Skeletal Muscle: Structure and Function Flashcards
What are the 3 functions of skeletal muscle?
Force production for motion and breathing, force production for postural support and heat production during cold stress.
What is the myonuclear domain?
region of cytoplasm surrounding an individual nucleus
Name the 3 separate layers of connective tissue in skeletal muscle.
Epimysium, Perimysium and Endomysium.
Which is the outer layer of skeletal muscle?
Epimysium
Inner layer of connection tissue?
Endomysium
Middle layer of skeletal muscle?
Perimysium
What is a fascicle?
a small bundle of muscle fibres
What is the sarcolemma?
the cell plasma membrane surrounding a muscle fibre
what is a satellite cell?
undifferentiated cell found adjacent to skeletal muscle fibres. They can fuse with existing muscle fibres and contribute to hypertrophy. They can form a new muscle fibre following muscle injury.
What are myofibrils?
the portion of muscle containing the thick and thin contractile filaments
What is myosin?
contractile protein in the thick filament of a myofibril that contains the cross-bridge that can bind actin and split ATP to cause tension development.
What is actin?
a structural protein of muscle that works with myosin in permitting muscular contraction
What are sarcomeres?
the basic contractile unit of a muscle fiber
What is the sarcoplasmic reticulum?
a membranous structure that surrounds the myofibrils of muscle cells. The Terminal cisternae that store Ca++ needed for muscle contraction is here.
What is the transverse tubule?
an extension of the muscle membrane that conducts the action potential into the muscle to depolarize the terminal cisternae
What is terminal cisternae?
portion of sarcoplasmic reticulum near the transverse tubule containing the Ca++ that is released upon depolarization of the muscle
What are motor neurons?
the somatic neutron that innervates skeletal muscle fibres
What is a motor unit?
a motor unit and all the muscle fibres innervated by that single motor neuron. Responds in an “all or none” matter to a stimulus.
What is the neuromuscular junction?
synapse between axon terminal of a motor neuron and the motor end plate of a muscle’s plasma membrane
What is end plate potential (EPP)?
depolarization of a membrane region by a sodium influx.
How does endurance and resistance training stimulate positive adaptations to the NMJ?
Training increases the size of the NMJ, expands the number of synaptic vesicles (containing acetylcholine) and increasing the number of acetylcholine receptors
What is the sliding filament/swinging cross-bridge model?
the process of muscular contraction. This process proposes that muscle shortening occurs due to movement of the actin filament OVER the myosin filament.
What is excitation-contraction coupling?
sequence of events in which the nerve impulse (action potential) depolarizes the muscle fibre leading to muscle shortening by cross-bridge cycling. Trigger to initiate muscle contraction.
How does muscle contraction occur?
via the binding of the myosin cross-bridge to actin and the repeated cycling of myosin pulling on the actin molecule resulting in the shortening of the muscle fibre.
How does muscle relaxation occur?
occurs when the motor neuron stops exciting the muscle fibre and calcium is pumped back into the sarcoplasmic reticulum. The removal of calcium causes a position change in tropomyosin which blocks the myosin cross bridge binding site resulting in muscle relaxation.
What is troponin?
a protein associated with actin and tropomyosin that binds Ca++ and initiates the movement of tropomyosin on actin to allow the myosin cross-bridge to touch actin and initiate contraction.
What is tropomyosin?
a protein covering the actin-binding sites that prevent the myosin cross-bridge from touching actin
Define muscle fatigue.
reduction in muscle power output that results from decreased muscle force generation and/or decreased shortening velocity.
What are muscle cramps?
spasmodic and involuntary muscle contractions
What are the two major theories of the cause of exercise-induced muscle cramps?
1: Caused by dehydration and electrolyte imbalance.
2: cramps originate in the central nervous system.
Which theory of muscle cramps is more accurate?
Motor neuron hyperexcitability is likely the general underlying cause of muscle cramps induced by exercises therefore they probably originate in the central nervous system.
List the muscle fiber types. And then if applicable, break them down into their subcategories.
Slow, Type I fibers. Fast, type II fibers. Type II can be broken down into type IIa and type Iix fibers.
When muscle fibres are viewed, what colour do each appear?
Type I are blue. Type IIa are green. Type IIx are black.
List the 3 biochemical characteristics of muscle that are important to muscle function.
Oxidative capacity, type of myosin isoform, abundance of contractile protein within the fiber.
What are the performance characteristics when companies muscle fiber types?
1: maximal force production; 2: speed of contraction; 3: maximal power output; 4: efficiency of contraction
How is power calculated?
Power = Force x Shortening velocity
What does Vmax represent?
highest speed at which a fiber can shorten.
Describe type I fibers.
contain large numbers of oxidative enzymes and are highly fatigue resistant. They are more efficient than type II fibers, produce a lower specific force than fast fibers and possess a slow maximal shortening velocity compared to the later.
Describe type IIx fibers.
fibers that have a relatively small number of mitochondria, a limited capacity for aerobic metabolism and less resistant to fatigue than slow fibers.
Describe type IIa fibers.
fibers that contain biochemical and performance (fatigue) characteristics that are between type IIb and type I fibers. Also known as intermediate muscle fibers.
What is the fastest muscle fiber type in humans?
Type IIx
Power athletes (sprinters) generally possess a large percentage of which muscle fiber type?
Type II muscle fibers.
Endurance athletes (marathon runners) typically possess a larger amount of which muscle fiber type?
Type I muscle fibers.
What is a muscle action?
term used to describe the movement movement (shortening or lengthening)
What is concentric contraction?
muscle shortens
What is eccentric contraction?
muscle lengthens
What is isometric contraction?
muscle contracts but does not change length
What is a twitch?
the tension generating response following the application of a single stimulus to muscle
Muscle Action-Relaxation Graph Parts.
Stimulus. Latent period. Contraction. Relaxation.
Describe the difference between fast and slow muscle fibers in terms of contraction.
Fast muscle fibers contract in a shorter time period than do slow fibers because: the speed of shortening is greater in fast fibers than in slow fibers due to the sarcoplasmic reticulum in fast fibers releasing Ca++ at a faster rate and fast fibers possess a high ATPase activity resulting in a more rapid splitting of ATP and a quicker release of energy required for contraction.
List the four factors that the amount of force exerted during muscular contraction are dependant on.
Number and types of motor units recruited. Initial length of muscle. Neural stimulation of the motor units. Contractile history of the muscle.
What is summation?
repeated stimulation of a muscle that leads to an increase in tension compared to a single twitch. (addition of successive twitches)
What is tetanus?
highest tension developed by a muscle in response to a high frequency of stimulation.
What is post activation potentiation (PAP)?
refers to the increase in muscle force production that occurs following a series of sub maximal muscle contractions.
