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Control Systems (PB Lecture 17 – Spring 2008 Althoff Ch. 34) • Nervous system Systems of Control: ENDOCRINE & NERVOUS • BOTH “SYNTHESIZE” MESSENGER CHEMICALS THAT ARE RELEASED INTO EXTRACELLULAR SPACES Hormones Distance to impact Approach Target Duration of impact Nerve cells Functions • Messenger (receive stimuli) • Communicator (process stimuli) • The critical “network” for maintaining homeostasis…for advanced animals, this means they are “wired” for quick response Nervous System: CNS = _____________________ (central nervous system) vs. PNS = all nerves & ganglia ________ the CNS (peripheral nervous system) ______ ______ CNS • Brain & spinal cord • __________ sensory input, __________ response PNS • Nerves: carries sensory info to CNS and motor commands from CNS • ______ to muscles & glands Nerves Bundles of nerve fibers outside the CNS, most notably the axon and dendrite(s) portion of neurons. Cell Types • ___________--conducts nerve impulses • ___________--supports and services neurons. Supplies nutrients, provides protection, and gets rid of waste Neuron Structure CELL BODY DENDRITE AXON AXON ENDINGS (= axon terminals) MYELIN Neuron Structure • CELL BODY --nucleus & most organelles • DENDRITE--receive incoming information (i.e., stimulus) • AXON--carry information away from cell body • AXON ENDING --makes contact with other neurons, muscles, glands • MYELIN--covering on some neurons 3 Types of Neurons __________ NEURON __________ NEURON _________________ (association neurons) •Not all neurons look alike •Not all neurons carry the same type of information Types of Neurons…con’t • Consider types relative to CNS • Collectively, they are the electronic communications network of the body…. …know these types as well as their relationship to one another! SENSORY NEURON • Carry ________ info from periphery to CNS (i.e., PNS CNS) • Both dendrite and axon are myelinated • ____________ is in the PNS • Examples: pain, pressure, touch, hot, cold, light, sound, blood pressure, blood CO2, bladder stretch, etc. MOTOR NEURON • Carry ___________________ from CNS to muscles or glands (i.e., CNS PNS) • Skeletal muscles - causes contraction Smooth muscles - “ “ Adrenal gland - secrete hormone • Cell body is in the CNS, therefore, axon is usually ______ INTERNEURONS (association neurons) • Found _____ inside the CNS • Connects ___________ (sensory to motor and vise versa) • Typically short dendrites and either long or short axons Hand moves PNS CNS PNS Nerve Impulse A small ___________________ that occurs across the plasma membrane of neurons and then conducted along the axon/dendrite of the neuron RESTING POTENTIAL NEURON AT REST RESTING POTENTIAL OUTSIDE +40mV -65mV INSIDE _________________ NEURON AT REST __________ __________ RESTING to __________________ Na+ in K+ out During ACTION POTENTIAL, _____ channels open first, Na+ rushes in resulting in depolarization…then _____ channels open, K+ rushes out. Summary RESTING POTENTAIL • Maintained at about -65mV by sodiumpotassium pump (i.e., Na-K pump) • _____ always diffusing back and forth because of ___________________ • Na+ higher outside an axon, K + higher inside the axon resulting in the axon having a negative charge ACTION POTENTIAL • A rapid change in polarity across the plasma membrane as the nerve impulse occurs • It is an “____________” phenomenon • If it causes depolarization to a certain level, it is called a ____________ and an “action potential” occurs ACTION POTENTIAL…con’t • Strength of an action potential does ____ change… • …but an intense stimulus can cause the axon to fire at a ______________ • Requires two types of GATED CHANNELS: one for ____ and one for _____ . The Na+ channel opens first ACTION POTENTIAL…con’t • During this process, Na+ moves to the inside of the axon during the depolarization phase (-65mV +40mV) • K + moves to the outside of the axon during the repolarization phase. (+40mV -65mV) • Review Fig. 34.5, pages 651 in Johnson and Losos Propagation of an Action Potential • As action potential travels down the axon, each successive portion of the axon undergoes depolarization, followed by repolarization • Like a _________________ • As the action potential moves on, previous portion goes through refractory period--Na+ channels are shut, then K + channels are shut Propagation of an Action Potential…con’t • With refractory period (i.e., Na+ gate closed), the action potential _________________ ______________….just forwards • At “nodes”, the action potentials jump from node-to-node. At nodes, voltage-sensitive Na+ channel gates are numerous. Speeds of _____ meters/second (_____ miles/hour) have been recorded along a motor neuron Synapse Structure & Function • Where “signal” is transmitted from ____ _____________________ • Axon bulb synaptic cleft postsynaptic neuron • ___________________--molecules that transmit the signal across the synaptic cleft Synapse (synaptic cleft) Presynaptic neuron Postsynaptic neuron Put graphic from text here Neurotransmitters • ____+ known substances or suspected to be neurotransmitters • Acetylcholine (ACh) and Norephinephrine (NE) best known • Acetylcholinestrease (AChE) is an enzyme that breaks down ACh Neurotransmitters • Others include: dopamine serotonin opioids (endorphin) • Many drugs either _________________ ________________________________ Integration • Neurons handle “excitatory” and “inhibitory” signals • Each neuron sums up the two signal types in a process known as INTERGRATION • Result: neuron either “fire” signal down axon…or not “fire signal