Muscle Tissue Flashcards
Muscle Tissue
- contains cells called myocytes or myofibrils that shorten (contract) when stimulated by the nervous system and produce movement in the body
- 3 types of muscle tissue
What are the 3 types of muscle tissue?
(1) Skeletal
(2) Cardiac
(3) Smooth
What are the 5 characteristics of muscle tissue?
- Contractability
- Excitability
- Extensibility
- Elasticity
- Conductivity
Contractility
- microfilaments (actin and myosin) that make-up muscle tissue allowing it to shorten in size
- shortening of muscle tissue pulls on bones, skin, etc to cause movement
What allows muscle tissue to contract?
Microfilaments (Actin, Myosin)
Excitability
- muscle tissue can respond to stimuli from the nervous system (somatic or autonomic) or the endocrine system
Conductivity
- muscle tissue can move electrical signals through its plasma membrane
- electrical signal provides the directive for contraction
Extensibility
- muscle tissue can stretch without damage which allows the opposing muscles to remain undamaged during the opposing movement
Elasticity
- muscle tissue can change in size (extend or contract) and return to its normal size/shape
- this allows the body to create movement and return to its resting form after that movement
Skeletal Muscle
- attached to bones and skin
- when it contracts it causes bones or skin to move
- contractions of this muscle help move blood (skeletal muscle pump), maintain posture and serve as sphincters
- they are voluntary (conscious/subconscious) under somatic control
- group of fasicles that are bundled together to form the muscle units in the body
- Histology: long, cylindrical, multinucleated (nuclei along edges) myocytes that are striated
Myocyte
- cells that make-up skeletal muscles that vary in length
- created by multiple myoblasts fusing into one cell
- nuclei are pushed to the periphery of the cell by the cytoplasmic components
- most of the cytoplasm is taken up by myofibrils that allow the fiber to contract and cause the myocyte to appear striated (sarcomere) in a longitudinal view
- Histology: cylindrical, multinucleated
Satellite Cells
- undifferentiated myoblast that hangs out on the outside of the myocyte for small damage repair
Sarcolemma
- the plasma membrane that surrounds the myocyte
Transverse Tubule (T-tubule)
- invaginations of the sarcolemma into the myocyte
- allows the nerve signal to pass quickly along the muscle fiber’s length and allows the whole cell to contract at one time
- these are present in skeletal and cardiac muscle tissue
What types of muscle tissue contain Transverse Tubules?
- Skeletal
- Cardiac
Myofibril
- internal structures found within the sarcoplasm of the myocyte that runs the entire length of the cell
- contains a collection of proteins (myofibrils) that allow the cell to contract
- found in skeletal and cardiac muscle tissue
What types of muscle tissue contain Myofibrils?
- Skeletal
- Cardiac
Sarcoplasmic Reticulum
- surrounds each myofibril
- modification of the smooth endoplasmic reticulum
- stores calcium ions that are integral in the muscle contraction process
- when it associates with a t-tubule (forms the triad) it helps with the release of calcium (integral in muscle contraction)
- in the cardiac myocyte this is not as developed and smooth myocytes lack these structures
Sarcoplasmic Reticulum
- surrounds each myofibril
- modification of the smooth endoplasmic reticulum
- stores calcium ions
- when it associates with a t-tubule (forms a triad) it helps with the release of calcium (integral in muscle contraction)
- this structure is not as developed in the cardiac myocyte and is absent in smooth myocytes
Terminal Cisternae
- the endpoints of the sarcoplasmic reticulum
- release calcium needed for muscle contraction via voltage-gated calcium pumps
- not as developed in cardiac cells and contact the t-tubule less often (exist in dyads)
Endomysium
- the areolar connective tissue that surrounds individual myocytes
- helps compartmentalize the cell from the cells around it
- provides the architecture for the nervous and vascular supply to travel along with the entire cell
Fascicle
- group of myocytes bundled together
Perimysium
- the dense irregular connective tissue that surrounds and compartmentalizes a fascicle
- provides the framework for the neurovasculature to travel
Epimysium
- dense irregular connective tissue covering that surrounds groups of fascicles together to create the overall named skeletal muscle
- provides a pathway for the main neurovasculature to move across the muscle before branching to supply the various parts of the muscle
Tendon
- all the -mysiums interconnect with each other at the tendinous insertion of the muscle to bone or skin
- when muscle contracts this structure ensures the muscle stays anchored to the origin and insertion, and ensures the forces are distriubuted in a manner that keeps the skeletal muscle together
Sarcomere
- the subunit of the myofibril that is responsible for muscle contraction
- each myofibril has thousands of sarcomeres lined up next to each other
- Histology: provides the striated appearance of skeletal and cardiac muscle tissue
What is the thin filament made-up of?
Actin
What are the thick filaments made-up of?
Myosin
Actin (Thin Filament)
- protein that is made-up of two globular chains of monomers
- Tropomyosin interacts with actin to cover myosin-binding sites to prevent contraction
- Myosin moves the actin towards the center of the sarcomere causing contraction
Myosin (Thick Filament)
- protein that is made-up of two intertwined chains with a head that can bind to actin, and move actin when ATP is present
Tropomyosin
- protein that interacts with actin to cover myosin-binding sites to prevent contraction
Z-Line (Z-Disc)
- the endpoint of one sarcomere and the beginning of the next – marks the endpoints
- each sarcomere runs from Z-disc to Z-disc
- the thin filaments (actin) anchor to this and when they move towards each other, muscle attraction occurs
- it is contained within the I-band and can be distinguished from the I-band by its darker appearance
During contraction the __-___s are brought closer together
Z-Discs
I-Band
- component of the sarcomere
- when the myofibril is relaxed, it only contains thin filaments (actin); does not contain myosin
- when the myofibril is contracting and the actin is moving, this area/band becomes smaller/reduced; when muscle is fully contracted the I-Band isn’t visible
- Microscope: fibers are less dense so they appear lighter
A-Band
- part of the sarcomere that contains both thick and thin filaments
- during full contraction this area fills the sarcomere, stretching from Z-disc to Z-disc
- includes further subdivision of H-Zone and M-Line
- Microscope: this area contains a lot of actin and myosin so appears darker
H-Zone
- part of sarcomere – subdivision of A-Band
- contains only thick filaments when muscle is contracted
- during contraction, actin moves into this area, causing it to disappear
- Microscope: area appears slightly lighter and is located near the center of the sarcomere
M-Line
- located at the center of the sarcomere – subdivision of A-Band
- the location where the thick filaments (myosin) attach
- this and the Z-disc are visible markers of the sarcomere during contraction
- the structure that marks the center at all times
Where does Myosin attach?
M-Line
What are the two visible markers of the sarcomere during contraction?
- Z-Disc
- M-Line
Sliding Filament Mechanism
- when a myocyte (sarcomere) contracts, the thin filaments (actin anchored to the Z-line) are pushed towards the M-line (center of sarcomere)
- As the thin and thick filaments overlap, the sarcomere shortens
- this process occurs along the length of every sarcomere in a myofibril within a myocyte, causing the entire muscle to contract (shorten)
- when troponin binds with calcium it moves tropomyosin which allows actin and myosin to interact with each other and this mechanism can then occur
How are skeletal muscle fiber types divided into groups?
Based on the type of contraction that occurs, and their ATP supply
What are the 3 types of skeletal muscle fibers?
- Slow Oxidative (Type 1 fibers, slow-twitch)
- Fast-Oxidative Glycolytic (Type 2a fibers, fast-twitch)
- Fast Glycolytic (Type 2b fibers, fast-twitch)
What fiber type are Slow-Oxidative Fibers?
Type 1, slow-twitch
What fiber type are Fast-Oxidative Glycolytic Fibers?
Type 2a, fast-twitch
What fiber type are Fast Glycolytic Fibers?
Type 2b, fast-twitch
Slow Oxidative Skeletal Muscle Fiber (Type 1, Slow-Twitch)
- fibers that appear red due to myoglobin (oxygen storage)
- the contraction is slower
- the fibers are the smallest in diameter and less powerful
- due to their myoglobin supply, high capillary level and mitochondria, they can carry out the oxidative process for longer periods without fatigue
- located in muscles that help with muscle tone
- Histology: stain darker than other fiber types
Fast Oxidative-Glycolytic Skeletal Muscle Fiber (Type 2a, Fast-Twitch)
- least numerous type of fibers
- intermediate in diamter
- they have raster ATPase which means faster, more powerful muscle contractions
- they undergo aerobic respiration and contain less myoglobin
- this type of muscle fiber is used in everyday use, such as the muscles of the legs
- Histology: stain an intermediate color
Fast Glycolytic Skeletal Muscle Fiber (Type 2b, Fast-Twitch)
- the largest in diameter
- most prevalent of the muscle fiber types
- they can create ATP quickly through glycolysis providing power and speed
- only able to contract for short burst because of their anaerobic process (lack of myoglobin and limited capillaries)
- they fatigue quickly
- used for limited-duration activities such as weight lifting or eye movements
- Histology: appear whiter
Where is cardiac muscle tissue found in the body?
In the walls of the heart (myocardium)
Cardiac Muscle Tissue
- found only in the walls of the heart (myocardium)
- cell structure is somewhat similar to the skeletal myocyte but the t-tubules and sarcoplasmic reticulum form dyads
- nucleus is normally centralized (can sometimes have 2)
- the tissue is under involuntary control (does not need outside innervation but is impacted by hormones and autonomic NS regulation), is heavily vascularized, and helps in moving/circulating blood through the circulatory system
- connective tissue that surrounds the myocytes and myocyte bundles creates the cardiac skeleton that assists in the heart functioning correctly
- Histology: short, striated (containing sarcomere/myofibrils), branched
Intercalated Disc
- dark staining line found in between the cardiac muscle fibers
- many gap junctions (and desmosomes) present in this area that allow electrical current to pass from one cardiac cell (cardiomyocyte) to the next to propagate the signal for heart muscle contractions
- these occur at Z-lines (fascia adherens connect two cells actin)
Smooth Muscle Tissue (Visceral Muscle Tissue)
- located in the walls of most internal organs such as blood vessels, digestive, urinary, reproductive, and respiratory organs
- muscle fibers are short and wide in the center and taper at the ends
- the central nucleus is elliptical
- myocytes in this tissue can undergo mitosis, and they can also produce an extracellular matrix
- this muscle is under involuntary control (autonomic NS and hormones)
- assists in the movement of substances through the body by squeezing (peristalsis) or regulating the diameter of passageways
- gap junctions help interconnect cells in this muscle tissue
- contractions of this muscle type are typically slower and more sustained than the other muscle tissue types
- resistant to fatigue
Myocytes in which tissue type are able to undergo mitosis?
Smooth Muscle Tissue
Dense Body (Cytoplasmic Density)
- component of smooth muscle
- the actin and myosin anchor to these sites on the outside of the cell (the actin and myosin crisscross the cell internally through the sarcoplasm)
- when they contract they cause the cell to shrivel and get shorter
Caveolae
- component of smooth muscle
- invaginations of the sarcolemma of a smooth myocyte
- these are thought to help with intracellular signaling and calcium sequestering
What structure is the basal lamina of a muscle fiber part of?
Endomysium
What do the two lateral components of a muscle fiber triad represent?
Sites for calcium sequestering and release
(at each sarcomere two terminal cisterns of the SR contact a deep invagination of the sarcolemma; the SR is specialized for Ca2+ release and sequestration)
What characteristic is unique to cardiac muscles?
They are branched
What characteristic is unique to smooth muscle?
Thin filaments attach to dense bodies
(thin actin filaments attach to dense bodies that are located throughout the sarcoplasm of smooth muscle cells; contraction causes the cells to shorten in length)
In cardiac muscle, what structure contains numerous gap junctions, desmosomes, and adherens junctions?
Intercalated Discs
(this structure represents the interface btwn adjacent cardiac cells)
Order of Sarcomere Landmarks/Structures (Z Disc to Z Disc)
“IZ Allie Hilger Married?
(1) I Band
(2) Z Disc (center of I Band)
(3) A Band
(4) H Zone
(5) M Line (center of H Band)
