Efferent Division of the Nervous System

1
Efferent Division of the Nervous System
2
Somatic Motor Division Controls Skeletal Muscles
pg. 381
Where are the cell bodies of most somatic motor
neurons located? Do motor neurons have a
threshold? Why or why not? Name at least two
sources of excitatory input to somatic motor
neurons. Are the axons of somatic motor neurons
myelinated? Name the type of ion channel
associated with nicotinic receptors at the motor
end-plate.
Figure 11-11 Summary of efferent pathways
3
Neuromuscular Junction Overview
Describe the concept of a motor unit. How would
the anatomy of a large motor unit compare to this
diagram?
pg. 382
Figure 11-12 Anatomy of the neuromuscular
junction
4
Neuromuscular Junction Mechanism of Signal
Conduction
pg. 383
Figure 11-13 Events at the neuromuscular junction
Why is depolarization the net effect of opening
these non-specific cation channels? Explain.
5
Autonomic Motor Division Homeostatic Balancing
pg. 370
Figure 11-1 Homeostasis and the autonomic
division
6
Autonomic Control Centers
pg. 371
What kinds of autonomic (nervous) functions are
regulated in the hypothalamus? endocrine?
behavioral responses? In addition to internal
chemical changes, name some of the other
influences on hypothalamic function. Is the
respiratory center in the medulla oblongata truly
an autonomic control center?
Figure 11-3 Autonomic control centers in the
brain
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Concept Map Autonomic Pathways
pg. 371
Many arterioles receive only sympathetic
innervation, if at all. How would arteriole
diameter be controlled if not by the Autonomic
NS? Speculate as to why arterioles do not
receive dual innervation. How would
acetylcholine affect GI smooth muscle tissue as
compared to norepineprhine?
Figure 11-2 The hypothalamus and brain stem
initiate autonomic, endocrine, and behavioral
responses
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Autonomic Motor Pathways Two Efferent (Motor)
Neurons
pg. 374

• All preganglionic neurons release Ach onto
  nicotinic receptors.
• Most postganglionic sympathetic motor neurons
  release NE onto adrenergic receptors at visceral
  effectors.
• Most postganglionic parasympathetic motor neurons
  release Ach onto muscarinic (cholinergic)
  receptors at visceral effectors.
• Most visceral organs receive dual innervation.

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Synapses in Autonomic Nerves
pg. 375

• Terminal varicosities
• NE released into ECF
• Impact
• Large area
• Slow acting
• Longer duration
• Subject to modulation by local paracrine messages

Figure 11-8 Varicosities of autonomic neurons
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Comparison of Neurotransmitters and Receptors in
Autonomic pathways
pg. 375
Describe the general locations of preganglionic
cell bodies of the sympathetic and
parasympathetic divisions. Generally describe
signal transduction following stimulation of
cholinergic receptors on target cells? Generally
describe signal transduction following
stimulation of adrenergic receptors on target
cells.
Figure 11-7 Sympathetic and parasympathetic
pathways
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Comparing Autonomic Pathways
Refer to the table that begins on p. 115 of your
packet for a list of effectors and the Autonomic
receptors they display.
Where else are nicotinic receptors located?
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Autonomic Reflexes visceral reflexes
pp. 430-431
Figure 13-2 Autonomic reflexes
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Since most visceral effectors have a combination
of sympathetic and parasympathetic receptors,
drugs used to treat certain conditions can have
different attacks, e.g. sympathomimetic and
anticholinergic asthma medications (see Student
Panel Presentation and Table 11-3, pg. 379)
Figure 11-5 Autonomic sympathetic and
parasympathetic pathways
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Adrenal Medulla A Modified Sympathetic Ganglion
pg. 377
Figure 11-10 The adrenal medulla
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Adrenergic Receptors
pg. 377

• Alpha 1 receptors are most common
• Respond strongly to both Epi and NE
• Alpha 2 receptors are found in the digestive
  system
• Respond strongly to both Epi and NE
• Beta 1 receptors found only in the heart and
  kidney
• Respond strongly to both Epi and NE
• Beta 2 receptors are not directly innervated by
  sympathetic nerves
• Which catecholamine (Epi or NE) would you expect
  these receptors to be most sensitive to?

16
Adrenergic Receptors utilize second messenger
systems

• Activating Phospholipase C changes the internal
  environment of the cell
• Ca concentration increases
• Activating a protein kinase, or causing smooth
  muscle contraction

1 generally excitatory 2 generally inhibitory
Caffeine inhibits the action of
phosphodiesterase, the enzyme that destroys cAMP.
How does this affect the effector cell?
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Mechanism Norepinephrine Release and Recycling
pg. 376
Figure 11-9 Norepinephrine release at a
varicosity of a sympathetic neuron
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Muscarinic Receptors utilize G proteins

• Most often to control K channels
• If channel opens gt hyperpolarization
• If channel closes gt depolarization
• May activate second messenger systems

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Review of Efferent Pathways Motor Autonomic
pg. 380
See also the figures posted on the course web
site.
Figure 11-11 Summary of efferent pathways