Biological Foundations of Behavior: The Nervous System and Brain

Chapter 2: The Biological Perspective

Introduction

This chapter explores the biological basis of behavior, focusing on the structure and function of the nervous system, neurons, neurotransmitters, and the brain. Understanding these foundations is essential for comprehending how psychological processes are rooted in biology.

Neurons and Neurotransmitters

Overview of the Nervous System

• Nervous system: A network of cells that carries information to and from all parts of the body.

• Neuroscience: The scientific study of the structure and functioning of the brain, neurons, nerves, and nervous tissue.

• Biological psychology (behavioral neuroscience): Focuses on the biological bases of psychological processes, behavior, and learning.

Structure of the Neuron

Neurons are the basic building blocks of the nervous system, specialized for receiving and transmitting messages.

• Dendrites: Branchlike structures that receive messages from other neurons.

• Soma: The cell body, responsible for maintaining the life of the cell.

• Axon: Long, tubelike structure that carries neural messages to other cells.

• Axon terminals: Rounded areas at the end of the axon branches, responsible for communicating with other nerve cells.

Glial Cells and Myelin

• Glial cells: Provide support, deliver nutrients, and produce myelin to insulate and protect axons.

• Myelin: Fatty substance that speeds up neural impulses.

The Neural Impulse: Action Potential

Neurons communicate via electrical impulses known as action potentials.

• Ions: Charged particles; the balance of ions inside and outside the neuron determines its charge.

• Resting potential: The state of a neuron when not firing.

• Action potential: The release of a neural impulse, involving a reversal of electric charge within the axon.

• All-or-none principle: A neuron either fires completely or not at all.

Neurotransmission

Neurons communicate with each other and the body using chemical messengers called neurotransmitters.

• Synaptic vesicles: Saclike structures in axon terminals containing neurotransmitters.

• Synapse (synaptic gap): Microscopic space between the axon terminal of one cell and the dendrites or soma of the next cell.

• Receptor sites: Proteins on dendrites shaped to fit specific neurotransmitters.

• Excitatory synapse: Neurotransmitter causes the receiving cell to fire.

• Inhibitory synapse: Neurotransmitter causes the receiving cell to stop firing.

• Agonists: Chemicals that mimic or enhance neurotransmitter effects.

• Antagonists: Chemicals that block or reduce neurotransmitter effects.

Table: Major Neurotransmitters and Their Functions

Neurotransmitter	Main Function
Acetylcholine (ACh)	Excitatory or inhibitory; involved in arousal, attention, memory, and controls muscle contractions
Norepinephrine (NE)	Mainly excitatory; involved in arousal and mood
Dopamine (DA)	Excitatory or inhibitory; involved in control of movement and sensations of pleasure
Serotonin (5-HT)	Excitatory or inhibitory; involved in sleep, mood, anxiety, and appetite
Gamma-aminobutyric acid (GABA)	Major inhibitory neurotransmitter; involved in sleep and inhibits movement
Glutamate	Major excitatory neurotransmitter; involved in learning, memory, and nervous system development

Cleaning Up the Synapse

• Reuptake: Neurotransmitters are taken back into synaptic vesicles for reuse.

• Enzymatic degradation: Enzymes break down neurotransmitters so they can no longer act on receptors.

Studying the Brain

Lesioning and Stimulation

• Lesioning: Destroying brain cells with electrical current to study function.

• Electrical stimulation of the brain (ESB): Using mild current to activate neurons.

• Deep brain stimulation (DBS): Implanted impulse generator stimulates specific brain areas.

• Optogenetics: Stimulates neurons using light.

• Transcranial magnetic stimulation (TMS): Magnetic pulses applied to the cortex.

• Transcranial direct current stimulation (tDCS): Uses electrical current to modulate brain activity.

Neuroimaging Techniques

Mapping Structure

• Computed tomography (CT) scan: Uses X-rays to create images of brain structure.

• Magnetic resonance imaging (MRI): Uses radio waves and magnetic fields for detailed brain images.

• MRI spectroscopy: Estimates concentrations of chemicals and neurotransmitters.

• Diffusion tensor imaging (DTI): Maps white matter tracts in the brain.

Mapping Function

• Electroencephalogram (EEG): Records electrical activity of cortical neurons.

• Magnetoencephalography (MEG): Detects magnetic fields from neuronal activity.

• Positron emission tomography (PET): Uses radioactive sugar to image brain activity.

• Functional MRI (fMRI): Measures changes in brain oxygenation to study function.

• Functional near-infrared spectroscopy (fNIRS): Uses infrared light to measure blood oxygen levels in the brain.

Brain Structure and Function

The Hindbrain

• Medulla: Controls life-sustaining functions (breathing, heart rate).

• Pons: Involved in sleep, dreaming, body coordination, and arousal.

• Reticular formation (RF): Regulates attention, alertness, and arousal.

• Cerebellum: Coordinates involuntary, rapid, fine motor movement and some cognitive functions.

Structures Under the Cortex: The Limbic System

• Thalamus: Relays sensory information to the cortex.

• Olfactory bulbs: Receive information about smell.

• Hypothalamus: Regulates motivational behaviors (sleep, hunger, thirst, sex).

• Hippocampus: Formation of long-term declarative memories.

• Amygdala: Responsible for fear responses and memory of fear.

• Cingulate cortex: Involved in cognitive and emotional processing.

The Cortex

• Cortex: Outermost covering of the brain, responsible for higher thought and sensory interpretation.

• Corticalization: Wrinkling of the cortex increases surface area.

• Cerebral hemispheres: Left and right sections of the cortex.

• Corpus callosum: Connects the two hemispheres.

Lobes of the Cortex and Their Functions

Lobe	Main Function
Occipital	Processes visual information
Parietal	Processes touch, temperature, and body position
Temporal	Processes auditory information and speech
Frontal	Higher mental processes, decision-making, motor commands, speech production

Association Areas

• Association areas: Coordinate and interpret information, involved in higher mental processing.

• Broca's aphasia: Damage to Broca's area (left frontal lobe) impairs speech production.

• Wernicke's aphasia: Damage to Wernicke's area (left temporal lobe) impairs language comprehension.

• Spatial neglect: Damage to right parietal lobe causes inability to recognize objects/body parts in left visual field.

• Balint's Syndrome: Disorder of visual/perceptual system; symptoms include optic ataxia, oculomotor apraxia, and simultanagnosia.

Cerebral Hemispheres: Specialization

• Left hemisphere: Language, writing, logical thought, analysis, mathematical abilities; processes information sequentially.

• Right hemisphere: Emotional expression, spatial perception, recognition of faces/patterns/melodies; processes information globally.

• Split-brain research: Studies patients with severed corpus callosum to demonstrate hemispheric specialization.

The Nervous System: Central and Peripheral Divisions

Central Nervous System (CNS)

• Brain and spinal cord: The CNS is responsible for processing information and reflexes.

• Spinal cord: Carries messages and controls reflexes.

• Afferent (sensory) neurons: Carry information from senses to CNS.

• Efferent (motor) neurons: Carry messages from CNS to muscles.

• Interneurons: Connect sensory and motor neurons; bulk of neurons in the brain.

• Reflex arc: Pathway for reflex actions.

• Neuroplasticity: Brain's ability to change structure/function in response to experience or trauma.

• Neurogenesis: Formation of new neurons.

Peripheral Nervous System (PNS)

• Somatic nervous system: Controls voluntary muscles.

• Sensory pathway: Carries messages from sensory organs to CNS.

• Motor pathway: Carries messages from CNS to voluntary muscles.

• Autonomic nervous system (ANS): Controls involuntary muscles, organs, and glands.

• Sympathetic division: Prepares body for stress (fight or flight).

• Parasympathetic division: Restores body to normal after arousal; responsible for day-to-day functioning.

The Endocrine System

Endocrine Glands and Hormones

• Endocrine glands: Secrete hormones directly into the bloodstream.

• Hormones: Chemicals that affect behavior and emotions by stimulating muscles, organs, and other glands.

Table: Major Endocrine Glands and Their Functions

Gland	Main Function
Pituitary	Secretes growth hormone; influences other glands
Pineal	Secretes melatonin; regulates sleep
Thyroid	Regulates metabolism
Pancreas	Controls blood sugar levels
Gonads (Ovaries/Testes)	Regulate sexual development and behavior
Adrenal	Regulate stress response, salt intake, secondary sex hormones

Pituitary Gland: Master of Hormonal Regulation

• Pituitary gland: Located in the brain; influences other endocrine glands.

• Oxytocin: Involved in reproductive and parental behaviors.

• Vasopressin: Controls water levels in the body.

Applying Psychology: Coping with ADHD

• ADHD: A biological disorder related to genetics, environment, and brain structure/function.

• Interventions include cognitive and behavioral strategies to lessen symptoms.

Additional info: These notes are based on textbook slides and objectives, providing a comprehensive overview suitable for exam preparation in a college-level psychology course.