7.2 Characteristics Of Skeletal Muscle Flashcards
___ with its associated connective tissue, constitutes approximately 40% of body weight
Skeletal muscle
Causes strations
thick and thin microfilaments
Ability of the muscles to shorten with force
Contractility
Capacity of skeletal muscle to respond the a stimulus
Excitability
Means that skeletal muscles can be stretched to their normal resting length and beyond to a limited degree
Extensibility
Ability of skeletal muscles to recoil to their original resting length after they have been stretched
Elasticity
Connective tissue sheath surrounding the skeletal msucle
Epimysium
Epimysium is also called ___
Muscular fascia
Numerous visible bundles composing the muscle
Muscle fasciculi
Muscle fasciculi are surrounded by loose connective tissue called ____
Perimysium
Several muscles cells composing a fasciculus
Muscle fibers
Loose connective tissue surrounding a muscle fiber
Endomysium
A single cylindrical fiber, with several nuclei located at its periphery
Muscle fiber
Largest human muscles are up to___
30cm long and 0.15mm in diameter
Cell membrane of the muscle fiber
Sarcolemma
Tubelike invaginations along the surface of the sarcolemma which occur at regular intervals along the muscle fiber and extend inward into it.
transverse tubules or T tubules
A highly organized smooth endoplasmic reticulum
Sarcoplasmic reticulum
Connects the sarcolemma to the sarcoplasmic reticulum
T tubules
Has a relatively high concentration of Ca2+
Sarcoplasmic reticulum
Cytoplasm inside each muscle fiber
Sarcoplasm
Threadlike structures that extend from one end of the muscle to the other
Myofibrils
Major protein fibers making up the myofibrils
Actin myofilaments and myosin myofilaments
Actin and myosil myofilaments re arranged into highly ordered, repeating units called ____ which are joined end to end to form the myofibrils
Sarcomeres
Actin myofilaments are also called
thin filaments
3 components making up actin myofilaments
actin, troponin, tropomyosin
Resemble two minute strands of pearls twisted together, have attachement sites for the myosin myofilaments
Actin myofilaments
____ molecules are attached at specific intervals along the actin myofilaments which have binding sites for Ca2+
Troponin
______ filaments are located along the groove between the twisted strands of actin myofilament subunits
Tropomyosin
Myosin myofilaments are also called
thick myofilaments
These resemble bundles of minute golf clubs
Myosin myofilaments
3 important properties of myosin heads
- The heads can bind to attachment sites on the actin myofilaments
- they can bend and straighten during contraction
- they can break down ATP, releasing energy
Basic structural and functional unit of skeletal muscle
Sarcomere
Smallest portion of skeletal muscle capable of contracting
Sarcomere
A network of protein fibers forming an attachment site for actin myofilaments
Z disk “Zwischensheibe”
Consists of only actin myofilaments, spans each Z disk and ends at the myosin myofilaments
I band “Isotropic”
A darker, central region in each sarcomere
A band “Anisotropic”
Second light zone in the center of each sarcomere which consists of only myosin myofilaments
H zone
The dark staining band where myosin myofilaments are anchored in the center of the sarcomere
M line “Mittelscheibe”
Inside of cell membranes is negatively charged compared to outside of the cell membrane
Polarized
Charge difference that occurs because there is an uneven distribution of ions across the cell memberance
Resting membrane potential
3 reasons for the developing of resting membrane potential
- The concentration of K+ inside the cell membrane is higher than the outside of the cell membrane
- The concentration of Na+ outside the cell membrane is higher that the inside of the cell membrane
- The cell membrane is more permeable to K+ than to Na+
Inside of the cell membrane if positively charged
Depolarization
The change back to the resting membrane potential
Repolarization
The rapid depolarization and repolarization of the cell membrane
Action potential
Are specialized nerve cells that stimulate muscles to contract
Motor neurons
They generate action potentials that travel to skeletal muscle fibers
Motor neurons
Each branch of the axon of a motor neuron forms a junction with a muscle fiber called ____
Neuromuscular junction
Refers to the cell-to-cell junction between a nerve cell and either another nerve cell or an effector cell, such as in a muscle or a gland
Synapse
A single motor neuron and all the skeletal muscle fibers it innervates constitutes a ____
motor unit
An enlarged axon terminal
Presynaptic terminal
The apace between the presynaptic terminal and the muscle fiber membrane
synaptic cleft
Components of a Triad
2 terminal cisternae and a T tubule
Acts as a conduit that enables action potential to reach sarcoplasmic reticulum
Triad
Muscle fiber membrane
Postsynaptic cleft
Small vesicles in each presynaptic terminal
Synaptic vesicles
Functions as a neurotransmitter, a molecule released by a presynaptic nerve cell that stimulates or inhibits a postsynaptic cell
Acetylcholine
Enzyme that rapidly breaks down the acetylcholine released into the synaptic cleft between the neuron and the muscle fiber
Acetylcholinesterase
The sliding of actin myofilaments past myosin myofilaments during contraction
Sliding filament model of muscle contraction
Is formed between the actin and myosin myofilaments when the exposed attachments sites on the sites of the actin myofilament bind to the heads of the myosin myofilaments
Cross-bridges
States that the threshold stimulus can cause a muscle to contract to the fullest or none at all
Lucas Law or All or None Law
Condition when a person dies and no ATP is available to release cross-bridges causing the muscles to stiffen
Rigor mortis
Is the contraction of a muscle fiber in response to a timulus
muscle twitch
A cycle of rapid contraction and relaxation occuring in a muscle fiber following the occurence/application of a neural stimulus to the muscle in vivo or application of electrical stimulus during experimentation/experimental setting
Twitch
The time between the application of a stimulus and the beginning of contraction
lag phase or latent phase
Is the time during which the muscle contracts
Contraction phase
The time during which the muscle relaxes
Relaxation phase
The force of contaction of individual muscle is increased by rapidly stimulating them
Summation
A sustained contraction that occurs when the frequency of stimulation is so rapid that no relaxation occurs
Tetanus
When the number of muscle fibers contracting is increased by increasing the number of motor units stimulated, and the muscle contracts with more force
Recruitment
Requires O2 and breaks down glucose to produce 38 ATP, CO2, and H2O
Aerobic respiration
Does not require O2, and results from the breakdown of glucose to yield 2 ATP and lactic acid
Anaerobic respiration
Provides a means for storing energy that can be used rapidly to hep maintain an adequate amount of ATP in a contracting muscle fiber
Creatine phosphate
A state of reduced work capacity
Fatigue
Results when muscle fibers use ATP faster than they produce it and when the effectiveness of CA2+ to stimulate actin and myosin is reduced
Muscular fatigue
Occurs when there is too little ATP to bind to myosin myofilaments
Physiological contracture
Common type of fatigue that involves the central nervous syatem rather than the muscles themselves
Psychological fatigue
The length of the muscle does not change, but the amount of tension increases
Isometric Contractions
The amount of tension produced by the muscle is constant during the contraction, but the length of the muscle decreases
Isotonic Contractions
Isotonic contractions in which muscle tension increases as the muscle shortens
Concentric contractions
Isotonic contractions in which tension is maintained in a muscle, but the opposing resistance causes the muscle to lenghten
Eccentric contractions
The constant tension produced by body muscles over long periods of time
Muscle tone
Twitch fibers that contain type I myosin as the predominant or even exclusive type
Slow-twitch fibers
Twitch fibers that contain either type IIa or type IIb myosin myofilaments
Fast-twitch fibers
Enlargening of muscle fibers
Hypertrophy
Undifferentiated cells just below the endomysium
Satellite cells