Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia –...

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Muscle Tissue

Transcript of Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia –...

Page 1: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Muscle Tissue

Page 2: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

3 Types of Muscle Tissue

• Skeletal muscle– attaches to bone, skin or fascia– striated with light & dark bands visible with scope – voluntary control of contraction & relaxation

Page 3: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

3 Types of Muscle Tissue

• Cardiac muscle– striated in appearance– involuntary control– autorhythmic because of built in pacemaker

Page 4: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

3 Types of Muscle Tissue

• Smooth muscle– attached to hair follicles in skin– in walls of hollow organs -- blood vessels & GI– nonstriated in appearance– involuntary

Page 5: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.
Page 6: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.
Page 7: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.
Page 8: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Skeletal Muscles• Attach to bones• Produce skeletal movement (voluntary)• Maintain posture• Support soft tissues• Regulate entrances to the body• Maintain body temperature

•muscle fibers increase in size during childhood = human GH•testosterone also increases muscle size•mature muscle fibers range from 10 to 100 microns in diameter•typical length is 4 inches - some are 12 inches long

Page 9: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Properties of Skeletal MusclesElectrical excitability

-ability to respond to stimuli by producing electrical signalssuch as action potentials-two types of stimuli: 1. autorhythmic electrical signals

2. chemical stimuli

Contractility-ability to contract when stimulated by an AP-isometric contraction: tension develops, length doesn’t change-isotonic contraction: tension develops, muscle shortens

Extensibility-ability to stretch without being damaged-allows contraction even when stretched

Elasticity-ability to return to its original length and shape

Page 10: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Gross Anatomy

•muscles are really groups offascicles

•the fascicles are groups of musclefibers = considered to be an individual muscle cell

Page 11: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

•the muscle fiber is made upof protein filaments = myofibrils

•each myofibril is comprised ofrepeating units = sarcomeres

Page 12: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Gross Anatomy•muscle is wrapped in a protective fascia

-fascia = sheet of fibrous connective tissue that supportsand surrounds muscle or organs

•a superficial fascia separates muscle from the overlying skin-also known as the subcutaneous layer-made up of areolar tissue and adipose tissue-provides support for blood vessel and nerves-the adipose tissue stores most of the body’s triglyceridesand provides insulation

•muscles with similar functions are grouped and held together by layers of deep fascia

-dense irregular connective tissue-allow free movement of muscles, carries nerves, BVs

Page 13: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

• three layers of connective tissue surround a muscle– Epimysium– Perimysium– Endomysium

• these layers further strengthen and protect muscle• outermost layer = epimysium

– encircles the entire muscle– separates them into bundles = fascicles

• next layer = perimysium– divides and surrounds groups of 10 to 100 individual muscle fibers– give meat its “grain” because the fascicles are visible– both epimysium and perimysium are dense irregular connective tissue– extend off the muscle to become organized as dense regular connective tissue =

tendon• when the tendon is a broad flat sheet = aponeurosis

• penetrating the muscle fibers and separating them into myofibrils = endomysium (areolar connective tissue)• myofibrils are made of filaments of proteins = myofilaments

Page 14: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

•generally muscles are supplied with one artery and two veins•they accompany the nerve•nerves that induce muscle contraction = somatic motor neurons (part of the somatic division of the PNS)•communication between muscle and these neurons

Neuromuscular junction (NMJ)

Page 15: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.
Page 16: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Microanatomy of Skeletal Muscle Fibers

• New terminology– Cell membrane = sarcolemma– Cytoplasm = sarcoplasm– Internal membrane system = sarcoplasmic reticulum

• Large, multinucleated cells– embryonic development – stem cells (satellite cells) differentiate into

immature myoblasts which begin to make the proteins of the myofibrils and myofilaments

– These myoblasts mature into myocytes– Multiple myocytes fuse to form the muscle cell (muscle fiber)– once fused, these muscle cells lose the ability of undergo mitosis – number of muscle cells predetermined before birth – they get larger as we

grow– but satellite cells can repair damaged/dying muscle cells throughout

adulthood• Exclusive to skeletal muscle only!!!

Page 17: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Muscle Cell Anatomy• Transverse tubules

– ingrowths of sarcolemma– Carry electrical impulses deep

into the fiber• Myofibrils within sarcoplasm

of the fiber– Contain a“skeleton” of protein

filaments (myofilaments) organized as Sarcomeres

• Myofilaments form the myofibrils– Thin filaments (actin, troponin,

tropomyosin)– Thick filaments (myosin)

Page 18: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Microanatomy of Skeletal Muscle Fibers

•muscle fibers are bound by a plasma membrane = sarcolemma

•thousands of tiny invaginations in this sarcolemma called T or transversetubules - tunnel in toward the center of the cell

-T tubules are open to the outside of the fiber - filled with interstitial fluid- action potentials generated in the neuron travel along the sarcolemma and the T tubules- allows for the even and quick spread of an action potential deep into the cell

•the cytoplasm is called a sarcoplasm-substantial amounts of glycogen - can be broken into glucose-contains myoglobin - binds oxygen needed for muscle ATPproduction-support multiple myofibrils – structures for contraction

Page 19: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Microanatomy of Skeletal Muscle Fibers

•contractile elements of the myofibrils = myofilaments-2 microns in diameter-comprised of primarily actin or myosin-give the muscle its striated appearance

•fibers also have a system of fluid-filled membranes = sarcoplasmicreticulum

-encircles each myofibril-similar to the endoplasmic reticulum of other cells-have dilated end sacs = terminal cisterns-stores calcium when at rest - releases it during contraction-release is triggered by an AP

Page 20: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

The Proteins of Muscle• Myofibrils contain two kinds of myofilaments

• Thin • Thick

• these Myofilaments are built of 3 kinds of protein– contractile proteins

• myosin and actin– regulatory proteins which turn contraction on & off

• troponin and tropomyosin– structural proteins which provide proper alignment, elasticity and

extensibility• titin, myomesin, nebulin, actinin and dystrophin• Dystrophin – connects myofibrils to sarcolemma

– -transmits tension along muscle• Actinin – part of Z-line• Titin – connects myosin to Z-line and M-line

– Role in recovery after being stretched• Nebulin – forms core of the actin chain/thin filament

Page 21: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

• sarcomere = regions of myosin (thick myofilament) and actin (part of thin myofilament)• bounded by the Z line • thin filaments project out from Z line – actin attaches via actinin (structural protein)• thick filaments lie in center of sarcomere - overlap with thin filaments and connect to them via cross-bridges• myosin/thick filament only region = H zone• myosin/thick filaments are held in place by the M line proteins at the center and titin at the Z-line• thin filament only region = I band• length of myosin/thick filaments = A band• contraction = “sliding filament theory”

-thick and thin myofilaments slide over each other and sarcomere shortens

Sarcomere Structure

M line

Page 22: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Contraction: The Sliding Filament Theory

• SF Theory: 1954– Explains how a muscle fiber exerts tension– Four step process

• Active sites on actin• Crossbridge formation• Cycle of attach, pivot, detach, return• Troponin and tropomyosin control contraction

• Contraction:– Active process– Elongation is passive– Amount of tension produced is proportional to degree of overlap of thick

and thin filaments

Page 23: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Contraction: The Sliding Filament Theory•Actin proteins in the thinfilament have myosin binding sites•these sites are “covered up” by troponin and tropomyosin in relaxed muscle•removal of troponin/tropomyosin from these sites is required for contraction •removal of troponin/tropomyosin is done through binding of calcium to troponin•calcium is release from the sarcoplasmic reticulum upon the action potential

Page 24: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

• myosin/thick myofilament is a bundle of myosin molecules

• myosin looks like a “golf club” with a head, a hinge region and a shaft

• each myosin protein has a globular “head” with a site to bind and breakdown ATP (ATPase site) and to bind actin (actin binding site)

• binding of actin and myosin binding sites = cross-bridging

Page 25: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

-for cross bridging- you will need two things:1. calcium – uncovers the myosin binding sites on actin – “pushes aside” the troponin-

tropomyosin complex2. myosin head bound to ADP

-for contraction – i.e. pivoting of the myosin head into the M line – the myosin head must be empty-to “reset” for a new cycle of cross-bridging – the myosin head must detach and pivot back

-the myosin head must bind ATP-once the myosin head pivots back – the ATP is broken down to ADP – head is ready to cross-bridge again – if actin is “ready”

Increase in Cai

Removal of troponin-tropomyosin

CONTRACTIONSliding of actin along myosin

RESETTING of system

Page 26: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Contracted Sarcomere

Page 27: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

CHECK OUT THESE ANIMATIONs!!!

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.htmlhttp://www.youtube.com/watch?v=EdHzKYDxrKchttp://www.youtube.com/watch?v=Vlchs4omFDM

Page 28: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

The Events in Muscle Contraction

Page 29: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Relaxation• Acetylcholinesterase (AChE) breaks down ACh

within the synaptic cleft• Muscle action potential ceases• Ca+2 release channels close• Active transport pumps Ca2+ back into storage in

the sarcoplasmic reticulum• Calcium-binding protein (calsequestrin) helps

hold Ca+2 in SR• Tropomyosin-troponin complex recovers binding

site on the actin

Page 30: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Rigor Mortis• Rigor mortis is a state of muscular rigidity

that begins 3-4 hours after death and lasts about 24 hours

• After death, Ca+2 ions leak out of the SR and allow myosin heads to bind to actin

• Since ATP synthesis has ceased, crossbridges cannot detach from actin until proteolytic enzymes begin to digest the decomposing cells.

Page 31: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

• Optimal overlap of thick & thin filaments– produces greatest number of crossbridges and the

greatest amount of tension• As stretch muscle (past optimal length)

– fewer cross bridges exist & less force is produced • If muscle is overly shortened (less than optimal)

– fewer cross bridges exist & less force is produced– thick filaments crumpled by Z discs

• Normally– resting muscle length remains between 70 to 130% of

the optimum

Length of Muscle Fibers

Page 32: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

The Neuromuscular Junction• end of neuron (synaptic terminal or axon bulb) is in very close association with the muscle fiber• distance between the bulb and the folded sarcolemma = synaptic cleft• nerve impulse leads to release of neurotransmitter (acetylcholine)• N.T. binds to receptors on myofibril surface• binding leads to influx of sodium, potassium ions (via channels)• eventual release of calcium by sarcoplasmic recticulum = contraction

• Acetylcholinesterase breaks down ACh• Limits duration of contraction

Page 33: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Motor Units• Each skeletal fiber has only ONE NMJ• MU = Somatic neuron + all the

skeletal muscle fibers it innervates• Number and size indicate precision

of muscle control• Muscle twitch

– Single momentary contraction– Response to a single stimulus

• All-or-none theory – Either contracts completely or not at

all

• Muscle fibers of different motor units are intermingled so that net distribution of force applied to the tendon remains constant even when individual muscle groups cycle between contraction and relaxation.

• Motor units in a whole muscle fire asynchronouslysome fibers are active others are relaxed delays muscle fatigue so contraction can be sustained

Page 34: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Muscle Metabolism

• Production of ATP:-contraction requires huge amounts of ATP-muscle fibers produce ATP three ways:1. Creatine phosphate2. Aerobic metabolism3. Anaerobic metabolism

Page 35: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Creatine Phosphate

• Muscle fibers at rest produce more ATP then they need for resting metabolism• Excess ATP within resting muscle used to form creatine phosphate

– creatine – arginine, glycine and methionine• made by kidneys and liver• phosphorylated in muscle to make creatine phosphate

• phosphorylated by the enzyme creatine kinase• takes a phosphate off of ATP and transfers it creatine• takes the phosphate off of creatine phosphate and transfers it back to ADP –

to make ATP• Creatine phosphate: 3-6 times more plentiful than ATP within muscle• Sustains maximal contraction for 15 sec (used for 100 meter dash).• Athletes often use creatine supplementation

– gain muscle mass but shut down bodies own synthesis (safety?)

Page 36: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Anaerobic Cellular Respiration• Muscles deplete creatine – can make ATP

in anaerobically or aerobically• Glycogen converted into glucose first• ATP produced from the breakdown of

glucose into pyruvic acid (sugar) during glycolysis – if no O2 present (anaerobic) - pyruvic

converted to lactic acid which diffuses into the blood

• Glycolysis can continue anaerobically to provide ATP for 30 to 40 seconds of maximal activity (200 meter race)

• If O2 is present the pyruvic acid is converted into acetyl coA (aerobic)

Page 37: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Aerobic Cellular Respiration

• ATP for any activity lasting over 30 seconds – if sufficient oxygen is available, pyruvic acid is converted into acteyl coA – Acetyl coA enters the mitochondria to enter the Kreb’s cycle– Kreb’s cycle generates NADH and FADH2 (electron carriers)– The electrons are carried to an enzymes located on the inner mitochondrial membrane – The electrons are then transported along three complexes of enzymes – ultimately transported to oxygen

• This results in the synthesis of ATP, water and heat

• Provides 90% of ATP energy if activity lasts more than 10 minutes• Each glucose = 36 ATP• fatty acids and amino acids can also be used by the mitochondria

– Fatty acid = ~100 ATP• Sources of oxygen – diffusion from blood, released by myoglobin

Page 38: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Types of Muscle Fibers• Fast fibers = glycolytic• Slow fibers = oxidative

• Fibers of one motor unit all the same type• Percentage of fast versus slow fibers is genetically

determined

• Proportions vary with the usual action of the muscle- neck, back and leg muscles have a higher proportion of postural, slow oxidative fibers- shoulder and arm muscles have a higher proportion of fast glycolytic fibers

Page 39: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Fast Fibers

• Large in diameter• Contain densely packed myofibrils• Large glycogen reserves• Fast oxidative-glycolytic (fast-twitch A)

– red in color (lots of mitochondria, myoglobin & blood vessels)– split ATP at very fast rate; used for walking and sprinting

• Fast glycolytic (fast-twitch B)– white in color (few mitochondria & BV, low myoglobin)– anaerobic movements for short duration; used for weight-lifting

Page 40: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

• Slow fibers– Half the diameter of fast fibers– Three times longer to contract– Continue to contract for long periods of time• e.g. marathon runners

Page 41: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

Exercise-Induced Muscle Damage

• Intense exercise can cause muscle damage– electron micrographs reveal torn sarcolemmas,

damaged myofibrils an disrupted Z discs– increased blood levels of myoglobin & creatine

phosphate found only inside muscle cells• Delayed onset muscle soreness– 12 to 48 Hours after strenuous exercise– stiffness, tenderness and swelling due to

microscopic cell damage

Page 42: Muscle Tissue. 3 Types of Muscle Tissue Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary.

• Atrophy– wasting away of muscles– caused by disuse (disuse atrophy) or severing of the

nerve supply (denervation atrophy)– the transition to connective tissue can not be reversed

• Hypertrophy– increase in the diameter of muscle fibers – resulting from very forceful, repetitive muscular

activity and an increase in myofibrils, SR & mitochondria