Anatomy Chapter 9A: Muscles

Front 1

Muscle Fibres

Back 1

Elongated multinucleate cell with a striated appearance.

Front 2

Sarcolemma

Back 2

Plasma membrane of a muscle fibre.

Front 3

Sarcoplasm

Back 3

Cytoplasm of a muscle fibre.

Front 4

Skeletal Muscle Tissue

Back 4

Striated muscle responsible for voluntary motion.

Front 5

Cardiac Muscle Tissue

Back 5

Striated muscle of the heart responsible for non-voluntary contractions at a relatively steady rate.

Front 6

Smooth Muscle Tissue

Back 6

Nonstriated muscle of the visceral organs responsible for nonvoluntary conduction of fluids and other substances through internal body channels.

Front 7

Excitability / Irritability

Back 7

The ability to receive and respond to a stimulus.

Front 8

Contractility

Back 8

The ability to shorten forcibly when adequately stimulated.

Front 9

Extensibility

Back 9

The ability to be stretched or extended.

Front 10

Elasticity

Back 10

The ability of a muscle fibre to recoil and resume its resting length after being stretched.

Front 11

Muscle Functions

Back 11

Producing movement, maintaining posture, stabilizing joints, and generating heat (skeletal muscle = most responsible for creating heat)

Front 12

Endomysium

Back 12

Fine sheath of connective tissue consisting mostly of reticular fibres that surrounds each individual muscle fibre.

Front 13

Fascicle

Back 13

Discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath.

Front 14

Perimysium

Back 14

Fibrous connective tissue which surrounds each fascicle.

Front 15

Epimysium

Back 15

An overcoat of dense irregular connective tissue which surrounds the whole muscle.

Front 16

Series Elastic Components

Back 16

Connective tissue sheaths and tendons which contribute to the natural elasticity of muscle tissue.

Front 17

Myofibril

Back 17

Rodlike contractile element which occupies most of the muscle cell volume. Composed of sacromeres arranged end to end.

Front 18

Sarcomere

Back 18

The contractile unit of a muscle fibre, composed of myofilaments made up of contractile proteins.

The distance between two Z discs.

Consists of an A band flanked by two half I-bands.

Functional unit of skeletal muscle.

Front 19

Insertion

Back 19

The movable bone to which a muscle is attached.

Front 20

Origin

Back 20

The immovable or less movable bone to which a muscle is attached.

Front 21

Aponeurosis

Back 21

Sheetlike, flat connective tissue tendon which anchors muscle to connective tissue covering of a skeletal element or to the fascia of other muscles.

Front 22

Direct/Fleshy Attachments

Back 22

The epimyseium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage.

Front 23

Indirect Attachments

Back 23

The muscle's connective tissue wrappings extend beyond the muscle either as a ropelike tendon or an aponeurosis. Tendons conserve space.

Front 24

Myoglobin

Back 24

A red pigment that stores oxygen in muscle cells.

Front 25

Glycosomes

Back 25

Granules of stored glycogen in muscle cells.

Front 26

A Band

Back 26

The dark, central region of a sarcomere consisting of thick filaments and thin filaments. The thin filaments don't overlap, leaving lighter region called the H zone.

Front 27

I Band

Back 27

Lighter bands on either end of a sarcomere, consisting only of thin filaments. Contains the midline interruption known as a Z disc.

Front 28

H Zone

Back 28

Lighter stripe in the midsection of the A band that corresponds to the region where there is only thick fibres and no thin fibres.

Front 29

M line

Back 29

Dark line at the centre of the H zone

Front 30

Z disc

Back 30

Darker area interrupting the midline of the I bands.

Front 31

Thick Filaments

Back 31

Myosin-based filaments extending the entire length of the A band in the sarcomere.

Front 32

Thin Filaments

Back 32

Actin-based filaments that extend across the I band and partway into the A band of a sarcomere.

Front 33

Myosin

Back 33

Protein which makes up thick filaments.

Consists of a rodlike tail made from two interwoven heavy polypeptide chains and two globular heads.

The heads link the thick and thin filaments together, forming cross bridges.

The heads also contain ATP binding sites and ATPases to generate energy for contraction.

Front 34

Actin

Back 34

Protein that coils back on itself to create a helix, forming the thin filament.

Front 35

G Actin

Back 35

Globular actin. The actin subunit which bears the active sites to which the myosin heads attach during contraction.

Front 36

F Actin

Back 36

Fibrous actin. Polymer of actin which forms up the backbone of each thin filament.

Front 37

Tropomyosin

Back 37

Two strands of this rod-shaped protein spiral about the actin core to help stiffen the thin filament.

In a relaxed muscle fibre, they block actin's active sites so that the myosin heads cannot bind to the thin filament.

Front 38

Troponin

Back 38

A three polypeptide complex consisting of TnI (actin-binding/inhibitor), TnT (tropomyosin-binding/positioner), and TnC (calcium binding)

Front 39

Agonist

Back 39

Muscle that has primary responsibility for an action.

Front 40

Synergist

Back 40

Muscle that has the same action as the prime mover.

Aids the agonist.

Front 41

Antagonist

Back 41

Muscle that opposes the action of the prime mover/agonist.

Front 42

Rectus

Back 42

Parallel to the long axis.

Front 43

Oblique

Back 43

At an angle to the long axis.

Front 44

Sarcoplamsic Reticulum

Back 44

An elaborate smooth ER with interconnecting tubules which surround each myofibril.

Regulates intracellular levels of ionic calcium.

Front 45

Terminal Cisternae

Back 45

Large, perpendicular cross channels of the sarcoplasmic reticulum at the A band-I band junctions.

Flank T-tubules.

Front 46

T-tubules

Back 46

Elongated tubes formed by the penetration of the sarcolemma into the muscle cell at each A band-I band junction.

Conducts impulses to the deepest regions of the muscle cell and to every sarcomere. Impulses signal for the release of Ca++ from the adjacent terminal cisternae. Ensures that every myofibril in the muscle fibre contracts at virtually the same time.

Front 47

Triads

Back 47

Successive groupings of the three membranous structures (terminal cisterna, T tubule, terminal cisterna)

Front 48

Contraction

Back 48

The activation of myosin's cross bridges, which are the force-generating sites.

Shortening occurs when the tension generated by the cross bridges on the thin filaments exceeds the forces opposing shortening.

Front 49

Relaxation

Back 49

Contraction ends when the cross bridges become inactive and the tension generated declines.

Front 50

Sliding Filament Theory of Contraction

Back 50

During contraction, the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree.

Overall, the distance between successive Z discs is reduced, the I bands shorten, the H zones disappear, and the contiguous A bands move closer together but do not change in length.

Front 51

Calcium in Muscle Contraction

Back 51

(1) The AP propagates along the sarcolemma and down the T tubules.

(2) Transmission of the AP past the triads causes the terminal cisternae to release Ca++

(3) Some of the Ca++ bind to troponin, which changes shape and removes the blocking action of tropomyosin.

(4) Myosin heads attach and pull the thin filaments toward the centre of the sarcomere.

(5) The short-lived Ca++ signal ends & the continually active ATP-dependent Ca pump moves Ca back to the sarcoplasmic reticulum.

(6) Tropomyosin blockade is re-established. Relaxation occurs.