Muscle Flashcards
what is a myocyte
an individual muscle cell
what is the sarcoplasm
cytoplasm of a muscle cell
what is the sarcolemma
plasma membrane of a muscle cell
what are the 3 types of muscles
skeletal, smooth, and cardiac
what is are muscle cells derived from
mesoderm
what is the function of skeletal muscle
movement of skeleton, under voluntary motor control
describe skeletal muscle cells
-multinucleate, large cytoplasm, striations, “irregular polygon shaped”
what are syncytia
muscle cells formed from fusion of myoblasts into multinucleate myotubes
what do myotubes do
synthesize contractile proteins which assemble into sarcomeres
what happens when nuclei of skeletal muscle cells move to the periphery of the cell
they lose their ability to proliferate
what are the layers in skeletal muscle organization
endomysium, perimysium, and epimysium
what does the endomysium cover
individual muscle fibers
what does the perimysium surround
fascicles
what are fascicles in muscle cells
several muscle fibers bound together
what makes up muscle
many fascicles together
what does the epimysium surround
the entire muscle
where are blood vessels and nerves found in skeletal muscle cells
they follow the epimysium and perimysium
what type of nerve innervate fast muscle fibers
fast nerves
what type of nerves innervate slow twitch muscle fibers
slow nerves
what types of myosin are there
fast and slow
describe type 1, slow twitch muscle fibers
-small fibers
- large amounts of myoglobin
- large number of mitochondria
-resistant to fatigue but only generate moderate muscle tension
- common in peripheral limbs
what type of respiration do type 1 slow twitch muscle fibers use
aerobic respiration for oxidative metabolism
describe type 2, fast twitch muscle fibers
-large fibers with less myoglobin and fewer mitochondria
- lots of glycogen
- extensive sarcoplasmic reticulum for rapid Ca release
- fatigue rapidly but generate high tension for short bursts of activity
what type of respiration do type 2 slow twitch fibers use
anaerobic glycolysis
why do type 2 fibers fatigue rapidly
because they use anaerobic respiration and have a low amount of mitochondria
what color are type 1 fibers
dark red
what color are fast twitch fibers
pink/tan
what are the intermediate muscle fibers
-type 2a
-type2b
describe type 2a fibers
oxidative and fatigue resistant
describe type 2b fibers
glycolytic and fatigue resistant
what type of respiration do both muscle fiber types use in peak periods of exertion and why
anaerobic respiration because they cant get enough oxygen
what does lactic acid build up do to muscle
forms crystal precipitates in muscle tissue that tear the fibers causing soreness after heavy exertion
what does severe oxygen debt cause
ischemia, muscle cramps, and even cell death
what is rhabdomyolysis
breakdown of actin and myosin as a result of extreme exertion
what can rhabdomyolysis be followed by and how
kidney failure (myoglobinuric nephrosis) due to release of myoglobin and clogging of glomeruli
how do muscle cells increase in size/hypertrophy
increase in number of mitochondria, and increase in volume of contractile proteins causes splitting/branching of individual muscle fibers
how often are new muscle fibers produced
relatively rarely
what is atrophy caused by
immobilization, denervation, and age
what happens in sacropenia
loss of skeletal muscle fibers that are not replaced. decrease in number of fibers and muscle mass
what do satellite cells do
regenerate skeletal muscle, they are small myogenic cells adjacent to sarcolemma
what do satellite cells do following injury
proliferate and differentiate into myoblasts
what are the types of proprioceptors in muscle cells
neuromuscular spindles and neurotendinous spindles
what are intrafusal fibers
modified skeletal muscle fibers associated with modified nerve endings
what do neuromuscular spindles sense and where are they located
sense changes in length and are located within the belly of muscle
what do neurotendinous spindles sense and where are they located
the sense changes in tension and they are located within the tendon
what do mechanoreceptors in muscle tissue do
prevent overstretching and tearing of muscles, used in postural reflexes and coordination
what is the ultrastructure in muscle cells
individual muscle fibers composed of myofibrils
what are myofibrils composed of
myofilaments or contractile proteins in parallel bundles
what are the 2 types of myofilaments
actin (thin) and myosin (thick)
what is the ratio of actin to myosin in skeletal muscle
2:1
what gives rise to the striated appearance of muscle tissue
parallel arrangement of contractile proteins
where do actin and myosin overlap
in the A band
what are sarcomeres
functional units of muscle cells that are arranged myofibrils
what do Z-discs do
act as anchoring points for actin myofilaments
what happens in the sliding filament theory of muscle contraction
during muscle contraction, sarcomeres shorten, but myofilaments remain the same length
what happens when thick and thin filaments slide over one another
-use energy via ATP
- shortening of sarcomere from binding and unbinding of actin and myosin filaments
what is the NMJ
site where skeletal muscle innervated by motor nerves
what is the motor end plate
the dilated terminal portion of the axon surrounded by myelin
what is the difference between a motor end plate and a terminal bouton
the motor end plate is myelinated
what is the synaptic cleft
space between motor end plate of nerves and sarcolemma of muscles
what neurotransmitter is released at the synaptic cleft on the NMJ
generally acetylcholine
what happens in the electrical stimulation of a neuron
-influx of Na+ into neuron
-wave of depolarization down axon
- release of NT
- binding to receptor proteins
-wave of depolarization of muscle fiber
what do transverse tubules do (T tubules)
extensive network of tubules continuous with sarcolemma that indirectly links extracellular space with ER and intracellular environment
- carries depolarization wave to the inside of the muscle cell cytoplasm
what are the ends of t tubules bound by
terminal cisternae of ER on both sides
what makes up a triad
a t tubule surrounded on both sides by cisternae
what act as Ca resevoirs in muscle tissue
sarcoplasmic reticulum and terminal cisternae
what is the mechanism for Ca release from ER and terminal cisternae into cytoplasm
influx of Na+ ions into cytoplasm from T tubules triggers depolarization of sarcolemma which triggers release of Ca
what does the sliding filament mechanism result in
muscle contraction
what are the steps in the sliding filament mechansim
- Ca causes conformational change in troponin, which interacts with tropomyosin molecules on actin to expose myosin binding sites on the actin filament
- myosin binding causes conformational change in myosin head and sliding of myosin past actin
- myosin heads repeatedly bind and unbind to actin in presence of Ca and Pi, causing contraction
what is a graded response
the strength of the overall contraction calculated by the total number of muscle fibers contracting at any given time
what is a motor unit
a group of muscle fibers supplied by single motor neuron
what does the stimulation of a motor neuron result in
contraction of all muscle fibers within that motor unit
what is recruitment
increase in number of motor units firing within a muscle
what does recruitment lead to
a graded response
what is muscular dystrophy
-degenerative wasting disease
- muscle weakness due to genetic defect in muscle protein and then muscle cell death
- most commonly affected muscle protein: dystrophin-
what is myasthenia gravis
autoimmune disease cause by production of antibodies to Ach receptors which leads to muscle weakness
how is myasthenia gravis treated
with AcHase inhibitors
describe inherent contractility in skeletal muscle
rhythmic, wave-like contractions independent of neurological stimulation
describe the orientation of smooth muscle fibers and function
highly irregular branching fascicles specialized for long contractions with low force
describe the size of smooth muscle fibers and the nuclei
smaller than skeletal muscle and the nucleus is long, single and central
how do you tell the difference between smooth muscle and skeletal muscle
the nucleus in smooth muscle is single and central
how do you distinguish between connective tissue and smooth muscle
-nuclei are long and ovular, the ends of nuclei are rounded and fibers are uniform in size in smooth muscle
what is the ratio of actin to myosin filaments in smooth muscle
15:1, randomly arranged
why are there no striations in smooth muscle
because myofilaments are not arranged in sarcomeres
what are dense bodies
functionally equivalent to z-discs in smooth muscle, provide attachment sites for actin
what does smooth muscle fibers use that controls myosin binding
calmodulin
what are caveolae
invaginations in membrane of smooth muscle cells. smooth muscle cells use these instead of the t-tubule/terminal cisternae system. rely on extracellular calcium for contraction
what type of innervation does skeletal muscle have
sympathetic and parasympathetic
what does a single unit of muscle fibers do and what is the example
fibers contract as a unit ex: visceral smooth muscle of gut
what does a multi unit of smooth muscle do and example
individual muscle fibers contract independently ex: erector pili muscle
can smooth muscle repair itself after injury
yes
what does smooth muscle develop from
endothelial cells, pericytes of blood vessels, fibroblasts
what can glandular epithelial cells differentiate into
myoepithelial cells
what is the CT layer called that surrounds the heart
pericardium
what are the layers of the pericardium and what do they contain
outer fibrous CT layer and inner serous layer containing mesothelial cells
what does the pericardium contain and what is its function
pericardial fluid for lubrication
what are the 3 layers of the heart
epicardium, myocardium and endocardium
what is the epicardium of the heart made of
simple squamous mesothelium
what is the epicardium supported by
the underlying fibroblastic CT and adipose tissue
where are the blood vessels and nerves located
within the subepicardial layer
what is the heart surrounded by
adipose tissue
where is the myocardium thickest
in the ventricles compared to atria
describe the myocardium
thick, collagenous, connective tissue skeleton made of fibroblasts and collagen
describe cardiac muscle fibers
have one centrally located nucleus (occasionally 2), fibers are striated but involuntary
describe the arrangement of cardiac muscle
contractile proteins are arranged into sarcomeres, contain a diad of one t-tubule and one cisterna of ER located at z-disc
where is endocardium found and what kind of cells are they
lines atria and ventricles, ccovers heart valves; simple squamous endothelium
what supports endocardium
subendothelial fibroblastic CT, with reticular fibers and smooth muscle
where is the endocardium the thickets
in atria compared to ventricles
where are purkinjie fibers located
subepi and endocardial layers
what do cardiac valves contain
layer of fibrous connective tissue called lamina fibrosa covered by endothelium
what are valves surrounded by
tough, fibrous rings at base of aorta and pulmonary artery, AV valves and extending into IVS
what is os cordis
at the base of AV valves when valves occasionally ossify to form bony rings
what is inherent automaticity
cardiac myocytes can contract themselves without external stimulation
what are intercalated discs
unique to cardiac muscle, special connections between the cells
what do intercalated discs do
enhance spread of contractile stimulus between cells and allow synchronous contractions, increase SA for attachment of myofibrils between adjacent cells
what are the types of cell junctions
desmosomes, fascia adherens, and gap junctions
what do desmosomes do
bind individual myocytes together laterally and on ends
what do fascia adherens do
like zonuls adherens but joins ends of muscle fibers
what do gap junctions do and where are they located
located laterally, provide ioninc communication between cells, synchronize contractions and allow muscles to behave as a syncitium
what does the cardiac conduction system look like
SA node, AV node, Bundle of His, and purkinje fibers
describe the cells surrounding the conduction system of the heart
they are larger surrounding cardiac conduction systems and conduct impulses 4x faster
-paler staining around these structures due to higher glycogen content
what is the pacemaker of the cell and where is it located
SA node located at junction of superior vena cava and RA
what does the SA node do
generates impulses that induce contraction of atria
-as impulses travel across atria, stimulate AV node
-delays impulses, give atria time to contract
-impulse travels down IVS via bundle of His, branches into L and R AV bundles within IVS
- fibers divide into ventricular myocardium and ramify into purkinje fibers within subendo and subepicardium of ventricular free wall, gradually merge with myocardium, initiate ventricular contraction
what does sympathetic and parasympathetic stimulation do in the SA node
-sympathetic stimulation from sympathetic ganglia increase HR
- parasympathetic stimulation from vagus nerve decreases HR
