Skeletal Muscles Flashcards
what are the three different types of muscles cells?
- cardiac muscle - contracts without conscious control, only found in heart
- skeletal muscles - also called stripped, striated or voluntary muscles that move the skeleton
- smooth muscle - involuntary muscle contracts without conscious control. Found in the walls of internal organs eg stomach, intestines etc
what are ligaments and tendons?
- made of collagen
- inelastic, flexible and don’t snap when pulled
ligaments = attach bones to bones, to hold them together
tendons = attach muscle to bones
what are antagonistic muscle pairs?
pairs of skeletal muscles contract and relax to move bones at a joint - the bones of a skelton are rigid so they act as levers
- one muscle contracts to bring about movement in one direction and the other relaxes
- when its pair contracts it brings about movemnt in the opposite direction.
- muscles can only exert a force when they are contracting
- can only lengthen again when they are passively stretched by the action of antagonistic muscle
what are the types of joints?
1) hinge joints = allows movement in one direction eg elbow
2) ball and socket = large range of motion eg shoulder
3) gliding joint = allows two types of movement eg wrists
how is antagonistic muscle action used in bending and straightening the elbow?
- To bend the elbow the bicep muscle contracts pulling the radius upwards and the triceps relaxes. The biceps is called a flexor muscle because it causes flexing of the elbow
- To straighten the elbow the bicep relaxes and the triceps contract pulling the ulnar downwards so the bicep is passively stretched. The triceps is called an extensor muscle because it straightens the elbow
what is the structure of a skeletal muscle?
made up of muscle fibres
- parts of the sarcolemma (cell membrane of muscle fibres ) fold inwards across the muscle fibre and stick into sarcoplasm, these folds are called T tubules and they help to spread the electrical impulses throughout the sarcoplasm so they can reach the muscle fibre
- sarcoplasmic reticulum stores and releases calcium ions that are needed from muscle contraction
- muscle fibres have a lot of mitochondria to provide energy for ATP
- muscle fibres are multinucleate
- each muscle fibre contains bundles of myofibrils
what are myofibrils?
made up of protein filaments which interlock on a regular way
there are
1) thin filaments (actin)
2) thick filaments (myosin)
gives muscles a striated appearance
what is a sarcomere?
Label the diagram
A sarcomere is a complicated unit of striated muscle tissue. It is the repeating unit between two Z lines
A band = myosin + actin overlapping
I band = actin only
H zone = myosin only
Z line = middle of actin (separates the sarcomere)
what happens to the structure of the sarcomere when the muscle contracts?
the actin filaments are drawn inbetween the myosin filaments thus shortening the sarcomere
A band stays the same
I band shortens
H zone descreases
sarcomere decreases
what is tropomyosin?
reinforces actin and blocks binding site
what is a neuromuscular junction?
a specialised synapse between a motor neurone and a muscle fibre
how does muscle contraction occur?
1) action potential arrives at many neuromuscular junctions simultaneously, this depolarises the membrane and causes calcium ions protein channels to open and calcium ions to diffuse into the synaptic knob
2) calcium ions cause synaptic vesicles to fuse with presynaptic membrane and release acetylcholine into the synaptic gap
3) acetylcholine diffuses across synaptic cleft and binds with receptors on the muscle sarcolemma causing depolarisation
4) action potential travels down the T tubules and causes calcium ions to be released from sarcoplasmic reticulum
5) calcium ions causes tropomyosin molecules that were blocking the binding site on the actin filament to pull away, unblocks binding site on the actin allowing actin myosin cross bridge to form
6) ADP molecules attached to the myosin head mean taht they are in a state to bind to the actin filament and form a cross bridge
7) once attached to the3 actin filament, the mysosin heads change their angle, pulling the actin filament along as they do so and releasing ADP and Pi. This is called the power stroke
8) an ATP molecule attaches to the myosin heads change their, causing it t detach from the actin filament
9) the calcium ions then activate ATP hydrolase, which hydrolyses the ATP to ADP and Pi. The hydrolysis provides the energy for the myosin head to return to its original position
10) the myosin head, once more with an attached ADP molecule then reattaches itself further along the actin filament and the cycle is repeated as long as the concentration of calcium ions remains high
what pulls the actin filaments towards each other?
- Myosin molecules are joined tail to tail in two oppositely facing sets, the movement of one set of myosin heads is in the opposite direction to the other set.
- This means the actin filaments are also moved in opposite directions.
- This movement pulls the actin filaments towards each other and so shortens the sarcomere.
how do muscles relax?
- when nervous stimulation stops, calcium ions are actively trasnported back into the sarcoplasmic reticulum using energy from the hydolysis of ATP.
- this reabsorpion of the calcium ions allows tropomyosin to block the actin filament again
- myosin heads are no longer able to bind and contraction stops, the muscle relaxes, actin filaments slide back to their original positions
what is the role of ATP (also means ADP +Pi) in muscle contraction?
1) ADP attached to the myosin head allows crossbridge3 between actin and myosin to form
2) releases of ADP + Pi = powerstroke
3) ATP attaches to the myosin head, causing head to detach from the actin filament
4) (ATP converts into ADP + Pi) myosin heads moves back to original position
what is calcium ions role in muscle contraction?
1) causes tropomyosin to move and unblock myosin head binding site
2) activate ATP hydrolase which hydrolyses ATP into ADP + Pi
what is creatine phosphate?
a molecule stored in the cytoplasm of muscle cells. The phosphate group can be used to phosphorylate ADP to ATP
what is the equation for creatine phosphate producing ATP?
what are the two different types of skeletal muscles?
slow twitch and fast twitch muscle fibres
describe the properties of slow twitch muscle fibres
- contract slowly
- work for a long time without tiring
- energy is released slowly through aerobic respiration
- lots of mitochondria
- good blood supply
- rich in myoglobin so are reddish in colour
describe the properties of fast twitch muscle fibres
- contract very quickly
- tire easily
- energy released quickly through anaerobic respiration using glycogen
- stores of creatine phosphate
- few mitochondria
- less myoglobin than slow twitch, so they are a whitish colour
what is myoglobin?
a red coloured protein that stores oxygen
compare the transmission across a synapse and across a neuromuscular junction for the following:
- postsynaptic cell
- neurotransmitter
- is synapse excitatory/inhibitory
- how are they similar?
what 2 ways do drugs act on synapses?
1) Stimulate the nervous system by creating more action potentials in post synaptic neurones. A drug may mimic a neurotransmitter/ stimulate the release of ore neurotransmitter/ inhibit enzymes that break down the neurotransmitter. The outcome is to enhance the body’s response to impulses/action potentials passed along the post synaptic neurone
2) Inhibit the nervous system by creating fewer action potentials in post synaptic neurones. A drug may do this by inhibiting the release of a neurotransmitter or blocking receptors on sodium potassium ion channels on the post synaptic neurones. The outcome is to reduce the impulses passed along the post synaptic neurone.
