When a neuron is stimulated and sodium channels open, the process of has begun. Structures of the nervous system surrounding, but not part of the central nervous system are part of the . Two consecutive neurons communicate at a , where they physically come together. are a group of natural chemicals that reduce the perception of pain. Supporting cells of the nervous system are collectively called . When potassium channels have been open long enough to go below resting membrane potential, has occurred.

- When a neuron is stimulated and sodium channels open, the process of depolarization has begun.  

- Structures of the nervous system surrounding, but not part of the central nervous system are part of the peripheral nervous system

- Two consecutive neurons communicate at a synapse, where they physically come together.  

- Endorphins are a group of natural chemicals that reduce the perception of pain.  

- Supporting cells of the nervous system are collectively called neuroglia

- When potassium channels have been open long enough to go below resting membrane potential, hyperpolarization has occurred.

Explanation:

Neurons undergo depolarization in response to diverse stimuli (e.g., heat, light, electrical, chemical, etc). The depolarization occurs when sodium (Na+) ions pass through specific channels  (i.e., open voltage-gated Na+ channels) into a neuron, which causes an increase in the positivity of membrane potential. On the other hand, hyperpolarization occurs when potassium (K+) channels remain open and Na+ channels reset, thereby producing an increase in negativity of membrane potential. The peripheral nervous system (PNS) is composed of the cranial nerves, spinal nerves, peripheral nerves, and neuromuscular junctions, which connect the Central nervous system (CNS) to the organs, limbs, and skin. Endorphins (e.g., serotonin) are polypeptides secreted by the pituitary gland and CNS to relieve stress and pain. Neuroglia refers to a class of neural cells that have ectodermal (e.g., astroglia, peripheral glial cells) or mesodermal (e.g., microglia) origins. Neuroglia cells are involved in diverse roles, including, among others, the formation of the blood-brain barrier, homeostatic support, provision of nutrients for neurons, structural support to nerve cells, etc.

volcanoes (an event in the geosphere) release a large amount of particulate matter into the atmosphere. these particles serve as nuclei for the formation of water droplets (hydrosphere). rainfall (hydrosphere) often increases following an eruption, stimulating plant growth (biosphere).