Genes and Behavior

• Genes and behavior are examined with the structures and mechanisms involved in heredity

Genes and Behavior Concepts

• DNA (deoxyribonucleic acid) contains genetic material and is passed down in the form of chromosomes from both parents
• Chromosomes are DNA wrapped around proteins. A normal individual has 46 chromosomes or 23 pairs
• Genome refers to the total amount of unique DNA
• Genotype refers to the entire genetic makeup of an organism
• Phenotype refers to an organism's observed characteristics
• Genes are small segments of DNA for producing proteins
• Polygenic refers to the process by which many genes interact to create a single characteristic
• Mutation is a random change in genetic sequence
• Monogenic refers to the hereditary passing on of traits determined by a single gene
• Alleles are the different forms of a gene, one inherited from each parent
• Dominant alleles show their effect even if there is only one allele for that trait
• Recessive alleles show their effects only when both alleles are the same

Principles of Behavioral Genetics

• The connection between genes and behavior is complex
• The relative effects of genes and environment can be teased apart
• The environment can change gene expression

The Nervous System

• The nervous system controls all actions and automatic processes of the body
• Experiences and actions result from nerve cell activity, organized in complex circuits

Organization of the Nervous System

• The central nervous system (CNS) comprises the brain and spinal cord
• The peripheral nervous system consists of all other nerve cells, including the somatic and autonomic nervous systems

Somatic Nervous System

• Sends messages to the skeletal muscles from the CNS and transmits sensory information back

Autonomic Nervous System (ANS)

• Serves as the involuntary systems of the body, like internal organs and glands
• The sympathetic nervous system activates bodily systems in emergencies, known as the fight-or-flight response
• The parasympathetic nervous system is responsible for relaxation, returning the body to a restful state

The Cells of the Nervous System: Glial Cells and Neurons

• Glial cells provide structural support for the CNS and remove cellular debris, playing a role in communication between neurons
• Neurons process and transmit information throughout the nervous system

Neuron Structure

• Soma: the cell body of the neuron and contains the nucleus
• Axon: transmits electrical impulses toward adjacent neurons and stimulates neurotransmitter release
• Dendrites: finger-like projections that receive incoming messages from other neurons
• Myelin Sheath: insulates the axon, making the nerve impulse travel more efficiently
• Synapse: the junction between the axon and the adjacent neuron, the site of information transmission
• Terminal Button: a knob at the end of the axon with tiny sacs of neurotransmitters
• Nodes of Ranvier: gaps in the myelin sheath across which the action potential jumps

Types of Neurons

• Sensory neurons receive incoming sensory information from the sense organs
• Motor neurons take command from the brain and carry them to the muscles of the body
• Mirror neurons activate when observing others performing an action
• Interneurons communicate only with other neurons connecting neurons in different brain regions

Neural Transmission

• Action potential: an electrical and chemical process, the positively charged impulse moving down an axon
  • Ions: chemically charged particles that predominate in bodily fluids
  • Resting potential: the difference in electrical charge between the inside and outside of the axon when the neuron is at rest
  • Refractory period: The time after an action potential during which the neuron cannot generate another action potential
• Neurotransmission: the arrival of an action potential triggers neurotransmitter release into the synaptic cleft
  • Synaptic vesicles: tiny sacs in the terminal button that contain neurotransmitters
  • Excess neurotransmitter in the synaptic cleft is removed through enzymatic degradation or reuptake

Major Neurotransmitters and Their Functions

• Neurotransmitters are chemicals that transmit information between neurons
  • Acetylcholine: controls muscle movement and plays a role in mental processes, slows ANS activity
  • Dopamine: plays an important role in arousal and mood, involved in voluntary muscle control and released during feelings of pleasure or reward
  • Epinephrine (adrenaline): increases ANS activity, triggers fight-or-flight response
  • Norepinephrine (noradrenaline): activates sympathetic response to stress, increasing alertness and attention, affects the CNS
  • Serotonin: plays a role in behaviors including dreaming and emotional states, such as anger, anxiety, and depression
  • GABA (gamma-aminobutyric acid): is a major inhibitory neurotransmitter, regulates neural activity and correlates with anxiety and intoxication
  • Glutamate: is a major excitatory neurotransmitter, important in learning, memory, neural processing, and brain development

Overview of Brain Regions

• The three major regions of the brain (earliest to newest) are the hindbrain, midbrain, and forebrain

• Hindbrain: oldest brain region, connected to the spinal cord, regulates basic survival functions

  • Medulla: regulates breathing, heart rate, and blood pressure
  • Pons: bridge between lower brain regions and higher midbrain and forebrain activity
  • Cerebellum: is involved in movement, balance, coordination, fine-tuning motor skills, and cognitive activities

• Midbrain: the next brain region to evolve, controlling eye muscles, processing auditory and visual information, and initiating voluntary movement

• Forebrain: the largest and most recently evolved part of the human brain; its structures control cognitive, sensory, motor function, regulates temperature, reproductive functions, eating, sleeping, and emotions

  • Thalamus: receives input from sensory organs and relays the sensory information
  • Limbic system: includes the hypothalamus, hippocampus, amygdala, and the cingulate gyrus and shares functions in emotion, memory, and motivation
  • Hypothalamus: regulates major drives like hunger and thirst, controls pituitary gland and hormone production
  • Hippocampus: plays a vital role in learning and memory, sensory information is transmitted here
  • Amygdala: determines emotional significance of stimuli and processing facial expressions
  • Cingulate Gyrus: plays a critical role in attention and cognitive control

Cerebrum and Cerebral Cortex

• Cerebrum is the uppermost portion of the brain, folded into convolutions and divided into two hemispheres

  • Frontal Lobes: located at the front of the brain and performs important functions, including attention, planning, abstract thinking and social awareness
  • Parietal Lobes: located at the top and rear sections of the brain and is important for sensation and perception of touch
  • Temporal Lobes: Located directly below the frontal and parietal lobes and houses the auditory cortex.
  • Occipital Lobes: Located at the rear of the brain and is important for visual processing

• Cerebral cortex is the outer layer of the brain where much of human thought, planning, reception, and consciousness take place

• Insula is a small structure deep inside the cerebrum, in the area that separates the temporal lobe from the parietal lobe. Is active in the perception of bodily sensation, emotional states, empathy, and addictive behavior

• Cerebral Hemispheres divides the cerebrum into equal parts

  • Left Hemisphere processes information in a focused and analytic manner
  • Right Hemisphere integrates information in a broader manner

• Corpus Callosum is the thick band of nerve fibers connecting the two hemispheres and provides a channel for extensive communication

Brain Plasticity and Neurogenesis

• Neuroplasticity: The brain's ability to adopt to situations or new functions without changing it organically
• Neurogenesis: The process of developing new neurons
• Arborization: The growth and formation of new dendrites
• Synaptogenesis: The formation of entirely new synapses or connections with other neurons