Chapter 9 - Muscles and Muscle Tissues

excitability

ability to receive and respond to stimuli

contractibility

ability to shorten forcibly while stimulated

extensibility

ability to be stretched

elasticity

ability to recoil to resting length

cardiac muscle

• found only in heart

• striated, branched, and connected by intercalated discs

• involuntary

  • do not have to think for heart to beat

smooth msucle

• found in walls of hollow organs (viscera)

• not striated, spindle shaped

• involuntary

  • ‘housekeeping” functions

  • digestion, blood circulation

skeletal muscle

• muscle fibers are the longest

• striations and multinucleated

• voluntary

fascicles

muscle fibers of skeletal muscles organized into bundles

epimysium

surrounds entire muscle

• dense irregular connective tissue

• most superficial

perimysium

surrounds muscle fascicles

• intermediate

• dense irregular tissue

endomysium

surrounds each muscle fiber

• areolar connective tissue

• most deep

sarcolemma

muscle fiber plasma membrane

sarcoplasm

muscle fiber cytoplasm

myofibrils

rodlike bundle of contractile filaments (myofilaments) found in muscle fibers (cells)

• made up of chains of sarcomeres

• organelle found inside skeletal muscles

sarcomere

functional unit of muscle fiber, smallest contractile unit

• in-between z-discs

sarcoplasmic reticulum

network of smooth ER tubules surrounding myofibril

contains terminal cisterns (end sacs)

stores and releases calcium

t-tubules

tube formed by protrusion of sarcolemma deep into cell interior

• increases surface area

triad

area formed by a t-tubule with a terminal cistern on either side

• important for muscle contraction

triad relationship

t-tubules and SR membranes are linked together by integral proteins

• t-tubules: voltage sensors proteins

• SR gated calcium channels

isometric contraction

no muscle shortening

isotonic contraction

muscle shortens

muscle twitch

simplest contraction resulting from a muscle fiber’s response to a single action potential from motor neuron

varicosities

bulbous swellings

skeletal muscle contains abundant amounts of…

mitochondria - necessary for ATP production via cellular respiration

glysosomes - micro-organelles that store glycogen (glyco - sugar and somes - vesicles)

myoglobin - protein that stores oxygen (gives meat its red pigment)

myofilament

filament that constitutes myofibrils

actin and myosin

actin

thin filament

subunits bear active (binding) cites for myosin head attachments

two long fibrous actin twist together

• troponin and tropomyosin

  • calcium binding regulatory protein

anchored to Z discs

• no overlapping of thin and thick filament

troponin

protein found in thin filaments

globular protein with three polypeptide subunits

one attaches troponin to actin

another binds tropomyosin and helps position it on actin

third binds calcium ions

tropomyosin

rod-shaped protein, spiral about the actin core and help stiffen and stabilize

block myosin-binding sites on actin to that myosin heads on the thick filaments cannot bind to thin

myosin

thick filament

contain heavy and light polypeptide chains

heavy chains - form myosin tail

light chains - form myosin globular head

• bind actin subunits

connected at M-line (middle of A band)

elastic filament

composted of the protein titin

holds thick filaments in place

helps recoil after stretch

resists excessive stretching

dystrophin

links thin filaments to proteins of sarcolemma

direct phosphorylation of ADP by creatine phosphate

creatine phosphate - located in muscle fibers that transfers a phosphate to ADP to form ATP

• creatine kinase - carries out transfer of phosphate

no oxygen use

1 ATP per CP, creatine

15 seconds of energy

aerobic respiration

complete breakdown of glucose for energy

produces ATP during rest and light-to-moderate exercise

occurs in mitochondria and requires oxygen

glucose + oxygen = CO + H2O + ATP

32 ATP per glucose, CO2 and H2O

hours of energy provided

anaerobic respiration (fermentation)

incomplete breaking down of glucose

• absence of oxygen

pyruvic acid is converted to lactic acid

produces ATP 2.5 times faster, but 5% of ATP in aerobic

no oxygen needed

2 ATP per glucose, lactic acid

30-40 seconds of energy

fascia

wrapping of skeletal muscles

connective tissue that surrounds and supports muscles, bones, organs, and other structures