Lecture 13 Notes
Animal Nervous System
| Note: these notes taken directly from your book!!!!!!!
So read the book!!
I. Nervous systems receive sensory input, respond to it, and help organisms react to environmental cues A. Three major facets 1. Sensor input i. conduction of signals from sensory receptors to integration centers 2. Integration - interpretation of signals from nerve cells 3. Motor output - conduction of signals from integration centers to effectors such as muscles B. Two main divisions of nervous systems 1. Central nervous system - where most integration occurs (brain and spinal cord in humans) i. sensory neurons - convey signals from sensory receptors (eyes, etc.) to central nervous system (CNS) ii. interneurons - move signals around in CNS and relay information to other neurons iii. motor neurons - receive signals from CNS and react (move muscles) 2. Peripheral nervous system - made up of mostly communication lines (nerves) i. nerves are bundles of nerve cells (also called neurons) ii. ganglia - clusters of neuron cell bodies in the nerves C. Neurons - Major parts 1. Motor neurons contain a cell body that houses the nucleus 2. Extensions that are fiber-like extend outward, called dendrites i. short and numerous 1. convey signals from tips inward to cell body 2. signals may come from a sensory neuron or interneuron 3. axon - long thin fiber that directs signals to other neurons - some can be very long (from your toes to your spine!!) D. Supporting cells for neurons 1. Axons surrounded by myelin sheath i. myelin sheath actually made of cells called Schwann cells ii. spaces between Schwann cells called nodes of Ranvier iii. Schwann cells insulate axon so electrical signals not lost during transmission iv. also these cells help speed up signal movement (can be 330 miles/hr!) v. see Figure 28.2 on page 565 for details of anatomy E. We won't go into how nerve cells fire - but if interested, see pgs. 566-568 F. Do know that an electrical signal travels down the axon and then reaches a gap between neurons 1. At the gap, chemicals may be released that diffuse across the gap - gap is called the synapse 2. When chemicals reach next neuron's dendrites, they stimulate that neuron to begin sending an electrical signal down it's axon, and so on and so on 3. some synapses don't rely on chemicals, but use the electrical signal to stimulate next neuron 4. really fast responses, like crayfish tails, use electrical synapses 5. chemicals that are used are called neurotransmitters i. one example is acetylcholine - important in the brain ii. dopamine is another 6. imbalances in these chemicals can lead to depression and other psychological disorders, as well as other diseases such as Parkinson's Disease, which Michael J. Fox suffers from 7. Caffeine and other alkaloids also interfere with synaptic transmissions II. Nervous system organization A. in bilateral organisms, system is symmetric for two halves of organism B. primitive radial organisms have nerve nets (see Figure 28.10, pg. 572) C. vertebrates have cephalization (concentration of nervous system at one end) 1. Brain and spinal cord make up CNS I won't test you on much beyond
this - so study the above concerning the nervous
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