Muscular System 1 Flashcards
Types of Muscular Systems
- Skeletal
- Smooth
- Cardiac
The study of the muscular tissues usually begins with the skeletal muscle & then the remaining types are compared
Myofiber
a muscle cell
Myofilaments
- bundles contained in a myofiber
- long proteins
Myofibril contains bundles of…
Myofibrils
General Characteristics of a myofiber
a muscle cell
sarcolemma- plasma membrane of myofiber
sarcoplasm- cytoplasm of a myofiber contain all the “normal” organelles of a typical cell
sarcoplasmic reticulum- endoplasmic reticulum of a myofiber
myofilaments- long protein fibers within a myofiber
2 Main Proteins In Myofilaments
- Myosin- thick filament
- Actin- thin filament
1500 myosin; 3000 actin per myofiber in skeletal muscle
Sarcomere
Basic unit of contraction in the Myofiber
Myofiber Contraction - Overview
Actin filaments are attached to protein fibers at each of their ends (Z disc)
When the Actin slide over the larger Myosin -the sarcomere shorts (Z Disc get closer together)
Each myofiber contains many sarcomeres joined end-to-end; Single muscle cell= 100,000 sarcomeres
When all sarcomeres shorten at once, the myofiber shortens
When all the myofibers shorten, the whole muscle shortens
2 Parts of a myofiber contraction
A. Mechanical Component
B. On/Off Switch Component
Sarcomere contracts means a myofiber contracts
Myofiber Contraction - Mechanical Component
What theory is used? What are the components?
Sliding Filament theory
- How a sarcomere shortens
- The action of a contraction
- sliding (“pulling”)
Components- myofilaments
- Actin: thin filament
- Myosin: thick filament
Myofiber Contraction - Mechanical Component: Myosin
- has extensions off the main protein structure
- located at each end
- called the Myosin Globular Heads
Myofiber Contraction - Mechanical Component: Myosin Globular Heads
- Form cross-bridges (bonds) to the surrounding Actin filaments
- Used to slide (pull) the Actin myofilaments toward the center
Myofiber Contraction - Mechanical Component: Process (Steps)
- At the start of a contraction -the myosin globular heads are put in the “cocked” position (like a hammer on a gun, ATP is used to achieve this position)
- When cocked, the Myosin Globular Head has stored energy (cocked & ready to fire)
- Also, the Myosin globular head is now in the correct position to cross-bridge (“grab on” to the Actin)
- Stored energy in the Myosin Globular Heads -Used to slide (pull) the Actin towards the center of the sarcomere -This pulling Action is called the Power Stroke
Myofiber Contraction - On/Off Switch Process (Steps)
- Signal travels from the brain along neurons to a muscle
- Signal reaches the muscle -All skeletal muscles MUST have a nerve connection for them to contract; neurons are called a motor neuron
- There is a space (gap) between the end of a motor neuron and sarcolemma of the muscle cell: called the Synapse
- The area of the sarcolemma on the other side of the synapse -Specialized area to receive the signal called the Motor End Plate
- The signal is transmitted from the motor neuron to the sarcolemma of the myofiber, crosses the synapse by a chemical signal (neurotransmitter), synapse to great a distance for a normal nerve impulse to cross. Neurotransmitter is the same for all skeletal muscle; Acetylcholine.
- Acetylcholine causes stored Ca2+ ions in the muscle cell’s Sarcoplasmic Reticulum to be released & enter the Sarcoplasm
- Increased Ca 2+ ions inside the sarcoplasm -This is the “switch” that allows the cross-bridge between the Actin & Myosin globular head to form -Then the Power Stroke occurs, sarcomere shortens.
Myofiber Contraction - On/Off Switch: Proteins that are associated with the Actin filaments
2 Proteins that function as part of the “switch”
- Troponin- binds Ca2+ ions
- Tropomyosin- covers the cross-bridging site on Actin
Troponin is linked to Tropomyosin to form an unit.
