40 Questions
Which type of muscle tissue has cells that lack striations and have slow, involuntary contractions?
Smooth muscle
What is responsible for generating the forces necessary for muscle contraction?
Actin microfilaments and associated proteins
Which type of muscle tissue is composed of elongated, often branched cells bound to one another at structures called intercalated discs?
Cardiac muscle
What is the origin of essentially all muscle cells?
Mesoderm
What are the three types of muscle tissue distinguished by?
Morphologic and functional characteristics
What is the term used to describe the process of exercise enlarging the skeletal musculature by stimulating the formation of new myofibrils and growth in the diameter of individual muscle fibers?
Hypertrophy
Which type of muscle cells have elongated nuclei located peripherally just under the sarcolemma?
Skeletal muscle fibers
What is the term for the small population of reserve progenitor cells adjacent to most fibers of differentiated skeletal muscle?
Muscle satellite cells
Which connective tissue layer surrounds each bundle of muscle fibers termed a fascicle?
Perimysium
What do collagens in the connective tissue layers of muscle primarily serve to do?
Transmit mechanical forces generated by contracting muscle cells
Which protein binds to tropomyosin and regulates the actin-myosin interaction?
Troponin
What protein anchors actin filaments perpendicularly on the Z disc?
Titin
What is the main reason for the light and dark banding pattern in sarcomeres?
Thick and thin myofilament arrangement
Which protein is responsible for connecting thick myofilaments to the Z disc?
Titin
What forms transient crossbridges between thick and thin filaments in muscle fibers?
Myosin
What triggers the release of Ca2+ from the terminal cisterns of the sarcoplasmic reticulum?
Depolarization signal at triads
What provides precise control of muscle activity by innervating single muscle fibers?
Single motor neurons
What do individual striated muscle fibers exhibit in terms of contraction?
Either all the way or not at all
Which sensory receptors act as proprioceptors in skeletal muscles?
Muscle spindles
What do Golgi tendon organs detect to regulate motor nerve activity?
Increases in tension within tendons
What holds the thick filaments in place at the M line in a sarcomere?
Myomesin
What triggers the release of Ca2+ ions into the cytoplasm around thick and thin filaments during muscle contraction?
Depolarization of the sarcolemma
What prevents myosin heads from binding to actin in resting muscles?
Tropomyosin blocking
Which enzyme catalyzes the transfer of phosphate groups from phosphocreatine to ADP for ATP supply during muscle contraction?
Creatine kinase
What is the role of acetylcholinesterase in muscle contraction?
Removes acetylcholine
Which characteristic helps in determining the fiber type in skeletal muscle?
Density of surrounding capillaries
What is the main energy source for fast glycolytic muscle fibers during rapid contractions?
Anaerobic metabolism of glucose
What causes a muscle to appear dark or red in color?
Presence of a high number of mitochondria
Which is a unique characteristic of cardiac muscle cells when compared to skeletal muscle cells?
Central location of nuclei
What are the main features that make fast glycolytic muscle fibers specialized for rapid, short-term contraction?
Dependence on anaerobic metabolism and few capillaries
Why are the less abundant regions of each intercalated disc filled with gap junctions?
To promote impulse conduction and contraction of cardiac muscle cells in various directions simultaneously.
How does cardiac muscle fiber contraction differ from skeletal muscle fiber contraction?
It is regulated by autonomic innervation affecting the frequency of impulses.
What role does atrial natriuretic factor (ANF) play in the body?
It affects Na+ excretion and water balance in the kidneys.
Why does cardiac muscle have a higher percentage of mitochondria compared to slow oxidative skeletal muscle fibers?
To support rapid impulse conduction and contraction through high energy production.
What distinguishes smooth muscle from cardiac and skeletal muscle?
Specialization for slow, steady contraction influenced by autonomic nerves.
Which of the following is true regarding the cross sections of smooth muscle cells?
Small plasmalemma invaginations compartmentalize signaling components.
What is the function of caveolae in smooth muscle cells?
Control the release of Ca2+ that initiates contraction.
How do smooth muscle actin filaments differ from those in striated muscle?
Use calmodulin and Ca2+-sensitive myosin light-chain kinase to produce contraction.
What is a characteristic feature of the myofilaments in smooth muscle cells?
Thin and thick myofilaments crisscross the sarcoplasm obliquely.
How is stimulation propagated in smooth muscle cells to achieve synchronous contraction?
With the help of gap junctions allowing synchronous contraction.
Study Notes
Muscle Tissue Classification
- Smooth muscle tissue cells lack striations and have slow, involuntary contractions.
- Cardiac muscle tissue is composed of elongated, often branched cells bound to one another at structures called intercalated discs.
- Skeletal muscle tissue has cells with elongated nuclei located peripherally just under the sarcolemma.
Muscle Cell Origin and Development
- Essentially all muscle cells originate from the mesoderm.
- The process of exercise enlarging the skeletal musculature by stimulating the formation of new myofibrils and growth in the diameter of individual muscle fibers is called hypertrophy.
Muscle Cell Structure
- The three types of muscle tissue are distinguished by the presence or absence of striations, the type of contraction, and the location of the nuclei.
- Collagens in the connective tissue layers of muscle primarily serve to provide structural support and tensile strength.
- The protein tropomyosin binds to and regulates the actin-myosin interaction.
- The protein titin anchors actin filaments perpendicularly on the Z disc.
Muscle Contraction Mechanism
- The main reason for the light and dark banding pattern in sarcomeres is the arrangement of actin and myosin filaments.
- Myosin is responsible for connecting thick myofilaments to the Z disc and forming transient crossbridges between thick and thin filaments in muscle fibers.
- The release of Ca2+ ions from the terminal cisterns of the sarcoplasmic reticulum is triggered by the action potential.
Muscle Fiber Characteristics
- Individual striated muscle fibers exhibit all-or-nothing contraction.
- Muscle spindles and Golgi tendon organs act as proprioceptors in skeletal muscles, detecting muscle length and tension to regulate motor nerve activity.
- The M line holds the thick filaments in place in a sarcomere.
Muscle Fiber Types
- Fast glycolytic muscle fibers are specialized for rapid, short-term contraction, with a high concentration of glycogen and myoglobin, and are characterized by a fast contraction speed and low fatigue resistance.
- Slow oxidative muscle fibers are specialized for slow, sustained contraction, with a high concentration of mitochondria and myoglobin, and are characterized by a slow contraction speed and high fatigue resistance.
- Cardiac muscle cells have a unique characteristic of being branched and interconnected, allowing for coordinated contraction.
Neurotransmission and Muscle Contraction
- Acetylcholinesterase breaks down acetylcholine, preventing continuous muscle contraction.
- The enzyme creatine kinase catalyzes the transfer of phosphate groups from phosphocreatine to ADP for ATP supply during muscle contraction.
- Atrial natriuretic factor (ANF) helps regulate blood pressure by reducing blood volume.
Smooth Muscle Characteristics
- Smooth muscle cells are distinguished from cardiac and skeletal muscle cells by the absence of striations and the presence of caveolae.
- The cross sections of smooth muscle cells are irregular and have a central nucleus.
- Smooth muscle actin filaments are shorter and more scattered than those in striated muscle.
- The myofilaments in smooth muscle cells are characterized by the presence of dense bodies and a lack of Z discs.
- Stimulation in smooth muscle cells is propagated through gap junctions to achieve synchronous contraction.
Learn about the structure and function of intercalated discs in cardiac muscle cells, which play a crucial role in rapid impulse conduction and synchronized contraction. Understand how the contractile apparatus in cardiac muscle cells is similar to skeletal muscle.
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