HUBS - Nervous System Module

• CNS


  • Central Nervous system
  • Consists of brain, spinal cord
  • 2 general cell types : Neurons and Gila
• PNS


  • Peripheral Nervous system
  • Consists of peripheral nerves and ganglia
  • 2 general cell types : Neurons and Gila
• Zones of Neurons

  • Input
  • Summation
  • Conduction
  • Output
• Cell body 


  • In the input zone
  • Contains organelle and nucleus
  • Sums temporal and spatial
• Axon

  • In the conduction zone
  • Carries electrical impulses (ie action potentials)
  • May or may not be myelinated (enclosed by myelin sheath)
  • Can be very long or short
• Dendrite 


  • in the input zone
  • receives inputs
  • Neurotransmitter released by pre-synaptic neuron binds
  • has chemically-gated ion channels
• Axon terminal 


  • in the Output zone
  • Axon termination point
  • Neurotransmitter releases
• Different Neuron morphological types

  • Multipolar - Axon and dendrites extend from cell body
  • Bipolar - has 2 things stick out (one is input and one is conduction axon)
  • Unipolar - 1 thing comes out from cell body (1st sensory neuron)
  • Anionic (axonless) - No distinct axon
• Glial Cells


  • Astrocytes
  • Microglia
  • Epidermal Cells
  • Oligodendrocytes - only in CNS
  • Schwann Cells - only in PNS
• Microglia


  • Immune cells of CNS ( in brain/spine)
  • Engulfs microorganisms and debris
• Astrocytes


  • Nutrient supply for neurons
  • Ensheaths blood capillaries
  • Injury response
• Ependymal Cells


  • Line the fluid-filled cells of brain and spinal cord
  • Has cilia
  • Circulates the CSF (Cerebrospinal fluid), by beating and waving cilia
• Oligodendrocytes 


  • ONLY IN CNS
  • Supports nerve fibers
  • ensheaths them with myelin, which increases conduction velocity
  • like Schwann cells in PNS
• Schwann Cells


  • Supports peripheral nerve fibers
  • Increases conduction velocity
  • Gaps between myelin is called Ranvier nodes
  • Only in CNS
• Afferent 


  • Sensory information from outside world
  • Information ascends up the nervous system to the brain
  • Dorsal
• Efferent 


  • Descending direction, down from brain
  • Motor response from the sensory information
  • Ventral
• Somatic 


  • Voluntary, aware of it
  • Can be efferent (motor) or afferent (sensory)
  • Neurotransmitter ACh (Acetylcholine)
• Autonomic 


  • involuntary, have no control over
  • can be efferent (motor) or Afferent (sensory)
  • Examples, heartbeat, blood pressure, breathing rate
• Somatic Efferent

  • Voluntary movement
  • 2 (both) myelinated axons between brain and effector (skeletal muscle)
  • Upper motor neuron has cell body in the brain and axon is in the spinal cord, synapse on to the lower motor neuron
  • lower motor neuron has cell body in spinal cord and axon is a spinal nerve in the PNS, synapse onto effector (skeletal muscle)
  • Acetylcholine (ACh) is neurotransmitter released in both synapses
• Autonomic Efferent 


  Two divisions are Sympatric and Parasympathic
• Somatic Efferent


  • Voluntary
  • motor signals
• Somatic Efferent


  1. Two neurons between brain and effector (upper and lower)

  2. Effectors are skeletal muscles

  3. Both motor neuron axons are myelinated

  4. Neurotransmitter for both upper to lower neuron synapse and neuro-muscular junction is Acetylcholine (Ach)
• Somatic, Efferent - Upper Motor neuron


  • Entirely in CNS
  • Has cell body in the brain
  • Axon in spinal cord
  • Synapses onto lower motor neuron
• Somatic, Efferent - Lower motor neuron

  • Cell body in spinal cord (CNS)
  • Axon in spinal cord (PNS)
  • Synapses onto skeletal muscle in a neuromuscular junction
• Autonomic Efferent nervous system


  • Involuntary
  • Consists of 2 divisions : Sympathetic and Parasympathetic
  • 3 neurons between brain and effector
  • Effectors include, adipose tissue, smooth muscle, cardiac muscle, smooth muscle and glands
• Autonomic Efferent -Neuron 1 (Sympathetic and Parasympathetic)

  • Just need to know it exists
  • Entirely in CNS
  • Cell body in brain
  • Axon in brain or spinal cord
• Autonomic, Efferent - Neuron 2 (Preganglionic neuron)

  • Cell body in the CNS (differs in location sympathetic to parasympathetic)
  • Axon extends out to autonomic ganglion in PNS
  • Myelinated axon
  • Synapses onto 3rd neuron in the sympathetic/parasympathetic ganglion
  • Neurotransmitter is Acetylcholine
• Autonomic, Efferent - Neuron 3 (Post-ganglionic neuron)

  • Cell body in the autonomic ganglion (in PNS)
  • Axon extends out to effector organ
  • Unmyelinated axon
  • Neurotransmitter for effector organ synapse is Ach or norepinephrine
• Autonomic Sympathetic Nervous system


  • Fight or flight system
  • Stress response
• Sympathetic chain ganglion is close to and lined up either side of spinal cord
• Neurotransmitters in Autonomic Sympathetic Nervous system

  • Acetylcholine is neurotransmitter for pre to post ganglionic neuronic synapse (#2 to #3)
  • Norepinephrine is neurotransmitter for postganglionic neuron synapse to effector
• Effects of Autonomic Sympathetic Nervous system


  • Increased heart rate
  • Increased pupil size (pupil dilation)
  • Increased sweating
  • Increased blood flow to muscles, via contraction of blood vessels to skin and viscera
  • Decreased gastric motility
  • Decreased salivation
• Structural differences of Autonomic Sympathetic Nervous system vs Parasympathetic


  • Preganglionic neuron (2nd) cell body in thoracolumbar region of spinal cord (T1-L2)
  • 2nd neuron (preganglionic) axon is short and synapse onto postganglionic neuron in sympathetic ganglion
  • Sympathetic Ganglionic neuron is close to CNS
  • Postganglionic neuron cell body in sympathetic ganglion
  • Postganglionic neuron (3rd) is long and synapse onto effector uses Norepinephrine
• Sympathetic chain ganglion


  • Line either side of spinal collum
  • 21-23 pairs, depending on height
  • Where preganglionic neurons (#2) synapse onto postganglionic neurons
  • Where postganglionic cell bodies are
• Autonomic Parasympathetic Nervous system

  • Rest and digest system
  • Restful situations
• Neurotransmitter in Autonomic Parasympathetic Nervous system

  Acetylcholine is neurotransmitter for both synapse
• Structural differences of Autonomic Parasympathetic Nervous system vs Sympathetic


  • Preganglionic neuron cell body is either in cranial brainstem level or sacral level
  • 2nd neuron (preganglionic) is long and synapse in parasympathetic ganglia
  • Parasympathetic ganglion is distant away from CNS
  • Postganglionic neuron cell body is in parasympathetic ganglia
  • 3rd neuron (post-ganglionic) is short and the synapse onto effector uses acetylcholine
• Effects of Autonomic Parasympathetic Nervous system


  • Increased gastric motility
  • Increased salivation
  • Decreased pupil size
  • Decreased heart rate