Physiology 1 Flashcards
how do skeletal and cardiac muscle differ in terms of initiation of contraction?
skeletal = neurogenic initiation of contraction - so have neuromuscular junctions cardiac = myogenic initiation of contraction - have gap junction instead of neuromuscular
how do skeletal and cardiac muscles differ in terms of excitation contraction coupling?
skeletal = calcium is all from sarcoplasmic reticulum cardiac = calcium from ECF and sarcoplasmic reticulum (Ca induced Ca release)
how are skeletal and cardiac contraction graded?
skeletal = by motor unit recruitment and summation of contractions cardiac = depends on preload
how are skeletal muscle fibres arranged?
motor units
alpha motor neurons come from spinal cord to supply more than 1 muscle fibre
how is cardiac muscle arranged?
individual muscle fibres are connected via desmosomes and intercalated discs
what does the number of nerve fibres supplied by one alpha motor neuron depend on?
functionality of the muscle
fine movement muscles have fewer fibres per motor unit as precision is more important than strength (e.g facial expression, eye, fingers)
where power is more important (thighs) 1 nerve can supply thousands
how are nerves and skeletal muscle fibres connected?
no continuation of cytoplasm
acetylcholine acts as a neurotransmitter at neuromuscular junctions
what does skeletal muscle consist of?
parallel muscle fibres bundled by connective tissue
how is skeletal muscle attached to skeleton?
tendons
what are the levels of organisation in skeletal muscle?
muscle as whole made up of muscle fibres (cells)
each muscle fibre made up of myofibrils
myofibrils are arranged into sarcomeres
sarcomers consist of contractile proteins actin (thin) and myosin (thick)
what does skeletal muscle consist of?
parallel muscle fibres bundled by connective tissue which run the entire length of the muscle
how is muscle tension produced?
sliding of actin filaments on myosin filaments to shorten the sarcomere which hence shortens the muscle
ATP is only required for contraction?
false
needed for both as ATP also breaks down the cross bridge as well as switching on its formation
what is needed for cross bridges to form?
calcium and ATP
when is calcium released from lateral sacs of sarcoplasmic reticulum?
when the surface action potential spreads down T tubules
where can sarcomers be found in skeletal muscle?
between two Z lines
where ends of thin filaments line up vertically - connects the thin filaments of two adjoining sarcomeres
what are the 4 zones of the sarcomere?
A band
H zone
M line
I band
what is the A band?
thick filaments in the middle as well as portion of thin filaments which overlap
why is ATP needed for relaxation?
it pumps calcium back into sarcoplasmic reticulum and binds to myosin head
what is the M line?
vertical line down middle of A band, within H zone
what is the I band?
remaining portion of thin filaments that don’t overlap with A band (areas between A bands)
ATP is only required for contraction?
false
needed for both as ATP also breaks down the cross bridge after aiding its formation
what is excitation contraction coupling?
where surface action potential results in activation of contractile structures of muscle fibre
what are the 2 functions of calcium?
switch on cross bridge formation
link between excitation and contraction
name 5 physiological functions of skeletal muscle
maintain posture movement respiratory movements heat production (metabolism, shivering) contributes to whole body metabolism
where is smooth muscle found?
internal viscera
vasculature
which muscle types are striated?
cardiac
skeletal
which muscles are involuntary?
cardiac muscle
smooth muscle
what causes striation in muscles?
alternating dark and light bands of myosin and actin
which nervous system innervated each muscle type?
skeletal = somatic
cardiac and smooth = autonomic
how does calcium aid contraction?
myosin binding site on actin is covered by tropomyosin
calcium binds to troponin which causes a conformational change and tropomyosin moves away exposing myosin binding site
cross bridge forms
summarise how action potential caused skeletal muscle contractgion
acetylcholine is released from motor neuron axon and binds to receptors
action potential created from acetylcholine binding spreads across membrane and down T tubules causing calcium to be released from lateral sacs of sarcoplasmic reticulum
calcium binds to troponin on actin exposing the myosin binding site
cross bridge forms, pulling actin filaments over myosin causing contraction
once action potential has finished, calcium taken back up into sarcoplasmic reticulum (aided by ATP)
troponin slips back over myosin bindng site and ATP binds to myosin head causing destruction of cross bridge resulting in relaxation
