BIOL 005B Lecture Notes - Lecture 14: Ventral Nerve Cord, Central Nervous System, Resting Potential
BIOL 005B Lecture 14: Nervous Systems
●Control of messages
○Neurons receive messages as generator potentials from many terminals (may or
may not be sufficient to trigger AP)
○These messages are received at synapses on the dendrites or soma (cell body)
○Generator potentials may be excitatory (depolarize) or inhibitory (polarize)
○Generator potentials are summed in terms of their effect on resting membrane
potential
○If, collectively, enough excitatory potentials are generated such that the
membrane potential is raised above the necessary threshold, an action potential
will occur and will self-propagate down the axon to the target cells
○Note: all action potentials on a particular neuron are identical
○Neurons can send different messages only by varying the number or frequency of
action potentials
○How do generator potentials from dendrites and soma influence action potentials?
■Affect membrane potential at axon hillock
■Lots of excitatory inputs depolarization → greater probability for an AP
■Lots of inhibitory inputs hyperpolarization → lower probability for an AP
■A mix of excitatory and inhibitory inputs produces an intermediate
generator potential
○What affects the influence of a particular input to dendrites or soma on the
probability of action potentials?
■Total number of synapses: the higher the number, the less influence each
one has
■Location: the nearer a particular synapse is to the base of the axon, the
more influence it has
■The number and timing of action potentials at each synapse: dendrites
and soma integrate over both time and distance
■Excitatory or inhibitory
●Overview of Nervous System Anatomy
○The simplest animals with nervous systems, the cnidarians, have neurons
arranged in nerve nets
○A nerve net is a series of interconnected nerve cells
○More complex animals have nerves
■Nerves are bundles of cells that consist of the axons of multiple neurons
○Bilaterally symmetrical animals exhibit cephalization
○Cephalization is the clustering of sensory organs at the front end of the body
○Relatively simple cephalized animals, such as flatworms, have a central nervous
system (CNS)
○The CNS consists of a brain and longitudinal nerve cords
○Annelids and arthropods have segmentally arranged clusters of neurons
called ganglia
○Invertebrates usually have a ventral nerve cord while vertebrates have a dorsal
spinal cord
Document Summary
Control of messages may not be sufficient to trigger ap) Neurons receive messages as generator potentials from many terminals (may or. These messages are received at synapses on the dendrites or soma (cell body) Generator potentials may be excitatory (depolarize) or inhibitory (polarize) Generator potentials are summed in terms of their effect on resting membrane. If, collectively, enough excitatory potentials are generated such that the potential membrane potential is raised above the necessary threshold, an action potential will occur and will self-propagate down the axon to the target cells. Note: all action potentials on a particular neuron are identical. Neurons can send different messages only by varying the number or frequency of. Lots of excitatory inputs depolarization greater probability for an ap. Lots of inhibitory inputs hyperpolarization lower probability for an ap. A mix of excitatory and inhibitory inputs produces an intermediate.
