Nerve_physiology.doc

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Department
Biology
Course
BIOL 153
Professor
Robert Harris
Semester
Summer

Description
Biology 153/155 - Nervous System Based on lecture and text material, you should be able to do the following: Control Systems; General give a concise account of homeostasis define and explain positive and negative feedback explain feed-forward control give neural examples of different types of feedback control Nervous System describe the important anatomical structures of a neuron and relate each structure to a physiological role define resting membrane potential and describe its electrochemical basis compare and contrast graded and action potentials explain how action potentials are generated and propagated along neurons define absolute and relative refractory periods and explain their significance define saltatory conduction and compare it to conduction along unmyelinated fibers define a synapse and describe how information is transferred across them distinguish between excitatory and inhibitory postsynaptic potentials describe how synaptic events are integrated and modified define summation and differentiate between temporal and spatial summation define neurotransmitter and describe how they are released and subsequently removed describe common patterns of neuron organization and neuronal processing describe the basic concept of sensory transduction compare and contrast receptor and action potentials discuss the mechanisms of sensory coding of information compare and contrast stretch, flexor and crossed extensor reflexes I. BASIC CONCEPTS OF CONTROL SYSTEMS A. TYPES OF CONTROL SYSTEMS 1) Endocrine (Hormonal) Control - slow general control 2) Neural Control - fast specific control B. WHAT IS CONTROLLED? Homeostatic Control - maintains a state of dynamic equilibrium % Adaptive Responses to Environmental Change - produce appropriate responses to internal and external changes. C. COMPONENTS OF A CONTROL SYSTEM 1) Sensors (Receptors ) 2) Afferent Pathways 3) Comparators (Integrators ) 4) Efferent Pathways 5) Effectors Afferent and efferent pathways can be neural or hormonal. D. TYPES OF CONTROL Negative Feedback Control Very common Maintains homeostasis Allows for adaptive responses to environmental (external) stimuli Examples include pain withdrawal reflex and "fight or flight" response. Positive Feedback Control Relatively Rare Never creates homeostasis Enhances change: causes changes to occur faster and to deviate further from starting values. Controls episodic events Self perpetuating and quite explosive Examples include ionic events associated with generations of action potentials, child birth, hormonal control of ovulation. Feedforward Control Produces change in anticipation of need for change Usually associated with input from "Higher Centers" or from "Other Inputs" Examples include change in the breathing rate in anticipation of exercise and changes in the lining of uterus during menstrual cycle, in anticipation of pregnancy. II. ORGANIZATION OF THE NERVOUS SYSTEM A. THE CENTRAL NERVOUS SYSTEM (CNS): Includes brain and spinal cord, serves as a primary integrating and control center B. THE PERIPHERAL NERVOUS SYSTEM (PNS): Consists of all the nerves, including Cranial nerves which arise directly from the brain (12 pairs in human) Spinal nerves, which arise from the spinal cord (32 pairs in human). Provides communication lines between the CNS and the rest of the body. There are two functional divisions of the PNS: 1. Sensory (Afferent) Nervous System conveys impulses to the CNS from sensory receptors has two sub-divisions: Somatic sensory; conveys information from the skin, muscles joints, and Visceral sensory; conveys information from the viscera (internal organs) 2. Motor (Efferent) Nervous System conveys information from the CNS to the effectors (muscles and glands) has two sub-divisions: Somatic motor N.S. conveys information to skeletal muscles, is under voluntary control, its effects are always stimulatory. Autonomic N.S. conveys information to cardiac and smooth muscles and glands; is under involuntary control, its effects can be either stimulatory or inhibitory. Has two functional sub-divisions: 1) Sympathetic Nervous System 2) Parasympathetic nervous System(These two systems usually have opposite effects on the same visceral organs. If one stimulates, the other inhibits) III. NERVOUS TISSUE Made up of two cell types: % Supporting Cells (glial cells) % Neurons (nerve cells) A. SUPPORTING CELLS (or GLIAL CELLS or GLIA): Make up more than 90% of the cells in the nervous system.There are six different types of cells involved; each type has different function(s), for example: % some form a scaffolding or glue, which holds the nervous tissue together, % some assist neurons by maintaining optimal environment around them, % two types form myelin, which plays an important role in regulating the speed with which nerves conduct information (action potentials). % unlike the neurons, which are amitotic, they reproduce themselves throughout life; for this reason most brain tumors are gliomas, formed by uncontrolled proliferation of glial cells. B. NEURONS: Are highly specialized. Are one of a few types of excitable cells (able to fire action potentials) in the body. Conduct messages in the form of action potentials (nerve impulses) from one part of the body to another. Are amitotic; they can not replace themselves; they do, however, have extreme longevity. Have a high metabolic rate and can not survive for more than a few minutes without oxygen. Have a cell body or soma and numerous thin processes (extensions). Most cell bodies of neurons are located in the CNS where they are protected by the cranium and vertebral column.Within cell bodies all standard organelles are contained 1. Types of neuron processes: Dendrites are processes that receive information, they are input regions of the neuron but they do not have the ability to generate action potentials. Axons are processes that can generate and conduct action potentials, they ari
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