PSYC 415 -- Study Points for Cells of the Nervous System (rev. 2019/8/23)

I. central nervous system (CNS) - brain and spinal cord
II. peripheral nervous system (PNS) - nerves and peripheral ganglia
III. neurons - the information processing cells
     A. three functionally different kinds
          1. sensory neurons - input from sensory organs
          2. interneurons - processing
          3. motor neurons - output to effectors (muscles and glands)
     B. basic structure
          1. soma (cell body)
          2. dendrites - input (multipolar neurons)
          3. axon - output (can be very long)
          4. collaterals (branches of axons)
          5. terminal arborizations
          6. terminal buttons - make synapses with other neurons
          7. myelin sheath - not actually part of the neuron
              a. membrane of Schwann cells in the PNS
              b. membrane of oligodendrocytes in the CNS
              c. not continuous - broken by gaps or nodes every mm or so
              d. some brain diseases strike the myelin sheath and result in
                 demyelinization - demylinating diseases
                     i. multiple sclerosis (MS)
                     ii. vitamin B12 deficiency
                     iii. tabes dorsalis - from untreated syphilis
                     iv. progressive multifocal leucoencephalopathy
                     v. optic neuritis
     C. polarization and synaptic connections
          1. under biological conditions, conduction is from cell body to the
               terminal buttons (synapses)
          2. within the neuron, info flow is electrical, while between neurons
               it is chemical (due to release of a neurotransmitter)
          3. neurotransmitter is (usually) stored in vesicles and is released
               due to an electrical change in the terminal caused by the
               action potentials arriving via the axon
          4. synapses can be excitatory or inhibitory
              a. when inhibition is deficient, the result is seizures
              b. this can be induced by drugs, e.g., Metrazol
          5. some diseases resulting from abnormal action of neurotransmitters
              a. myasthenia gravis (grave muscle weakness) - acetylcholine
              b. Parkinson's disease - degeneration of dopamine neurons
              c. excitotoxicity - excessive release of glutamate
              d. perhaps epilepsy, depression, schizophrenia, OCD, etc.
     D. bipolar and unipolar neurons - sensory
     E. nerves (PNS) and tracts (CNS) are bundles of axons
          1. after damage, nerves often regenerate, but tracts cannot
          2. this is due to differences in the myelin-generating cells
IV. glial cells
     A. oligodendrocytes - myelin sheath in the CNS
     B. astrocytes - contribute to the blood-brain barrier by plastering the
          capillaries in the brain with "end feet"
     C. microglia - waste disposal and immune response
V. blood-brrain barrier
     A. due to tight junctions between cells making up the capillaries
     B. and due to astrocytic end feet coating outside of capillary
     C. clinical significance
          1. prevents blood-borne pathogens from entering the CNS
          2. but make brain infections hard to treat if antibiotics or anti-
               viral drugs can't cross the BBB
          3. diseases due to disruption of BBB
               a. seizure disorders
               b. maybe Alzheimer's disease
               c. De Vivo disease - a developmental disorder of the BBB
VI. nerve cells are electrically polarized (i.e., there is a voltage across the
     cell membrane)
     A. membrane potential - voltage across the cell membrane
     B. resting potential - roughly about -70 mV (negative inside)
     C. graded potential - slow forming but rapidly conducting voltage change
          that is variable in size and dies out as it propagates
     D. action potential - rapidly forming but relatively slow conducting,
          all-or-none voltage change that can propagate along the entire length
          of axons without dying out (in myelinated axons they only form at the
          nodes of Ranvier)
     E. properties of cell membranes
          1. membranes are electrical insulators - ions cannot pass through them
          2. ion pumps - pump sodium out and potassium in
               a. maintains the resting potential
               b. this is how the brain expends most of its energy requirement
          3. ion channels - allow ions to move through the membrane when the
               channels are open
          4. ion pumps and channels are proteins embedded in the membrane
     F. action potential - sodium flows in followed by potassium flowing out
     G. ion channel poisons - tetrodotoxin (and many others)
VII. networks
     A. withdrawal reflex in the spinal cord
     B. visual system
          1. begins in the retina, which is already a fairly complex network
          2. info sent to the primary visual cortex via the thalamus
          3. thence to many other parts of the brain - a large percentage of
               brain resources is devoted to vision in the human brain