Nervous System

• Neurons


  Transmit nerve impulses along nerve fibers to other neurons. Typically have a cell body, axons and dendrites

  
• Nerves


  Made up of bundles of nerve fibers
• Neuroglia


  Carry out a variety of functions to aid and protect components of the nervous system

  
• Types of neuroglia in the CNS

  • Astrocytes
  • Microglial
  • Ependymal cells
  • Oligodendrocytes

  
• Types of neuroglia in the PNS

  • Satellite cells
  • Schwann cells

  
• Central nervous system (CNS)

  Made up of the brain and spinal cord
• Peripheral nervous system (PNS)


  Made up of peripheral nerves that connect the CNS to the rest of the body

  
• Functions of the nervous system

  • Sensory
  • Integrative
  • Motor

  
• Somatic nervous system


  Consciously controlled voluntary system
• Autonomic nervous system


  Unconscious system
• Gray matter


  Without myelin sheaths
• White matter


  With myelin sheaths (faster electrical impulse)
• Sensory receptors


  • Gather information and convert it into nerve impulses

  
• Integrative function


  • Sensory impulses are integrated in the brain as perceptions

  
• Motor function


  • Conscious or subconscious decisions lead to motor functions via effectors
• Microglial cells


  Small cells that phagocytize bacterial cells and cellular debris
• Oligodendrocytes


  Form myelin in the brain and spinal cord
• Astrocytes


  Near blood vessels and support structures, aid in metabolism, and respond to brain injury by filling in spaces
• Ependyma(l)


  Cover the inside of ventricles and form choroid plexuses within the ventricles (CSF)
• Schwann cells


  The myelin-producing neuroglia of the peripheral nervous system

  
• Neuron structure


  • Cell body with mitochondria, lysosomes, Golgi apparatus, chromatophilic substance (Nissl bodies) containing rough endoplasmic reticulum, and neurofibrils

  
• Dendrites


  Carry impulses from other neurons (or from receptors) toward the cell body
• Axon


  Transmits the impulse away from the axonal hillock of the cell body and may give off side branches
• Myelinated fibers


  Larger axons enclosed by sheaths of myelin provided by Schwann cells
• Nodes of Ranvier


  Narrow gaps in the myelin sheath between Schwann cells
• Unmyelinated fibers


  Smallest axons lacking a myelin sheath
• Peripheral neurons are able to regenerate because of the neurilemma but the CNS axons are myelinated by oligodendrocytes thus lacking neurilemma and usually do not regenerate
• Types of neurons based on structure

  • Bipolar
  • Unipolar
  • Multipolar
• Types of neurons based on function

  • Sensory (afferent)
  • Interneurons
  • Motor

  
• Cell membrane potential


  Polarized, with an excess of negative charges on the inside of the membrane
• Resting potential


  Separation of charge, or potential difference, due to active transport maintaining greater concentration of sodium ions outside and greater concentration of potassium ions inside the membrane
• Action potential


  1. Sodium channels open, sodium ions rush in, membrane becomes depolarized

  2. Potassium channels open, potassium ions leave the cell, membrane becomes repolarized, resting potential reestablished
• Salutatory conduction


  Myelinated fibers conduct impulses from one Node of Ranvier to the next, faster than conduction on unmyelinated neurons
• All-or-none response


  • If a nerve fiber responds at all to a stimulus, it responds completely by conducting an impulse

  
• Synapse


  Junction between two communicating neurons, with a synaptic cleft between them
• Synaptic transmission


  Impulse in the presynaptic neuron is transmitted across the synaptic cleft to the postsynaptic neuron

  
• Excitatory neurotransmitters


  Increase postsynaptic membrane permeability to sodium ions, may trigger impulses
• Inhibitory neurotransmitters


  Decrease membrane permeability to sodium ions, reducing the chance that it will reach threshold
• Neuronal pools


  Neurons within the CNS are organized into pools that receive input from afferent nerves and process the information
• Facilitation


  A neuron becomes more excitable to incoming stimulation when it receives net excitatory but subthreshold stimulation