skeletal muscles Flashcards
describe the role of muscles
- act in antagonistic pairs
- against an incompressible skeleton
- creating movement
- part of reflex or controlled by conscious thought
what is a myofibril?
- fused cell
- shares a nucleus & cytoplasm (sarcoplasm)
- has many mitochondria
- membrane bound channels (sarcoplasmic reticulum)
what are myofibrils made up of?
myosin and actin proteins forming a sarcomere
describe the myosin proteins
thick protein filament
describe the actin proteins
thin protein filament
describe the position of the sarcomere proteins
each myosin filament surrounded by six actin filaments
what is the sliding filament theory?
when an action potential reaches a muscle, it stimulates the response
first stage of sliding filament
Ca2+ ions enter and cause trypomyosin to move and uncover binding sites
describe the position of the trypomyosin
- wrapped around actin protein
- blocks binding sites for myosin head when muscle is relaxed
second stage of sliding filament
- ADP is attached to myosin head
- myosin head binds to binding site on actin, forming a cross bridge
third stage of sliding filament
- angle created in cross bridge creates tension
- actin filament is pulled and slides along the myosin
- releasing ADP
fourth stage of sliding filament
- ATP molecule binds to myosin
- causes it to change shape and detach from actin
fifth stage of sliding filament
- Ca2+ ions activate enzyme ATPase in sarcoplasm
- ATPase hydrolyses ATP on myosin head into ADP and releases enough energy for myosin head to return to original position
what happens when aerobic respiration cannot create enough ATP to meet the demand?
- anaerobic respiration
- phosphocreatine which is stored in muscles, provides phosphate to regenerate ATP from ADP
what does the I band show?
only actin
what does the A band show?
total width of myosin
what does the H zone show?
only myosin
what is the M line?
middle point of myosin
what is the Z line?
the point where actin filaments attach to each other
how do micrographs show thick and thin filament?
actin is paler and myosin is darker
what happens to the I band during muscle contraction?
decreases
what happens to the H zone during muscle contraction?
decreases
what happens to the A band during muscle contraction?
nothing
- myosin isn’t moving
what happens to the Z lines during muscle contraction?
they slide closer together, shortens the sarcomere
describe the structure of slow twitch fibres
- small diameter
- contains a large store of myoglobin, rich blood supply and many mitochondria
- red due to containing a lot of myoglobin
where are slow twitch fibres located?
calf muscles
what are the general properties of slow twitch fibres?
- slower contraction
- aerobic respiration for long periods of time due to rich blood supply and myoglobin O2 store
- adapted for endurance work
describe the structure of fast twitch fibres
- larger diameter
- more myosin filaments
- large store of glycogen, store of phosphocreatine to help make ATP from ADP
- high conc of enzymes involved in anaerobic respiration
where are fast twitch fibres located?
biceps
describe the general properties of fast twitch fibres
- fast contraction
- provides short bursts of powerful contraction
- adapted for intense exercise
explain why muscle fibres contain many mitochondria (2)
- they produce ATP during aerobic respiration
- ATP is needed to provide energy for muscle contraction
suggest the advantage of having myoglobin in slow twitch muscle fibres (3)
- acts as an oxygen store
- allows muscle fibre to respire aerobically
- even when blood can’t supply enough oxygen directly
what is the sarcomere?
distance between 2 Z lines
describe the structure of skeletal muscle (3)
- made up of bundles of muscle fibres
- each fibre made up of bundles of myofibrils
- myofibrils made up of actin and myosin protein filaments
name the protein present in the I band
actin
name the proteins present in the A band
actin and myosin
name the protein present in the H zone
myosin
when the sarcomere contracts, what happens to the I, A and H band/zone?
I gets shorter
A stays the same
H gets shorter or disappears
describe the role played by Ca2+ in the contraction of striated muscle (3)
- released from sarcoplasmic reticulum
- binds to troponin
- troponin changes shape
- tropomyosin moves so myosin binding site is exposed
- myosin head binds to actin
describe the role of ATP in muscle contraction
- broken down by ATPase
- provides energy to move myosin head which pulls actin filament
- provides energy to break cross bridge so that myosin head detaches from actin
- used up very quickly so has to be continuously generated
describe aerobic respiration as energy production for muscle contraction
- most ATP generated via oxidative phosphorylation in cell mitochondria
- aerobic reps only works when oxygen is present
- good for long periods of low intensity exercise
describe aerobic respiration as energy production for muscle contraction
- ATP is made rapidly by glycolysis
- end product is pyruvate which is converted to lactate
- lactate can quickly build up in muscles and cause muscle fatigue
- good for short periods of intense exercise
describe ATP CP system as energy production for muscle contraction
- ATP is made by phosphorylating ADP
- creatine phosphate is stored inside cells and the system generates ATP quickly
- CP runs out after a few seconds
- good for short bursts of vigorous exercise
- anaerobic & lactic
give one advantage and one disadvantage of generating ATP via the ATP creatine phosphate system
+ quick
+ used for short bursts of vigorous exercise
+ don’t require oxygen
- not long lasting
describe the function of skeletal muscle
- contraction is controlled consciously
- made of muscle fibres that contract quickly or slowly
describe the structure of skeletal muscle
- alternating shade colour stripes: A and I bands
- long muscle fibres
- many nuclei in each muscle fibre
describe the function of smooth muscle
- involuntary
- controlled unconsciously
- contract slowly
describe the structure of smooth muscle
- no striped appearance
- found in the walls of hollow internal organs
- one nucleus in muscle fibres
- spindle shaped muscle fibres
describe the function of the cardiac muscle
- contracts on its own (myogenic)
- pumps blood around the body
- contract rhymically and don’t fatigue
describe the structure of the cardiac muscle
- found in heart walls
- made of muscle fibres connected by intercalated discs
- low electrical resistance so nerve impulses pass easily between cells
- muscle fibres are branched to allow nerve impulses to spread quickly
- each cardiac muscle has 1 nucleus
- muscle fibres are shaped like cylinders
describe the similarities between all 3 muscle types
- contains actin and myosin which interact to bring about contraction
- antagonistic pairs ( eg one contracts whilst other elongates)
what is an EMG?
electromyogram
what does an EMG look at?
electrical impulses to muscles
- motor neurone activity
how does an EMG work?
- electrical signals in muscles can be detected by electrodes on the skin
- electrodes connected to a computer
