are the chemicals that facilitate the flow of electrical impulses from one neuron to the next across nerve synapses; and the presence or absence of both serotonin and noradrenaline have been linked to aggressive behavior in human beings.

Neurotransmitters

Explanation:

Neurotransmitters are chemicals synthesized in neuron and bloodstream and move to distal sites where they functions by transmitting signals across a synaptic junction, from one neuron to another.

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when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.