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The Nervous System

The Nervous System. Introduction. Two organ systems, the nervous and endocrine systems, coordinate organ system activity. The nervous system provides swift but brief responses to stimuli The endocrine system adjusts metabolic operations and directs long-term changes.

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The Nervous System

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  1. The Nervous System

  2. Introduction • Two organ systems, the nervous and endocrine systems, coordinate organ system activity. • The nervous system provides swift but brief responses to stimuli • The endocrine system adjusts metabolic operations and directs long-term changes

  3. The Nervous System • The nervous system includes al the neural tissue in the body. • Its anatomical divisions include the central nervous system (CNS) (the brain and spinal cord • And the peripheral nervous system (PNS) (all neural tissue outside the CNS)

  4. Functionally it can be divided into an afferent division which brings sensory information to the CNS • And an efferent division which carries motor commands to muscles and glands

  5. The efferent division includes the somatic nervous system (voluntary control over skeletal muscle contractions • And the autonomic nervous system (involuntary regulation of smooth muscle, cardiac muscle, and glandular activity.

  6. 8-1

  7. Cellular Organization in Neural Tissue • There are two types of cells in neural tissue • Neurons, which are responsible for information transfer and processing • Neuroglia, which provide a supporting framework and act as phagocytes.

  8. Neurons • Sensory neurons: form the afferent division of the PNS and deliver information to the CNS • Motor neurons: stimulate or modify the activity of a peripheral tissue, organ or organ system

  9. Interneurons: may be located between sensory and motor neurons; they analyze sensory inputs and coordinate motor outputs.

  10. A typical neuron has a cell body, an axon, and several branching dendrites and synaptic terminals

  11. 8-2

  12. Neurons may be described as unipolar, bipolar, or multipolar • 8-3

  13. Neuroglia • Four types • Astrocytes: largest and most numerous • Oligodendrocytes: myelinate CNS neurons • Microglia: phagocytic white glod cells • Ependymal: produce and help circulate cerebral spinal fluid

  14. 8-4

  15. Nerve cell bodies in the PNS are clustered into ganglia. • Their axons are covered by myelin wrappings of Schwann cells.

  16. 8-5

  17. Anatomical organization • In the CNS, a collection of neuron cell bodies that share a particular function is called a center • A center with a a discrete anatomical boundary is called a nucleus. • Portions of the brain surface are covered by a thick layer of gray matter called the neural cortex

  18. The white matter of the CNS contains bundles of axons, or tracts that share common origins, destinations and functions. • Tract in the spinal cord form larger groups called columns

  19. 8-6

  20. Neuron Function: Membrane Potential • The resting potential, or membrane potential of an undisturbed nerve cell, is due to a balance between the rate of sodium ion entry and potassium ion loss and to the sodium-potassium exchange pump

  21. Any stimulus that affects this balance will alter the resting potential of the cell • 8-7

  22. An action potential appears when the membrane depolarizes to a level known as the threshold. • Steps include; opening of sodium channels and opening of potassium channels, return to normal permeability

  23. 8-8

  24. Propagation of an Action Potential • In continuous propagation, an action potential spread across the entire excitable membrane surface in a series of small steps. • During saltatory propagation, the action potential appears to leap from node to node.

  25. 8-9

  26. Action potential

  27. Neural Communication • A synapse is a site where intercellular communication occurs through the release of chemicals called neurotransmitters. • A synapse where neurons communicate with other cell types is a neuroeffector junction.

  28. Structure of a Synapse • Neural communication moves from the presynaptic neuron to the postsynaptic neuron over the synaptic cleft • 8-10

  29. Synaptic function and Neurotransmitters • Cholinergic synapses release the neurotransmitter acetylcholine (Ach) • Ach is broken down in the synaptic cleft by the enzyme acetylcholinesterase (AChE)

  30. Other neurotransmitters • Norepinephrine-excites • Dopamine-inhibits • GABA -inhibits • Serotonin-inhibits

  31. 8-11, table 8-1

  32. neurotransmitters

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