Transcript autonomic nervous system

• Comparisons of somatic nervous system (SNS)
and autonomic nervous system (ANS)
• SNS
• Motor neurons exert voluntary control over skeletal
muscles
• Lower motor neurons may be controlled by
• Reflexes based in spinal cord
• Upper motor neurons with cell bodies in brain nuclei or at
primary motor cortex
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A schematic of the somatic nervous system
(SNS), which provides conscious and subConscious control over skeletal muscles
Upper motor
neurons in
primary motor
cortex
BRAIN
Somatic motor
nuclei of brain
stem
Skeletal
muscle
Lower
motor
neurons
Spinal cord
Somatic
motor
nuclei of
spinal cord
Skeletal
muscle
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Section 1: ANS Functional Anatomy and
Organization
• Comparisons of somatic nervous system (SNS) and
autonomic nervous system (ANS) (continued)
• ANS
• CNS motor neurons synapse with visceral motor
neurons in autonomic ganglia, which control visceral
effectors
• Integrative centers located in hypothalamus
• Two types of visceral motor neurons
1. Preganglionic neurons (cell bodies in CNS)
•
Activities represent direct reflex responses
2. Ganglionic neurons (cell bodies in autonomic ganglia)
•
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Innervate effectors like cardiac and smooth muscle
Visceral motor
nuclei in
hypothalamus
BRAIN
Preganglionic
neuron
Visceral Effectors
Smooth
muscle
Glands
Cardiac
muscle
Autonomic
ganglia
Ganglionic
neurons
Adipocytes
Preganglionic
neuron
A schematic of the autonomic
nervous system (ANS), which
controls visceral functions largely
outside our awareness
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Autonomic
nuclei in
brain stem
Spinal
cord
Autonomic
nuclei in
spinal cord
Module 14.1: ANS divisions
• Three ANS divisions
1. Sympathetic (or thoracolumbar) division
•
Axons emerge from thoracic and superior lumbar
segments of spinal cord
•
•
Innervate ganglia relatively close to spinal cord
“Kicks in” only during periods of exertion, stress, or
emergency
2. Parasympathetic (or craniosacral) division
•
Axons emerge from brain stem and sacral spinal
segments
•
•
Innervate ganglia very close (or within) target organs
Most often, effects are opposite to sympathetic
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Autonomic Nervous System
Sympathetic Division
Parasympathetic Division
In the sympathetic division, or thoracolumbar
(thor-a-kō-LUM-bar) division, axons emerge from
the thoracic and superior lumbar segments of the
spinal cord and innervate ganglia relatively close
to the spinal cord.
In the parasympathetic division, or craniosacral (krā-nē-ō-SĀ-krul) divions, axons
emerge from the brain stem and the sacral
segments of the spinal cord, and they innervate
ganglia very close to (or within) target organs.
Cranial nerves
(III, VII, IX, and
X)
The two main divisions
of the ANS: the sympathetic
and parasympathetic
divisions
Thoracic
nerves
Lumbar nerves
(L1, L2 only)
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
S2
S3
S4
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Sacral nerves
(S2, S3, S4 only)
Module 14.1: ANS divisions
• Three ANS divisions (continued)
3. Enteric nervous system (ENS)
•
Extensive network of neurons (~100 million) and
nerve networks within walls of digestive tract
•
Influenced by sympathetic and parasympathetic
divisions
•
•
However, many complex visceral activities are coordinated
on a local level (without CNS instructions)
Will be discussed more in Digestive System
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The extensive system of neurons and
nerve networks of the enteric nervous
system (ENS)
Esophagus
Stomach
Large intestine
Small intestine
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Aortic arch
Right vagus nerve
Trachea
Autonomic Plexuses
and Ganglia
Cardiac plexus
Pulmonary plexus
Thoracic sympathetic
chain ganglia
Esophageal plexus
Left vagus nerve
Thoracic spinal
nerves
Esophagus
Splanchnic nerves
Celiac plexus
and ganglion
Superior mesenteric
ganglion
Diaphragm
Superior mesenteric
artery
Inferior mesenteric
plexus and ganglion
Inferior mesenteric
artery
Hypogastric plexus
Pelvic symapthetic
chain
Representative plexuses, ganglia,
and nerves of the sympathetic and
parasympathetic divisions
© 2011 Pearson Education, Inc.
•
Autonomic ganglia
•
Sympathetic division
•
Preganglionic fibers (neurons) are relatively short
while postganglionic fibers (neurons) are
relatively long
•
•
Accordingly, sympathetic ganglia (where these fibers
synapse) are relatively near spinal cord
Specific ganglia
1.
Sympathetic chain (on either side of spinal cord)
• Innervates visceral effectors in thoracic cavity, head,
body wall, and limbs
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•
Sympathetic division (continued)
•
Specific ganglia (continued)
2.
Collateral ganglia (within abdominopelvic
cavity)
•
Includes celiac, superior, and inferior mesenteric
ganglia
•
Innervates visceral effectors in abdominopelvic cavity
3. Adrenal medulla
•
Center of adrenal gland
•
Acts as endocrine gland
•
Targets organs and systems throughout body
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Module 14.2: Autonomic ganglia
•
Sympathetic division (continued)
•
Prepares body for heightened levels of somatic activity
•
Known as “fight or flight” division
•
Typical responses
1.
Heightened mental alertness
2.
Increased metabolic rate
3.
Reduced digestive and urinary functions
4.
Activation of energy reserves
5.
Increased respiratory rate and dilation of passageways
6.
Elevated heart rate and blood pressure
7.
Activation of sweat glands
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Organization of the sympathetic division of the ANS
KEY
Preganglionic fibers
Postganglionic fibers
Ganglionic Neurons
Preganglionic
Neurons
Lateral gray
horns of
spinal
segments
T1-L2
Each sympathetic chain
consists of a series of
interconnected ganglia
located on either side of the
vertebral column.
Hormones released
into circulation
Target Organs
Visceral effectors
in thoracic cavity,
head, body wall,
and limbs
The collateral ganglia,
located within the
abdominopelvic cavity,
include the celiac, superior
mesenteric, and inferior
mesenteric ganglia.
The center of each adrenal
gland contains a sympathetic
ganglion, the adrenal
medulla, that acts as an
endocrine organ.
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Ganglionic neurons in
the sympathetic chain
and collateral ganglia
exert their effects
through innervation
of peripheral target
organs.
Visceral effectors
in abdominopelvic cavity
Ganglionic neurons in
the adrenal medullae
affect target organs
throughout the body
through the release of
hormones into the
general circulation.
Organs and
systems
throughout the
body
•
Parasympathetic division
•
Typical preganglionic fiber synapses on 6–8
ganglionic neurons
•
May be situated in:
•
Terminal ganglia (near target organ)
•
Usually paired
•
Ciliary ganglion (intrinsic eye muscles)
•
Pterygopalatine and submandibular ganglia
(nasal, tear, and salivary glands)
•
Otic ganglion (parotid salivary gland)
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•
Parasympathetic division (continued)
•
Typical preganglionic fiber synapses on 6–8
ganglionic neurons (continued)
•
May be situated in: (continued)
•
Intramural (murus, wall) ganglia (embedded in
target organ wall)
•
Typically interconnected masses/clusters of cells
•
Innervate visceral organs of neck, and of thoracic
and abdominopelvic cavities
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Module 14.2: Autonomic ganglia
•
Parasympathetic division (continued)
•
Concerned with regulation of visceral function
and energy conservation
•
Known as “rest and digest” system
•
Typical responses
1. Decreased metabolic rate
2. Decreased heart rate and blood pressure
3. Increased salivary and digestive gland
secretion
4. Increased digestive tract motility and blood flow
5. Stimulation of urination and defecation
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Organization of the parasympathetic division of the ANS
KEY
Preganglionic fibers
Postganglionic fibers
Preganglionic
Neurons
The midbrain, pons,
and medulla oblongata
contain parasympathetic
nuclei associated with
cranial nerves III, VII, IX,
and X.
Ganglionic Neurons
III
Ciliary ganglion
Intrinsic eye muscles
(pupil and lens shape)
Pterygopalatine and
submandibular
ganglia
Nasal glands, tear
glands, and salivary
glands
Otic ganglion
Parotid salivary gland
VII
IX
X
Intramural ganglia
In sacral segments of the
spinal cord, parasympathetic
nuclei lie in the lateral gray
horns of spinal segments
S2–S4.
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Target Organs
Pelvic
nerves
Intramural ganglia
Visceral organs
of neck,
thoracic cavity,
and most of
abdominal cavity
Visceral organs in
inferior portion of
abdominopelvic
cavity
Module 14.3: Autonomic innervation patterns
•
Autonomic innervation patterns
•
Sympathetic division
• Every spinal nerve has a gray ramus carrying
sympathetic postganglionic fibers
• Preganglionic fibers passing to collateral ganglia
form splanchnic nerves
• Postganglionic fibers innervating thoracic cavity
structures form bundles or sympathetic nerves
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Module 14.3: Autonomic innervation patterns
•
Parasympathetic division
•
Vagus nerve (X) alone provides ~75% of all
parasympathetic outflow
•
•
Numerous vagus nerve branches intermingle
with sympathetic fibers forming nerve plexuses
Preganglionic fibers in sacral spinal cord
segments form distinct pelvic nerves
•
Innervate intramural ganglia in kidneys, bladder,
terminal portions of large intestine, and sex
organs
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The innervation of the parasympathetic division on
one side of the body; the innervation on the opposite
side (not shown) follows the same pattern
KEY
Preganglionic neurons
Ganglionic neurons
Pterygopalatine ganglion
Lacrimal gland
Eye
Ciliary ganglion
PONS
VII
IX
III
Submandibular
ganglion
Salivary glands
Otic ganglion
Vagus nerve (X),
which provides
about 75 percent
of all parasympathetic outflow
Heart
Cardiac plexus
Lungs
Celiac plexus
Spinal
cord
Liver and
gallbladder
Stomach
Spleen
Inferior mesenteric
plexus
Pancreas
Hypogastric
plexus
Preganglionic
fibers in the
sacral segments
of the spinal cord,
which carry sacral
parasympathetic
output
Large
intestine
Small
intestine
Rectum
S2
S3
Kidney
S4
Penis
Uterus
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Ovary
Scrotum
Urinary bladder
Module 14.4: Autonomic neurotransmitters and
receptors
•
Autonomic neurotransmitters and receptors
•
Sympathetic division
•
Adrenergic receptors (bind “adrenaline”)
•
Located in plasma membranes of target cells
•
Binding of epinephrine (E) or norepinephrine (NE)
activates enzymes (2nd messenger system) within cell
•
Two classes
1.
Alpha receptors (generally stimulated by NE & E)
• α1 receptors – generally excitatory
• α2 receptors – generally inhibitory
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Module 14.4: Autonomic neurotransmitters and
receptors
•
Sympathetic division (continued)
•
Adrenergic receptors (continued)
•
Two classes (continued)
2.
Beta receptors (generally stimulated by E)
•
β1 receptors – cardiac muscle stimulation and
increased tissue metabolism
•
β2 receptors – relaxation of respiratory passage and
blood vessel smooth muscle
•
β3 receptors – release of fatty acids from adipose
tissue for metabolic use in other tissues
© 2011 Pearson Education, Inc.
Module 14.4: Autonomic neurotransmitters and
receptors
•
Sympathetic division (continued)
•
Neurotransmitter release
•
Epinephrine (E) and norepinephrine (NE) can be
released
•
Locally, involving more norepinephrine
•
•
Effects last a few seconds
Generally, from adrenal medulla
•
3× more epinephrine than norepinephrine
•
More beta receptors activated
•
Effects may last several minutes
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The effects of sympathetic stimulation, which result primarily from the interactions of NE and E with adrenergic
receptors in the target cell’s plasma membrane
The stimulation of alpha receptors by
norepinephrine, which activates enzymes
on the inside of the target cell’s plasma
membrane
The stimulation of beta receptors by epinephrine, which triggers
changes in the metabolic activity of the target cell
Epinephrine
Norepinephrine
Plasma membrane
Alpha
receptor
Beta
receptor
If α2
receptor
If α1
receptor
Second messengers
activated
Activation of
adenylate cyclase
Reduction of
cAMP levels
cAMP
Release of Ca2+
from ER
Smooth muscle
contraction
Gland cell
secretion
CYTOPLASM OF TARGET CELL
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Inhibition of
cell
If β1
receptor
Cardiac muscle
stimulation
and increased
tissue
metabolism
ATP
If β2 receptor
Relaxation of smooth
muscle in respiratory
passages and in the
blood vessels of skeletal
muscle
CYTOPLASM OF TARGET CELL
If β3
receptor
Release of fatty
acids by adipose
tissue for metabolic
use in other tissues
Module 14.4: Autonomic neurotransmitters and
receptors
•
Parasympathetic division
•
Receptors (all bind ACh)
1. Nicotinic receptors (also bind nicotine)
•
Located on ganglion cell surfaces
•
•
Also on sympathetic ganglion cells and at SNS
neuromuscular junctions
Always excitatory
2. Muscarinic receptors (also bind muscarine toxin)
•
Located at cholinergic neuromuscular and neuroglandular
junctions as well as some sympathetic cholinergic junctions
•
Can be excitatory or inhibitory
© 2011 Pearson Education, Inc.
Module 14.5: Anatomical and physiological
characteristics of ANS divisions
•
Characteristics of ANS divisions
•
Sympathetic activation
•
Can occur at:
•
Local level using mainly NE
•
•
Affect only target organs
Generalized body using E and NE
•
Have effects in many organs
• Also alters CNS activity
•
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Controlled by hypothalamus
Module 14.5: Anatomical and physiological
characteristics of ANS divisions
•
Sympathetic activation effects
•
Increased alertness through reticular activating system
•
Feeling of energy and euphoria
•
Increased activity in cardiovascular and respiratory
centers of pons and medulla oblongata
•
Increased blood pressure, heart/breathing rate, inspiration
depth
•
General elevation in muscle tone
•
Mobilization of energy reserves
•
Breakdown of liver and muscle glycogen
•
Release of adipose tissue lipids
© 2011 Pearson Education, Inc.
Module 14.5: Anatomical and physiological
characteristics of ANS divisions
•
Parasympathetic activation
•
Under normal conditions, not controlled or
activated as a whole
•
Active continuously as individual reflex
responses
•
Effects center on relaxation, food processing,
and energy absorption
•
Also called anabolic division (anabole, a rising
up) because blood nutrients generally increase
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Module 14.5: Anatomical and physiological
characteristics of ANS divisions
•
Parasympathetic activation effects
•
Constrictions of pupils and focusing of eye lenses
for nearby objects
•
Secretion of digestive glands
•
Secretion of hormones that promote nutrient
absorption and utilization
•
Blood flow and glandular activity changes
associated with sexual arousal
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Module 14.5: Anatomical and physiological
characteristics of ANS divisions
•
Parasympathetic activation effects (continued)
•
Increased digestive organ smooth muscle activity
•
Stimulation and coordination of defecation
•
Contraction of urinary bladder during urination
•
Constriction of respiratory passageways
•
Reduction in heart rate and force of contraction
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Section 2: Autonomic Regulation and Control
Mechanisms
•
Autonomic Regulation and Control Mechanisms
•
ANS output affects virtually every body system
•
Unconscious ANS control can maintain
homeostasis and vital physiological processes
without conscious input
• Survival in a coma can continue for decades
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A general overview of the
way the nervous system
distributes information and
issues motor commands
Central nervous
system (CNS)
processing
Sensory processing
centers
Processing at the conscious
level, which can be affected by
memory, learning, or planning.
Motor centers operating
at the subconscious level.
Motor Responses
Motor pathways
Somatic
Visceral
Sensory pathways
Stimulus
General sensory
receptors
Somatic nervous
system (SNS)
Autonomic nervous
system (ANS)
Somatic effectors
(skeletal muscles)
Visceral effectors
(smooth muscle,
glands, cardiac
muscle, adipocytes)
Figure 14 Section 2
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Module 14.6: Visceral responses to ANS control
•
Visceral responses to ANS control
•
Even in the absence of stimuli, autonomic motor
neurons maintain continuous activity
• = Autonomic tone
•
Many organs receive signals from both ANS
divisions
• = Dual innervation
• Effects may be opposing or complementary
•
In organs with only sympathetic innervation,
response may vary with receptor type
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Module 14.6: Visceral responses to ANS control
•
Dual innervation example: heart
•
Heart consists of cardiac muscle tissue triggered
by specialized pacemaker cells affected by ANS
•
Parasympathetic: ACh release decreases heart rate
•
Sympathetic: NE release accelerates heart rate
•
Small amounts of both neurotransmitters released
continuously to maintain autonomic tone
•
Under resting conditions, parasympathetic
dominates
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At rest, both ANS
divisions are active
at low levels, but
parasympathetic
effects predominate.
Increased
parasympathetic
stimulation
lowers the
heart rate.
Parasympathetic
inhibition or sympathetic
stimulation increases the
heart rate. The balance
between these factors
can be precisely adjusted.
Increased sympathetic
stimulation combined
with parasympathetic
inhibition result in an
increase in heart rate to
maximum levels.
Heart rate
(beats per minute)
180
120
72
50
Time
The effects of both autonomic divisions on the heart, which receives dual innervation
2
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Module 14.7: Visceral reflexes
•
Visceral reflexes
•
Provide automatic motor responses that can be modified,
facilitated, or inhibited by higher centers (especially those
of hypothalamus)
•
All are polysynaptic
•
Components of reflex arc
1. Receptor (interoceptors such as nociceptors,
thermoreceptors, baroreceptors, chemoreceptors, etc.)
2. Sensory neuron
3. Processing center (spinal cord nuclei and solitary nuclei of
brain stem)
4. Visceral motor neurons (one or two)
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Module 14.7: Visceral reflexes
•
Two visceral reflex types
1. Short reflexes
•
Bypass CNS entirely
•
•
Control simple motor responses with localized
effects
•
•
Impulses relay with interneurons in ganglia
Usually just one part of an organ
Predominate in enteric nervous system
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A short reflex, which bypasses the CNS and involves
sensory neurons and interneurons whose cell bodies are
located within autonomic ganglia
Stimulus
Receptors in
peripheral tissue
Afferent
(sensory) fibers
Short
reflex
Autonomic
ganglion
Response
Peripheral
effector
Ganglionic
neuron
1
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Module 14.7: Visceral reflexes
•
Two visceral reflex types (continued)
2.
Long reflexes
•
Pathway
•
Visceral sensory neurons in cranial nerves and autonomic
nerves enter CNS through dorsal roots
•
Interneurons process information in CNS
•
ANS motor neurons carry response to visceral effectors
•
Predominate over short reflexes
•
Activate entire organs and coordinate responses of
multiple organ systems
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A long reflex, which is the autonomic equivalent
of a polysynaptic reflex
Central nervous
system
Stimulus
Receptors in
peripheral tissue
Long
reflex
Response
Processing center
in spinal cord
(or brain)
Peripheral
effector
Preganglionic
neuron
Autonomic
ganglion
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The sites and functions of the
body’s baroreceptors
Baroreceptors of Carotid
Sinus and Aortic Sinus
Provide information on blood
pressure to cardiovascular and
respiratory control centers
Baroreceptors of Lungs
Baroreceptors of
Digestive Tract
Provide information on
volume of tract segments,
trigger reflex movement of
materials along tract
Baroreceptors of
Bladder Wall
Provide information
on volume of urinary
bladder, trigger urination
reflex
Provide information on lung
stretching to respiratory
rhythmicity centers for control
of respiratory rate
Baroreceptors of Colon
Provide information on volume
of fecal material in colon, trigger
defecation reflex
1
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The body’s chemoreceptors, which play important roles in the
reflexive control of respiration and cardiovascular function
Chemoreceptors in Respiratory
Centers in the Medulla Oblongata
Trigger reflexive
adjustments in
depth and rate of
respiration
Respond to the concentrations of
hydrogen ions (pH) and carbon
dioxide (PCO2) in cerebrospinal fluid
Chemoreceptors of Carotid Bodies Via cranial
Sensitive to changes in the pH,
PCO2 , and PO2 in arterial blood
Chemoreceptors of Aortic Bodies
Sensitive to changes in the pH,
PCO2, and PO2 in arterial blood
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nerve IX
Via cranial
nerve X
Trigger reflexive
adjustments in
respiratory and
cardiovascular
activity
The body’s chemoreceptors, which play important roles in the
reflexive control of respiration and cardiovascular function
A photomicrograph of
a carotid body
Chemoreceptive
neurons
Blood vessel
Carotid body
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LM x 400
2
Module 14.9: Levels of ANS motor control
•
Autonomic activities are controlled mainly in two CNS
areas
1.
Autonomic ganglia and spinal cord
•
2.
Simple reflexes
Medulla oblongata
•
More complex reflexes
•
Cardiovascular reflexes
•
Respiratory reflexes
•
Salivation
•
Swallowing digestive secretions
•
Peristalsis
•
Urinary function
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Module 14.9: Levels of ANS motor control
•
Lower CNS centers are subject to regulation
by higher brain areas
•
Hypothalamus
•
Limbic system
•
Thalamus
•
Cerebral cortex
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