Physiology Of Muscle Contractions

Front 1

Nerve signal arrices at synaptic knob causing calcium channels to open and calscium ions to enter

Back 1

Excitation

Front 2

Calcium ions trigger exocytosis of synaptc vesicles which release ACh into synaptic cleft

Back 2

Excitation

Front 3

ACh binds to receptors on motor end plate allowing sodium ions to enter muscle fiber and potassium ions to leave muscle fiber

Back 3

Excitation

Front 4

Movement of ions across sarcolemma creates muscle action potential to excite muscle fiber

Back 4

Excitation

Front 5

Muscle actin potential spreads through T-tubules into sarcoplasm

Back 5

Excitation-Contraction Coupling

Front 6

Calcium-release channels in sarcoplasmic reticulum open in calcium ions diffues into sarcoplasm

Back 6

Excitation-Contraction Coupling

Front 7

Calcium ions bind to troponin molecules on thin filaments causing them to change shape

Back 7

Excitation-Contraction Coupling

Front 8

Troponin-tropomyosin complex shifts to new position exposingmyosin-binding sites on actin filament so cross-bridges can form

Back 8

Excitation-Contraction Coupling

Front 9

Thin actin filaments slide inward over thick myosin filaments causing sarcomere to shorten

Back 9

Sliding filament mechanism

Front 10

ATP attaches to ATP-binding site on myosin head and is split by myosin ATPase to energize head

Back 10

Sliding filament mechanism

Front 11

Myosin head attaches to binding site on actin toform cross bridge

Back 11

Sliding filament mechanism

Front 12

Myosin head swivels toward center of sarcomere creating a power stroke

Back 12

Sliding filament mechanism

Front 13

Second ATP attaches to ATP-binding site on myosin head allowing it to detach from actin filament

Back 13

Sliding filament mechanism

Front 14

Myosin head forms new cross-bridge farther along thin filament to produce another power stroke

Back 14

Sliding filament mechanism

Front 15

Cycle is repeatred over and over to shorten sarcomere as long as ATP and calcium ions are present

Back 15

Sliding filament mechanism

Front 16

When nerve signals no longer arrive at NMJ, synaptic knob stops releasing ACh

Back 16

Relaxation

Front 17

Acetylcholine is broken into fragments by acetylcholinesterase

Back 17

Relaxation

Front 18

Calcium ions are actively transported out of sarcoplasm and back into sarcoplasmic reticulum where they bind to calsequestrin

Back 18

Relaxation

Front 19

Calcium ions dissociate from troponin and troponin-tropomyosin complex moves back into position to block myosin-binding sites on actin

Back 19

Relaxation

Front 20

When a person dies, calcium ions leak into sarcoplasm and bind to troponin to initiate cross-bridge formation triggeing rigor mortis within three to four hours

Back 20

Relaxation

Front 21

Force of muscle contraction depends on sarcomere length within muscle before contraction begins

Back 21

Length-tension relationship

Front 22

Maximum tension is developed when resting length of sarcomere is optimal due to degree of overlap between thick and thin filaments

Back 22

Lenth-tension relationship

Front 23

If sarcomere is over-streched, littl overlap exists between thik and thin filamens and few cross-bridges form and muscle tension falls to zero

Back 23

Length-Tension Relationship

Front 24

If sarcomere is contracted, too much overlap exists between thick and thin filaments and thick filaments crumple as they are compressed against Z discs and muscle tension falls to zero

Back 24

Length-Tension Relationship

Front 25

Nerve signal will stimulate individual muscle fiber to contract with less than maximum force so total tension produced depends on frequency of stimulation of fiber

Back 25

Motor Units

Front 26

Nerve signal will stimulate all muscle fibers in a motor unit to contract in unison

Back 26

Motor Units

Front 27

Contraction does not always involve shortening muscle but could produce only internal tension

Back 27

Isometric and isotonic contractions

Front 28

muscle fibers exert constant tension but change lengths as load is moved

Back 28

Isotonic contraction

Front 29

muscle shorens and pulls on tendon to produce movement and decrease angle at joint

Back 29

Concentrc isotonic contraction

Front 30

Muscle lengthens to maintain tension as joint angle increases

Back 30

Eccentric isotonic contraction

Front 31

Musle fibers remain same length but increase tension as load is supported

Back 31

Isometric contracion