 Movement
 Heat production
 Maintenance of posture
 Muscle contraction produces 85% of body heat

 Excitability - able to be stimulated
 Contractibility - able to shorten and thicken
 Extensibility - stretchable and extendable
 Elasticity - the ability to return to its original shape

 Skeletal - found attached to bone, striated, voluntary
 Cardiac - forms the walls of heart, striated, involuntary
 Smooth - found in viscera, non-striated, involuntary

 Each muscle is an organ, containing muscle, blood vessels, nerves, & connective tissue

 Fascia - found under the skin, covering organs, and muscles
 Epimysium – surrounds entire muscle
 Perimysium – surrounds groups of muscle fibers called “fascicles”
 Endomysium – surrounds individual muscle fibers
 Tendons; Aponeurosis – connect muscle to bones

 Muscle Cell = Muscle Fiber
 Elongated, multi-nucleate, striated cells containing parallel bundles of myofibrils
 Sarcolemma – plasma membrane
 Sarcoplasm – cytoplasm containing:
 Myoglobin – stores oxygen
 Glycosomes – store starch
 Peripheral nuclei
 Sarcoplasmic reticulum – smooth E.R. – maintains calcium levels
 Transverse tubules – network of membranes connected to sarcolemma; penetrates deep into each contractile unit.

Specialized contractile organelles
 Myofibrils - thread-like structures
 100’s to 1000’s in each muscle fiber (cell)
 Actin - thin filaments containing actin protein, 2 strands of tropomyosin, & troponin
 Myosin - thick protein filaments composed of myosin molecules

 Actin
 Myosin

SARCOMERE – the basic contractile unit
 Z discs (lines) - separate sarcomeres; anchor thin filaments
 A band - overlapping area of thick and thin filaments
 I band - contains only actin
 H zone - part of A band containing only myosin
 M line - center of H zone; anchors myosin

 Muscle contraction occurs when actin and myosin are allowed to interact with each other and form crossbridges
 The binding sites on actin are blocked by the troponin/tropomyosin complex
 Calcium ions in the sarcoplasm will bind to troponin

 This binding will cause the troponin / tropomyosin complex to pull away from the active binding site on actin, thus allowing myosin to bind
 The myosin head pivots, pulling the thin filaments toward the center of the sarcomere thus shortening the sarcomere
 Repeated cycles of attachment, pivoting, detach and release occurs

 Successive interaction causes “sliding” of the filament, shortening of the sarcomere, thus shortening of the entire muscle
 Calcium is removed from the troponin molecule and returned to the S.R.
 Relaxation occurs

What triggers the release of calcium?

The sudden change in the transmembrane potential

 Resting Membrane Potential
 Polarized - positive charge outside, negative charge inside
 Depolarized - positive charge inside, negative charge outside
 Repolarized - positive charge reestablished outside, negative charge inside

 When muscle is relaxed, the sarcolemma is polarized having a charge difference between the inside /outside of the cell
 When a stimulus is received opening a channel gate , Na+ ions will flow into the cell changing the polarity of the cell

 The net charge of the sarcolemma becomes negative in regards to the inside of the cell which is now positive.
 The cell is said to be depolarized and the muscle contracted

 Membrane pumps quickly restore the original status or condition
 The positive charge outside is reestablished once again and resting membrane potential is restored

 Each fiber is controlled by a motor neuron at a neuromuscular junction
 Motor neurons stimulate muscle fibers
 Acetylcholine (ACh ) is released into the synaptic cleft with the arrival of an action potential
 ACh diffuses across the cleft, binding to receptors on the motor end plate, initiating a muscle action potential

 Resting membrane potential is restored by:
 Acetylcholinesterase
 active transport pumps that pump Ca +2 ions back into the sarcoplasmic reticulum
 Calsequestrin – binds calcium

 Used to activate the myosin head in order to bind to actin
 After power stroke, ATP used to break the bond between actin and myosin
 ATP used to pump calcium back into the
SR

 Direct phosphorylation
 Creatine phosphate couples with ADP to form ATP
 Provides about 15 sec of energy
 Glycolysis
 Glucose broken down anaerobically
 Produces lactic acid as waste product
 Provides about 30-60 sec of energy
 Aerobic Respiration
 Glucose broken down with oxygen
 Hours of energy

 Insufficient oxygen
 Build-up of lactic acid
 Depletion of glycogen
 RECOVERY OXYGEN CONSUMPTION
 OXYGEN DEBT

 Muscle fibers will contract fully OR not at all once they are stimulated
 Threshold stimulus
 minimal level of stimulation needed to cause the muscle to contract

 Motor units - motor neuron and all the muscle fibers it controls
 Number of muscle fibers in motor unit will vary
 The fewer the number of fibers per motor unit, the more precise the contraction
 The number of motor units being stimulated will determine the strength of contraction of the entire muscle

 Twitch contraction
 rapid, jerky contraction to a single stimuli
 phases: latent, contraction, relaxation,refractory
 Wave summation
 increase in the strength of muscle contraction due to rapid successive stimulation
 Tetany
 continuous, smooth, sustained contraction

 Treppe
 repeated stimulation following stimulation causing a staircase effect
 Isotonic
 tone or tension remains constant-muscle shortens
 Isometric
 tension increases - muscle length remains same

 Red oxidative fibers
 more myoglobin
 more capillaries
 more mitochondria
 long, slow contraction
 sustained energy
 aerobic respiration
 non-fatiguable fibers
 White glycolytic fibers
 less myoglobin
 less capillaries
 fewer mitochondria
 rapid,powerful contraction
 quick energy
 anaerobic respiration
 fatigue easily

 Increase the size of size and strength of each fiber
 Increase muscle tone
 Increases the blood supply, thus increasing the number of red blood cells
 Increased respiratory and cardiovascular function
 Lowers blood pressure

 Involuntary
 Intercalated discs
 Forms syncytium
 Long refractory period
 Long contraction rate
 More mitochondria than skeletal muscle

 Involuntary - neural & hormonal stimulation
 No sarcomeres - no striations
 Very, very long contraction rate
 Calmodulin - regulatory protein
 No tendons or aponeuroses

 Origin – attachment of a muscle to a stationary bone
 Insertion – attachment of a muscle to a movable bone
 Prime mover – provides major force for specific movement
 Antagonist – opposes prime mover
 Synergist – assists the prime mover (secondary muscle)

 Levers – rigid bar (bones) moving on fixed point
 Fulcrum = fixed point (joints)
 Effort = applied force
 Resistance = load

 First class
 Fulcrum in center = seesaw
 Lifting head off chest
 Second class
 Load (resistance) in center = wheelbarrow
 Least common
 Standing on tiptoes
 Third class
 Effort in center = tweezers
 Biceps brachii
 Most common