Nervous system

• Nervous System


  An important complex network of nerves and cells that transmit or send signals between different parts of the body
• Divisions of the Nervous System

  • Peripheral Nervous System
  • Central Nervous System
• Peripheral Nervous System


  • Consist of different nerves cells or neurons in the body

  
• Central Nervous System


  • Consist of Brain and Spinal cord
• Peripheral Nervous System


  Responsible for GATHERING sensory information via "sensory receptor"
• Sensory Receptors


  • Touch Receptors
  • Temperature Receptors
  • Pain Receptors
  • Pressure Receptors
• Sensory Information Processing


  1. Sensory receptors gather sensory information

  2. Sensory neuron sends information to CNS

  3. CNS processes and interprets sensory information

  4. CNS formulates responses

  5. Responses relayed back to PNS

  
• Afferent Division


  Consist of Sensory Neurons which carry stimuli from the Periphery to the CNS

  
• Efferent Division


  Consist of Motor Neurons which carry Nerve Impulses from the CNS to the effector organ

  
• Somatic Nervous System


  Responsible for controlling or coordinating our VOLUNTARY MOVEMENT
• Somatic Nervous System


  • Effector Cell: Skeletal Muscle Cells
  • One neuron set-up

  
• Autonomic Nervous System


  Responsible for Controlling INVOLUNTARY MOVEMENT (e.g. Digestion, heart contraction, release of gland)
• Autonomic Nervous System


  • Effector Cell: Smooth Muscle cells, Cardiac Muscle Cells, Exocrine Glands
  • Two neuron set-up

  
• Divisions of the Autonomic Nervous System

  • Sympathetic Nervous System
  • Parasympathetic Nervous System
  • Enteric Nervous System

  
• Sympathetic Nervous System


  Fight or flight response of the body during emergency situations
• Parasympathetic Nervous System


  Rest or Digest during basal condition
• Enteric Nervous System


  Located in the gastrointestinal tract, with specific functions for the control of this organ system
• Enteric Nervous System


  • Controls peristalsis movement of intestine, secretion of digestive enzymes and hormones, blood flow to digestive organs, coordination of food movement through GI tract
• Differences between Sympathetic and Parasympathetic Nervous Systems

  • Origin: Sympathetic - Thoracolumbar, Parasympathetic - Craniosacral
  • Length of Fibers: Sympathetic - Preganglionic shorter, Postganglionic longer, Parasympathetic - Preganglionic longer, Postganglionic shorter
  • Location of Ganglion: Sympathetic - Near CNS, Parasympathetic - Near Effector Organ

  
• Receptors and Neurotransmitters


  • Receptors: Nicotinic Receptors in Ganglia, Muscarinic Receptors and Alpha/Beta Receptors in Effector Organs
  • Neurotransmitters: Sympathetic - Acetylcholine (Preganglionic), Acetylcholine/Norepinephrine (Postganglionic), Parasympathetic - Acetylcholine

  
• Sympathetic nervous system has extensive preganglionic fiber branching and wide distribution, leading to a diffuse response, while Parasympathetic nervous system has minimal preganglionic fiber branching and limited distribution, leading to a discrete response

  
• Acetylcholine


  The primary neurotransmitter in all autonomic ganglia, at synapses between parasympathetic postganglionic neurons and effector cells, and at the somatic skeletal muscle neuromuscular junction

  
• Synthesis, Storage, Release, and Termination of Action of Acetylcholine

  1. Uptake of choline from extracellular fluid

  2. Acetylation of choline by ChAT enzyme

  3. Storage of acetylcholine in vesicles

  4. Calcium influx triggers release of acetylcholine into synaptic cleft

  5. Acetylcholine binds to receptors
• CoA & Choline


  Substrates for ChAT enzyme
• ChAT


  Choline acetyltransferase enzyme responsible for transferring acetyl group from acetyl CoA to choline, forming acetylcholine
• Acetylcholine synthesis


  1. Acetyl group transfer from acetyl CoA to choline

  2. Acetylcholine formation
• ChAT


  • Responsible for acetylation of choline to form acetylcholine
• Acetylcholine storage


  1. Stored inside vesicles

  2. To protect from metabolic degradation

  3. For proper regulation

  4. Released when needed
• VESAMICOL


  Drug that can inhibit the storage of acetylcholine
• Acetylcholine release


  1. Calcium influx triggers release from vesicles into synaptic cleft

  2. Acetylcholine can now bind to receptors
• Acetylcholine inactivation


  1. Metabolic degradation by acetylcholinesterase enzyme

  2. Breaks down acetylcholine into choline
• VAMPS & SNAPs


  Protein membranes/molecules that facilitate fusion of vesicles and cell membrane
• Botulinum toxin


  Inhibits the release of acetylcholine
• Rate limiting step in acetylcholine synthesis is the uptake of choline from extracellular environment
• Norepinephrine


  Primary neurotransmitter at sympathetic postganglionic neuron-effector cell synapses in most tissues

  
• Exceptions where acetylcholine is present in the sympathetic nervous system include sweat glands
• Catechol nucleus


  1,2 dihydroxybenzene
• Norepinephrine synthesis


  1. Uptake of tyrosine

  2. Conversion of tyrosine to DOPA by tyrosine hydroxylase

  3. Conversion of DOPA to dopamine by dopa decarboxylase

  4. Uptake of dopamine into vesicles by VMAT

  5. Conversion of dopamine to norepinephrine by dopamine beta-hydroxylase
• Metyrosine


  Inhibits the conversion of tyrosine to DOPA
• Reserpine


  Inhibits the storage of dopamine in vesicles