Neurons, Neurotransmission, and the Brain: Foundations of Biological Psychology

Neural Components and Communication

Structure and Function of Neurons

Neurons are specialized nerve cells that serve as the fundamental building blocks of the nervous system. They transmit information via electrical and chemical signals, enabling communication throughout the body.

• Cell body (soma): The central part of the neuron, responsible for building new cell components and maintaining cell health.

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

• Axons: Long, tail-like structures that transmit information away from the cell body.

• Axon terminal: The knob at the end of the axon containing synaptic vesicles filled with neurotransmitters (e.g., dopamine, serotonin).

• Synapse (synaptic cleft): The space between neurons where neurotransmitters travel, allowing communication between cells.

Glial cells are plentiful in the brain and play a supportive role, including producing myelin and protecting neurons.

• Myelin sheath: Fatty insulation made by glial cells that surrounds axons, increasing the speed and efficiency of electrical signal transmission.

• Multiple sclerosis (MS): A disease where loss of myelin causes erratic signals and impaired neural function.

How Neurons Fire: The Action Potential

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

1. Resting potential: The neuron is polarized (negative inside, positive outside). Selectively permeable gates do not allow sodium ions (Na+) to pass through.

2. Action potential: A brief electrical charge travels down the axon, transmitting neural messages to other neurons or muscles. When stimulated, the neuron goes from negative to positive as gates open.

3. Repolarization: The neuron becomes negative again as potassium ions (K+) flow out, repolarizing the axon.

4. Return to resting potential: The neuron resets to its original state.

5. Refractory period: A brief period during which the neuron cannot fire, regardless of stimulation.

Electrochemical communication occurs when an electrical signal reaches the end of an axon, triggering the release of neurotransmitters into the synapse.

Neurotransmitters and Their Functions

Types and Roles of Neurotransmitters

Neurotransmitters are chemical messengers that help neurons communicate. They influence a wide range of functions:

• Serotonin & dopamine: Influence emotions and mood.

• Acetylcholine: Controls movement.

• GABA & norepinephrine: Regulate sleep and alertness.

• Glutamate: Involved in learning and memory.

Neurotransmitters can be excitatory (increase the likelihood of neuron firing) or inhibitory (decrease the likelihood).

Neurotransmission: Release and Reuptake

After neurotransmitters are released into the synaptic cleft, they bind to receptors on the postsynaptic neuron. Excess neurotransmitters are removed by:

• Drifting away

• Being broken down

• Reuptake: Neurotransmitters are reabsorbed by the presynaptic neuron. Some drugs (e.g., cocaine) block reuptake, prolonging neurotransmitter effects.

Agonists and Antagonists

Drugs can affect neurotransmitter activity:

• Agonists: Mimic or enhance the effect of a neurotransmitter (helpers), resulting in more receptor activation.

• Antagonists: Block or impede the normal activity of a neurotransmitter (blockers).

Major Neurotransmitters

• Glutamate: Excitatory, associated with learning and memory. High doses may contribute to schizophrenia and other disorders.

• GABA: Inhibitory, dampens neural activity. Less brain activity compared to glutamate.

• Acetylcholine: First neurotransmitter discovered. Involved in arousal, attention, memory, and sleep. Loss of acetylcholine is linked to Alzheimer's disease.

• Dopamine: Associated with pleasure, reward, voluntary movement, and attention. Deficiency leads to Parkinson's disease; excess is linked to schizophrenia.

• Serotonin: Regulates mood, sleep-wake cycles, satiety, cognition, emotional memory, and pain perception. Low levels are associated with depression and anxiety.

Selective serotonin reuptake inhibitors (SSRIs) are used to treat depression by blocking the reuptake of serotonin (e.g., Zoloft, Prozac).

The Nervous System: Organization and Overview

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord. It interprets and stores information, and communicates with muscles, glands, and organs.

• Brain: Finishes developing at age 25. Responsible for higher cognitive functions and voluntary actions.

• Spinal cord: Pathway connecting the brain and peripheral nervous system.

Neural Plasticity

The brain is adaptable and can change throughout life. Key processes include:

• Myelination: Increases neuron speed and efficiency.

• Pruning: Reorganizes synaptic connections, making neural pathways more efficient.

• Plasticity decreases in adulthood.

Intergenerational trauma has been observed in children of Holocaust survivors and other trauma-exposed populations, suggesting that trauma can be passed down through environmental or behavioral mechanisms.

Major Regions of the Brain

Hindbrain

The hindbrain controls basic functions such as eating, sleeping, and breathing. Damage to this region can be fatal.

• Medulla: Controls vital functions (heartbeat, muscles for breathing, vomiting, blood pressure, swallowing).

• Pons: Regulates sleep and arousal.

• Cerebellum: Coordinates motor activity (timing of leg and arm movements).

• Reticular Activating System: Key in arousal and attention; dysregulated in ADHD.

Midbrain

The midbrain controls movement and transmits information that enables seeing and hearing.

Forebrain

The forebrain manages complex cognitive activities, sensory and associative functions, and voluntary motor activities.

• Cerebral cortex: Outermost layer, "grey matter," responsible for higher mental processes (sense, self, reasoning). Consists of two hemispheres (4 lobes) connected by the corpus callosum.

• Thalamus: Sensory relay station, sends signals to the right places.

• Hypothalamus: Regulates hunger, thirst, sleep, and links emotions to physical reactions.

• Limbic system: Emotional center, involved in smell, motivation, and memory.

Cerebral Cortex: Lobes

Lobe	Main Function
Frontal	Planning, decision making, executive functions
Parietal	Sensation (somatosensory: pressure, pain, temperature)
Temporal	Auditory processing, language, autobiographical memory
Occipital	Vision, visual processing

Lateralization

Cognitive functions may rely more on one side of the brain than the other. For example, language production is typically left-lateralized, while visuospatial skills are right-lateralized.

Split-brain Surgery

A procedure that severs the corpus callosum to reduce the spread of epileptic seizures, revealing lateralized brain functions.

Frontal Lobes

• Broca's area: Responsible for language production. Damage leads to Broca's aphasia (impaired speech).

• Phineas Gage: Famous case of prefrontal cortex damage resulting in dramatic personality change.

• Psychopathy connection: Prefrontal cortex injuries can result in deficits in moral judgment, empathy, and impulse control.

Parietal Lobe

• Somatosensory cortex: Sensitive to pressure, pain, and temperature; communicates with the motor cortex.

Temporal Lobe

• Responsible for hearing, understanding language, and storing autobiographical memories.

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

Occipital Lobe

• Specialized for visual processing and higher-order visual functions (e.g., recognizing complex shapes).

Limbic System

Key Structures and Functions

• Amygdala: Detects danger, triggers fear or aggression.

• Hippocampus: Forms new long-term memories; damage leads to inability to form new memories.

• Hypothalamus: Regulates hunger, thirst, sleep, and links emotions to physical reactions.

• Thalamus: Sensory relay station.

Toxoplasmosis

A parasitic infection that can reduce fear responses by destroying the amygdala. Research suggests links between toxoplasmosis and changes in risk-taking, personality, and reaction to fear.

Concussion

A traumatic brain injury that affects brain function. Types include direct impact injury, acceleration-deceleration injury, and blast brain injury.

Autonomic Nervous System

Divisions and Functions

• Sympathetic: Fight or flight response.

• Parasympathetic: Rest and digest functions.

Physiological measurements linked to the autonomic nervous system (e.g., skin response, heart rate, breathing) can be used to detect deception.

Brain Mapping Methods

Overview of Techniques

• Phrenology: Discredited method that linked bumps on the skull to personality traits.

• Brain damage studies: Understanding brain function by observing cognitive changes after injury.

• Neuropsychology tests: Assess cognitive function, language, and motor skills.

• Computerized Tomography (CT) scan: Uses X-rays to create images of the brain.

• Positron Emission Tomography (PET) scan: Uses radioactive substances to monitor brain activity.

• Magnetic Resonance Imaging (MRI) & Functional MRI (fMRI): Uses magnetic fields to produce images and show changes in metabolic activity.

• Magnetoencephalography (MEG): Measures magnetic fields generated by neural activity; useful for detecting epilepsy.

• Deep Brain Stimulation (DBS): Implants electrodes to treat disorders (e.g., Parkinson's, depression).

• Transcranial Magnetic Stimulation (TMS): Applies changing magnetic fields to the brain surface to test function.

Summary Table: Major Neurotransmitters

Neurotransmitter	Main Function	Associated Disorders
Serotonin	Mood, sleep, appetite, pain perception	Depression, anxiety
Dopamine	Pleasure, reward, movement	Parkinson's, schizophrenia
Acetylcholine	Movement, memory, attention	Alzheimer's disease
GABA	Inhibitory, sleep, relaxation	Anxiety disorders
Glutamate	Excitatory, learning, memory	Schizophrenia, neurotoxicity

Key Equations and Concepts

• Action Potential: The change in electrical charge across the neuron's membrane can be represented as: $V_{m} = V_{rest} + ext{change due to ion flow}$

• Refractory Period: The time after an action potential during which a neuron cannot fire again.

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the summary tables and equations.