Central Nervous System

Brain and spinal cord; interacts with all processes in the body.

Peripheral Nervous System

Relays messages from the central nervous system to the rest of the body and includes the autonomic and somatic nervous systems.

Autonomic Nervous System

Governs processes that are involuntary and includes the parasympathetic and sympathetic nervous systems.

Sympathetic Nervous System

The division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations.

Parasympathetic Nervous System

The division of the autonomic nervous system that calms the body, conserving its energy.

Somatic Nervous System

The division of the peripheral nervous system that controls the body's skeletal muscles; governs processes that are voluntary.

Neurons

Neural cells that transmit information.

Glial Cells

Cells in the nervous system that support, nourish, and protect neurons.

Reflex Arc

In the spinal cord; demonstrates how neurons within the central and peripheral nervous systems work together to respond to stimuli.

Sensory Neurons

Neurons that carry incoming information from the sensory receptors to the brain and spinal cord.

Motor Neurons

Neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.

Interneurons

Neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs.

Neural Transmission

Electrochemical communication within and between neurons and the final destination.

Action Potential

A neural impulse; a brief electrical charge that travels down an axon.

All-or-Nothing Principle

Once action potential reaches the threshold, it either fires or doesn't.

Depolarization

Change in charge when neuron fires positive ions through the cell membrane.

Refractory Period

The time following an action potential during which a new action potential cannot be initiated.

Reuptake

A neurotransmitter's reabsorption by the sending neuron.

Neural Threshold

The minimum level of stimulation required to get a neuron to fire.

Multiple Sclerosis

A chronic disease of the central nervous system marked by damage to the myelin sheath.

Myasthenia Gravis

A chronic autoimmune disease that affects the neuromuscular junction and produces serious weakness of voluntary muscles.

Excitatory Neurotransmitters

Chemicals released from the terminal buttons of a neuron that provoke the next neuron into firing.

Inhibitory Neurotransmitters

Chemicals released from the terminal buttons of a neuron that prevent the next neuron from firing.

Dopamine

A neurotransmitter associated with movement, attention, learning, and the brain's pleasure and reward system.

Serotonin

Affects mood, hunger, sleep, and arousal. Undersupply linked to depression.

Norepinephrine

A neurotransmitter involved in arousal, as well as in learning and mood regulation.

Glutamate

A major excitatory neurotransmitter involved in memory.

GABA

A major inhibitory neurotransmitter that regulates sleep and wake cycles.

Endorphins

Natural, opiate-like neurotransmitters linked to pain control and pleasure.

Substance P

A neurotransmitter involved in the transmission of pain messages to the brain.

Acetylcholine

Enables muscle action, learning, and memory.

Hormones

Chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues.

Adrenaline

A hormone secreted by the adrenal glands, increasing blood circulation, breathing, and preparing muscles for exertion.

Leptin

A hormone produced by fat cells that acts as a satiety factor in regulating appetite.

Ghrelin

A hunger-arousing hormone secreted by an empty stomach.

Melatonin

A hormone produced by the pineal gland that regulates sleep.

Oxytocin

A hormone released by the posterior pituitary that stimulates uterine contractions and milk ejection during breastfeeding.

Psychoactive Drugs

Chemicals that affect the nervous system and result in altered consciousness.

Agonist

A molecule that binds to a receptor and stimulates a response.

Antagonists

Drugs that block the actions of neurotransmitters.

Reuptake Inhibitors

Drugs that interfere with neurotransmitter reabsorption, leaving more in the synapse.

Stimulants

Drugs that excite neural activity and speed up body functions (e.g., caffeine, nicotine).

Caffeine

A mild stimulant found in coffee and tea.

Cocaine

A powerful stimulant that increases alertness and euphoria.

Depressants

Drugs that reduce neural activity and slow body functions.

Alcohol

A common depressant.

Hallucinogens

Drugs that distort perceptions and evoke sensory images without sensory input.

Marijuana

A drug whose effects include euphoria, impairment of judgment and concentration, and sometimes hallucinations.

Opioids

Synthetic opiates prescribed for pain relief.

Heroin

A highly addictive narcotic derived from opium.

Tolerance

The diminishing effect of a drug with regular use, requiring higher doses.

Addiction

Compulsive drug craving and use despite negative consequences.

Withdrawal

The discomfort and distress that follow discontinuing an addictive drug.