Answer:
C) esophagus - moves air from the nose into the lungs
Explanation:
The oesophagus is a muscular tube with a sphincter valve at each end. Its main function is to transport food and fluid, after being swallowed, from the mouth to the stomach.This is propelled from the pharynx into the oesophagus, and towards the stomach in a peristaltic waves. The peristalsis also pushes food along the alimentary canal
A neuromuscular junction (or myoneural junction) is a chemical synapse formed by the contact between a motor neuron and a muscle fiber.[1] It is at the neuromuscular junction that a motor neuron is able to transmit a signal to the muscle fiber, causing muscle contraction.
Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy. Synaptic transmission at the neuromuscular junction begins when an action potential reaches the presynaptic terminal of a motor neuron, which activates voltage-dependent calcium channels to allow calcium ions to enter the neuron. Calcium ions bind to sensor proteins (synaptotagmin) on synaptic vesicles, triggering vesicle fusion with the cell membrane and subsequent neurotransmitter release from the motor neuron into the synaptic cleft. In vertebrates, motor neurons release acetylcholine (ACh), a small molecule neurotransmitter, which diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors (nAChRs) on the cell membrane of the muscle fiber, also known as the sarcolemma. nAChRs are ionotropic receptors, meaning they serve as ligand-gated ion channels. The binding of ACh to the receptor can depolarize the muscle fiber, causing a cascade that eventually results in muscle contraction.
Neuromuscular junction diseases can be of genetic and autoimmune origin. Genetic disorders, such as Duchenne muscular dystrophy, can arise from mutated structural proteins that comprise the neuromuscular junction, whereas autoimmune diseases, such as myasthenia gravis, occur when antibodies are produced against nicotinic acetylcholine receptors on the sarcolemma.
Answer:
Many fossils of organisms that are no longer living have been discovered.
Explanation:
Mass extinctions could be first identified because of the traces they left in the fossil record. In the strata, the lower, older rock layer shows a diversity of fossil life forms, and the younger lawyer above is depauperate if we compare.
The physical barrier that the mRNA must pass is the nuclear membrane.
The process of gene expression involves two main stages; transcription ; the production of messenger RNA by the enzyme RNA polymerase, and the processing of the mRNA molecule. Then the process of translation which takes place outside the nucleus, therefore the mRNA must cross the nuclear membrane to enter the cytoplasm.
