Histology of Muscle Flashcards
what is the main function of muscle tissue?
why do muscle cells generate force?
what are the 2 classes of muscle tissue?
what is the difference between striated muscle and smooth muscle?
What is striated muscle associated with?
where is striated muscle also found?
Where is smooth muscle found?
The main function of muscle tissue is to generate force for movement of tissues and organs in the human body.
Muscle cells generate force for motility by contracting.
Muscle tissue found in the human body falls into two classes: striated and smooth muscle. Striated muscle undergoes very powerful contractions of short duration.
Smooth muscle undergoes slower, weaker but prolonged contractions. Striated muscle is associated with the skeletal system and generates force to move the bones of the body (skeletal muscle).
Striated muscle is also found in the lining of the heart chambers and is responsible for the powerful contractions of the heart walls that expel blood from the heart (cardiac muscle).
Smooth muscle is found in the lining of the digestive system where it slowly pushes food through the abdominal cavity. Smooth muscle is also found in the lining of blood vessels.
How is skeletal muscle subdivided?
What does each fasicle consist of?
what are muscle fibers?
what are muscle cells called?
what gets ensheathed by interconnected connective tissue?
what is the connective tissue surrounding the entire muscle linked to?
What does the interconnection of connective tissue associated with muscle allow?
Skeletal muscles are subdivided into units called muscle fascicles.
Each fascicle consists of numerous skeletal muscle fibers.
Muscle fibers are single cells. (Muscle cells are called fibers because they are very long and narrow).
The entire muscle, the individual fascicles within a muscle, and the individual muscle fibers within a muscle are ensheathed by interconnected connective tissue.
The connective tissue surrounding the entire muscle is linked to tendons and ligaments. The interconnection of connective tissue associated with muscle allows the force from the muscular contraction to be transferred to move the bones of the body.
What is endomysium?
What is perimysium?
What is epimysium?
The connective tissue surrounding muscle fibers (remember-single cells!) is called endomysium. The connective tissue sheath surrounding muscle fascicles is called perimysium, and the connective tissue sheath surrounding the entire muscle is called epimysium.
What shapre are muscle fibers?
Where do muscle fibers originate from?
What do muscle fibers contain?
What are myofibrils?
What is the composition of a myfibril? and how are they arranged?
What does this arrangement allow?
Muscle fibers are cylindrically-shaped cells with multiple, peripherally-located nuclei. They originate from the fusion of many muscle precursor cells.
Muscle fibers contain myofibrils in their cytoplasm.
Myofibrils are groups or units of cytoskeletal filaments. Each myofibril is striated when viewed along its length.
All of the myofibrils in a single muscle fiber are aligned so that their striations are in register. This highly organized pattern of registered striations is what allows skeletal muscle fibers to generate powerful contractions.
What is the contractile apparatus of the muscle fibers?
How are resting myfibril organized?
what are the dark bands in myofibrils called?
what are the light bands in myofibrils called?
What is at the center of each I-band?
What is a sarcomere?
What is the contractile unit of the myofibril?
What happens to all the sarcormeres during contraction?
Myofibrils are the contractile apparatus of the muscle fibers. In a resting (non-contracted) myofibril alternating dark and light bands of approximately equal width are visible. The dark bands are called A-bands, and the light bands are called I-bands. At the center of each I-band, dark lines called Z-lines or Z-disks are found. The distance between two consecutive Z-lines defines a sarcomere. The sarcomere is considered to be the contractile unit of the myofibril; During a contraction, all of the sarcomeres located in a myofibril shorten.
What does each sarcomere contain that overlaps?
What are thin filaments?
what are thick filaments?
why are myofibrils striated?
Where do thin filaments originate from?
What helps bind thin filaments to z-disks?
How far can thin filaments extend?
Where do thick filaments originiate from?
How far can thick filaments extend?
What is the distance that corresponds to A-bands?
What is the distance the corresponds to an I-band?
What can an I-band also be though of?
What happens during contraction whith the sets of thin filaments?
What does this cause?
Each sarcomere contains an overlapping array of thick and thin cytoskeletal filaments. Thin filaments are actin filaments and thick filaments are myosin II molecules. The striated appearance of myofibrils is due to an incomplete overlap between thick and thin filaments. Thin filaments originate from the Z-disk (the edge of the sarcomere). A protein called alpha-actinin helps bind thin filaments to Z-disks. Thin filaments extend towards but do not reach all the way to the center of the sarcomere. Thick filaments originate from the center of the sarcomere and extend outwards. Thick filaments do not extend all the way out to the Z-disks. The distance spanned by the thick filaments corresponds to the A-bands (dark appearing bands), while the distance between two groups of thick filaments (in two adjacent sarcomeres) corresponds to I-bands. The I-band can also be thought of as the parts of the thin filaments (in two adjacent sarcomeres) that do not overlap with the thick filaments. During contraction, the two sets of thin filaments in a sarcomere move closer together to each other. This increases the amount of overlap between the thin and thick filaments, decreases the length of the sarcomere, and causes the I-band to disappear.
what are the 2 main events that happen during contraction of skeletal muscle?
what are the 2 modifications that muscle fibers have to help with these physiological changes?
-what happens first?
What does this allow?
Where are T-tubules specifically located?
What so muscle fibers also contain ?
What is associated with the T-tubles at the A-I intersection plane?
What lies along the terminal cisternae alongside the T-tubules?
What does this allow for?
What forms a triad?
Contraction of skeletal muscle involves two main physiological events. 1) Depolarization of the plasma membrane (sarcolemma) of the muscle fiber (similar to an action potential), and 2) Release of Ca2+ from the endoplasmic reticulum (sarcoplasmic reticulum) of the muscle fiber into the cytoplasm of the muscle. The muscle fiber has two modifications of their organelles that help convey these physiological changes to all the myofibrils in the muscle fiber. First, the plasma membrane of muscle fibers contains large infoldings called T-tubules that extend into the cytoplasm of the fiber, and contact all of the myofibrils in a muscle fiber. This allows all myofibrils in the muscle fiber to be depolarized simultaneously. T-tubules are specifically located in the plane between the A and the I-bands, near the myosin II heads. Muscle fibers also contain a very extensive endoplasmic reticulum called the sarcoplamsic reticulum that envelopes each myofibril. At the A-I intersection plane, the sarcoplasmic reticulum is associated with the T-tubules. There the sarcoplasmic reticulum forms terminal cisternae that lie alongside the T-tubules. This allows for efficient release of Ca 2+ ions at the region of interaction of thick and thin filaments. Two terminal cisternae of the sarcoplasmic reticulum are associated with each T-tubule, forming a triad when observed in cross-section.
What is the composition of cardiac muscle?
What makes cardiac muscle unique?
Cardiac muscle is also striated (i.e. contains A- and I- bands) and undergoes strong contractions that require large amounts of energy. However, cardiac muscle contractions are continuous and initiated by inherent (involuntary) mechanisms.
What is the name for cardiac muscle?
What is the space between cardiac myocytes filled with?
What does the endomysium between cardiac myocytes support?
Morphologically, cardiac muscle cells (myocytes) are branched cylindrical cells (shorter than skeletal muscle fibers) with one or two nuclei that are centrally located. The space between cardiac myocytes is filled with a delicate collagenous tissue, analogous to the endomysium of skeletal muscle. The endomysium between cardiac myocytes supports the rich capillary network required by cardiac myocytes to meet their high metabolic demands.
What do cardiac muscle cells contain?
what is the signature feature of cardiac myocytes?
What are the 2 distinct regions of intercaladed disks?
What is found along the transverse side of the intercalated disk?
What is one type of cell-cell junction found here?
What attaches to fascia adherins?
Where is a gap junction found?
What are gap junctions?
what does this result in?
where are the difference function of intercalated disks found?
Cardiac muscle cells contain intercalated disks at the interfaces between adjacent cells. Intercalated disks are a signature feature of the cardiac myocytes, and appear in histological sections like a jagged stairstep dark line.
Intercalated disks consist of two distinct regions.
Along the transverse side of the intercalated disk cell-cell adhesion junctions are present. One cell-cell junction found here is the fascia adherens (analogous to adherens junctions in epithelial cells). The actin (thin filaments) of cardiac myocytes attach to the fascia adherens.
The longitudinal region of the intercalated disk between two adjacent cells is a gap junction. Gap junctions are essentially openings that allow a flow of ions between two adjacent cells.
Gap junctions electrically couple adjacent cardiac myocytes together.
This results in cardiac muscle cells contracting in synchrony.
The different functions of the intercalated disks (mechanical adhesion and electrical coupling) are localized to different regions of the disks- the transverse and the longitudinal portions.
What are some similarities between cardiac muscle and skeletal muscle?
What is a difference between the sarcoplasmic reticulum in cardiac myocytes and skeletal muscle?
How does this differ in the number of tubules that lie along the T-tubules in cardiac muscle vs skeletal muscle?
Where are dyads of cardiac muscle found?
What is the difference in caldium release in the SR in cardiac cells vs skeletal muscle?
Where do cardiac muscles obtain large amounts of calcium?
Where does calcium enter in cardiac myocyte? how does this differ to skeletal muscle cells?
Each sarcomere in a cardiac muscle possesses the same structure as its skeletal muscle counterpart, and the bandings of cardiac muscle cells are identical to those of skeletal muscle, including alternating A and I bands. However, the sarcoplasmic reticulum of cardiac myocytes is not as extensive as that of skeletal muscle fibers. Thus, only one tubule of the sarcoplasmic reticulum lies alongside the T-tubules of cardiac myocytes (dyads in cardiac muscle versus triads in skeletal muscle). Dyads of cardiac muscle cells are also located at the Z-plane rather than at the A-I band interface. The sarcoplasmic reticulum of cardiac muscle cells also does not release as much Ca2+ as does the sarcoplasmic reticulum of skeletal muscle cells. Cardiac myocytes also obtain large amounts of Ca2+ from the extracellular space. The Ca2+ enters into the cardiac myocyte intracellular space through their T-tubules, which have very large diameters compared to T-tubules of skeletal muscle cells.
what makes smooth muscle unique?
What does fusiform mean?
What happens to the shape of the nucleus when smooth muscle contracts?
what makes contraction of smooth muscle different from skeletal muscle?
Where is smooth muscle found?
What type of configuration is smooth muscle often found?
Smooth muscle is non-striated muscle. Morphologically, smooth muscle cells are fusiform: slightly elongated cells with tapered ends and a centrally located nucleus. During contraction of smooth muscle, the nucleus takes on a corkscrew shape. Smooth muscle contraction is weaker, slower and prolonged compared to skeletal muscle. Smooth muscle contractions are involuntary. Smooth muscle is found in linings of the viscera such as the gut and in the linings of blood vessels. Smooth muscle is often found in layers, with cells in different layers oriented perpendicular to one another.
What kind of filaments does smooth muscle contain?
What do the thick and thin filaments connect to?
Where are dense bodies located?
What is a type of protein is found in dense bodies?
what do dense bodies also link the thin and thick filaments to what?what does this help in?
what do dense bodies also connect to?
Smooth muscle contains thin and thick filament assemblies but they are oriented randomly in the cell. In smooth muscle cells thin and thick filament groups connect to dense bodies, which contain proteins similar to those found in Z-disks. Dense bodies are located randomly throughout the plasma membrane of the smooth muscle cells. One protein found at dense bodies is alpha-actinin. Dense bodies also link the thin/thick filaments to the intermediate filament network which helps transmit the forces of contraction throughout the cell. Dense bodies also connect to the external lamina, thus transferring contractile forces outside the cell.
what do smooth muscle cells not have?
What does smooth muscle cells have?
What does caveolae release?
How does this mode of regulation differ to the regulation in skeletal muscle?
Smooth muscle cells do not contain T-tubules or an extensive sarcoplasmic reticulum. Rather, smooth muscle contain caveolae which are vesicles located just beneath the plasma membrane. Caveolae release Ca2+ ions, which through a series of steps exposes the actin binding sites in the myosin chains. This mode of regulation of contraction involves more steps than the regulation of contraction in skeletal muscle.
