Alexis Rice Summary Chapter 11 Nervous System Has Two Principal Parts Central nervous system CNS Components brain and spinal cord Peripheral nervous system PNS Components nerves outside CNS Functions receives processes and transfers information Sensory division carries information toward the CNS Motor division carries information away from CNS Neurons Communication Cells of the Nervous System Neurons are specialized cells for communication Generate and conduct electrical impulses Sensory neurons neurons found in the PNS that receive stimuli and transmit information to Interneurons transmit information between components of the CNS Motor neurons neurons found in the PNS that transmit information away from the CNS Types of neurons the CNS Neurons Cell Structure Three parts of the neuron Cell body main part og the cell has the nucleus and most of the cytoplasm and organelles Dendrites small slender extensions of the cell body receive incoming information Axon long slender extension specialized to conduct electrical impulses away from the cell body Neurons Initiate Action Potentials Neurons generate and transmit action potentials An action potential is basically an electrical impulse Primary means of communication throughout the nervous system Sodium Potassium Pump Maintains Resting Potential Functions of NA K Pump Maintain cell volume the cell Establish and maintain resting potential by active transport of NA out of the cell and K into Resting potential measurable difference in voltage across the cell membrane in a resting cell 70mV Interior of cell negative relative to the exterior Graded Potentials After the Resting Potential Graded potential Transient local changes in the resting potential May depolarize or hyper polarize Summation Graded potentials can add up in space or time This additive effect may reach a trigger point or threshold which initiates an action potential Action Potential Sudden Reversal of Membrane Voltage Initiated when graded potentials reach a certain threshold triggering point Depolarization NA moves out of the axon this reverses the voltage Re polarization K moves out of the axon this restores the initial polarity The normal activity of the sodium potassium pump Action Potentials are All or None and Self Propagating All or Non Individual neuron threshold sets extent of stimulus needed If it achieves threshold it fires Once triggered an action potential is always the same in form and voltage Self propagating Continues to propagate itself in the next region of the axon Moves like a wave down the axon with constant speed and amplitude More About Action Potentials The number of action potentials unit time encodes the strength of the stimulus Stronger stimuli generate more action potentials unit time Speed of action potential Always the same for a particular neuron Can be different in different neurons In larger diameter axons action potentials travel at greater speed Neuroglial Cells Support Protect Axons Neuroglial cells make up 80 of nervous system Function Support Protection Two types Schwann cells Oligodendrocytes Do NOT transmit action potentials Neuroglial Cells Form Myelin Sheath on Neurons Schwann cells Form myelin sheath in PNS Save the neuron energy Speed up the transmission of impulses Saltatory conduction leaping pattern of action potential conduction Help damaged or severed axons regenerate Oligodendrocytes Form myelin sheath in CNS Demyelinating Diseases Multiple sclerosis MS Disorders associated with degeneration of myelin sheaths Progressive damage to myelin sheaths in brain and spinal cord Weakness visual impairment incontinence Amyotrophic lateral sclerosis ALS Progressive damage to myelin sheaths in motor area of spinal cord Progressive weakening and wasting of skeletal muscle Information is Transferred form Neuron to Target Targets another neuron muscle cell or gland Synapse special junction between axon terminus and target cell Synaptic transmission Process of transmission of impulse form sending presynaptic neuron across synaptic cleft to receiving postsynaptic target Involves release and diffusion of chemical neurotransmitter Synaptic Transmission Neurotransmitter Release Action potential arrives at axon terminus causing Ca2 to diffuse into axon bulb Ca2 causes release of neurotransmitter from vesicles Neurotransmitter diffuses across synaptic cleft Neurotransmitter binds to receptors on target postsynaptic membrane and opens gated channels Graded potential results form Na movement through opened channels Neurotransmitters Exert Excitatory or Inhibitory Effects Response of postsynaptic target cell depends on Type of neurotransmitter 50 types Type of receptors Type of gated ion channels Excitatory neurotransmitters Depolarize the postsynaptic cell approaching or exceeding threshold Inhibitory neurotransmitters Hyper polarize the postsynaptic cell Postsynaptic Neurons Integrate and Process Information Response in postsynaptic cell depends on How many neurons are forming synapses with it Whether the neurons forming synapses with it are excitatory or inhibitory Convergence occurs when on neuron receives input from many others Divergence occurs when one neuron sends action potentials to multiple other neurons Peripheral Nervous System Relays Information Between Tissues and CNS Nerve Contains axons of many neurons wrapped together in a protective sheath Carries information to and from the CNS Cranial nerves 12 pairs Connect directly to brain Spinal nerves 31 pairs Connect to spinal cord