Autonomics

Question 1

Differentiate between Somatic and Autonomic nervous systems

Answer 1

• Somatic
  
  • part of the peripheral nervous system associated with voluntary control of the body movements through skeletal muscles and mediation of involuntary reflex arcs
  • from CNS to voluntary muscle in one neuron
• Autonomic
  
  • part of the peripheral nervous system and controls the viseceral functions that occur below the level of consciousness
  • subdivided into the parasympathetic and sympathetic nervous systems
  • maintains homeostasis
  • controls all non striated or involuntary muscle
  • found in all parts of the body
  • from CNS to ganglion then to involuntary muscle and glands in 2 neurons

Question 2

functional neuron: somatic afferent

what?

cell bodies located where?

pathway and impulse carried by?

Answer 2

• general sensory, impulses travel into the CNS
  
  • sensory receptors in skin, joints, muscles
  • fibers enter the CNS through individual neurons whose cell bodies are located in
    
    • posterior/dorsal root ganglia
    • cranial nerve ganglia
  • pathway from sensory receptor into spinal cord is one neuron
  • impulse carried by the peripheral process of the ganglia cell - axon of neuron - at central process it enters the CNS

Question 3

functional neuron: somatic efferent

what?

cell bodies located where?

pathway to where?

Answer 3

• motor impulses travel away from CNS
  
  • motor nuerons within the CNS found in
    
    • anterior/ventral horn of spinal cord
    • certain cranial nerve motor nuclei
  • motor impulses are sent directly to skeletal muscle through fibers in anterior/ventral rootlets/roots and peripheral nerves

Question 4

functional neuron: visceral afferent

what?

cell bodies located where?

pathway?

Answer 4

• sensory impulses travel into the CNS
  
  • receptors associated with viseral structures
• cell bodies are located in
  
  • posterior/dorsal root ganglia
  • cranial nerve ganglia
• receptor into spinal cord is one neuron

Question 5

functional neuron: visceral efferent

what?

how do they travel?

cell bodies where?

where do they end up?

Answer 5

• motor: autonomic nervous system - impulses travel away from CNS
  
  • impulses travel through a circuit formed by two neurons in tandem
    
    • preganglionic neuron - with cell body located in CNS in lateral horn/interomediolateral column of gray matter
      
      • ​preganglionic axon synapses with the second neuron
    • postganglionic neuron - outside the CNS in an autonomic ganglion
  • motor impulses from CNS go to
    
    • glands
    • cardiac muscle
    • smooth muscle

Question 6

Distinguish actions of sympathetic nervous system and parasympathetic nervous system

Answer 6

• sympathetic (fight or flight)
  
  • increases heart rate and force or contraction
  • dilates arterioles of the heart muscle and limb muscles
  • constricts blood vessels in certain circulations (ie renal, splanchnic, cutaneous, muscular, etc)
  • inhibits digestive glands and contraction of smooth muscle in the gut
  • dilates pupil
• parasympathetic (rest and digest)
  
  • slows the heart
  • constricts arterioles in the heart
  • stimulates digestive glands
  • relaxes sphincter muscles of the gut
  • constricts the pupil and accomodates the lens for close vision

Question 7

preganglionic sympathetic fibers

length?

origination?

leave CNS where?

Answer 7

• short preganglionic fibers
• originating in spinal cord segments T1 - L2
  
  • in the interomediolateral nucleus/column in the LATERAL GRAY HORN
• axons leave CNS through
  
  • ventral root > spinal nerve > ventral primary ramus > WHITE COMM RAMUS > sympathetic chain/trunk

Question 8

preganglionic sympathetic fibers meet postganglionic sympathetic fibers

where?

ways to get to post ganglionic fiber?

Answer 8

• meet with postganglionic fibers in sympathetic chain/trunk
• to find post-g,
  
  1. pre-g will synapse with post-g at that same level in the trunk
  2. pre-g will ascend to higher level to synapse with post-g (esp. upper thoracics)
  3. pre-g will descend to lower chaing ganglion to synapse with post-g (esp. lower thoracics)
  4. pre-g will pass through the sympathetic trunk to enter splanchnic nerve and synapse in a collateral ganglion (prevertebral ganglion)
     
     • prevertebral ganglion is located in the abdomen ganglia associated with the large vessels arising from the abd. aorta

Question 9

when postganglionic sympathetic fibers EXIT from the SYMPATHETIC TRUNK they go through….

Answer 9

• gray communicating rami to ventral rami spinal n. (ALL SPINAL N. RECEIVE GRAY COMM RAMUS)
• they can either
  
  1. follow spinal n and their branches
     
     • to sweat glands, smooth muscle of blood vessels, and erector pili muscles
  2. independent n branches - visceral branches
     
     • to organs, named for the organ they go to
  3. within the head by following blood vessels
     
     • superior cervical ganglia, running along arteries, forming plexuses
       
       • ie, internal and external carotid plexuses

Question 10

when postganglionic sympathetic fibers EXIT via the COLLATERAL/PARAVERTEBRAL way…

Answer 10

• they exit around single large branches of the aorta and follow the vessel to innervate both vessels and glands
• or they exit as independent visceral branches
  
  • hypogastric n. which innervates pelvic organs

Question 11

preganglionic parasympathetic fibers

length?

origination?

Answer 11

• preganglionic parasympathetic fibers are long
• they originate in nuclei of brainstem along with the gray matter of the sacral spinal cord segments of S2-S4

Question 12

preganglionic parasympathetic fibers exit the CNS from where and where do they go to find the postganglionic parasympathetic fibers?

Answer 12

• pre-g exit the brainstem with CN 3, 7, 9, 10 and follow varied and complex routes to find the post-g
  
  • CN3 - oculomotor > ciliary ganglia
  • CN7 - facial > submandibular and pterygopalatine ganglia
  • CN9 - glossopharyngeal > otic ganglia
  • CN10 - vagus > numerous small ganglia, in plexuses near thoracic or abdominal visceral walls
• pre-g exit the sacral spinal cord through the ventral root as pelvic splanchnic nerve
  
  • goes to autonomic plexuses and goes via the hypogastric n. to the inferior mesentric plexuses (descending and sigmoid colon)

Question 13

what is the exception to the 2 neuron pathway?

Answer 13

going to the adrenal medulla gland; direct stimulus for rapid change, induces epinepherine

Question 14

What is the enteric nervous system?

Answer 14

• GI tract’s own intrinsic nervous system
• formed by two interconnected layers of nerve cells distributed from lower esophagus through the rectum (myenteric and submucosal plexuses)
• sympathetic inputs tend to inhibit activity, slowing digestion
• parasympathetic inputs tend to facilitate activity, enhancing digestion

Question 15

what is the difference between visceral afferent fibers and visceral sensory fibers?

Answer 15

• visceral afferent fibers evoke a reflex response
• visceral sensory fibers mediate conscious sensory experience