Introduction to Behavioral Neuroscience

Introduction to Behavioral Neuroscience Chapter 1: Structure of the Nervous System

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Attributions

  • Chapter by: Irina Calin-Jageman, PhD.
  • Slides prepared by: Elizabeth D. Kirby, PhD.

Chapter Outline

  • 1.1 Building a Nervous System
  • 1.2 Organization of the Nervous System
  • 1.3 The Central Nervous System (CNS)
  • 1.4 The Brain: Structure and Function
  • 1.5 The Peripheral Nervous System (PNS)

1.1 Building a Nervous System

  • Your nervous system is composed of eukaryotic cells:
      - Key components of a cell:
        - Mitochondrion
        - DNA (in the nucleus)
        - Nucleus
        - Lysosome
        - Plasma membrane
        - Ribosomes
        - Endoplasmic reticulum
        - Golgi apparatus

Neurons and Glia

  • Neurons
      - There are two main types: neurons and glia.
      - Neurons exhibit a variety of shapes and sizes; the types and functions are defined by their gene expression.
      - Neurons are specialized for communication through electrical and chemical signals.
      - Communication between neurons occurs at synapses.
      - The average brain is 2% of body mass but uses 25% of daily energy production; it contains approximately 86 billion neurons.

  • Gene Expression
      - Genes are sequences of nucleotides in DNA.
      - DNA is transcribed into mRNA (messenger RNA) within the nucleus.
      - mRNA is translated into a sequence of amino acids, thereby forming a protein; the unique collection of proteins in a cell helps define its type, or phenotype.

Types of Neurons
  • Neurons are categorized by direction of impulse:
      - Afferent neurons: carry messages toward the brain (sensory neurons).
      - Efferent neurons: carry messages away from the brain (motor neurons).
      - Interneurons: convey messages between neurons.
Neuron Structure
  • Major components include:
      - Soma (cell body)
      - Dendrites: receive information; they are covered in dendritic spines that can vary in shape and size, changing over time.
      - Axons: send information; they can branch into multiple collaterals and are often covered in myelin (insulation).
      - Nodes of Ranvier are gaps in the myelin sheath where action potentials occur.
Multiple Sclerosis
  • It is a condition caused by the loss of myelin in the central nervous system.
Synaptic Structures
  • Synapses occur between neurons and can involve muscles (neuromuscular junction) or glands (neuroglandular synapse).
      - Basic synaptic structure: presynaptic terminal, neurotransmitters, and postsynaptic membrane.
Glia
  • Glia (from the Greek "nerve glue") constitutes about 30-60% of total brain mass.
  • Roles include:
      - Development of the nervous system
      - Energy metabolism
      - Synaptic function support
      - Maintenance of the blood-brain barrier (BBB).

Astrocytes and the Blood-Brain Barrier (BBB)

  • Astrocytes wrap around blood vessels in the brain with specialized end-feet to facilitate the formation of the BBB.
  • Small, uncharged, lipid-soluble molecules can cross the BBB more easily than large, charged or lipid-insoluble molecules.
Astrocytes' Functions
  • They help isolate synapses and regulate neurotransmitter levels, and are involved in the immune response within the brain and synaptic remediation.

Types of Glia

  • Major types of glia include:
      - Astrocytes
      - Microglia
      - Oligodendrocytes: myelinate central nervous system.
      - Schwann cells: myelinate peripheral nervous system.
Historical Theories on Neurons
  • Golgi's Reticular Theory: proposes that the brain is a single interconnected network.
  • Cajal's Individual Neuron Theory: states that the brain comprises individual, separate cells.
  • Visualizing Cells:
      - Golgi stain: highlights individual neurons.
      - Immunofluorescent staining: employs antibodies with fluorescent labels to visualize specific proteins within neurons.

Test-like Questions

  • Example questions to reinforce knowledge acquisition.
1.2 Organization of the Nervous System
  • Neuroscience Across Species
      - Key defining features include neuronal organization patterns and symmetry.
      - Two General Principles for neuronal organization:
        - Neural nets: simple, mesh-like systems seen in organisms like cnidaria.
        - Ganglia: collections of neuronal cell bodies, observed in both invertebrates and vertebrates.

      - Symmetry:
        - Centralization involves the consolidation of neurons, leading to cephalization, which concentrates nervous system structures in the head.
Classifications
  • CNS (Central Nervous System): composed of the brain and spinal cord.
      - PNS (Peripheral Nervous System): includes motor and sensory nerves connected to CNS.
CNS and PNS Structures
  • Gray Matter: collections of cell bodies and dendrites. In the CNS, termed nuclei, while in the PNS, referred to as ganglia.
  • White Matter: consists of myelinated axons; CNS bundles are called tracts, while PNS bundles are nerves.
Protective Layers of CNS: Meninges
  • Comprises three layers:
      - Dura mater: outermost layer.
      - Arachnoid: middle layer.
      - Pia mater: innermost layer.
  • Cerebral Spinal Fluid (CSF): cushions the brain, exchanges materials between blood and brain, generated by the choroid plexus within the ventricles.
      - Pathway: Lateral → 3rd → 4th → central canal; finally, entering the subarachnoid space, and exiting through arachnoid villi to venous sinuses.
Circuits in Neurons
  • A circuit is defined as a group of neurons connected by synapses that process specific types of information. Examples include the patellar reflex arc.

1.3 The Central Nervous System (CNS)

  • Functional Organization of the Spinal Cord:
      - Dorsal horn (gray matter) houses sensory interneurons.
      - Ventral horn (gray matter) contains motor neurons that emerge in bundles as dorsal/ventral roots, merging into mixed nerves that transmit sensory and motor information.

1.4 The Brain: Structure and Function

  • Neurodevelopmental origins lead to five major divisions of the brain:
      - Telencephalon
      - Diencephalon
      - Mesencephalon
      - Metencephalon
      - Myelencephalon

Telencephalon Functions

  • Comprised of the cerebral hemispheres, the cerebral cortex includes:
      - Lobes: frontal, parietal, temporal, occipital.
        - Frontal Cortex: involved in motor control, personality, and higher cognitive functions.
        - Parietal Cortex: processes somatic sensation, sensory integration, and proprioception.
        - Occipital Cortex: primarily responsible for vision.
        - Temporal Cortex: plays a role in language, memory, and auditory processing.
  • Subcortical Structures:
      - Limbic System: located within the telencephalon, playing a role in emotion, memory, and behavior, comprised of
        - Cingulate gyrus
        - Hippocampus
        - Amygdala
  • Basal Ganglia: involved in motor control, includes striatum, globus pallidus, and subthalamic nucleus.
Diencephalon Functions
  • Includes the thalamus (sensory and motor relay) and hypothalamus (regulation of hormones and homeostasis).
Brainstem Anatomy
  • Mesencephalon: includes tectum (auditory and visual processing) and tegmentum (motor coordination).
  • Metencephalon: includes the pons, which connects the cerebellum to the brain and regulates many basic bodily functions like breathing.
  • Myelencephalon: contains the medulla, regulating vital functions such as heart rate and breathing.
Cerebellum Functions
  • Coordination and fine-tuning of movement; sensitive to alcohol exposure.
Visualization Techniques of the Brain
  • Structural Techniques: CT (Computerized Tomography), MRI (Magnetic Resonance Imaging).
  • Functional Techniques: PET (Positron Emission Tomography), fMRI (functional Magnetic Resonance Imaging), measure brain metabolism and activity levels via blood flow and oxygen concentration variations.

1.5 The Peripheral Nervous System (PNS)

  • Divided into:
      - Somatic Nervous System: voluntary muscle control.
      - Autonomic Nervous System: involuntary muscle and gland control, consisting of:
        - Sympathetic Division: responsible for fight or flight responses.
        - Parasympathetic Division: responsible for rest and digest responses.
        - Enteric Division: governs gastrointestinal function via the brain-gut axis.
PNS Components
  • Nerves: include 12 cranial nerves and 31 spinal nerves facilitating communication between the brain and the body.
Important PNS Concepts
  • Dermatomes: areas of the body innervated by specific spinal nerves.
  • Ganglia: sensory ganglia in the somatic system and autonomic ganglia in the autonomic system.
Clinical Application
  • Examples presented include patients with spinal injuries and their corresponding symptoms to illustrate functional anatomy of the nervous system.

Test-like Questions

  • A collection of example questions for self-assessment and reinforcing the comprehensions of structures and functions covered in the nervous system topics.