Chapter 2: The Biological Perspective

Introduction

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

Neurons and Neurotransmitters

The Nervous System and Neuroscience

• 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 cells of the nervous system, responsible for receiving and sending messages.

• Dendrites: Branch-like structures that receive messages from other neurons.

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

• Axon: Long, tube-like structure that carries the neural message to other cells.

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

Example: Sensory neurons in the skin transmit touch information to the brain via these structures.

Glial Cells and Myelin

• Glial cells: Support neurons by providing nutrients, producing myelin, cleaning up waste, and aiding neuron growth.

• Myelin: Fatty substance produced by glial cells that insulates and protects axons, speeding up neural impulses.

Example: Multiple sclerosis is a disease where myelin is damaged, leading to impaired neural transmission.

Action Potential

The action potential is the process by which neurons transmit electrical impulses.

• Ions: Charged particles whose balance inside and outside the neuron determines its charge.

• Resting potential: The state of the neuron when not firing; inside is negatively charged, outside is positively charged.

• Action potential: A reversal of electrical charge within the axon, allowing positive sodium ions to enter the cell.

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

Neurotransmission

Neurons communicate with each other and the body using neurotransmitters.

• Synapse/Synaptic gap: Microscopic fluid-filled space between axon terminals of one cell and dendrites of the next.

• Synaptic vesicles: Sac-like structures in axon terminals containing neurotransmitters.

• Neurotransmitter: Chemical messenger released into the synapse, affecting the next cell.

• Receptor sites: Proteins on dendrites or muscle/gland cells shaped to fit specific neurotransmitters.

Types of Synapses

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

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

Agonists and Antagonists

• Agonists: Mimic or enhance the effects of neurotransmitters.

• Antagonists: Block or reduce a cell's response to neurotransmitters.

Example: The venom of the black widow spider causes a flood of acetylcholine, leading to convulsions.

Major Neurotransmitters and Their Functions

Cleaning Up the Synapse

• Reuptake: Process by which neurotransmitters are taken back into synaptic vesicles.

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

Example: Cocaine blocks the reuptake of dopamine, increasing its effects.

Studying the Brain

Lesioning and Brain Stimulation

• Lesioning: Inserting a wire into the brain and sending an electrical current to destroy cells at the tip.

• Electrical stimulation of the brain (ESB): Milder current causes neurons to react as if they received a message.

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

• Transcranial magnetic stimulation (TMS): Magnetic pulses applied to the cortex using coils over the head.

• Transcranial direct current stimulation (tDCS): Direct electrical current applied to the cortex.

Neuroimaging Techniques

Mapping Structure

• Computed tomography (CT): 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): Uses MRI data to map white matter pathways.

Mapping Function

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

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

• Positron emission tomography (PET): Radioactive sugar injection shows color-coded images of brain activity.

• Functional MRI (fMRI): Produces a "movie" of changes in brain activity over time.

• Near-Infrared Spectroscopy (NIRS): Measures brain activity using infrared light to detect blood oxygen changes.

Structures of the Brain

The Hindbrain

• Medulla: Controls life-sustaining functions such as breathing, swallowing, and heart rate.

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

• Reticular formation (RF): Responsible for selective attention.

• Cerebellum: Coordinates involuntary, rapid, fine motor movement.

Structures Under the Cortex: The Limbic System

• Limbic system: Group of brain structures involved in learning, emotion, memory, and motivation.

• Thalamus: Relays sensory information to the cortex and processes some sensory input.

• Hypothalamus: Regulates motivational behaviors such as sleep, hunger, thirst, and sex.

• Hippocampus: Responsible for formation of long-term declarative memories.

• Amygdala: Involved in fear responses and memory of fear.

• Cingulate cortex: Plays roles in cognitive and emotional processing.

The Cortex

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

• Corticalization: Wrinkling of the cortex, allowing more cortical cells in a small space.

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

• Corpus callosum: Thick band of neurons connecting the hemispheres.

Lobes of the Cortex

Specialized Cortical Areas

• Primary visual cortex: Processes visual input from the eyes.

• Visual association cortex: Interprets visual information.

• Somatosensory cortex: Processes touch, temperature, and body position.

• Primary auditory cortex: Processes sound from the ears.

• Auditory association cortex: Interprets auditory information.

• Motor cortex: Sends motor commands to muscles.

Association Areas of the Cortex

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

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

• Wernicke's aphasia: Damage to Wernicke's area (left temporal lobe) causes difficulty in understanding or producing meaningful language.

• Spatial neglect: Damage to right hemisphere association areas leads to inability to recognize objects/body parts in the left visual field.

The Cerebral Hemispheres

• Cerebrum: Upper part of the brain, consisting of two hemispheres and connecting structures.

• Split-brain research: Studies patients with severed corpus callosum, revealing hemispheric specialization.

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

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

The Nervous System

The Central Nervous System (CNS)

• Central nervous system: Consists of the brain and spinal cord.

• Spinal cord: Carries messages to/from the body and brain; responsible for fast, lifesaving reflexes.

• Sensory (afferent) neuron: Carries information from senses to CNS.

• Motor (efferent) neuron: Carries messages from CNS to muscles.

• Interneuron: Found in spinal cord and brain; connects sensory and motor neurons.

• Reflex arc: Connection of afferent, interneuron, and efferent neurons resulting in reflex action.

• Neuroplasticity: Ability of the brain to change structure/function in response to experience or trauma.

• Neurogenesis: Formation of new neurons.

The Peripheral Nervous System (PNS)

• Peripheral nervous system: All nerves/neuron outside the brain and spinal cord.

• Somatic nervous system: Controls voluntary muscles; includes sensory and motor pathways.

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

• Sympathetic division: "Fight-or-flight" system; reacts to stress and arousal.

• Parasympathetic division: "Eat-drink-and-rest" system; restores body to normal 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.

Major Endocrine Glands

Pituitary Hormones

• 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 variations.

• Interventions including cognitive and behavioral strategies can lessen symptoms.

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