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Unit #7 Nervous System: Neurons Introduction • Two systems of communication – Nervous system • Rapid response • Uses action potentials – Endocrine system • Slower response • Uses hormones Tortora Pages 225 Did You Know? • Many types of mental illnesses are related to imbalances in chemicals that transmit messages between neurons Tortora Pages 225 Introduction • Nervous system – CNS – PNS Tortora Pages 205 - 207 Introduction • Endocrine system – Ductless glands – Pituatary (master gland) Tortora Pages 205 - 207 Functions of Nervous System • Sensory Tortora Pages 205 - 207 Functions of Nervous System • Integrative Tortora Pages 205 - 207 Functions of Nervous System • Motor Tortora Pages 205 - 207 Organization of Nervous System • Central Nervous System – Brain – Spinal cord Tortora Pages 205 - 207 Organization of Nervous System • Peripheral Nervous System – Cranial nerves – Spinal nerves Tortora Pages 205 - 207 Organization of Nervous System • Sensory, Motor, and Connecting Neurons – Sensory are referred to as afferent. – Motor are referred to as efferent. – Connecting are referred to as association Tortora Pages 205 - 207 Organization of Nervous System • Somatic Vs Autonomic – Somatic is voluntary • Sensory nerves and motor nerves. – Autonomic is involuntary • Mostly motor nerves leading to smooth muscle, cardiac muscle, and glands. Tortora Pages 205 - 207 Organization of Nervous System • Symapathetic Vs Parasymnpathetic ANS – Oppose each others actions. – Regulates homeostasis. Tortora Pages 205 - 207 Histology Tortora Pages 207 - 210 • Two types of cells – Neurons conduct impulses. – Neuroglial cells support and protect neurons. Neurons found in the spinal cord. Histology Tortora Pages 207 - 210 • Neuroglia – Smaller than neurons. – Outnumber neurons 5 to 50 times. – Six different types. Neurons found in the spinal cord. Histology Tortora Pages 207 - 210 • Neurons. – 3 distinct areas • Cell body. • Dendrites. • Axons. Neurons found in the spinal cord. Histology Tortora Pages 207 - 210 • Cell body of neuron. – Nucleus – Typical cell organelles. – No mitotic spindle. Neurons found in the spinal cord. Histology • Neurons are in three forms. – Multipolar – Bipolar – Unipolar Tortora Pages 207 - 210 Histology Tortora Pages 207 - 210 • Neurons are in three sizes. – Type A • Largest diameters • 130 M/sec – Type B • Middle sized • 10 M/sec – Type C • Smallest • .5 M/sec • unmyelinated Neurons and their many branches Histology Tortora Pages 207 - 210 • Dendrites – Usually short and thick. – Usually highly branched. – Receives impulses. – Conducts impulses towards cell body. Dendrites surrounded by neuroglial cells. Histology Tortora Pages 207 - 210 • Axons – Neurons have a single axon. – Usually long and very thin. – Can be branched (collaterals) – Terminates in many terminals. – Terminals contain vesicles. – Vesicles contain neurotransmitters. Axon surrounded by neuroglial cells Histology Tortora Pages 207 - 210 • Myelin sheath – Speeds impulse along axon. – Insulates axon . – Composed of neuroglial cells. (PNS) – Schwann cells produce myelin (lipoprotein) – Nodes of Ranvier create gaps in myelin sheath. Myelin sheath structure Histology • Grouping of Neural tissue – White matter is myelinated. – Gray matter is unmyelinated. Tortora Pages 207 - 210 Nerve Impulses • Nerve impulse – An imlpulse is a change in the electrical charge (potential) on the membrane of the neuron. – Due to ions moving into and out of the neuron. Tortora Pages 210-213 Nerve Impulses – Ions move through very selective membrane channels. – Channels are transmembrane proteins. – Channels open or close in response to certain changes. – Voltage gated channels Tortora Pages 210-213 Nerve Impulses • Membrane Potentials. – Resting potential - no impuse. • Positive outside • Negative inside. – Action potential. • Positive inside. • Negative outside. – Potentials are due to ions. • Na + • K+ • Large negative ions (proteins) Tortora Pages 210-213 Nerve Impulses Tortora Pages 210-213 • Resting potential – No impulse. – Positive outside neurolemma – Negative inside. – 30x more K+ inside. – 15x ore Na+ outside. – Large negative ioins trapped inside. – Sodium - Potassium pump creates these conditions. – Membrane is “polarized”. Creating An Impulse Along An Axon Caffeine & the Nervous System Histology • Nerves are groups of neurons. – Mixed contain dendrites and axons. – Motor contain axons only. (Efferent) – Sensory contain dendrites only. (Afferent) Tortora Pages 207 - 210 Conduction Across Synapses • Impulses are sent to: – Glands – Muscles – Other neurons. • Impulse must bridge synapse Tuesday 1/20/04 Pages 213-214 Conduction Across Synapses • Synapses have ability to transmit impulse or inhibit impulse transmission. Tuesday 1/20/04 Pages 213-214 Conduction Across Synapses • Most brain disorders involve disruption of synaptic communication. Tuesday 1/20/04 Pages 213-214 Conduction Across Synapses Tuesday 1/20/04 Pages 213-214 • Presynaptic neuron – Synaptic vesicles – Neurotransmitter – Role of calcium ions • Synaptic cleft • Postsynaptic neuron. – receptors Voltage gated channels Na+/K+ Pump Conduction Across A Synapse Saltatory Conduction Tuesday 1/20/04 Pages 213-214 REGENERATION OF NERVOUS TISSUE • Neurons have limited power of regeneration. • Ability to reproduce lost at 6 months of age. • A destroyed neuron is lost. • PNS neurons can repair. • CNS neurons cannot repair. Tuesday 1/20/04 Pages 213-214