Muscle Flashcards
What are the three major types of muscle?
Skeletal, cardiac and smooth.
What are features of skeletal muscle?
Voluntary, attached to the bone, striated and uninuclear.
What are the features of cardiac muscle?
Involuntary, not attached to the bone and a specialised form of skeletal muscle. Mae up on intercalated discs.
What are the features of smooth muscle?
Involuntary, not attached to the bone and myocytes with a fusiform shape (spindle).
What is the sarcomere?
The functional unit of the skeletal muscle (Z line to Z line).
What is the A band?
Thick filaments of myosin that are found at the centre of the sarcomere.
What is the I band?
Contains the thinner filaments actin that do not overlap with the myosin. They are found either side of the A ban with the Z disc in the centre.
What is the M line?
Proteins that link the central regions of the thick filaments.
What is the H zone?
The light area between the ends of the thin filaments that is found in the centre of the sarcomere.
What is the Z line?
The network of proteins that anchor the thin filaments.
What lies on top of actin?
A band called tropomyosin.
What does troponin do?
Connects the tropomyosin to the actin and blocks the receptors so that myosin cannot bin. This is the case when the muscle is not contracting.
What binding sites do myosin heads contain?
Ones for ATP and for actin.
What role does calcium have in muscle contraction?
It causes a conformational change to move the tropomyosin so a cross bridge can form and contraction can occur.
What are thin filaments made up of?
G-actin - this forms protein chains that are called filament-actin.
What is the first step in the sliding filament mechanism?
An increase in calcium in the muscle energises the cross-bridge position - ADP and phosphate are attached to the molecule.
What is the second step in the sliding filament mechanism?
As the levels of calcium increase they bind to the troponin complex and cause a conformational change. Troponin moves away from the binding site and pulls tropomyosin with it, which exposes the binding site
What is the third step in the sliding filament mechanism?
The binding site is exposed and is in an energised position and the myosin head can now bind to the actin.
What happens when the myosin head is bound in the sliding filament mechanism? (fourth step).
ADP and phosphate are released from the head and the myosin head changes shape to 45 degrees and the affinity for ATP increases.
The bending of the head causes the filament to move.
What happens after the myosin head changes shape? (fifth step)
An ATP molecule binds which causes the head group to detach from the actin filament and hydrolyses the ATP to re-energise the head.
What is the final step in the sliding filament mechanism?
The myosin head returns to its original position of 90 degrees from the 45 degrees.
How is the synaptic cleft adapted for efficient binding of neurotransmitter?
Lots of folds to increase the surface area.
What happens to choline after ACh has been broken down?
It is recycled and goes back into the terminal.
What happens to acetate after ACh has been broken down?
It is transferred by choline acetyl transferase, which transfer it onto choline to form ACh ready to be released.
What does tubocurarine do?
It blocks ACh from binding to the receptor.
What do anticholinesterases do?
Prevent ACH being broken down and hemicholinium prevents sodium travelling through a choline carrier.
What is the sarcoplasmic reticulum a store of?
Calcium.
What are the purpose of T tubules?
They project down into the reticulum and means that action potentials can travel deep down into the muscle fibre/cell.
What happens after action potentials are spread across the muscle cell into the T tubules?
Depolarisation spreads down the tubules and activates the DHP receptor. DHP receptor changes shape and interacts with the Ryanodine receptor. The change in shape is transmitted from DHP to the ryanodine receptor which changes shape and causes the calcium channel to open. Yhe sarcoplasmic reticulum releases the calcium into the cytosol which activates the cross-bridge cycling.
How is calcium recycled?
Calcium ATPase aids the transfer across the sarcoplasmic reticulum membrane back into the lumen of the reticulum, along with ATP as a source of energy.
What is Myasthenia Gravis?
A condition that affects skeletal muscle - if the individual exercises, the muscle starts to lose the ability to contract. It is an autoimmune disease - antibodies destroy ACh receptors.
ie dysfunctional skeletal muscle
How can individuals suffering from Myasthenia Gravis be treated?
AChesterase inhibitors which increases the time ACh is in the synapse so there is a greater chance of contraction occuring.
What is the sarcoplasmic reticulum
Homologous to endoplasmic reticulum in other cells
Ca2+ store in muscle
What type of neurones innervate skeletal muscle
motor
What neurotransmitter do motor neurones release
Ach
The region directly under the axon terminal of a motor neurone is called ……………. and the junction between them is ……..
motor end plate
neuromuscular junction
relative striation of different types of muscle
skeletal is striated
cardiac has striations
smooth has no striations
what is a myofibril
individual muscle cell formed from bundles of actin and myosin
