Vesicles containing neurotransmitters must bind to the membrane at the axon terminal in order to release their contents into the synapse. This binding is dependent upon an influx of calcium ions that occurs with an action potential. The other ions listed are important for other parts of the action potential, but it is calcium that is crucial for this particular step. 

Voltage-gated potassium ion channels are responsible for bringing the membrane potential back to or below resting the potential. This is achieved when these channels open, which can only happen at very positive voltages (hence voltage-gated), and as the potassium ions rapidly leave the cell, the cell repolarizes to a negative potential.

The dendrites receive the messages sent from other neurons. Neurotransmitters are released into synaptic clefts between two neurons and bind receptors on the postsynaptic neuron's dendrites. Axons are nerve fibers that carry electrical impulses away from the cell body of a neuron. The nodes of Ranvier are unmyelinated spots on myelinated axons that facilitate conduction of a nerve impulse down an axon.

The effect of acetylcholine is terminated by acetylcholinesterase breaking down acetylcholine. If acetylcholinesterase is inhibited, the degradation of acetylcholine would not occur, and the effects of acetylcholine will be prolonged. 

GABA is only found in the brain and has an inhibitory function. Although glycine is also inhibitory and found in the central nervous system, it's mainly concentrated in the spinal cord and brainstem. Glutamate and acetylcholine are also found in the central nervous system, but are excitatory. Norepinephrine is excitatory and associated with the adrenal glands, not the central nervous system. 

When thinking of hormones, it helps to remember that they are generally slow acting, affect all types of tissues at once, and can last for long periods of time in the body. As a result, hormones would not be described as fast-acting in the body.

In contrast, neurotransmitters are generally considered fast-acting, as they are released to a small, targeted area and elicit an immediate response.

The pituitary gland is composed of an anterior and a posterior pituitary lobe, both of which are responsible for the secretion of various hormones.

The anterior pituitary secretes thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), prolactin, luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), and growth hormone (GH). It can help to remember these hormones with the pneumonic "FLAT PEG."

The posterior pituitary secretes oxytocin and antidiuretic hormone (ADH). Antidiuretic hormone is also known as vasopressin.

Calcitonin is secreted by the thyroid gland, not the pituitary.

Endocrine glands only secrete their products into the blood. Sweat glands secrete sweat outside the body and never touch the blood. Similarly, anything inside the gastrointestinal tract is technically outside the body! For something (broken-down food molecules, water, salts etc.) to enter the body, it must be absorbed across the walls of the gastrointestinal tract. Remember, humans are like hollow cylinders in the sense that we have a tube from mouth to anus, which is considered outside the body. 

Endocrine glands are glands of the endocrine system that secrete hormones (their products) directly into the blood rather than through a duct (exocrine organs use ducts). The major glands of the endocrine system include: adrenal glands, hypothalamus, parathyroid glands, thyroid gland, testes, ovaries, pancreas, pituitary gland, and pineal gland. The hypothalamus and pituitary gland are considered neuroendocrine organs. The pineal gland is located in the brain and secretes the hormone melatonin, which helps regulate the circadian (sleep-wake) cycle, especially before sleep.

The adrenal cortex has three zones. The first zone releases aldosterone, the second releases cortisol, and the third releases androgens, which includes testosterone. Vasopressin (antidiuretic hormone) is synthesized by the hypothalamus and released by the posterior pituitary.