Question

Describe the i band, h zone, and a band, what stucture would you expect of find in each of theses zones or bands.

describe the conducting system of skeletal muscles and the specific role of sarcolemma, sarcoplasmic reticulum reticulum, t tubules draw and label the conducting

easy simple straight to the point answers

Answer 1

I band: I bands are composed of thin actin filaments and proteins that bind actin and they are bisected by the Z line. The thin filaments extend in each direction from the Z-disk, where they do not overlap the thick filaments, they create the light I band.

h zone : It the region of a striated muscle fibre that contains only thick (myosin) filaments. The H zone appears as a lighter band in the middle of the dark A band at the centre of a sarcomere.

A-Band: the comparatively dark area entirely within a sarcomere. This area is composed of thick filaments and thin filaments. This area does not shrink during muscle contraction.

As skeletal muscle cells are long and cylindrical, they are commonly referred to as muscle fibers. The plasma membrane of muscle fibers is called the sarcolemma, the cytoplasm is referred to as sarcoplasm, and the specialized smooth endoplasmic reticulum, which stores, releases, and retrieves calcium ions (Ca++) is called the sarcoplasmic reticulum (SR). All living cells have membrane potentials, or electrical gradients across their membranes. An action potential is a special type of electrical signal that can travel along a cell membrane as a wave. This allows a signal to be transmitted quickly and faithfully over long distances.

Signaling begins when a neuronal action potential travels along the axon of a motor neuron, and then along the individual branches to terminate at the NMJ (Neuro muscular junction). At the NMJ, the axon terminal releases a chemical messenger, or neurotransmitter, called acetylcholine (ACh). The ACh molecules diffuse across a minute space called the synaptic cleft and bind to ACh receptors located within the motor end-plate of the sarcolemma on the other side of the synapse. Once ACh binds, a channel in the ACh receptor opens and positively charged ions can pass through into the muscle fiber, causing it to depolarize, meaning that the membrane potential of the muscle fiber becomes less negative As the membrane depolarizes, another set of ion channels called voltage-gated sodium channels are triggered to open. Sodium ions enter the muscle fiber, and an action potential rapidly spreads (or “fires”) along the entire membrane to initiate excitation-contraction coupling.

The muscle fiber action potential, which sweeps along the sarcolemma as a wave, is “coupled” to the actual contraction through the release of calcium ions (Ca++) from the SR. Propagation of an action potential along the sarcolemma is the excitation portion of excitation-contraction coupling. Recall that this excitation actually triggers the release of calcium ions (Ca++) from its storage in the cell’s SR. For the action potential to reach the membrane of the SR, there are periodic invaginations in the sarcolemma, called T-tubules (“T” stands for “transverse”). Once released, the Ca++ interacts with the shielding proteins, forcing them to move aside so that the actin-binding sites are available for attachment by myosin heads. The myosin then pulls the actin filaments toward the center, shortening the muscle fiber.