Genetic Predisposition

The inherited likelihood of developing specific traits or conditions due to genetic factors from biological parents.

The Nervous System

is the body's communication network, consisting of a complex system of nerves, neurons, and specialized cells.

Central Nervous System

responsible for processing information, coordinating responses, and regulating bodily functions.

Peripheral Nervous System

consists of all the nerves and ganglia (nerve bundles) outside the brain and spinal cord.

It serves as a communication network, transmitting sensory information from the body to the central nervous system (CNS).

Autonomic Nervous System

A division of the peripheral nervous system that regulates involuntary bodily functions, It operates automatically, without conscious control.

• Consists of two main branches: the sympathetic nervous system and the parasympathetic nervous system.

Sympathetic Nervous System

is responsible for activating the body's "fight or flight" response in times of stress or danger.

Increases heart rate, dilates airways, and redirects blood flow to essential organs, preparing the body to respond to perceived threats.

Parasympathetic Nervous System

is responsible for promoting relaxation and restoring the body to a calm state after experiencing stress or danger.

It slows heart rate, constricts airways, and enhances digestion, allowing the body to conserve energy and recover from stressors.

Somatic Nervous System

A division of the peripheral nervous system responsible for controlling voluntary movements and relaying sensory information from the body to the central nervous system.

Reflex Arc

A neural pathway that controls reflex actions, allowing for rapid, automatic responses to sensory stimuli without conscious thought (primitive reflexes).

Sensory neurons detect stimuli and send signals to the spinal cord. Interneurons relay this information to motor neurons, which trigger reflexive muscle or gland responses, such as withdrawing a hand from a hot surface.

They protect the body and enable quick reactions to potential dangers.

Sensory Neurons

Specialized (afferent) nerve cells that transmit sensory information from sensory receptors, such as those in the skin, muscles, and organs, to the central nervous system (brain and spinal cord).

• They detect various stimuli, including touch, temperature, and environmental changes, and convert these stimuli into electrical signals that can be processed by the brain

Motor Neurons

Specialized (efferent) nerve cells that transmit signals from the central nervous system (brain and spinal cord) to muscles, glands, and organs, initiating and controlling voluntary and involuntary movements.

They receive commands from the brain or spinal cord and convey these signals to muscles, causing them to contract or relax.

Interneurons

Nerve cells that serve as connectors within the central nervous system, relaying signals between sensory neurons and motor neurons.

Stimulus

You accidentally touch the hot stove while reaching for a pot.

Sensory Neurons

Specialized sensory neurons in your skin detect the extreme heat from the stove. These sensory neurons quickly transmit electrical signals to your spinal cord.

Interneurons

Upon reaching your spinal cord, interneurons quickly relay the sensory signals to motor neurons.

Motor Neurons

… receive the signal and send a rapid response back to the muscles in your hand.

Muscle Response

The motor neurons trigger your hand muscles to contract involuntarily. This reflex action causes your hand to jerk away from the hot stove, protecting you from further injury.

Neurons

• The cell’s single lengthy axon fiber passes the message through its terminal branches to other neurons or to muscles or glands 

• Axons are as long as centimeters or meters long.  A human neuron carrying orders from the brain to a leg muscle, for example, has a cell body and axon roughly on the scale of a basketball attached to a rope that’s 4 miles (6.4 kilometers) long. 

Glial Cells

The "glue cells" of the nervous system.  Glia provide structural support, insulation, and nourishment to neurons.

• Neurons are like queen bees; on their own, they cannot feed or sheathe themselves. Glial cells are the worker bees.

• They provide nutrients and insulating myelin (Oligodendrocytes/Schwann cells), guide neural connections, and clean up waste after neurons send messages to one another (Microglia/Astrocytes).

Multiple Sclerosis “MS”

A chronic autoimmune disease that affects the central nervous system, including the brain and spinal cord.

• It occurs when the immune system mistakenly attacks the protective myelin sheath, a fatty substance that surrounds and insulates nerve fibers, causing inflammation and damage.

Neural Transmission

The process by which neurons communicate with each other through electrical and chemical signals.  2 to 200 mph (milliseconds-neurons vs nanoseconds-wire vs picoseconds-computer chips).

Resting Potential

The stable, negative electrical charge that exists on the inside of the cell membrane of a neuron when it is not actively transmitting signals.

• It is maintained by the unequal distribution of ions, with more cations (+) outside the cell and more anions (-) inside.

Threshold

The level of stimulation required to trigger an action potential in a neuron. It is the minimum amount of stimulation necessary to produce a response.

Depolarization

The phase of action potential where the inside of the neuron becomes less negative compared to the outside due to the influx of positively charged ions, such as sodium ions, through ion channels in the cell membrane.

• This change in electrical charge triggers the neuron to fire an action potential, initiating the transmission of an electrical impulse along the neuron's axon.

Action Potential

A brief electrical impulse that travels along the axon of a neuron.

• It occurs when the neuron receives a stimulus that causes the inside of the cell to become more positively charged than the outside.

• The temporary inflow of positive ions is the neural impulse — the action potential.

• This electrochemical process can repeat up to 100 times a second.

Refractory Period

A brief period following an action potential during which a neuron is unable to generate another action potential.

• This period occurs because the neuron's sodium channels are temporarily inactivated and the cell membrane returns to its resting state.

The Synapse

The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or synaptic cleft. 

• “Like elegant ladies air-kissing so as not to muss their makeup, dendrites and axons don’t quite touch,” noted poet Diane Ackerman (2004, p. 37). 

• Within 1/10,000th of a second, the neurotransmitter molecules cross the synaptic gap and bind to receptor sites.

Reuptake

The process in which neurotransmitters that have been released into the synapse are reabsorbed by the presynaptic neuron from which they were originally released.

Reuptake Inhibitors

Medications that block the reabsorption of neurotransmitters by the sending neuron, thereby increasing the concentration of neurotransmitters in the synaptic cleft and enhancing neurotransmission.

Myasthenia Gravis

A chronic autoimmune disorder that affects the neuromuscular junction, where nerve impulses are transmitted to muscles.

• It occurs when the immune system produces antibodies that block or destroy the receptors for acetylcholine, a neurotransmitter that stimulates muscle contraction.

Neurotransmitters

 Chemical messengers produced in the CNS that transmit signals between neurons, allowing for communication within the nervous system.

• They are released from presynaptic neurons into the synaptic cleft, where they bind to specific receptor sites on postsynaptic neurons, initiating or inhibiting a neural impulse.

Excitatory Neurotransmitters

Chemicals released by neurons that increase the likelihood of an action potential occurring in the postsynaptic neuron.

• They bind to receptor sites on the postsynaptic membrane, causing depolarization and making the neuron more likely to fire an action potential.

Glutamate

The primary excitatory neurotransmitter in the CNS, playing a key role in synaptic transmission and neuronal communication. 

• It is involved in various brain functions, including learning, memory, and neural plasticity.  

• Too much glutamate leads to migraines and seizures.

Acetylcholine

The neurotransmitter that plays a fundamental role in both the central nervous system and the peripheral nervous system.

• It is involved in various functions, including muscle contraction, memory, and learning.  

• ACh production in motor neurons decreases with Alzheimer's.

Norepinephrine

The neurotransmitter that functions as both a hormone and a neurotransmitter in the body. It is involved in the body's daily function and the "fight or flight" response, regulating arousal, attention, and stress.

• It plays a critical role in maintaining heart rate, blood pressure, and alertness especially during times of stress or danger.  

• Also regulates mood and undersupply is linked with depression while oversupply leads to excessive stress.

Serotonin

A neurotransmitter that plays a vital role in regulating mood, sleep, appetite, and stress.

• Serotonin pathways in the brain influence mood and emotional well-being, making it an essential neurotransmitter for mental health.  Undersupply leads to depression.

• Selective Serotonin Reuptake Inhibitors (SSRI drugs) like Prozac and Zoloft, alleviate depression symptoms by ensuring that serotonin remains in the synaptic cleft.  

Endorphins

The inhibitory neurotransmitters produced by the brain and central nervous system that act as natural pain relievers and mood enhancers.

• They are released in response to stress, pain, or intense physical activity, such as exercise or excitement.

• Not enough endorphins can be linked to depression, anxiety, chronic pain, and substance use disorders.

GABA

A neurotransmitter that acts as the primary inhibitory neurotransmitter in the central nervous system. It promotes relaxation and reduces anxiety. 

• Undersupply leads to seizures, tremors and insomnia.

Oxytocin

Hormone and neurotransmitter that plays a key role in social bonding.

Melatonin

The hormone that regulates the sleep-wake cycle and circadian rhythms in the body.

• Melatonin plays a crucial role in maintaining the body's internal clock and ensuring restful sleep.

Leptin

The hormone produced primarily by fat cells that regulates energy balance and appetite. It acts on the hypothalamus in the brain to suppress appetite and increase energy expenditure.

Ghrelin

Ghrelin The hormone produced primarily by the stomach and small intestine that stimulates appetite and promotes hunger.

Psychoactive Drugs

are substances that alter brain function, leading to changes in perception, mood, consciousness, cognition, or behavior.  

• Drugs are not made by our bodies, rather they are manufactured by humans.

• They act on the central nervous system and can be categorized into stimulants, depressants, hallucinogens, and opioids.

Opioids

Psychoactive drugs that act on opioid receptors in the brain and body, producing pain relief, euphoria, and sedation.

nicotine

which increase alertness, and dopamine, which calms anxiety.

• 7 million (primary smokers) & 1.2 million

Heroin

 highly addictive opioid drug derived from morphine. It produces intense euphoria, pain relief, and sedation by binding to opioid receptors in the brain.

Fentanyl

A highly addictive opioid drug made in labs. It is cheap and highly potent, increasing opioid overdoses in the U.S. to 85,000/year, at twice that of car accident death rates, (CDC, 2023).

Marijuana

 A psychoactive drug derived from the cannabis plant. It contains THC, which alters mood, perception, and cognition. Effects include relaxation, altered perception of time, and heightened sensory experiences.

• One study of nearly 4000 Canadian seventh graders concluded that marijuana use at that early age was “neurotoxic”; it predicted long-term cognitive impairment (Harvey, 2019). 

Hallucinogens

Drugs that alter perception, mood, and cognitive processes, often causing hallucinations or profound changes in consciousness.

Methamphetamine

eads to heightened energy and euphoria and massive release of dopamine, can last for 8 hours or longer.  35,000 overdoses annually in the U.S.

MOlly

triggers dopamine release, but its major effect is releasing stored serotonin and blocking its reuptake, thereby prolonging serotonin’s feel-good flood (Braun, 2001).