H2 Introducing the brain

• Neurons


  Cells that transmit information through electrical and chemical signals
• Neurons


  • All neurons have the same structure, but there are some significant differences between different types of neurons in terms of the spatial arrangements of the dendrites and axons
• Synapse


  The small gap between neurons in which neurotransmitters are released, permitting signaling between neurons
• Neuron signaling


  Presynaptic neuron is active, action potential is propagated down the axon, neurotransmitters are released into the synaptic cleft
• Action potential


  A sudden change (depolarization and repolarization) in the electrical properties of the neuron membrane in an axon, which forms the basis for how neurons code information
• Neurotransmitters


  Chemical signals that are released by one neuron and affect the properties of other neurons
• Synaptic potential

  Neurotransmitters bind to receptors on the postsynaptic neuron, creating a synaptic potential that is conducted passively through the dendrites and soma
• Summed synaptic potentials exceed threshold

  Action potential is triggered in the postsynaptic neuron
• Cell membrane


  • Acts as a barrier to the passage of certain chemicals, with gate keepers allowing Na+ and K+ ions in and out under certain conditions
• Resting potential


  • 70 mV across the membrane, with the inside more negative than the outside
• Action potential generation


  Passive current of sufficient strength opens voltage-gated Na+ channels, causing depolarization, reversal of charge, and then repolarization
• Hyperpolarization


  Brief period after action potential where the inside is more negative than at rest, making it more difficult for the axon to depolarize straight away
• Myelin


  A fatty substance deposited around the axon of some neurons that speeds conduction by blocking the normal Na+/K+ transfer
• Myelinated axon conduction


  Action potential jumps, via passive conduction, down the length of the axon at the points where the myelin is absent (nodes of Ranvier)
• Chemical signaling at the synapse

  Action potential reaches axon terminal, initiating release of neurotransmitters into synaptic cleft, which bind to receptors on postsynaptic neuron and create synaptic potential
• Spiking rate


  The number of action potentials propagated per second, which varies and carries information
• Gray matter


  Matter consisting primarily of neuronal cell bodies, forming the outer layer of the brain (cerebral cortex)
• White matter


  Tissue consisting primarily of axons and support cells, lying underneath the gray matter
• Glia


  Support cells of the nervous system involved in tissue repair and myelin formation
• White matter tracts


  • Association tracts (between different cortical regions in same hemisphere)
  • Commissure tracts (between different cortical regions across hemispheres)
  • Projection tracts (between cortical and subcortical regions)
• Cerebrospinal fluid (CSF)


  Fluid that fills the ventricles and provides protection, carries waste metabolites, and transfers messenger signals
• Ventricles


  • Lateral ventricles (in each hemisphere)
  • Third ventricle (centrally around subcortical structures)
  • Fourth ventricle (in brainstem)
• Directional terms


  • Anterior (toward the front)
  • Posterior (toward the back)
  • Superior/Dorsal (toward the top)
  • Inferior/Ventral (toward the bottom)
  • Lateral (the outer part)
  • Medial (in or toward the middle)
• Cerebral cortex


  • Two hemispheres, lateral surface made up of four lobes (frontal, parietal, temporal, occipital) with characteristic gyri and sulci
• Brodmann's areas


  Regions of cortex defined by the relative distribution of cell types across cortical layers (cytoarchitecture)
• Subcortex


  Gray matter structures underneath the white matter, including the basal ganglia and limbic system
• Basal ganglia


  • Regions of subcortical gray matter involved in aspects of motor control, skill learning and reward learning
• Limbic system


  • Region of subcortex involved in relating the organism to its present and past environment, including the amygdala, hippocampus, cingulate cortex and mammillary bodies
• Thalamus


  A major subcortical relay center, processing station between all sensory organs (except smell) and the cortex
• Hypothalamus


  Consists of nuclei specialized for functions primarily concerned with the body and its regulation
• Midbrain


  • Contains the superior colliculi (sensory pathway for eye movements) and inferior colliculi (auditory pathway)
• Cerebellum


  • Attached to the hindbrain, important for dexterity and smooth execution of movement
• Pons


  Part of the hindbrain, a key link between the cerebellum and the cerebrum
• Medulla oblongata


  Part of the hindbrain, regulates vital functions like breathing, swallowing, heart rate and wake-sleep cycle