chapter 9 - muscle tissues

functions of skeletal muscle? list 4

1. produces body movements

2. stabilize body positions

3. store proteins, calcium, glucose

4. helps regulate body temperature

properties/functions of muscle? list 4

1. excitable = produces APs when enough stimulation

2. contractile = generate force by shortening and pulls structures together

3. extensibility = can stretch w/o damage; critical to moving or for movement to happen

4. elastic = muscle tissue stretched = can go backt o resting length afterwards w/o damage

STRUCTURE OF A SKELETAL MUSCLE: what is muscle belly?

• numbers?

• truth?

• arrangement?

a body of muscle connected to skeleton by tendons

• hundreds to thousands of muscle fibers

• highly vascular

• may be arranged in a variety of shapes depending on function

STRUCTURE OF A SKELETAL MUSCLE: what are tendons?

• bundles?

• shapes?

made up of dense regular ct and minimally vascular

• parallel bundles of collagen fibers with few fibroblasts to maintain dense regular ct

• many shapes depending on function

• can be broadsheaths

CT COVERINGS: endomysium

• type of ct?

• function?

• carries?

innermost layer that covers each muscle fiber

• reticular; loose ct = lots of elastic fiber

• bind muscle fibers while allowingn them to move freely

• carries small blood supply called capillaries

CT COVERINGS: perimysium

• what is fassicle?

• ct?

• movement?

• carries?

covers each fasicle and holds the muscle bundle together. allows muscle fibers to act w/o interrupting e/o

• dense irregular ct

• allows some freedom of movement

• carries blood vessels

CT COVERINGS: epimysium

• ct?

• function?

• truth?

covers muscle belly on top of the outside, outer most layer

• dense irregular

• binds fasicles together

• continuous layers, fibers interwoven to keep muscles together

MICROSCOPIC ANATOMY: mature muscle fibers size?

• develops from?

• mature fiber?

• what can it not do?

10-100 micrometer in diameter, 10-30 cm long

• develop from fusion of 100+ myoblasts (immature muscle stem cells)

• mature fiber: single cell with 100+ nuclei

• cannot divide = terminally differentiated

MICROSCOPIC ANATOMY: hypertrophy

• truth?

• increased…?

• fiber?

• function?

enlargement of existing fibers

• muscle growth is due to hypertrophy

• increased production of myofibrils, mitochondria, organelles

• fiber increases in diameter

• capable of more forceful contractions (can lift heavy things)

MICROSCOPIC ANATOMY: satellite cells

• what can it do?

• ability?

• damage effect?

myoblasts in mature skeletal muscles scattered through diff muscles and muscle groups

• can divide and fuse to make new muscle fibers

• limited ability to regenerate muscle fibers after damage

• significant muscle damage leads to muscle fibers replaced with scar tissue

MICROSCOPIC ANATOMY: what is scar tissue?

dense ct; cannot contract but reduces power and connect and stretch. muscle is less functional than before

MICROSCOPIC ANATOMY: myostatin

knocked down: signals not as strong as they should be

knocked out: not sending signals at all; myostatin not made

MICROSCOPIC ANATOMY: sarcolemma, sarcoplasm (truth?), myoglobin, mitochondria

1. sarcolemma: plasma membrane of muscle fibers

2. sarcoplasm: cytoplasm of a muscle fiber (evreything inside the muscle fiber but not the nucleus)

• has lots of glycogen that stores glucose to release and generate ATP

3. myoglobin: protein, binds to oxygen to carry out blood.

4. mitochondria: present in rows throughout fiber

MICROSCOPIC ANATOMY: transverse tubules / aka

• what is it

• looks like

• opens to

• importance

t tubules

• invaginations (inward folding) of sarcolemma

• tunnel from surface toward center of each fiber

• open to the outside, filled with interstitial fluid surrounding the cells

• importance: signal to contract spreads, signals go through and stimulates to contract together

MICROSCOPIC ANATOMY: sarcoplasmic reticulum

• similar to

• expanded section is called

• what’s triad

system of membranous sacs

• smooth er, stores calcium to trigger contraction

• terminal cisterns = end sacs against t tubules

• triad: 1 t tubule + 2 terminal cisterns

MICROSCOPIC ANATOMY: myofibrils vs filaments

1. myofibrils = contractile elements

   1. bundles of contractile protein filaments

   2. striated

2. filaments

   1. thin = 8 nm diameter, made primarily of actin

   2. thick = 16nm, made primarily of myosin

MICROSCOPIC ANATOMY: sarcomere, z-discs, I band, A band

1. sarcomere = basic functional unit of a myofibril

2. z discs = narrow regions of dense protein, separate one sarcomere from the next (start and stop of a sarcomere)

3. I band = thin filaments only, lighter region

4. A band = length of thick filament, darker region

MICROSCOPIC ANATOMY: A band regions:

zone of overlap

h zone

m line

1. zone of overlap = edges of A band, where thin and thick filaments overlap

2. H zone = center of A band, thick filaments only

3. M line = center of H zone, line of proteins holding thick filaments in place

PRACTICE: what part of sarcomere changes in size when a muscle contracts?
think: I band, overlap zone, H zone

1. i band changes and contract

2. overlap zone increases

3. h zone decreases

PRACTICE: label this sarcomere

CONTRACTILE MUSCLE PROTEINS: what are contractile proteins?

myosin

motor protein

generate force occuring w/ contraction

1. myosin: main component of thick filaments, type of contractile protein

2. motor protein: converts chemical energy from ATP to mechanical energy

   1. 300 molecules of myosin from 1 thick filament

CONTRACTILE MUSCLE PROTEINS: myosin 2 components

1. tails = point towards M line, line parallel to each other

2. heads = extend towards thin filaments

   1. break ATP = functional area to hold myosin together

CONTRACTILE MUSCLE PROTEINS: actin

• truth?

main component of thin filaments

• each has a myosin binding site where myosin heads can attach

• can’t break ATP = can’t generate force

• acts like a rope that myosin pulls to generate force

REGULATORY MUSCLE PROTEINS: what are they?

type: tropomyosin

turn contraction on and off; associated with actin to regulate myosin’s access to actin

• tropomyosin: covers myosin binding sites on actin to get in between thin and thick proteins to block contraction

REGULATORY MUSCLE PROTEINS: troponin

• bounded to

complex proteins holding tropomyosin in place; regulates its location

• when bound to calcium, will move tropomyosin away from myosin binding sites and changes its shape

• contraction only happens when calcium is present

STRUCTURAL MUSCLE PROTEINS: what are they

• how many?

contribute to alignment of thin and thick filaments, stability, elasticity, and extensibility of myofibrils

• dozen identified

STRUCTURAL MUSCLE PROTEINS: titin

3rd most abudant protein in skeletal muscle

• extends from z disc to m line

• largest known protein

• anchors thick filament to both z discs and m line, stabilizes position of the filament

• accounts for elasticity and extensibility of myofibrils

STRUCTURAL MUSCLE PROTEINS: myomesin vs nebulin

1. myomesin = forms M line stabilizing thick filaments, binds to titin

2. nebulin = anchors thin filaments to Z discs and hold it in place

STRUCTURAL MUSCLE PROTEINS: dystrophin

links think filaments to integral membrane proteins of sarcolemma, transmits tension to tendons

CONTRACTION: sliding filament mechanism/theory

myosin heads walk along thin filaments and pulls the thin filaments towards M line so sarcomere shortens

• REMEMBER: thick and thin filaments are not shortened, just overlapping them more

SKELETAL MUSCLE FIBERS: red vs white fibers

1. red fibers = high myoglobin (related to hemoglobin)

   1. ex: red liquid on meat packaging is myoglobin leaking out from the meat, not blood

2. white fibers = low myoglobin

SKELETAL MUSCLE FIBERS: slow oxidative fibers

aka SO or type 1

• dark red - lots of myoglobin; stockpile of oxygen

• generate atp aerobically; uses atp efficiently

• slow contraction, uses atp slowly

• fatigue resistant = capable of sustained contraction, endurance

SKELETAL MUSCLE FIBERS: fast oxidative glycolytic fibers

FOG or type IIa

• red = contains some myoglobin

• generate atp both aerobically and anaerobically (glycolysis)

• faster contraction with some fatigue resistance

  • uses atp faster

  • used for walking and jogging

SKELETAL MUSCLE FIBERS: fast glycolytic fibers

FG or type IIb

• white = low myoglobin

• stores lots of glycogen

• generates ATP by glycolysis; anaerobic, least sufficient with 2 atp

• contracts strong and fast and fatigues quickly

• intense anaerobic movements of short duration; ex weight lifting

contraction of type 1, type 11a and type 11b

• type 1 motor units = fast > weak contractions

• type i + type iia = stronger contraction

• type 1 slowest, type 11a second slowest, type 11b fastest in terms of fatigue

• most skeletal muscle contain all 3 fiber types

SKELETAL MUSCLE FIBERS: exercise and muscle fibers

affects characteristics of existing fibers

1. endurance exercises = gradual transformation of some FG fibers to FOG

2. high intensity exercises = increase size and strength of FG fibers

PRACTICE: label this muscle fiber

PRACTICE: label this