Lecture 10

Autonomic Nervous System 

 
 

1. The Autonomic Nervous System:
   
   1. Sympathetic Nervous System
      
   2. Para-sympathetic Nervous Systems 
      

       
       

• They both have a system of the upper motor neurons going to pre-synaptic neurons and post-synaptic neurons (and then go to the target tissue) in place of the lower motor neuron (note: upper motor neurons went to lower motor neurons in the CNS). 
  
• The Sympathetic nervous system can trace its pre-synaptic neurons to the sympathetic trunks
  
  • This is the anatomical definition of the Sympathetic nervous system
    
• The Para-sympathethic Nervous system cannot trace any of its neurons to the sympathetic trunks
  
  • This is the anatomical definition of the Para-sympathetic nervous system
    

     
     

• The two systems differ in neurotransmitters that they use at the target tissue
  
  • Pre-synaptic neurons in both Sympathetic and Parasympathetic secrete ACh (Acetylcholine)
    
  • The Parasympathetic system uses ACh at both the pre-synaptic and post-synaptic spaces
    
  • The Sympathetic uses Norepinephrine as the post-synaptic on or near the target tissue
    
  • There are 3 exceptions to this rule that the SNS uses Norepinephin
    
    • The SNS post-synaptic neurons, during flight or fight, are going to dilate the blood vessels to the skeletal muscles and use ACH. When you sit down and then stand up – your blood pressure was changed by the SNS – that is called Vasomotor Tone. When it changed the blood pressure it used Norepinephin.???At presynaptic???
      
    • Sympathetic post-synaptic neurons that innervate the Sweat Glands use ACH.
      
    • Sometimes there are no post-synaptic fibers.  When this happens the pre-synaptic fiber goes all the way to the adrenal medulla.  There the pre-synaptic fibers synapse (raining ACH out) on:
      
      • Chromaffin cells
        
        • These are endocrine cells that secrete hormones and they get released into the blood stream
          
        • Secrete things called Circulating Catecholamines - which are 80% epinephrine and 20% norepinephine
          

           
           

• The effect of the Parasympathetic system:
  

   
   

  • Constricts the pupils of the eye
    
    • it is the only one innervating the circular smooth muscles of the iris)
      
    • Contracts the ciliary muscle of the eye, which is attached to the lens of the eye. 
      
    • The lumen is getting smaller since this is a circular muscle. 
      
    • There are suspensory ligaments going to the lens, and it allows the lens to bulge (for close vision) and get fatter. 
      
    • The Sympathetic system does not innervate the ciliary muscle of the eye. 
      
  • It decreases the heart rate
    
    • When you sit down, your heart rate decreases b/c of the PNS b/c it has increased the firing rate to do that.  But when you stand up and increase your heart rate, it increases b/c of a decreasing the firing of the PNS. The SNS kicks in through regulating your heart rate, and there is a constant sending through there.  All you have to do to increase it or decrease it is change the PNS up and down.
      
  • It constricts coronary blood vessels
    
  • It increases the activity of the GI tract
    
    • it relaxes the sphincters to allow movement, it will increase the secretions, and it will increase the smooth muscle contractions in the GI tract.
      
  • It constricts the bronchioles of the lungs 
    
  • It is responsible for the contraction of the bladder, but it does not effect the kidneys (the PNS does not innervate the kidneys) 
    
  • It causes sexual excitation in both males and females
    

     
     

1. The effects of the Sympathetic system
   
   1. It dilates the pupil of the eye. 
      
      1. It innervates the radial muscles of the Iris, making the pupils larger. 
         
      2. During flight or fight, we will dilate your eyes, but when we walk into a dark room your eyes will dilate too, which is not flight or fight.  During the Sympathetic stimulation of flight or fight, if we monitor the lens of the eye, we do find that the lens of the eye does flatten some.  This is probably due to the change in the blood flow/circulation or the changing of the firing of the PNS, b/c there is no ciliary muscle to do that.
         
   2. It constricts and dilates all the necessary arteriole and venous systems for fight or flight (to accommodate for changes in the blood flow)
      
   3. It increases the heart rate, and increases the force of the heart beat. 
      
   4. It dilates the arterioles of the heart and skeletal muscle (you are thinking more about flight or fight when you do this)
      
   5. It constricts the arterioles of the:
      
      1. GI tract
         
      2. Kidney
         
      3. Skin
         
      4. Sex organs
         
   6. It constricts the arterioles to the lungs
      
      1. When running, you are expanding the lungs.  When you start to take deeper breathes, this will drop your blood pressure.  This is why we constrict our arterioles to make the blood pressure rise and stay at the proper pressure of the lungs.  You don't want your blood pressure to drop.  
         
   7. It dilates the Bronchioles of the Lungs (allowing more in)
      
   8. It shuts down the GI tract completely (this is definitely a flight or fight thing), closing sphincters, decreasing secretions, and relaxing the smooth muscle contractions.  
      
   9. It relaxes the bladder (this is not urinating) and closes the sphincter urethra (this is a flight or fight thing too)
      
   10. It increases Renin secretion by the kidney, making more Angiotensin II available giving you increased blood pressure.
       
   11. It increases sweating and pilli muscle contraction (Haripilation occurs – goosebumps)
       
   12. It stimulates fat break down in adipose tissue 
       
   13. It mobilizes glycogen stores of the liver raising blood glucose levels
       
   14. It also contracts the spleen, this does not make much of a difference in humans. 
       
       1. In larger animals, like a horse, if they contract the spleen they raise their Hemoatocrit by 5 points, because they have large stores of RBC's in the spleen. 
          
   15. Causes sexual orgasm in both male and female. 
       

• The Sympathetic system cannot shut down the sexual excitation that the Parasympathetic system created; the only way to end the excitation is through orgasm. 
  

 
 

• The sympathetic system is usually the winner over the parasympathetic system. 
  

   
   

• Sympathetic Tone – is the tonal firing of the sympathetic systems, especially the heart. 
  
  • When we talk about Sympathetic tone we only think of the Sympathetic Vasomotor tone, b/c there are no innervations of the blood vessels that are responsible for blood pressure regulation
    

     
     

• Parasympathetic Tone - is not due to the lack of Sympathetic innervations, it just sits there doing the same thing with the exception of when you have flight or fight.   
  
  • The heart has Parasympathic Tone firing and constant sympathetic tonal firing to blood vessels, increasing and decreasing tonal firing of sympathetic fibers – Sympathetic Vasomotor Tone
    
  • Regulating the blood pressure as you are walking back and forth. 
    
  • This is not in fight or flight. 
    
  • 3 systems of Parasympathetic Tone
    
    • these systems are generally regulated by the Parasympathetic system, except in the case of fight or flight. The Parasympathetic system is the ruler, unless we have fight or flight.
      
    • The heart is run by the parasympathetic system except you are in fight or flight (the PNS tells the heart to slow down and the SNS tells the heart to speed up: they are on both sides of the SA node)
      
    • The GI tract is under parasympathetic control except in fight or flight
      
    • The bladder is controlled parasympathtically except in fight or flight. 
      

   
   

• The Autonomic Nervous system: (we cover EEGs and Sleep)
  
  • Reticular Activating System (RAS): 
    

1. Reticular Formation is comprised of sensory afferents bound for the cerebrum going up to the brain stem (medulla, pons, and midbrain). 
   
2. The sensory afferents are going to have clusters of nuclei in white matter:
   
   1. As they go through the brain stem the more mid-line nuclei are called Raphe Nuclei.  
      
   2. Farther from the midline, but closer than the lateral line we have a medial group called a Large cell group. 
      
   3. Farther out from that we have a lateral group called a Small cell group. 
      
   4. The neurons of virtually all the senses send neurons to this area. (Such as from the eye or ear, they are above and go directly to the brain and talk to it).  They send messages into the reticular formation down into the brain stem.
      
3. The Reticular formation is an integral part of the RAS, but it is only one single part of the RAS system
   
4. The RAS sends a continual stream of impulses to the brain
   
   1. The messages change but the flow is continuous
      
5. It keeps the brain alert or puts the brain to sleep
   
6. The RAS system filters out what it considers unnecessary information. 
   
   1. You don't feel something if you are not paying attention to it.  (ex. Can you feel your socks?)
      
7. The RAS has the cerebral cortex disregarding 99% of the sensory stimuli that are sent to the brain. If we did not have this filter, the brain could not handle all the messages. 
   
   1. The filtering of the RAS system is shut down by LSD, and then you can feel more of the sensory stimuli. 
      
   2. Bad trips – take LSD and something scares you and you stay scared (LSD stops itself)
      
   3. You don't have flash backs, but there is only a sense of flashbacks
      
      

 
 

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