Comparison of Properties of: Skeletal, Smooth & Cardiac Muscle Comparison of functional organisation, electrical properties and mechanical properties of skeletal, cardiac and smooth muscle

Myosin Molecule

Motor Unit

Cardiac Muscle Major types- atrial, ventricular & specialized excitatory and conductive muscle fibers. Characteristic features: Striated, having myofibrils that contain actin & myosin filaments, T system at Z line. Syncytial arrangement of fibers

Cardiac Muscle Forms the bulk of the wall of the heart. Like skeletal muscle tissue, it is striated (the muscle fibers contain alternating light and dark bands (striations) that are perpendicular to the long axes of the fibers). Unlike skeletal muscle tissue, its contraction is not under conscious control (Involuntary).

Intercalated Discs At intercalated discs the cell membranes fuse forming permeable “communicating” junctions (gap junctions) that allow free diffusion of ions. so the AP travel easily from one cardiac muscle cell to the next. Thus, cardiac muscle is a functional syncytium so when one cell gets excited, the AP spreads instantaneously to all of them.

Morphological & Functional characteristics of the three types of muscles

Points of differences Molecular basis of contraction Excitation contraction -coupling

Contractile process The contractile process is activated by calcium ions in all the three types of muscle However, the source of the calcium ions in skeletal muscle is the sarcoplasmic reticulum, which provides virtually all the calcium ions needed for contraction In most smooth muscle SR is not well developed & almost all the calcium ions required for contraction enter the muscle cell from the extracellular fluid at the time of the action potential

Role of Ca ions-Cardiac Muscle Cardiac muscle requires extracellular calcium ions for contraction. Like sk muscle, the initiation and upshoot of the AP in ventricular muscle cells is derived from the entry of Na ions across the cell memb. & an inward flux of ECF Ca ions sustains the depolarization (plateau) of cardiac muscle cells.

Smooth Muscle- - Contractile State is controlled by hormones & local chemical signals Also develop tonic & phasic contractions in response to changes in load / stretch or length. Relaxation is brought about by removal of Ca++ from cytosol & stimulation of myosin phosphatase.

Smooth Muscle Contractile Activity Determined primarily by the: Phosphorylation state of the light chain of myosin— a highly regulated process. In some smooth muscle cells, the phosphorylation of the light chain of myosin is maintained at a low level even in the absence of external stimuli. This results in “smooth muscle tone” and its intensity can be varied.

Characteristic Features of Smooth Muscle 1. no troponin instead uses calmodulin 2. no sarcomeres (thin filaments attach to dense bodies via actinin) 3. Action potential- activated Ca release 4. contraction- phosphorylation of myosin by Myiosin light -chain kinase (MLCK) 5. relaxation- dephosphorylation of myosin by Myosin light-chain phosphatase ( skeletal relaxed

What maintains skeletal muscle tone ?

Compare and contrast the electrical and mechanical properties of the three types of muscles

Electrical properties of three muscle types

Electrical Properties Skeletal MCardiacSmooth RM P -90mvsVent.-90mvs Sp -60mvs Unstable Avg -50mvs AP Dur Sharp depol. repo. 2-4ms Dep plateau 2ms, 200ms Spikes, plateau, Slow waves

Skeletal Muscle

Mechanical Properties Skeletal MCardiacSmooth dura tion Twitch Brief contract Varies with type of fib. Vent: 300ms Avg 1-3Sec 0.2 – 30Sec Can be tetanized Can not be tetanized

Twitch contraction of some muscles (extraocular) are rapid and brief, others (gastrocnemius, soleus) are slower and longer

Cardiac muscle can not be tetanized. Explain the physiological basis.

Phases of AP of Cardiac Muscle

Neural Control Smooth muscle - controlled by the autonomic nervous system; Cardiac muscle - modulated by neural activity (autonomic nervous system) and hormones Skeletal muscle –dependent on innervation & by axons of the motor neurons

Learning Outcomes Describe Morphological & Functional characteristics of the three types of muscles Compare the actin myosin organization of skeletal and smooth muscle. Compare arrangement of muscle fibers in a motor unit and syncytial cardiac muscle.

Learning Outcomes ( Cont. ) Compare and contrast the electrical and mechanical properties of the three types of muscles Briefly describe the role of gap junctions in the heart and in the visceral smooth muscle

Learning Outcomes ( Cont. ) Outline the molecular basis of smooth muscle contraction, How does it differ from that in skeletal muscle. Cardiac muscle can not be tetanized. Explain the physiological basis. Describe the role of cystolic Ca in the Skeletal, Cardiac and Smooth muscle contraction and its source.

Thank You