1.3 The Neuron and Neural Firing

Neurons and glial cells are the building blocks of our nervous system, making all our behaviors and mental processes possible. These specialized cells talk to each other through electrical and chemical signals, creating complex networks that process info and make us do stuff.

Neural transmission is like a game of telephone, but with precise steps from resting potential to action potential firing. Neurotransmitters and hormones are the chemical messengers that influence our behavior and mental states. Psychoactive drugs can mess with these processes, affecting how neurotransmitters work and changing our behavior.

quick cram review

• neurons send signals to control behavior and thinking; glial cells support them.
• neural transmission is how neurons communicate using electrical and chemical signals.
• psychoactive drugs change behavior by affecting neurotransmitters (stimulants → speed up activity, depressants → slow down activity, hallucinogens → change perception, opioids → relieve pain)

Neuron structures and functions

Neural cells in behavior

Neurons and glial cells work together as the basic functional units of the nervous system. While neurons are the primary information processors, glial cells provide essential support that enables proper neural function.

• Neurons are specialized cells that:
  • Transmit information via electrical and chemical signals
  • Form complex networks for information processing
  • Connect to create neural circuits

Glial cells perform several critical support functions:

• Create structural scaffolding for neural networks
• Insulate neurons to enhance signal transmission
• Facilitate communication between neurons
• Remove waste products to maintain healthy function

Together, these neural cells enable all behavior and mental processes, from basic sensory input to complex decision-making and motor output.

Spinal cord reflex arc

The reflex arc demonstrates a simple but essential neural circuit that enables rapid, automatic responses without brain involvement. This process occurs in the spinal cord and involves multiple types of neurons working in sequence.

Example: Quickly pulling your hand away from a hot stove before consciously feeling pain

Key components of the reflex arc:

• Sensory neurons detect initial stimulus (heat)
• Interneurons relay information within the spinal cord
• Motor neurons activate muscles for response (pulling the hand away)
• Entire process occurs before conscious awareness

Neural transmission process

Neural transmission mechanisms

Neural transmission follows a precise sequence that enables neurons to communicate effectively. This process begins with the resting state and proceeds through several distinct phases.

The basic sequence includes:

1. Maintenance of resting potential (negative charge inside cell)
2. Stimulus reaches threshold
3. Action potential fires (all-or-nothing principle)
4. Depolarization occurs
5. Refractory period follows
6. Reuptake completes the cycle

Disruptions to this process can cause various disorders:

• Multiple sclerosis: Damage to the insulation (myelin) around neurons impairs signal transmission
• Myasthenia gravis: Antibodies attack receptors for the neurotransmitter acetylcholine, weakening muscle contractions

Neurotransmitter functions

Neurotransmitters serve as the chemical messengers ✉️ of the nervous system, each with specific roles in neural communication.

Excitatory neurotransmitters increase likelihood neural firing:

• Glutamate (most common in brain)
• Norepinephrine (increases arousal alertness)

Inhibitory neurotransmitters decrease likelihood of neural firing:

• GABA (main inhibitory transmitter, balances out excitation)
• Serotonin (regulates mood, sleep, and appetite)

Some neurotransmitters have both excitatory and inhibitory effects:

• Dopamine (motivation, reward, and motor control)
• Acetylcholine (muscle contractions, learning and memory)
• Endorphins (natural pain relief and euphoria-inducers)
• Substance P (pain signaling from body to brain)

Hormones in behavior

Hormones act as chemical messengers throughout the body, similar to neurotransmitters but produced by glands and traveling via bloodstream to influence behavior and mental processes.

The key hormones affecting behavior and mental-processes include:

• Adrenaline (epinephrine): triggers "fight-or-flight" response during stress
• Leptin: controls feelings of fullness to regulate appetite and body weight
• Ghrelin: stimulates hunger and food-seeking behavior
• Melatonin: regulates sleep cycles based on light exposure
• Oxytocin: promotes social bonding, trust, and maternal behavior

Psychoactive drugs and behavior

Drug effects on neurotransmitters

Psychoactive drugs interact with neurotransmitter systems in several ways to alter neural communication and behavior.

Three main mechanisms of action:

1. Agonists mimic or enhance neurotransmitter effects, ✅ neural firing

   • Example: Opioids like heroin and morphine mimic endorphins

2. Antagonists block neurotransmitter effects, 🚫 neural firing

   • Example: Caffeine blocking adenosine

3. Reuptake inhibitors block the reabsorption of neurotransmitters back into the releasing neuron, prolonged neurotransmitter activity

   • Example: Antidepressants like Prozac are serotonin reuptake inhibitors, helping to elevate mood

Psychological and physiological effects

Different classes of psychoactive drugs produce distinct effects on behavior and mental processes.

Stimulants increase arousal and activity:

• Mild: caffeine, nicotine
• Potent/addictive: cocaine, amphetamines

Depressants reduce neural activity and have sedating effects:

• Alcohol affects judgment, coordination, and memory
• Benzodiazepines (Xanax, Valium) treat anxiety and sleep issues

Hallucinogens alter perception:

• Marijuana contains THC which affects sensory processing, judgement, and memory
• LSD and psilocybin ("magic mushrooms") can cause vivid hallucinations and feelings of dissociation from reality

Opioids are powerful pain relievers that also induce euphoria and relaxation

• Prescription versions treat severe pain (OxyContin, Vicodin)
• Illegal forms like heroin carry high risks (Heroin)

Drug tolerance and addiction

Drug tolerance develops as the brain adapts to repeated drug exposure, requiring larger doses to achieve the same effects. This adaptation reflects the brain's attempt to maintain balance despite the drug's presence.

Addiction involves:

• Compulsive drug use despite negative consequences
• Activation of brain reward systems, reinforcing the behavior
• Withdrawal symptoms upon cessation:
  • Physical symptoms (nausea, tremors)
  • Psychological symptoms (anxiety, cravings)
  • Severity varies by drug type and usage pattern