Neurons, Neurotransmitters, and the Nervous System: Foundations of Biological Psychology

Neurons: The Brain’s Communicators

Overview of Neurons

Neurons are specialized nerve cells responsible for communication within the nervous system. They transmit information using electrical signals known as action potentials.

• Communication: Neurons interact with each other to process and transmit information.

• Electrical Signals: Information is transmitted via action potentials.

Neural Components

• Cell Body (Soma): Contains the nucleus and builds new cell components.

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

• Axons: "Tails" that transmit information away from the cell body.

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

• Synapse (Synaptic Cleft): Space between neurons where neurotransmitters travel.

Dendrites: Listen/Receive    Axons: Speak/Transmit

Glial Cells

Glial cells support neurons by providing structure, insulation, and nutrients. They play a vital role in psychological functioning and can influence mood and cognition.

• Myelin Sheath: Fatty insulation surrounding axons, speeds up neural transmission.

• Loss of Myelin: Can lead to diseases such as multiple sclerosis.

How a Neuron Fires

Action Potential

An action potential is an electrical charge that travels down the neuron, allowing it to transmit messages to other neurons, muscles, or glands.

• Resting Potential: Neuron is polarized (negative inside, positive outside).

• Selective Permeability: Only certain ions can pass through the neuron’s membrane.

• Action Potential: Brief electrical charge that moves down the axon.

• Return to Resting Potential: Neuron resets after firing.

• Refractory Period: Brief period when the neuron cannot fire again.

Equation:

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

Electrochemical Communication

When an electrical signal reaches the end of an axon, it triggers the release of neurotransmitters into the synapse. These chemical messengers bind to receptors on the receiving neuron’s dendrites.

• Excitatory: Increases likelihood that the neuron will fire.

• Inhibitory: Decreases likelihood that the neuron will fire.

Neurotransmitters

Functions and Examples

Neurotransmitters are chemical messengers that help neurons communicate. They influence mood, emotion, movement, and cognition.

• Serotonin: Regulates mood, appetite, sleep, and pain sensitivity.

• Dopamine: Controls reward, motivation, and voluntary movement.

• Acetylcholine: Involved in muscle action, learning, and memory.

• Glutamate: Major excitatory neurotransmitter, involved in learning and memory.

• GABA: Major inhibitory neurotransmitter, reduces neural activity.

• Norepinephrine: Regulates alertness and arousal.

Agonists and Antagonists

• Agonist: Mimics or enhances the effect of a neurotransmitter.

• Antagonist: Blocks or impedes the normal activity of a neurotransmitter.

Examples: SSRIs (agonist for serotonin), Botox (antagonist for acetylcholine).

Neurotransmitter Table

Neurotransmitter	Major Functions
Glutamate	Excitatory; learning, memory, and autonomic NS reactions
GABA	Inhibitory; lowers arousal, anxiety, facilitates sleep
Acetylcholine	Muscle action, attention, sleep, learning, memory
Serotonin	Mood, sleep, appetite, pain, emotional regulation
Dopamine	Reward, motivation, voluntary movement
Norepinephrine	Alertness, arousal, memory

Nervous System

Peripheral Nervous System (PNS)

The PNS transmits information to and from the central nervous system. It includes the autonomic nervous system, which regulates involuntary functions.

• Sympathetic Division: Prepares the body for "fight or flight" responses.

• Parasympathetic Division: Promotes "rest and digest" functions.

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord, responsible for processing and integrating information.

• Major Components: Cerebral Cortex, Thalamus, Hypothalamus, Limbic System

The Brain

Major Divisions

• Forebrain: Higher cognitive functions

• Midbrain: Movement, sensory processing

• Hindbrain: Basic life functions (breathing, heart rate)

Cerebral Cortex

The cerebral cortex is the outer layer of the brain, divided into four lobes, each responsible for different functions.

• Frontal Lobe: Planning, decision making, motor control, language production

• Parietal Lobe: Sensation, spatial orientation

• Temporal Lobe: Auditory processing, language comprehension

• Occipital Lobe: Visual processing

Lateralization

Left Hemisphere	Right Hemisphere
Fine-tuned language skills, speech comprehension, reading, writing, actions (facial expressions, motion detection)	Coarse language skills, simple speech, tone of voice, visuospatial skills (perceptual grouping, face perception)

Subcortical Structures

• Limbic System: Emotion, motivation, memory

• Thalamus: Sensory relay station

• Hypothalamus: Regulates hunger, thirst, sleep, and homeostasis

• Hippocampus: Memory formation

• Amygdala: Emotion, especially fear and aggression

Brain Mapping and Imaging Techniques

Structural and Functional Imaging

• CT Scan (Computed Tomography): Uses x-rays to create images of brain structure.

• PET Scan (Positron Emission Tomography): Shows brain activity by tracking radioactive substances.

• MRI (Magnetic Resonance Imaging): Uses magnetic fields to produce detailed images of brain tissue.

• fMRI (Functional MRI): Shows changes in metabolic activity over time.

• EEG (Electroencephalography): Records electrical activity of the brain via electrodes on the scalp.

• MEG (Magnetoencephalography): Measures tiny magnetic fields generated by the brain.

• DBS (Deep Brain Stimulation): Modifies brain functions through implanted electrodes.

• TMS (Transcranial Magnetic Stimulation): Applies magnetic fields to the skull to enhance or interrupt brain function.

Example: Brain Mapping

• Phrenology: Early method using skull shape to infer brain function (now obsolete).

• Modern Imaging: CT, MRI, PET, EEG, MEG, DBS, TMS provide insights into brain structure and function.

Additional info: Some explanations and examples have been expanded for clarity and completeness, including definitions and applications of imaging techniques and neurotransmitter functions.