PSYC_1110-05_03_Brain-mind-behaviour_chp3

Overview and Learning Objectives

• Understand the different divisions of the nervous system

• Describe the basic structure and function of neurons

• Examine neural plasticity with links to drug addiction

• Understand general brain architecture

• Describe methods for measuring brain structure and function

Divisions of the Nervous System

• Neurons: the building blocks of the nervous system

  • CNS (Central Nervous System): brain and spinal cord

  • PNS (Peripheral Nervous System): nerves carrying information from CNS to body

    • SNS (Somatic Nervous System): sense organs; skeletal muscle control

    • ANS (Autonomic Nervous System): internal organs and glands

      • Sympathetic: increases arousal (fight/flight response)

      • Parasympathetic: decreases arousal (rest/digest)

Types of Neurons

• Motor Neurons: control and regulate movement, located in motor cortex, brainstem, spinal cord

• Sensory Neurons: transduce stimuli into action potentials, located in various brain regions

• Interneurons: facilitate information processing within the CNS

Spinal and Cranial Nerves

• Spinal Nerves: 31 pairs carrying sensory and motor information

  • Afferent Neurons: sensory neurons carrying information to the brain

  • Efferent Neurons: motor neurons carrying information from the brain to the body

Structure of Neurons

• Dendrites: receive incoming messages

• Soma (Cell Body): contains the nucleus

• Axon: carries information (action potential) away from the soma

• Axon Terminals: form synapses with other cells

Function of Neurons

• Action Potential: results from the exchange of ions; an all-or-nothing event

  • Opening and closing of ion channels propagate the signal along the axon

  • Saltatory Conduction: increases speed of nerve impulses via myelin sheath jumping

Synapses and Neurotransmitters

• Neuronal Communication: electrical signals within and chemical signals between neurons

  • Neurotransmitters activate receptors; can excite or inhibit postsynaptic cells

  • Chemicals mimicking neurotransmitters can activate specific receptors

Main Classes of Neurotransmitters

• Amino Acids:

  • Glutamate: binds to excitatory receptors; aids memory formation

  • GABA: binds to inhibitory receptors; influences muscle tone

• Monoamines:

  • Norepinephrine: involved in fight-or-flight responses

  • Dopamine: associated with pleasure and reward

  • Serotonin: contributes to mood, appetite, sleep

  • Acetylcholine: affects both inhibitory and excitatory receptors; muscle control

Endocrine System - HPA Axis

• HPA Axis:

  • Hypothalamus secretes corticotropin-releasing hormone (CRH)

  • Pituitary gland releases adrenocorticotropic hormone (ACTH)

  • Adrenal glands release cortisol (stress hormone)

  • Receptors in areas like the hypothalamus detect cortisol and stop stress response

Impact of Stress

• Chronic Stress: causes structural and functional changes in neurons

  • In rats, reduces dendritic branching in the prefrontal cortex

  • In humans, impacts functional connectivity and attention

Psychoactive Drugs and Addiction

• Psychoactive Drugs: alter cognition, memory, mood, and perception

  • Substance abuse is common; drug taking is symptomatic

• Drug Dependency and Tolerance:

  • Drugs may create physical and psychological dependence

  • Tolerance indicates a shift in the dose-response curve

Mechanisms of Drug Action

• Can be Diffused (e.g., alcohol) or Specific (e.g., psychoactive drugs)

  • Agonist Drugs: mimic and facilitate neurotransmitter effects

  • Antagonist Drugs: block or interfere with effects

Neural Plasticity

• Refers to structural and functional changes in neurons with experience

  • Plasticity diminishes with age, particularly in the CNS

  • Peripheral nervous system (PNS) can recover and regrow after damage

Types of Neural Plasticity

• Critical Periods: specific times for essential learning experiences

• Damage Plasticity: reorganization following an injury (e.g., phantom limb phenomenon)

• Adult Plasticity: structural modifications due to experiences (e.g., learning new skills)

Neurogenesis

• New nerve cells generated in specific regions of the brain (e.g., olfactory bulb, hippocampus)

• Important for memory and learning

Neural Networks

• Interlinked connections combine inputs influencing action potentials

  • Example: the linkage of sensory neurons to motor neurons for physical responses

General Brain Architecture

• Frontal Lobes: responsible for complex thought, movement control

• Parietal Lobes: process touch and spatial awareness

• Temporal Lobes: involved in hearing and memory

• Occipital Lobes: process visual information

Frontal Lobes

• Serve as the "executive" of behavior; plan and direct actions

• Integrative functions primarily in the prefrontal cortex

Parietal Lobes

• Primary somatosensory cortex processes bodily sensations

• Regulates position and movement

Temporal Lobes

• Primary Auditory Cortex: tonotopic representation of sounds

Occipital Lobes

• Primary Visual Cortex: visual impairments may arise from injury

Brainstem

• Components:

  • Pons: connection hub for pathways

  • Cerebellum: controls muscle tone and coordination

  • Medulla: regulates vital functions

• Reticular Activating System (RAS): regulates wakefulness and sleep cycles

Subcortical Architecture and Limbic System

• Limbic System: connection of ancient structures with the neocortex

  • Involved in motivation, learning, and memory

• Hypothalamus: regulates basic drives (e.g., eating, stress responses)

• Thalamus: sensory relay point (except olfactory)

• Basal Ganglia: crucial for motor learning and coordination

Limbic System - Amygdala and Hippocampus

• Amygdala: detects threats and processes emotions linked with memories

• Hippocampus: core memory functions related to time and space

Hemispheric Specialization

• Left Hemisphere: controls language and analytical tasks

• Right Hemisphere: manages nonverbal, perceptual skills

Mapping Brain Function

• Methods:

  • Localization of Function: through case studies

  • Electrical Stimulation and Ablation: during neurosurgery to map functions

• Imaging Techniques:

  • MRI: strong magnetic fields; visualizing brain structure

  • fMRI: measures metabolic changes; blood flow increases indicate activity

  • EEG: measures electrical potentials; useful in diagnosing conditions

  • TMS: stimulates brain activity non-invasively; helps in understanding brain dynamics