Autonomic and Somatic
Motor Control

LECTURE OUTLINE

I. INTRODUCTION

  A. Brief Comparison CNS and PNS.
     1. Muscle contraction, glandular secretion, metabolism
  B. Overview of PNS organization  
     1. Autonomic Nervous System (ANS)
     2. Somatic Nervous System (SNS)

II. AUTONOMIC NERVOUS SYSTEM: SYMPATHETIC & 
    PARASYMPATHETIC

  A. General functions of sympathetic and parasympathetic
  
  B. Functional organization
      1. How do they operated in general?
      2. ANS often works in opposition, but not always
          a. Examples of opposing regulation 
          b. Origins in CNS differ
          c. Important role of the ANS in homeostasis
  C. Neuronal organization of the ANS
     1. Efferent nerve path consists of two neurons
          a. The adrenal medulla
     2. How can two neurotransmitters (NE and Ach) have many effects?
 D. Receptor subtypes
     1. Alpha1, beta1, beta3 excite; alpha2 & beta2 inhibit
     2. Where and how do these receptors act?      
     3. NE/E effectiveness varies
     4. Agonists and antagonists of these receptors
 E. Ach receptor subtypes
     1. Nicotinic and muscarinic receptors
     2. Where and how do these receptors act?
     3. Agonists and antagonists of these receptors 
  F. Summary

III. SOMATIC NERVOUS SYSTEM

  A. Review relationships between the nerve and muscle cell
  B. Neuromuscular junction
     1. Structure and function of the motor end plate
     2. End plate potential
          a. Transmitter-dependent Na+/K+ gate  
 C. Drugs and poisons acting at the neuromuscular junction.
     1. Nicotine
     2. Curare and cobra toxin
  D. Medical Notes (if time permits)
     1. Myasthenia gravis
     2. Duchenne Muscular Dystrophy

Reading Assignment. Please read Chapter 12 for the next lecture.

BASIC FACTS AND TERMS
1. What are the general functions of the autonomic and somatic nervous systems? How is the autonomic nervous system subdivided?

2. Diagram the neuronal characteristics of the sympathetic and parasympathetic nervous systems with regard to: 1) number of neurons involved, 2) location of the ganglion, and 3) receptor subtype at each synapse.

3. List the receptor subtypes for NE and Ach. Where is each found in the Autonomic Nervous System? Which subtypes are excitatory and which are inhibitory? In what ways is epinephrine (E), a hormone, functionally similar to NE? Functionally different? Explain with examples. Where is E released and how does it travel to its target tissue?

4. What are varicosities in the autonomic nervous system (see Figures 11-8 and 11-9) and how do they function?

5. List the autonomic control centers in the brain (Figure 11-3). Review your notes on the Central Nervous System regarding these regulatory centers.

6. Define and give the physiological significance (how or why it is important) for the following terms:
   • Ganglion
     
   • Neurotransmitter-sensitive Na+/K+ gate
     
   • Voltage-sensitive ion gate
     
   • Pre- and post-synaptic neurons of the ANS
     
   • Acetylcholinesterase
     
   • Neuromuscular junction
     
   
   CONCEPTS

7. Starting with the presynaptic release of Ach, outline the sequence of cellular events that eventually results in an action potential on the muscle fiber.

8. What is an end plate potential? Compare and contrast with an excitatory post-synaptic potential (EPSP).

9. A number of paralytic poisons, such as curare and cobra toxin, act at the neuromuscular junction. How might they act to cause paralysis? There are a number of possibitilites. How many can you think of?

10. Homeostasis of a number of physiological parameters is accomplished through opposition of the sympathetic and parasympathetic nervous systems. List three examples of where these two systems work in opposition. List some examples where they do not work in opposition. Is the parasympathetic nervous system always inhibitory? Is the sympathetic nervous system always excitatory? (See Fig. 11-5)

11. Does output from the motor component of the PNS always result in muscle contraction? Explain.

12. What is Myasthenia Gravis? How is homeostasis disrupted to cause this disease? See page 274.

13. Describe the cellular events which occur at the neuromuscular junction, eventually resulting in muscle contraction. How does the neuromuscular junction differ from a synapse between two neurons?

14. Many of the drugs used in research and medicine act at the autonomic or somatic nervous systems. Read pages 386-387 in Silverthron, and review Table 11-3 with this in mind.

15. Many of the drugs used as medical treatments act at the synapse between two nerves or at the synapse between nerve and muscle. What are the specific cellular actions for the following drugs? See Table 11-3.
    
    • Atropine
      
    • Beta-blockers, such as Propanolol
      
    • Alpha-blockers, such as Phentolamine
      
    • Nicotine
      
    • Muscarine
      
    • Amphetamines
      
    • Ephedrine
      
    • Neostigmine
      
    
    REASONING AND PROBLEM SOLVING

16. You are shown a nerve innervating an exocrine gland (e.g., a salivary gland). You decide that it is not part of the somatic nervous system. Why did you make that decision? What anatomical criteria might you use to determine if the nerve originates in the parasympathetic or sympathetic nervous systems? What different pharmacological or physiological approaches (provide more than one possibility) might you employ to confirm your anatomical evidence?

17. The venom of certain poisonous snakes contains alpha bungarotoxin, which binds tenaciously to acetylcholine receptor sites on the motor end-plate membrane. What would the resultant symptoms be?

18. Patients with myasthenia gravis have a deficiency of nicotinic Ach receptors. Why would administration of an anti-acetylcholinesterase drug, such as neostigmine, improve their muscle function? Explain.

19. You are affraid of snakes. You see on the hiking path just ahead of you. Your heart rate increases, you feel anxious, and you decide to run in the other direction. Use Figure 11-2 to trace the neural pathways involved in your response to the snake.
20. Botox is a vanity drug that eliminates wrinkles under your eyes. It is a weak solution of Botulinum toxin that is subcutaneously injected under the eye. The effect lasts for months. Given your knowledge of muscle contraction, what are the possible actions of this drug in eliminating wrinkles? (click here for the correct answer.) Why can it only be locally administered?

21. The Ach-dependent Na/K channels at the end plate permit more Na to pass than K (click here for figure), resulting in a voltage change that then opens the adjacent voltage-dependent Na channels (=via passive current flow). What the the biophysical basis for this difference in ion flux? Hints: Consider the equilibrium potentials for Na+ and K+. The resting potential for skeletal muscle is about -80 mV.