Production of ATP 1. From creatine phosphate. When muscle fibers are relaxed they produce more ATP than they need. This excess is used to synthesize creatine phosphate (an energy rich compound).

Production of ATP 2. Anaerobic cellular respiration. Glucose undergoes glycolysis, yielding ATP and 2 molecules of pyruvic acid. Does not require oxygen.

Production of ATP 3. Aerobic cellular respiration. The pyruvic acid enters the mitochondria where it is broken down to form more ATP. Slower than anaerobic respiration, but yields more ATP. Utilizes oxygen. 2 sources of oxygen. Diffuses from bloodstream. Oxygen released from myoglobin.

Heat production Muscle contractions produce heat and as much as 70% of body heat is produced by energy produced in muscle tissue

Heat Production in muscle The contraction of a muscle is accompanied by the liberation of heat in two major phases: The initial heat is liberated during the contraction-relaxation cycle . The recovery heat is liberated in the period immediately following the contraction - cycle.

-There is also a slight amount of resting heat production from the basal metabolism of the muscle cell, which represents the normal metabolism that must be maintained to keep the cell in a living functional state.

The recovery heat results from the processes of glycolysis and oxidative-phosphorylation that restore the muscle to its normal state following contraction.

If a muscle is stimulated to perform under anaerobic conditions, only the initial heat appears, why?

The amount and the time course of initial heat production is independent of the presence of oxygen. Under anaerobic conditions, there is no recovery heat.

The initial heat is divided into the following stages : The activation heat: This is the heat produced during excitation and activation of muscle tissue . It is independent of shortening.

This is liberated during the actual shortening of a muscle. Shortening heat: This is liberated during the actual shortening of a muscle. It is independent of the load the muscle lifts ( work performed ).

Relaxation heat: This is produced at the end of an isotonic contraction when a muscle has done work by lifting a load . It consists of the mechanical work dissipated as heat while the load is lowered.

Cardiac and smooth muscle tissue O B J E C T I V E • Describe the main structural and functional characteristics of cardiac and smooth muscle tissue.

Cardiac muscle tissue

Cardiac muscle is found only in the heart. Cardiac muscle fibers have the same arrangement of actin and myosin and the same bands, zones, and Z discs as skeletal muscle fibers.

The fibers connect to one another through intercalated discs are unique to cardiac muscle fibers. intercalated discs are irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to one another, which contain both desmosomes and gab junction.

Cardiac muscle tissue remains contracted 10 to 15 times longer than skeletal muscle tissue due to prolonged delivery of Ca+2 into the sarcoplasm.

Ca2 enters the sarcoplasm both from the sarcoplasmic reticulum and from the interstitial fluid. a cardiac muscle contraction lasts much longer than a skeletal muscle twitch. Because the channels that allow inflow of Ca2 from interstitial fluid stay open for a relatively long time.

Cardiac muscle tissue contracts when stimulated by its own autorhythmic fibers. Under normal resting conditions, cardiac muscle tissue contracts and relaxes about 75 times a minute.

The mitochondria in cardiac muscle fibers are larger and more numerous than in skeletal muscle fibers. Cardiac muscle depends largely on aerobic cellular respiration to generate ATP, and thus requires a constant supply of oxygen.

Physiological characteristics of cardiac muscle Cardiac muscle obeys all – or – none law , ie . the muscle fibers contract fully if they respond at all. The action potential in cardiac muscle lasts much longer than that in skeletal muscle . This ensures the excitement of all ventricular cells and their contraction as one unit ( in unison ).

The mechanism of contraction is similar in cardiac and skeletal muscle: The electrical activity (action potential) leads to the mechanical response (contraction). As Ca2 concentration rises inside a contractile fiber, Ca2 binds to the regulatory protein troponin, which allows the actin and myosin filaments to begin sliding past one another, and tension starts to develop.

Each cardiac AP is followed by a relatively long refractory period of about 300 milliseconds. ( Refractory period is the period of increased membrane threshold immediately following an action potential )

The long period of refractoriness prevents tetanus contractions , allows the muscle to relax and permits the ventricle to fill with blood between action potentials.

Smooth muscles Smooth muscles lack the characteristic striations produced by the organized groups of actin and myosin filaments that form sarcomeres. Smooth muscle fibers contain intermediate filaments and dense bodies; the function of dense bodies is similar to that of the Z discs in striated muscle.

The filaments of smooth muscle are distributed somewhat randomly within the sarcoplasm. Smooth muscle is also sometimes called involuntary muscle because its activity arises either spontaneously or through activity of the autonomic nervous system.

Smooth muscle fibers contract in response to nerve impulses, hormones, and local factors. Thin filaments in smooth muscle do not contain troponin.

calcium does not bind to troponin but, rather, to a protein called calmodulin. calcium-calmodulin complex 'activates‘ myosin which then binds to actin & contraction (swivelling of cross-bridges) begins.

There are two types of smooth muscle tissue: 1-Visceral (single-unit) smooth muscle Tissue It is found in the skin and in the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus, and urinary bladder.

Like cardiac muscle, visceral smoothmuscle is autorhythmic. The fibers connect to one another by gapjunctions, forming a network through which muscle action potentials transmitted to neighboring fibers, which then contract in unison, as a single unit.

Smooth muscle tissue. (a) One autonomic motor neuron synapses with several visceral smooth muscle fibers, and action potentials spread to neighboring fibers through gap junctions.

2. Multiunit smooth muscle ( MUSM ): This is activated only by an incoming nerve signal. It consists of individual fibers, each with its own motor neuron terminals and with few gap junctions between neighboring fibers. Therefore , MUSM is neurogenic in character .

MUSM is found in The walls of large arteries. Airways to the lungs. Arrector pili muscles that attach to hair follicles. Muscles of the iris that adjust pupil diameter. Ciliary body that adjusts focus of the lens in the eye. Precapillary sphincters.

(b) Three autonomic motor neurons synapse with individual multiunit smooth muscle fibers; stimulation of one multiunit fiber causes contraction of that fiber only.

Smooth muscle fibers also lack transverse tubules and have only a small amount of sarcoplasmic reticulum for storage of Ca2. Although there are no transverse tubules in smooth muscle tissue ,there are small pouch like invaginations of the plasma membrane called (caveolae) that contain extracellular Ca2 that can be used for muscular contraction.

Physiology of Smooth Muscle Contraction in a smooth muscle fiber starts more slowly and lasts much longer than skeletal muscle fiber contraction. Calcium ions flow into smooth muscle cytosol from both the interstitial fluid and sarcoplasmic reticulum.

Not only do calcium ions enter smooth muscle fibers slowly, they also move slowly out of the muscle fiber, which delays relaxation. The prolonged presence of Ca2 in the cytosol provides for smooth muscle tone, a state of continued partial contraction.