Muscles (5) Flashcards
Involuntary (smooth) muscle.
unstriated
controlled by autonomic nervous system
contracts slowly and fatigues slowly
functions: peristalsis, pupil dilatation and contraction, vasodilation and vasoconstriction.
Cardiac muscle
striated
controlled by the autonomic nervous system (some under myogenic control)
contracts quickly, does not fatigue.
function: cause the heart to contract and relax.sk
Skeletal muscle
striated
controlled by the somatic nervous system
contracts quickly, fatigues quickly
function: to move bones of the skeleton about the joints.
Myogenic
generates their own electrical impulse to contract muscle (found in SAN)
Structure of involuntary muscle
single, spindle - shaped cells each with its own nucleus.
Structure of cardiac muscle
single, cylindrical branched cells, separated by intercalated disks, each with its own nucleus
Structure of skeletal muscle.
multinucleate, cylindrical cells.`
Fast twitch fibres
Used for short bursts of energy.
present in skeletal muscle.
contract rapidly but quickly fatigue.
gain energy from anaerobic respiration, stores creatine phosphate (can rapidly generate ATP from ADP in anaerobic conditions)
slow twitch muscle fibres
contract less rapidly, fatigues very slowly.
gain energy from aerobic respiration
rich in myoglobin which creates a darker colour under the microscope
Neuromuscular junctions
specialised synapses which occur at the end of a motor neurone where it meets a muscle fibre.
synaptic knob at the end of the motor neurone is the motor end plate.
when the action potential reaches the motor end plate, the end plate releases acetylcholine which causes muscle fibre to depolarise = muscle contraction
Differences between NMJ and synapse
connects motor end plate (NMJ) connects 2 motor neurones (S)
sarcolemma depolarise (NMJ)
post synaptic neurone depolarise (N)
Depolarisation of muscle fibre membrane causes contraction (NMJ)
depolarisation sets up action potential which is a nerve impulse (S)
NMJ end plate has a flat surface known as a brush border (NMJ)
Synaptic knob is smooth and rounded (S)
Motor units
muscle fibres are arranged in clusters known as motor units.
Gradation of response
all muscle fibres in one motor unit are stimulated by a single motor neurone.
the brain controls the strength of contraction by altering the number of motor units that are stimulated.
the finer the function the fewer the number of muscle fibres.
How a neuromuscular junction works
- an impulse arrives at the neuromuscular junction, causing calcium ion channels to open, this causes the vesicles to fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft by exocytosis.
- acetylcholine binds to receptors on the muscle fibre membrane (sarcolemma) causing depolarisation
- depolarisation wave travels down t-systems (tubules)
- t-system depolarisation leads to calcium ions to be released from stores in the sarcoplasmic reticulum.
- Ca2+ binds to proteins in the muscle, which leads to contraction.
- acetylcholinesterase in the synapse rapidly breaks down acetylcholine so that the contraction only occurs when impulses arrive continuously.
Sliding filament theory diagram of a myofibril.
[notes]
How do the different regions of a myofibril change during contraction
sarcomere = shorter
H zone = shorter
I band = shorter
Z lines = closer together
A band = no change
Structure of actin
each actin filament is made of 2 actin molecules.
protein made of globular beads
2 actin molecules coiled around eachother.
tropomyosin wraps around the actin filament
troponin forms balls along the length of the actin filament
structure of myosin
each molecule of myosin has 2 protruding heads and a long tail.
heads contain ATPase (enzyme which hydrolyses ATP)
myosin heads can bind to actin filaments, but in relaxed muscles, the binding sites are blocked by tropomyosin
Sliding filament theory movement
- tropomyosin molecule prevents myosin head from attaching to the binding site on the actin molecule
- calcium ions released from the sarcoplasmic reticulum causes the tropomyosin molecule to pull away from the binding sites on the actin molecule
- myosin head now attaches to the binding site on the actin filament
- head of myosin changes angle (45*) moving the actin molecule along as it does so. ADP molecule is released.
- ATP molecule binds to myosin head causing it to detach from the actin filament.
- hydrolysis of ATP to ADP by myosin provides the energy for the myosin head to resume its normal position
- head of myosin reattaches to a binding site further along the actin filament and the cycle is repeated.
What is the role of ATP in muscle contraction
ATP binding breaks the cross-bridge, which allows the myosin to reattach to the next binding site.
ATP is used to actively transport Ca2+ ions back into the sarcoplasmic reticulum when contraction stops.
in relaxed muscle, ATP reacts with creatine phosphate which is used to maintain ATP supply in contracting muscle.
ATP is used in protein synthesis to make actin and myosin
How is the energy supply generated and maintained in muscle contraction using anaerobic respiration
Muscle cells quickly run out of O2 , anaerobic respiration in sarcoplasm releases some ATP (by glycolysis)
Also releases lactic acid (causes muscle fatigue)
Used for short periods of high intensity exercise
How is the energy supply is generated and maintained in muscle contraction using aerobic respiration
Requires a good supply of oxygen and glucose, delivered by blood capillaries.
Some glucose comes from hydrolysis of glycogen
oxygen levels drop quickly during exercise therefore aerobic respiration is used for long periods of low intensity exercise
How is the energy supply is generated and maintained in muscle contraction using creatine phosphate
Acts as a reserve supply of phosphate, which is available to combine with ADP.
Used for short bursts of vigorous exercise.
During muscle relaxation, creatine phosphate is replenished.
