Download Chapter 11 Efferent Division: Autonomic and Somatic Motor Control

Chapter 11
Efferent Division:
Autonomic and Somatic Motor Control
Part 1
Exam 3 will start here. Exam 2 only covers up through
the end of Chapter 10
For Wednesday (after the exam), start with the table
on p. 390. Did everything before that
On Friday, go back over slide #50 (alpha receptors)
Figure 8-1
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Autonomic Division
Functions of this division are NOT under voluntary
control
2 Branches:
– Sympathetic
– Parasympathetic
The two branches can be distinguished anatomically
(discussed later in chapter)
Functionally, they are harder to separate
Autonomic Division
The 2 branches can be distinguished based on the
types of situations when they are each most active
Parasympathetic branch is dominant when:
– You are resting quietly after a meal
– Routine, quiet, day-to-day activities
– “Rest and Digest” functions
Sympathetic branch is dominant during:
– stressful situations:
– “Fight or Flight” response
Autonomic Division
“Fight or Flight” response
– Mediated through the hypothalamus
– Massive simultaneous sympathetic discharge
throughout the body
• Heart speeds up
• Blood vessels to muscles of arms, legs, heart all
dilate
• Liver starts to produce lots of glucose
• Digestion becomes a low priority, so blood is
diverted from the GI tract to the skeletal muscles
• etc.
Autonomic Division
“Fight or Flight” response is a special case
Most sympathetic responses are not on such a
massive scale
Activation of one sympathetic pathway does not
activate all of them except in crisis situations
Most of the time, autonomic control “seesaws” back
and forth between sympathetic and parasympathetic
branches (fig. 11-1, p. 387)
Figure 11-1
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Autonomic Reflexes and Homeostasis
Homeostasis is maintained by interactions among:
– Autonomic NS
– Endocrine system
– Behavioral state system
Homeostatic control centers are found in the
– Hypothalamus
– Pons
– Medulla
See Fig. 11-2, p. 387
Figure 11-2
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Autonomic Reflexes and Homeostasis
See fig. 11-3, p. 388 for details
Homeostatic control centers monitor and regulate
important functions:
– Blood pressure
– Temperature regulation
– Water balance
– Osmolarity
– Etc.
Figure 11-3
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Autonomic Reflexes and Homeostasis
Motor output from hypothalamus and brain stem
create appropriate autonomic, endocrine, and
behavioral responses
Examples:
– Drinking
– Food-seeking
– Temperature regulation (putting on a sweater,
moving out of the hot sun)
– etc.
Autonomic Reflexes and Homeostasis
The behavioral responses are integrated in the brain
centers responsible for :
– Motivated behaviors
– Control of movement
Sensory information integrated into the cerebral
cortex and the limbic system can create emotions
which can furter influence autonomic output
– Blushing
– Fainting at the sight of a hypodermic needle
– “Butterflies in the stomach”
Figure 11-2
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Spinal reflexes (autonomic)
– Take place without input from the brain
– Can be influenced by the brain, but does not
require input from it
This is why some people with spinal cord injuries may
retain some spinal reflexes, but lose the ability to
sense or control them
Spinal reflexes include:
– Urination
– Defecation
– Penile erection
– etc.
Dual Antagonistic Innervation
Most internal organs are under antagonistic control:
– One autonomic branch is excitatory while the other
is inhibitory (Fig. 11-5, table)
– Example:
• Sympathetic innervation increases heart rate
• Parasympathetic innervation decreases it
Exceptions:
– Sweat glands and smooth muscle
• Only sympathetic innervation
Not all target tissues are antagonistically controlled
Sometimes the two branches work cooperatively on
different tissues to achieve a common goal
Example:
Blood flow for penile erection is controlled by
parasympathetic branch
Muscle contraction for sperm ejaculation is controlled
by sympathetic branch
In some autonomic pathways, the neurotransmitter
receptor determines the response of the target tissue
Example:
Most blood vessels contain one type of adrenergic
receptor that causes smooth muscle contraction
(vasoconstriction)
Some blood vessels contain a second type of
adrenergic receptor that causes smooth muscle to
relax (vasodilation)
Both receptors are activated by catecholamines
(p.224)
Autonomic Pathways (fig. 11-4, p. 388)
All autonomic pathways (sympathetic and
parasympathetic) consist of 2 neurons in series
The first or preganglionic neuron, originates in the
CNS
It projects to an autonomic ganglion outside the CNS
There the preganglionic neuron synapses with the
second or postganglionic neuron
Its cell body is within the ganglion and its axon projects
to the target tissue
Figure 11-4
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Exam 2 is graded
Class Average: 79
Figure 11-5, part 3
For Exam 3:
learn this
entire table
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Figure 11-5, part 4
For Exam 3:
learn this
entire table
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Sympathetic and Parasympathetic Innervation:
Anatomical Differences
(fig. 11-5, p. 390)
Main anatomical differences:
• Point of origin of the pathways
• Location of the autonomic ganglia
• Relative lengths of pre and postganglionic neurons
Sympathetic Pathways (red lines in fig. 11-5)
• Most originate in the thoracic and lumbar regions
of the vertebrae
Sympathetic ganglia:
• Found in 2 chains (along either side of the
vertebral column)
• Some are found along the descending aorta
Most have short preganglionic and long postganglionic
neurons
Preganglionic neurons are short, because their ganglia
are close to the spinal cord
Figure 11-5, part 1
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Parasympathetic Pathways (blue lines in fig. 11-5)
• Most originate in the brain stem OR in the sacral
region
• Those which originate in the brain stem leave the
brain in several of the cranial nerves
• Those which originate in the sacral region control
pelvic organs
Parasympathetic ganglia:
• Located on or near target organs
• Have long preganglionic and short postganglionic
neurons
Figure 11-5, part 1
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Parasympathetic Innervation
• Head
• Neck
• Internal organs
Vagus nerve (cranial nerve X)
• Major parasympathetic tract
• Contains 75% of all parasympathetic fibers
• Carries sensory information from internal organs
to the brain
• Carries parasympathetic output from brain to
organs
Figure 11-6
Vagus nerve
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Autonomic System: Neurotransmitters, etc.
(Figure 11-7, p. 391)
Sympathetic and Parasympathetic branches can be
distinguished by their neurotransmitters and receptors
1. Preganglionic neurons (both branches) release
acetylcholine (ACh) onto nicotinic cholinergic
receptors on the postganglionic neuron
2. Most postganglionic sympathetic neurons secrete
norepinephrine (NE) onto adrenergic receptors on the
target cell
Figure 11-7
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Autonomic System: Neurotransmitters, etc.
3. Most postganglionic parasympathetic neurons
secrete acetylcholine onto muscarinic cholinergic
receptors on the target cell
Exceptions:
Some sympathetic postganglionic neurons secrete
ACh rather than norepinephrine
• example: the neurons that terminate on sweat
glands
More exceptions on next slide:
A small number of autonomic neurons secrete neither
ACh or NE:
Nonadrenergic, noncholinergic neurons
Can be either sympathetic or parasympathetic;
depends on their origin
They use the following neurotransmitters:
• Substance P
• Somatostatin
• Vasoactive intestinal peptide (VIP)
• Adenosine
• Nitric oxide
• ATP
Targets of Autonomic Neurons:
• Smooth muscle
• Cardiac muscle
• Many exocrine glands
• A few endocrine glands
• Lymphoid tissues
• Some adipose tissue
Autonomic Synapse or Neuroeffector Junction
(Figure 11-8, p. 392)
Very different from the “model” synapse
(figure 8-20, p. 274)
Model synapse has preganglionic axon, synaptic cleft,
postganglionic axon
Neurotransmitter released from preganglionic axon,
travels across synaptic cleft, binds to receptor on
postsynaptic ganglion
Figure 8-20
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Autonomic Synapse or Neuroeffector Junction
(Figure 11-8, p. 392)
The autonomic postganglionic axon ends with a series
of swollen areas which look like beads on a string
Swollen areas are called varicosities
Each varicosity contains vesicles filled with
neurotransmitter
The branched end of the axon lies across the surface
of the target tissue
Figure 11-8
Copyright © 2010 Pearson Education, Inc.
Autonomic Synapse or Neuroeffector Junction
(Figure 11-8, p. 392)
The underlying target cell membrane does not
possess clusters of receptors in specific sites
Instead, neurotransmitter is released into the interstitial
fluid and diffuses to wherever the receptors are
located
Less direct, but one postganglionic neuron can affect a
large area of the target tissue
Autonomic Synapse or Neuroeffector Junction
(Figure 11-8, p. 392)
Neurotransmitter release can be modulated here by
hormones and paracrines (e.g. histamine) which can
either facilitate or inhibit neurotransmitter release
Some preganglionic neurons co-secrete
neuropeptides along with ACh
The peptides act as neuromodulators, producing slow
synaptic potentials which modify postganglionic neural
activity
Autonomic Synapse or Neuroeffector Junction
Neurotransmitter synthesis takes place in the axon
varicosities
Neurotransmitter release at the autonomic synapse is
similar to that at a “model” synapse:
• AP arrives at the varicosity
• Voltage-gated Ca++ channels open
• Ca++ enters the neuron
• Neurotransmitter released into the synapse
• Diffuses through interstitial fluid to a receptor
• Or, it drifts away from the synapse
Figure 11-9, overview
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Autonomic Synapse or Neuroeffector Junction
The concentration of neurotransmitter in a synapse is
a major factor in control over the target
More neurotransmitter means a longer and/or stronger
response
The concentration of neurotransmitter is influenced by
its rate of breakdown OR by its rate of removal
Neurotransmitter activation of its receptor terminates
when the neurotransmitter is removed:
1. Can be removed by diffusing away
2. Can be metabolized by ECF enzymes
3. Can be actively transported into cells around the
synapse and then recycled
Figure 8-22, p. 278: ACh synthesis and re-uptake
Figure 11-9, p. 393: NE Synthesis and re-uptake
Figure 11-9, overview
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Adrenergic Receptors
All adrenergic receptors are G protein-coupled
receptors rather than ion channels
See Table 11-2, p. 394, for details
Sympathetic pathways secrete catecholamines which
then bind to adrenergic receptors on their target cells
Catecholamines
– Made from the amino acid tyrosine
– Includes epinephrine, norepinephrine, dopamine
Table 11-2
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Adrenergic Receptors
Adrenergic receptors come in 2 varieties:
α (alpha)
β (beta)
• Each of these has several subtypes
Alpha receptors are the most common sympathetic
receptor
• Respond most strongly to NE
• responds more weakly to epinenphrine
α (alpha) receptors
(p. 393)
Alpha 1 receptors
– In general, activation causes muscle contraction or
secretion by exocytosis
Alpha 2 receptors
– Activation causes a decrease in intracellular
cyclic AMP
– Also causes smooth muscle relaxation (GI tract) or
decreased secretion (pancreas)
Table 11-1
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Adrenergic Receptors
Beta receptors
3 main subtypes:
– Beta-1
– Beta-2
– Beta-3
They differ in their affinity for catecholamines
(next slide)
They differ in their affinity for catecholamines:
– Beta-1 receptors respond equally strongly to both
epinephrine and norepinephrine
– Beta-2 receptors are more sensitive to epinephrine
than to norepinephrine
• Beta-2 receptors are not innervated
• This limits their exposure to norepinephrine
because there are no terminal ends of
sympathetic neurons near them
They differ in their affinity for catecholamines:
– Beta-3 receptors
• Found primarily on adipose tissue
• Are innervated
• More sensitive to norepinephrine than to
epinephrine