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PNS

PNS. Assumption that chapter has already been read If you have not read the chapter I strongly suggest you get your book out now. If you have already read the chapter, use this PowerPoint as a test for understanding. Neuron. Draw and label a typical myelinated neuron. Schwann Cells.

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PNS

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  1. PNS

  2. Assumption that chapter has already been read • If you have not read the chapter I strongly suggest you get your book out now. If you have already read the chapter, use this PowerPoint as a test for understanding.

  3. Neuron • Draw and label a typical myelinated neuron.

  4. Schwann Cells • What are Schwann Cells?

  5. Schwann Cells • Special cells that wrap around axons forming the myelin sheath in neurons in the PNS.

  6. What is the name of the spaces in the myelin sheath?

  7. Node of Ranvier

  8. Myelin Sheath • What are the three major functions of the myelin sheath?

  9. Myelin Sheath • Insulator • Protection • Increase speed of transmission

  10. Types of Neurons • Sensory • Motor • Interneuron's Give a definition of each of the three types.

  11. Types of Neurons • Sensory- carry messages from receptors in sense organs, or in the skin, TO CNS • Motor- carry messages FROM CNS to muscles and glands • Interneuron- located in CNS, links between sensory and motor neurons.

  12. Structures of Neurons • Why are the neurons below classified as multipolar neurons?

  13. Structures of Neurons • Why are the neurons below classified as bipolar neurons?

  14. Structures of Neurons • Why is the neuron below classified as a unipolar neuron?

  15. Structures of Neurons • One axon and multiple dendrites • Most common type- interneurons and motor neurons to skeletal muscle

  16. Structures of Neurons • One axon and one dendrite- axon and dendrite have many branches • Eye, ear and nose- take impulses from receptor cells to other neurons

  17. Structures of Neurons • One extension- an axon • Cell body to one side • Most sensory neurons that carry messages to spinal cord are this type

  18. Neurons, Nerve fibre and Nerves • Neuron- a nerve cell • Nerve Fibre- any long extension of cytoplasm of a nerve cell body, although the term usually refers to an axon • Nerve- a bundle of fivres held together by connective tissue

  19. Synapses • What are they and what do they do?

  20. Synapses • Junction between branches of adjacent neurons • Occur between end branches of one neuron and a dendrite or cell body of another neuron • Messages carried across synapse • Where nerve attaches to muscle synapse called neuromuscular junction

  21. Synapse

  22. Divisions of Nervous system • CNS- Brain + spinal cord • PNS- nerves that connect body to CNS • PNS- Ganglia (groups of nerve bodies) outside CNS • 12 Cranial nerves • 31 spinal nerves • Joined to spinal cord by 2 roots- ventral and dorsal • Ventral- motor, cell bodies in grey matter • Dorsal- sensory, cell body in dorsal root ganglion

  23. Peripheral Division • Afferent- sensory • Somatic sensory neurons- impulses into nervous system from receptors in skin, muscles and joints • Visceral sensory neurons- impulses from internal organs • Efferent- motor • Somatic- impulses from CNS to skeltal system • Autonomic- impulses from CNS to heart muscle, involuntary muscle and glands • Divided into sympathetic and parasympathetic nervous systems

  24. Reflexes • What is a reflex?

  25. Reflexes • A reflex is a rapid, automatic response to a change in the external or internal environment.

  26. Reflexes • What are the four important properties of reflexes?

  27. Refelxes • A stimulus is required to trigger off a reflex, it is not spontaneous • A reflex is involuntary- it occurs without any conscious through • A reflex response is rapid- only a small number of neurons are involved • A reflex response is stereotyped- it occurs in the same way each time

  28. Reflexes • Most coordinated by spinal cord- spinal reflex • involuntary • Awareness does not occur until after the response has been initiated

  29. Reflex arc • Path an impulse follows from receptor to effector • 5 basic components • Receptor- ending of sensory neuron or specialised cell associated with sensonry neuron, reacts to change • Sensory neuron- carries impulse to CNS • Synapse- at least one • Motor Neuron- carries impulse to effector • Effector- receives impulse and carries out response, muscle or secretory cell.

  30. Reflexes • Eg • Blinking • Sneezing • Coughing • Constriction of pupil

  31. Learned Reflexes • Suckling, chewing, tracking with eyes • Acquired reflexes- adjustments required to maintain balance when riding a bike, jamming the brakes of a car or catching a ball- learned through repetition.

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