Muscle tissue Flashcards
What is a muscle fascicle composed of?
Bundles of muscle fibers
What are myofibrils?
The principal cytoplasmic component of the muscle fiber: branched rod-like structures that extend the full length of the fiber. Made of sarcomeres.
What is the structure of myofibrils?
Repeating segments of identical sarcomeres. Ultrastructurally, composed of 2 types of myofilaments: actin and myosin.
What is the sarcolemma?
The muscle’s name for the plasmalemma.
The ____ bands are dark and the ___ bands are light.
A bands are dark
I bands are light
Striations are oriented ____ to myofibril axis.
Perpendicular
What defines the size/borders of a sarcomere?
Z line to Z line
What makes up the bulk of the sarcoplasm (muscle cell cytoplasm)?
Myofibrils
How many nuclei do cardiomyocytes have?
1 occasionally 2
What is the sarcoplasmic cone?
The lighter staining portion in a cardiomyocyte when the myofibril moves around the nucleus.
How do intercalated discs appear?
Thin basophilic lines that mark the junctions between myocytes. Perpendicular to the long axis.
What is the function of intercalated discs?
Unique characteristic of cardiac muscle. Serve to link the ends of cardiac muscle electrically and physically.
Describe the shape/appearance of smooth muscle.
Small, non-striated, spindle-shaped cells each with a single, elongated, centrally located nucleus.
What are satellite cells?
Myoblast stem cells that lie in contact with adult fibers, enclosed within the fiber’s external (basal) lamina.
Can the number of muscle fibers increase after birth?
No
What is cachexia?
Severe wasting of muscle accompanying disease states such as cancer and immunodeficiency.
Can muscle regenerate if injured?
If the basal lamina and satellite cells remain intact.
How much muscle mass and muscle strength is lost from age 20 to 80?
30% mass, 30-40% strength
What is normal age-related reduction in muscle called?
Sarcopenia
How is muscle lost due to age?
Loss of muscle fibers and atrophy of remaining fibers.
What do myoepithelial cells do?
Help expel fluids from glands
When are myofibroblasts useful?
Wound healing
What are pericytes?
Contractile/phagocytic/stem cells around blood vessels.
What are type I muscle fibers? Describe it.
Red.
Slow-twitch, oxidative.
Capable of repeated contraction without fatigue
What are type IIa muscle fibers? Describe it.
Intermediate. Fast-twitch Glycolytic-oxidative Fatigue resistant Can convert to one or the other with training
What are type IIb muscle fibers? Describe it.
White
Fast-twitch
Glycolytic
Strong and fast but fatigues easily
What part of the muscle sequesters calcium?
Sarcoplasmic reticulum using calsequestrin
What does nebulin do?
Provides a template for precise filament assembly. Controls the length of actin filament.
What does titin do?
Confers elasticity on the sarcomere, anchors the myosin to the z line.
What does desmin do?
An intermediate filament keeps sarcomeres in a vertical array (i.e. all A bands/I bands lined up)
Is muscle contraction a shortening of fibers?
No! sliding of filaments past one another.
Maximum range of contraction is related to muscle _____. Maximum strength is related to muscle ______.
Length, diameter
On PAS stain, how do red and white fibers appear?
Red stain small and pale
White stain large and dark
PAS stains glycogen
In a cytochrome oxidase stain, how do red and white fibers stain?
Red = small and dark White = large and light
What type of fiber predominates in postural fibers?
Red
What type of fiber predominates in sprinting (e.g. gastrocnemius)?
White
What determines what a muscle subtype will be?
The neuron that innervates
Myoblasts fuse to form a _____, which then assembles in a row to form a ______ which eventually forms a muscle ______.
Syncytium, myotube, muscle fiber
In a muscle fiber, remaining myoblasts are called what?
Satellite cells. Along with nuclei, move to periphery when the fiber fills with central myofibrils
No new muscle fibers are formed after ~______ weeks of gestation
24
What type of muscle contains a lot of mitochondria?
Cardiac
T-tubules are larger in diameter and located at z-lines in _____ .
Cardiac muscle
Cardiac muscle has _____s instead of triads.
Dyads
Is cardiac muscle or skeletal muscle more dependent on extracellular calcium?
Cardiac
What is ANP?
Granules located primarily in the atria that are released in response to the stretch of the atrial wall. Acts on kidneys to reduce fluid (and thus return to the heart).
What are cardiac conducting cells?
Purkinje fibers. Large cells with many gap junctions and lots of glycogen that initiate electric signaling.
What are unique gross properties of smooth muscle?
Capable of mitotic division
Can secrete fibers and nonfibrillar ECM
Exhibit plasticity
In contrast to skeletal muscle, smooth muscle nuclei are…
centrally located
What are the fine structures of smooth muscle?
Dense plaques (membrane) and dense bodies (within cell) that attach actin. Contain many gap junctions electrically connect cells ("nexus")
Cytoplasm dominated by cytoplasmic filaments
