Muscoskeletal System 1 Flashcards
define excitability?
capacity of muscle to respond to stimulus
define contractility?
ability of muscle to shorten + generate pulling force
define extensibility?
muscle can be stretched back to original length
elasticity?
ability of muscle to recoil to original resting length after stretched
what are the different types of muscle?
- skeletal
- smooth
- cardiac
skeletal
- makes up 40% body weight
- responsible for locomotion, facial expressions, posture, respiratory movements
- controlled by somatic motor neurones (VOLUNTARY)
smooth
- in walls of hollow organs, blood vessels, eyes etc
- functions: properly urine, mix food in digestive tract, dilate/constrict pupils, regulate blood flow
- controlled by endocrine + autonomic nervous systems (INVOLUNTARY)
cardiac
controlled involuntarily by endocrine + autonomic nervous systems
what is the epimysium?
dense regular connective tissue surrounding entire muscle
- separates muscle from surrounding tissues + organs
- connected to deep fascia
what is the perimysium?
collagen + elastic fibres surrounding group muscle fibres = fascicle
contain blood vessel + nerves
what is the endomysium?
loose connective tissue that surrounds individual muscle fibres
contains blood vessels, nerves + satellite cells
motor neurones
- stimulate muscle fibre to contract
- neurone axons branch so each muscle fibre = innervated
- forms NMJ (myoneural junction)
sarcolemma
= cell membrane
surrounds sarcoplasm
- has abundance of myoglobin
- has openings called Transverse T tubules
what are T tubules?
narrow tubes that extend into sarcoplasm at right angles to surface
filled with extracellular fluid
what are myofibrils?
cylindrical structures in muscle fibre
a bundle of protein filaments is known as…
myofilaments
what are the 2 myofilaments?
actin (thin)
myosin (thick)
what is the sarcomere?
region between two z lines
what is the I band?
zone of thin filaments not superimposed by thick filaments
what is the A band?
entire length of single thick filament
what is the H zone?
zone of thick filaments not superimposed by thin filaments
what is the M line?
middle of sarcomere
what is the sarcoplasmic reticulum?
smooth ER
forms chambers = terminal cisternae on either side of T tubule
a single T tubule + 2 terminal cisternae form …
triad
what is tropomyosin?
elongated protein that winds along groove of F actin double helix
troponin is composed of 3 subunits, what are they?
- Tn-I site ; binds to actin
- Tn-T site ; binds to tropomyosin
- Tn-C site ; binds to ca2+ ions
the tropomyosin/troponin complex regulates the…
interaction between active sites on G actin + myosin
describe the myosin heads?
- form cross bridges with actin
- attached to rod portion by hinge region that can bend + straighten during contraction
- have ATPase activity —> breaks down ATP
what are the components of the synapse (NMJ)?
- synaptic knob (swollen at end of axon terminal)
contains ACh - motor end plate (region of sarcolemma that abuts synaptic knob - highly folded)
- synaptic cleft
what is the function of the motor end plate?
- inc surface area to allow more ACh receptors
- contains AChE that breaks down ACh and causes relaxation
what is the synaptic cleft?
tiny gap between synaptic knob + sarcolemma of muscle fibre
what are the 4 actions involved in muscle contraction + relaxation?
- excitation
- excitation-contraction coupling
- contraction
- relaxation
describe the sliding filament theory?
- calcium binds to troponin
- troponin moves, moving tropomyosin, exposing actin active site
- myosin head forms crossbridge + bends towards H zone
- ATP allows release of cross bridge
muscle contraction summary
- nerve impulse reaches NMJ
- ACh released from motor neurone
- ACh binds with nicotinic receptors in muscle membrane to allow na+ ions to enter
- na+ influx generates AP in sarcolemma
- AP travels down t tubule
- SR releases ca2+
- ca2+ binds to troponin, to move troponin tropomyosin complex
- binding site in actin exposed
- myosin head attaches to binding sites = power stroke
- atp detached myosin head + energises for another contraction
- when AP cease, muscle stop contracting
functions of ATP in skeletal muscle contraction
- energises cross bridges
- providing energy for force generation
- dissociates cross bridges bound to actin
- energises ca2+ pumps that actively transport ca2+ back into SR
- lowers cytosolic ca2+ levels —> relaxation
- runs na+-k+ pump in sarcolemma
- maintains resting membrane potential of sarcolemma
ATP is produced from 3 sources, what are they?
- creatine phosphate
- aerobic respiration
- anaerobic respiration (glycolysis)
what are the 2 types of skeletal muscle fibre?
fast twitch
slow twitch
slow twitch/ high-oxidative fibres
- contract slowly
- moderate power output
- consume atp at moderate rate
- rich blood supply
- more mitochondria
- smaller in diameter (minimise diffusion distance)
- large amount myoglobin
- more fatigue resistant
fast twitch/ low oxidative fibres
- rapid movement
- anaerobic resp (glycolysis)
- less blood supply (pale colour)
- fewer mitochondria
- fatigue rapidly
- lower limbs in sprinter, upper limbs of most people
- contain myosin
what is a motor unit?
motor neurone and all muscle fibres it supplies
muscles that control fine movements have …
small motor units
large weight bearing have…
large motor units
back muscle motor unit ratio
1:100
finger muscle motor unit ratio
1:10
eye muscle motor unit ration
1:1
what is the force of contraction affected by?
- relative size of muscle
- number of muscle fibres contracting
- degree of muscle stretch
relative size of muscle
- larger muscles have larger + more muscle fibres
- larger fibres generate more force
- more muscle fibres generate more force
number of muscle fibres contracting
greater no of motor units generate more force than smaller no of motor units
degree of muscle stretch
muscles contract strongest when muscle fibres = 80-120% normal resting length
smooth muscle features?
- cells not striated
- smaller fibres
- more actin
- no sarcomeres (not arranged symmetrically)
- cavoeolae- indents in sarcolemma
- dense bodies instead of Z disks
what is the longitudinal layer?
muscle fibres run parallel to organs long axis
what is the circular layer?
muscle fibres run around circumference of organ
role of ca2+ ions?
ca2+ binds to calmodulin + activates it
activated calmodulin activates MLCK enzyme
activated kinase transfers P from ATP to myosin cross bridge
phosphorylated cross bridge interacts with actin —> shorten
smooth muscle relaxes when intracellular ca2+ drop
