CNS (Part A)

• Nervous System


  Components: Brain, spinal cord, nerves, sensory receptors

  Responsible for: Sensory perceptions, mental activities, stimulating muscle movements, secretions of many glands

  Subdivisions: Central nervous system (CNS), Peripheral nervous system (PNS)

  
• Central Nervous System (CNS)


  Consists of: Brain (located in cranial vault of skull), Spinal cord (located in vertebral canal)

  Brain and spinal cord are continuous with each other at foramen magnum

  
• Peripheral Nervous System (PNS)

  Two subcategories: Sensory or afferent division, Motor or efferent division

  Subdivisions: Somatic nervous system, Autonomic nervous system (Sympathetic, Parasympathetic, Enteric)

  
• Neurons


  Receive stimuli and transmit action potentials

  Cell body or soma, Dendrites (input), Axons (output)

  
• Neuroglia or glial cells


  Support and protect neurons
• Types of Neurons


  • Sensory or afferent: Action potentials toward CNS

  Motor or efferent: Action potentials away from CNS

  Interneurons or association neurons: Within CNS from one neuron to another
• Structural classification of neurons

  • Multipolar, Bipolar, Unipolar
• Astrocytes


  Regulate extracellular brain fluid composition, Promote tight junctions to form blood-brain barrier
• Ependymal Cells


  Line brain ventricles and spinal cord central canal, Help form choroid plexuses that secrete CSF

  
• Microglia


  Specialized macrophages
• Oligodendrocytes


  Form myelin sheaths surround axon
• Schwann cells or neurolemmocytes


  Wrap around portion of only one axon to form myelin sheath
• Satellite cells


  Surround neuron cell bodies in ganglia, provide support and nutrients
• Myelinated axons


  Myelin protects and insulates axons from one another, Not continuous, Nodes of Ranvier
• The average weight of adult brain is about 3 lbs or 1.5kg
• Meninges


  Dura Mater (tough and dense fibrous membrane of connective tissue, abundance of blood vessels), Arachnoid Mater (middle layer, resembles a fine cob-web fluid filled spaces), Pia Mater (cover the brain surface, consists of blood vessels and fine areolar connective tissue)
• Cerebral Ventricles


  4 line cavities filled with cerebrospinal fluid (CSF): Right and left lateral ventricles, Third ventricle, Fourth ventricle

  Interconnected via interventricular foramen, cerebral aqueduct, and Foramen of Magendie

  
• Choroid Plexus


  Rich network of blood vessels in each ventricle, Capillaries have different permeability forming the Blood Brain Barrier
• Cerebrospinal Fluid (CSF)


  Formed in the ventricles by the choroid plexuses and cell lining, Colorless liquid derived from blood plasma, Acts as shock absorber, source of nutrients, and removes metabolic waste, Fills the subarachnoid space and returns to bloodstream via arachnoid villi
• Corpus Callosum


  Major pathway (connection) between the left and right cerebral hemispheres, Connects comparable structures, Permits data received on one side to be processed in both hemispheres, Aids motor coordination of left and right side
• Cerebral Lateralization


  Differences in functions and specialization between the left and right hemispheres

  Left hemisphere is specialized for language, sequential and analytical reasoning

  Right hemisphere is specialized for imagination, insight, perception of patterns and spatial relationships
• Sensory information


  Crosses over in pathways leading to the cortex (contralateral organization)

  Visual information: Left visual field to right hemisphere, Right visual field to left hemisphere

  
• Motor control


  Right hemisphere controls left side of body, Left hemisphere controls right side

  Motor nerves cross sides in spinal cord