Muscle tissue- Skeletal, cardiac and smooth Flashcards
what are the three main types of muscle?
skeletal muscle
Cardiac muscle
smooth muscle
what are the cells of skeletal muscle?
long, cylindrical, multinucleated cells, the cells form obvious striations
what is the function of skeletal muscle?
volentary movement
locamotion
manipulation of the environment
facial expression
voluntary control
where is skeletal muscle located?
in skeletal muscles attached to bones or occasionally to skin
why do skeletal muscles look striated?
due to proteins and filaments involved in contraction
what are the layers of the skeletal muscle?
epimysium
Endomysium
Perimysium
Fascicles
what is the epimysium?
connective tissue sheathing the muscle
what is the endomysium?
protecting individual muscle fibers
what is the perimysium?
sheaths bundles of muscle fibers
what are the fascicles?
Bundles of muscle fibers
what is a muscle fiber?
a single muscle cell
what is a myofibril?
a fibre within a single muscle cell
can be hundreds of myofibrils in a muscle fiber
what is a motor neuron?
initiates the signal for skeletal muscle contraction
what is the neuromuscular junction?
where the motor neuron meets the skeletal muscle
what is a sarcolemma?
cell membrane of muscle fibre
what is a transverse T-tubule?
Invagination of sarcolemma into cell
what is the sarcoplasmic reticulum?
simila to endoplasmic reticulum. Store and release Ca 2+
what is the role of Ca2+ in skeletal muscle contraction?
Used to initiate contraction of the myofibril contractile units.
how does a muscle contract?
binding of thin filaments to thick filaments allows contraction to occur.
what makes up the thin filament?
Actin
Tropomyosin
Troponin
what is actin in thin filaments?
contain binding sites for thick filament
what is thin filament tropomyosin?
Protein strand that covers binding sites in relaxed state
what is thin filament troponin?
sits on tropomyosin and responds to signals for contraction
what is myosin?
Main protein of thick filament, elongated with distinctive head
how does the sarcomere contract?
the head of myosin binds and “walks” along thin filament
what causes the striations?
sarcomere zones
what is a sarcomere I-band?
only thin filament in the sarcomere (no overlap with the thick filaments)
what is a sacromere A-band?
where there is thick filament
what is the H-zone?
where there is only thick filament
what is the neuromuscular junction?
where the motor neuron joins with the plasma membrane of a skeletal muscle
how is a muscle fibre action potential?
when acetylcholine is released which causes the membrane to be depolarised
what releases Ca2+ into the muscle cells?
sarcoplasmic reticulum
how does the Action potential spread?
along the sarcolemma and then into the T-tubule
how does Ca2+ causes sarcolemma contraction?
binding of Ca2+ to troponin causes movemen to tropomyosin, exposing the binding sites for the myosin from the thick filament to bind to actin of the thin filament
how does the sarcomere contract?
Myosin head changes shape and pulls thin filament to centre of sarcomere
ATP binds to myosin, and energy is utilized to detach myosin, reverting shape
Myosin head binds to another actin molecule further towards the Z-line
what happens to the I-band when the sarcomere contracts?
The I-band decreases
what happens to the A-band when the sarcomere contracts?
The A-band does not change as it is only dependednt on the length of the thick filaments
what happens to the H-band when the sarcomere contracts?
The H-band decreases
what happens to the distance between Z-lines when the sarcomere contracts?
decreases
what happens within skeletal muscle during rigor mortis?
Ca2+ leaks from sarcoplasmic reticulum into muscles fibres following death, exposing actin binding sites
Myosin automatically binds and pulls thin filament (no ATP required)
New molecules of ATP needed for the unbinding of myosin and actin are not produced
Thus, myosin remains attached to actin and thus the contracted muscles do not relax
what is nemaline myopathy?
Muscle weakness, swallowing dysfunction, impaired speech
mutations that cause changes in the thin filaments
what are the features of cardiac muscle cells?
Branching, striated, generally uninucleate cells that interdigitate at specialized junctions (intercalated discs)
what is the function of cardiac muscles?
As it contracts, it propels blood into the circulation; involuntary control
where is cardiac muscle located?
The walls of the heart
what forms intercalated discs?
Desmosomes
Fascia adherens
Gap junctions
what is the role of desmosomes in the cardiac muscle?
anchor cells to each other via the cytoskeleton
what is the role of Fascia adherens in the cardiac muscle?
anchor actin filaments and transmit contractile forces
what is the role of gap junctions in the cardiac muscle?
transmit contraction stimulus
what is a disease caused by desmosome dysfunction?
Arrhythmogenic right ventricular cardiomyopathy
what are the cells of smooth muscle?
Spindle-shaped cells with central nuceli; no striations; cells arranged closely to form sheets
what is the function of smooth muscle?
Propels substances or objects (food stuffs, urine, a baby) along interal passageways; involuntary control
where is smooth muscle located?
Mostly in the walls of hollow organs
how do smooth muscles contract?
with contractile filaments that criss-cross the cell
how are contractile filaments anchored?
to the cell at focal densities in the cytoplasm and focal adhesion densities on the cell membrane
how do smooth muscles contract?
works on the sliding filament theory as skeletal muscle. Thin actin molecules slide over thick myosin molecules and the smooth muscle cell takes on a globular shape.
what are focal densities?
Focal densities are functionally and structurally similar to Z line
how do actin filaments work in smooth muscle?
Actin filaments link to both sides of focal densities
how do myosin filaments work in smooth muscle?
Myosin filaments partially overlap actin like in skeletal muscle
how do intermediate filamets work in smooth muscle?
intermediate filaments provide cytoskeletal structure between densities
