Muskler

1. Contractility (the muscle is able to contract or shorten).
2. Excitability (the capacity to respond to a stimuli).
3. Extensibility (that a muscle can be stretched beyound its normal resting length and still be able to contract).
4. Elasticity (the ability to recoil to its original resing length).

Skeletal: Primary voluntary (expect for reflexes). Function: body movement.
Smooth: Involuntary. Function: internal processes like moving food through the system etc.
Cardiac: Involuntary. Function: pumping blood.

The connective tissue layer which surround muscle fibers, muscle fasciculi, and whole muscles is called epimysium.
Muscular fascia is located superficial to the epimysium, separates and compartmentalizes individual muscles or groups of muscles.
Sarcolemma is located inside the plasma membrane of a muscle fiber cell.

T tubules are tubelike invaginations of the sarcolemma. They occur at regular intervals along the muscle fiber and extend inward, connecting the extracellular environment with interior of the muscle fiber.

Highly organized smooth endoplasmic reticulum in the skeletal muscle fiber. It surrounds every myofibril.

Myofibrils are bundles of protein filaments inside the sarcoplasmic reticulum. One myofibrill contains two different kinds of protein filaments: myofilaments and action.

Myson myofilaments are composed of myosin molecules. Myosin molecules consist of two spindle myosin heavy chains, which create a rod portion which is lying parallel to the myosin myofilaments and to myosin heads that extend laterally.

1) The heads can bind to active sites on the actin molecules to form cross-bridges.

2) The heads are attached to the rod portion by a hinge region that can bend and straighten during contraction.

3) the heads are ATPase enzymes, which break down ATP, realising energy.

The smallest part of the mucle capable of contract. It consist of z-disk, actin myofilament, myosin myofilament, cross-bridges, tintin, and m-lines.

A motor unit is a single motor neuron and all the muscle fiber it innervates. They don't contain the same amount of muscle fibers. The more precise and delicate a muscle has to perform the smaller muscle fibers.

As the muscle lenght increases, its active actin also increases. If a muscle stretches so that the actin and myosin myofilaments within the sarcomeres do not overlap - or overlap to a very small extent - the muscle produces very little active tension when it is stimulated.

Active tension = is the force applied to an object to be lifted when a muscle contracts.
Passive tension = is the tension applied to the load when a muscle stretches but is not stimulated.

Isometric = the length of the muscle does not change but the amount of tension increases during contraction.
Isotonic = the amount of tension produced by the muscle is constant during contraction but the lenght of the muscle changes.
Concentric = are isotonic contractions in which tension in the muscle is great enough to overcome the opposoing resistance, and the muscle shortens.
Eccentric = are isotonic contractions in which tension is maintained on a muscle but the opposing resistance is great enough to cause the muscle to increase in length.

Creatine phosphat accumulates in muscle fibers, where it stores energy that can be used to synthesize ATP from ADP.
Through creatine kinase, it occurs rapidly and is able to maintain ATP levels as lons as creatine phosphat is available in the fiber.

After glycolysis (glucose with ATP synthesize to pyruvic acid and latic acid).

Slow-twitch (type I fibers) = contract more slowly, have a better developed blood supply, have more mitochondria, and are more fatigue-resistant.

Fast-twitch (type II fibers) = respond rapidly to nervous stimulation, and their myosin heads have a fast form of myosin ATPase, which allow them to break down ATP more rapidly than slow type I. This allows their cross-bridges to release and form more rapidly than thos in type I.

In humans there is no clear seperation for muscle fiber - almost all muscles have both. The amout difference , thou.

Ca^2. Make the muscle contract.

Visceral = the most common, occurs in sheets and includes the digestive, reproductive, and urinary tracts. Has numerous gap junction and make it function as one unit.

Multiunit = occurs in various configurations sheets in the walls of blood vessels, small bundles, in the arrector pili muscle. Has fewer gap junctions, and group of cells act as independent units.

1) Some visceral smooth muscle exhibits autorhythmic contractions.

2) Smooth muscle tends to contract in response to being stretched.

3) Exhibits a relatively constant tension, called smooth muscle tone, over a long period and maintains that tension in response to a gradual increase in the lenght.

4) The amplitude of contraction produced by a smooth muscle remains constant, although the muscle length varies.

Most important neurotransmitters that stimulates smooth muscle to contract are acetylcholine and norepineephrine. They must fit with the right ion receptor located at the plasma membrane to make a contraction. The ion channel decide if the neurotransmitter activate or inhibit a contraction.

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