Autonomic Nervous System

Question 0

Innervation of Autonomic Nervous System

Answer 0

• mediated by a two-neuron chain from the CNS to the target tissue.
  1. Neuron 1 = Preganglionic:
• Located in CNS
• Sympathetic: intermediolateral nucleus (IML) of spinal cord
  
  • from T1 – L2
• Parasympathetic:CN nuclei in brainstem or sacral parasympathetic nucleus-
  
  • LAM VII from S2 – S4
• Axon in spinal/cranial nerve to reach autonomic ganglion in PNS.
  2. Neuron 2 = Postganglionic
• Located in PNS ganglion
• Sympathetic = sympathetic trunk ganglia (paravertebral ganglia) or prevertebral ganglia
• Parasympathetic = ganglia near the effector tissue
• Axon directly innervates the target tissue

Question 1

general features of the autonomic nervous system.

Answer 1

• controls visceral functions maintaining homeostasis of organism.
• regulates the functions of heart muscle, smooth muscle, and secretory glands.
• consists of two different functional and anatomical divisions:
  
  1. Sympathetic Nervous System (fight or flight functions)
  2. Parasympathetic Nervous System (sedentary functions)

Question 2

General Features of Sympathetic Innervation

Answer 2

• two motor neuron pathway from CNS to effector tissue
  1. preganglionic cell body location:
• intermediolateral (IML) cell column in lateral horn of T1 – L2/L3
  2. postganglionic cell body location:
• Sympathetic chain ganglion
  
  • celiac
  • superior mesenteric ganglion
  • inferior mesenteric ganglion
    
    3. Course of preganglionic axons:
• ventral roots T1-L2/3
• to white rami communicantes
• to sympathetic chain
  4. Course of post ganglionic axons:
• sympathetic chain ganglia
• to gray rami communicantes
• to spinal nerve
  5. Effector Tissues: glands, smooth muscle in vessels & lungs, heart, smooth muscle in orbit, GI tissue, repro

Question 3

Functions of Sympathetic Nervous System

Answer 3

• dilates airways
• piloerection
• inhibits digestion
• accelerates heartbeat
• relaxes urinary bladder
• stimulates ejaculation
• pupillary dilation
• vasoconstriction and sweat production

Question 4

Sympathetic Innervation of the Head

Answer 4

1. no preganglionic sympathetic fibers in cranial nerves.
2. Location of preganglionic cell bodies:
   - Intermediolateral cell column of T1 – T4 spinal cord segments
3. Course of preganglionic axons:
   - T1-T4 ventral roots–>spinal nerves–>white rami communicantes–> sympathetic trunk–>ascend to & synapse in superior cervical ganglion
4. Location of postganglionic cell bodies:
   - Superior cervical ganglion
5. Course of postganglionic axons:
   - Internal and External Carotid nerves–> form sympathetic plexus around these 2 arteries & branches–>plexus fibers jump onto cranial nerve branches–>effector tissues
6. Effector Tissues: glands, smooth muscle in blood vessels and eyes and arrector pili muscles.
7. Controls:
   - vasoconstriction of blood vessels in the face
   - pupillary dilation
   - sweat glands of the face

Question 5

Horner’s Syndrome

Answer 5

• Disruption of sympathetic innervation of the face
• Signs:
  1. Pseudoptosis: a narrowed palpebral fissure due to a loss of innervation of the superior tarsal muscle
  2. Redness (flushing) of the face & conjunctiva due to a loss of innervation of smooth muscles of vessels
  3. Enopthalmos: Sinking of the eyeball into the orbit due to loss of innervation of smooth muscle fibers associated with the floor of the of the orbit
  4. Miosis: pupillary constriction due to loss of innervation of the dilator papillae muscle
  5. Dryness of skin of the face due to loss of sweat gland innervation for the face
• Remember: PREMD

Question 6

Lesions Resulting in Horner’s Syndrome

Answer 6

-T1 –T4 ventral roots
-T1 – T4 spinal nerves
-White rami associated with T1 –T4 spinal nerves
-Cervical sympathetic trunk
-Superior cervical ganglion
-Descending autonomic pathway in the brain stem
-Descending autonomic pathway in the lateral funiculus of the cervical spinal cord segment
Note – these cause an Ipsilateral Horner’s Syndrome

Question 7

General Features of Parasympathetic Nervous System

Answer 7

1. innervation by specific cranial nerves (CN III, CN VII, CN IX and CN X) and sacral spinal nerves (S2 –S4)
   - often called the cranialsacral outflow.
2. Preganglionic Cell Body Location:
   - CNS parasymp CN nuclei & sacral parasymp nuclei.
3. Location of Postganglionic Cell Bodies:
   - PNS autonomic ganglia near the effector tissue.
4. Effector Tissues: glands, smooth muscle and cardiac muscle.

Question 8

Function of Parasympathetic Nervous System

Answer 8

• Constricts airways
• Slows heartbeat
• Stimulates digestion
• Stimulates urinary bladder to contract
• Stimulates penile erection
• Stimulates lacrimation
• Stimulates salivation
• Constricts pupil

Question 9

Differences Between Parasympathetic Innervation of Thorax/Abdomen, Pelvis and Head/Neck Region

Answer 9

1. In thorax, abdomen and pelvis:
   - Postganglionic cell bodies located in un-named autonomic ganglia in walls of the innervated viscera.
   - Postganglionic axons very short since their cell bodies are located in the walls of the viscera.
2. In the head and neck region:
   - Postganglionic cell bodies located in 4 named autonomic ganglia near but not w/in effector tissue.
   - Postganglionic axons are longer and extend from the named ganglia to the effector tissue.

Question 10

Descending Autonomic Pathway

Answer 10

1. Origin
   -Hypothalamic nuclei
   -Brainstem nuclei
2. Course
   -Fibers descend ipsilaterally thru brainstem and spinal cord.
   -spinal cord: fibers located in the medial part of lateral funiculus
   *adjacent to the intermediate zone of the gray matter.
3. Termination
   -Preganglionic sympathetic neurons:
   *intermediolateral nucleus from T1 – L2
   Preganglionic parasympathetic neurons:
   *S2 – S4
4. Function
   -Control of sympathetic outflow for whole body
   -Control of parasympathetic flow to lower abdominal/pelvic region
   -damage to these fibers causes ipsilateral Horner’s Syndrome