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Understanding the Nervous System: Neurons, Impulses, and Reflexes

This chapter covers the basics of the nervous system, including neuron structure, nerve impulses, synaptic transmission, and reflex arcs. Learn about the functions of the spinal cord and the classification of neural tissue.

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Understanding the Nervous System: Neurons, Impulses, and Reflexes

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  1. Chapter 10 The Nervous System: Introduction, Spinal Cord, and Spinal Nerves

  2. Introduction • Control center and communication network • Directs functions of body’s organs and systems • Interprets external environment • Determines reaction to change

  3. Introduction (cont’d.) • Homeostasis: balanced internal environment • Controlled by nervous and endocrine systems

  4. Organization

  5. Organization (cont’d.) • Central nervous system: brain and spinal cord • Peripheral nervous system • Afferent peripheral system • Sensory neurons • Efferent peripheral system • Somatic • Autonomic - sympathetic and parasympathetic

  6. Organization (cont’d.)

  7. Classification of Nerve Cells

  8. Neuroglia Cells • Astrocytes: support, connection, blood brain barrier • Oligodendroglia: support, myelin sheath formation • Microglial: phagocytosis • Ependymal: line the ventricles of the brain

  9. Neuroglia Cells (cont’d.) • Schwann: myelin sheaths in peripheral nervous system

  10. The Structure of a Neuron • Cell body • Dendrites: receptive areas • Axon: extension of cell body • Schwann cells • Nodes of Ranvier

  11. The Structure of a Neuron (cont’d.)

  12. The Structure of a Neuron (cont’d.) • Multipolar: several dendrites coming off cell body • Bipolar: one dendrite and one axon • Unipolar: one process extending from cell body

  13. The Structure of a Neuron (cont’d.) • Receptors: detect environmental stimuli • Sensory: receive impulse from receptor site • Internuncial: transmit impulse for interpretation and processing • Motor: reaction to the stimulus

  14. The Physiology of the Nerve Impulse

  15. The Physiology of the Nerve Impulse (cont’d.) • Nerve cell fiber resting potential • Na+ concentration higher on outside • K+ concentration higher on inside • Negative charge on inside • Positive charge on outside

  16. The Physiology of the Nerve Impulse (cont’d.) • Depolarization: Na+ rush inside cell • Repolarization: K+ rush out to restore balance • Depolarization: Repolarization moves in one direction • Myelinated vs. unmyelinated • All-or-none law

  17. The Synaptic Transmission

  18. The Synaptic Transmission (cont’d.) • Synapse: axon terminal branches close to next dendrites • Impulse reaches axon terminals • Triggers neurotransmitter release into synaptic cleft

  19. The Synaptic Transmission (cont’d.) • Neurotransmitters • Acetylcholine • Most common • Epinephrine • Norepinephrine • Serotonin • Dopamine • Endorphins

  20. Animation – Firing of Neurotransmitters • This animation illustrates the physiology of the nerve impulse Click Here to Play Firing of Neurotransmitters Animation

  21. The Reflex Arc

  22. The Reflex Arc (cont’d.) • Knee-jerk reflex • Maintain homeostasis • Heartbeat/breathing rates • Digestion • Coughing • Sneezing

  23. The Reflex Arc (cont’d.) • Maintain homeostasis • Swallowing • Vomiting

  24. The Reflex Arc (cont’d.) • Involuntary reaction to external stimulus

  25. Grouping of Neural Tissue

  26. Grouping of Neural Tissue (cont’d.) • White matter • Groups of myelinated axons • Forms nerve tracts in CNS • Gray matter • Nerve cell bodies and dendrites • Unmyelinated axon bundles • Cortex: gray matter on surface of brain

  27. Grouping of Neural Tissue (cont’d.) • Nerve: bundle of fibers outside CNS • Ganglia: nerve cell bodies outside CNS • Tract: bundle of fibers inside CNS • Nucleus: nerve cell bodies and dendrites inside CNS • Horns: areas of gray matter in spinal cord

  28. The Spinal Cord

  29. Introduction • Continuation of medulla oblongata • 31 segments each with pair of spinal nerves • Protected by meninges • Dura mater • Arachnoid • Pia mater

  30. Spinal Cord

  31. Functions of the Spinal Cord • Conveys sensory impulses to the brain • Integrates reflexes • Spinal nerves connect at roots • Dorsal root: sensory • Ventral root: motor

  32. The Spinal Nerves

  33. The Spinal Nerves (cont’d.) • All 31 pairs arise from union of dorsal and ventral roots • Mixed nerves consisting of motor and sensory fibers • Most exit vertebral column between vertebrae

  34. The Spinal Nerves (cont’d.) • Named and numbered according to region and level of spinal cord • Cervical: 8 pairs • Thoracic: 12 pairs • Lumbar: 5 pairs • Sacral: 5 pairs • Coccygeal: 1 pair

  35. Summary • Named the major division of the nervous system • Classified neurons and neuroglial cells • Discussed the physiology of the nerve impulse and transmission at synapses • Named the different types of neural tissue

  36. Summary (cont’d.) • Discussed the structure of the spinal cord • Named the spinal nerves

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