Biological Psychology: Genes, Nervous System, and Brain Function

Biological Psychology: Genes, Nervous System, and Brain Function

Introduction

Biological psychology explores the connections between biological processes and behavior. This field examines how genes, the nervous system, and brain structures influence thoughts, emotions, and actions. Understanding these relationships is essential for comprehending both normal and disordered psychological functioning.

Genetics and Heredity

DNA, Chromosomes, and Genes

Genetic information is stored in the nucleus of cells as DNA, which is organized into chromosomes. Each chromosome contains many genes, which are sequences of DNA that code for proteins and determine inherited traits.

• DNA (Deoxyribonucleic Acid): The molecule that carries genetic instructions for life. It has a double helix structure.

• Chromosomes: Structures within the cell nucleus made of DNA and proteins; humans have 23 pairs.

• Genes: Segments of DNA that code for specific proteins and influence traits.

Example: The ability to taste the bitter compound PTC is determined by specific gene variants.

Genotype vs. Phenotype

• Genotype: The unique genetic makeup inherited from one's parents.

• Phenotype: The observable physical and behavioral traits resulting from the interaction of genotype and environment.

• Homozygous: Having two identical versions (alleles) of a gene.

• Heterozygous: Having two different versions (alleles) of a gene.

Genetic Inheritance and Variation

Genes can exist in different forms called alleles. The combination of alleles inherited from parents determines specific traits. Inheritance patterns can be predicted using tools like Punnett squares.

Behavioural Genetics and Genomics

• Behavioural Genetics: Studies how genes and environment influence behavior, often using twin and adoption studies to estimate heritability (ranging from 0 to 1).

• Behavioural Genomics: Investigates how specific genes relate to behavior, aided by projects like the Human Genome Project.

• Heritability: A statistical estimate of how much variation in a trait is due to genetic differences.

Example: Identical twins (monozygotic) share nearly 100% of their genes, while fraternal twins (dizygotic) share about 50%.

Gene Expression and Epigenetics

• Gene Expression: The process by which information from a gene is used to synthesize proteins, influenced by environmental factors (diet, stress, sleep).

• Epigenetics: The study of changes in gene expression caused by experience, without altering the DNA sequence.

• CRISPR-Cas9: A technology that allows scientists to edit genes at specific locations, with potential for treating genetic disorders.

Evolutionary Psychology

Natural Selection and Adaptation

Evolutionary psychology applies principles of evolution to understand human behavior. Traits that enhance survival and reproduction become more common over generations through natural selection.

• Natural Selection: The process by which heritable traits that confer a reproductive advantage become more prevalent in a population.

• Adaptation: A trait shaped by natural selection that increases an organism's fitness.

Example: Spatial memory differences between males and females may reflect ancestral roles in hunting and gathering.

Neural Communication

Structure and Function of Neurons

Neurons are specialized cells that transmit information throughout the nervous system.

• Cell Body (Soma): Contains the nucleus and genetic material.

• Dendrites: Receive signals from other neurons.

• Axon: Conducts electrical impulses away from the cell body.

• Axon Terminals: Release neurotransmitters to communicate with other cells.

Types of Neurons

• Sensory Neurons: Carry information from sensory receptors to the brain and spinal cord.

• Motor Neurons: Transmit signals from the brain and spinal cord to muscles.

• Interneurons: Connect sensory and motor neurons within the central nervous system.

Glial Cells

• Support neurons by providing nutrients, removing waste, and synchronizing activity.

• Produce myelin, a fatty sheath that insulates axons and increases the speed of neural transmission.

• Multiple sclerosis is a disease where the immune system attacks myelin, disrupting neural communication.

Neurogenesis and Neural Plasticity

• Neurogenesis: The formation of new neurons, especially in the hippocampus, linked to learning and memory.

• Neural Plasticity: The brain's ability to reorganize and adapt in response to experience or injury.

Neural Firing: Resting and Action Potentials

Neurons communicate via electrical impulses called action potentials.

• Resting Potential: The neuron is polarized, with more positive ions outside and negative ions inside.

• Action Potential: Triggered when the neuron is stimulated; positive ions rush in, reversing the charge and sending an electrical wave down the axon.

• Refractory Period: A brief pause after firing during which the neuron cannot fire again.

• All-or-None Principle: Neurons fire with the same strength every time; stronger signals result from more neurons firing or firing more frequently.

Synaptic Transmission

• Synapse: The gap between neurons where neurotransmitters are released.

• Presynaptic Cell: Sends the signal.

• Postsynaptic Cell: Receives the signal.

• Reuptake: The process by which neurotransmitters are reabsorbed by the presynaptic neuron.

Chemical Messengers: Neurotransmitters and Hormones

Neurotransmitters

Neurotransmitters are chemicals that transmit signals across synapses. Each has specific effects on behavior and physiology.

Neurotransmitter	Main Function
Glutamate	Excitatory; supports learning and memory
GABA (gamma-aminobutyric acid)	Inhibitory; reduces arousal, anxiety, and promotes sleep
Acetylcholine	Controls voluntary movement; found at nerve-muscle junctions
Dopamine	Mood, movement, reward-seeking behavior
Norepinephrine	Stress response, attention, heart rate
Epinephrine	Adrenaline; hormone and neurotransmitter
Serotonin	Regulates mood, sleep, aggression, appetite

Drug Effects on Neurotransmission

• Agonists: Facilitate the effects of neurotransmitters.

• Antagonists: Block the effects of neurotransmitters.

• Example: SSRIs (e.g., Prozac) block serotonin reuptake, increasing its availability in the synapse.

Hormones and the Endocrine System

• Hormones: Chemical messengers released into the bloodstream, affecting distant organs.

• Endocrine System: Includes glands such as the pituitary, adrenal, and hypothalamus; regulates homeostasis, metabolism, and stress responses.

• Adrenal Glands: Release cortisol and epinephrine during stress (fight-or-flight response).

• Endorphins: Reduce pain and increase pleasure; released during exercise, sex, or injury.

• Testosterone: Influences aggression, dominance, and social status-seeking behavior.

Organization of the Nervous System

Divisions of the Nervous System

Division	Main Function
Central Nervous System (CNS)	Brain and spinal cord; processes information and coordinates activity
Peripheral Nervous System (PNS)	Connects CNS to the rest of the body
Somatic Nervous System	Controls voluntary movements
Autonomic Nervous System	Regulates involuntary functions (e.g., heart rate, digestion)
Sympathetic Division	Prepares body for action (fight-or-flight)
Parasympathetic Division	Restores body to resting state (rest-and-digest)

Brain Structure and Function

Major Brain Regions

• Hindbrain: Includes medulla, pons, and cerebellum; controls basic life functions (breathing, heart rate, balance).

• Midbrain: Relays sensory and motor information; involved in reflexes to sights and sounds.

• Forebrain: Responsible for emotion, memory, reasoning, and higher cognitive functions.

Key Forebrain Structures

• Basal Ganglia: Supports movement, skill learning, and reward processing; dysfunction linked to Parkinson's and Huntington's diseases.

• Limbic System: Network for emotion and memory; includes hypothalamus (regulates drives), amygdala (emotional memory, fear), hippocampus (forms new memories), and thalamus (sensory relay station).

Cerebral Cortex

• Frontal Lobes: Planning, impulse control, emotion regulation, language production, voluntary movement.

• Parietal Lobes: Sensory integration, spatial awareness, touch perception.

• Occipital Lobes: Visual processing.

• Temporal Lobes: Auditory processing, language comprehension, memory, object recognition.

Motor and Somatosensory Cortex

• Motor cortex controls voluntary movements; somatosensory cortex processes touch and body sensations.

• These regions are mapped to specific body parts, allowing precise control and sensation.

Corpus Callosum and Hemispheric Specialization

• Corpus Callosum: Thick band of axons connecting the left and right hemispheres, enabling communication between them.

• Hemispheric Specialization: Left hemisphere typically handles language; right hemisphere specializes in spatial and nonverbal tasks.

• Broca's Area: Speech production; damage leads to expressive aphasia.

• Wernicke's Area: Language comprehension; damage leads to receptive aphasia.

Neuroplasticity and Brain Injury

• The brain can reorganize and adapt after injury, especially in children.

• Rehabilitation and therapies (e.g., Melodic Intonation Therapy) can help regain lost functions.

• Neurogenesis and plasticity are influenced by factors such as hormones, metabolism, and environment.

Measuring and Observing Brain Activity

Neuroimaging Techniques

Technique	Main Purpose
CT Scan (Computed Tomography)	Structural imaging; detects injuries and anomalies
MRI (Magnetic Resonance Imaging)	Detailed structural imaging of brain anatomy
DTI (Diffusion Tensor Imaging)	Maps white matter tracts in the brain
EEG (Electroencephalogram)	Measures electrical activity; useful for diagnosing epilepsy
PET (Positron Emission Tomography)	Shows active brain areas using radioactive tracers
fMRI (Functional MRI)	Measures changes in blood flow to identify active brain regions during tasks

• fMRI and PET provide correlational data; active areas may not be essential for a task.

• Neuroimaging is central to mapping brain networks and understanding psychological disorders.

Summary Table: Major Neurotransmitters and Their Functions

Neurotransmitter	Function
Glutamate	Excitatory; learning, memory, autonomic reactions
GABA	Inhibitory; lowers arousal, anxiety, facilitates sleep
Acetylcholine	Movement, attention
Dopamine	Movement, reward, cognition
Serotonin	Sleep, mood, appetite
Norepinephrine	Attention, stress response
Epinephrine	Adrenaline; stress response

Key Equations and Concepts

• Heritability: $h^2 = \frac{\text{Genetic Variance}}{\text{Total Phenotypic Variance}}$

• Action Potential Threshold: Neuron fires when membrane potential exceeds a critical value (typically around $-55$ mV).

Conclusion

Biological psychology integrates genetics, neuroscience, and evolutionary theory to explain behavior. Understanding the structure and function of the nervous system, the role of neurotransmitters and hormones, and the adaptability of the brain is crucial for comprehending both normal and abnormal psychological processes.