Nervous Systems

What’s actually happening when the brain “learns” new information? 3. I’m too old to learn anything new anymore; I hire people do that for me. 1. Communication b/w neurons is basically binary code. If the neuron fires, then something is learned. 2. I’m exercising my brain right now, in order to grow new neurons & increase my capacity to learn! 4. Brain power is electromagnetic energy that carries our thoughts. I’d like to keep my thoughts to myself, thank you.

Learning Objectives (3/5/08) 1.Use examples to illustrate the 3 overlapping functions of nervous systems: sensory input, integration, and motor output. 2.Relate structure with function at various levels of organization in nervous systems: neuron, synapse, reflex arc, and integrative processes. 3.Describe the increasing complexity that likely reflects the stages in the evolution of nervous systems. 4.Differentiate between inhibitory and excitatory post- synaptic potentials, and the generation of a grand synaptic potential 5.Differentiate between synaptic potentials and action potentials

Structure of a Vertebrate Neuron Fig. 45.2What other cell types are found in nervous tissues?

Diversity of Nervous Systems Cephalization: More complex and active animals tend to cluster ganglia together at the anterior end to form a brain. Simple, slow moving animals like hydra have neurons arranged in a network of bipolar neurons called a nerve net. What is a ganglion? Fig. 48.2

Basic Tasks of a Nervous System Sensory Input: Receptors monitor both external and internal environments. Integration: Process the information (at synapses) and often integrate it with stored information. Motor output: If necessary, signal effector organs to make an appropriate response. How is this similar to the normal function of the endocrine system? Describe the receptor, control center, and effector in several neural reflexes.

Overview of the Transmembrane Electrochemical Potential How does the Na-K pump contribute to the potential? Why is the cell membrane described as “polarized”? p. 1029

Chemical Synapses Compare with the structure and function of an electrical synapse. What determines whether a synapse is excitatory or inhibitory?

Graded Membrane Potentials The membrane potential can be altered depending upon which ion channels are opened by a stimulus. These synaptic potentials are graded. Open K + channels allows K + efflux from the cell at a higher than resting rate, driving the cell interior more negative (hyperpolarization). Open Na + channels allow Na + to influx into the cell, driving the cell interior more positive (depolarization). Excitable cells have several types of voltage-gated channels that respond to changes in membrane potential. p. 1041

The Action Potential A depolarizing potential that reaches a critical level called the threshold potential (or firing threshold) will trigger an action potential or nerve impulse. Unlike the graded potentials that get larger with increasing stimulus strength, the action potential is an all-or-none response. Action potential size is independent of the stimulus and reaches a value of about +30 mV. Name the ion channel that opens at the threshold voltage. What happens during repolarization? p. 1032

Unidirectional Propagation Refractory Period p & 1038 p. 1036

Myelinated Neuron Fibers Many vertebrate peripheral neuron fibers have an insulating sheath around their fibers called myelin which is formed by Schwann cells. Myelin sheathing allows these neurons to conduct action potentials much faster than in non-myelinated neurons. How does the structure of unmyelinated neurons in invertebrates allow for the rapid conduction of action potentials during e.g. escape responses? p. 1038

Giant axons in the earthworm ventral nerve cord. A cross section of the nerve cord is shown. Stellate ganglion Squid giant axon Giant Axons Where is the nerve cord located in Chordates?

Chemical Synapses The calcium channels on the synaptic terminal are ________ gated. The sodium channels on the post- synaptic membrane are ______ gated. The ion channels involved in the propagation of the A.P. are _______ gated. p. 1040

Review: Excitatory vs. Inhibitory Synapses Which ion channels may be opened to hyperpolarize a cell membrane (i.e. create an inhibitory post-synaptic protential)? What would opening Ca ++ channels do to the potential?

Synaptic Summation Is it possible for one kind of neurotransmitter molecule to have an excitatory effect at one cell, and an inhibitory effect at another? Explain, using an example. p

Reflex Arc The Simplest Behavioral Unit of the Nervous System: Reflex Arc What is the difference between a reflex arc and a “reflex act”? Name the neurotransmitter released by motor neurons at the muscle cells.

Photomicrograph of the neuromuscular junction