reflex , somatic

• Autonomic nervous system (ANS)


  A system of motor neurons that innervate smooth muscle, cardiac muscle and glands

  
• Autonomic nervous system


  • Has two divisions: Sympathetic and Parasympathetic
  • They mostly innervate the same structures but cause opposite effects
• Sympathetic division


  Mobilizes the body during extreme situations such as exercise, excitement and emergencies. Colloquially known as "fight or flight."
• Parasympathetic division


  Controls routine maintenance functions such as to conserve body energy and is colloquially called as "rest and digest."
• Anatomy of autonomic motor pathways

  1. Two neurons from CNS to effector organ are involved:

  2. Preganglionic neuron (cell body in CNS - B fiber)

  3. Postganglionic neuron (entirely outside CNS, cell body in autonomic ganglion) – terminates on visceral effector

  
• Somatic motor division


  • Lacks ganglia entirely
• Pathway from spinal cord to sympathetic trunk ganglia

  Lateral Gray Horns - Intervetebral foramina - Preganglionic axons → anterior root of a spinal nerve → white ramus → sympathetic trunk ganglion
• White rami communicantes


  Structures containing sympathetic preganglionic axons that connect the anterior ramus of the spinal nerve with the ganglia of the sympathetic trunk
• Sympathetic ganglia


  • Sympathetic trunk (vertebral chain) ganglia
  • Superior cervical region
  • Middle & inferior cervical ganglion
  • Thoracic sympathetic trunk
• Prevertebral (collateral) ganglia


  • Celiac
  • Superior mesenteric
  • Inferior mesenteric
  • Aorticorenal
  • Renal
• Sympathetic division - Postganglionic neurons

  1. Axons leave the sympathetic trunk ganglia (STG) in 4 possible ways:

  2. Spinal nerves

  3. Cephalic periarterial nerves

  4. Sympathetic nerves

  5. Splanchnic nerves
• Gray ramus


  Axons of some postganglionic neurons leave the sympathetic trunk by entering a short pathway called a gray ramus and merge with the anterior ramus of a spinal nerve
• Gray rami communicantes


  Structures containing sympathetic postganglionic axons that connect the ganglia of the sympathetic trunk to spinal nerves
• Cephalic periarterial nerves


  Some sympathetic preganglionic neurons that enter the sympathetic trunk ascend to the superior cervical ganglion where they synapse with postganglionic neurons. Some of these leave the sympathetic trunk by forming cephalic periarterial nerves.
• Sympathetic nerves


  Some axons of the postganglionic neurons leave the trunk by forming sympathetic nerves. Innervate the heart and lungs.
• Sympathetic division - postganglionic neurons

  1. Some sympathetic preganglionic axons pass through the sympathetic trunk without terminating in it and form nerves called splanchnic nerves which extend to prevertebral ganglia.

  2. Some sympathetic preganglionic axons pass without synapsing, through the sympathetic trunk, greater splanchnic nerves and celiac ganglion into the adrenal medulla (modified sympathetic ganglia).
• Parasympathetic division


  Craniosacral division: Preganglionic neurons originate from the cranial nerves III, VII, IX and X and sacral spinal nerves S2-S4

  
• Parasympathetic ganglia


  • Ciliary ganglia
  • Pterygopalatine ganglia
  • Submandibular ganglia
  • Otic ganglia
• Parasympathetic division - Sacral Outflow

  Consists of S2-S4. Preganglionic neurons → ventral root → sacral spinal nerve → Pelvic splanchnic nerves
• Autonomic tone


  A balance between the sympathetic and parasympathetic activity
• Hypothalamus


  The major control and integration center of the ANS
• Differences between sympathetic and parasympathetic nervous system

  • Origin of preganglionic fibers
  • Location of ganglia
  • Neurotransmitter
  • Functions

  
• Reflex


  An automatic, sudden, involuntary response to a stimulus
• Reflex arc


  Includes: sensory receptor, sensory neuron, integrating center, motor neuron, effector