A & P - Muscles Flashcards
describe the structure of a cardiac muscle cell
small, branched cells
interconnected by selectively porous jucnctions (intercalated discs)
central nucleus
straited
how are cardiac muscles innervated?
cardiac self-contractile pacemaker cells
how are cardiac muscles regulated?
autonomic/involuntary nerves
what is the function of cardiac muscle?
blood circulation
hydrostatic blood pressure
describe the structure of smooth muscles
small, spindle shaped
single centre nucleus
non-striated
where would smooth muscle be found in the body?
blood vessel walls
hollow organs
respiratory, digestive, cardiovascular and repro. tracts
how is smooth muscle innervated?
self-contractile (dig. tract)
autonomic/involuntary nerves
what is the function of smooth muscle?
move food, urine and repro secretions
regulation of airway and blood vessel diameter
describe the structure of skeletal muscle
very long
striated
multinucleus
where in the body would skeletal muscle be found?
throughout
how is skeletal muscle innervated?
somatic/voluntary motornerves
what is the function of skeletal muscle?
movement/stabilisation of skeleton guards entrance/exit of dig, resp, urinary tracts generates heat protects organs stores nutrients
where would the origin of a skeletal muscle be?
where fixed end of muscle meets bone
where would the insertion of a skeletal muscle be?
where moveable end of muscle meets bone
if skeletal muscle was described as synergist what would this mean?
muscles work together in same direction
if skeletal muscle was described as antagonist what would this mean?
muscle works in opposite direction to given muscle (eg. tricep/bicep)
if a particular skeletal muscle was described as the prime mover (agonist) what would this mean?
that muscle is responsible for a particular movement
if skeletal muscle was described as the fixator muscle what would this mean?
the muscle stabilises the origin of an agonist muscle (eg. scapula)
name the three layers of skeletal muscle, inner to outer
endomysium
perimysium
epimysium
describe the structure of epimysium in skeletal muscle
surrounding muscle
dense collagen layer
separates from nearby tissue
describe the structure of perimysium in skeletal muscle
divides muscle into fascicles
contains collagen, elastic fibres, nerves, blood vessels
describe the structure of endomysium in skeletal muscle
flexible layer inside fascicle
contains fine capillaries and nerves
name the three types of skeletal muscle and describe them in terms of metabolism, endurance and contractility
type I - slow contraction, low force, high endurance, aerobic metabolism
type IIa - fast contraction, medium force/endurance, mixed metabolism
type IIb - fast contraction, high force, low endurance, anaerobic metabolism
what does muscle size depend on? what alters this?
abundance of type I vs. II muscle fibres
altered by : genes, sex, age, training
describe the size of the muscle produced by type I and II fibres
type I : smaller muscles
type II : bigger muscles
what is myopathy?
heterogeneous group of disease with various causes (when muscle go wrong)
name some causes of myopathy
gene mutation metabolic origin inflammation autoimmune drugs infection
what is affected in myopathy?
just the muscle - not the neuromuscular junction or nerve
what innervates muscle fibres?
motorneurones (MN)
how do motorneurones and muscle fibres communicate?
in close proximity at neuromuscular junction (NMJ)
chemical signals used
describe the innervation of muscle at the NMJ
- electrical signal in MN axon
- Ca2 channels open in pre-synaptic MN
- Ca2 enters - fusion of vesicles containing ACh with membrane
- ACh released into synaptic cleft - binds with ACh receptors on muscle cell
- ACH degraded in synaptic cleft by ACh esterases
- opening of ACh gated ion channels on muscle cell allows Na+ and K+ to flood muscle cell - electrical signal
- muscle contracts
what is myasthenia gravis?
severe muscle weakness - NMJ affected
what are the causes of myasthenia gravis?
auto immune - antibodies attack ACh receptors
congenital - transfer of antibodies to baby from mum (reversible)
genetic - mutation affecting ACh production or signalling
what are the symptoms of myasthenia gravis?
abnormal muscle fatigue - in prolonged/repetitive contraction
variation in severity - daily basis/overtime
what are the treatments for myasthenia gravis?
prevention ACh degradation needed (ACh esterase inhibitor, steroids, immune suppress)
thymectomy - removal of thymus (antibodies made here)
plasmapheresis and immunoglobulin therapy
what is the term used for the cell membrane of a muscle cell?
sarcolemma
what does the term sarcoplasm mean?
cytoplasm relating to a muscle cell
what does sarcoplasm contain?
long, protein rich fibres called myofibrils
what does a myofibril consist of?
many parallel protein strands:
thin - actin
thick - myosin
what is a sarcomere?
arrangement of thin and thick strands making up the basic contractile unit
how many sarcomeres are in one myofibril?
10,000
describe the sliding filament mechanism
- ATP turns into ADP releasing energy -converts myosin head to ‘cocked’ state (potential energy)
- calcium binds to troponin - exposes sites on actin so myosin can grab actin (cross bridges formed)
- myosin pushes on actin - actin moves (power stroke complete)
- ATP binds to myosin making it release actin
which two elements are needed for the sliding filament mechanism to work?
ATP
Ca2+
where is the ATP needed for the sliding filament mechanism obtained from?
creatine phosphate
aerobic metabolism
anaerobic metabolism
what is ATP needed for in the sliding filament mechanism, what happens without it?
ATP needed to release myosin from actin binding site
without ATP strands are permanently cross linked (rigor mortis)
where is the Ca2+ needed for the sliding filament mechanism obtained from?
at rest Ca2+ is stored in the sarcoplasmic reticulum (SR)
AP triggers release of Ca2+ - this binds to actin causing a structural change making binding site available
what can affect the active reuptake of Ca2+ by the sarcoplasmic reticulum?
myopathies and myotoxicity (induced by statins) affect the reuptake of Ca2+ affecting the sliding filment mechanism
what is excitation-contraction coupling?
mechanism whereby excitation of muscle cell causes contraction nearly simultanously
what would happen if the sarcomere where too stretched or too contracted?
reduced number of cross bridges = reduced tension
what is an isometric contraction?
muscle develops tension but does not shorten (during no movement of object)
what is an isotonic, concentric contraction?
muscle shortens, tension remains constant (during upward movement)
what is an isotonic, eccentric contraction?
muscle lengthens while maintaining tension (during downward movement)
