Chapter 9 - Muscular System Flashcards
General Properties of Muscle Tissue
-Contractibility
-Excitability
-Extensibility
-Elasticity
Contractibility
The ability of muscles to shorten forcefully/contract
Excitability
The capacity of muscles to respond to electrical stimuli
Extensibility
Muscles can be stretched beyond their normal resting length and still be able to contract
Elasticity
The ability of muscles to spring back to their original resting lengths after being stretched
Functions of the muscular system
-Movement
-Maintenance of posture
-Respiration
-Production of body heat
-Communication
-Constriction of organs and vessels
-Contraction of the heart
Epimysium
Layer of CT that surrounds a muscle (many fasicles)
Perimysium
-Loose CT surrounding a group of muscle fibers
-Passage for blood vessels and nerves
Fascicle
Bundle of muscle cells
Endomysium
Loose CT separating individual muscle fibers within each fascicle
Caveolae
-In smooth muscle cells
-Indentations in sarcolemma
-Many act like T tubules
What do smooth muscle cells have instead of Z disks?
-Dense bodies
-Have non-contractile intermediate filaments
Myosin phosphatase
Causes relaxation in smooth muscle cells
Triad
Formed from two terminal cisternae and their associated T tubule
Myofibrils
-Bundles of protein filaments
-Contain myofilaments that cause contraction
Z disk
-Filamentous network of protein
-Serves as attachment for actin myofilaments
I bands
-Lighter-staining region
-Each contains a Z disk
-Extends to end of myosin myofilaments
A bands
-Central darker-staining region
-Overlapping actin and myosin myofilaments (except at center)
H zone
Region in A band where actin and myosin do not overlap
M line
-Middle of H zone
-Delicate filaments holding myosin in place
Depolarization
Inside of the plasma membrane becomes less negative
Repolarization
Return of the resting membrane potential
Stages of Action Potential
-Resting: All Na and some K channels closed; inside cell more (-) than outside
-Depolarization: Na channels open
-Repolarization: Na channels closed, more K channels open
Excitation-Contraction Coupling
Links mechanical and electrical components of contraction
Muscle relaxation
-Ca2+ moves back into sarcoplasmic reticulum by active transport (needs ATP)
-Ca2+ moves away from troponin-tropomyosin complex
-Complex reestablishes its position and blocks binding sites
Isometric Contractions
-No change in length but tension increases
-Postural muscles
Isotonic Contractions
Change in length but tension constant
Motor unit
-A single motor neuron and all muscle fibers innervated by it
-Large muscles have units with many muscle fibers, small/delicate muscles have units with only a few
Treppe
-Graded muscle response
-Occurs in muscle rested for long period
-Each subsequent contraction is stronger than the last until all are equal (after a few stimuli)
-More Ca2+ in sarcoplasm, not all taken up into SR after each contraction
Incomplete tetanus
Muscle fibers partially relax between contractions
Complete tetanus
No relaxation between contractions
Active tension
-Force applied to an object to be lifted when a muscle contracts
-Increases or decreases as a muscle fiber changes in length
Passive tension
Tension applied to load when muscle stretches but is not stimulated
Sub-threshold stimulus
No action potential - no contraction
Threshold stimulus
Action potential - contraction
Submaximal stimuli
Stronger stimuli that produce action potentials in axons of additional motor units
Maximal stimulus
Action potentials are produced in axons of all motor units of a muscle
Size principle
During recruitment, small motor units are recruited first, then larger motor units
Muscle tone
Constant tension by muscles for long periods of time
Types of Isotonic Contractions
-Concentric (overcomes opposing resistance and muscle shortens)
-Eccentric (tension maintained, muscle lengthens)
Physiological contracture
State of fatigue where due to lack of ATP neither contraction nor relaxation can occur
Sarcopenia
Muscle atrophy
Power stroke
Movement of myosin head during contraction
Recovery stroke
Returning of myosin head to low-energy position
Major ATP-dependent events for relaxation
-Sodium-potassium pump to return to resting membrane potential
-ATP required to detach myosin heads from active site for recovery stroke
-ATP needed for active transport of Ca2+ into SR
Major factors that increase number of cross-bridges that form
-Frequency of stimulation
-Muscle fiber diameter
-Muscle fiber length at time of contraction
