MUSCLE ACTION MUSCLE ACTION POTENTIALPOTENTIAL

EXCITATION-CONTRACTION EXCITATION-CONTRACTION COUPLING MECHANISMCOUPLING MECHANISM

MUSCLE ACTION POTENTIALMUSCLE ACTION POTENTIAL

• Skeletal fibers• Resting membrane

potential• -80-------90mv

• Duration of action potential

• 1-----5ms

• Myelinated fibers• Same in myelinated

fibers

About five times as in large myelinated fibers

MUSCLE ACTION POTENTIALMUSCLE ACTION POTENTIAL

• Skeletal fibers• Velocity of conduction• 3--------5ms

• Myelinated fibers• About 1/3 velocity of

conduction

SPREAD OF ACTION POTENTIAL SPREAD OF ACTION POTENTIAL TO INTERIOR OF MUSCLE FIBERTO INTERIOR OF MUSCLE FIBER• Skeletal muscle fiber is large• Action potential spreading along its

surface membrane cause no deep current flow

• Deep into the muscle fibers to the vicinity of separate myofibrils

• Transverse tubules

SPREAD OF ACTION POTENTIAL TO SPREAD OF ACTION POTENTIAL TO INTERIOR OF MUSCLE FIBERINTERIOR OF MUSCLE FIBER

• Penetrate all the way from one side of muscle fiber to another side

• T. tubules release calcium ions• Excitation-contraction coupling mechanism• Excitation of muscle fibers• Contraction

T-TUBULEST-TUBULES

• Tubules branches• Run transverse to myofibrils• Starting at cell membrane• Form branches• Interlacing with myofibrils• Originate from cell membrane and also open to

exterior• Communication with extracellular fluid• Extracellular fluid in lumen

Release of calcium ionsRelease of calcium ions

• Actuall Internal extensions of cell membrane• Action potential reaches• Sarcoplasmic reticulum• Two parts• 1.Large chambers• Terminal cisternae, abut the t tubules• 2.Longitudional tubules• Surround the surfaces of myofibrils

SARCOPLSMIC RETICULUMSARCOPLSMIC RETICULUM

• Two parts• Terminal cisternae• These are large chambers• Long longitudional tubules• Surround all myofibrils• Vesicular tubules• Excess calcium ions

CALCIUM PUMPCALCIUM PUMP

• Active calcium pump• In the walls of sarcoplasmic reticulum• Pump calcium ions away from myofibril

back to sarcoplasmic • Concentration of calcium ions upto10,000

folds inside the tubules

CALCIUM PUMPCALCIUM PUMP

CALSEQESTRINCALSEQESTRIN

• Inside the sarcoplasmic reticulum• Calsequestrin• A unique protein present• Binding of calcium ions upto 40 times

more

CALSEQESTRINCALSEQESTRIN

EXCITATORY PULSE OF EXCITATORY PULSE OF CALCIUM IONSCALCIUM IONS

The normal resting stateConcentration Too little to elicit concentration500 fold increasesThe total duration of calcium pulse lasts 1/20secContinuation of contractionContinuous series of repetitive action potential

CONTRACTION AND EXCITAION CONTRACTION AND EXCITAION OF SMOOTH MUSCLESOF SMOOTH MUSCLES

• Smaller fibers• 1-5micrometer in diameter• 20-500micrometer in length• Organization into bundles or sheets• Response to different types of stimuli• Characteristics of innervation and function

TYPES OF SMOOTH MUSCLESTYPES OF SMOOTH MUSCLES

• Multi-unit smooth muscles• Unitary smooth muscles

MULTIUNIT SMOOTH MUSCLESMULTIUNIT SMOOTH MUSCLES

• Discrete smooth muscle fibers• Independent of each other• Innervated by single nerve ending• Outer surface is covered by basement

membrane• A mixture of collagen and glycoprotein• Help to insulate fibers from one another• Control is exerted mainly by nerve signals

MULTIUNIT SMOOTH MUSCLESMULTIUNIT SMOOTH MUSCLES

CONTROL OF MULTIUNIT CONTROL OF MULTIUNIT SMOOTH MUSCLESSMOOTH MUSCLES

• Control is exerted by non-nervous stimuli• Examples• Ciliary muscles• Iris muscles• Polioerector muscles