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The NERVOUS System

The NERVOUS System. Functions of the Nervous System. Sensory senses stimuli from both within the body and from the external environment Integrative analyzes, interprets, and stores information about the stimuli it has receives from the sensory portion of the nervous system Motor

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The NERVOUS System

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  1. The NERVOUS System

  2. Functions of the Nervous System • Sensory • senses stimuli from both within the body and from the external environment • Integrative • analyzes, interprets, and stores information about the stimuli it has receives from the sensory portion of the nervous system • Motor • responds to stimuli by some type of action • muscular contraction • glandular secretion

  3. Divisions of the Nervous System • Central Nervous System (CNS) • Peripheral Nervous System (PNS) • Somatic Nervous System (SNS) • Voluntary • Autonomic Nervous System (ANS) • Involuntary • Sympathetic Division • Parasympathetic Division

  4. Nervous System Schematic

  5. The Central Nervous System • Consists of the brain and the spinal cord • Sorts incoming sensory information • Generates thoughts and emotions • Forms and stores memories • Stimulates muscle contractions • Stimulates glandular secretions

  6. The Peripheral Nervous System • Connects sensory receptors, muscles, and glands in the peripheral parts of the body to the central nervous system • Consists of cranial and spinal nerves • Afferent Neurons (Sensory) • conduct nerve impulses from sensory receptors toward the CNS • Efferent Neurons (Motor) • conduct nerve impulses from the CNS to muscles and glands

  7. The Somatic Nervous System • Made up of sensory neurons that convey information from the cutaneous and special sense receptors in the head, body wall, and extremities to the CNS • Also contains the motor neurons from the CNS that conduct impulses to the skeletal muscles

  8. The Autonomic Nervous System • Contains sensory neurons mainly from the viscera that convey information to the CNS • Contains the efferent neurons that conduct impulses to smooth muscle, cardiac muscle, and glands • Unconscious control • Two divisions of the ANS • Sympathetic Division - stimulatory effect • Parasympathetic Division - inhibitory effect

  9. Neurons • The nerve cells responsible for the special functions of the nervous system • sensing - remembering - thinking • controlling muscle activity • controlling glandular secretions • Synapse - the functional relay points between two neurons or between a neuron and an effector organ • Neuromuscular Junction • Neuroglandular Junction

  10. Parts of A Neuron • Cell Body (Soma or Perikaryon) • nucleus, cytoplasm, organelles of a neuron • Dendrites - tapered, highly branched processes protruding from the cell body • usually very short • AFFERENT FUNCTION • Axons - long, thin, cylindrical process • usually myelinated • EFFERENT FUNCTION

  11. Neuron

  12. Neurons

  13. Classification of Neurons • Functional Classification of Neurons • Based upon the direction of the transmission of the impulses • Afferent Neurons - toward CNS • Efferent Neurons - away from CNS

  14. Types of Afferent Neurons • General Somatic Afferent Neurons • impulses for pain - vibration • pressure - touch • Special Somatic Afferent Neurons • cranial nerve impulse transmission for: • vision - hearing - balance • General Visceral Afferent Neurons • distension of organs - chemical balance • Special Visceral Afferent Neurons • taste and smell via cranial nerves

  15. Types of Efferent Neurons • General Somatic Efferent Neurons • conduct impulses to skeletal muscles • General Visceral Efferent Neurons • conduct impulses from CNS to: • smooth muscle • cardiac muscle • glands • Special Visceral Efferent Neurons • impulses from from the CNS to the: • facial muscles - larynx - pharynx

  16. Terms and Definitions • Nerve Fibers - a general term used to describe any neural process (axon or dendrite) • Nerve - a bundle of nerve fibers that follow the same path within the PNS • Ganglia - nerve cell bodies in the PNS that are clustered together • Tract - a bundle of nerve fibers within the CNS

  17. Neuroglia • Nervous system cells that support, nurture and protect the neurons • Types of Neuroglia found in the CNS • Astrocytes • Oligodendrocytes • Microglia • Ependymal Cells • Types of Neuroglia found in the PNS • Neurolemmocytes (Schwann Cells)

  18. Astrocytes • Star-shaped cells with many processes • Participate in metabolism of neurotransmitters • Maintain K+ balance for generation of nervous impulses • Participate in brain development • Help form the blood brain barrier • Provide a link between neurons and blood vessels

  19. Astrocyte

  20. Oligodendrocytes • Small cells with few processes • Form a supporting network around the neurons by twining around neurons and producing a lipid and protein wrapping around the neurons (myelin sheath)

  21. Oligodendrocyte

  22. Microglia • Small phagocytic cells that protect the central nervous system by engulfing and invading microbes • Clears away debris from dead cells

  23. Microglia

  24. Ependymal Cells • Neuroglia cells that line the brain ventricles • Line the central canal of the spinal cord • Helps form and circulate cerebral spinal fluid

  25. Ependymal Cells

  26. Neuroglia of the PNS • Schwann Cells - Neurolemmocytes • Cells responsible for producing the myelin sheaths around the PNS neurons

  27. Schwann Cell Myelination

  28. Schwann Cell(Neurolemmocyte)

  29. Myelination • The process of developing or producing a Myelin Sheath • Insulates the axon of a neuron • Increases the speed of nerve impulse conduction • CNS - oligodendrocytes • PNS - neurolemmocytes (Schwann Cells) • Diseases such as Tay-Sachs disease and Multiple Sclerosis involve destruction of the myelin sheaths around the nerve

  30. Myelination

  31. Myelinated Axon

  32. Unmyelinated Axon

  33. Gray and White Matter • White Matter - the aggregation of myelinated processes from many neurons • Visible upon freshly dissected brain or spinal tissue • White color is due to myelination • Gray Matter - unmyelinated nerve cell bodies, axons, dendrites, ganglia, and axon terminals • Appears gray because of lack of myelin

  34. Gray and White Matter

  35. Neurophysiology The transmission of nerve (electrical) impulses from nervous tissue to other nervous tissue, organs, glands, and muscles.

  36. Neuron Action Potential

  37. Neuron Membrane Potential

  38. Transmission of Nerve Impulses • An electrical event due to movement of ions across a membrane • Also called an action potential • Lasts about 1 msec (1/1000 of a second) • Dependent upon diameter of the axon • larger diameter axons - 0.4 msec (1/2500 sec) • 2500 impulses per second • smaller diameter axons - 4 msec (1/250 sec) • 250 impulses per second

  39. All or None Principle • Ff depolarization reaches a threshold, an action potential (impulse) is conducted • Each action potential (impulse) is conducted at maximum strength unless there are toxic materials within the cell or the membrane has been disrupted

  40. Neuron Impulse

  41. Neuron Action Potential

  42. Types of Impulse Conduction • Continuous Conduction - step by step depolarization of each sequential, adjacent area of of the nerve cell membrane • typical of unmyelinated nerve fibers • type of action potential in muscle fibers • Saltatory Conduction - the jumping of an action potential across specialized neurofibril nodes along the axon • Nodes of Ranvier

  43. Nerve Conduction

  44. Saltatory Conduction • Occurs in myelinated neurons • Axons have Nodes of Ranvier • Action potentials jump from node to node • much faster than continuous flow • Critical in situations where a fast response is necessary • Much more energy efficient

  45. Speed of Impulse Conduction • Determined by the diameter of the axon and the presence or absence of a myelin sheath • Can be influenced by temperature

  46. Transmission of Nerve Impulses at Synapses • Most nervous conduction is from neuron to neuron (interneurons - 90%) • Types of Synapses • Axon to dendrite • Axon to soma • Axon to axon • Two ways to transmit impulses across a synapse • Electrical Synapses • Chemical Synapses

  47. Electrical Synapses • Ionic current spreads directly from one cell to another cell across Gap Junctions • Allows a very fast transmission from one neuron to the next neuron • Can easily synchronize a group of neurons or muscle fibers

  48. Chemical Synapses • The most typical type of synapse • neuron to neuron • neuron to muscle fiber • No direct contact between structures • synaptic cleft • Action potential must cross the synaptic cleft by means of a neurotransmitter • Ach - Epinephrine - Norepinephrine • One way impulse transfer mechanism

  49. Chemical Synapses

  50. Factors Effecting the Rate of Impulse Conduction • Alkalosis - pH > 7.45 • increased excitability of neurons • Acidosis - pH < 7.35 • depressed neural activity • Pressure (excessive or prolonged) • can block neural activity • Depressants - increases excitation threshold • Stimulants - reduces excitation threshold

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