Muscular System

-Produce movement

-Maintain posture

-Stabilize joints

-Generate heat

-Striated

-Uninucleate

-Joined to another muscle cell at an intercalated disc

-Involuntary

-Found only in the heart

-No striations

-Spindle-shaped cells

-Uninucleate

-Involuntary- no conscious control

-Found mainly in the walls of hollow organs

-Slow, sustained wavelike motion= peristalsis

-Most are attached by tendons to bones

-Cells are multi-nucleate

-Striated- have visible banding

-Voluntary-- subject to conscious control

Muscles are surrounded and bundled by connective tissue.

-Skeletal muscle: bundles of muscle fascicles surrounded by epimysium.

-Muscle cell/fiber: bundle of myofibrils surrounded by endomysim.

-Myofibril: connections of sarcomeres linked end-to-end surrounded by sarcoplasmic reticulum

-Sarcomere: functional unit of the muscle cell containing actin and myosin filaments.

-Actin: protein filament ~ 5nm in diameter (Thin filament)

-Myosin: protein filament~ 15 nm in diameter (Thick filament)

-Sarcomere- overlap of myofilaments create striations

-I band= light band

-A band= dark band (length of one myosin)

-M line= center of sarcomere

-H zone= middle of thick filaments only

-Z line= border of the sarcomere where thin filaments attach

-Explains the relationship between actin and myosin filaments

-Filaments of actin and myosin slide past each other which shortens the length of each sarcomere.

-An impulse is transmitted along the nerve too the end of the axon (axon terminal)

-The location where the nerve and muscle meet is called the neuromuscular junction

-A chemical [the neurotransmitter acetylcholine (ACh)] is released from the axon terminal and into the synaptic cleft.

-ACh crosses the synaptic cleft and binds to receptors on the sarcolemma.

-The sarcolemma continues to transmit the impulse to the transverse tubule (T-tubule)

-The impulse runs down T-tubule into muscle cell/fiber to the sarcoplasmic reticulum.

-Calcium stored in the sarcoplasmic reticulum (SR) is released into the sarcomere.

-Calcium binds to Troponin which is a "gatekeeper" molecule on the actin strand.

Troponin moves the strand of tropomyosin which was covering the actin binding sites.

-Energized Myosin heads are now attracted to the exposed binding sites.

-Myosin heads attach and "ratchet"

-ATP comes in to detach and reset myosin heads

-Contraction stops when calcium is reabsorbed.

-Muscle fiber contraction is "all or none"

-The force of a muscle contraction depends on the number of motor units recruited.

-A motor unit is a single neuron and the muscle fibers that it stimulates.

-Within a skeletal muscle, not all fibers may be stimulated during the same interval.

-A greater stimulus strength recruits more motor units

-More fibers contracting results in greater muscle tension.

-Muscle can continue to contract unless they run out of energy

-Initially, muscles use stored ATP for energy

-Creatine Phosphate Breakdown (anaerobic)

-High energy compound built up while the muscles are resting.

-Fastest way to get ATP to muscle

-CP contained within sliding filaments.

-Lasts only 4-8 seconds.

-After this initial time, other pathways must be utilized to produce ATP.

-Fermentation (anaerobic)

-Breakdown of glucose into lactic acid without the use of oxygen

-Supplies ATP necessary for short bursts (ex. 50-yard dash, running bases)

-Lasts a few minutes (2-3) then lactate accumulates. The sarcoplasm becomes acidic and the cell no longer functions properly. ATP is no longer available leading to fatigue and cramping b/c actin-myosin crossbridges cannot be broken.

-Cellular Respiration (aerobic)

-Glucose from glycogen and fatty acids is broken down w/ the use of oxygen to produce ATP.

-CR accounts for most of the ATP produced for muscle use.

-CR lasts as long as oxygen is adequately supplied; or, depletion of glycogen stores.

-Inadequate supply of oxygen leads to anaerobic production of ATP resulting in oxygen debt.

-Depletion of glycogen stores related to carbohydrate loading.

-When a muscle is fatigued, it is unable to contract

-A common reason for muscle fatigue is oxygen debt

-Oxygen must be "repaid" to tissue to remove oxygen debt.

-Oxygen is required to get rid of accumulated lactic acid.

-Increasing acidity from lactic acid and a lack of ATP causes the muscle to contract less.

-Slow twitch fibers

-Fast twitch fibers

Slow twitch fibers

-Smaller diameter

-Darker color due to myoglobin

-Resist fatigue

-Extensive capillary supply

-Able to contract for long periods of time

Fast twitch fibers

-Large in diameter

-Paler in color

-Easily fatigued

-Produce rapid, powerful contractions of short duration

-Improved use of glucose and oxygen

-Increased capillaries

-Increase in Creatine Phosphate resynthesis

-Increase in regulation of byproducts: K+, H+, lactate

-Increased neuromuscular firing

-Muscles only contract

-Muscles work antagonistic pairs

-Muscles attach to bone and cross a joint

-Muscles are attached to at least two points

-Origin- attachment to an immoveable bone

-Insertion- attachment to a moveable bone

-Prime mover (Agonist)- Muscle with the major responsibility for a certain movement.

-Antagonist- muscle that opposes or reverses a prime mover

-Synergist- muscle that aids a prime mover in a movement.

-Direction of muscle fibers

Ex:

-(straight) Rectus Abdominis; Rectus Femoris

-(angled) Internal/External Abdominal Oblique; Vastus Medialis/Lateralis Obliques

-(circular) Obribicularis Oris/Oculi

-Relative size of the muscle (long/short; big/small)

Ex:

-(largest) Gluteus Maximus; Pectoralis Major; Teres Major

-(medium) Gluteus Medius

-(small) Gluteus Minimus; Pectoralis Minor

-(long) Extensor Pollicus Longus; Fibularis Longus

-(short) Extensor Pollicus Brevis;

-Location of the muscle

-Example:

-(near bones) Temporalis; Frontalis

-(body regions) Pectoralis; Femoris; Brachialis

Number of origins

Ex:

-Triceps Brachii (3 heads), Biceps bracii (2 heads), quadriceps (4 heads)

Location of the muscle's origin and insertion

Ex: sterno (on the sternum)

Shape of the muscle

Ex: deltoid (triangular)

Action of the muscle

-Example: flexor and extensor (flexes or extends a joint)