HESI A2 Exam: Muscular System
• Which type of muscle does not have visible striations?
• What is the thick filament found in sacromeres? What does it do?
• What is a well-known demyelinating disorder which prevents electrical impulses along the nerve cell from being transferred effectively?
• Messages that are communicated between the brain and the muscular system through electrical signals are called _________
Intro
The functional characteristics of muscle involved in carrying out various functions are contractibility, elasticity, excitability and extensibility as well.
Muscles only do work when they contract. They do not actively push things further apart. Muscle cells contract and exert a pulling force.
Smooth, Cardiac and Skeletal Muscle
Smooth muscle is responsible for involuntary muscular contractions and is found in the walls of visceral organs such as the gastrointestinal tract. Smooth muscle can also be found in blood vessels. You would find smooth muscle cells in both the small and large intestine. However, they do not have visible striations when viewed under a microscope. This is actually the reason it is called smooth muscle.
Cardiac muscle is also involuntary but only occurs in the heart and only cardiac muscle cells pass electrical signals to each other
.
Skeletal muscle cells are voluntary striated muscle cells that control body movements.
Cartilage is part of the skeletal system, not the muscular system. While it might be confusing at first, skeletal muscle is part of the muscular system, as are smooth and cardiac muscle.
Muscular System
Muscle fibers are composed of myofibrils, and multiple muscle fiber bundles form a fascicle. A muscle fascicle is a bundle of muscle fibers.
Myofibrils are long filaments that run parallel to each other to form muscle (myo) fibers.
Myofilaments are filaments of myofibrils constructed from proteins.
Skeletal muscle is made up of these fascicles, which are bundles of cells surrounded by connective tissue.
There are sarcomeres within each myofibril. Sarcomeres are the unit of the muscle cell. A sacromere is the basic unit of striated muscle tissue.
There is both a thick and a thin filament found in sarcomeres. The thin filament is actin and the thick filament is myosin. Actin serves as the anchor point for myosin, which contracts and pulls actin closer together, shortening the sarcomere during muscle contraction.
Contraction of a muscle occurs when myosin binds and releases actin.
Neural Regulation
Action potentials are messages that are communicated between the brain and the muscular system through electrical signals. These action potentials travel along the axon.
Myelin helps to increase the speed of the electrical impulse along the nerve cell. Multiple sclerosis, which is a demyelinating disorder, prevents these impulses from being transferred effectively.
A synapse allows a neuron to send a chemical signal to another neuron. A synapse is a space between a terminal branch of a neuron and another neuron.
A neurotransmitter, such as dopamine, is released at the synapse.
A buildup of lactic acid leads to muscle fatigue. Lactic acid decreases the pH in the muscle fibers, and a lower pH interferes with calcium binding and muscle contraction.
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