Question

a diagram with written steps showing the different components of skeletal muscle and how these interact to generate muscle contraction, from a neuron to skeletal muscle cell to contraction of the muscle cell. things to include and label are:

-axon terminal

-synaptic cleft

-neurotransmitter

-neurotransmitter binding channels on muscle cell

-t-tubules

-depolarization

-sarcoplasmic reticulum

-receptors/channels working together to release Ca2+

-Ca2+ (where is it, where it goes, what it binds to)

-sacromeres, components (actin, myosin, tropomyosin, troponin, ATP) and how it works

Answer 1

• A muscle is made up of number of motor units. The motor end plate (also known as the neuromuscular junction) is the junction of the motor neurons axon and the muscle fibres it stimulates.
• A space between two endings of neuromuscular junction is known as synaptic cleft.
• On the molecular basis , the functional unit of contractile system in muscle is sarcomere.
• Each sarcomere consists of two types of myofibrils : thick and thin
• Thick fibres are consists of protein myosin.
• Thin fibers are consists of protein actin.
• ​​​​​
• H = lighter band formed only by myosin .
• A = dark band formed by myosin and actin overlapping it.
• I = light band formed only by actin. It is the region between 'A' bands of the adjoining sarcomeres.
• Z = consists of short elements which interconnects thin filaments from adjoining sarcomeres.

• Actin and myosin are the structural proteins in the muscle.
• Apart from these , other proteins such as troponin and tropomycin are also present. These are regulatory proteins which do allow actin and myosin to interact for the contraction of muscle.
• Troponin and tropomysin are inhibited Ca2+ and stimulated by K+.
• calcium is another important constituent of the muscle required for the contraction.
• The source of Ca2+ is sarcoplasmic reticulum.
• The membrane of sarcoplasmic reticulum has ability to concentrate calcium with the help of ATP.
• For a contraction to occur stimulation of the muscle in the form of an impulse ( action potential) from a motor neuron.
• When impulse reaches the muscle fibres of a motor unit , it stimulates a reaction in each sarcomere between the actin and myosin filaments. This reaction results in the start of a contraction and The sliding filament theory.
• The reaction ,created from the arrival of an impulse stimulates the heads on the myosin filament to reach forward, attach to the actin filament and pull actin towards the centre of sarcomere.This process occurs simultaneously in all sarcomeres, the end process of which is shortening of all sarcomeres.
• Troponin is a complex of three proteins that are integral to muscle contraction. Troponin is attached to the protein tropomyosin within the actin filaments , as seen in image .
• When the muscle is relaxed tropomyosin blocks the attachment sites for the myosin cross bridges, thus preventing contraction.
• When the muscle is stimulated to contract by the nerve impulse , calcium channels open in the sarcoplasmic reticulum and released calcium into the sarcoplasm .
• Some of this calcium attaches to troponin which causes a change in the muscle cell that moves tropomyosin out of the way so the cross bridge can attach and produce muscle contraction.
• The transient increase in Ca2+ ions during the action potential induces the vesicles of acetylcholine to fuse with nerve ending. The release of acetylcholine them occurs by the process of exocytosis.
• Acetylcholine thus released interacts with nicotinic receptors of the end plate and depolarizes it to generate end plate potential.
• This causes the release of Ca2+ from the transverse tubules and sarcoplasmic reticulum.
• The Ca2+ binds to troponin - tropomyosin and actin is released. The actin thus released interacts with myosin in the presence of ATP and the actin-myosin filaments slide over each other to produce contraction.