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THE NERVOUS SYSTEM. INTRODUCTION TO THE NERVOUS SYSTEM. Communication system 100 Billion nerve cells in the brain alone 2 main divisions to a vertebrate nervous system:. TWO MAIN DIVISIONS. Central Nervous System (CNS) nerves, brain, spinal cord coordinating centre - PowerPoint PPT Presentation
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THE NERVOUS SYSTEM
INTRODUCTION TO THE NERVOUS SYSTEM
Communication system 100 Billion nerve cells in the brain alone2 main divisions to a vertebrate nervous system:
TWO MAIN DIVISIONS
Central Nervous System (CNS)– nerves, brain, spinal cord – coordinating centre
Peripheral Nervous System (PNS)nerves that carry info between the CNS and the organs
Somatic Nervesskeletal muscle, bones and skinsensory and motor somatic nerves
Autonomic Nervesspecial motor nerves that control the internal organssympathetic nervous system and parasympathetic nervous system
NERVE CELLS
Two cells types: neurons and glial cells•Glial cells (neuroglial cells): structural support and metabolism of nerve cells (do not conduct)
Neurons: nerve cells that conduct nerve impulses (functional unit). A nerve is a bundle of many neurons.
Sensory Neurons: (afferent neurons) carry impulses from sensory receptors to the CNS
Sensory receptors ex. 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.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).
NERVE CELL ANATOMY
Cell body: nucleus and majority of cytoplasm.Dendrites: projections of cytoplasm
that carry impulses TOWARD the cell bodyAxon: extension of cytoplasm that
carries nerve impulses AWAY from the cell body.Myelin Sheath: insulated covering
(fatty protein) over the axon of some nerves, “myelinated”
prevents loss of chargeSchwann cells: type of glial cell that
produces myelin sheathnodes of Ranvier: regularly occuring
gaps between sections of the myelin sheath
ANATOMY continued
nerve impulses jump from one node to another – increases speed of the impulse
nonmyelinated nerves carry impulses at a slower rateaxon diameter also effects speed – narrower = faster.
Neurilemma: PNS axons have a thin membrane surrounding the axon. Promotes regeneration of damaged axons.Cells without myelin sheath or neurilemma do not regenerate, damage is
permanent. (“grey matter” in brain and spinal cord; white matter has myelin sheath).PNS has greater ability to regenerate than the CNS (spinal cord injuries).
Presence of a growth inhibitor in the CNS. Scientists are looking for ways around this (stem cells)
REFLEX ARC
Simplest nerve pathway.Involuntary, unconscious.Neural circuit though the spinal cord that provides a framework for a reflex action.Ex. Accidentally touching a hot stove:
Heat detected by temperature receptors in skinnerve impulse carried by a sensory neuron to the spinal cordinterneuron in spinal cord passes the impulse to a motor neuronmotor neuron causes the muscles in the hand to contract and pull away from heat
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.
For interest: Reflexes p452, Reflex Lab HandoutHOMEWORK: Handout Questions #1-9
REFLEX ARC
●http://www.free-ed.net/sweethaven/MedTech/NurseCare/fig91902_05.jpg