Answer:
The two major proteins, actin and myosin, appear in muscle cells
Explanation:
Answer:
4,3,1,5,2
4. Vesicles full of acetylcholine are stored at the axon terminal.
3. Action potential arrives at the neuromuscular junction.
1. Action potential is propagated in the sarcolemma.
5. Acetylcholine is released into the synaptic cleft.
2. Acetylcholine binds to ligand gated sodium channels.
Explanation:
Nerve impulse is generated from somatic motor neurons and reaches neuromuscular junction. The nerve impulse specifically reaches a region named 'synaptic end bulbs' at axon terminal. These synaptic end bulbs are in turn connected to the motor end plate region of a sarcolemma.
As soon as the nerve impulse reaches neuromuscular junction, it triggers the opening of voltage gated ion channels which in turn facilitate the influx of Ca²⁺ from the extracellular fluid to the inside of neuron where synaptic vesicles containing neurotransmitter acetylcholine are already stored.
The Ca²⁺ causes the exocytosis of synaptic vesicles which fuse with the plasma membrane of motor neuron as a result of which acetylcholine is released in the synaptic cleft.
The acetylcholine further binds with the acetylcholine receptor which is present at the motor end plate of a skeletal muscle fibre. These receptors are ligand gated ion channels.
Binding of acetylcholine with its receptor causes the ion channels to open and cations like Na⁺ enter the muscle fibre so as to make the electric potential inside the muscle positive.
All cells in the body have the same DNA and the same genes. In organs & tissues the expression changes.
The answer is that they have traits that enabled them to survive in a changing environment.
During the evolution of the Earth, and later during the evolution of life, the environment was not constant. Change in the environment could lead to an extinction of some species. But, some species were able to adapt or could tolerate a wide range of environmental factors. One of the explanation, why unicellular organisms did not evolve into complex multicellular organisms is because they have traits that help them to tolerate the wide range of factors, and thus, survive in changing environment.
