Answer: During the Cambrian Explosion of Animal Life
The smallest item in the list would be organelles. Organelles are tiny structures within a cell, that help it to function. Example of organelles are-- nucleus, mitochondria, cell membrane to name a few. Cells are the basic unit of structure and function of all living things, therefore, cells would have to be placed second. They are microscopic. A group of similar cells that work together to perform a specific function, is known as a tissue. Therefore, tissue is next largest. Examples of tissues include, muscle tissue, epithelial tissue, adipose tissue. When different types of tissues work together to perform a function in the body, this group of tissues forms an organ. An example of an organ is the heart. Inside the heart are many types of tissue-- cardiac muscle,nerve, blood, connective, etc. The job it performs is to pump blood. When various organs work together to perform a specific function in the body, this makes up a system. An example is the circulatory system. In this system are many organs that work together. Arteries, veins, capillaries and heart are all part of the circulatory system. Its job is to circulate blood containing nutrients and oxygen to cells and to pick up cellular wastes. All the systems of the body comprise the organism. An organism is a living thing. It can be as tiny as a microbe, or a complex as a human. When referring to a multicellular organism, the correct order from smallest to largest is-- organelle, cell, tissue, organ, system, organism
Answer:
Neurotransmitters are released from axon terminals via exocytosis
Explanation:
Dendrite is the receiving part of the presynaptic neuron, while axon is the transmitting part of the neuron. So, after initiation, action potentials travel down axons to the terminals. Action potential travels through the membrane of the presynaptic cell causing the voltage-gated channels permeable to calcium ions to open. Ca2+ flow through the presynaptic membrane and increase the Ca concentration in the cell which will activate proteins attached to vesicles that contain a neurotransmitter (e.g. acetylcholine). Vesicles fuse with the membrane of the presynaptic cell, thereby release their contents into the synaptic cleft-space between the membranes of the pre- and postsynaptic cells (exocytosis of the vesicle's content). Neurotransmitter ACh (from the vesicles) binds to its receptors on the postsynaptic membrane and its binding causes depolarization of the target cell (muscle cell). Depolarization occurs because sodium enters the cell as a result of neurotransmitter receptor binding.
