Function of Muscles
-Produce movement
-Maintain posture
-Stabilize joints
-Generate heat
Cardiac Muscle Characteristics
-Striated
-Uninucleate
-Joined to another muscle cell at an intercalated disc
-Involuntary
-Found only in the heart
Smooth Muscle Characteristics
-No striations
-Spindle-shaped cells
-Uninucleate
-Involuntary- no conscious control
-Found mainly in the walls of hollow organs
-Slow, sustained wavelike motion= peristalsis
Skeletal Muscle Characteristics
-Most are attached by tendons to bones
-Cells are multi-nucleate
-Striated- have visible banding
-Voluntary-- subject to conscious control
Organization of Skeletal Muscle
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)
Microscopic Anatomy of Muscle Cell/Fiber
-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
The Sliding Filament Theory of Muscle Contraction
-Explains the relationship between actin and myosin filaments
-Filaments of actin and myosin slide past each other which shortens the length of each sarcomere.
Skeletal Muscle Contraction
-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.
1-Skeletal Muscle Contraction
-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.
2-Skeletal Muscle Contraction
-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.
3-Skeletal Muscle Contraction
-Energized Myosin heads are now attracted to the exposed binding sites.
-Myosin heads attach and "ratchet"
4- Skeletal Muscle Contraction
-ATP comes in to detach and reset myosin heads
-Contraction stops when calcium is reabsorbed.
1-Control of Muscle Contraction
-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.
2-Control of Muscle Contraction
-A greater stimulus strength recruits more motor units
-More fibers contracting results in greater muscle tension.
1--Energy for Muscle Contraction
-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.
2-Energy for Muscle Contraction
-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.
3--Energy for Muscle Contraction
-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.
Muscle Fatigue and Oxygen Debt
-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.
Types of Skeletal Muscle Fibers
-Slow twitch fibers
-Fast twitch fibers
1-Types of Skeletal Muscle Fibers
Slow twitch fibers
-Smaller diameter
-Darker color due to myoglobin
-Resist fatigue
-Extensive capillary supply
-Able to contract for long periods of time
2- Types of Skeletal Muscle Fibers
Fast twitch fibers
-Large in diameter
-Paler in color
-Easily fatigued
-Produce rapid, powerful contractions of short duration
Effects of Exercise on Muscle
-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 and Body Movements
-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
Types of Moving Muscles
-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.
1-Naming of Skeletal Muscles
-Direction of muscle fibers
Ex:
-(straight) Rectus Abdominis; Rectus Femoris
-(angled) Internal/External Abdominal Oblique; Vastus Medialis/Lateralis Obliques
-(circular) Obribicularis Oris/Oculi
2-Naming of Skeletal Muscles
-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;
3-Naming of Skeletal Muscles
-Location of the muscle
-Example:
-(near bones) Temporalis; Frontalis
-(body regions) Pectoralis; Femoris; Brachialis
4- Naming of Skeletal Muscles
Number of origins
Ex:
-Triceps Brachii (3 heads), Biceps bracii (2 heads), quadriceps (4 heads)
5-Naming of Skeletal Muscles
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)