Neuroscience Foundations in Psychology: Neurons, Neurotransmitters, and Brain Structure

The Nervous System: Structure and Function

Neurons: The Building Blocks

Neurons are specialized cells responsible for transmitting information throughout the nervous system. They communicate via electrical and chemical signals, forming the basis of all neural activity.

• Cell Body (soma): The central part of the neuron, containing the nucleus and building new cell components.

• Dendrites: Branch-like extensions that receive incoming signals from other neurons.

• Axons: Long "tails" that transmit electrical impulses away from the cell body.

• Axon Terminals: Knobs at the end of the axon containing synaptic vesicles filled with neurotransmitters.

• Synapse (synaptic cleft): The gap between neurons where neurotransmitters are released to transmit signals to the next neuron.

Glial Cells

Glial cells are non-neuronal cells that provide support, protection, and nutrition to neurons. They play a crucial role in psychological functioning and brain health.

• Glial means "glue"; they are plentiful in the brain.

• Support neurons, involved in making myelin.

• Bodyguard function: feed and protect neurons.

Myelin Sheath

The myelin sheath is a fatty insulation produced by glial cells that surrounds axons, increasing the speed and efficiency of electrical signal transmission.

• Loss of myelin (e.g., in Multiple Sclerosis) causes erratic signals and impaired function.

Action Potential: How Neurons Fire

Neurons communicate via electrical impulses called action potentials. This process involves several steps:

• Step 1: Resting Potential Neuron is polarized (negative inside, positive outside). Sodium gates are closed, preventing Na+ from entering.

• Step 2: Action Potential When stimulated, sodium gates open, Na+ rushes in, depolarizing the neuron. The action potential travels down the axon. All-or-none law applies: the neuron either fires or it doesn't. Frequency = intensity.

• Step 3: Repolarization Neuron returns to resting state.

Formula:

$\text{Action Potential} = \text{Depolarization} \rightarrow \text{Repolarization}$

Neurotransmitters: Chemical Communication

Definition and Function

Neurotransmitters are chemical messengers that allow neurons to communicate across synapses. They influence mood, movement, learning, and are implicated in mental illness.

• Examples: Serotonin (mood), Dopamine (reward, movement), Acetylcholine (motor control), GABA (inhibition), Glutamate (excitation).

Neurotransmitter Lifecycle

• Release: Action potential triggers release of neurotransmitters into the synaptic cleft.

• Reuptake: Excess neurotransmitters are reabsorbed by the presynaptic neuron for recycling. Some drugs (e.g., cocaine) block reuptake, prolonging effects.

Neurotransmitter Effects

• Agonists: Mimic or enhance the effect of neurotransmitters.

• Antagonists: Block or dampen the effect of neurotransmitters.

Glutamate & GABA

• Glutamate: Main excitatory neurotransmitter; increases likelihood of neuron firing. Excess can be toxic and is linked to disorders like schizophrenia.

• GABA: Main inhibitory neurotransmitter; dampens neural activity.

• Examples: Caffeine (ups glutamate, downs GABA); Alcohol (ups GABA, downs glutamate).

Dopamine

• Involved in pleasure, reward, voluntary movement, and attention.

• Deficit: Parkinson's disease.

• Excess: Schizophrenia symptoms.

Serotonin

• Made from tryptophan; found in brain, gut, and blood platelets.

• Regulates mood, sleep-wake cycles, satiety, pain perception, and emotional support.

• Influenced by diet, exercise, sunlight, and sleep.

• SSRIs (e.g., Zoloft, Prozac) block serotonin reuptake to treat depression.

Major Divisions and Regions of the Brain

Overview

The brain is divided into the forebrain, midbrain, and hindbrain. The cerebral cortex (outer layer) is responsible for higher-order thinking and voluntary action, while subcortical structures (e.g., limbic system) lie beneath the cortex.

Hindbrain

• Controls basic functions like eating and sleeping.

• Major components:

  • Medulla: Controls heartbeat, breathing, swallowing, blood pressure.

  • Pons: Sleep and arousal.

  • Cerebellum: Motor coordination (timing, leg/arm movements).

  • Reticular Activating System: Regulates arousal, sleep/wakefulness, attention.

Midbrain

• Controls movement and transmits information between the brain and eyes/ears.

Forebrain

• Manages complex cognitive activities, sensory and associative functions, and voluntary motor activities.

• Major components: cerebral cortex, thalamus, hypothalamus, limbic system.

Lobes of the Brain

• Frontal: Planning, decision making.

• Parietal: Sensation (somatosensory).

• Temporal: Auditory processing.

• Occipital: Vision.

Lateralization

Cognitive functions can be specialized to one hemisphere of the brain.

Left Hemisphere	Right Hemisphere
Fine-tuned language skills: speech comprehension, production, reading, writing Actions: making facial expressions, motion detection	Coarse language skills: simple speech, simple writing, tone of voice Visuospatial skills: perceptual grouping, face perception

Split Brain Surgery

• Procedure to sever the corpus callosum to reduce spread of epileptic seizures.

Frontal Lobes

• Responsible for planning, executive functions, and motor control.

• Contains Broca's area (language production) and prefrontal cortex ("CEO" of thinking, planning, language).

Phineas Gage: Prefrontal Cortex Damage

• Railroad foreman who suffered severe prefrontal cortex injury, resulting in dramatic personality change.

The Psychopathy Connection

• PFC damage linked to deficits in moral judgment, empathy, and impulse control.

Parietal Lobe

• Somatosensory cortex: sensitivity to pressure, pain, temperature.

• Communicates sensory info to motor cortex.

Temporal Lobe

• Hearing, understanding language, storing autobiographical memories.

• Contains auditory cortex and Wernicke's area (language comprehension).

Neural Plasticity

The brain is adaptable and can change throughout life.

• Myelination: Makes neurons faster and more efficient.

• Pruning: Removes unused synaptic connections to improve efficiency.

• Plasticity decreases in adulthood.

Intergenerational Trauma

Trauma can be passed down through generations, affecting brain structure, function, and chemistry.

• Observed in children of Holocaust survivors, Vietnam veterans, and residential school survivors.

• PTSD may be associated with changes in brain function that are heritable.

Summary Table: Neurotransmitters and Effects

Neurotransmitter	Main Function	Associated Disorders
Acetylcholine	Motor control, learning, memory	Alzheimer's disease (deficit)
Dopamine	Pleasure, reward, movement	Parkinson's (deficit), Schizophrenia (excess)
Serotonin	Mood, sleep, appetite	Depression (deficit)
GABA	Inhibition, dampens neural activity	Anxiety (deficit)
Glutamate	Excitation, learning, memory	Schizophrenia (excess)

Additional info: Some explanations and examples have been expanded for clarity and completeness.