment of myofibril between two successive Z disks; Contractile unit of Muscle Fibers.

Myofibril consist of many:

Sarcomeres

Striated Muscle:

Contain Dark (A bands) and Light Stripes (I bands)

A bands:

AKA dark stripes; Light H zone that runs across the midsection of each dark A band.

I bands:

AKA light stripes; Dark Z disk extends across the center of each light I band.

T-tubules:

Transverse tubules formed by inward extensions of the sarcolemma that conduct electrical impulses deep into the muscle cell. Membrane has ion pumps that continually transport Ca++ ions inward from sarcoplasm.

Triad:

Triplet of T-tubules; t-tubule that is sandwiched between two sacs of SR.

What allows an electrical impulse traveling along T-Tubule to stimulate membranes of adjacent sacs of SR?

Triads.

Myofilaments contain:

Thick and Thin myofilaments.

What are the four protein molecules that make up myofilaments:

Myosins

Actin

Tropomyosin

Troponin

Myosin:

Thick filament

Actin:

Globular protein that forms two fibrous strands twisted around each other to form the bulk of thin filament.

Tropomyosin:

Protein that blocks the active sites on actin molecules.

Actin or Thin Filaments attach to:

Both z disks (Z-lines) of a sarcomere and extend partway toward the center.

Thick myosin don't:

attach to Z disks.

Sliding Filament Model:

where active actin sites are exposed, myosin binds to them, myosin heads bend & pull thin filament past them, each head releases and binds to the next active site & pulls again, then myofibril shortens.

Relaxation of Muscle Contraction:

Ca++ is released, the SR begins actively pumping it back into sacs, Ca++ removed from the troponin molecules, thereby shutting down the contraction

Energy required for muscular contraction is obtained from:

ATP after it breaks into ADP and phosphate.

ATP only provides how much time for muscle contraction?

Few seconds

Phosphorylation:

Muscles recharge ADP by adding phosphate back

What is a “quick charger” that buys a few seconds of ATP energy?

Creatine

What energy source do you need for a contraction that will last more than a few seconds?

Glucose

What enters the aerobic pathway called oxidative phosphorylation to create ATP?

Pyruvate

What binds to the myosin head and transfers its energy there to perform the work of pulling the thing filament during contraction?

ATP

What is required for Catabolism by muscle fibers?

Glucose & Oxygen.

Myoglobin:

Oxygen storage molecule with a red color.

What is the stored in the form of Glucose?

Glycogen

Aerobic Pathway of Respiration:

Produces the maximal amount of energy available from each glucose molecule.

When does Aerobic pathway to respiration occur?

When adequate O2 is available from blood, but is slower than anaerobic respiration, thus it supplied energy for long term.

Anaerobic Pathway for Respiration:

Produces minimal amount of ATP, very rapid, that provides energy during first minutes of maximal exercise.

Anaerobic Pathway can produce what during endurance activity when O2 is depleted?

ATP

When Anaerobic process supplement Aerobic, pyruvate is converted into what?

Lactate

Dissolved form of lactic acid is what?

Lactate

Oxygen Debt:

Lack of oxygen in some tissue.

What causes the production of excessive lactic acid?

Oxygen debt

Twitch Contraction:

A quick jerk of muscle produced as a result of a single, brief threshold stimulus.

Twitch Contraction has 3 phases which are the:

Latent Phase

Contraction Phase

Relaxation Phase

Latent Phase:

Nerves impulse travels to the SR to trigger release of Ca++.

Contraction Phase:

Ca++ binds to troponin & sliding of filaments occurs.

Relaxation phase:

Sliding of filaments cease.

Treppe is also known as:

The staircase phenomenon.

Gradual, steplike increase in the strength of contraction that is seen in a series of twitch contractions that occur 1 second apart is what?

Treppe

Tetanus:

Smooth, sustained contractions

Multiple Wave Summation:

Multiple twitch waves added together to sustain muscle tension for a longer time.

Incomplete Tetanus:

Very short periods of relaxation between peaks of tension

Complete Tetanus:

Twitch waves fuse into a single, sustained peak.

The availability of Ca++ determines whether:

A muscle will contract.

If Ca++ is continuously available, than what will be sustained:

Contraction

Graded Strength Principle:

Skeletal Muscles contract with varying degrees of strength at different times.

The greater the number of fibers contracting:

The stronger contraction.

Length Tension Relation: Maximal Strength that a muscle can:

Develop bears a direct relation to the initial length of its fibers.

Length Tension Relation: Shortened muscle’s sarcomere are:

Compressed so the muscle can’t develop much tension.