PCOL

• Divisions of the Nervous System

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
• Functional Divisions of the Nervous System

  • Autonomic Nervous System (ANS)
  • Somatic Nervous System (SNS)
• Autonomic Nervous System (ANS)

  Autonomous, Independent. Its activities are not under direct conscious control. It involves visceral organs that are needed for sustenance of life
• Somatic Nervous System (SNS)


  Consciously controlled functions such as movement, respiration, and posture
• Nervous System and Endocrine System

  • Both have the ability to influence processes in distant regions of the body, extensive use of negative feedback
  • Both use chemicals for transmission of information
  • In NS: chemical transmission occur between nerve cells and effector cells
  • Chemical transmission takes place through the release of small amounts of transmitter substances form the nerve terminals into the synaptic cleft
  • Transmitter proceeds to the postsynaptic cell by binding to a specialized receptor molecule
• Action Potential


  The change in voltage across a membrane
• Resting Membrane Potential


  • Neurons have negative concentration gradient (between -40 to -90 millivolts, mostly -70) most of the time: there are more positively charged ions outside than inside the cell
• Ions outside the cell

  • Na+
  • Cl-
  • Ca2+
• Ions inside the cell

  • K+
  • A- (Negatively charged anions)
• Voltage Gated Ion Channels

  • They open when there is a change in the membrane potential
  • Only opens once an action potential has been triggered
  • 3 types: Activation gate for Na, Deactivation gate for Na, Potassium gate
• Ligand Gated Ion Channels


  • They open when there is an attachment of a ligand (i.e. neurotransmitters)
• Action Potential


  1. Resting membrane potential (-70 mV)

  2. Ligand-gated Na channel opens, Na+ enters cell, making it less negative

  3. Threshold activated (-50 to -55 mV)

  4. Depolarization, voltage-gated Na+ channels open, large entry of Na+

  5. Overshoot/spike/action potential (+30 mV)

  6. Na+ channels inactivate, voltage-gated K+ channels open

  7. Repolarization, K+ leaves cell to restore resting membrane potential

  8. Hyperpolarization, K+ channel gates remain open, cell becomes too negative, Na+/K+ ATPase pump restores balance
• Autonomic Nervous System involves involuntary physiological functions like heart rate, blood pressure, digestion, sexual arousal
• Anatomy of a Neuron

  • Dendrite
  • Cell body
  • Axon
  • Synapse
• Somatic Nervous System


  Has only one motor neuron from the spinal cord to the effector organ
• Autonomic Nervous System


  Has 2 motor neurons from the CNS to the effector organ: Preganglia to Ganglia to Postganglia
• Divisions of the Autonomic Nervous System

  • Sympathetic Nervous System (fight or flight)
  • Parasympathetic Nervous System (Rest and Digest)
• Anatomy of the Sympathetic Nervous System

  • Preganglionic fibers leave the CNS through the thoracic, lumbar, AND SACRAL
  • Preganglionic is SHORT AND MYELINATED, Postganglionic is LONG AND NONMYELINATED
  • Location of ganglion: Near the CNS
  • Preganglionic neurotransmitter: Acetylcholine, Postganglionic neurotransmitter: Norepinephrine
• Anatomy of the Parasympathetic Nervous System


  • Preganglionic fibers leave the CNS through the cranial nerves especially CN 10 (vagus nerve), 9 (parotid), 7 (lacrimal), 3(cilliary)
  • Preganglionic is LONG and MYELINATED, Some preganglionic parasympathetic fibers terminate in parasympathetic ganglia located outside the organs innervated, majority terminate on ganglion cells distributed diffusely or in networks in the walls of the innervated organs
• Enteric Nervous System


  Large and highly organized collection of neurons located in the walls of the GI system. It is referred as the 3rd division of the ANS. It can move independently of the CNS
• Components of the Enteric Nervous System

  • Myenteric plexus (plexus of auerbach), which controls motility
  • Submucous plexus (the plexus of meissner), which controls secretion
• Neurotransmitters


  Chemical signals produced by a neuron to carry a message into another neuron
• Primary Neurotransmitters


  • Acetylcholine
  • Norepinephrine
• Preganglionic Neurotransmitters


  Usually Acetylcholine, regardless of whether its parasympathetic or sympathetic
• Postganglionic Sympathetic Fibers


  Usually release Norepinephrine (Adrenergic fibers)
• Postganglionic Parasympathetic Fibers


  Usually release Acetylcholine (Cholinergic fibers)
• Key Features of Neurotransmitter Function

  • Synthesis of NT
  • Storage of NT
  • Release of NT
  • Termination of action of NT
  • Receptor effects
• Cholinergic Transmission


  1. Na-dependent membrane choline transporter (CHT) transports choline into neuron terminal

  2. Choline + Acetyl-CoA through choline acetyltransferase (ChAT) = Acetylcholine

  3. Vesicle-associated transporter (VAT) transports ACh to vesicles

  4. Vesicle-associated membrane proteins (VAMPs) align vesicle with release sites

  5. Synaptosomal nerve-associated proteins (SNAPs) are the release sites

  6. Voltage gated calcium channel opens during depolarization, allowing Ca2+ entry to trigger vesicle fusion and ACh release

  7. Cholinoceptor on postsynaptic cell binds ACh

  8. Acetylcholinesterase (AChE) breaks down ACh in synaptic cleft
• Adrenergic Transmission


  1. Tyrosine is the precursor of catecholamines

  2. Tyrosine hydroxylase converts tyrosine to L-dopa

  3. L-dopa decarboxylase converts L-dopa to Dopamine

  4. Vesicular monoamine transporter (VMAT) transports catecholamines into vesicles

  5. Ca2+ channels facilitate Ca2+ entry to trigger vesicle fusion

  6. VAMP and SNAP facilitate vesicle fusion

  7. Norepinephrine transporter (NET) reuptakes catecholamines

  8. Monoamine Oxidases (MAO) and Catechol-O-Methyltransferase (COMT) break down catecholamines