Movement-sometimes locomotion, sometimes movement within a given area 

Posture-maintains body in stable positions

Thermogenesis (heat production)-as much as 85% produced by contractions

Regulating orgain volume-contraction of sphincters may prevent outflow of contents of hollow organ 

Heat production-as much as 85% of body heat is from muscle contractions 

Excitability (irritability)

Contractility

Extensibility

Elasticity

ability to recieve and respone to stimuli

ability to shorten and thicken 

ability to stretch 

ability to return to original shape after stretching 

Sketetal-striated, voluntary muscle (100's nuclei in perphery)

Smooth-visceral (organs), involuntary muscle (1 nuclei in center)

Cardiac-striated, involuntary (1 nuclei in center)

Fibrous connective tissue sheath that envelops each muscle 

partitions each muscle into fascicles or bundles of fibers 

extension between individual muscle fibers (muscle cell) 

Broad flat sheet of fibrous connective tissue continous at one border with fibrous wrapping of muscle and at other border with fibrous covering of adjacent structure, usually another muscle

• in the cat, linea alvea, it connects to external oblique, underneath it is rectus abdominus 

Tube of fibrous connective tissue that enclose certain tendons (wrist and ankle)

• synovial membrane line tendom sheath->fluid filled cavity which reduces friction 

• Loose connective tissue that separates muscle from skin
• Stores water and fat
• Forms layer of insulation 
• Provides mechanical protection against blows
• Provides pathway for nerves and blood vessels to enter and exit muscles 

Cell membrane of muscle fiber 

Cytoplams of muscle fiber 

fine fibers packed close together in sacroplams; consist of 3 kinds of myofilaments 

Section of myofibril between Z lines 

Thick filament-myosin molecules

Thin filaments-actin, tropomyosin, and troponin molecules arranged in complex fashion

Elastic filaments-titin biggest protein in the body 

myosin molecules

heads of myosin are cross bridges of thick filaments

made up of actin, tropomyosin, and troponin molecules arrange in complex fashion

contains myosin-binding site

Made up of titin biggest protein in the body (connectin)

Third most plentiful protein after action and myosin in muscle fibers

Anchors thick filaments Z discs; stabilizes thick filament 

50 times larger than average protein 

Connects Z discs to the M line of sarcomeres, stabilizes thick filaments 

Can stretch to 4 times its resting length; responsible for extensibility and elasticity of myofibrils 

Composed of both thick and thin filaments. Appear as dark strips (EM microscope)

Composed of only thick filaments

Run across midsection of each dark A band 

Divides H zone

Formed by protein molecules that connect to protein in neighboring M lines->connecting adjacent thick filaments 

Composed only of thin filaments 

Appears as light stripes 

Extends across center of each light I band

Regions of dense material; separates sarcomere

Structural proteins in muscle fiber 

Found in Z disc-binds actin to titin 

Forms M line of sarcomere

Binds to titin and to protein adjacent to M line 

wraps around entire length of each thin filament; anchors thin filaments to Z discs 

Links thin filament to integral membrane protein in sarcolemma, which are attached to proteins in surrounding connective tissue endosyium->structural support, helps to transmit tension from contracting sarcomere to tendons 

Terminal cisterns

Transverse tubules and 2 cisterns on either side; triple layered structure consisting of T tubule sandwiched between sacs of SR 

one motor neuron together with all the skeletal muscle fibers its supplies; number of muscle fibers per unit varies

Examples: 

Precise movement: one motor neuron supplying fewer muscle fibers (voice: 2-3 muscle fibers/motor unit)

Gross movement: greater number of muscle fibers supplied by a single motor neuron (bicepts brachii as many as 2000/motor unit)

one motor neuron supplying fewer muscle fibers

example:(voice: 2-3 muscle fibers/motor unit)

o   Channels open for Na+ to diffuse into muscle fiber generating action potential which leads to muscle contraction

cross bridges of thick filaments (myosin) attach to thin filaments (actin) and pull them toward the middle of the sarcomere 

Calcium is stored in SR 

ATP is attached to cross bridges 

Tropomyosin-troponin complex is covering the myosin binding site on actin 

-Upon stimulation by nerve impulse acetyoline is released by motor axon synaptic end bulbs

-Ach diffuses across myoneural junction and initiates an action potential in the muscle fiber (movement of Na into fiber and K out of fiber)

-impulse is conveyed from T tubules to SR-> induces release of Ca by opening Ca release channels 

-Ca ions combine with troponin causing troponin-tropomyosin complex to move which exposes the myosin-binding site on the actin molecule 

-Energy release from hydrolyzed ATP is used for the attachment of myosin cross bridges to myosin-binding sites on actin

-Energy is then used to pull actin filamemts inward (power stroke) resulting in sliding of thin filaments past thick filaments

-sliding draws Z discs toward each other, sarcomere shortens, muscle fiber contracts, muscle contract

-ACh is inactivated by acetycholinestrase (AChe)

-Ca is transported back into SR

-Tropomyosin-troponin complex reattaches to actin

-Myosin cross bridges seperate from actin

-ATP is resynthesized; muscle relaxes 

1. From creatine phosphate

2. By anaerobic respiration

3. By aerobic respiration 

*note: average cellular levels of ATP and creatine phosphate together provide enough energy for muscles to contract maximally for about 15 sec. 

Part of muscle metabolism 

-muscle fibers contain creatine phosphate

-creatinine phosphate->creatine and phosphate and energy

-Phosphate and energy can be used to remake ATP

-Creatine Phosphate is 3-5 times more plentiful than ATP

-together stores of creatinine phosphate and ATP provide enough energy for muscles to maximally contract for 15 sec. 

Storage form of energy in muscle fiber 

Creatine:synthesized in the liver, kidneys, and pancreas and transported to muscle fibers

Creatine kinase (CK) catalyzed the additon/removal of phosphate 

Part of muscle metabolism

-when creatine phosphate is gone:

• glycogen is broken down and glucose is catalyzed
• if oxygen is not available, anaerobic respiration takes place in the form of glycolysis with formation of lactic acid and some energy (for 2 mins of max muscle activity)
• lactic acid diffuses into blood; liver can convert lactic acid back into glucose 

Aerobic system 

• longer activity depends on aerobic process
• with oxgen available cellular respiration occurs to produce ATP, carbon dioxide and water
• oxgens comes from blood and is bound/released from myoglobin inside muscle fibers
• Provides ATP for prolonged activity as long as oxygen and glucose are available  

-Maximum rate of oxygen consumption is called max oxygen uptake; affected by gender, age, size, training

-After heavy muscle activity, heavy breathing continues to repay oxygen used in activity (oxygen debt or recovery oxygen consumption)

Muscle cells either contract with all force possible under existing conditions or do not contract at all 

-Continual, partial contractions produced by stimltaneous activation of small form of motor units, followed by relaxation of their fiber and activation of another group of motor units 

-Muscle tone-keeps skeletal muscles firm but is not strong enough to produce movement 

-Flaccid-state of limpness in which muscle tone is lost

-Muscle spindles and neurotendinous end-organs: detect degree of muscle stretch 

State of limpness in which muscle tone is lost in tonic contraction 

-a muscle shortens but its tension remains constant

-isotonic contraction produce movement

-Two types:concentric and eccentric 

-shortening of a muscle that results in reducing the angle at a joint

-example: picking up a book requires concentric contraction of biceps brachii muscle 

Controlled lengthening of a muscle during contraction that results in increasing the angle at a joint (repeated contractions produce more muscle damage that concentric)

Example: lowering the book requires eccentric contraction of the bicep brachii 

Muscle length remains unchanged but tension within muscle increases; isometric contractions "tighten" muscles but do not produce movements: energy expended 

Example: holding a book steady using outstretched arm

     -the book pulls the arm downward stretching the shoulder and arm muscle. The isometric contraction of these muscles counteracts the stretch 

A quick, jerky contraction in response to single stimulus; consists of 3 phases-this is rare in normal body

1.latent period

2.contraction phase

3.relaxation phase

Sustained smooth contraction produced by series of stimuli bombarding muscle in rapid succession 

series of increasingly stronger contractions in response to constant strength stimuli applied at rate of 1 or 2 per second 

incomplete relaxation after repeated stimulation 

failure of muscle to contract in response to strongest stimuli after repeated stimulation; true muscle fatigue seldom occurs in body 

-action potential travels down axonaterminal bulb (neuron)

-influx of Ca2+

-Fusion of vesicles with neurolemma release of acetylcholine into the neuro muscular junction 

-acetylcholine binds to receptors on motor end plate

-initation of action potential in muscle fiber (Na+ flows in, K+ flows out)

1. Latent period (2 sec): muscle action potential sweeps over the sarcolemma inducing release of Ca2+ from the SR

2. Contraction period (10-100msec): Ca2+ binds to troponin: myosin binding sites on actin are exposed and cross bridges form (ATP,ADP)

3. Relaxation period (1-100msec): Ca2+ is actively transported back into SR, myosin head detach from actin (ATP), myosin binding sites are covered by tropomyosin and tension in the muscle fiber decreases

A second stimulus occurs before the skeletal muscle fiber has relaxed. The second contraction will be stronger than the first. Must occur after the refractory period 

sustained but wavering contraction when a skeletal muscle fiber is stimulated at a rate of 20-30 times per second such that is can partially relax between stimuli 

sustained contraction. A muscle fiber is stimulated 80-100 times per second; no relaxation; individual twitches can't be detected 

Required recovery period between consecutive stimulations of nerve of muscle fibers. If two stimuli are applied during this time only the first stimululs will induce a response. Why? Time need to restore K+ and Na+ to their appropriate sides of the sarcolemma by Na+/K+ pumps

   -resting potential state 

Why is the peak tension generated during fused tetanus 5-10 times larger than the peak tension produced during a single twitch? 

There is a buildup of Ca2+ levels in the sarcoplasms as more and more Ca2+ is released from the SR; also the elastic components (connective tissue, tendons) aren't given time to spring back between contractions 

high myoglobin content; more mitochondria and blood capillaries 

Type one-slow twitch or fatigue-resistant fibers

-appear as red (lots of myoglobin), many blood capillaries, high capacity to generate ATP by aerobic system 

-Split ATP at slow rate so have slow contraction velocity

-resistant to fatigue; capable of prolonged, sustained contractions

-Found in head and neck muscle-maintain posture

-Needed for long endurance activities-running a marathon 

Type 2-fast-twitch A or fatigue-resistant fibers

-largest fibers

-large amounts of myoglobin and many blood capillaries need oxygen for aerobic respiration, dark red

-generates a lot of ATP by aerobic cellular respiration-hence moderatly resistant to fatigue

-High intracellular glycogen levels-also generates ATP by anaerobic glycolysis 

-3-5 times faster ATPase activity in their myosin head com paerd to SO fibers 

-contribute to activities such as walking and sprinting 

type 2-fast twitch B or fatigable fibers

-appear white

-contain large amounts of glycogen

-generates ATP by anaerobic process-so fatigue easily 

-split ATP fast, so strong rapid contraction

-adapted for intense anaerobic movements of short duration 

Example: weight lifting or throwing a ball

after the first 30 mins of exercise the body runs out of its glycogen storage and then turns mainly to what is left of glucose in the blood, then to fat and amino acids derived from muscle protein 

• fibers are quadrangular shape and single nucleus
• Same bands and composition of actin and myosin as skeletal muscle due to striation
• Fibers branch and interconnect with each other; intercalated discs are irregular transverse thickenings of sarcolemma that connects neighboring fibers
• Two networks of fibers: one in atria and one in ventricles; allows entire network to contract together 

• Contracts and relaxes an average 75 times/minute thus requiring constant oxggen supply 
• Contains more mitochondria than skeletal muscle; depends on aerobic system to supply
• Cardiac muscle can contract without extrinsic stimulus; has specialized conducting network within heart (autorhythmicity)
• Remains contracted 10-15 times longer than skeletal muscle but also has long refractory period 

• Smaller fiber than skeletal; thickest in middle and tapered at end with single nucleus
• Contains thick and thin filaments but not arranged in sarcomeres as in striated muscle
• Contains intermediate filaments which attach to structures called dense bodies(Similar to Z discs); some dense bodies are scattered in sarcoplasm and some attach to sarcolemma
• Bundles of intermediate fibers stretch from one dense body to another; actin/myosin based contraction causes intermediate filaments to pull on dense bodies causes lengthwise shortening of muscle fiber 

Single unit-most common; forms part of walls of small arteries and veins and hollow viscera such as stomach, intestines, uterus and bladder; contains gap junctions which allows stimulation of many fibers at once

-entire muscle contracts as one unit

individual fibers each with own motor neuron terminals and with few gap junctions between neighboring fibers; stimulation causes contraction of only one fiber; found in walls of large arteries, in large airways of lungs, in arrector pili muscles, and in radial and circular muscles of the iris

-each muscle fiber contracts individually, multiple contracting units per smooth muscle 

• Contraction starts more slowly and lasts longer than striated muscle; can shorten and stretch more than striated
• No T tubulus and Ca enters through sarcolemma as well as released from SR
• Contains calmodulin (analogous to troponin) and myosin light chain kinase which are needed for myosin binding to actin
• Ca moves slowly out of cell, which delays relaxation resulting in prolonged muscle tone
• Smooth muscle contraction is controlled by the automatic nervous system (involuntary)