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THE NERVOUS SYSTEM

THE NERVOUS SYSTEM. THE NERVOUS SYSTEM. Communication system 100 Billion nerve cells in the brain alone. DIVISIONS of the Vertebrate Nervous System. 1. Central Nervous System (CNS) nerves, brain, spinal cord coordinating centre. DIVISONS of the Vertebrate Nervous System.

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THE NERVOUS SYSTEM

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  1. THE NERVOUS SYSTEM

  2. THE NERVOUS SYSTEM • Communication system • 100 Billion nerve cells in the brain alone

  3. DIVISIONS of the Vertebrate Nervous System 1. Central Nervous System (CNS) • nerves, brain, spinal cord • coordinating centre

  4. DIVISONS of the Vertebrate Nervous System 2. Peripheral Nervous System (PNS) • nerves that carry info between the CNS and the organs • Somatic Nerves • To/from skeletal muscle, bones and skin • sensory and motor somatic nerves

  5. PNS continued • Autonomic Nerves • special motor nerves that control the internal organs • sympathetic nervous system and parasympathetic nervous system

  6. NERVOUS SYSTEM CELLS • Neurons: cells that conduct nerve impulses (functional unit). • A nerve is a bundle of many neurons. • Glial cells (neuroglial cells): structural support and metabolism of nerve cells (do not conduct)

  7. NEURON ANATOMY • Cell body: nucleus and majority of cytoplasm. • Dendrites: projections of cytoplasm that carry impulses TOWARD the cell body • Axon: extension of cytoplasm that carries nerve impulses AWAY from the cell body.

  8. NEURON ANATOMY • Myelin Sheath: insulated covering (fatty protein) over the axon of some nerves, “myelinated” • prevents loss of charge • Schwann cells: type of glial cell that produces myelin sheath

  9. NEURON ANATOMY • nodes of Ranvier: regularly occurring gaps between sections of the myelin sheath • nerve impulses “jump” from one node to another – increases speed of the impulse • axon diameter also effects speed; narrower = faster.

  10. NEURON ANATOMY • Neurilemma: PNS axons (myelinated or unmyelinated) have a thin membrane surrounding the axon. • Promotes regeneration of damaged axons.

  11. The PNS has greater ability to regenerate than the CNS (spinal cord injuries). • Neurons without myelin sheath or neurilemma do not regenerate, damage is permanent. (“grey matter” in brain and spinal cord; white matter has myelin sheath). • Presence of a growth inhibitor in the CNS. Scientists are looking for ways around this (stem cells)

  12. Types of Neurons • Sensory Neurons: (afferent neurons) carry impulses from sensory receptors to the CNS • Sensory receptors examples: photoreceptors in eyes (light), chemoreceptors in nose and skin (chemicals), thermoreceptors in skin, hypothalamus (heat/cold). • Ganglia (singular – ganglion): clusters of sensory nerve cell bodies located outside of the CNS.

  13. Motor Neurons: (efferent neurons) carry impulses from the CNS to effectors (muscles, organs, glands...i.e. Things that produce a response) • Interneurons: link neurons within the body (found mostly in the CNS).

  14. THE REFLEX ARC • Neural circuit through the spinal cord that provides a framework for a reflex action. • Simplest nerve pathway. • Involuntary, unconscious.

  15. Ex. Accidentally touching a hot stove • Heat detected by thermoreceptors in skin • nerve impulse carried by a sensoryneuron to the spinal cord • interneuron in spinal cord passes the impulse to a motor neuron • motorneuron carries impulse to muscles inarm /hand • causes the muscles to contract and pull hand away

  16. THE REFLEX ARC • Happens in less than a second – information has not even travelled to the brain. When it does, the sensation of pain will become noticeable and you may scream! • If you had to wait to feel the pain first – the burn would be a lot worse. • HOMEWORK: Handout Questions #1-9

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